Abstract
The objective of the present study is to investigate the effects of nickel (Ni) on the microstructure and impact toughness of coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steel. It was observed that the microstructure of CGHAZ predominantly consisted of bainite and a small proportion of martensite-austenite (M-A) constituents and acicular ferrite (AF). With increased Ni content, the percentage of M-A constituent decreased and AF increased; consequently, the impact toughness of CGHAZ increased. The study revealed that a small addition of nickel significantly affected the formation of M-A constituents and AF; however, no obvious influence was observed on the bainitic microstructure of high-strength low-alloy steel.
Highlights
High-strength low alloy steels (HSLA) are widely used in applications requiring welding because of their high toughness, high strength, cold formability, and good weldability
The microstructure of all observed that the prior austenite grains became coarse in all the samples
The microstructure of all the samples predominantly consisted of bainite and a small percentage of acicular ferrite (AF) and M-A constituents
Summary
High-strength low alloy steels (HSLA) are widely used in applications requiring welding because of their high toughness, high strength, cold formability, and good weldability. Several studies have been carried out using high heat input welding to reduce cost and improve welding efficiency. The high heat input welding thermal cycle results in a coarse-grained heat-affected zone (CGHAZ), as well as degradation in the toughness of steels [1]. Improvement in the toughness of HAZ is an important aspect when high heat input is used. The toughness of HAZ is strongly influenced by the microstructural features of steels [2]. Coarse bainite in the HAZ of HSLA steel contains parallel bainitic ferrite and martensite-austenite (M-A) constituents [3]. It is difficult to obtain superior HAZ toughness because of the hard
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