Heat Treatment and Wear of High-Alloyed Irons

研究了高合金铁（高速钢型白口铁）在无润滑滚滑工况和润滑滚滑工况下的热处理和耐磨性。在铁中加入6mass%Cr， 2mass%Mo， 4mass%W和6mass%V的碳化物形成元素，碳含量在1.5 ~ 2.5mass%之间变化。在2.0质量%C的铁中加入4mass%或8mass%的Co来强化基体组织。这些铁在高频炉中熔化，然后在砂型中铸造。结果总结如下：(1)当奥氏体化温度为1373K，冷却速度为5 ~ 10k /min时，基体组织转变为马氏体，而在823K回火时，基体组织发生了充分的二次回火硬化。从1273K淬火时，二次回火硬化不足。(2)随着铁的含碳量增加，铸态硬度增大。在二次回火淬火中，2.5%C铁的硬度低于2.0%C铁。这是由于马氏体中的碳和合金元素随着铁的碳的减少而减少。(3)铁中添加Co后，其淬火性能自然变差，淬火组织硬度下降，MC型碳化物呈粒状，M_2C、M_6C和M_7C_3较少，出现了明显的二次回火硬化，残余奥氏体趋于稳定。(4)在铁中加入8mass%的Co，可以显著提高铁在无润滑滚动滑动下的耐磨性。(5)高速钢型白口铁在润滑条件下的轧制疲劳寿命是高铬白口铁的10倍左右。加入8mass%Co后，白口铁变得特别优异。(6) Co的加入提高了高速钢型白口铁的耐磨性。然而，少量Co的加入是无效的，需要Co超过8mass%来改善。

The heat treatment and the wear resistance under unlubricated rolling-and-sliding condition and lubricated rolling condition of high-alloyed irons (the white iron of high-speed steel type) were investigated. The carbide forming elements, 6mass%Cr, 2mass%Mo, 4mass%W and 6mass%V,were added to irons and the carbon content was varied from 1.5mass% to 2.5mass%. 4mass% or 8mass%Co was also added to the 2.0mass%C iron to strengthen the matrix structure. These irons were melted in a high-frequency furnace and cast in a sand mold. Results were summarized as follows.(1) The matrix structure transformed to martensite by quenching of austenitizing temperature of 1373K and cooling rate 5-10K/min, and the secondary temper hardening occurred sufficiently by tempering at 823K.The secondary temper hardening was insufficient in the case of quenching from 1273K.(2) The amount of carbides increased and the as-cast hardness became high with the carbon content of iron. However, the hardness of 2.5%C iron was lower than 2.0%C iron at the secondary temper hardening. This is due to that carbon and alloying elements in the martensite decreased with the carbon of iron.(3) By addition of Co to iron, its quenching properties naturally deteriorated and the hardness of the quenched atructure decreased, but MC type carbide became granular and M_2C,M_6C and M_7C_3 being small : besides, the secondary temper hardening appeared remakably and the retained austenite became stable.(4) The wear resistance under unlubricated rolling-and-sliding was considerably improved by adding 8mass%Co to the iron.(5) The rolling fatigue life of the white iron of high-speed steel type under lubrication was about 10 times as long as high Cr white iron. The white iron became particularly excellent by adding 8mass%Co.(6) The addition of Co improved the wear resistance of the white iron of high-speed steel type. However, a small amount of Co addition was ineffective and Co over 8mass% should be necesarry to improve.