Numerical simulation and experimental investigation on the induction hardening of a ball screw

Highlights: • Austenitization temperature varies linearly with the logarithm of heating rate. • Non-uniformity of temperature causes non-uniformity of hardened layer and hardness. • Increasing distance of coil and cooling water circle can reduce temperature gradient. • Perfect hardened layer can be obtained using double coils induction hardening. - Abstract: To improve the distribution of the hardened layer and avoid potential defects, the effects of induction hardening parameters on the hardened layer were researched using the finite element method (FEM). A FEM model of single coil induction hardening was built, and temperature curves on the surface region of a ball screw were attained by numerical simulation. The hardenability and phase transformation of 55CrMo steel were researched by experiment. The simulation and experimental results show that the temperatures Ac1 and Ac3 rise with increasing heating rate. Non-uniformity of temperature at the groove region can lead to non-uniformity of austenitization and hardness. High temperature can result in cracks, coarse grain size and overheating defects at the groove tip. Martensite produced during cooling transforms into tempered martensite due to the residual heat, and the remaining austenite transforms into martensite at a low cooling rate. A 5010-type ball screw cannot attain a hardened layer with the thickness of 2.5 mm at the groove bottom without defects at the groove tip by single coil induction hardening. Multiple induction coils with a certain gap would be helpful to improve the uniformity of temperature and hardness.