Basis And Application Of Multiple-layer Sandwiched Surfacing Of Large-scale Forging Die Remanufacturing For Ultra-high Strength Steel

When applying traditional method to manufacture large-scale forging die on the 800MN hydraulic press for difficult-to-deformation materials (such as ultra-high strength steel, titanium alloy etc.), problems such as remarkable deformation of die cavity, severe abrasion, extremely short life-time, high cost and so on are encountered frequently. Because of the higher forming temperature, higher deformation resistance and longer holding time, which lead to greater stress and temperature rising rate, the die surface temperature rises to over 700? quickly and aggravate these problems.Therefore, based on the success of our former patent for aluminum alloys--"Bimetal-gradient-layer Surfacing Bbased on Cast-steel Substrate", this study further proposes another new method:Multiple-layer Sandwiched Surfacing of Forging Die Manufacturing/Remanufacturing for difficult-to-deformation materials. Its principle is as following:surfacing a sandwiched layer between die substrate and bimetal-gradient-layer materials, which is sealed and has better plasticity than that of substrate and transition layer. Under higher stress, the sandwiched layer is allowed to have elastic deformation or even slight plastic deformation, which could diffuse the peak stress under the die cavity and uniformly transform the stress onto substrate. Thus, cast-steel substrate is protected and will not be fractured due to excessive peak stress. To recycle invalid dies effectively, the original 5CrNiMo die is gouged as substrate and multiple-layer sandwiched surfacing process is conducted on on it, which prolongs the life-time significantly.Deform 3D is applied to simulate one aircraft landing gear's forming process on 800MN hydraulic press to analyze the stress, temperature and bearing safety under working condition. By combining the simulation results and performance parameters of 5CrNiMo, JX09, JX20 and JX22 are chosen as the sandwiched layer, transition layer and surface layer, respectively. Then, the allowable strength and theoretical dividing line of each layer, which is adopted as structural model of multiple-layer sandwiched surfacing on 5CrNiMo.Following the technological process, specimen are prepared to analyze the mechanical properties, bonding strength, micro-hardness and microstructure of each layer. The results show that the mechanical properties and micro-hardness transit smoothly; the bonding strength between substrate and JX09/JX20 is 786Mpa and 802Mpa, respectively; the bonding strength between JX09 and JX20 is 1130Mpa and that of JX20/JX22 is 988Mpa, which demonstrates good bonding in interface.A set of die remanufactured by multiple-layer sandwiched surfacing technology is applied on 800MN hydraulic press for the deformation of an aircraft landing gear. After producing 6 forgings, no crack and apparent plastic deformation can be found on die cavity and the remanufactured die maintains good. The dimensional accuracy and stability of forgings are much better than before. Besides extension of die life, the overall cost decreases by almost 50%, which justifies the effectiveness and rationality of this new method.