Abstract
An effect of tempforming on the microstructure, the carbide precipitation, and the strengthening mechanisms of high-strength low-alloyed steel has been analyzed. The quenched steel was subjected to 1 h tempering at a temperature of 873 K, 923 K, or 973 K followed by plate rolling at the same temperature. Tempforming resulted in the formation of an ultrafine grained lamellar-type microstructure with finely dispersed carbides of (Nb,V)C, Fe3C and Cr23C6. A decrease in tempforming temperature resulted in a reduction of the transverse grain size from 950 nm to 350 nm. Correspondingly, the size of Fe3C/Cr23C6 particles decreased from 90 nm to 40 nm while the size of (Nb,V)C particles decreased from 17 nm to 4 nm. Refining the tempformed microstructure with a decrease in thetempforming temperature provided an increase in the yield strength from 690 MPa to 1230 MPa.
Highlights
Microstructure and StrengtheningHigh-strength low-alloyed (HSLA) steels are widely used structural materials [1,2,3,4].The first generation of HSLA steels exhibited yield strength above 350 MPa [1]
The aim of the present study is to evaluate the strengthening mechanisms in a low carbon HSLA steel subjected to tempforming
The grain boundaries appear as straight lines parallel to RD on the cross-section of the samples tempformed at 873 K (Figure 1a)
Summary
Microstructure and StrengtheningHigh-strength low-alloyed (HSLA) steels are widely used structural materials [1,2,3,4].The first generation of HSLA steels exhibited yield strength above 350 MPa [1]. The yield strength of modern HSLA steels increased up to 700 MPa owing to both the dispersion hardening provided by Ti, Nb, V, Mo microalloying and the grain refinement due to thermomechanical controlled processing (TMCP) involving accelerated cooling after hot/warm rolling [2,3,4]. A route of thermo-mechanical processing called tempforming was proposed by Japanese scientists to increase the impact toughness of plain carbon steels at low temperatures [6]. Besides the improvement of impact toughness, tempforming strengthens the steels, increasing their yield strength [6,7,8]. The grain size and dislocation strengthening were considered as major contributors to the strength of medium carbon steels with lamellar microstructure [9,10]
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