Effect of Mg addition on nucleation of intra-granular acicular ferrite in Al-killed low carbon steel

In order to understand the effects of deoxidizer such as aluminium, titanium and magnesium on the impact toughness of heat affected zone (HAZ), three low carbon steels deoxidized by Ti-Al, Mg and Ti-Mg were obtained. After smelting, forging, rolling and welding simulation, the effects of Al, Ti and Mg addition on the impact toughness of HAZ in low carbon steel were studied. The inclusion characteristics (size, morphology and chemistry) of samples before welding and the fracture pattern of the specimens after the Charpy-type test were respectively analyzed using optical microscope and scanning electron microscopy (SEM). The following results were found. The density of inclusion in Ti-Mg deoxidized steel is bigger than Ti-Al deoxidized steel. The average diameter is decreased for the former than the latter. The addition of Ti-Mg can enhance the impact toughness of the HAZ after welding simulation. The maximal value of the impact toughness is 66.5J/cm2. The complex particles of MgO-TiOx-SiO2-MnS are most benefit to enhance impact toughness. The improvement of HAZ is attributable to the role of particle pinning and the formation of intergranular ferrite.

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Characterization of Microstructure in High-Hardness Surface Layer of Low-Carbon Steel

Metals ◽

10.3390/met10080995 ◽

2020 ◽

Vol 10 (8) ◽

pp. 995

Author(s):

Haitao Xiao ◽

Shaobo Zheng ◽

Yan Xin ◽

Jiali Xu ◽

Ke Han ◽

...

Keyword(s):

Surface Layer ◽

Carbon Steel ◽

Yield Strength ◽

Carbon Content ◽

Acicular Ferrite ◽

Lath Martensite ◽

Low Carbon Steel ◽

Low Carbon ◽

Upper Bainite ◽

Mixed Microstructure

Surface hardening improves the strength of low-carbon steel without interfering with the toughness of its core. In this study, we focused on the microstructure in the surface layer (0–200 μm) of our low-carbon steel, where we discovered an unexpectedly high level of hardness. We confirmed the presence of not only upper bainite and acicular ferrite but also lath martensite in the hard surface layer. In area of 0–50 μm, a mixed microstructure of lath martensite and B1 upper bainite was formed as a result of high cooling rate (about 50–100 K/s). In area of 50–200 μm, a mixed microstructure of acicular ferrite and B2 upper bainite was formed. The average nanohardness of the martensite was as high as 9.87 ± 0.51 GPa, which was equivalent to the level reported for steel with twenty times the carbon content. The ultrafine laths with an average width of 128 nm was considered to be a key cause of high nanohardness. The average nanohardness of the ferrites was much lower than for martensite: 4.18 ± 0.39 GPa for upper bainite and 2.93 ± 0.30 GPa for acicular ferrite. Yield strength, likewise, was much higher for martensite (2378 ± 123 MPa) than for upper bainite (1007 ± 94 MPa) or acicular ferrite (706 ± 72 MPa). The high yield strength value of martensite gave the surface layer an exceptional resistance to abrasion to a degree that would be unachievable without additional heat treatment in other steels with similar carbon content.

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Crystallographic analysis for acicular ferrite formation in low carbon steel weld metals

Welding International ◽

10.1080/09507116.2014.921042 ◽

2014 ◽

Vol 29 (4) ◽

pp. 254-261 ◽

Cited By ~ 5

Author(s):

Atsushi Takada ◽

Yu-Ichi Komizo ◽

Hidenori Terasaki ◽

Tomoyuki Yokota ◽

Kenji Oi ◽

...

Keyword(s):

Carbon Steel ◽

Acicular Ferrite ◽

Low Carbon Steel ◽

Crystallographic Analysis ◽

Steel Weld ◽

Low Carbon ◽

Ferrite Formation ◽

Weld Metals

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Mechanism of Acicular Ferrite Formation in Low Carbon Steel Ti–B Weld Metals with Different Oxygen Levels

Tetsu-to-Hagane ◽

10.2355/tetsutohagane.96.608 ◽

2010 ◽

Vol 96 (10) ◽

pp. 608-613 ◽

Cited By ~ 3

Author(s):

Tomonori Yamada ◽

Hidenori Terasaki ◽

Yu-ichi Komizo

Keyword(s):

Carbon Steel ◽

Acicular Ferrite ◽

Low Carbon Steel ◽

Low Carbon ◽

Ferrite Formation ◽

Oxygen Levels ◽

Weld Metals

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Three-Dimensional Morphology and Growth Behavior of Acicular Ferrite in Low Carbon Steel Weld

The Proceedings of the Materials and processing conference ◽

10.1299/jsmemp.2003.11.37 ◽

2003 ◽

Vol 2003.11 (0) ◽

pp. 37-38

Author(s):

Kaiming WU ◽

Youhei INAGAWA ◽

Masato ENOMOTO ◽

Toshio MURAKAMI

Keyword(s):

Carbon Steel ◽

Acicular Ferrite ◽

Three Dimensional ◽

Low Carbon Steel ◽

Growth Behavior ◽

Steel Weld ◽

Low Carbon

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Effect of Vanadium on Development of Acicular Ferrite Microstructure in Low Carbon Steel

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.135.111 ◽

2008 ◽

Vol 135 ◽

pp. 111-114 ◽

Cited By ~ 1

Author(s):

Hyung Ha Jin ◽

Chan Sun Shin ◽

Hu Chul Lee

Keyword(s):

Carbon Steel ◽

Acicular Ferrite ◽

Low Carbon Steel ◽

Isothermal Transformation ◽

Low Carbon ◽

Side Plate ◽

Intragranular Ferrite ◽

Microstructural Constituent ◽

Austenite Grains ◽

Sympathetic Nucleation

The influence of vanadium on the development of an acicular ferrite microstructure has been investigated in a low carbon steel. Optical and electron microscopy were carried out to identify the precipitates, inclusions and constituents of the acicular ferrite microstructures. By the addition of vanadium, the main microstructural constituent was changed from a side plate ferrite to an acicular ferrite. VCN precipitates, which were known to favor the nucleation of acicular ferrite, were formed on the (Mn,Si) oxide and MnS particles. The presence of vanadium in alloys suppressed the formation of a side plate ferrite and reduced the transformation of ferrite during an isothermal transformation. Nucleation of intragranular ferrite and a subsequent sympathetic nucleation of ferrite within austenite grains were favored in the vanadium containing steel and an acicular ferrite microstructure was developed.

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