The Effection of Elements In Steel

Steel is an alloy composed of iron and C (carbon), Si (silicon), Mn (manganese), P (phosphorus), S (sulfur) and a small amount of other elements. In addition to Fe (iron), the content of C plays a major role in the mechanical properties of steel, so they are collectively referred to as iron-carbon alloys. It is the most important and most used metal material in engineering technology.

What role do various elements play in steel?

Carbon

Exist in all steels, it is the most important hardening element. It helps to increase the strength of steel. We usually hope that tool-grade steel has more than 0.6% carbon and becomes high-carbon steel.

Chromium

Increase wear resistance, hardness, and most importantly, corrosion resistance. More than 13% of them are considered to be stainless steel. Despite the name, all steel will rust if not maintained properly

Manganese

Important elements help to generate texture structure, increase firmness, strength, and wear resistance. Deoxidize the inside of the steel during heat treatment and rolling, which appears in most of the steel for knife and scissors, except A-2, L-6 and CPM 420V.

Molybdenum

Carbonization agent prevents the steel from becoming brittle and maintains the strength of the steel at high temperatures. It appears in many steels. Air hardening steels (such as A-2, ATS-34) always contain 1% or more molybdenum, so that they can Harden in the air.

Nickel

Maintain strength, corrosion resistance and toughness. It appears in L-6, aus-6 and aus-8.

Silicon

Helps to increase strength. Like manganese, silicon is used in the production of steel to maintain the strength of the steel.

Tungsten

Enhance wear resistance. The mixture of tungsten and appropriate proportion of chromium or manganese is used to make high speed steel. High speed steel m-2 contains a lot of tungsten.

Vanadium

Enhance wear resistance and ductility. A vanadium carbide used to make striped steel. Vanadium is found in many kinds of steels, among which m-2, vascowear, CPM, t440v and 420va contain a lot of vanadium. The biggest difference between bg-42 and ATS-34 is that the former contains vanadium.

The role of various elements

1、Al

(1) When the content of Al in steel is less than 3-5%, it is a beneficial element. Its function is: high oxidation resistance and resistance.

① The addition of Al as a strong deoxidizer can produce highly fine and ultra micro oxides dispersed in the steel volume. Therefore, it can prevent the grain growth of the steel when it is heated (Al content is less than 10%, only when it is heated at less than 1200 ℃) and improve the hardenability of the steel. So these oxides become the center of crystallization, and promote the decomposition of a body when the steel is cooled.

② As an alloying element, it is helpful to the nitriding of steel, so it can improve the thermal stability of steel. Therefore, AlN itself has high stability during heating, and both (1) and (2) are conducive to reducing the overheating tendency of steel.

③ It can improve the oxidation resistance of steel,

④ It can improve the resistance of steel, and can be used together with Cr to make high resistance CR Al alloy, such as cr13al4, 1cr17al5, 1cr25al5. The resistance of Al is much higher than that of CR. The addition of Al to Cr steel will lead to coarse grains and brittleness, so the amount of Al is generally less than 5%, and only 8-9% in some cases.

⑤ For silicon steel, Al can be reduced α The loss of iron core, the decrease of magnetic induction and the combination with oxygen can weaken the phenomenon of magnetic aging, but the oxide of Al will make the magnetism worse. Al (> 0.5%) can also make silicon steel brittle.

(2) Adverse effects of Al

① It can promote the graphitization of steel and reduce the concentration of carbon solution in alloy phase, so the hardness and strength are reduced.

② Accelerated decarbonization

When the Al content increases to 3-5%, 8-9% will greatly promote the columnar crystallization process. Therefore, the difficulty of mechanical hot working of steel is greatly increased, and the steel is easy to decarburize（ The reason why the hot working is difficult is that the alloy ingot has a coarse-grained structure, and the cleavage of the crystal is very weak, so the thermal conductivity is low. When heated, it is easy to have a large temperature difference and forging crack. Even the peeling of the ingot will cause the grain boundary oxidation and damage. In addition, it is easy to become brittle when it is stopped at high temperature above 800 ℃ for a long time.

The content of Al in general alloy steel is as follows:

Alloy structural steel: Al = 0.4-1.1% (38crala, 38CrMoAlA, 38crwvala, etc.)

Heat resistant and non peeling steel: Al = 1.1 ～ 4.5% (cr13sial, cr24al2si, cr17al4si, etc.)

Electrothermal alloy: Al = 3.5-6.5% (cr13al4, 1cr17al5, cr8al5, 0cr17al5, etc.)

Even al = 8% cr7al7: the electrothermal alloy can be used even though it has brittleness.

2、Si

(1) The Si content in general alloy steel will not be higher than 3.5%, and when more (4.8-6.5%), the steel will have high brittleness.

The beneficial effect of Si is high thermal strength and elastic limit, high permeability and less eddy current loss.

① Like Al and Cr, the oxide is spinel type. Lattice constant and α- Fe、 γ- Fe has little difference. Because the oxide and the cell at the metal boundary are tightly and strongly bonded together, the oxide scale is closely attached to the metal, and even does not peel off at high temperature. Therefore, it has strong oxidation resistance and heat resistance, and is added to heat-resistant steel.

② It is helpful to improve the elastic limit of steel. 1-2% Si is added to medium carbon steel, and the tempering is carried out σ B will increase by 15-20%, and Aku will also be increased and improved σ S and δ。 ③ It is helpful to promote graphitization in steel and is used for refining graphite steel. This steel can be made of bearings, even as tool steel, punch, drawing die, bending die, etc.

④ The deoxidation ability is strong, which is commonly used in steelmaking. Therefore, Si is contained in general steel, and its quantity is less than 0.5%.

⑤ Silicon can reduce the anisotropy of crystal, make magnetization easy, reduce magnetic resistance, and it can reduce the harm of other impurities in steel to magnetic field magnetic induction (graphitization of%c, deoxidation, formation of hydrogenated silicon with N, etc.). So the eddy current loss can be greatly reduced. Due to the brittleness of silicon, the silicon content of high silicon steel sheet is less than 4.5%, only 4.8% at most, and is being studied to 6.5%.

⑥ Silicon can significantly slow down the decomposition rate of tempered martensite at low temperature (200 ℃)（ Si is an element of ferrite formation, and adding Si will make a- α Transformation.

(2) The adverse effects of Si

① It promotes graphitization and decarbonization (it is an element to prevent carbide formation), and Si containing steel is not carburized generally.

② The development of temper brittleness is promoted, and the plasticity is reduced.

The influence of Si on the temperature reserves of impact toughness and toughness is not equal.

The results showed that the effect was good when Si = 1-1.5%. The influence is bad when Si = 2.5-3%, and it is difficult to forge if Si = 2-2.5%.

When Si ≤ 2.3%, the sensitivity of silicon chromium steel to tempering brittleness is very low, but when Si = 2.5-3.5%, the sensitivity to tempering is high. The toughness treatment must be adopted for this steel (immersion in water after tempering and less toughness treatment for forging). When Si > 3.5%, even holding toughness treatment can not eliminate the brittleness of silicon chromium steel（ However, Mo can improve the brittleness slightly), and brittle crack may occur at room temperature when Si = 4%.

③ For carbon tool steel, when Si content increases, hardenability grade will be reduced. Si should not be added in general structural steel, and 0.4% for high-speed steel.

④ Because of the existence of silicon, it is difficult to increase carbon in steel and reduce the carburizing speed, so it is not carburized.

⑤ When silicon manganese is combined, Mn can decrease, because of decarburization caused by Si, Si has a weak effect on inhibiting grain growth, but it can decrease slightly. Mn causes coarse grain adjustment and tempering, which has mutual improvement effect, but it is easy to generate white spots. It is necessary to pay attention to drying and baking of raw materials during smelting.

⑥ Silicon is often found in steel with silicate inclusions of Fe and Mn, which will reduce the properties of steel and have lower plasticity than sulfide. The light transmittance of these inclusions is very high, but the reflection is low, so it is usually gray black under microscope.

(3) Si content in general alloy steel:

General carbon steel: Si < 0.5%

Alloy structural steel: Si = 0.9-1.6% (27SiMn, 40CrSi, 20CrMnSi, 35CrMnSiA, etc.)

Spring steel: Si = 1.5-2% (55si2mn, 60cr2mn, etc.)

Bearing steel: Si = 0.4-0.7% (gcr9simn, GCr15SiMn, gcr6simn, etc.)

Tool steel: Si = 0.65-1.8% (SIMN, 9SiCr, 5simnmov, 6simov, etc.)

Heat resistant steel: Si = 1-4.3% (cr17al4si, cr20si3, 4Cr9Si2, 4cr3si4, etc.)

Silicon steel sheet of motor: Si = 0.8-1.8%, 1.8-2.8%, 2.8-3.8%, 3.8-4.8% of which are low, medium, high and high grade silicon steel sheet.

3、Mn

(1) The beneficial effects of manganese are high strength and wear resistance, hardening, carburizing and cold work hardening.

14% (high wear resistant steel), 17-19% (retaining ring steel)

① It is used as deoxidizer in steelmaking, because the content of Mn in general steel is less than or equal to 0.7%.

② Mn and s counteract the effect of s on the red brittleness of iron.

③ The effects of Mn on various steels are as follows

Pearlite Mn steel: can improve its strength and wear resistance, plasticity is also good. So it can refine pearlite structure（ For the steel with high carbon content, Mn ↑, the plasticity decreases slightly. For low carbon steel, it contains Mn ↑, but toughness ↑.

Austenitic Mn steel: high enough plasticity and high wear resistance. Therefore, Mn can increase the stability of austenite and enlarge the temperature range γ Austenite is obtained in the phase region. Reduce the critical cooling rate during quenching. Reducing the critical points (A1 and A3) of steel is 25-30 ℃ lower than that of carbon steel, so the hardenability of steel can be improved and the deformation during quenching is relatively small, so it is suitable for making large cross-section and complex parts. When Mn = 5%, Mn decreases to 0 ℃.

Martensitic Mn steel: easy to make it brittle, quenching crack. Mn is easy to dissolve in ferrite and form weak carbide, which is not stable. Therefore, it is very easy to completely dissolve in austenite in the heating process, and the critical point is low, so the grain is very easy to coarsen and crack. Therefore, the quenching heating temperature and holding time should be strictly controlled. Generally, oil quenching or cooling in flowing air is appropriate. Only simple shape parts are easy to use water quenching.

Quenched and tempered steel: will reduce its plasticity (temper brittleness effect).

Carburizing steel: the existence of Mn can promote carburizing, so it can greatly improve the surface hardness and wear resistance of the steel, especially the less soft spots on the surface during carburizing, and it does not change the tendency of excessive carburization（ Before the final quenching, the carburized manganese steel should be normalized or annealed once to eliminate the overheating of the core caused by long time carburizing.

Structural steel: it will enhance its temper brittleness.

Tool steel: adding about 1% Mn can reduce the volume deformation during quenching, which is of great significance for precision tools and long tools（ Such as CrMn, CrWMn steel, etc.).

④ Mn can improve the weldability and low temperature properties of the steel, and also slow down the decarburization of the steel.

⑤ The cutting performance of the steel can be improved by adding Mn.

⑥ For some steels, the effect of Mn can be replaced by Ni and can be extended γ Austenite in phase zone, such as die steel (enhanced hardenability), austenitic steel, etc.

⑦ High manganese steel is sensitive to cold work hardening, which can improve the strength and wear resistance of steel（ Mn = 10-14% and C = 1-1.4%)

⑧ The hot strength of Cr Mn austenitic steel is very good, even higher than that of Cr and Ni steel. The red hot wear resistance of Cr Mn austenitic steel with 4% Cr and Ni is better. Mn is cheap.

(2) The adverse effects of manganese are as follows

① Increase of overheat sensitivity (coarse grain): This is due to the poor stability of Mn containing cementite, which is easy to completely dissolve in austenite during heating. In addition, the critical point of Mn steel is also low, so it is easy to coarsen. Therefore, the heating temperature and holding time should be strictly controlled in forging and heat treatment. Among all alloy elements, Mn can not reduce the tendency of austenite grain growth, on the contrary, it causes coarse grain.

② To enhance the sensitivity of steel to white spot, slow cooling is necessary（ When the content of C is more than 0.3%, the effect is greater.)

③ It is easy to form banded and fibrous structure. Therefore, the longitudinal and transverse properties are poor (Mn > 2.4% elongation ↓)

④ High manganese steel has low melting point (mn13-14%, t-melt 1350-1400 ℃), high average coefficient of linear expansion (equivalent to 1.9 times of steel silicon steel), low thermal conductivity (about 1 / 3-1 / 4 of the same kind of silicon steel), and difficult hot working.

⑤ When the cooling rate of high manganese steel is not enough, it is easy to form massive carbides and precipitate along the grain boundary, which makes the steel brittle. When the cooling rate of water quenching is used, the carbides can not precipitate in time, resulting in uniform austenite structure and improved properties. But because of the high Mn content and poor thermal conductivity, the quenching times should not be too many.

(3) Classification of Mn containing steels

① Carbon steel: A, normal Mn content of carbon steel Mn = 0.25 ~ 0.8%

B. High Mn content carbon steel Mn = 0.7-1.0% and 0.9-1.2%

② Manganese steel: Mn = 1.1 ~ 1.8%, a few ~ 2.4%

③ High manganese steel: Mn = 13-14% (C = 1.0-1.3%)

Note: Mn ＜ 1.2% is deoxidized for steelmaking and slightly changed steel properties, so it can be used as general silicon steel. Mn = 1.1-1.8% or 2.4% is used for high plasticity, wear resistance and strength. Mn = 2.4-13% is coarse-grained, extremely brittle and unusable. Mn = 13-14% is cold hardening and becomes high wear resistant steel.

4、Ni

(1) The beneficial effects of nickel are: high strength, high toughness, good hardenability, high resistance and high corrosion resistance.

① On the one hand, the strength of steel is greatly improved, on the other hand, the toughness of iron is always kept at a very high level. The brittleness temperature is very low（ When the content of Ni is less than 0.3%, the brittleness temperature is below - 100 ℃. When the content of Ni is increased, the brittleness temperature can be reduced to - 180 ℃. Therefore, the strength and plasticity of quenched structural steel can be improved at the same time. The Cr steel containing 3.5% Ni can be air quenched, and the Cr steel containing 8% Ni can also be transformed into m-body at very low cooling rate.

② The lattice constant of Ni and its relationship γ- Iron is similar, so it can be a continuous solid solution. Ni can reduce the critical point and increase the stability of austenite, so the quenching temperature can be reduced and the hardenability is good. Generally, heavy steel with large section is made of steel with Ni. When it is combined with Cr, w or Cr, Mo, the hardenability can be increased. Ni Mo steel also has high fatigue limit（ Ni steel has good thermal fatigue resistance and works repeatedly in cold and hot conditions. σ、α K (high)

③ The purpose of using Ni in stainless steel is to make the steel have uniform A-body structure and improve corrosion resistance.

④ Ni steel is not easy to overheat, so it can prevent grain growth at high temperature and keep fine grain structure.

⑤ The steel with high Ni content has low coefficient of thermal expansion and can be used as invariable steel (Ni36%) and substitute platinum (ni42%).

⑥ When the content of Ni is higher, it can combine with Cr as high resistance alloy (cr15ni60, Cr20Ni80).

⑦ Ni, like V, has no effect on the decarburization process.

Ni itself is not an effective antioxidant element, so it is rarely used as an alloying element of stainless steel, but it has a good effect on concentrated caustic.

⑨ Ni can improve the creep resistance of A-body steel, but the effect is weakened by a certain value. Other alloying elements must be added to solve the problem by solution strengthening or precipitation hardening.

⑩ The weldability and low temperature performance of Cr and Ni steels are also good.

(2) The side effects of Ni are as follows

① Ni can not improve the creep resistance of ferrite, on the contrary, it can increase the hot brittleness of pearlite m-body steel. Therefore, pearlite and martensite steels do not add nickel.

② The corrosion resistance of Ni steel in sulfur-containing atmosphere is not as good as that of Ni free steel, because nickel sulfide can cause red hot embrittlement of steel.

③ Chromium nickel steel is easy to feel temper brittleness and form white spots (the former can be prevented by rapid cooling after tempering, while the latter should be prevented by correct smelting specification, forging and cooling specification)

④ For high speed steel, because it reduces its hardness, it is regarded as harmful impurity. When Ni ≈ 2% or higher, the hardness of high speed steel decreases due to the decrease of tempering stability at 600 ~ 660 ℃ and the deterioration of hot hardness (making a body stable and not decomposed).

⑤ Similarly, because Ni reduces the hardness of the quenched layer of the steel, it is not desirable to have it in the bearing steel. Ni is not more than 0.30%, and Ni + Cu is not more than 0.50% (Cu is not more than 0.25%).

⑥ Although Ni can increase the resistance and promote the graphitization of silicon, it can reduce the magnetic induction and maximum permeability. So the silicon steel sheet does not want to have Ni.

⑦ Ni is early in China and its price is high.

⑧ The scale of Ni steel is easy to scale when it is oxidized, and the scale of Ni steel is not easy to fall off when it adheres to the steel surface.

(3) The content of Ni in general alloy steel is as follows:

Carburizing steel: C = 0.15-0.25%, Ni = 1-4.5%

Quenched and tempered steel: C = 0.35-0.55% Ni = 1-1.75%

Stainless steel: m-body stainless steel with Ni ≤ 2%, A-body stainless steel with Ni = 8 ~ 18%. M-P type stainless steel containing 2-8% Ni.

Heat resistant and non peeling steel: containing 9-36% Ni, it belongs to A-body steel.

Magnetic steel: the steel containing less than 25% Ni (Ni25, ni9mn9, etc.) is weak magnetic steel. It can be quenched at 930 ~ 1000 ℃ to avoid magnetization. It can be used to make machine, instrument and other parts that should not be magnetized (motor ring, compass box, resistance, etc.).

The aged magnetic steel containing 25-30% Ni has very high magnetism. When the residual magnetic induction is 5000-7500 Gauss, the coercive force can reach 500-700 oerst or even 1000. However, it has high brittleness (and hardness), so it is often used as casting magnet.

The alloy containing 35-37% Ni is a constant alloy

Ni = 42-44% is platinum like alloy.

The alloy containing 50-80% Ni is of high permeability.

5、Cr

(1) The beneficial effect of chromium: it has many valuable properties: high hardness, high strength, yield point, high wear resistance, but has little influence on plasticity and toughness, high oxidation resistance, corrosion resistance, and can also improve resistance and permeability.

1) Cr is a medium carbide forming element. Among all kinds of carbides, Cr carbide is the smallest one, which can be distributed evenly in the volume of steel, so it has high strength, hardness, yield point and high wear resistance. Because it can make the structure fine and distributed, so the plasticity and toughness are good, which is of great value to tool steel.

2) The carbide of Cr is also difficult to dissolve, which can hinder the growth of the grain under short heating time, and coarse crystal will be formed after long carburizing. So it can reduce the overheat sensitivity effect.

3) CR can slow down the decomposition speed of a body and reduce the critical cooling speed during quenching, which helps to form and improve the stability of m-body. Therefore, Cr steel has excellent hardenability and little quenching deformation. Note: Cr is the element of ferrite formation, reducing γ Therefore, when there is no A-body element, the high Cr steel will show ferrite structure.

4) CR combined with W or Mo can increase the retained austenite in quenched steel, and help to obtain carbide phase which needs to be crushed.

5) CR can greatly improve the strength and plasticity of structural steel, especially in the steel with Cr and Ni. Such as 12crni3n, etc.

6) When Cr is more than 12%, it has good corrosion resistance, and the corrosion resistance will be greatly improved by adding 8-9% Ni. The effect of Cr on corrosion resistance will decrease with the increase of carbon content, because CR does not work when combined with C.

7) Cr ≥ 25-30%, it has good antioxidant property. If CR = 27-28%, it can be used as the protective cover of thermocouple thermometer at 1300 ℃, and when Cr is combined with Si and Al, even Cr is relatively small and has high oxidation resistance. If CR 6-10% and Si 2-3% have high heat resistance and oxygen resistance.

8) Cr, Al binding (1cr17al5, cr13al4, etc.) and Cr, Ni bonding (such as cr15ni60, Cr20Ni80, etc.) have high resistance.

9) CR can improve the coercive force and prevent the aging of steel, so Cr steel is used to make permanent magnet.

10) Cr is low.

11) Because CR can form stable carbides, slow down the diffusion of carbon and form a tight oxide film, it can reduce decarbonization.

12) The multi element alloy steel with Cr > 2.5%（ 18cr3mowva, 20cr3mowva, etc.) are good hydrogen corrosion resistant steels.

Cr content is less than 0.08% which is the requirement of graphite steel, so Cr is an element to prevent graphitization.

Cr ≠ 1.2%

Low alloy high strength steel (general Mn steel and SIMN steel)

CR = 0.5-1.65% as bearing steel (C ≈ 1%), its alloy content is low, cheap, and has high strength, high wear resistance, good fatigue resistance and hardenability, and the heat treatment is simple.

The effect of Cr = 3-10% on the strength and toughness of steel is the most significant when Cr is less than 2%. But exceeding this limit will damage its thermal strength. The intensity of the samples increased again when CR > 12%. But when Cr content increases to 3%, the tempering stability of martensite increases significantly. Therefore, it has high hardness and wear resistance and is used in mold. When Cr content increases to 3%, the magnetic coordination with C1% is also the best. So it is also used as magnetic steel. It is widely used in high-speed tool steel, and steel containing Cr5% can be quenched in air. Although the strength of silicon chromium steel containing cr5-6% and cr6-10% and SI2-3% is not very high, it also has enough heat resistance and oxidation resistance for use in gas valve and petroleum and chemical industries (ammonia synthesis equipment, etc.).

The steel with Cr = 12-14% is the most typical stainless steel (1cr13-4cr13) which has high corrosion resistance and good strength. The surface Cr12 and cr12mo are typical die steels with high hardenability and high wear resistance（ These are mostly martensitic steels)

Some of the steels with Cr = 16-18% have only one phase (ferrite), some are biphase (m-ferrite). The corrosion resistance of Cr steel with single phase is higher than that of steel containing Cr = 12-14%. For example, the corrosion resistance of Cr17 and 9Cr18 will be greatly increased if 8-9% Ni is added. For example, 1Cr18Ni9 and 1Cr18Ni9Ti are typical stainless steel with good acid resistance. The disadvantage of CrNi steel is intergranular corrosion, and Ti and Nb can be improved.

The steel containing Cr = 23-32% has good corrosion resistance and high oxidation resistance. It can resist the corrosion of concentrated nitric acid, phosphoric acid and sulfuric acid at ordinary temperature. The steel containing 27-28% Cr can be used as a protective cover for thermocouple thermometer at 1300 ℃. This kind of steel is pure ferrite steel, so it can not change its structure and performance by heat treatment. The recrystallization temperature is low, the coarse crystal is strong and has high brittleness, so it can not be used as vibration and impact parts. The performance can be changed by adding Mo, W and V. The heat strength of cr-9si2 and cr10si2mo can be increased by reducing Cr content and adding Si. Ni addition can also be made, such as cr20ni14si, cr25ni20, cr18ni25si, cr14mn14w, cr18ni6mn5, etc.

Cr is different from Mn and Ni, and it is reduced γ The alloy element of the zone（ It's the same α- Fe has body centered cubic lattice, and the pure chromium is the same from 1849 ℃ to absolute 0ok. Therefore, AC3 decreases from 910 ℃ with the increase of Cr content, but its speed is very slow, but Ac4 decreases rapidly from 1400 ℃ to 8% of chromium, and AC3 is 850 ℃ at the lowest. The increase of Cr content leads to the rapid increase of AC3. When Cr content reaches 13%, AC3 and Ac4 will converge to a point, γ The region is closed, so it will change into pure ferrite phase when CR > 13%, and the grain size can no longer be changed by heat treatment—— That is, ferritic steel. When Cr content continues to increase, it is about 25-60% especially 45-48% region. When the temperature is lower than 950 ℃, it will be cooled slowly (mostly 820 ℃), and a non magnetic brittle component will be precipitated—— σ Phase. These will be separated after secondary heating, which results in a large volume change in the solid solution, which causes a lot of stress, so it is very brittle. But when it is cold under 950 ℃, the, σ The phase can not precipitate in the solid solution, but the effect is small. δ Phase problem: it is pointed out that when Cr and C content are matched, especially when the content is left and right, it is very easy to produce free ferrite δ Phase, it will reduce the process performance and heat resistance of steel, so it is important to pay attention to the fact that CR = 10.9% can make the steel with Cr = 0.11% δ The phase quantity is reduced to the minimum.

Cr is very beneficial to improve its corrosion resistance, but the effect of Cr on creep is complex. It should be noted that when CR = 1% of the steel is contained, the creep resistance is the highest. Cr ↑ is found. CR > C3 three-way lattice, to CR = 7% creep strength to the lowest point, when Cr content increases to 12%, Cr23C6 will replace Cr7C3, creep resistance (heat resistance) can be slightly improved, adding V, Nb, Ti can obtain very fine dispersion phase, which is very beneficial to improve the creep strength (heat resistance).

6、W

(1) W has a good effect on:

1) The grain is refined, and its action is stronger than Cr, so it can reduce the superheat tendency of steel and improve the strength, toughness and thermal stability.

2) The stability of m-body can be improved greatly. Any cooling speed of 18crniwn can be completely quenched. The m-body can be obtained. The stability of M body can reach 600 ℃ and the red hardness can be maintained by mixing w18% with Cr4%.

3) It can improve the strength and improve the toughness without reducing the plasticity.

4) The coercive force of quenched steel is improved to prevent the aging of steel.

5) The carbide is extremely stable and difficult to dissolve into solid solution at high temperature, so it can be used as high-speed tool steel.

6) W steel has good hardness and wear resistance, small deformation in heat treatment, not easy to crack and good tempering stability.

7) W is used in valve steel because it can improve stability of body a, and reduces γ Zone, same as CR.

8) The results show that the heat strength and recrystallization temperature of Pearlite Heat-resistant steel can be improved.

9) The yield point, fatigue strength and thermal stability of the steel can be improved by adding 2-4% w to Cr and Ni steels. The tendency of crystal corrosion is reduced because of the formation of carbides (fe3w2 and fe2w are extremely stable compounds, which are highly dispersed, so the strength and thermal stability can be improved.)

(2) Adverse effects of W:

1) Increase decarburization (carbide stability) to prevent graphitization.

2) W is a strong carbide element, and it should prevent the carbide from being uneven and make waste products (it can increase the number of upsetting and normalizing treatment to correct).

3) The hardness of W > 9% was significantly increased, while δ、ψ It decreased significantly.

4) W reduces the thermal conductivity of steel, and the heat conductivity of steel containing w > 10% is 0.7 times of pure iron.

5) The range of malleable temperature decreases with the increase of W.

(3) W content in general alloy steel:

Alloy structural steel: w = 0.3-1.0% (for example, 20cr3mowva, 18cr3mowva, etc.)

Heat resistant and non skin steel: w = 0.3-3.2% (the first two are hydrogen resistant steel, such as cr15ni36w3ti, etc.)

Alloy tool steel: w = 1-18% (CrWMn, W, W2, 3Cr2W8V, P9, P18, etc.)

It is not suitable to add more than 20-22% w to the steel. So the improvement of steel performance by exceeding this value w has no better effect, so it is not economical to add more.

The methods to reduce temper brittleness are as follows:

1) 0.3-1.0% Mo or 1-1.5% w were added to the steel.

2) The tempering shall be conducted with quick cooling, and water-cooled or oil cooled.

3) The tempering temperature is improved. This method is less used because the property (strength) is reduced and can not be fully exerted.

4) Prolong tempering time or increase the number of repeated high temperature tempering.

5) Reduce the quenching temperature, or use secondary quenching ① normal quenching of AC3 or ac1-ac3 to eliminate temper brittleness.

6) V (about molybdenum content% +0.1% can be equivalent) is added to the steel to improve the tempering stability and restrain the tempering brittleness, but the effect is very small.

7) The deformation heat treatment was used, that is, the deformation (the best deformation degree is 15-20%) after heating to AC3 is immediately quenched and tempered, and the toughness is increased by 3 times.

8) The last two methods are not used because it is difficult to realize in production.

Note: the temper brittleness is the second type (that is, 450-570 ℃ can be 650-700 ℃), while the first type of tempering brittleness (250-400 ℃) is inevitable for all steel, and can be eliminated by repeated tempering, so it is not discussed.

7、Mo

(1) The good effect of molybdenum is:

1) The effect of grain refinement is stronger than W, so it can reduce the tendency of overheating and improve the strength, hardness and thermal stability of steel.

2) Mo will make forgings in steel σ b、 σ s. HB ↑, and δ、ψ、α k↓。 The improvement of tempering stability of m-body and the combination of Cr and Ni can greatly improve the hardenability, refine the grain, improve toughness, and make forging easier.

3) Reducing temper brittleness can eliminate temper brittleness (such as 24crmov5) for some structural steels, so strength can be improved and plasticity is not reduced, and molybdenum can improve impact toughness of steel. ① In other words, the alloy elements (including Mo) can not eliminate the temper brittleness only by inhibiting the tempering brittleness. Mo has a good effect when the content reaches 0.2%. Therefore, the ordinary alloy structural steel containing mo0.25-0.4% only specifies that the Mo content of steel with tempering brittleness temperature range of 550-600 ℃ is 0.5-0.6% for long-term operation. When the content of Mo exceeds a certain value (the limit for low carbon steel is 1.0%), the high temperature tempered water-cooled steel will become brittle instead. Mo steel is brittle after tempering for a long time. ② When P and Mo are higher, temper brittleness can not be avoided even if Mo or W are present. ③ The method of reducing temper brittleness is attached (see the previous paragraph).

4) Improve the coercive force of steel and improve the magnetic properties.

5) Its carbides are also stable and prevent other carbides from precipitation. It is also difficult to transfer to solid solution at high temperature.

6) Molybdenum can replace tungsten (1% Mo can be used instead of 2% w because the atomic weight is in a half relationship).

7) Mo can also improve the stability of austenite and be used in valve steel.

8) The intergranular corrosion resistance of Cr and Ni stainless steel can be improved.

9) In some reducing medium, acid resistant stainless steel is easy to passivate, thus improving the corrosion resistance（ Such as sulphuric acid, boiling phosphoric acid and acetic acid, oxalic acid, ant acid, etc.).

10) The heat strength of Pearlite Heat-resistant steel can be improved, and the heat-resistant steel can be added to the steel only, with a volume of about 0.5-1% (and it will be graphitized when used as alloy element alone).

(2) Adverse effects of molybdenum:

1) Volatile, when heated, brown flue gas (molybdenum oxide) will be evaporated.

2) Therefore, the quenching temperature should be reduced by 10-20 ℃ to prevent decarburization.

3) Mo is an element of ferrite formation, so in order to obtain austenite, Ni, Mn and other austenite elements should be added accordingly. Otherwise, ferrite will appear easily when Mo content is more δ Phase or other brittle phase to reduce toughness.

4) Mo reduces the heat conductivity of steel as W, but Mo can prevent overheating.

5) Mo steel has higher deformation resistance than carbon steel.

(3) Molybdenum content in general alloy steel:

Alloy structural steel and tool steel: Mo = 0.15-0.30% (for example 5CrNiMo, 35CrMo, 40CrMnMo, 38CrMoAlA, etc.)

Stainless acid resistant steel: Mo = 1-2.6% (such as cr17mo2ti, cr25moti, cr18ni18mo2cu2ti, etc.)

Heat resistant non peeling steel: Mo = 0.4-1% (16mo, 20CrMo, Cr5Mo, 25cr2mo1va, 15cr11mov, etc.)

High temperature alloy for aviation: Mo = 0.35-7% (e.g. alloy 901 = cr12ni43mo6ti3bmo2ti).

8、V

(1) The good effect of vanadium is:

1) The fine grain has strong effect, which can improve the strength and toughness of steel, reduce the overheat sensitivity and improve the thermal stability.

2) The tempering stability of m-body is improved. The effect of the effect on the hardness of quenched steel is related to the temperature: at the normal quenching temperature (i.e. slightly higher than AC3). Because VC is synthesized by V and C, the alloy degree of solid solution is reduced, so the hardness decreases. When the quenching temperature is increased to more than AC3 (and there is a long holding time), VC will be transferred into the solid solution, so the hardness can be improved. Generally speaking, V has a bad effect on hardenability, but toughness is good, and V is not easy to crack. The V strength of medium carbon steel is ↑, and the toughness is not low.

3) V has a great affinity with O and N, and it is also a strong carbide element. The dispersion of VC is very high and very stable. Therefore, it not only benefits deoxidation and degassing to obtain compact fine grain structure, improves plasticity, toughness and high strength, its impact performance and fatigue strength are higher than V-Steel, and high strength and toughness are available at high temperature and low temperature (＜ 0 ℃). Because the high dispersion of vanadium carbide prevents the weld grain from being coarse, the weldability of steel can be improved, but the steel crystal will grow strongly when heated to VC solution temperature.

4) Because V can improve the creep energy of steel at high temperature, it is one of the alloy elements of Hot-Strength steel.

5) Because the surface of V steel has fine grain structure, it is advantageous to carburizing, and it can extend the carburizing time, without secondary quenching, and can be directly quenched to the required performance.

6) The influence of V on mechanical properties of structural steel has not been determined.

(2) Adverse effects of vanadium:

1) V has no effect on reducing temper brittleness, because V can improve tempering stability and refine grain. Therefore, when V is not high, toughness can also be improved appropriately, and temper brittleness can be reduced.

2) It has the function of hindering the decarburization and graphitization of steel.

3) The coercive force of silicon steel will be reduced when the content reaches 0.05%, which may be due to the deoxidation.

4) When carbon content is certain, V ↑ will make HB ↓, so it generally contains V ＞ 1% (because it is not dissolved into solid solution).

(3) V content in general steel:

Alloy structural steel: v = 0.07-0.35

(examples: 20mnv, 10crv, 45crv, 12CrMoV, 25cr2mo1va, etc.)

In alloy structural steel, the temper brittleness tends to be urgent when v > 0.3%, and it will increase and be used less.

Heat resistant steel: v = 0.1-1 (for example, 20cr3mova, etc.) V can improve the creep performance and deoxidation ability. The Dispersion Hardening of vanadium nitride can make it have corrosion resistance and high thermal strength, but the aging brittleness of V makes the content of V not too high.

High speed steel: v = 0.1 ~ 2.6 has been increased to 5% recently. It is mainly because it can improve the thermal strength of the tool, especially the cutting performance (which is also favorable for cutting high hardness materials), so it is much more, but the performance will not increase significantly after the amount reaches a certain value.

9、Co

(1) Co works well:

1) The results show that the grain can be refined, the tendency of overheating can be reduced. The durability of high-speed steel can be improved by adding Co into the high-speed steel.

2) It can improve the thermal strength (thermal hardness) of steel, which increases the alloying strength and promotes the formation of tempered carbide.

3) It can improve the coercive force of magnetic steel and improve its magnetic base retention induction value, so it has a good influence on the magnetic steel (it is magnetic material itself).

4) When the carbon content is high, it will promote the graphitization of carbon in steel.

(2) Adverse effects of CO:

1) The content is too high to forge. Because it is easy to precipitate hard and brittle metal compounds.

2) There is a high decarbonization tendency.

3) The price is expensive, so the following kinds of cobalt steel are rarely used.

4) One of the characteristics of cobalt is to reduce the stability of austenite and to make the Austenite Isothermal Transformation Curve (C-curve) shift left in steel.

5) The mechanical properties of the intermetallic compounds which are hard and brittle are easy to precipitate.

(3) Cobalt content of general alloy steel:

1) Hot steel: containing CO = 2-4%

(mainly chromium cobalt molybdenum steel group)

2) High speed steel: including co = 4.5-10.5%

(the effect of bco5, bco10 and so on was no longer significantly increased.

3) Magnetic steel: including co = 2.5-16.5%

(cr6co3, cr6co5, cr7co10mo, cr9co15mo, etc.).

10、Ti

(1) The beneficial effects of titanium are:

1) It can form a strong solid tic, which can be stabilized to 1300 ℃, and has a highly dispersed TiC particle which can be stabilized to high temperature, so the grain can be refined and the superheat tendency of steel can be reduced.

2) It is known that the best effect is when ti:c=5 (general c=0.03) can prevent intergranular corrosion. When ti:c=3, the creep resistance is the highest. When the above conditions are met, because all free carbon is combined to form strong solid tic, chromium carbide will not be precipitated along the austenite grain boundary during heating. Otherwise, the chromium carbide formation will appear in the chromium poor region of the solid solution at the grain boundary, and its potential will be reduced relatively. However, the micro temperature difference couple with the solid solution matrix and carbide will be formed, and the intergranular solid solution itself is corroded by anode. The degree of intergranular corrosion will be enhanced with the increase of carbon content（ Coarse grains are also easy to etch)

3) Titanium steel is easy to produce aging hardening, and the aging hardening of low carbon alloy with titanium content more than 2% is especially obvious.

4) Titanium can improve the welding performance of stainless steel.

5) Ti is a strong ferrite forming element. 0.65% Ti will enable γ The area is completely closed. It is also a strong carbide forming element.

6) Ti can reduce the hot embrittlement of sulfur by the action of S, which is similar to Mn.

(2) Adverse effects of titanium:

1) Ti containing steel, especially low carbon Ti steel, is often mixed with non-metal because of its high viscosity of liquid steel, so it is not easy to separate and float out. Attention should be paid to prevent defects. It is possible to pay attention to the high temperature operation and deoxidation of the steel liquid during smelting.

2) The hardness of quenched titanium steel decreases with the increase of Ti content. Because tic is very stable, it can not be dissolved into solid solution even when heated to 1300 ℃, which reduces the carbon concentration in the alloy solid solution.

3) Titanium has a great affinity with N and O, and it is easy to form tin and TiO2. When the ingot is at a low temperature, there are many defects such as non-metallic inclusions and subcutaneous porosity.

4) Ti is also an element of ferrite formation, so it is easy to form ferrite when its content is more than 2% δ Phase or other brittle phase to reduce toughness.

5) Copper V, as with Ti of 0.05%, will reduce the coercive force of silicon steel, which may be deoxidation, and it will promote secondary recrystallization of silicon steel, which can obtain coarse crystal and improve magnetic properties.

(3) Ti content in general steel:

1) Generally, the content of Ti in steel depends on its carbon content, which is generally about 4-8 times *c%.

2) The alloy structural steel contains Ti in chromium manganese titanium steel, stainless steel and heat-resistant steel, which is generally 0.06% - 2%.

11、Nb

(1) The beneficial effects of Nb are as follows:

1) The high dispersion of NBC (melting point 3500 ℃) can be produced, so the grain can be refined, and the grain growth can be prevented when the carbide is heated directly to 1100-1200 ℃.

2) Ti can prevent intergranular corrosion. It is known that Ni = 8 * C% is preferred.

3) It can form intermetallic compound fe2nb2 with Fe, which is α The hearing solubility in iron is ⅶ with temperature \,, so the Nb containing low carbon steel can promote aging hardening.

4) NB can improve the strength and yield point of low carbon steel (25%), improve the high temperature corrosion resistance and strength of stainless steel, and improve the acid resistance.

(2) The adverse effects of Nb are:

1) With Ti steel, the hardness of Nb steel will also be determined by Nb content ↑.

2) NB can refine the grain and improve the toughness of steel, but when the content is too high, ferrite will be formed δ The toughness of the phase or other brittle phase is reduced and the heat processing performance is deteriorated.

Nb content in general alloy steel: NB is only contained in stainless steel, and its content is 8-12 * C% = 1.5%.

12、Cu

(1) The beneficial effect of copper:

1) It can improve the stability of austenite in steel, so it can improve the hardenability and hardenability. Add 2 to the A-body steel

To 4% Cu, the acid resistance can be improved.

2) It can strengthen ferrite, add Cu to ferrite, improve its corrosion resistance in some reducing medium and improve toughness of steel.

3) When adding about 0.20% Cu to low alloy steel, especially when combined with P, the corrosion resistance of steel to atmosphere can be improved. When the content of Cu exceeds 0.75%, the steel strength can be improved by precipitation hardening treatment.

4) Cu is a strong graphitization element, which is used for the refining of graphite steel（ The aging hardening of Cu steel is due to the fact that Cu is α The solubility of iron varies greatly, reaching 3.5% at 830 ℃ and 0.35% at 20 ℃, so the aging hardening can be promoted if Cu > 0.35%

(2) The adverse effects of copper are:

1) The high Cu content will lead to the hot brittleness of steel, which makes it difficult to be forged and rolled.

2) The excess Cu content will increase the coercive force and hysteresis loss, which is unfavorable to the magnetic steel.

3) "Copper embrittlement" - it is pointed out in the article that when Cu > 0.2%, the selective oxidation occurs on the surface during heating process, which causes Fe to oxidize first Cu, while the Cu content on the surface increases to form a film, and then forms a Cu containing network to diffuse, and it is easy to forge at 1030 ℃. The Cu Ni solid solution with high melting point can be formed by adding Ni appropriately, which can reduce the "copper embrittlement".

In general, Cu content < 0.7% can be dissolved in α- In Fe, the carbon does not oxidize, and has no significant effect on the magnetic properties. The anti rust ability can be increased 15 times when Cu = 0.5%; When Cu is more than 0.7%, the mixture will appear inhomogeneous, which increases the coercive force and hysteresis loss, and makes the copper brittle.

(3) Copper content in general alloy steel:

1) Silicon steel: containing Cu = 0.2-0.3%

2) Bearing steel: containing Cu ≤ 0.25%, and Cu + Ni ≤ 0.50%, because Cu will cause aging hardening and affect bearing accuracy, Ni will reduce hardness of quenching layer.

3) Low alloy steel: Cu ≤ 0.2% (for low alloy high strength steel, the content of alloy elements is generally limited to ≠ 0.2%).

4) Stainless steel: containing Cu = 2-4% (cr18ni9cu3ti, etc.).

5)Graphite steel: containing Cu = 0.6%.

13、S

(1) The beneficial effects of sulfur are:

1) Because of its brittle chip, it can get very glossy surface, so it can be used to make steel parts with low load and high surface finish (called fast cutting steel).

2) The surface of a high speed steel tool steel is vulcanized to achieve the following purpose.

(2) The adverse effects of sulfur are:

1) Hot embrittlement: mainly due to the distribution of fusible co crystals in austenite grain boundaries.

2) Sulfur can reduce the plastic screen of structural steel, and increase the cracking sensitivity of tool steel.

(3) The content of s in general alloy steel:

1) Generally speaking, sulfur is harmful to all kinds of steel, so its content is limited.

The s ≤ 0.05% of ordinary carbon steel, smelting by acid converter, and allowable s ＞ 0.05% of 18mnsi and 25mnsi steel

Bearing steel s ≤ 0.02%

High quality carbon steel s ≤ 0.04%

High quality steel s ≤ 0.03%

Only a few steel (such as cr14) with very smooth surface are intentionally added with a small amount of sulfur (=0.2-0.4%) (cr14 can be used as screw, nut, magnetic wheel and other threaded parts, and its surface is smooth and wear-resistant is good)

14、P

(1) The beneficial effects of phosphorus:

1) Because of its brittle chip to get a smooth surface and add the fast cutting steel, the parts with little load are made.

2) Some high speed steel and tool steel are phosphated to achieve the following purposes

3) Phosphorus can improve the specific resistance, and the coercivity and eddy current loss can be reduced because of the easy coarse grain. In terms of magnetic sense, the magnetic sensitivity of steel with high phosphorus content will be improved in weak medium magnetic field. But in the magnetic field, the phosphorus content increased and the magnetic sense decreased slightly. It is not difficult to heat process P-containing silicon steel. So phosphorus is sometimes added to silicon steel, but it makes silicon steel cold brittle. So the quantity is very small ＞ 0.15% (for example, P = 0.07-0.10% in silicon steel used for cold rolling motor).

4) Phosphorus is the most powerful element to strengthen ferrite（ The effect of P on recrystallization temperature and grain growth of silicon steel will be 4-5 times higher than that of the same silicon content

(2) Adverse effects of phosphorus:

1) Phosphorus dissolves in ferrite, which distorts its lattice, grows grain and has cold brittleness. The brittleness is very high when p > 0.13%, and the effect of P on the transformation temperature of fracture energy is about 20 times stronger than that of carbon.

2) The grain of steel is coarsened as Mn.

(3) Phosphorus content of general alloy steel:

Ordinary carbon steel p ≠ 0.055%

Bearing steel: P ≠ 0.027% P + s ≠ 0.045%

High quality carbon steel: P ≠ 0.045%

Alloy steel: P ≠ 0.15% P + C ≠ 0.025%

High quality steel: P ≠ 0.035%

15、B

(1) The beneficial effect of boron:

1) The addition of boron (0.0005-0.005%) in the steel can significantly improve the hardenability of the steel, and at this time, it has no effect on other properties or has little influence—— This can replace Ni (Cr, Mo) to some extent

2) Boron has little effect on the cracking sensitivity of steel.

3) Boron in structural steel can reduce the impact value of steel after normalizing, but after quenching and tempering at low temperature, good impact value can be obtained.

4) The carburizing performance of low carbon boron steel is good, and the surface carbon concentration is not easy to increase excessively. Therefore, the high strength and fatigue strength can be obtained. After carburizing, it can be quenched directly, and the notch sensitivity is also very small. The carburized boron steel should be C ＞ 1%.

5) The medium carbon boron steel has good comprehensive mechanical properties after tempering（ The tempering stability, temper brittleness, fatigue limit, strength and hardness are basically the same as that of boron free steel.

6) The heat treatment performance of boron steel is good, which is the same as that of general alloy structural steel.

7) Boron is soluble in solid solution, and the lattice increases, which improves the strength. Boron in the grain boundary can prevent recrystallization diffusion, so it can increase the thermal strength of steel.

(2) Adverse effects of boron:

1) When the content of B is more than 0.007%, brittleness is easily caused (pearlite is said to be the value, and other steel types can be more).

2) It can reduce the temperature of coarsening of A-body grains, and it is easy to coarse grains, but aluminum can improve.

3) Needle ferrite is easy to produce in the center of the boron steel during the heat treatment of the size boron steel, which affects the mechanical properties.

4) Boron has strong affinity with O and N, which makes it easy to produce nonmetallic inclusions, and therefore boron should be added more. In order to overcome this defect, 0.1-0.12% Al and 0.06-0.04% Ti can be added to deoxidize and nitrogen (the burning loss value is not considered for Al and Ti).

B content in general alloy steel: 0.001-0.005%

(at present, only the boron content of alloy structural steel is as before, but other boron containing steel is rare. There are many kinds of boron steel abroad, but the content is not more than 0.005%, otherwise the hardenability will be worse).

16、N

(1) The beneficial effects of nitrogen:

1) N is also a strong A-body forming element, which is similar to Ni, 27 times stronger than Ni, especially in stainless steel. It may be one of the important elements replacing Ni, especially with Ni, which has better stability of A-body, and eulide Ni.

2) N can also be used in A-body steel to produce diffusion hardening by precipitation of nitride. Therefore, the thermal strength of the system can be improved without significant brittleness.

3) N can improve the thermal hardness of high chromium steel, especially the high chromium tool steel with V. N can increase the interval of tempering temperature of secondary hardness of these steels and move the section to higher temperature, so it can get better comprehensive performance, and N can improve its heat processing performance in high chromium steel.

4) N can promote the formation of A-body in ferrite, because γ The appearance of phase can reduce the tendency of grain coarsening, so the toughness and welding properties of steel can be improved.

5) N has a great influence on magnetic steel: for example, when the solid solution state of N dissolves in steel, the coercivity will increase slightly and the permeability will decrease, and the influence of AlN, fens and other nonmetallic inclusions will be intensified. N is one of the main factors that cause the magnetic aging of silicon steel sheet. Generally speaking, a certain number of inclusions are beneficial to the formation of oriented organization. So it can block the growth of the grains which are not suitable. The results show that the grains with suitable orientation can grow rapidly. N also has a great influence on the quality of the orientation cold rolling, too much or too little N content can not make the N content make the cold rolled silicon steel sheet obtain large grain and high magnetic properties. The suitable content is n = 0.01-0.1% or lower than 0.001%, but to obtain better magnetism, it is better to remove the N remaining in the cold-rolled silicon steel sheet after heat treatment.

6) The surface penetration of steel n can make it obtain high surface hardness (rc70) in 500-600 ℃ and wear resistance, high fatigue limit and corrosion resistance (carried out at 600-700 ℃).

7) A single A-body structure can be obtained by adding more than 0.35% to 0.45% N in chromium manganese steel.

(2) Adverse effects of nitrogen:

1) It is a non-metallic inclusion to form nitrides with alloy elements, and it reduces the effect of alloy elements.

2) The plasticity of N-containing steel will be reduced significantly due to the precipitation of nitride during annealing.

3) N-containing steel will volatilize during forging, so it is difficult to formulate the standard of N-component in industrial steel.

4) It is shown that there must be a minimum Mn content suitable for a certain content of Cr and N steel. If it is lower than this Mn content, n will escape and form porosity when the steel is solidified. The minimum content of Cr 15%, n 0.45% and Mn was 14.5-15%.

(3) N content in general alloy steel:

1) Silicon steel (cold rolled): n = 0.01-0.1% or lower to 0.001%

2) Stainless Chromium Steel: n= (1/75 ～ 1/100) Cr%

3) Nitriding steel: 38CrMoAlA, 25crmo2va, etc

Cr18mn10ni5mo3 steel contains n ≤ 0.3% (for urea industry), and has chromium manganese nitrogen steel and chromium manganese nitrogen nickel steel. For example, cr17mn8ni5n, because of its good oxidation resistance and corrosion resistance, other performance requirements are not bad, so it has achieved considerable results in replacing chromium nickel A-body steel, but chromium manganese nitrogen steel without nickel is easy to produce serious bubbles in ingots and can not be used more.

Note: tin is usually regular crystal, and its color is golden.

17、H

Hydrogen action:

1) H can improve the permeability of steel, but also increase the coercive force and iron loss (the coercive force can increase by 0.5-2 times after H).

2) The interaction of H and C can generate methane (CH4), so the presence of H promotes decarburization.

3) H is the most harmful element in general steel. Because it is the main cause of white spot in steel, it is found that the dangerous content of H in steel is 5-6cm3 / 100g Fe, mainly because the soluble H content of a is large, and the solubility of pearlite is greatly reduced when it is cold to low temperature. Therefore, when cooling is too fast, high pressure hydrogen cannot be released from steel, the tension of high pressure hydrogen and other stresses may exceed the material σ b. So there are many microcracks, which is called the white point. It is known that 640-650 ℃ is the most easy to change a body into pearlite, while 200 ℃ is the most important for dangerous H content in steel, and different data have different data.

18、O

The role of oxygen:

1) The remaining oxygen in ingot or oxygen diffused to the surface of metal can easily oxidize the grain boundary and form brittle oxide interlayer, which insulates (A-body grains). Even intergranular cracks (the latter is often referred to as over firing) are caused in subsequent deformation. It is known that the strength and plasticity of steel will decrease obviously as long as the content of O in steel is more than 0.03 ~ 0.04%.

2) The action of oxygen and carbon may cause carbon loss in steel to cause decarbonization. However, when there is excessive oxygen, the decarbonization layer on the surface will be completely burnt into oxide skin and become a protective film instead, which slows the decarbonization process（ At this time, there are more metal burned, and the effect depends on the tissue improvement of oxide skin.

3) Oxygen will increase the iron loss, decrease the permeability and magnetic induction strength of silicon steel, and increase the effect of magnetic aging.