Characteristic of martensite–austenite constituents in coarse grained heat affected zone of HSLA steel with varying Al contents

Abstract

The fine microstructure of martensite-austenite (M-A) constituents in simulated coarse grained heat affected zone (HAZ) of high strength low alloy steel with varying aluminium content (0?038 and 0?070 wt-%) at 100 kJ cm 21 heat input welding was investigated. The result shows that M-A constituents with 0?038%Al consisted of lath martensite and retained austenite. The retained austenite was distributed along the martensite lath. Whereas, the M-A constituents with 0?070%Al consisted of lath martensite and retained austenite, as well as a small amount of twinned martensite. The amount of retained austenite in M-A constituents with 0?070%Al was becoming higher slightly than that with 0?038%Al. Accordingly, the volume fraction of M-A constituents was reduced with 0?070%Al. Appropriate aluminium addition could decrease not only the area fraction but also the size of M-A constituents, which are beneficial for improving the toughness of HAZ.

Micromechanism of Decrease of Impact Toughness in Coarse-Grain Heat-Affected Zone of HSLA Steel with Increasing Welding Heat Input

“…Therefore, more studies were concentrated on studying microstructures and properties of the heat-affected zone (HAZ) by varying peak temperatures, heat inputs, and alloy compositions. [7][8][9][10][11][12][13][14][15][16][17][18][19] In Reference 12 coarse austenite grain size associated with coarse M-A constituent along grain boundary was revealed as the dominant factor in promoting brittle fracture. The combination of fine prior austenite grain size and smaller M-A constituent was favorable in obtaining high toughness.…”

Influence of Cold-Wire Submerged Arc Welding on the Toughness of Microalloyed Steel

“…The fraction of M-A constituents in the CGHAZ was reduced as a consequence of PAG size reduction (Refs. 23,24) by the cold wire addition. Quantitative analysis of the M-A regions indicates the fraction of M-A constituents in the CGHAZ with sizes larger than 2 m for the TSAW and cold-wire TSAW samples is 3.2 ± 0.2% and 1.0 ± 0.1%, respectively.…”

Influence of cold-wire tandem submerged arc welding parameters on weld geometry and microhardness of microalloyed pipeline steels

“…The M-A fraction in the CGHAZ of the TSAW and CWTSAW samples, calculated from the SEM micrographs (Fig. 7n, m), was 7.6 and 5.4 %, respectively, indicating a reduction in the fraction of M-A as a consequence of PAG size reduction [32][33][34][35] by cold-wire addition. The M-A fraction in the CGHAZ calculated from the optical micrographs (Fig.…”

“…Therefore, a coarser PAG size increases the fraction and size of the M-A constituent. Li et al [33] and Yu et al [35] showed that a coarse PAG size associated with a coarse M-A constituent is the dominant factor in promoting brittle fracture in the CGHAZ. Accordingly, there is a concurrent effect of both grain size refinement and M-A transformation, which plays a significant role in the strength, hardness, and toughness of the HAZ.…”