Effect of Temperature and Stress on Residual Magnetic Signals in Ferromagnetic Structural Steel

Although we know that stress in ferromagnetic steels can induce magnetic signals on the surface, temperature could be another critical factor to impact the signals of the steels used under high temperature conditions. To better understand the mechanism of the residual magnetic signals, a modified Jiles–Atherton (J-A) model based on thermal and mechanical effects was developed. In the experiment, ferromagnetic structural steel Q345B was tested under static tensile stress, and the variation of magnetic signal normal component
$H_{p}(y)$
and its mean value
$H_{p}(y)_{\mathrm{ ave}}$
were investigated during the tests. Experimental results showed that the mean value
$H_{p}(y)_{\mathrm{ ave}}$
decreased with the increase in temperature, however, increased with the increase in tensile stress. The microstructures were observed at the location of fracture and it was found that the size of inclusions increased with the increase in temperature, which blocked the irreversible movement of magnetic domains and leaded to the decrease of magnetic signals. The experimental results were consistent with the theoretical analysis, which indicated that the variation of effective field
$H_{e}$
calculated based on the modified J-A model was similar to the mean value
$H_{p}(y)_{\mathrm{ ave}}$
in the tests.