A 2D axisymmetric numerical model was established to investigate the variations of molten pool with different melt rates during the vacuum arc remelting of 8Cr4Mo4V high-strength steel,and the ingot growth was simulat...A 2D axisymmetric numerical model was established to investigate the variations of molten pool with different melt rates during the vacuum arc remelting of 8Cr4Mo4V high-strength steel,and the ingot growth was simulated by dynamic mesh techniques.The results show that as the ingot grows,the molten pool profile changes from shallow and flat to V-shaped,and both the molten pool depth and the mushy width increase.Meanwhile,the variation of both the molten pool shape and the mushy width melt rate is clarified by the thermal equilibrium analysis.As melt rate increases,both the molten pool depth and the mushy width increase.It is caused by the increment in sensible heat stored in the ingot due to the limitation of the cooling capacity of the mold.The nonlinear increment in sensible heat leads to a nonlinear increase in the mushy width.In addition,as melt rate increases,the local solidification time(LST)of ingot decreases obviously at first and then increases.When melt rate is controlled in a suitable range,LST is the lowest and the secondary dendrite arm spacing of the ingot is the smallest,which can effectively improve the compactness degree of 8Cr4Mo4V high-strength steel.展开更多
采用双真空熔炼制备了8Cr4Mo4VE轴承钢并对其进行均匀化处理,以控制其碳化物的数量、大小、形态及分布。利用旋转弯曲疲劳试验测试了8Cr4Mo4VE轴承钢的旋弯疲劳性能,采用扫描电镜、体式显微镜和能谱仪等分析了其旋弯疲劳试样的断口形貌...采用双真空熔炼制备了8Cr4Mo4VE轴承钢并对其进行均匀化处理,以控制其碳化物的数量、大小、形态及分布。利用旋转弯曲疲劳试验测试了8Cr4Mo4VE轴承钢的旋弯疲劳性能,采用扫描电镜、体式显微镜和能谱仪等分析了其旋弯疲劳试样的断口形貌和起裂源成分。结果表明:8Cr4Mo4VE轴承钢疲劳极限达到915 MPa。断口观察表明,其疲劳损坏方式主要有表面起裂和次表面碳化物起裂。次表面碳化物起裂扩展模式有3种:碳化物起裂快速扩展断裂、碳化物起裂扩展形成鱼眼区(FIE)、碳化物萌生微裂纹形成光学黑区(Optical dark area,ODA)后扩展形成鱼眼区。碳化物周围萌生裂纹及扩展时其扩展速率da/dN同应力强度因子ΔK满足Forman公式。碳化物应力强度因子ΔK_(carb)远小于光学黑区应力强度因子ΔK_(ODA)时,碳化物周围出现ODA,其裂纹扩展速率约为(1.84~2.10)×10^(-12) m/cycle。8Cr4Mo4VE轴承钢中的碳化物形状及所受应力对其疲劳寿命循环次数具有显著影响。展开更多
基金financially supported by National Natural Science Foundation of China(Nos.U1908223 and U1960203)Fundamental Research Funds for the Central Universities(Grant No.N2125017)Talent Project of Revitalizing Liaoning(Grant No.XLYC1902046).
文摘A 2D axisymmetric numerical model was established to investigate the variations of molten pool with different melt rates during the vacuum arc remelting of 8Cr4Mo4V high-strength steel,and the ingot growth was simulated by dynamic mesh techniques.The results show that as the ingot grows,the molten pool profile changes from shallow and flat to V-shaped,and both the molten pool depth and the mushy width increase.Meanwhile,the variation of both the molten pool shape and the mushy width melt rate is clarified by the thermal equilibrium analysis.As melt rate increases,both the molten pool depth and the mushy width increase.It is caused by the increment in sensible heat stored in the ingot due to the limitation of the cooling capacity of the mold.The nonlinear increment in sensible heat leads to a nonlinear increase in the mushy width.In addition,as melt rate increases,the local solidification time(LST)of ingot decreases obviously at first and then increases.When melt rate is controlled in a suitable range,LST is the lowest and the secondary dendrite arm spacing of the ingot is the smallest,which can effectively improve the compactness degree of 8Cr4Mo4V high-strength steel.
文摘采用双真空熔炼制备了8Cr4Mo4VE轴承钢并对其进行均匀化处理,以控制其碳化物的数量、大小、形态及分布。利用旋转弯曲疲劳试验测试了8Cr4Mo4VE轴承钢的旋弯疲劳性能,采用扫描电镜、体式显微镜和能谱仪等分析了其旋弯疲劳试样的断口形貌和起裂源成分。结果表明:8Cr4Mo4VE轴承钢疲劳极限达到915 MPa。断口观察表明,其疲劳损坏方式主要有表面起裂和次表面碳化物起裂。次表面碳化物起裂扩展模式有3种:碳化物起裂快速扩展断裂、碳化物起裂扩展形成鱼眼区(FIE)、碳化物萌生微裂纹形成光学黑区(Optical dark area,ODA)后扩展形成鱼眼区。碳化物周围萌生裂纹及扩展时其扩展速率da/dN同应力强度因子ΔK满足Forman公式。碳化物应力强度因子ΔK_(carb)远小于光学黑区应力强度因子ΔK_(ODA)时,碳化物周围出现ODA,其裂纹扩展速率约为(1.84~2.10)×10^(-12) m/cycle。8Cr4Mo4VE轴承钢中的碳化物形状及所受应力对其疲劳寿命循环次数具有显著影响。
