焊后热处理对TP310HCbN耐热钢性能的影响

Effect of Postwelding Heat Treatment on Microstructure and Mechanical Properties of TP310HCbN Heat-resisting steel

对TP310HCbN奥氏体耐热钢进行了3种模拟的焊后热处理,即分别在715℃加热0.5 h、755℃加热0.5 h和755℃加热1.5 h后炉冷到400℃以下空冷,以及焊后热处理后再分别于650℃时效1×10^(3) h、3×10^(3) h、6×10^(3) h、10×10^(3) h。检测了焊后热处理及时效后钢的冲击韧度、硬度、冲击断口形貌和显微组织。结果表明:经3种模拟焊后热处理的TP310HCbN钢的显微组织均为奥氏体,具有良好的冲击韧度和较高的硬度;随着在650℃时效时间的延长,TP310HCbN钢的硬度先降低后升高,冲击韧度下降至20 J左右;M23C6碳化物在晶界聚集并呈网状分布导致时效后钢的冲击韧度降低,而晶内均匀细小Z相的沉淀强化提高了钢的硬度;焊后热处理对TP310HCbN钢650℃时效后的组织没有影响,焊后热处理温度较高和保温时间较长能加速时效过程中钢的组织变化。

TP310HCbN austenitic heat-resisting steel was subjected to three types of simulated postwelding heat treatments,that is,heating at 715℃ for 0.5 h,755℃ for 0.5 h,and 755℃ for 1.5 h,furnace-cooling to 400℃ and air-cooling,respectively,as well as to postwelding heat treatments followed by aging at 650℃ for 1×10^(3) h,3×10^(3) h,6×10^(3) h and 10×10^(3) h,respectively.The steel was tested for impact toughness,hardness,pattern of impact fracture and microstructure after the postwelding heat treatment and after the postwelding heat treatment followed by the aging.The results indicated that(a)the TP310HCbN steel subjected to three types of simulated postwelding heat treatments all exhibited microstructure consisting of austenite,good impact toughness and higher hardness;(b)as aging time at 650℃ became longer,hardness of the TP310HCbN steel decreased at first and then increased,and impact toughness reduced to about 20 J;(c)M23C6 carbides aggregated and were distributed at grain boundary in the form of network,resulting in the decrease in impact toughness of the steel after aging,whereas the hardness was enhanced due to precipitation strengthening of uniform fine Z phase in the grain interior;and(d)higher postwelding heat treatment temperature and longer time at the temperature were likely to render change in microstructure of the TP310HCbN steel during the aging treatment faster.