Basis And Application Of Large-scale Forging Die Manufacturing For Gradient Layer Surfacing Based On Cast-steel

With the rapid development of the heavy equipment manufacturing industry,such as aerospace,large-scale ships and other countries,an 800 MN hydraulic press,the biggest hot die forging press in the world,has been applied in China.The weight of its forging die can reach 20–40t,the die demands are increasing apparently.Due to the abominable working conditions,hot forging dies are subject to extremely high mechanical stress and thermal stress in die cavity,which brings out die failure,such as plastic deformation,surface wear,fatigue and crack.On the contrary,the Non-working areas such as swallowtail,forging die bottom is extremely difficult to produce failure due to the small stress and lower temperature.Currently,the traditional method of manufacturing hot forging die is to adopting 5CrNiMo or 5CrMnMo material to make forged dies,due to poor cavity part of the premature failure of working conditions,non-cavity parts are still intact,resulting in the whole forging die,this method has resulted in a great waste of die steel materials.Although surfacing welding technology can extend the service life of forging die to some extent,but this technology cannot solve the high cost of large forging die and lower life.In order to solve this problem,a new method,bimetal-gradient-layer surfacing based on cast-steel matrix cavity module,was adopted to manufacture hot forging die,which has showed significant potential to replace die steel with “cast steel + bimetal surfacing layers”,The bimetal surfacing layers are composed of wear layer and transition layer with high strength and wear resistance,which can save peening,nitriding,and other surface treatment methods on it.It can save processes such as open die forging,rough machining,and heat treatment after forging compared with traditional forging die manufacturing methods.Thus,this new method can not only shorten the manufacturing period but also improve the die's service life.It is an environ-mentally friendly method,which has a wide application fore-ground and better economic benefit.In this paper,the mechanical properties and microstructure of cast steel and welding consumables are analyzed and studied.JXZG3 is chosen as the base material of cast steel and JX09,JX20,JX22 are used as the sandwich layer,transition layer,wear resistant layer respectively.The gradient transition from the substrate to the wear layer is realized in the gradient welding structure of the cast steel substrate to avoid the large welding quality defects caused by the large differences in the composition,it has avoided the shedding and cracking of welding gradient layer cracking effectively.The forging process of forging die for titanium alloy forgings which used in 800 MN hydraulic press was simulated by Deform 3D.The distribution of temperature field and equivalent stress field was researched and analyzed during forging process.According to the mechanical properties of the casting steel matrix and welding layer,under the conditions to meet the safety performance,the thickness of cast-steel matrix and surfacing layers are determined by the die stress and properties of materials.Finally,the optimization of thickness of cast-steel matrix and surfacing layers were completed and the 3D model was established.The manufacturing process of a bimetallic gradient forging die of titanium alloy die-cast steel which used in 800 MN hydraulic press was designed and manufactured by the designed method.After the produce is completed,cast steel substrate forging die has good condition,no plastic deformation defects,the surface layer remained intact and die wear loss is small.Production of forging size precision and performance is superior and stable,production tests verify the rationality and applicability of sandwich gradient welding method of steel casting matrix gradient welding die forging.