Calculation of secondary hardening parameters of high-alloyed iron alloys after integrated chemical-thermal processing

Abstract

Purpose. It is of interest to investigate the relationship between secondary hardening and microstresses in the crystal lattice on the tempering temperature of iron alloys doped by the principle of high-speed steels after complex chemical-thermal treatment. It is necessary to identify structural transformations in a complex treated alloy of type 20P18 after the final heat treatment (quenching and tempering) by electron microscopic. It is of interest to study the regularities of the formation of preallocation zones of the Guinier−Preston type in high-alloyed iron alloys after the final thermal treatment. Methodology. The materials for investigation was the cast alloy of type 20P18 made on the basis of standard P18 steel with the addition of carbon to ~2 %. The degree of perfection of the crystal lattice of the 20P18 alloy was evaluated after the implementation of complex chemical-thermal treatment (decarburization + carburization) and tempering at various parameters. Methods of research − electron microscopy and optical microscopy. Results. It was found that the maximum lattice tension and high microhardness for the type 20P18 alloy correspond to tempering at temperatures of 550...560 °C. It is shown that fine-dispersed carbides of the M₃C type are distinguished in the diffusion layer after tempering, which are also characteristic of standard high-speed steel, but in a larger quantity. The maximum of the secondary hardness of high-alloyed iron alloys corresponds to the stage of formation of the Guinie−Preston preallocation zones, which corresponds to tempering at temperatures of 550...560 °C was established. Originality.  It is established that formation zones of the Guinier−Preston in the process of tempering to secondary hardness contribute to the distortion of the crystal lattice of the solid solution. Practical value. The using of the obtained results will allow more flexible control over the final structure of specific products, and, consequently, successfully solve practical problems of improving the technological and operational characteristics of the cutting tools.