【作者】 潘金芝；

【导师】 任瑞铭；

【作者基本信息】 大连交通大学 ， 材料加工工程， 2010， 博士

【摘要】 通过轧制可以有效细化高碳高合金钢的碳化物,提高韧性,从而提高工模具的使用寿命。但经大轧制比轧制后钢板的厚度有限,难以满足大尺寸工模具钢的要求。因此通过将性能优异的高碳高合金钢板与低成本、高强韧性的中高碳合金钢焊接成复合工模具钢,既可以发挥高碳高合金钢的性能优势,又能降低成本,对生产实际应用具有重要意义,特别是对大尺寸的冷作模具。针对目前广泛使用的Cr12MoV和高速钢碳化物偏析严重、韧性差的缺点,首先研制了一种适合于制造复合冷作模具的高碳高合金钢。在Cr12MoV基础上通过降低C和Cr含量、增加Mo和V含量研制了一种新的高强韧冷作模具钢Crl0Mo1V1。该钢的淬火温度范围较宽(1000℃～1100℃)；在热处理时可采用低淬低回工艺也可采用高淬高回工艺。经常规热处理后,Cr10M01V1的抗弯强度、冲击韧性、耐磨性等各项力学性能均高于Cr12MoV。新型冷作模具钢Cr10M01V1所制模具的使用寿命是Cr12MoV制模具的五倍以上。对冲头在冲裁过程中的应力分布及变化情况的有限元分析表明,复合模具钢与整体模具钢的应力分布基本相同,因此可以根据被冲材料的材质和厚度判断冲头上应力的分布,确定复合冲头刃口部分厚度以及基材的选材原则。研究了5CrMnMo、42CrMo和60Si2Mn三种中碳结构钢作为复合模具钢基材的可行性。针对复合模具钢需要按照模具钢热处理的要求,研究了其热处理后的组织与性能。结果表明,高温淬火可以显著减少钢中韧性差的片状马氏体,全部得到位错型板条马氏体组织,故虽然奥氏体晶粒粗化,但塑性、韧性与强度均无太大变化。高温淬火后如采用低温回火,硬度在60HRC左右,如采用550。C的高温回火,所选的三种中碳合金结构钢的硬度也可达到40HRC。根据应力分析结果,均能满足复合冷作模具钢基体材料的不同需要。对高压力下的真空扩散焊技术及其机理进行了研究,结果表明,焊接质量主要决定于变形率,不论焊接温度T、焊接压力P和保温时间t如何变化,只要变形率达到一定的数值就可以获得相同的焊接效果。根据上述结果,高压力下真空扩散焊工艺参数可以通过下列步骤确定：首先,根据设备条件确定压力P；然后,根据P及工件截面S计算压应力σ,根据σ确定RP,要求RP<σ，其次,根据RP确定焊接温度T；最后,保温时间t根据要求的变形率来确定。另外,焊后应进行一次退火以消除焊缝上的平直晶界,使焊缝强度得到进一步提高。对于异种材料的焊接,焊接压力P应根据强度较低的材料的屈服强度来确定。实物试验表明,用M2和5CrMnMo制成的复合冷作模具钢搓丝板寿命比Cr12MoV搓丝板寿命提高了一倍以上。更多还原

【Abstract】 The ductility of high-carbon high-alloy steels can be improved via refining the carbides by high-ratio rolling, and the service life of the mold fabricated by this type of steels could be prolonged consequently. However, high-ratio rolling leads to thickness limitation of the as-rolled sheet, which is hard to meet the requirement of large size dies. If weld the as-rolled sheet to medium-carbon alloy steel which is relatively inexpensive but possesses good ductility to prepare composite die steels, not only combines the strength and ductility of different materials and prolongs the service life of the die, but also lowers the cost. It is of great significance to the practical application especially to the large size cold work die steels.In order to overcome the disadvantages of serious carbide segregation and poor toughness of Cr12MoV and high speed steel that widely used in industry, a new type high-carbon high-alloy steel that is suitable to prepare composite cold work die steel was developed by reducing the content of C and Cr and increasing the content of Mo and V based on the composition of Cr12MoV, named after Cr10Mo1V1.The range of quenching temperature of this steel is wide (1000℃-1100℃). The hardness of Cr10Mo1V1 can reach to 63.5HRC after quenching at 1050℃and tempering at 150℃or 61.5HRC after quenching at 1150℃and tempering at 550℃. The mechanical properties of Cr10Mo1V1 such as the bending strength, the toughness and the abrasive resistance etc. are all better than Cr12MoV after conventional heat treatment. The working life of the mold die made of the newly developed cold work die steel Cr10Mo1V1 is more than five times longer than that of Cr12MoV.The finite element analysis of the stress distribution and it’s variation of the puncher head during punching shows that the stress distributions of both the composition die steel and conventional die steel are the same. Therefore, the thickness of the edge and the type of base materials of a composite punching head can be determined by the evaluation of the stress distribution of the punching head according to the type and thickness of the materials being blanked.Considering that the heat treatment of composite die steel should be in accordance with the normal die steel, the feasibility of three kinds of mild carbon structural steel 5CrMnMo, 42CrMo and 60Si2Mn as base materials of composite die steel was studied mainly on the microstructure and mechanical property after heat treatment. The results show that though high temperature quenching results in the coarsen of austenite, plasticity, toughness and strength do not change too much because the plate martensite with poor toughness is eliminated notably, instead, lath martensite is obtained. After quenching at the high temperature followed low temperature tempering, the hardness is about 60HRC. in case the followed tempering temperature is 550℃,the hardness is 40HRC. The selected three medium carbon structural steels all can meet the different requirement of base materials of composite die steel according to stress analysisThe technique as well as the mechanism of vacuum diffusion welding using relatively higher pressure is studied, the results show that the welding quality is determined mainly by the deformation rate during the process. No matter how the temperature, pressure and the holding time change, same welding quality will be obtained as long as certain deformation rate is achieved to same extent.According to the above mentioned results, the parameters of vacuum diffusion welding using relatively higher pressure can be determined through procedures listed below:the pressure (P) is determined to ensureσ>RP under certain temperature while taking the conditions of equipment, the relationship between materials yield strength (RP) and temperature and the welding cross sectional area(S) into account.The holding time was determined based on the deformation rate and the microstructure requirements. Post welding annealing helps to eliminate the straight welding interface so that the welding quality can be improved further, meanwhile shortens the holding time. In case of dissimilar metals, the pressure (P) should be determined based on the yield strength of the material whose strength is lower. The working life of the screw plate made of composite die steel M2/5CrMnMo is more than two times longer than that made of Cr12MoV.更多还原