RESEARCH AND DEVELOPMENT OF NEW ROLL MATERIALS WITH MULTI-COMPONENT SYSTEM

本研究项目的目的是研究和开发具有高耐磨性和高性能的新型轧辊材料，用于多组分合金轧辊和制粉机。多组分合金中碳化物析出类型为MC、M_2C、M_7C_3和M_3C。碳化物的形态可分为花瓣状、结节状和珊瑚状三种。M_2C碳化物分为片层状和粗板状两种类型，M_7C_3碳化物为棒状或雷氏体型。在Cr和Co含量一定的情况下，碳化物的类型和形态随合金化学成分的不同而有明显的变化，特别是C和V， Mo和W以钨当量（W_<eq>）表示。然而，它们不会被钴改变。每种碳化物析出的化学成分区域用C / V和W_<eq>的简单方程表示。MC和M_2C等温合金的凝固过程为：首先析出奥氏体（γ）相或MC碳化物作为初相，然后发生L* γ +MC共晶反应，凝固结束L* γ +M_2C共晶反应。在MC和M_7C_3碳化物共存的合金中，凝固过程首先析出初生γ相或MC碳化物，然后发生L*gamma+MC共晶反应，最后发生L*gamma+M_7C_3共晶反应。对于含有MC、M_7C_3和M_2C共晶碳化物的合金，凝固顺序如下：L_0 *伽马+ MC + (l1), l1 *伽马+ M_7C_3 + (l2)和l2 *伽马+ M_2C。多组分合金的连续冷却转变（CCT）曲线由珠光体和贝氏体转变两条曲线组成，两者相隔约200K。两种转变曲线的位置受化学成分和奥氏体化温度的影响较大。因此，通过选择合金元素的组合，可以得到具有不同基体组织的多组分合金。一般来说，C含量的增加延缓了珠光体的转变，促进了贝氏体的转变，降低了M_S温度。较高的奥氏体化温度使CCT曲线向长时间侧移动，提高了合金的淬透性。Co降低了多组分合金的淬透性，因为Co促进了珠光体和banite的转变。然而，Co并没有使M_S温度降低那么多。V对珠光体和贝氏体相变均有延缓作用，且珠光体相变的延缓程度大于贝氏体相变。对这些合金进行热处理时，在800K左右回火，二次析出硬化明显，残余奥氏体减少近3%。二次硬化获得的最大硬度范围为HV 900 ~ HV 1050。表明C、V含量的增加和奥氏体化温度的升高必须提高回火温度才能获得最大的硬度。少

The purpose of this research project is to research and develop the new roll materials with high wear resistance and performance for rolling and pulverizing mills using multi-component alloys. The type of carbide precipitaion in multi-component alloys are MC,M_2C,M_7C_3 and M_3C.Morphology of the MC carbide is classified into three of petal-like, nodular and coral-like types. The M_2C carbide is classified into two of lamellar and coarse plate-like types, and the morphology of M_7C_3 is rod-like or ledeburitic types. The type and morphology of carbides varied remarkably depending on chemical compossition of alloy, particularly C and V,and Mo and W expressed by a parameter of tungsten equivalent (W_<eq>), when Cr and Co contents are constant. However, they are not changed by cobalt. Region of chemical compositions in which each type of carbide precipitates is expressed by simple equations in relation to the contents of C vs. V and W_<eq>.Solidification of the alloy with MC and M_2C eute … More ctic carbides takes the following process ; austenite (gamma) phase or MC carbide precipitates firstly as a primary phase, then L*gamma+MC eutectic reaction occurs and the solidification finishes the eutectic reaction of L*gamma+M_2C.In the alloy where MC and M_7C_3 carbides coexist, the solidification begins with precititation of primary gamma phase or MC carbide, followed by the L*gamma+MC eutectic reaction, and finally the L*gamma+M_7C_3 eutectic reaction. As for the alloy with MC,M_7C_3 and M_2C eutectic carbides, the solidification sequence is as follows ; L_0*gamma+MC+(L_1), L_1*gamma+M_7C_3+(L_2) and L_2*gamma+M_2C.The continuous cooling transformation (CCT) curve of the multi-component alloy was found to consist of two curves of pearlite and bainite transformations separated far about 200K betweem them. The positions of both transformation curves are largely changed by the chemical composition and austenitizing temperature.By selecting a combination of alloying elements, therefore, the multi-component alloys with different matrix structures can be obtained. Generally, an increase in C content delays the pearlite transformation and advances the bainite transformation and lowers the M_S temperatures. Higher austenitizing temperature shifts CCT curve to the long time side and this improves the hardenability of the alloy.Co decreases the hardenability of multi-component alloy because Co promotes both of the pearlite and banite transformation. However, Co does not reduces the M_S temperature so much. V delays both of pearlite and banite transformation and the delaying degree of the pearlite transformation is more than the bainite transformation.In the case of heat treatment of these alloys, the secondary precipitation hardening occurs greatly by tempering at around 800K,and there the retained austenite reduces almost less than 3%. The maximum hardness obtained by the secondary hardening ranges from HV 900 to HV 1050. It is made clear that the increase in C and V contents and the austenitizing temperature must increase the tempering tempering temperature to obtain the maximum hardness. Less