A method for fast high-temperature aging of steels

Abstract

elements. In our reasoning, we proceeded from the nonequivalence of the equilibrium solubility and diffusion mobility of hydrogen in a metal at different temperatures. As the temperature decreases, the diffusion processes are retarded (the diffusion coefficient of hydrogen in iron at 100 and 570~ is, respectively, 0.44 and 2.0 m2/sec [2]) and the equilibrium solubility of hydrogen in iron considerably drops (10 -6 and 10 -5 m2/kg, respectively, [3]). The proposed method enables one to record the equilibrium concentration of hydrogen at 100~ in the bulk of the specimen that is typical of a temperature of 570~ This supersaturation favors the active displacement of hydrogen to the nearest free (interior or exterior) surfaces. By leaving a solid solution, excess hydrogen either emerges from the metal or tries to settle on phase boundaries or defects. In the process of migration, it redistributes atoms of alloying elements [4]. Therefore, an abrupt cooling of a hydrogenated metal must, on the one hand, increase local stresses due to an excessive concentration of hydrogen and, on the other, intensify diffusion of alloying elements, i.e., favor the transformation of its structure. A prismatic specimen of 180 x 22 x 15 mm was placed in a hermetic chamber, which was filled out with a gas-like hydrogen under a pressure of 0.3 MPa. The ends of specimens were specially not clamped to avoid the appearance of temperature stresses. We performed heating up to 570~ with a rate of - 3~ by passing an electric alternating current of - 1.8 kA with a frequency of 50Hz. The temperature in the working section was maintained with an accuracy of + 5~ by using an automatic control system of a signal from a thermocouple fixed in the middle of the specimen. The specimen was held at 570~ for an hour to obtain a concentration of hydrogen across the whole thickness at this temperature. Thereafter, we stopped heating and abruptly cooled the specimen (with a rate