Abstract
We have studied here the evolution of inclusions in ladle furnace (LF), Ruhrstahl & Heraeus furnace (RH), and simulated welded samples during Ti-Mg oxide metallurgy treatment and the mechanical properties of the heat-affected zone (HAZ) after high heat input welding. The study indicated that inclusions in an LF furnace station are silicomanganate and MnS of size range ~0.8–1.0 μm. After Mg addition, fine Ti-Ca-Mg-O-MnS complex oxides were obtained, which were conducive to the nucleation of acicular ferrite (AF). The corresponding microstructure changed from ferrite side plate (FSP) and polygonal ferrite (PF) to AF, PF, and grain boundary ferrite (GBF). After a simulated welding thermal cycle of 200 kJ/cm, disordered arrangements of acicular ferrite plates, fine size cleavage facets, small inclusions, and dimples all promoted high impact toughness.
Highlights
During the steel-making process, clean steel is the main objective and inclusions are harmful to steel properties, such as toughness and strength [1,2]
Xu et al [12] studied the effect of Mg content on the toughness and microstructure of the heat-affected zone (HAZ) after high heat input welding and found that with the increase of Mg content from 0 to 0.0099 wt %, the major microstructure in the HAZ changed from ferrite side plate (FSP), upper bainite (Bu), and grain boundary ferrite (GBF) to acicular ferrite (AF) with the austenite size decreased from 437 μm to 122 μm
In order to compare the ability of AF nucleation by different types of inclusions and the change in microstructure from the ladle furnace (LF) furnace to the Ruhrstahl & Heraeus furnace (RH) furnace, samples from a steel shop were machined to 3 mm in diameter and 10 mm in length for a continuous cooling transformation with Formastor-FII
Summary
During the steel-making process, clean steel is the main objective and inclusions are harmful to steel properties, such as toughness and strength [1,2]. For high-strength, low-alloy steels, many researchers found that certain types of fine oxide inclusions with a high melting point could increase the toughness of the HAZ after high heat input welding [5,6,7]. Zhu et al [11] found that the toughness of the HAZ in Ti-bearing low-carbon steels was improved by adding 0.005 wt % Mg. Xu et al [12] studied the effect of Mg content on the toughness and microstructure of the HAZ after high heat input welding and found that with the increase of Mg content from 0 to 0.0099 wt %, the major microstructure in the HAZ changed from ferrite side plate (FSP), upper bainite (Bu), and grain boundary ferrite (GBF) to AF with the austenite size decreased from 437 μm to 122 μm. A number of studies have investigated the properties of the HAZ, few studies have focused on the evolution behavior during the steel-making process. The properties of the HAZ after thermal welding simulations are explored
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