Features of heat treatment quality testing of U8A steel articles during pulsed bipolar asymmetric magnetization

Abstract

To detect deviations of required heat treatment temperature of tool carbon steel U8A is one of the important tasks of manufactured products quality assurance. By analyzing researchings, held earlier, it was found that most of instrumental carbon steels standard magnetic characteristics have ambiguous dependence from the heat treatment temperature and cannot be used for purposes of nondestructive testing. Results of researching magnetic parameters of high-quality tool carbon steel U8A, which are good for heat treatment quality testing, are considered. The parameters were defined on steel cylindrical samples by the instrument IMI–I, suited for measuring the ferromagnetic rods magnetic induction during pulsed magnetization in open magnetic circuit. Applicability of the difference δBmp–Br between the magnetic induction of maximum demagnetizing pulse amplitude and the residual magnetic induction for tool carbon steel U8A hardening temperature testing is determined. The coercive force Hс and the coercive force taking on asymmetric magnetic hysteresis loop Hса of the steel can be used to determine underheating and overheating during hardening but these magnetic parameters are inapplicable for hardening temperature testing. It is given that the magnetic induction taking on asymmetric magnetic hysteresis loop Brа and the magnetic induction ВδmH of the magnetic field strength of maximum difference δmH along the axis Н can give measurement sensitivity more than 40 % per 100 °C in low temperature (under 350 °C) tempering testing.