回火温度对E690海洋用钢组织和显微硬度的影响

在Gleeble-3500型热模拟试验机上,对E690海洋用钢进行直接淬火及快速加热条件下不同温度的回火处理,并采用光学显微镜等设备研究了不同的回火温度对其组织、析出物及显微硬度的影响。结果表明:实验钢直接淬火态组织以板条贝氏体为主,经回火后,组织为板条贝氏体、粒状贝氏体、多边形铁素体的混合组织,不同的回火温度下各自所占比例不同;回火后的析出物主要是10 nm以内的ε-Cu颗粒和20 nm以内的Nb、Ti、Cu的复合析出颗粒,它们均匀、弥散、细小地分布于基体上;550、580和620℃回火时的晶界取向差以≤15°的小角度晶界较多,使材料具有优良的韧塑性;不同回火温度对试样的显微硬度值影响较大,其随回火温度的升高呈现先升高后下降再略微升高的趋势。

Effect of tempering temperature on microstructure and microhardness of an E690 off-shore steel

Steel E690 used in oceanographic engineering were direct-quenched and tempered at different temperatures under rapid heating by using a Gleeble-3500 thermo-mechanical simulator.Effects of different tempering temperatures on microstructure,precipitation and micro-hardness of the steel were investigated by means of optical microscopy,SEM,TEM and hardness measurement.The results show that the microstructure of the specimen direct quenched is mainly lath bainite,and after tempering,it mainly consists of lath bainite,granular bainite and polygonal ferrite with different proportion of them for different tempering temperatures.The precipitation uniformly dispersed in laths are mainly several nanometer ε-Cu and complex precipitation particles of Nb,Ti,Cu with the size 20 nm in the steel after tempering treatments.The quite a number of low-angle boundary with misorientation angle lower than 15° are observed in the steel tempered at 550 ℃,580 ℃ and 620 ℃,resulting in good ductility and toughness.The micro-hardness of the steel increases first and then decreases with increasing tempering temperature when tempered at 520 ℃ to 700 ℃.