18CrNiMo7-6钢齿轮热处理后开裂失效分析

一批在生产加工后进行了淬火和低温回火的齿轮在库房存放过程中发生开裂。通过超声波探伤、金相检验、化学成分分析、硬度测试、断口形貌观察、端淬试验和补充热处理等手段,对齿轮开裂原因进行了分析。结果表明,开裂齿轮强度高导致氢脆敏感性高,在次表面产生氢致延迟裂纹是引起齿轮快速脆性开裂的直接原因。开裂齿轮淬硬性和淬透性过高,超出了BS EN 10084-2008对18CrNiMo7-6+HH钢淬透性要求,是齿轮开裂的根本原因;通过调整淬火介质,降低淬火时高温区冷速,从而降低淬回火后齿轮的强度和硬度,可有效避免开裂。

Cracking failure analysis of 18CrNiMo7-6 steel gear after heat treatment

A batch of gears after production and processing, quenching and low temperature tempering cracked during storage in the warehouse. The causes of gear cracking were analyzed by means of ultrasonic flaw detection, metallographic examination, chemical composition analysis, hardness test, fracture morphology observation, end quenching test and supplementary heat treatment. The results show that the high strength of the cracked gear leads to high hydrogen embrittlement sensitivity, and the hydrogen induced delayed crack at the sub-surface is the direct cause of rapid brittle cracking of the gear. The root cause of the gear cracking is that the hardening capacity and hardenability of the cracked gear are too high, which exceed the hardenability requirements of BS EN 10084-2008 for 18CrNiMo7-6+HH steel. Thus, the cracking can be effectively avoided by reducing the strength and hardness of the quenched and tempered gear through adjusting the quenching medium and reducing the cooling rate of the high temperature zone during quenching.