Abstract
The effects of Al content on inclusions, microstructures, and heat-affected zone (HAZ) toughness in a steel plate with Mg deoxidation have been investigated by using simulated high-heat-input welding and an automated feature system. The studies indicated that the main kind of oxysulfide complex inclusions in two steels without and with Al addition were both MgO-MnS. The number densities and mean sizes of inclusions were 96.65 mm−2 and 3.47 μm, 95.03 mm−2 and 2.03 μm, respectively. The morphologies of MgO-MnS complex inclusions in steel were changed obviously with the addition of Al. When containing 0.001 wt.% Al, they consisted of a central single MgO particle and outside, the MnS phase. When containing 0.020 wt.% Al, they comprised several small MgO particles entrapped by the MnS phase. Because the former could nucleate intragranular acicular ferrites (IAFs) and the latter was non-nucleant, the main intragranular microstructures in HAZs were ductile IAFs and brittle ferrite side plates (FSPs), respectively. Therefore, HAZ toughness of the steel plate without Al addition after high-heat-input welding of 400 kJ/cm was significantly better than that of the steel plate with Al addition.
Highlights
In steelmaking, extensive efforts have been made to remove massive inclusions, which deteriorate the final qualities of products
Inclusions can act as intragranular nucleation sites for acicular ferrite, resulting in interlocked fine intragranular acicular ferrites (IAFs) and improved heat-affected zone (HAZ) toughness of the steel plate [5]
The present study mainly focused on these inclusions with the equal-circle diameter (ECD) larger than 1 μm
Summary
Extensive efforts have been made to remove massive inclusions, which deteriorate the final qualities of products. In this regard, Takamura et al [1] introduced the concept termed ”oxide metallurgy” for the first time at the sixth international iron and steel congress in 1990. Oxide metallurgy technology has been deemed as the most effective method to improve the heat-affected zone (HAZ) toughness of steel plates after high-heat-input welding [2,3,4]. Inclusions can act as intragranular nucleation sites for acicular ferrite, resulting in interlocked fine intragranular acicular ferrites (IAFs) and improved HAZ toughness of the steel plate [5].
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