利用TEM和三维原子探针(3DAP)研究了一种Fe-Cr-Ni-Mo高强钢中碳化物随回火温度的变化及其对力学性能的影响. 结果显示, 回火温度较低(400 ℃)时, 钢中析出M₃C合金渗碳体及M₇C₃合金碳化物, M为Fe, Cr和Mn的组合, 其中M₃C长度约为1 μm, 而M₇C₃尺寸较小, 小于200 nm; 回火温度较高时(500和600 ℃), 碳化物析出数量增加, 但M₃C合金渗碳体尺寸变小, 数量减少甚至不出现, 同时析出尺寸较小的M₂C和M₆C(小于200 nm); 继续提高回火温度(650 ℃), 除M₂C外还出现MC型碳化物, 其尺寸小于100 nm, 析出数量减少. 合金碳化物M₂C, M₆C和MC的合金元素主要以V, Cr和Mo为主. 高强钢的强度随回火温度的升高而下降, 但在500~600 ℃回火温度区间, 由于V碳化物析出会引起二次硬化效果, 强度下降不明显, 因此实验钢在530~600 ℃内回火后可获得较好的强韧性配合.

The variation of carbides with tempering temperature in a Fe-Cr-Ni-Mo high-strength steel and their effect on mechanical properties are investigated by means of TEM and three-dimensional atom probe (3DAP). The results show that there mainly appear M₃C and M₇C₃ when tempering temperature is rather low (400 ℃), the former is thick with a length of about 1 μm and the latter is fine and the length is less than 200 nm, and M is composed of Fe, Cr and Mn. Tempering at 500 and 600 ℃, the amount of carbide increases gradually, and there appear M₂C and M₆C types of carbide which are both less than 200 nm in length, simultaneously M₃C becoming fine or disappear. When tempering temperature further increases to 650 ℃, besides M₂C there also appears MC type of carbide. The size of both M₂C and MC are less than 100 nm, meanwhile the amount of carbide decreases. The M of M₂C, M₆C and MC is a combination mainly of Cr, Mo and V. The strength of the Fe-Cr-Ni-Mo high-strength steel gradually reduces with increasing tempering temperature, but the downtrend of strength is rather small when tempering temperature is in the range of 500~600 ℃, owing to secondary hardening induced by the appearance of V-carbide. In short, the high-strength steel could obtain better combination of strength and impact toughness after tempering at about 530~600 ℃.