热处理工艺对G115钢铸件组织与性能的影响

Effect of heat treatment on microstructure and properties of G115 steel casting

以均匀化退火后的G115钢铸件为对象,研究了不同正火+回火工艺处理对其显微组织及力学性能的影响,其中正火工艺分别为1070℃×1 h,AC和1100℃×1 h,AC,回火工艺分为一次回火(780℃×3 h,AC)和两次回火(780℃×3 h,AC+750℃×3 h,AC)。结果表明:随着正火温度的上升,G115钢铸件的室温强度和650℃高温强度均有所上升,而韧性有所下降,塑性无明显变化;随着回火次数的增加,G115钢的室温强度和650℃高温强度均有所降低,韧性和塑性无明显影响。正火+回火处理后G115钢铸件中的析出相主要有Laves相、M_(23)C_(6)以及MX(NbC、VN)相,冲击断口形貌呈解理或准解理断裂特征。随着正火温度升高,马氏体板条块(Block)宽度有所增加,排列相对整齐。原奥氏体晶粒尺寸是G115钢室温强度贡献值中晶界强化量的有效晶粒尺寸。推荐的热处理制度为1100℃×1 h(AC)正火+780℃×3 h(AC)回火。

Taking homogenizing annealed G115 steel casting as research subject,the effects of different(normalizing+tempering)treatment process on microstructure and mechanical properties of the steel casting were studied.The normalizing temperatures were respectively 1070℃and 1100℃,both holding for 1 h then air cooling(AC).The tempering processes were single tempering(780℃×3 h,AC),and double tempering(780℃×3 h,AC then 750℃×3 h,AC),respectively.The results show that with the increase of normalizing temperature,both the room temperature strength and the 650℃high temperature strength of the G115 steel casting increase somewhat,while the toughness decreases somewhat,and the plasticity does not change obviously.With the increase of tempering times,both the room temperature strength and the 650℃high temperature strength decrease somewhat,while the toughness and plasticity do not change obviously.Laves phase,M_(23) C_(6) and MX(NbC,VN)phases are the main precipitated phases in the G115 steel casting after normalizing and tempering,and the impact fracture is characterized by cleavage or quasi-cleavage fracture.With the increase of normalizing temperature,the width of martensite blocks increases and the arrangement is relatively neat.The prior austenite grain size is the effective grain size for grain boundary strengthening in the contribution value of the room temperature strength of G115 steel casting.In summary,the recommended heat treatment process is normalized at 1100℃for 1 h,AC,then tempered at 780℃for 3 h,AC.