Design And Research On "Skin" Layer Of "Fist-Like" Forging Die Based On Nickel-Cobalt-Based Alloy

When the traditional 5CrNiMo or H13 material forging die is used for forging the difficult-to-deform materials,due to the high forming temperature and large deformation resistance,the die cavity has severe deformation,wear and cracking,resulting in extremely low die life.Therefore,our research group proposed a new method named a large-scale "fist-like" forging die based on cast steel matrix: that is,casting steel is used as the substrate of the forging die.Then the first layer of welding material JX01 is welded on the substrate by additive manufacturing technology as the strength and hardness transition layer I,and the second layer of welding material JX02 is a high-strength and high-hardness reinforced transition layer II(about HRC50).The matrix,transition layer I and transition layer II are combined together as the "bone" layer of the "fist-like" forging die,which can withstand large load.Finally add a layer of softer superalloy welding material(around HRC30)as the "skin" layer,which can withstand high temperatures up to 650 ? during hot forging.And the nickel-based alloy with good toughness is used in the tensile stress area of the cavity surface,the area under compressive stress uses a higher-strength cobalt-based alloy,which can realize the horizontal functional partition of the surface "skin" layer,so that it can better meet the performance requirements of the forging die.To further improve the quality of "fist-like" forging dies,It need to start from all aspects of die production.In this paper,from the perspective of the surfacing current of the nickel-based alloy selected for the "skin" layer,and optimize this most critical surfacing process parameter.The nickel-based alloy CHN327 and cobalt-based alloy D812 were surfacing welded on 45 steel by melt-arc gas-shielded arc surfacing.During the test,the other surfacing parameters were controlled unchanged,the influence law on the related mechanical properties at the junction of nickel-cobalt-based alloy and the properties of nickel-based alloy was studied.The experimental results show that a good metallurgical bond can be formed between the nickel-based and cobalt-based alloys,and as the nickel-based alloy surfacing current increases,the impact energy and shear strength at the nickel-cobalt-based alloy joint surface increase largely,the wear resistance of the nickel-based alloy is enhanced,but its hardness is showing a downward trend.Based on the mechanical performance experiments carried out,it can be concluded that when the surfacing current of the nickel-based alloy is 190 A,the properties of nickel-based alloys are better and the bonding strength of nickel-cobalt-based alloys is higher.The microstructure of the alloy joint surface at the190 A nickel-based alloy surfacing current was observed by metallography and scanning electron microscopy,and the interface element diffusion at the joint surface was analyzed by energy spectrum.At the same time,the influence of deformation temperature and strain rate on the tensile properties of nickel-based and cobalt-based alloys was studied.Based on the high-temperature tensile experimental data,a mathematical model of the relationship between the flow stress and deformation conditions of nickel-based and cobalt-based alloys was established.In this paper,a "fist" forging die repair trial production was carried out on a large aircraft landing gear failure die(5CrNiMo material).Firstly,the temperature field and stress field distribution of the forging die after the forming of the landing gear forgings are analyzed,and then combined with the performance of each material of the "bone" layer and the performance of the nickel-based and cobalt-based alloys of the "skin" layer,then established the layering principle of the "fist-like" forging die of the outer cylinder of the landing gear and the principle of functional division of the "skin" layer.Finally,an additive manufacturing model of arc surfacing welding(hereinafter referred to as: arc additive manufacturing model)of a "fist-like" forging die of the outer cylinder of a large aircraft landing gear was established,and design the production and remanufacturing process.