Development of High Speed Steels with a Fine Grain Size by Carbide Dispersion Carburization (CDC) Process.

近年来，人们提出了一种制备超细晶粒和均匀分布的颗粒组成的高速钢的新工艺，即碳化物弥散渗碳（CDC）工艺。在该工艺中，高Ti、V、Mo、W等含量的无碳铁基合金渗碳可获得上级耐磨性和优异的韧性。在本研究中，试图通过CDC工艺生产的高速钢具有非常高的硬度超过Hv 1000的计算相图的基础上的信息。（1）为了建立估算铁基多元体系相平衡的数据库，对Fe-C和Fe-N基体系进行了热力学分析。(2)在热力学分析结果的基础上，模拟了Fe-V-Mo-C合金在渗碳和热处理过程中的组织演变（包括碳化物的种类、含量和体积分数）。(3)测定了CDC法生产的几种不同成分的Fe-V-Mo-C试样中碳化物的体积分数、尺寸和分布。试验结果表明，碳含量和钒钼原子比是决定碳化物尺寸和分布的最重要因素。(4)在此基础上，对获得高硬度和高韧性的合金进行了组织控制的计算和试验。目前正在与钢铁企业进行实际应用的合作项目。

Recently, a new type of process to fabricate high speed steels consisted of hyperfine grains together with uniformly distributed particles, which is called as carbide dispersion carburization (CDC) process, is proposed. In this process, the superior resistance to wear and the outstanding toughness can be obtained by carburizing C-free Fe base alloys with high contents of Ti, V,Mo, W etc..In this study, an attempt by CDC process was made to produce high speed steels with very high hardness over Hv1000 on the basis of information of the calculated phase diagrams. The obtained results are as follows :(1) In order to establish a data base for estimating phase equilibria of the Fe-base multi-component systems, thermodynamic analysis of Fe-C and Fe-N base systems were performed.(2) On the basis of results of the thermodynamic analysis, microstructural evolution (including the kind, content and volume fraction of carbides appearing during carburizing and heat treatment) of Fe-V-Mo-C alloys was simulated.(3) Volume fraction, size and distribution of carbides in several Fe-V-Mo-C specimens with different composition produced by CDC process have been measured. The result of the examination suggests that the carbon content and the atomic ratio between V and Mo are the most important factors for determining the size and distribution of carbides.(4) On the basis of such the calculation and examination for the microstructural control, some alloys with suitable composition for obtaining both high hardness and toughness have been produced and examined. Consequently we could get some excellent alloys with hardness over Hv 1000.At the present, a cooperation project for practical applications with steel making companies is running.