The effect of heat treatment parameters on the microstructure and torque response of a 13 wt% Cr steel

Abstract

Shafts intended for magnetomechanical sensors require a combination of mechanical properties and/or characteristics in addition to good magnetic properties. In the case of X46Cr13, this can be attained by the appropriate selection of heat treatment parameters. In fact this study discusses the effect of these parameters on the microstructure, mechanical and magnetic properties of this material.The B-H curves showed that irrespective of the heat treatment condition, the material was harder to magnetize in the axial direction than circumferentially. Also, quenched and tempered structures were harder to magnetize than those in the annealed condition. Changes in the austenitising temperature or time were not observed to lead to major changes in the B-H curve. On the other hand, increasing the tempering temperature from 350 °C to 500 °C, led to a significant drop in coercivity, attributed to a decrease in M3C precipitates. This change in coercivity was comparable to that observed as the tempering temperature increased from 500 °C to 600 °C, in which case the matrix structure changed from martensite to ferrite.Martensitic structures showed a lower magnetic response to a given applied torque than their annealed counterparts. On the other hand, with martensitic structures, the signal to torque relationship remained linear even at high torque values. This was not the case with the annealed structures.The study concludes that austenitising at 1040 °C for 45 min and tempering at 350 °C and 375 °C for 2 h yields an optimal combination of properties and performance.