共析鋼のオーステナイト領域における延性と破断挙動

抄録

The hot ductility and fracture behaviour of an eutectoid carbon steel in the austenite range were studied by tensile tests in a wide range of strain rates from 10^-5 s^-1 to 1 s^-1. Flow curves and ductility (elongation to failure ε_f) were expressed uniquely by a parameter Z=ε·exp (Q/RT) or stress peak σ_p, Where R and T have usual meanings and Q is 270 kJ/mol. The ε_f versus σ_p (or Z) curve showed a remarkable transition from low to high ductility in a range of σ_p between 55 MPa and 80 MPa. This result is associated critically with the relative difference between the nucleation strain of intergranular crack ε_c, and that of dynamic recrystallization ε_r. In the range of low ductility, where ε_c<<ε_r, intergranular cracks can be nucleated at the initial grain boundaries and propagated easily along them. In the transition range from low to high ductility, where ε_c_??_ε_r, the initiations of cracks and dynamic recrystallization take place simultaneously and then cracks become isolated apart from the new grain boundaries and can not grow, leading to increasing ductility. In the range of high ductility, where ε_c>>ε_r, dynamic recovery and subsequent dynamic recrystallization can make initial grain boundaries serrated and cause the sliding of them to prevent, leading to no crack initiation in low strains.