Further insights on compositional control and heat treatment for improving the impact behaviour of hot-rolled steels containing Nb and Al

The effect of Al and Nb contents, cooling rate and rolling condition on the microstructure and corrosion behaviour of HSLA steel

“…To identify optimisation potential in corrosion resistance, H2 steel was further enriched with an additional 0.018%Nb, for H3 steel, whilst it is common to find 0.015-0.03%Nb in commercial steels. The contents of Al and Nb were selected based on their previous reported benefits to mechanical properties; 0.16%Al is the optimum content needed to improve impact behaviour while its combination with 0.018%Nb promotes strength considerably [8][9][10]. This is to explore any further benefits to corrosion behaviour.…”

“…The key concept of the current work emerges as a continuation of our research on the effect of Al, Nb and their combination along with variation in the cooling and rolling conditions on the changes in the microstructural features and mechanical performance of HSLA steel [8][9][10]. The inherent protection capabilities of Al and Nb are well-documented, but the impact of small alloying addition on the corrosion behaviour of steel requires further attention.…”

“…The current authors [8] reported that adding 0.16%Al to HSLA steels enhances toughness considerably without impairing strength. A further study [9] revealed that the addition of 0.018%Nb is beneficial to improve the strength through grain size refinement and precipitation hardening [10,11]. Moreover, mechanical properties are affected by the processing conditions including the rolling condition that has a marked effect on properties, in which controlled rolling is known to further increase strength and toughness in comparison with hot rolling, but the effect of cooling rate after rolling must be taken care of [12].…”

“…The most effective processing parameters on microstructural features are the type of rolling, hot and controlled rolling, and the cooling rate after rolling. Controlled rolling contributes to refining the carbides, as well as giving a finer grain size [9]. Increasing the cooling rate gives a marked refinement of grain size as well as promoting the formation of lower transformation products such as martensite [9].…”

“…Controlled rolling contributes to refining the carbides, as well as giving a finer grain size [9]. Increasing the cooling rate gives a marked refinement of grain size as well as promoting the formation of lower transformation products such as martensite [9]. These factors can have varying degrees of influence on corrosion rates; in the case of steel, studies can be contradictory and thus, the consensus remains inconclusive.…”