Effect of Titanium Oxide on Phase Transformation for Low Alloy High Strength Steel Welds

Aimed at improving mechanical properties of high strength low alloy steel welds, oxides with high melting point and high stability were added into steel liquid. By thermodynamics calculation and thermal simulating technology, phase transformation characteristics of low alloy steel weld with TiO2addition were investigated. The results showed that TiO2added in welds led to the decrease of phase transformation temperature and the wideness of γ→α transformation temperature range. The starting and finishing transformation temperature of ferrite respectively dropped about 311K and 486K on the cooling condition of 373K/s. Moreover, the complex inclusions of TiOx-MnO-SiO2-MnS with spherical shape and 0.67μm mean size formed in weld metal. In addition, only acicular ferrite existed in the titanium oxide added welds. So it was concluded that titanium oxide can effectively be used to control phase transformation and then achieve fine and favorable microstructure.

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Inclusions and Microstructure of Steel Weld Deposits with Nanosize Titanium Oxide Addition

Journal of Nanomaterials ◽

10.1155/2014/138750 ◽

2014 ◽

Vol 2014 ◽

pp. 1-7 ◽

Cited By ~ 1

Author(s):

Cuixin Chen ◽

Haitao Xue ◽

Huifen Peng ◽

Liang Yan ◽

Lei Zhi ◽

...

Keyword(s):

Phase Transformation ◽

Titanium Oxide ◽

Molten Pool ◽

Processing Parameters ◽

Phase Transformation Temperature ◽

Columnar Crystal ◽

Oxide Addition ◽

Intragranular Ferrite ◽

Mean Size ◽

Steel Welds

Nanosize TiO2particles were added directly into welding molten pool through electrode for the difficulty of accurate control of oxygen potential and production processing parameters. The characteristics of phase transformation and thermal behavior of inclusions for Fe-C-Mn-Si-Ti-O system and Fe-C-Mn-Si-TiO2system were analyzed. Results show that the added TiO2particles are more helpful for the formation of Mn-Ti-O complex inclusion and can induce the decrease of phase transformation temperature of austenite to ferrite. Intragranular ferrite can be obtained under the condition of continuous cooling transformation with cooling rate of 293 K/s–373 K/s. The inclusions in steel welds are spherical in shape and mainly composed of TiO2, Ti3O5, Ti2O3, MnO, and SiO2. The mean size of inclusions is 0.67 μm. These complex inclusions can supply a large number of nucleating cores for their precipitation at higher temperature, which will disturb the growth of columnar crystal during solidification. Moreover, Mn-containing titanium oxides will promote the transformation of austenite to intragranular ferrite for the formation of manganese depleted zones in steel welds around oxides. So it can be concluded that nanosize titanium oxide added directly in welding molten pool can be effectively used to control phase transformation and achieve fine and favorable microstructure.

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Controlling distortion in gas metal arc high strength low alloy steel welds

Materials Today Proceedings ◽

10.1016/j.matpr.2021.06.010 ◽

2021 ◽

Author(s):

Rami Rafea Abdul-Ameer ◽

Saad Hameed Al-Shafaie ◽

Abdulsameea Jasim Jilabi

Keyword(s):

Alloy Steel ◽

High Strength ◽

Low Alloy Steel ◽

Steel Welds

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Capability of martensitic low transformation temperature welding consumables for increasing the fatigue strength of high strength steel joints

Materials Testing ◽

10.1515/mt-2020-620906 ◽

2020 ◽

Vol 62 (9) ◽

pp. 891-900

Author(s):

Jonas Hensel ◽

Arne Kromm ◽

Thomas Nitschke-Pagel ◽

Jonny Dixneit ◽

Klaus Dilger

Keyword(s):

Residual Stress ◽

Phase Transformation ◽

Fatigue Strength ◽

High Strength Steel ◽

Transformation Temperature ◽

Fatigue Cracks ◽

High Strength ◽

Filler Material ◽

Phase Transformation Temperature ◽

Filler Materials

Abstract The use of low transformation temperature (LTT) filler materials represents a smart approach for increasing the fatigue strength of welded high strength steel structures apart from the usual procedures of post weld treatment. The main mechanism is based on the effect of the low start temperature of martensite formation on the stress already present during welding. Thus, compressive residual stress formed due to constrained volume expansion in connection with phase transformation become highly effective. Furthermore, the weld metal has a high hardness that can delay the formation of fatigue cracks but also leads to low toughness. Fundamental investigations on the weldability of an LTT filler material are presented in this work, including the characterization of the weld microstructure, its hardness, phase transformation temperature and mechanical properties. Special attention was applied to avoid imperfections in order to ensure a high weld quality for subsequent fatigue testing. Fatigue tests were conducted on the welded joints of the base materials S355J2 and S960QL using conventional filler materials as a comparison to the LTT filler. Butt joints were used with a variation in the weld type (DY-weld and V-weld). In addition, a component-like specimen (longitudinal stiffener) was investigated where the LTT filler material was applied as an additional layer. The joints were characterized with respect to residual stress, its stability during cyclic loading and microstructure. The results show that the application of LTT consumables leads to a significant increase in fatigue strength when basic design guidelines are followed. This enables a benefit from the lightweight design potential of high-strength steel grades.

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