淬火保温时间对高硼高速钢组织和硬度的影响

Effect of Quenching Holding Time on Microstructure and Hardness of High Boron High Speed Steel

传统高速钢有大量昂贵合金元素来形成高硬度碳化物,而用硼元素来替代昂贵金属元素形成高硬度硼化物是一种经济可行的方法,从而开发出新型高硼高速钢。借助扫描电子显微镜、X射线衍射仪、洛氏硬度计等研究了B含量为1.5%、C含量为0.4%的高硼高速钢铸态及淬火后的组织与性能。结果表明,铸态高硼高速钢由铁素体、珠光体、硼化物和少量马氏体组成,硼化物呈网状及鱼骨状分布于金属基体,组织中的硬质相主要由M_(2)B、Fe_(3)(C,B)、M_(6)(C,B)组成。淬火后,部分硬质相出现断网和溶解。当淬火保温时间不超过2h时,部分小颗粒硼碳化物溶入基体,边缘发生钝化,合金硬度显著提高。当保温时间超过3h后,硼碳化物溶解严重,残余奥氏体增多,导致宏观硬度出现下降。

The microstructure and properties of high boron high speed steel with B content 1.5% and C content 0.4% were studied by means of scanning electron microscope(SEM),X-ray diffraction(XRD)and Rockwell hardness tester.The results show that the as-cast high boron high speed steel is composed of ferrite,pearlite,boride and a small amount of martensite.The borides are distributed in the metal matrix in the form of mesh and fishbone.The hard phase in the structure is mainly composed of M_(2)B,Fe_(3)(C,B)and M_(6)(C,B)-After quenching,part of the hard phase appears broken and dissolved.When the quenching holding time is less than 2 h,some small boron carbide particles dissolve into the matrix,passivation occurs at the edge,and the hardness of the alloy is significantly increased.When holding time exceeds 3 h,the boron carbide dissolves seriously,the residual austenite increases,and the macro hardness decreases.