高速齿轮轴齿表面凹坑产生原因分析

高速齿轮轴在经过渗碳和淬、回火热处理后的喷丸过程中，其齿部表面出现多处凹坑。利用光学显微镜、扫描电子显微镜、直读光谱仪和显微硬度计等对齿部表面的凹坑进行了失效分析。结果表明：齿部表面的凹坑区域存在沿晶扩展的微裂纹，另还存在沿晶界分布的碳化物；表面出现凹坑是由于在渗碳后的空冷过程中表面产生了“⊥”型裂纹，在随后的停放期间和等温淬火时“⊥”型裂纹沿轴向或径向进一步扩展形成剥离裂纹，继而于喷丸过程中表层断裂脱落，产生凹坑。

Analysis on Pits on the Surface of High-speed Gear Shaft

Many pits were found on the tooth surface of high-speed gear shaft in the blasting shot treatment process after the gear shaft was carburized, quenched and tempered. Optical microscope, scanning electronic microscope, direct-reading spectrograph and microhardness tester were employed to analyze the pits. The results show that intercrystalline-extended micro cracks existed on the pit zone of the tooth surface, and there was intercrystalline-distributed carbide at the same time. “⊥”type cracks were generated on the surface after carburized in the process of air cooling. “⊥” type cracks expanded longitudinally to form decotlement crack during the subsequent storage period and isothermal quenching, broke and sloughed in the process of blasting shot, then the pits appeared.