Influence of Al Content on the Inclusion-Microstructure Relationship in the Heat-Affected Zone of a Steel Plate with Mg Deoxidation after High-Heat-Input Welding

et al. 2021

steel research int.

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Mg treatment is conducted in the production of peritectic steel, which greatly reduces the average value of incidence of transverse corner crack in continuous casting slab from 3.10% to 1.06% by 65.8%. In the industrial experiment with the stages of Ar station, before magnesium treatment, after magnesium treatment, and in the slab, the maximum Mg content is 30 ppm after Mg treatment. A large number of Mg containing complex inclusions are formed, and most of Al2O3 are transformed into MgO·Al2O3. In the inclusions, the content of MgO significantly increases from 3.58% to 27.2%. The number density of Mg containing inclusions increases from 45.2 to 168 mm−2. The oxide inclusions smaller than 2 μm account for more than 90%, indicating that Mg treatment can promote the refinement of inclusions. In the slab, most oxide inclusions are transformed into the complex inclusions with Mg containing oxides as the core covered by TiN and sulfide precipitates. These complex inclusions with a size above 1 μm can effectively promote the nucleation and growth of intragranular ferrite to prevent the generation of transverse corner cracks.

Section: Resultssupporting

confidence: 90%

Characteristics and Evolution of Inclusions in Ti‐Bearing Peritectic Steel with Mg Treatment

Cai

Deng

et al. 2021

steel research int.

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“…Nowadays, oxide metallurgy technology has been considered as an effective method to improve the heat-affected zone (HAZ) toughness of steel plates after high-heat-input welding [2][3][4]. The oxide metallurgy technology is to make use of oxide particles or other kinds of inclusions and precipitate particles as the nucleation sites of intragranular acicular ferrite (IAF), or for pinning the growth of austenite grain in HAZ of steel plate during the welding process.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Improving Heat-Affected Zone Toughness of Steel Plate with Mg Deoxidation after High-Heat-Input Welding

Park

et al. 2020

Metals

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In the present study, the mechanism of improving HAZ toughness of steel plate with Mg deoxidation after the simulated welding with the heat input of 400 kJ/cm was investigated through in situ observation, characterization with SEM-EDS and TEM-EDS, and thermodynamic calculation. It was found that intragranular acicular ferrite (IAF) and polygonal ferrite (PF) contributed to the improvements of HAZ toughness in steels with Mg deoxidation. With the increase of Mg content in steel, the oxide in micron size inclusion was firstly changed to MgO-Ti2O3, then to MgO with the further increase of Mg content in steel. The formation of nanoscale TiN particles was promoted more obviously with the higher Mg content in the steel. The growth rates of austenite grains at the high-temperature stage (1400~1250 °C) during the HAZ thermal cycle of steels with conventional Al deoxidation and Mg deoxidation containing 0.0027 and 0.0099 wt% Mg were 10.55, 0.89, 0.01 μm/s, respectively. It was indicated that nanoscale TiN particles formed in steel with Mg deoxidation were effective to inhibit the growth of austenite grain. The excellent HAZ toughness of steel plates after welding with a heat input of 400 kJ/cm could be obtained by control of the Mg content in steel to selectively promote the formation of IAF or retard the growth of austenite grain.

“…Therefore, microstructures in 0Al show observably more favourable to the HAZ toughness than those in 200Al. In our previous study [20], the influence of Al content on the micron inclusion-microstructure relationship in the two investigated steels has been described in detail. It was stated that IAFs are nucleated by the MgO-MnS complex inclusions in the Mg-deoxidized steel without Al, while the MgO-MnS complex inclusions with different morphologies in the Mg-deoxidized steel containing 0.02 wt-% Al hardly nucleate to IAFs.…”

Section: Prior Austenite Grain Size and Microstructuresmentioning

confidence: 99%

Effects of coarse particles, prior austenite grains, and microstructures on impact toughness in heat-affected zone of Mg deoxidation steel plates without or with Al addition

Pan

Ironmaking & Steelmaking

Zhong

et al. 2020

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The effects of coarse TiN particles, prior austenite grains, and intragranular microstructures on the impact toughness in heat-affected zone of Mg deoxidation steel plates without Al (0Al) or with 0.02 wt-% Al (200Al) were studied from the cleavage initiation and propagation. The coarse particles are mainly TiN. 0.02 wt-% Al addition increases coarse TiN particles (>0.5 μm) from 124 to 151 mm -3 , increases brittle microstructures from 25% to 78%, and increases dislocations between ferrite laths, which impairs the toughness, although the austenite grain size is reduced from 213 to 184 μm. Coarse TiN particles alone can't govern the brittle fracture with the additional effect of microstructures in the case of intragranular acicular ferrites (IAFs). The importance of intragranular microstructures on preventing crack propagation is greater than that of austenite grain boundaries when the grain size is smaller than a critical size to suppress the IAF formation for ferritic steels.