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The influence of materials It can be seen from the test data that the effective hardened layers of the three kinds of carburized steels are shallower than the depth of the layer measured by the metallographic method, and under the same process conditions, the 18Cr2Ni4WA is slightly deeper than the effective hardened layer of 18CrMnNiMoA steel. Mainly for parts with a certain carburization concentration distribution, the hardness distribution depends on the hardenability of the carburized layer and the core, that is, the higher the hardenability of the material, the deeper the effective hardened layer. Compared with 20CrMnTi steel, 18Cr2Ni4WA and 18CrMnNiMoA steels have higher hardenability in the core due to their higher alloy content, but only Ni element in the infiltration layer does not form carbides, which improves the hardenability of the layer, and 18CrMnNiMoA steel. The content of Ni is only 1/3 of that of 18Cr2Ni4WA steel. Therefore, the hardenability of 18Cr2Ni4WA steel layer is higher than that of 18CrMnNiMoA steel, and the depth of effective hardened layer is also slightly deep.
After carburizing the same material test piece, as the quenching temperature increases, the holding time is prolonged, and the effective hardened layer depth is also deepened. This is because the diffusion of carbon in austenite is determined by its diffusion coefficient and concentration gradient. When the quenching temperature is increased and the diffusion coefficient is increased, the diffusion ability of carbon in austenite is stronger. At the same temperature, the longer the holding time, the deeper the diffusion depth, and the deeper the effective hardened layer.
The influence of the quenching cooling medium and the like is known from the test data. When the other conditions are the same, the effective hardened layer is also related to the quenching medium and the sample size. Since the cooling ability of the oil is weaker than that of water, less martensite is obtained during quenching, and more martensite is obtained by water cooling, and the hardness is also higher, so that the effective hardened layer is also deep. The larger the sample size, the slower the cooling rate and the less the amount of martensite obtained after quenching, so the depth of the effective hardened layer is also shallower.
The effect of the quenching method It can be seen from the test data of the secondary quenching of different samples that, with an increase in quenching, carbon increases the chance of diffusion to the core, and the effective hardened layer depth tends to increase.