Steel for fine grain carburizing gear and method of manufacturing the same

Abstract

The invention belongs to the alloy steel field, particularly relating to steel for a fine grain carburization gear and a preparation method thereof. The steel comprises the following chemical compositions in weight percentage: 0.15 to 0.25 percent of C, less than or equal to 0.35 percent of Si, 0.60 to 0.90 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, 0.80 to 1.20 percent of Cr, 0.15 to 0.35 percent of Mo, 0.02 to 0.08 percent of Nb, 0.0005 to 0.0035 percent of B, 0.02 to 0.06 percent of Al, 0.01 to 0.04 percent of Ti, less than or equal to 0.015 percent of [N], less than or equal to 0.0015 percent of [O], the balance being Fe and inevitable impurities. Meanwhile, Ti is more than or equal to 2[N] and B is more than or equal to ([N] minus Ti / 3.4) / 1.4 plus 0.001; and the rolling production process with the finish-to-gage temperature below 900 DEG C is adopted. Compared with the prior carburization gear steel 20CrMoH, the grain size of the steel after carburizing and quenching exceeds ten grade, the bending fatigue resistance(sigama-1) is improved by more than 15 percent and the contact fatigue life(L10) is improved by more than 30 percent.

Description

technical field [0001] The invention belongs to the field of alloy steel, and in particular relates to a fine-grain carburized gear steel and a manufacturing method thereof. Background technique [0002] 20CrMoH steel (equivalent to SCM420H steel in Japan and SAE4118H steel in the United States) is one of the most commonly used carburized gear steels at home and abroad, and is widely used in the manufacture of important gears in automotive transmission systems. With the increasing production and consumption of automobiles, the pressure on resources, environment and energy is also increasing. Therefore, it is urgent to improve the performance of automobiles, including weight reduction and longevity. The improvement of the performance of the automobile transmission system is very important to the long life and weight reduction of the automobile, so it is of great significance to improve the fatigue performance of the automobile gear steel. Grain refinement is an important met...

AI Technical Summary

Problems solved by technology

[0005] In addition, the hardenability of gear steel will be reduced due to grain refinement. According to the SAE J406 standard, each increase in grain size will reduce the hardenability by 8%.

In addition, the precipitation of NbC will reduce the solid solution C content in austenite, thereby further reducing the hardenability

If Nb microalloying 20CrMoH is used to refine grains to improve fatigue performance, the problem of hardenability decrease due to grain refinement and NbC precipitation must also be considered

Obviously, the hardenability of gear steel can be effectively improved by adding B, but at the same time, it must be ensured that the added B will not fail to improve the hardenability due to the precipitation of BN

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