30Cr2MoV枪管钢碳化物溶解与析出规律

枪管钢重要发展方向是采用二次硬化效应确保高温强度，然而这类钢韧性普遍偏低。为改善韧性，研究了30Cr2MoV新型二次硬化枪管钢中碳化物溶解与析出规律及其对韧性的影响。采用扫描电子显微镜、透射电子显微镜、碳复型和相分析技术对碳化物进行表征，结果表明：随着淬火温度（850~1 050 ℃）升高，碳化物溶解越多，回火时二次硬化相析出动力越大；在950 ℃温度（略低于MC型碳化物全固溶温度）淬火时，奥氏体晶界处未溶MC型碳化物可有效抑制原奥氏体晶粒长大，冲击功保持较高水平（107 J）；在950 ℃温度淬火后回火时，随着回火温度（600~700 ℃）升高，M₃C型碳化物不断溶解，M₂C型碳化物逐渐析出，M₇C₃型碳化物在略小于650 ℃时开始析出，MC型碳化物含量几乎不变，碳化物总量减少约14%；在600 ℃、625 ℃和650 ℃温度回火时冲击断口分别呈准解理、解理和韧性断裂；625 ℃温度时解理断裂原因可能是在625 ℃温度回火时M₃C型碳化物向M₂C型碳化物转变过程中发生了晶内强化和晶界弱化、有害元素向晶界偏聚和碳化物粗化。

Dissolution and Precipitation Rule of Carbides in 30Cr2MoV Gun Barrel Steel

The important development direction of gun barrel steel is to use the secondary hardening effect for ensuring a high temperature strength. This type of steels is generally of low toughness. The dissolution and precipitation behaviors of carbides as well as their effects on the toughness of a new 30Cr2MoV secondary hardened gun barrel steel were studied to improve the steel toughness. The carbides were characterized by using scanning electron microscope, transmission electron microscope, carbon replica and phase analysis technologies. The results show that, as the quenching temperature is raised from 850 to 1 050 ℃, the dissolution quantity of carbides increases, then so does the precipitation kinetics of secondary hardened phase. At the quenching temperature of 950 ℃ (slightly lower than the total solution temperature of MC carbides), undissolved MC at the austenite grain boundaries can effectively inhibit the growth of original austenite grains, and the impact energy remains high (107 J). As the tempering temperature increases from 600 to 700 ℃ after quenching at 950 ℃, the dissolution of M₃C and the precipitation of M₂C increase, the precipitation of M₇C₃ starts at a temperature slightly lower than 650 ℃, the content of MC remains almost unchanged, and the total content of carbides is decreased by about 14%. The impart fractures show quasi-cleavage, cleavage and ductile fracture, respectively, at the tempering temperatures of 600, 625 and 650 ℃. The cleavage fracture at 625 ℃ may be correlated with the transition from M₃C to M₂C, which causes intragranular strengthening and grain boundary weakening, segregation of impurity elements at grain boundaries and coarsening of carbides.