Improvement of impact toughness of simulated heat affected zone by addition of aluminium

Abstract

The effect of aluminium content (0?023, 0?038 and 0?070 wt-%) on microstructure and impact toughness of simulated coarse grained heat affected zone (CGHAZ) of high strength low alloy steels with different heat inputs (20, 100 and 200 kJ cm 21 ) was investigated. The microstructure of simulated CGHAZ consisted of predominantly granular bainite. The martensite-austenite constituents became finer and its volume fraction decreased with increasing aluminium content, irrespective of heat input level. The impact toughness of the simulated CGHAZ improved remarkably with increasing aluminium content even at high heat input of 200 kJ cm 21 . It was attributed to the reduction in volume fraction of martensite-austenite constituents and the refined martensite-austenite constituents by addition of appropriate aluminium.

Effect of martensite–austenite constituent on toughness of simulated inter-critically reheated coarse-grained heat-affected zone in X70 pipeline steel

“…Less carbon atoms in transformed ferrite drove ferrite growing up more easily and the carbon-rich area was compressed accordingly. 24,25 Therefore, the increase in second heat input resulted in the increase of slender M-A constituent and reduction of blocky M-A. The relationship between the Charpy impact energy at −20°C and volume fraction of M-A constituent is shown in Fig.…”

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

“…It was reported that even the slight variation in fraction and size of M-A constituents can affect the impact toughness of CGHAZ significantly. 23 Because the addition of aluminium increases the fraction of retained austenite in M-A constituents, and then decreases the fraction and size of M-A constituents consequently, it can be proposed that the addition of small amount of aluminium will improve the impact toughness of CGHAZ effectively.…”

Effect of Aluminum, Nitrogen and Silicon Content on the Toughness of C-Mn Steel Weld Heat Affected Zone

“…Effect of Al addition on the base metal and HAZ toughness has been reported several researchers in the viewpoint of a carbide precipitation 1,2) , a M-A constituent formation 1,3) , and a rejection of free nitrogen [4][5][6] as a function of Al content and welding heat input. Fukuda 1) investigated the effect of 0.015wt%Al-addition to 0.1C-0.2Si-1.4Mn-0.01Ti steel which showed lower crack tip opening displacement (CTOD) compare to ultra-low Al (<0.001w%) steel in the submerged arc welded multi-pass heat affected zone due to the promotion of bainite and M-A constituent, rather than ferrite and cementite.…”

“…Mintz 6) reported that effect of Al content on the strength and toughness of (0.02, 0.1%C)-(10,40ppm N) steel, and concluded that HAZ toughness was increased with 0.2%Al as a result of cementite refinement and rejection of free nitrogen with no significant change of the strength. As described above, all of the test reports about weld HAZ have limited to the steels containing Al less than 0.07wt% 1,[3][4][5] while the steels that contain Al higher than 0.1wt% show quite good toughness 2,6) due to the various beneficial effect of Al addition.…”