40B, alloy structural steel. Unified digital code: A70402

   [] Chemical composition (mass fraction) (%)

C: 0.37 ~ 0.44

Si: 0.17 ~ 0.37

Mn: 0.60 ~ 0.90

B: 0.0005 ~ 0.0035

[40B] mechanical properties of alloy steel
    Blank sample size (mm): 25

 Heat treatment:

The first quenching temperature (℃): 840; coolant: water

Second quenching temperature (℃): - tempering heating temperature (℃): 550;

    Coolant: water

Tensile strength (σb / MPa): ≧ 785

Yield point (σs / MPa): ≧ 635

Elongation (δ5 /%): ≧ 12

Reduction of (ψ /%): ≧ 45

Impact absorbed energy (Aku2 / J): ≧ 55

Brinell hardness (HBS100/3000) (annealing or tempering condition): ≦ 207 [main features] hardenability steel more than 40 high critical quenching in water diameter 17 ~ 32mm, the critical quenching in oil diameter 7 ~ 16mm; quenching in oil, its hardness, toughness and section shrinkage rate is higher than 40 steel. After quenching and good overall performance, can replace 40Cr.

  [Application Example] This steel is usually used in the quenched state, for the manufacture of steel cross-section larger than 40, higher performance parts such as gears, steering rod, shaft, convex axis, tractor parts such as crank handle. In addition, instead of 40Cr steel production performance can be less demanding of the small size parts.

[Representation] ① steel beginning of the two numbers indicate the carbon content of steel, the average carbon content of the very few that, as 40Cr, 25Cr2MoVA alloy pipe

     ② the main alloying elements in steel, in addition to individual micro-alloying elements, the general said to a few percent. When the average alloy content <1.5%, the steel elements generally marked only symbols, but not marked content, but prone to cause confusion in those special circumstances, after the element symbol can also be marked with the number "1", such as steel "12CrMoV" and "12Cr1MoV", the former chromium content of 0.4-0.6%, 0.9-1.2% for the latter, all the remaining ingredients the same. When the average content of alloying elements ≥ 1.5%, ≥ 2.5%, ≥ 3.5% ... ... when, after the element symbol should be marked content, can be expressed as the corresponding 2,3,4 ... etc. For example 18Cr2Ni4WA.

③ vanadium steel V, Ti Ti, Al AL, boron B, and other rare earth RE alloying elements, are micro-alloying elements, although the content is very low, should bid out in steel. For example 20MnVB steel. To 0.07-0.12% vanadium, boron is 0.001-0.005%.

 ④ High quality steel should be added in the last steel "A", as distinct from the general high quality steel. ⑤ special purpose alloy structural steel, steel, known (or suffix) represents the symbol of the use of steel.

     For example, rivet screw special 30CrMnSi steel, steel, said to ML30CrMnSi.