Research On Forging Process And Defects Control Of Die Block Forgings Of5CrNiMo

Hot die steel was often used as block forgings with working under high temperature andhigh wear. The die block forgings were often formed from ingots with the various internaldefects, such as coarse-grained, internal porosity and voids, were often broken and closed byusing upsetting and stretching. In addition, the reasonable forging process parameters must beobtained to avoid cracks, folds and other defects. The research subject was supported byScience and Technology Project of Shaoguan city (2011CXY/C15)“Research ondevelopment of die block forgings of5CrNiMo hot die steel”.The deferent forging methods and parameters on the8t electro-hydraulic hammer werecarried out based on the software DEFORM-3D, the whole process are simulated and theeffect on quality of die block forgings was obtained. The main research contents andconclusions are as follows：（1）The forging process was established and simulated based on DEOFRM-3D software.Effects of three different forging method, such as axial repeated upsetting and stretchingmethod, radial cross forging method, integrated forging method on forging were studied andanalyzed. The results show that when using axial repeated upsetting and stretching method,the distributions of temperature and stress fields are uniform, the forging load is small, crackoccurs difficultly, and the forging operation is convenient.（2）The experimental verification of finite element model was combined with theexisting experimental equipment. The comparison results show that the trend of finite elementsimulation and experimental measurements is entirely consistent. The maximum relative errorof forging surface temperature and dimensional changes is8.5%and is acceptable within thescope of the project. The reliability and accuracy of the finite element model are verifiedeffectively.（3）The defects control, such as crack on forging surface, internal porosity and voidsdefects of upsetting process, were simulated and analyzed. The critical hole expansion ratio ofductile failure was adopted to predict crack defects that may occur during upsetting, thecriterion for cracks was established, and the crack prediction finite element model wasverified by experiment. The effect of upsetting process on internal porosity and voids defectswas analyzed. The closure law of porosity and voids defects and forging together upsettinglaw and reasonable process parameters were obtained.（4）The crack on forging surface, folding and voids defects of stretching process were simulated and analyzed. The critical hole expansion ratio of ductile failure was adopted topredicted crack defect, and forging process was improved. Criterion folding defect wasestablished, the condition for folding defect arising was obtained and verified by experiment.The internal void defect was closed and the reasonable amount of feed and reduction wereobtained at last.