42CrMo4 steel gear forgings have higher fatigue strength limit and resistance to multiple impacts.

42CrMo4 steel gear compared with 40Cr forged gears

Compared with 40Cr forged gears, 42CrMo4 forged gears are better than the former, especially the hardenability is higher than 40Cr steel gears. After quenching and tempering, 42CrMo4 steel gear forgings have higher fatigue strength limit and resistance to multiple impacts, and the low temperature impact toughness is good.

Chemical composition

The main chemical composition (mass fraction) of forged gear 42CrMo4 steel is: 0.38% ~ 0.45% c, 0.17% ~ 0.37% Si, 0.50% ~ 0.80% Mn, 0.90% ~ 1.20j% Cr, 0.15% ~ 0.25% Mo, ≤ 0.30% Ni, ≤0.030% P, ≤0.030% S.

The phase transition points are: Ac1730 ℃, Ac3800 ℃, Ms310 ℃.

Forging 42CrMo4 steel gears, the initial forging temperature is 1130 ~ 1180 ℃, and the final forging temperature is 850 ℃. After forging, the diameter size is more than 50mm and it needs to be cooled slowly.

The carbon content of 42CrMo4 steel gear is kept at about 0.42%, which ensures that the steel has a good combination of strength and toughness. The addition of Cr and Mo elements is mainly to improve the hardenability of steel. When quenching and heating, Cr and Mo elements are completely dissolved in austenite to improve the hardenability of steel. After quenching, Cr and Mo elements solid solution strengthen the matrix structure and improve the tempering stability of the matrix structure. During high temperature tempering, some Cr and Mo elements diffuse from the matrix structure to the precipitated cementite Fe3C to form alloy cementite (Cr, Mo, Fe) 3C. In addition, the addition of Mo element can eliminate the temper brittleness. Adding a small amount of Ni element can improve the toughness of steel.

There are many factors to consider when choosing. In general, the working conditions of gear forgings are different, and the damage form of gear teeth is different. It is the basis for determining the calculation criterion of gear strength, selecting materials and heat treatment.

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Ms Sharon Wan

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