钒对高铁制动盘钢中碳化物析出及力学性能的影响

随着列车时速不断提高,制动盘承受的热负荷不断增大,这对制动盘材料提出了更高的要求.为了提高制动盘钢的机械性能及耐热疲劳性,钒元素被添加到制动盘钢中.本文研究了不同淬火温度时V含量对Cr-Mo-V系制动盘钢组织及力学性能的影响,并通过Thermo-Calc热力学软件、碳复型、透射电镜、能谱分析等方法对不同V含量时析出相的演变规律进行研究.结果表明,增加钒含量使高温析出的V(C,N)含量增加,细化奥氏体晶粒和回火马氏体组织.淬-回火态析出相主要为V(C,N)、(Mo,V)C、M7 C3和M23 C6.随钒含量增加,大尺寸M23 C6和M7 C3的析出被抑制,对韧性损害降低;小尺寸(Mo,V)C含量增多,析出强化效果增强.淬火温度为880～900℃时,增加钒含量能细化马氏体和减少大尺寸碳化物,弥补了析出强化对韧性的损害,故冲击功变化不大.淬火温度为920～940℃时,提高钒含量促使(Mo,V)C量急剧增加,冲击功快速下降.实验钢淬火温度不应超过900℃.

Effect of V on carbide precipitation behavior and mechanical properties of brake disc steel for high-speed trains

With the increasing speed of high-speed trains, the brake disc heat load has also been increasing, particularly during emergency braking. Therefore, to address such issues, strict requirements for brake disc materials are suggested. Thus, the addition of V was implemented to improve the mechanical properties and thermal fatigue performance of brake disc steel. The effect of V on the mi-crostructure and mechanical properties of Cr-Mo-V steel for brake discs at different quenching temperatures was investigated. The pre-cipitation behavior of carbides at different V levels was also investigated through thermodynamics calculation using the Thermo- Calc software, carbon replica, transmission electron microscopy ( TEM) , and energy dispersive spectroscopy ( EDS) . The results indicate that the amount of V( C, N) , which precipitates at high temperatures, increases;therefore, the austenite grains and martensite packets are refined. The precipitates in the tested steels after being quenched and tempered are mainly V( C, N) , ( Mo,V) C, M7 C3 , and M23 C6 . With an increase in V content, the precipitation of large size carbides, such as M23 C6 and M7 C3 , is suppressed; therefore, its negative effect on toughness is reduced. With the increase in the amount of small-size ( Mo,V) C, the precipitation strengthening effect is enhanced. When the quenching temperature is in the range of 880-900℃, the increments of vanadium content could refine martens-ite and reduce the content of large size carbides, which negatively affect toughness. Therefore, the impact energy changes little. When the quenching temperature is in the range of 920-940℃, increasing the vanadium content results in a significant increase in the ( Mo, V) C content;therefore, the impact energy drops rapidly. Thus, it is concluded that the quenching temperature of tested steel should not exceed 900℃.