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利用Gleeble-1500热模拟机、光学显微镜(OM)、扫描电镜(SEM)以及透射电镜(TEM)对渗碳钢23CrNi3Mo的连续冷却相变规律以及等温转变规律进行了研究,并基于此,设计了一种新的热处理冷却工艺.研究结果表明,渗碳后试样以0.05 ℃/s和0.1 ℃/s的冷速连续冷却时,表面渗碳层为高碳马氏体组织,过渡区为高碳马氏体+下贝氏体的混合组织,基体为下贝氏体组织;渗碳试样外表面在高温段以较低的冷速(0.05~3 ℃/s)连续冷却时,碳化物沿晶界析出形成网状碳化物;无渗碳的实验钢的贝氏体等温转变温度范围为375~450 ℃.新的热处理冷却工艺为:试样在880 ℃保温完成后,采用快速冷却工艺,以冷速大于等于5 ℃/s进入贝氏体转变温度区,直接入450 ℃的盐浴炉,入炉后均温5~10 min,在低温转变区即贝氏体转变温度区间,采用慢速冷却工艺,冷速小于等于0.1 ℃/s.获得的试样渗碳层深度为1.4 mm,国外的阿特拉斯钎头渗碳层深度为1.2 mm,两者基本相同,但前者硬度分布更加平缓;两者表面显微组织均为高碳马氏体组织,过渡区均为马氏体加下贝氏体组织,基体均为贝氏体组织.通过设计新的热处理冷却工艺,获得了与国外钎头相同水平的试样.

The continuous cooling transformation and isothermal transformation were investigated by thermal simulation machine Gleeble-1500, optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM).Based on the investigation, a new heat treatment cooling process was designed.Results show that the microstructures at the surface, the transition zone and the matrix of the steel after carburizing at the cooling rates of 0.05 ℃/s and 0.1 ℃/s are high carbon martensite, a mixed microstructure of lower bainite and high carbon martensite and lower bainite, respectively.The network carbide was formed along the boundary in the microstructure at the surface when the carburizing steel was cooled from the quenching temperature with a lower cooling rate from 0.05 ℃/s to 3 ℃/s.The temperature of bainite transformation of steel without carburizing ranges from 375 ℃ to 450 ℃.The new heat treatment cooling process was set as follow: the carburizing steel was cooled from 880 ℃ with a fast cooling rate of 5 ℃/s to the bainite transformation zone, and put into the salt bath furnace soaking for 5-10 minutes at 450 ℃;after that, the steel was slowly cooled at the cooling rate lower than 0.1 ℃/s.Microstructural examination indicates that the depth of carburizing case of the specimen after the new process is 1.4 mm, which is nearly the same with the drill bit from Atlas abroad (1.2 mm).The hardness distribution of the specimen after the new process is smoother.The obtained microstructures at the surface, the transition zone and the matrix of the specimen after the new process and the drill bit from Atlas abroad are both high carbon martensite, a mixed microstructure of lower bainite and high carbon martensite and lower bainite, respectively.The carburizing steel which has a same level as the drill bit abroad was obtained by designing the new heat treatment cooling process.