大型铸钢基体“拳头”式锻模制备新方法与失效机理研究

When applying traditional method to manufacture large forging die on the 800MN hydraulic press (the largest one around the world) for hard-to-deform materials, high temperature and heavy load result in problems such as severe deformation/abrasion of die surface layer, extremely short life time, high cost etc. An effective method --Bimetal-gradient-layer surfacing based on cast-steel substrate was put forward, which improved the situation to some extent. However, the graded increase of hardness brought about new problems like surface crack etc. when the surface hardness reached a high level. This study further proposes another new method: “Fist-like” Structure of Forging Die Manufacturing. Its principle is: surfacing a relatively soft material (as the “skin”, nickel-based or cobalt-based, HRC ≈30 under room temperature) on the available forging die (as the “bone”, with graded increase of hardness, HRC≈50 under room temperature). The “bone” can support the whole structure under heavy load and the “skin” can bear the high temperature (650 ℃). By conducting simulation and experiments, the following scientific problems will be solved: component and thickness design of the surface layer(the “skin”); the connection mechanism and strength; the microstructure and property changing rules of the “skin” and the “bone” under actual working conditions； the failure mechanism and modes of the new “fist-like” forging die under high temperature and heavy load. This new method subverts the idea that high surface hardness (through additive manufacturing with graded increase of hardness) is necessary for a large forging die, which is of great scientific significance and application prospect.

为解决在世界上最大吨位8万吨压机上模锻大型高温难变形材料时，采用传统方法所制锻模在高温重载下表层剧烈磨损/变形、寿命极低、制造成本高等问题，曾提出采用大型铸钢基体双金属梯度堆焊制备锻模新方法，但因硬度梯度增加时，表层硬度较高又出现表面裂纹等新问题，为此提出一种“拳头式”锻模设计制造新方法：即将现有研究所得的锻模（表层硬度HRC50）作为“拳头”的骨头，再增材一层常温下硬度较低（HRC30左右）的软质材料（钴基或镍基）作为“拳头”的皮肤层，该层材料在高温650℃左右时强度硬度不发生明显降低。通过模拟和试验研究将解决以下科学问题：皮肤层材料及厚度设计；皮肤层与骨头层连接机理及连接强度；皮肤层/骨头层在实际服役条件下的组织性能变化规律；“拳头式”锻模在高温重载下的失效机理及失效模式。该方法颠覆了大型锻模表面要求高硬度的思想，也颠覆了硬度梯度增加的增材制造思路，具有重大科学意义和应用前景。

为解决现有“夹心层”大型锻模在服役过程中锻模表层出现裂纹的情况，提升模具的性能与寿命，本项目提出了大型铸钢基体“拳头”式锻模制备新方法。项目的研究内容包括：锻模“皮肤层”与“骨头层”材料在高温、重载环境下的力学性能及微观组织特点；“皮肤层”与“骨头层”的连接机理及强度；工艺参数对“皮肤层”、“骨头层”的质量的影响；“皮肤层”材料的的损伤演化规律；“皮肤层”“骨头层”厚度对锻模服役过程应力场、温度场分布的影响规律等。通过开展本项目，建立了各功能梯度层合金体系选用标准，获得了各功能层的最佳厚度分布及最佳电弧增材制造工艺，通过缩尺比试验锻模解剖，获得了各功能梯度层材料成分、组织性能在热-力循环后的性能变化规律。研究项目解决了大型模锻液压机(8万吨) 上大型难变形材料模锻用锻模寿命偏低及模具表面易产生裂纹的问题，在中国二重集团万航模锻有限公司使用的航空发动机机匣模锻用锻模上成功应用。