Mproving the properties of steels by producing in their structure along with other components of metastable austenite and the following hardening

Abstract

The relevance. Improving the mechanical properties of steels and their wear resistance makes it possible to increase the service life of machine parts, which is an important task of materials science. One of the promising directions in its solution is combined processing technologies of steels based on the principle of obtaining in them in various ways a structure containing, along with other components (various types of martensite, lower bainite, in some cases carbides) of an increased amount (³ 25 %) of metastable austenite, and subsequent strengthening. In this case, a certain amount of austenite transforms into deformation martensite, and the its remaining part undergoes dynamic deformation martensitic transformation (DDMT) – the effect of self-hardening under loading (SHL). Combined processing technologies include thermal (in some cases, chemical-thermal) and deformation effects on the metal, carried out in various combinations and sequences. Processing technologies for obtaining an increased amount of metastable austenite in the structure of steels can include: holding in the intercritical temperature interval (ICTI) with various hardening methods, plastic deformation stabilizing austenite with respect to the formation of cooling martensite, thermal cycling, etc. Strengthening of steels with an increased amount of metastable austenite is carried out by cold plastic deformation, after which tempering is carried out in some cases. However, the principle is currently being considered and the combined processing technologies that implement it are not used in industry. This excludes the use of metastable austenite, which is an internal resource of the material itself, and its transformation under loading, which increases its ability to self-defense against destruction during testing of properties and operation. In this regard, it is advisable to introduce the proposed combined processing technologies into practice, which will ensure resource saving. In work on a number of steels their effectiveness has been shown.
 Рurpose is to show the possibility of increasing the mechanical properties or wear resistance of the studied steels by using combined processing technologies based on the principle that provides for the production of an increased amount of metastable austenite in their structure and subsequent hardening, which preserves the possibility of DDMT and the implementation of the effect SHL.
 Research methods. Durometric, metallographic and X-ray research methods were used. The tensile properties and impact strength, as well as abrasive wear resistance, were determined. These properties were compared with those obtained for the studied steels after a typical heat treatment.
 Results. It is shown that the proposed combined treatment technologies, including the production of an increased amount of metastable austenite in the structure of the studied steels and subsequent hardening, which retains the possibility of DDMT and the implementation of the effect SHL, increase the mechanical properties or wear resistance in comparison with their level after the commonly used treatment.
 Scientific novelty. To improve the mechanical properties or wear resistance of alloys an innovative principle was proposed, which consists in obtaining in them an increased amount of metastable austenite before strengthening treatments, preserving after them a part of it that can undergo DDMT and, accordingly, realize the effect SHL when testing properties and operation.
 Practical value. For the studied steels, rational modes of combined processing technologies have been determined, including obtaining an increased amount of metastable austenite in their structure and subsequent hardening, which have shown their effectiveness in increasing mechanical properties or wear resistance in comparison with commonly used treatments.