大型难变形材料模锻用锻模“夹心层”制造新方法基础研究

When applying traditional method to manufacture forging die on the 800MN hydraulic press (the largest press in the world) for difficult-to-deformation material ( such as high temperature alloy, titanium alloy etc.), problems such as remarkable deformation of die cavity, severe abrasion, extremely short life-time, high cost, and etc. are encountered frequently. Based on the success achieved on aluminum alloy forging die by applying a new method-- Bimetal-gradient-layer surfacing based on cast-steel substrate, this study further proposes another new method: Multiple-layer Sandwiched Surfacing of Forging Die Manufacturing. Its principle is as following: surfacing a sandwiched layer between cast-steel substrate and bimetal-gradient-layer surfacing, which has lower yield strength than that of cast-steel substrate.This sandwiched layer will diffuse the peak stress under the die cavity and uniformly transform the stress onto cast-steel substrate. Thus, cast-steel substrate is protected and will not be fractured due to excessive peak stress. By conducting research on the connection theory、microstructure and property between sandwiched layer and cast-steel substrate and gradient layers,we will get a gradient mathematical model for each different material layer; by studying the stress diffusion rule of sandwiched layer during die forging、 the distribution rule of stress and strain and the impact of thickness and location of the sandwiched layer on the decreasing of peak stress, the criteria of pressure bearing capacity for each layer material is got; a set of scale testing forging die is going to be manufactured to verify the results. Finally, the material composition、mechanical property, thickness, and location of each surfacing layer and their changing pattern of microsturcture and property before and after service are obtained.

为解决在世界上最大吨位模锻液压机（8万吨）上模锻大型高温难变形材料（高温合金、钛合金等）时，采用传统方法所制锻模，型腔变形大、磨损严重、寿命极低，制造成本高等问题，基于所发明的大型铸钢基体双金属梯度堆焊制备锻模新方法在铝合金模锻上获得成功应用，又提出了大型锻模夹心层堆焊制造新方法，其原理是:在铸钢基体与双金属梯度堆焊层之间先堆焊一层比基体屈服强度更低的夹心层焊材，形成软垫，将模具型腔下面的峰值应力扩散后以近均布方式传递到铸钢基体上，从而保护铸钢基体不因峰值应力过高而破裂。通过研究夹心层与铸钢基体和过渡层的连接机理及检测组织性能，建立各材料层性能梯度数学模型；研究并获得模锻时夹心层应力扩散规律，应力应变分布规律，其厚度、位置对峰值应力衰减的影响规律，各层材料的承压能力判据；设计制造一套缩尺比试验锻模，并进行试验验证及解剖；最终获得各堆焊层材料成分、性能、厚度及位置及模锻前后组织性能变化规律。

本项目基于项目组所发明的大型铸钢基体双金属梯度堆焊制备锻模新方法在铝合金模锻上获得成功应用，又提出了大型锻模夹心层堆焊制造新方法。完成的主要研究内容包括：夹心层与铸钢基体和过渡层的连接机理及组织性能检测；模锻过程中夹心层材料应力扩散规律和应力应变分布规律；夹心层材料厚度、位置对峰值应力衰减的影响规律等。通过开展本项目，建立了各材料层性能梯度数学模型，获得了各层材料的承压能力判据，通过缩尺比试验锻模解剖，获得了各堆焊层材料成分、组织性能在模锻前后组织性能变化规律。解决了大型模锻液压机(8万吨) 上制约大型难变形材料模锻用锻模寿命极低及模具制造成本昂贵的关键瓶颈问题，在中国二重集团万航模锻有限公司使用的大型钛合金钓尾框模锻用锻模上获得了成功应用。