Research On Crack Formation Mechanism And Numerical Simulation Of Cast Steel Parts For Construction

The rear seat is an important component used to connect the arms of construction machinery,and its quality has an important impact on the safe operation of construction machinery,so the product process design and manufacturing requirements are very high.Hot cracks are cracks that occur when the castings are at the end of solidification and are in low plasticity and strength.The solidification shrinkage of the castings is hindered.Based on the thermal crack defects of a company’s construction machinery excavator rear seat parts during the casting production process,this paper comprehensively uses experiments and numerical simulations to conduct a series of studies on the influencing factors and the formation mechanism of casting cracks,and discusses the cracks of the castings.Improvement plan.Related work has important engineering application value and theoretical research significance for improving the quality of castings and reducing production costs.After sampling the defects of the rear seat,metallographic and SEM analysis showed that the grain size near the hot cracks was large,and there were non-metallic inclusions in the cracks.The calculation of the filling and solidification process of the rear seat with ProCAST casting simulation software shows that the hot cracking defect on the rear seat is at the position where the wall thickness is large and the final solidification position,and due to technological reasons,the non-metal produced during the pouring process The inclusions will flow back to the inside of the casting along with the liquid feeding,which will reduce the strength of the part.When the alloy shrinks,the tensile stress on this part is greater than its strength limit,and thermal cracks will occur.In this regard,a corresponding process solution was proposed,and the simulation and experimental verification showed that the hot crack defect was successfully eliminated.The thermal cracking of steel castings is closely related to the solidification process.The high-temperature mechanical properties of cast steel in the mushy zone directly affect the stress and strain that can be achieved when it is solidified in the brittle temperature range.Through the high temperature tensile test,the zero strength temperature(ZST)of the experimental steel SC450W is 1405℃ and the zero ductility temperature(ZDT)is 1390℃,and the temperature range of the hot crack sensitive zone is obtained.Through the analysis of the microscopic morphology of the tensile fracture,the change trend of plasticity with temperature is explored,and combined with the characteristic temperature,it is determined that when the SC450W steel drops to 1390℃ during solidification and cooling,the tensile stress generated by shrinkage is greater than 0.1 8MPa At this time,cracks will occur,and because the liquid feeding is hindered,the cracks will remain inside the casting.Through the structural analysis of the rear seat,the thermal crack is in the hindered position,so the complicated rear seat is simplified into an I-shaped structural experimental piece with different lengths and cross-sectional ratios.The relationship between grain size and stress on the occurrence and expansion of thermal cracks is determined.The larger the average radius of the grains,the longer the crack length;the larger the maximum effective stress,the wider the crack width.And through simulation analysis,the shrinkage cavity,shrinkage porosity and thermal cracking defects in the experimental parts are predicted.The thermal cracking criterion based on stress,solid phase ratio and cross-sectional area is proposed for the experimental parts,and the simulation results obtained are consistent with the actual production situation.The shrinkage cavities,shrinkage porosity and thermal cracks are basically the same.Through the CAFE section of the ProCAST software,three parameters in the Gaussian distribution:nucleation undercooling,body nucleation undercooling standard deviation,and maximum nucleation density per unit volume have been analyzed on the impact of solidification tissue simulation,and passed the EBSD experiment The results were compared and analyzed,and the nucleation parameters of the steel during solidification and nucleation were obtained.