Research On The Formation Mechanism Of Forged Steel Crankshaft Magnetic Marks

Forged steel crankshaft is one of the key parts on the engine, the quality of crankshaft are largely decide the quality and the life of engine. Forging crankshaft has been widely used, because it can meet the strength, toughness and plasticity when worked. While the magnetic particle indication is one of the main factors which cause the crankshaft scrap, so to do the research on crankshaft magnetic particle indication is very necessary.In this paper, Gleeble-1500 D thermal simulation testing machine was used for thermal compression tests of crankshaft usual material 42 CrMo alloy steel, and the flow stress curve of 42 CrMo alloy steel was got, the relationship between flow stress and temperature, strain rate was analyzed, when the deformation temperature was constant, the flow stress increased with the increase of strain rate, when the strain rate was constant, the flow stress decreased with the increase of temperature, and the thermal deformation constitutive model of 42 CrMo alloy steel was established based on the Arrhenius hyperbolic sine function.High temperature tensile tests were carried out on Gleeble-1500 D thermal simulation testing machine, Normalized Cockroft & Latham damage model was selected to calculated the critical damage value of different deformation temperature and deformation rate, high temperature damage model was established considering deformation temperature and deformation rate by the introduction of thermal deformation Zener-Hollmon parameter; The fracture mechanism of 42 CrMo alloy steel was analyzed of ductile fracture by means of scanning electron microscope on the tensile fracture, in addition, in order to study the damage evolution process of 42 CrMo alloy steel, high temperature tensile tests were carried out under different strains according to the high temperature tensile stress-strain curve, high temperature tensile process was simulated through Deform-2Dsimulation software, the selected damage model was proved accuracy by compared the simulated critical damage and the experimental critical damage value, which was in good agreement with each other.The information of the magnetic particle indication was related with center defects mental material, which judged preliminary by observing the magnetic particle indication position and magnetic particle indication surface morphology of magnetic particle inspection on crankshaft block and combining with the enterprise related inspection standard; Hot forging process of crankshaft was simulated by using simulation software Transvalor Forge-3D, discovered that the central mental was easy flow to the inside of rod neck, and the simulated metal flow with the actual forging experimental mental flow were in good agreement with each other by compared them, therefore, central mental exposure is one of the main factors in the formation of crankshaft magnetic particle indication.