Research On The Effect Of The Deformation Nitro Carburizing On The Performance And Organization Of The 3Cr2W8V Mold

With the development of manufacturing industry features information, intelligence,and high performance, higher requirements have been placed on various properties of the die, which serves as a critical process tool in the industry. Hot-die steel is one of the materials widely applied in the tool and die industry around the world. As it needs to bear intensive frictions and impacts at high temperatures. For this reason, the material must have high toughness, thermal fatigue resistance, and wear resistance.3Cr2W8V hot-die steel, a specialized die material is used to produce vehicle intake and exhaust valves. Moderate deformation was created on the surface of the 3Cr2W8V hot-die steel by difference approaches including cold compression, hot compression,cold hammer forging,and thermal shock,so as to form sub-structures inside the surface structure, and nitro carburizing thermal treatment was conducted.Subsequently, surface hardness, hardness gradient of nitro carburized layer,size variations of test blocks, depth of nitro carburized layer, structure of nitro carburized layer, and fracture were analyzed, to investigate the influences of deformation nitro carburizing on the behaviors and structure of 3Cr2W8V hot-die steel.Through analysis on the failed dies from the aspects of stress, cracks, structures, and hardness, in order to found out underlying reasons for failure. By doing so, both the structures and behaviors of die steel could be improved, and guidance could be provided for determining heat treatment processes, and extending the service life of dies.The influences of different deformation approaches and degrees on the specimen size,nitro carburized layer depth, surface layer hardness, and nitro carburized layer hardness gradient were researched through experiments. Results indicated that for cold deformation within a certain deformation range (from 4.87% to 10.52%), the hardness gradient of the nitro carburized layer was properly distributed, as the hardness gradient the subsurface and matrix transitioned smoothly; the binding force between the subsurface and matrix was desirable; the surface of nitro carburized layer had a high hardness and the size almost remained unchanged before and after nitro carburizing. In addition, the depth of the nitro carburized layer was not significantly affected by deformation. For specimens of thermal deformation, within the selected range of deformation (from 0.12% to 12.39%), the hardness gradient of the nitro carburized layer and matrix transitioned smoothly, and the hardness was properly distributed.A white-bright layer appeared in 3Cr2W8V steel after nitro carburizing, with the presence of network or enervation-like nitrides. When the deformation degree was lower than 1%, such a white-bright layers was broadened with finer network-like nitrides. When the deformation degree fell between 4.87% and 10.52%, the white-bright layer was narrowed, with enervation-like nitrides becoming longer and thinner and network-like nitrides still existing. When the deformation degree fell between 13.56% and 37.5%, the white-bright layer was narrowed, with a small amount of enervation-like nitrides becoming shorter and thinner and network-like nitrides still existing. For specimens of thermal deformation, with the increase in deformation, the white-bright layer was thin and continuous, enervation-like nitrides were shorter and fewer, and the tempered marten site structure was not noticeable. For specimens not deformed, there were a lot of scattered pores inside their structures. By contrast, the pores inside specimens of cold compression were concentrated, while those inside specimens of thermal deformation were fewer and uniformly distributed. This suggested that the white-bright layer formed through thermal deformation had better toughness and plasticity. The un-deformed impact fractures showed obvious brittleness, while specimens of both cold and hot compression showed better plasticity than those not deformed. Dimples could be obviously observed on the fractures of thermal deformation, and they could also be observed on those of cold deformation but not as obviously.