Development of a new multi-component white cast iron for cold work roll

为开发新型冷轧工作辊用多元白口铸铁，研究了最佳化学成分，研究了最佳化学成分下的凝固组织与凝固条件的关系、相变及热处理特点和磨料磨损特性。推荐以下化学成分为最佳化学成分。碳含量为1-1.5%。铬含量为5%。钼含量为5%或更多。钒含量为1%或更多。化学成分最佳的铸铁含有9%~12%的MC和M_2C共晶碳化物。铸铁件的凝固组织依赖于冷却速度，MC和M_2C碳化物的二次枝晶间距和尺寸随冷却速度的增加而变小。在淬火状态下，由于未观察到熔化现象，铸铁中马氏体和残余奥氏体共存。由于珠光体和贝氏体相变的机头偏长，铸铁件的硬度较好。回火硬度曲线显示出高合金化工具钢和高碳多元白口铸铁中常见的二次硬化现象，回火硬度在800K左右达到最大值(约850HV)。其硬度高于冷轧工作辊所需的硬度(800HV)。从Suga磨料磨损试验结果可以看出，铸铁的耐磨粒磨损性能略低于高碳多组分白口铸铁。

In order to develop a new multi-component white cast iron for cold work roll, the optimum chemical compositions were investigated, and the relationship between the solidification structure and the solidification conditions, and the characteristics of transformation and heat treatment, and abrasion wear characteristics were examined about the cast iron with the optimum chemical compositions. Following chemical composition is recommended as the optimum chemical composition. Carbon content is 1-1.5%. Chromium content is 5%. Molybdenum content is 5% or more. Vanadium content is 1% or more. The cast irons with optimum chemical compositions contain MC and M_2C eutectic carbides of 9% to 12%. Solidification structure of the cast irons depends on the cooling rate, and the secondary dendrite arm spacing and sizes of MC and M_2C carbides, which are shown as a function of the cooling rate, become smaller with an increase in cooling rate. Martensite and retained austenite coexist in the cast irons in hardened state because Mf was not observed in the cast irons. The hardnabihty of the cast irons is good because the noses of pearlite and bainite transformation are on a long time side. The curves of temper hardness of the cast irons show the secondary hardening which is usually seen in highly alloyed tool steels and multi-component white cast irons with high carbon, and the tempered hardness of the cast irons reached the maximum value(about 850HV) at around 800K. It's hardness is higher than the necessary hardness (800HV) for cold work roll. It is thought from the results of suga abrasion wear tests that abrasion wear resistance of the cast irons is somewhat lower than that of the multi-component white irons with high carbon.