Low-alloy steel development has made great progress

Low-alloy steel development has made great progress

The research and development of modern low-alloy steel made great progress in Shihua Caixue. New achievements have been made in the basic research of microalloyed steel, and the progress in process technology has made new ideas in the design of low-alloy steel alloys.

Comprehensive media reported on June 25 that since the 1970s, the development of low-alloy high-strength steels worldwide has entered a new era, based on controlled rolling technology and micro-alloying metallurgy, forming a modern low High-strength alloy steel is a new concept of microalloyed steel. Into the 1980s, a variety of developments involving a wide range of industrial fields and specialty materials, with the help of metallurgical process technology achievements reached its peak. In the four-in-one relationship between the chemical composition of steel—process—organization—performance, for the first time the dominant position of steel microstructure and microscopic fine structure is highlighted, and it also shows that the basic research of low-alloy steel has matured. Design alloys with unprecedented new concepts.

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Emphasis on the development of Nb microalloyed steels, Nb-V and Nb-Ti composite microalloyed steels, according to statistics, accounted for almost 51.3% of the newly developed steel grades from 1985 to 2004 and 41.5% of the total microalloyed steel production. In recent years, it has been noticed that trace amounts of Ti (≤0.015%) are very beneficial. The micro treatment of Ti not only changes the form of sulfides in the steel, but also becomes a particle of ferrite grain nucleation in austenite grains. Nb-Ti composite microalloying constitutes the metallurgical foundation of IF steel for ultra-deep-drawn automobiles, and it also significantly improves the crack sensitivity of Nb steel continuous casting.

A systematic summary of the low-carbon steel-enhanced Hall-Petch relationship was made and a more in-depth study of the accelerated cooling principle was conducted. People are very interested in adopting a staged accelerated cooling process. Accelerated cooling is used to suppress ferrite transformation. The purpose of accelerated cooling in the later stage is to control the grain size and fine structure of the intermediate and low temperature products so as to achieve adjustment in a wide range. The strength and toughness of the steel match. 350MPa high-strength steel: micro-alloying + thermo-mechanical treatment, the mechanism for grain refinement + precipitation strengthening. 500MPa grade high strength steel: ferrite + bainite, martensite, strengthening mechanism for grain refinement, grain boundary strengthening and dislocation strengthening. 700MPa high-strength steel: ultra-low carbon bainite structure, the mechanism for the transformation of strengthening + precipitation strengthening.

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