热处理温度对长期服役T23钢焊缝微观组织的影响

Effect of heat treatment temperature on microstructure of long-term serviced T23 steel weld

以服役时间超过6万小时的T23钢水冷壁管对接接头作为研究对象,对焊接接头进行不同温度的热处理,通过显微硬度分析、金相分析、扫描电镜、能谱分析等手段深入研究不同温度热处理后的焊缝区微观组织变化,分析合金碳化物在晶界的分布规律,揭示T23钢焊接接头焊缝区再热裂纹的形成机理。结果表明,T23钢焊态试样的盖面焊缝组织为粗大板条马氏体和贝氏体的混合组织,原奥氏体晶界明显,最大晶粒尺寸超过300μm,大部分晶粒尺寸在150~200μm;T23钢盖面焊缝区在580℃热处理后出现了明显二次硬化现象,晶粒细化和弥散强化是导致二次硬化的主要原因;T23钢盖面焊缝区在720℃和760℃热处理时,均在焊缝晶界位置出现了孔洞及析出物,且析出物主要以M_(23)C_(6)和MC为主;析出物与孔洞的位置关系模式主要有两种,一种是孔洞在析出物前部沿晶界长大,另一种是孔洞在析出物靠近晶内一侧长大,形成机理有待进一步研究。

Butt joints of T23 steel water-cooled wall pipes with a service time of more than 60000 h were taken as the research object.The welded joints were subjected to heat treatment at different temperatures.The microstructure evolution of the weld zone after heat treatment at different temperatures was deeply studied by means of microhardness analysis,metallographic analysis,scanning electron microscope and energy spectrum analysis.The distribution law of alloy carbides on grain boundaries was analyzed,and the forming mechanism of reheat cracks in weld zone of the T23 steel welded joints was revealed.The results show that the weld structure of the welded specimen of T23 steel is a mixture of coarse lath martensite and bainite,with obvious prior austenite grain boundaries,the maximum grain size exceeding 300μm,and size of most grains being 150-200μm.After heat treatment at 580℃,the weld zone has obvious secondary hardening phenomenon,and grain refinement and dispersion strengthening are the main reasons for secondary hardening.When heat treated at 720℃and 760℃,holes and precipitates appear on the grain boundaries of the T23 steel cap weld zone,and the precipitates are mainly M_(23)C_(6)and MC.There are two main modes of the positional relationship between precipitates and pores.One is that the pores grow along the grain boundary in the front of the precipitates,and the other is that the pores grow on the side of the precipitates near the inner grain.The formation mechanism needs to be further studied.