不同焊后热处理对铬钼耐热钢室温冲击韧性的影响

Effect of different post-weld heat treatment on room temperature impact toughness of Cr-Mo heat resistant steel

试验对铬钼耐热钢焊接接头进行三种不同的焊后热处理(690℃×1 h,690℃×8 h,730℃×2 h),采用扫描电镜、显微硬度计等设备观察焊接接头的显微组织类型、冲击断口形貌,探究其室温冲击韧性出现差异的原因。结果表明,耐热钢焊接接头焊态的金相组织由M-A组元和尺寸较小的铁素体组成,而其焊后热处理态的显微组织由块状铁素体以及碳化物组成;碳化物的析出导致铁素体亚晶粒尺寸减小、屈服强度和硬度降低,从而推迟解理断裂的发生,这是焊接接头730℃×2 h热处理后冲击韧性较高的主要原因。

Three post weld heat treatments( 690 ℃× 1 h,690 ℃× 8 h,730 ℃× 2 h) were conducted on the welded joint of Cr-Mo heat resistant steel. A combination of scanning electron microscope and microhardness tester was employed to characterize the microstructures and observe fracture surface of impact specimen,and then the mechanism of toughness variation at room temperature was revealed. It is shown that the welded metallographic microstructures of heat resistant steel welded joint are composed of martensite-austenite constituent and ferrite at smaller size. However,the microstructures of the welded joint after post heat treatment are made up of ferrite and carbide. The precipitation of carbide results in reducing the sub-grain size of ferrite,yield strength and microhardness,therefore,high toughness value of the welded joint obtained by post heat treatment( 730 ℃× 2 h) can be mainly attributed to the delayed occurrence of cleavage fracture.