20Si2MnCrNi钢复杂变截面铸件的热流场协同调控与强韧化机制OA

To meet the urgent requirements for lightweighting and high strength-toughness in heavy-duty vehicle steering knuckles,and to address the susceptibility to shrinkage cavities and porosity in complex variable cross-section castings of a novel 20Si2MnCrNi steel(C 0.19％,Si 1.56％,Mn 1.02％,Cr 0.765％,Ni 0.94％),this study proposes a multi-structure synergistic thermal-fluid field control strategy.The ProCAST software was employed for coupled thermal-fluid simulation of mold filling and solidification processes of the castings at a pouring temperature of 1 585℃,and the optimized process incorporated smooth bottom-gating filling,dual-riser lateral feeding,and localized chilling(chills 70 mm×22 mm×45 mm with 8 mm gaps),and was compared with a conventional mid-gating process.The simulation results showed that the conventional process triggered flow separation and turbulence at abrupt cross-section changes,causing premature closure of feeding channels in thin-walled regions and a shrinkage porosity ratio of 1.35％in load-bearing zones;after optimization,the shrinkage porosity ratio was reduced to 0.32％,with all defects transferred to the risers(riser shrinkage porosity ratio 4.1％),achieving a fully densified casting body.After normalizing at 1 000℃,quenching at 920℃,and tempering at 610℃,the dense castings exhibited uniformly fine tempered martensite/sorbite structures with nanoscale dispersed carbides.Mechanical testing revealed that the disc housing-shaft neck transition zone achieved a 0.2％proof strength(Rp0.2)of 809.4 MPa,tensile strength of 915.2 MPa,elongation of 16.1％,and reduction of area of 36.4％;the lateral bracket root exhibited tensile strength of 918.6 MPa and elongation of 15.8％;the thick-section adjacent area exhibited tensile strength of 914.3 MPa and elongation of 14.9％,demonstrating excellent cross-sectional property uniformity.The study demonstrates that the thermal-fluid field synergistic control strategy,by reconstructing the axial temperature gradient and enforcing directional solidification,eliminates shrinkage cavity and shrinkage porosity defects in the load-bearing zones,thereby fully releasing the contributions of solid-solution strengthening from alloying elements(Si,Mn,Cr,Ni)and dispersed carbide precipitation,ultimately achieving outstanding strength-toughness synergy in complex variable cross-section cast steel components.