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高耐磨性和高性能的多元合金轧制机用新型轧辊材料。多元合金中碳化物的析出类型为MC、M_2C、M_7C_3和M_3C。MC碳化物的形态可分为花瓣状、球状和珊瑚状三种类型。M_2C碳化物分为片层状和粗片状两种类型，M_7C_3的形态为棒状或莱氏体型。当铬和钴含量不变时，碳化物的类型和形态随合金化学成分的不同而显著不同，尤其是C和V，且Mo和W用钨当量参数(W_&lt；eq&gt；)表示。然而，它们不会因钴而改变。每种碳化物析出物的化学成分区域，用简单的公式表示，与C与V和W_&lt；E_q&gt；含量的关系。合金在MC和M_2C…中的凝固在MC和M7C3碳化物共存的合金中，凝固始于初生伽马相或MC碳化物的精细化，然后是L伽马+MC共晶反应，最后是L伽马+M7C3共晶反应。对于含有MC、M_7C_3和M_2C共晶碳化物的合金，其凝固顺序为：L_0*伽马+MC+(L_1)、L_1*伽马+M_7C_3+(L_2)和L_2*伽马+M_2C。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，通过选择不同的合金元素组合，可以得到具有不同基体组织的多元合金。一般情况下，C含量的增加延缓了珠光体转变，促进了贝氏体相变，降低了M_S温度。较高的奥氏体化温度使CCT曲线向长时间方向移动，从而提高了合金的淬透性。Co同时促进珠光体和贝氏体相变，降低了多元合金的淬透性。然而，Co对M_S温度的降低幅度不大。V对珠光体和贝氏体相变均有延迟作用，且珠光体相变的延迟程度大于贝氏体相变的延迟程度。在热处理过程中，这些合金在800K左右回火后发生二次析出硬化，残余奥氏体量减少不到3%。二次硬化获得的最大硬度范围为HV 900~HV 1050。结果表明，提高C、V含量和奥氏体化温度，必须提高回火温度才能获得最大硬度。较少

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