On the Change of Electrical Resistance of High Carbon High Chromium Steels by Heat Treatment

Abstract

The electric resistance of high carbon high chromium steels by heat treatment was measured and the following results were obtained: (1) The resistivity curve of the annealed specimen that was measured in the course of slow heating and cooling (notationed R_α) was convex for the temperature axis and the one measured by air-cooling from 1130° (notationed R_γ) was concave. The experimental equations of these curves were parabolic. (2) The increase in resistivity after the quenching was considered to be caused mainly by the existence of supersaturated carbide and retained austenite in the quenching structure. (3) The resistivity curves measured by air-cooling from 1050°, 1000° and 950° consisted of the following three parts: (a) the parallel part with R_γ curve; (b) the part where the resistivity decreases; (c) the part where the inclination is close to the R_α curve’s. These changes was caused by Ar″ transformation which decreased the resistivity with the increase of spontaneous magnetization. (4) The specimen of steel B (containing about 0.3%W) which was air-cooled from 1050° showed the higher resistivity than the specimen air-cooled from 1130° at room temperature. But even in this case the type of the resistivity curve was similar to case 3. (5) It was observed that the effect of quenching to the aging temperature from 1130° and tempered to this temperature from 1130-air-cooled state were similar in principle. (6) The measuring values of resistivity in the cooling process after the hot bath quenching or tempering coincided with the values calculated in the consideration of the quantity of transformation, at high temperature. But when the temperature lowered the measuring values generally showed to be less than the calculated values. This may be considered have been caused by Ar″ transformation as in case 3.