Study On High-temperature Diffusion Process Of30Cr1Mo1V Steel Rotor Forging

Large forgings are necessary basic components of major constructions and majortechnical equipments, and their quality grade requirements are higher. Steel ingot is rawmaterials of large forgings, internal defects such as non-metallic inclusions, cracks,shrinkage, porosity, segregation and others are often exists in them which has a badinfluence on the quality of forging products, and makes the forging process morecomplicated. The larger the size is, the severer the defect will be. For large forgings,segregation is one of internal defects which cannot be neglected, componentinhomogeneous can cause the difference of microstructure, reduce impact toughness andcorrosion resistance of forgings and etc.In order to eliminate or mitigate inhomogeneous distribution of alloy elements,improve hot-working properties and mechanical properties of forgings, high-temperaturediffusion is often used in producing large forgings. However, heating metal materials athigh temperature for long time will also lead to oxidation, decarburization, overheatingand even overburning, which affects the properties of forgings, and even leads to scrap.Beside, equipment resources are taken up, and the production efficiency is reducedbecause of long time heat preservation for ingots and billets in furnace. At present, theunderstanding of heat diffusion is relatively shallow, there are still many disputes for theunclear process principle in the use of this technology.Based on the material of30Cr1Mo1V steel and the segregation ratio SR tested byexperimental method of different high-temperature diffusion processes, combined with themathematical model of dendrite segregation homogenization, the influence of heatingtemperature and holding time on distribution of alloy elements was studied, rules ofsegregation ratio SR changing with heating temperature and holding time before and afterhigh-temperature diffusion were analyzed, and the mathematical model of dendritesegregation homogenization of30Cr1Mo1V steel was built in this paper.Based on microstructure experiments and mechanical properties experiments,influence rules of high-temperature diffusion on microstructure and mechanical properties were analyzed. Results show the banded structure produced by dendritic segregation andforging deformation can be eliminated by high-temperature diffusion. The grain size canrefined by high-temperature diffusion before forging, and mechanical properties offorgings can also be improved by homogenization effect of diffusion. while the grain arecoarsened because of long time high temperature heating after forging, which leads to theworse mechanical properties of the steel.Relying on hot compression test and hot tensile test, the influence ofhigh-temperature diffusion process on flow stress, hot ductility and fracture limit C wasanalyzed in the paper. Experimental results show that the high-temperature diffusion isuseless to improve hot ductility and fracture limit C in low temperature forging, while,high temperature forging does in high temperature forging.