A method for quickly evaluating heat treatment quality of 35CrMo steel cylinder using magnetic properties

Abstract

Seamless steel cylinders are widely used in real-life situations, and heat treatment has an important effect on their service life. The common methods used for heat treatment quality monitoring have many shortcomings, such as destructive operation, high cost and low coverage. To quickly and accurately evaluate the performance of the cylinder after heat treatment, a fast non-destructive testing method is introduced based on the coercive force measurement. The amount of residual stress for 35CrMo steel cylinder before and after heat treatment was evaluated quantitatively by the Metal Magnetic Memory technique, and the structural-mechanical dependence of coercive force was also revealed. Due to the grain refinement and the stress relief, the modified magnetic field index △H and k(x)of 35CrMo steel after heat treated are significantly decreased by 54% and 56%, respectively. Correspondingly, the magnetic coercive force is inversely proportional to the grain size, which is verified by hardness test. The structural-mechanical states of 35CrMo steel cylinder can be justified by measuring their coercive force, which is potential to be used as a reliable, accurate and non-destructive tool for mass production.