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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A_(c1)、A_(c3)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A_(c1),原始组织对A_(c1)的影响比A_(c3)大。
The solid state transformation point of AISI 4340 steel was measured by thermal expansion method. The microstructure and hardness of AISI 4340 steel were observed. The influence of different heat treatment conditions on the critical point and the continuous cooling transformation curve of austenite (CCT curve) were studied. The results show that the test steel has good hardenability. When the cooling rate is 0.03 ℃ / s, single bainite structure is obtained, and the mixed microstructure of martensite and bainite is obtained at the cooling rate of 0.03 ~ 0.78 ℃ / s, When the cooling rate is higher than 0.78 ℃ / s, the phase transformation microstructure is martensite. Different heat treatment conditions affect A_ (c1) and A_ (c_3) of ATSI4340 steel, while there is no obvious difference in CCT curve. Differentially distributed, metastable tissue has a lower A c1, and the original tissue has a greater impact on A c 1 than c c 3.