A. Yu. Kaletin, Yu. V. Kaletina

EFFECT OF LOW-TEMPERATURE TEMPERING ON THE PROPERTIES OF STRUCTURAL CARBIDE-FREE BAINITIC STEELS

Mechanical properties of chromium-nickel-molybdenum-silicon steels with carbon contents of 0.18% and 0.27 % after slow continuous cooling with the cooling rate Vcool = 5 °С/min in the bainitic temperature range are investigated. It is shown that, after this heat treatment, a carbide-free bainitic structure is formed in the investigated steels, which is a two-phase mixture of carbon-depleted bainitic ferrite and carbon-enriched retained austenite with different morphology. The retained austenite in the carbide-free bainite is substantially enriched with carbon and contains its considerable part from the total carbon content in the steel. It is demonstrated that tempering for 1...2 hours at a temperature of 300 °С raises the values of impact strength of the 18Kh2N2SM and 27Kh2N2SM steels after slow continuous cooling, which have a different proportion of lower lath and upper globular bainite, retained austenite and martensite in their structure. It has been found that such tempering is accompanied by retained austenite stabilization due to a noticeable increase in carbon content in it.

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