NCREASE IN IMPACT STRENGTH OF STRUCTURAL STEELS BY THE CARBIDE-FREE-BAINITE FORMATION

Abstract


Structure and mechanical properties of chrome-nickel-molybdenum steels with carbon content from 0,1 to 0,4 % after slow continuous cooling in the bainitic temperature range with cooling rate V cool = 5 °С/min were investigated. It was shown that at carbon content about 0,10-0,15 % after such heat treatment the structure of carbide-free-bainite represented as two-phase mixture of carbon depleted bainitic ferrite and carbon enriched retained austenite with different morphology were formed in steel. It was found that such carbide-free-bainite possesses significantly more high values of impact strength in comparison with bainite containing carbide precipitations having practically the identical level of hardness and strength. Retained austenite in such carbide-free-bainite is substantially enriched with carbon and contain the considerable part of steel total carbon content. The impact strength level increase is associated with the presence of significant quantity of carbon enriched retained austenite in carbide-free-bainite. It was assumed that for steels with bainitic structure formed under continuous cooling the carbon share content in retained austenite can characterize the morphological peculiarities of the phase transformation structural constituent (carbide-free-bainite ore bainite with carbides) and impact strength level of steel.

About the authors

A. Yu Kaletin

Institute of Metal Physics, Ural Branch of RAS

Yu. V Kaletina

Institute of Metal Physics, Ural Branch of RAS

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