| Forging die is an important modern industrial process equipment, the level of thistechnology has become one of the important symbols to measure one country’smanufacturing level. With traditional forging die manufacturing method，the open dieforging permeability of large hydraulic press (800MN)forging die is difficult and thecracks appear easily after heat treatment. To solve these key challenges, the gradientmanufacturing is firstly proposed by Chongqing University, which takes special caststeel as the forging die base and a dual metal gradient layer welded on the working areaof the die cavity. However, this method is still in the exploratory stage, also need to gainmore experience as a guide, so exploring the feasibility and practicality of this type offorging dies in production became a necessary issue to study.The object of this paper is a cast-steeldie forging with dual metal gradient layerwhichused in63MN hot forging press. Study on its performance changes of mouldbefore and after served through the temperature field simulation.The first part introduces the development of forging die, describes the advantagesof casting molds. Because the development of the casting mold has many problems, itmakes the gradient manufacturing emerged, then introduces the functionalcharacteristics of steel substrate, transition layer and cladding layer.The second part describes the forging die failure form and primary factors of thefailure, pointed out that the most important reason forging die failure is die thermal andmechanical load in work.Describes the distribution and transmission characteristics ofdie temperature field and the thermodynamic theory. Finally, introduce the features andfunctions of numerical simulation software DEFORM.The third part introduces the cast-steel base material ZG29MnMoNi, transitionlayer surfacing material RMD142and wear-resistant layermaterial RMD248. Determinethe welding process, the mould trial process, the sample preparation and testingmethods and instruments.The fourth part is the finite element analysis use DEFORM-2D, proved that theforging die temperature fieldhas extremely difference in first cycle and stable work. Sothe analysis of temperature field of hot forging die should be based on the latter.According to the characteristics of the temperature field under stable work, the diebody can be divided into three regions, namely cavity surface temperature fluctuation zone, near-surface temperature gradient zone, substrate temperature balance area. Thendetails the heat penetration depth and temperature distribution in each region.The fifth part give a detailed analysis of the cast-steel base forging surfacing eachfunctional layer (wear-resistant layer, transition layer, steel base) organizationperformance before and afterserved, combining the temperature field of stable workcondition.①The surface layer during a temperature of500-650℃in stable work,it’seasyto occur tempering recrystallization, carbon and iron in material diffusion, grainsbecome larger. Rib plate of die is easy to produce fatigue crack, the micro hardness ofcrack area decreased significantly.②Transition layer and the weld zone during atemperature of400-450℃and400℃in stable work, it’s easyto occurmedium-temperaturetempering,Martensite content decreased, maximal micro-hardnessdecreased amplitude ΔH is40HV.③The microstructure before and after served ispearlite and ferrite, but microstructure and mechanical properties after served hasdifferent changes in the different distance from the weld. More closer weld, the carbideprecipitation more clearer, the more obvious dendritic segregation weakened moreobvious, more dense tissue. Afterserved, the decline of σs, σb, δ, φ of cast-steel base is17%，7%，18%，24%, and the micro hardness and toughness decrease the proportion of10%and28.6%.The cast-steel substrate after forging still meets the requirements of theforging die surfacing.④Determine the sensitive indicators likely cause failure andproposed optimization of steel matrix. The alloying elements should be reasonablyselected, reduce Cr, Mo content suitably. Add normalizing before heat treatment toeliminate the network organization and improve toughness. |
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