采用热膨胀法测定了AISI4340钢的固态相变点,观察了组织和硬度,研究了不同热处理状态对临界点和奥氏体连续冷却转变曲线(CCT曲线)的影响.结果表明,试验钢具有较好的淬透性,冷速为0.03℃/s时得到单一贝氏体组织,冷速为0.03~0.78℃/s之间得到马氏体和贝氏体混合组织,冷速大于0.78℃/s时相变组织都为马氏体.不同热处理状态对ATSI4340钢的Ac1、Ac3有影响,而CCT曲线没有明显差别.弥散分布、介稳定的组织具有较低的Ac1,原始组织对Ac1的影响比Ac3大.
The critical transformation temperature of AISI4340 steel was determined by thermal expansion method,and the microstructure and hardness were observed. The effects of heat treatment process on critical temperature and austen-ite continuous cooling transformation curve(CCT curve)were studied. The results show that the hardenability of the ex-perimental steel is good. The austenite transformation product is bainite when the cooling rate is 0.03℃/s. The austenite transformation products are marensite and bainite when the cooling rates lie in range of 0.03-0.78 ℃/s and martensite when the cooling rate is greater than 0.78℃/s. Ac1 and Ac3 are different with different heat treatment processes and CCT curve is similar. Ac1 of the unstability initial microstructure is lower than the equilibrium initial microstructure. Effect of different initial microstructure to Ac1 is larger than Ac3.
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