深冷处理降温速率对304LN焊接接头组织和热应力的影响

Effect of Deep Cryogenic Treatment Cooling Rates on Microstructure and Thermal Stress of 304LN Welding Joint

为探究深冷处理中降温速率对304LN焊接接头组织和热应力的影响,对304LN焊接钢板分别以2 K/min和5 K/min 2种降温方式做深冷处理,并通过应变仪、温度传感器和光学显微镜等考察了深冷处理前后焊接接头组织及热应力的变化。试验结果表明:随着降温速率的增加,深冷处理过程中焊接接头的热应力在数值上增大,但其均小于材料的屈服强度;深冷处理后明显可观察到马氏体的生成和碳化物的析出,且随着降温速率的增加,碳化物数量更多且分布更加均匀;同时借助能谱仪(EDS)对焊接接头碳化物含量进行了测定,证实了降温速率的增加将促使碳化物析出的观点。由此建议对工件采取降温速率为5 K/min的深冷处理从而获得较为稳定的微观组织。

In order to investigate the influence of the cooling rate on the microstructure and thermal stress of 304LN welded joints during cryogenic treatment,304LN welded steel plates were subjected to cryogenic treatment with 2 K/min,5 K/min,respectively.And the microstructure and thermal stress of the welded joint before and after cryogenic treatment were investigated by strain gauge,temperature sensor and optical microscope.Results showed that with the increase of the cooling rate,the thermal stress of the welded joints during the deep cryogenic treatment increased in value,but still less than the yield strength of the material.Martensite and carbides could be clearly seen after deep cryogenic treatment,and with the increase of the cooling rate,carbides were increased in number and the distribution was more uniform.At the same time,the content of carbides in welded joints was measured with the aid of energy dispersive spectrometer(EDS),which confirmed the view that the precipitation of carbides was promoted with the increase of the cooling rate.Therefore,it is suggested to adopt cryogenic treatment with a cooling rate of 5 K/min for the workpiece to obtain a more stable microstructure.