Bainite

About: Bainite is a research topic. Over the lifetime, 9520 publications have been published within this topic receiving 145305 citations.

Experimental determination of the stability of retained austenite in low alloy TRIP steels

Abstract: The stability of retained austenite is the most important parameter controlling the transformation plasticity effects in multiphase low alloy TRIP steels. In this work the thermodynamic stability of the retained austenite has been determined experimentally by measuring the M s σ temperature as a function of bainite isothermal transformation (BIT) temperature and time in two low alloy TRIP steels. A single-specimen temperature-variable tension test technique (SS-TV-TT) has been employed, which allowed to link the appearance of yield points in the stress-strain curve with the mechanically-induced martensitic transformation of the retained austenite. The results indicated that the M s σ temperature varies with BIT temperature and time. Higher austenite stability is associated with a BIT temperature of 400°C rather than 375°C. In addition, the chemical stabilization of the retained austenite associated with carbon enrichment from the growing bainite is lowered at short BIT times. This stability drop is due to carbide precipitation and comes earlier in the Nb-containing steel. At longer BIT times the retained austenite dispersion becomes finer and its stability rises due to size stabilization. The experimental results are in good agreement with model predictions within the range of anticipated carbon enrichment of the retained austenite and measured austenite particle size.

Nanoindentation study of ferrite–martensite dual phase steels developed by a new thermomechanical processing

Abstract: Dual phase (DP) steels consisting different volume fractions of ferrite and martensite and different ferrite grain size were produced by a new route utilizing cold-rolling and subsequent intercritical annealing of ferrite/martensite duplex starting structure at 770 °C for different times. Scanning electron microscopy has been supplemented by nanoindentation and tensile test to follow microstructural changes and their correlations to the variation in phase's hardness and mechanical properties. The results showed that longer holding times resulted in coarser and softer ferrite grains in DP microstructures. Martensite nanohardness variation with holding time is related to change in its carbon content. Mechanical properties such as strength, elongation and toughness are well correlated with the martensite/ferrite hardness ratio.

Quantitative analysis of the dilatation by decomposition of Fe-C austenites; Calculation of volume change upon transformation

Abstract: A detailed analysis has been made of the length changes due to decomposition of iron-carbon austenites into ferrite and carbon enriched austenite above the A 1 temperature, and into ferrite and cementite below the A 1 temperature, using lattice-parameter data for the phases involved. The calculations have been performed as a function of carbon content, temperature and degree of transformation. A general definition for the total degree of transformation has been proposed for the case that more than one product phase develops. This definition also holds when the product phases develop consecutively, allowing an analysis of the kinetics of the austenite decomposition. Above the A 1 temperature, the relation between the degree of transformation and the dilatation is linear within good approximation. However, below the A 1 temperature a strong deviation from such a linear relationship occurs, as the result of subsequent decomposition of austenite into ferrite and carbon enriched austenite, and decomposition of the carbon enriched austenite into ferrite and cementite.