中炭素鋼の軟窒化特性に及ぼす合金元素の影響

概要

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Nitrocarburizing is widely applied to automobile parts such as crankshafts and gears. For improvement in strength of these parts, it is important to give the optimal hardness distribution by nitrocarburizing. Therefore, influence of alloying elements on hardness distribution after nitrocarburizing in normalized medium carbon steel was investigated in this study. Steels with different levels of carbon, silicon, manganese, and chromium contens were nitrocarburized at 873K for 7.2ks. The hardness distributions of these steels were measured. Effects of alloying elements on surface hardness (H1) and core hardness (H0) were shown by the following equations respectively. H0(HV)=14.8+288×[C]eq.;[[C] eq.=C+0.07×Si+0.16×Mn+0.19×Cu+0.17×Ni+0.20×Cr]H1(HV)=65.8+392×[Cr]eq.:[[C]eq.=0.48×C+0.16×Si+0.24×Mn+Cr] The hardness distribution of nitrocarburized steels has been estimated with the following equation. H(x,t)=H0+(H1-H0)(1-erf(x⁄2(αDt)1⁄2));[α=exp(-2.53×C-2.71×Si-1.82×Mn-6.81×Cr+3.84)] These equations have made it possible that the hardness profile of nitrocarburized parts can be controlled with alloying elements.