Advanced high-strength steels for automotive engineering

Abstract

Diagrams of supercooled austenite decomposition are constructed for new steels of the Kh2G2C2MF alloying system. They provide the application of a science-based approach to the development and improvement of technological heat treatment processes with the use of furnaces with oxidising atmosphere. It is shown that the bainite transformation cannot exist separately from the martensite transformation even at slow cooling speeds. Regimes of heat treatment are selected, providing a possibility to receive the necessary structure for formation of a required complex of mechanical properties in a wide range. It is established that the most perspective heat treatment regime scheme from the point of view of time savings is continuous cooling from the heating temperature. It is revealed that the main structural components of steels after various heat treatment regimes are bainite and martensite, whose ratio determines the mechanical characteristics. Bainite is carbide-free, which favourably influences the complex of mechanical characteristics. The excessive ferrite and ferrite-carbide mixture formed in the structure at slow rates of continuous cooling in the upper temperature range do not affect the mechanical properties since their amount is insignificant. It is established that new economically alloyed steels with chromium, manganese, silicon, molybdenum, vanadium, and different carbon content belong to third-generation automotive steels, which gives prospects of using this material for manufacturing various automotive parts to improve the entire structure.