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The role of several common alloying elements in steel

    The most commonly used alloying elements for alloying are silicon, manganese, chromium, nickel, molybdenum, tungsten, vanadium, titanium, niobium, boron, and aluminum. Now explain their roles in steel respectively.
    3 q, a& K! c J’ e3 w+ o8 B. c 1. The role of silicon in steel:
    4 G) Z- Z% j7 D B2 A. c& I& B (1) Improve the strength of the solid solution in the steel and the degree of cold work hardening to reduce the toughness and plasticity of the steel. % a1 R% L# j& L- g0 ]. Z’ R
    (2) Silicon can significantly improve the elastic limit, yield limit and yield ratio of steel, which is a general spring steel. 8 O& S’ c” ~* H5 W/ b# Z
    (3) Corrosion resistance. High-silicon cast iron with a silicon content of 15%-20% is a very good acid-resistant material. When steel containing silicon is heated in an oxidizing atmosphere, a layer of SiO2 film will also be formed on the surface, thereby improving the oxidation resistance of the steel at high temperatures. , \5 ]! \; f f1 h; T) H9 ]4 p
    Disadvantages: (4) Deteriorating the welding performance of steel. ) R& S! S$ Z! s6 w
    2. The role of manganese in steel
    -f$ A0 T7 i2 F. E (1) Manganese improves the hardenability of steel. 6 t! u$ r% \, c1 ]3 ]: t$ O6 {
    (2) Manganese has a significant effect on improving the strength of low-carbon and medium-carbon pearlite steel.
    * c8 S. J& x( s$ I$ o (3) Manganese improves the high temperature instantaneous strength of steel. 4 Q+ q5 Y/ r+ }) j8 l
    The main disadvantages of manganese steel are: ①When the manganese content is high, there is obvious temper brittleness; ②Manganese has the effect of promoting the growth of grains, so manganese steel is more sensitive to overheating. Pay attention to the heat treatment process. This shortcoming can be overcome by adding grain-refining elements such as molybdenum, vanadium, titanium, etc.: ⑧When the mass fraction of manganese exceeds 1%, the welding performance of steel will deteriorate, and ④manganese will reduce the corrosion resistance of steel. .
    + b( o* _5 p( q; o8 M2 o4 t2 h 3. The role of chromium in steel + |” _! V: e H* e! A: l8 J9 n
    (1) Chromium can improve the strength and hardness of steel.
    8 a5 q1 a& d” {+ ^$ P9 `$ |3 R (2) Chromium can improve the high temperature mechanical properties of steel.
    -S# ~( `+ C6 K! P7 g8 g, W (3) makes the steel have good corrosion resistance and oxidation resistance) W3 k2 Y3 e5 C# y# Y6 p
    (4) Prevent graphitization 8 S! ^5 t6 N( O1 ?* j/ d, H
    (5) Improve hardenability. -D% i! i+ J1 x( f
    Disadvantages: ① Chromium can significantly increase the brittleness transition temperature of steel ② Chromium can promote the temper brittleness of steel.
    9 N( w6 F: v/ W 4, the role of nickel in steel
    1 Q; p) K! Z! \0 B- \8 D. f0 L (1) It can increase the strength of steel without significantly reducing its toughness.
    5 ~; o5 p& L6 ?.] (2) Nickel can reduce the brittle transition temperature of steel, which can improve the low temperature toughness of steel.
    ; B1 k. J/ o- R8 E; o! u (3) Improve the workability and weldability of steel. $ j# e: U7 Q6 s7 d
    (4) Nickel can improve the corrosion resistance of steel, not only acid resistance, but also alkali and atmospheric corrosion. : q1 H/ ^: E: S3 n: Y) S
    5. The role of molybdenum in steel
    & |. s9 s) w& p$ ~5 d% k5 ~ (1) Mo has a solid solution strengthening effect on ferrite. + o1 D” W! A) L
    (2) Improve the thermal strength of steel
    (A& T: N$ T) Q5 W$ E (3) Anti-hydrogen corrosion effect. # M5 X# |+ T9 y4 p, s
    (4) Improve the hardenability of steel. 6 i8 P) b1 Y5 W” j* l’ r
    Disadvantages: The main undesirable effect of molybdenum is its tendency to graphitize low-alloy molybdenum steel.
    : ~5 O) Q( a+ }0 V$ m$ w! g 6. The role of tungsten in steel
    \% ?: H9 r0 k/ P (1) Increase intensity 4 `& R9 d! }/ }$ \0 s9 Y
    (2) Improve the high temperature strength of steel.
    % ~4 n! S# G) g (3) Improve the hydrogen resistance of steel.
    , ?, {$ b( X! X (4) is to make the steel hot hard. Therefore, tungsten is the main alloying element in high-speed tool steel.
    . v6 F# `8 q; M* s6 y+ i 7. The role of vanadium in steel
    9 W- h8 R” N# I. l: V/ p+ ^ (1) Thermal strength.” y* ]9 Q: Z9 W
    (2) Vanadium can significantly improve the welding performance of ordinary low-carbon low-alloy steel. 5 x& F: o/ I8 |- [; M$ u
    8. The role of titanium in steel 4 f. {# V, M* m8 {7?
    (1) Titanium can improve the thermal strength of steel, improve the creep resistance and high temperature durability of steel;
    / i. h- j/ X a (2) and can improve the stability of steel in high temperature and high pressure hydrogen. The stability of the steel to hydrogen under high pressure is as high as 600℃. In the pearlitic low-alloy steel, titanium can prevent the graphitization of molybdenum steel at high temperature. Therefore, titanium is one of the important alloying elements in the heat-strength steel used in boiler high-temperature components.
    ! R5 b# j# U; H 9, the role of niobium in steel
    ‘i& `0 |9 I’@ (1) Niobium has a strong binding force with carbon, nitrogen and oxygen, and forms a corresponding extremely stable compound with it, which can refine grains and reduce the overheating sensitivity of steel Sex and temper brittleness.
    ; g0 d) O+ M1 I” m3 Q (2) Has excellent hydrogen resistance.
    4 v/ b, |3 P( E (3) Niobium can improve the thermal strength of steel; C7 T/ A; C$ U) d; `
    10. The role of boron in steel;
    & c8 Q. Q \3 K9 b4 R7 ]3 L (1) Improve the hardenability of steel. “L+ z, h’ |% G* l/ D
    (2) Improve the high temperature strength of steel. Strengthen the role of grain boundaries.
    4 R6 t# i9 g4 z$ ]7 K 11. The role of aluminum in steel
    & \$ P) p9 ^/ X5 t (1) Used as a deoxidizing and nitrogen-fixing agent in steelmaking, to refine grains, inhibit the aging of low-carbon steel, and improve the toughness of steel at low temperatures, especially reducing steel Brittleness transition temperature;
    0 A2 n. m1 d+ N. D/ Z (2) Improve the oxidation resistance of steel. There have been many studies on the oxidation resistance of iron and aluminum alloys; 4% AI can change the structure of the oxide scale, and the addition of 6% Al can make the steel have oxidation resistance below 980C. When aluminum and chromium are used together, their oxidation resistance is greatly improved. For example, an alloy containing 50% to 55% iron, 30% to 35% chromium, and 10% to 15% aluminum still has good oxidation resistance at a high temperature of 1 400C. Due to this role of aluminum, in recent years, aluminum is often added as an alloying element to heat-resistant steel. / C4 S; }6 h3 b& E’ N&]
    (3) In addition, aluminum can also improve the corrosion resistance to hydrogen sulfide and V2O5.
    -f: S0 f# h2 n/ T! z% n {Disadvantages: ① If too much aluminum is used during deoxidation, it will promote the graphitization tendency of steel. ② When the aluminum content is higher, its high temperature strength and toughness are lower.