Effect of Mg on Behavior and Particle Size of Inclusions in Al-Ti Deoxidized Molten Steels

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.

Section: Effect Of Mg Content On the Behavior Of Ti-containing Inclusmentioning

confidence: 99%

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

Yang

Park

et al. 2020

“…This indicated that due to the possible formation of the liquid-capillary force, decomposition reaction of TiO 2 , and higher Gibbs free energy of the nanoparticle, inclusion agglomeration and growth occurred, causing TiO 2 nanoparticles to become micrometer-scale Ti-bearing inclusions. Moreover, Zhang et al [26] have indicated that if there is a trace of dissolved magnesium in the liquid steel, the Previous studies have shown that Mg addition can refine oxide. To confirm this effect, the relationship between the oxide size and number density of the EAM-treated sample was compared with that of the non-treated sample and Ti IPM-treated sample (mass percentage, C: 0.04%, Si: 0.20%, Mn: 1.15%, P: 0.01%, S: 0.005%, Al s : 0.0031%, and Ti: 0.0064%), which is shown in Figure 3.…”

Section: Resultsmentioning

confidence: 99%

“…This indicated that due to the possible formation of the liquid-capillary force, decomposition reaction of TiO2, and higher Gibbs free energy of the nanoparticle, inclusion agglomeration and growth occurred, causing TiO2 nanoparticles to become micrometer-scale Ti-bearing inclusions. Moreover, Zhang et al [26] have indicated that if there is a trace of dissolved magnesium in the liquid steel, the Al2O3-Ti3O5 system inclusions will be unstable and change into Al2O3-Ti3O5-MgO system inclusions. This was consistent with the results of the elements mapping in Figure 1.…”

Section: Resultsmentioning

confidence: 99%

“…Firstly, the phase diagram and liquid area of the Al 2 O 3 -Ti 3 O 5 -MgO system were calculated using thermochemical software FactSage 7.2, (Thermfact/CRCT, Montreal, Canada and GTT-Technologies, Aachen, Germany), as shown in Figure 4. The choice of Ti 3 O 5 was based on previous research [26], which indicated that the deoxidized product is usually Ti 3 O 5 at the common concentrations of titanium and oxygen in the steel production process. Additionally, Miia et al [24] also pointed out that TiO 2 was first reduced to Ti 3 O 5 in liquid steel.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Inclusion and Microstructure Characteristics in a Steel Sample with TiO2 Nanoparticle Addition and Mg Treatment

Cai

Kong

2019

TiO2 nanoparticles and Mg alloy were added to molten steel in sequence to investigate the inclusion and microstructure characteristics. Compared with a non-treated sample, these additives resulted in the formation of Ti–Mg-bearing inclusions, which proves that the additives were valid. The size evolution from nanometer-scale TiO2 to micrometer-scale oxides hints at the agglomeration and growth of the TiO2 nanoparticles, which is due to the possible formation of a liquid-capillary force, the decomposition reaction of TiO2, and the higher Gibbs free energy of the nanoparticle. Furthermore, the statistical analysis of the oxides indicated that with the addition of the TiO2 nanoparticles and Mg alloy, the oxides were refined and their density was higher. Few pure MnS were observed in the treated sample. This is due to the fact that most oxides separated out in the liquid region at 1873 K based on the oxide composition and the calculated Al2O3–Ti3O5–MgO phase diagram. Thus, MnS preferred to segregate on them during solidification. After etching, it was found that the Ti–Mg-bearing oxide can induce the nucleation of intragranular acicular ferrites. The appearance of these acicular ferrites was not observed in the non-treated sample. This comparison indicates the effectiveness of the external adding method in oxide metallurgy.

“…Recently, magnesium is being widely used to disperse and refine inclusion, as it has strong agglomeration characteristics, such as Al 2 O 3 particles in molten steel [1][2][3][4][5][6]. In those published works, after the magnesium addition, the large-sized and irregularly shaped Al 2 O 3 inclusion in the steel were modified into small-sized and approximately spherical MgAl 2 O 4 inclusion.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics and Agglomeration Behavior on Spinel Inclusion in Al-Deoxidized Steel Coupling with Mg Treatment

Lei

Wang

Yuan

et al. 2019

There are many types of non-metallic MgAl2O4 inclusions observed in Al-deoxidized steel coupling with Mg treatment, including single-particle MgAl2O4, agglomerated MgAl2O4, and MgAl2O4-MnS. Thermodynamic calculation shows that MgAl2O4 precipitates in the liquid phase. The phase transformation follows liquid + Al2O3 + MgAl2O4 → liquid + MgAl2O4 → liquid + MgO + MgAl2O4 → liquid + MgO with the Mg content increasing when the Al content is a constant in molten steel, and it is in agreement with the experimental results for the formation of MgAl2O4 in molten steel. The calculation results of various attractive forces between two particles show that the cavity bridge force plays a dominant role in the agglomeration process and results in the agglomerated MgAl2O4. The lattice mismatch calculation result shows that MgAl2O4 can provide effective sites for MnS nucleating in steel.