Cold Formabilities of Martensite-Type Medium Mn Steel

Cold stretch-formability and stretch-flangeability of 0.2%C-1.5%Si-5.0%Mn (in mass%) martensite-type medium Mn steel were investigated for automotive applications. High stretch-formability and stretch-flangeability were obtained in the steel subjected to an isothermal transformation process at temperatures between Ms and Mf − 100 °C. Both formabilities of the steel decreased compared with those of 0.2%C-1.5%Si-1.5Mn and -3Mn steels (equivalent to TRIP-aided martensitic steels), despite a larger or the same uniform and total elongations, especially in the stretch-flangeability. The decreases were mainly caused by the presence of a large amount of martensite/austenite phase, although a large amount of metastable retained austenite made a positive contribution to the formabilities. High Mn content contributed to increasing the stretch-formability.

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Effect of Dew Point and Alloy Composition on Reactive Wetting of Hot Dip Galvanized Medium Manganese Lightweight Steel

Coatings ◽

10.3390/coatings10010037 ◽

2020 ◽

Vol 10 (1) ◽

pp. 37 ◽

Cited By ~ 2

Author(s):

Tong Yang ◽

Yanlin He ◽

Zhang Chen ◽

Weisen Zheng ◽

Hua Wang ◽

...

Keyword(s):

Alloy Composition ◽

Dew Point ◽

Reactive Wetting ◽

Application Development ◽

Lightweight Steel ◽

Unstable Phase ◽

Medium Mn Steel ◽

Mn Content ◽

Mn Steel

For its application development, the medium manganese lightweight steel with 3 wt.% and 10 wt.% Mn contents was galvanized in continuous hot dip galvanizing (HDG) simulator and the process parameters on the production line were adopted. Combined with the experimental analysis and thermodynamic calculation, the effect of dew point and alloy composition on the reactive wetting of the steel was investigated. It was shown that MnO existed as a stable oxide for the medium Mn steel with 5 wt.% Al as long as Mn content exceeded 5.1 wt.%. The galvanizability of the steel with 10 wt.% Mn was deteriorated resulting from the formation of a thick and continuous external MnO layer, which had adverse effects on the wettability. MnO particles in the form of unstable phase can be found at the surface of 3Mn steel galvanized at dew point +10 °C. It distributed sparsely and the reactive wettability can be obtained by “bridging connection”, which mitigated the damage of external oxidation. Moreover, the lower dew point, the less tendency to form external oxide. Although the decrease of dew point to −30 °C had a certain benefit for coating quality, the galvanizing quality of 10Mn steel could not be improved due to the formation of a thick MnO layer. Therefore, the Mn content played a stronger role than dew point on the reactive wetting of hot dip galvanized medium manganese lightweight steel.

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Low and Medium Carbon Advanced High-Strength Forging Steels for Automotive Applications

Metals ◽

10.3390/met9121263 ◽

2019 ◽

Vol 9 (12) ◽

pp. 1263 ◽

Cited By ~ 1

Author(s):

Koh-ichi Sugimoto ◽

Tomohiko Hojo ◽

Ashok Srivastava

Keyword(s):

Mechanical Properties ◽

Hot Forging ◽

High Strength ◽

Isothermal Transformation ◽

Transformation Process ◽

Automotive Applications ◽

Medium Carbon ◽

Sheet Steels ◽

The Third ◽

The Matrix

This paper presents the microstructural and mechanical properties of low and medium carbon advanced high-strength forging steels developed based on the third generation advanced high-strength sheet steels, in conjunction with those of conventional high-strength forging steels. Hot-forging followed by an isothermal transformation process considerably improved the mechanical properties of the forging steels. The improvement mechanisms of the mechanical properties were summarized by relating to the matrix structure, the strain-induced transformation of metastable retained austenite, and/or a mixture of martensite and austenite.

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Low and Medium Carbon Advanced High-Strength Forging Steels for Automotive Applications

10.20944/preprints201910.0337.v1 ◽

2019 ◽

Author(s):

Koh-ichi Sugimoto ◽

Tomohiko Hojo ◽

Ashok Kumar Srivastava

Keyword(s):

Mechanical Properties ◽

Hot Forging ◽

High Strength ◽

Isothermal Transformation ◽

Transformation Process ◽

Automotive Applications ◽

Medium Carbon ◽

Sheet Steels ◽

The Third ◽

The Matrix

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Strengthening Mechanism and Carbide Precipitation Behavior of Nb-Mo Microalloy Medium Mn Steel

Materials ◽

10.3390/ma14237461 ◽

2021 ◽

Vol 14 (23) ◽

pp. 7461

Author(s):

Chunquan Liu ◽

Fen Xiong ◽

Yong Wang ◽

Yuxin Cao ◽

Xinbin Liu ◽

...

Keyword(s):

Intercritical Annealing ◽

Strengthening Mechanism ◽

Carbide Precipitation ◽

Reverse Transformation ◽

Precipitation Behavior ◽

Medium Mn Steel ◽

Mn Content ◽

Cyclic Quenching ◽

Mn Steel ◽

Positive Effect

This study investigates the strengthening mechanism and carbide precipitation behavior of medium Mn steel with Nb-Mo microalloy after cyclic quenching and austenite reverse transformation treatment. The results show that the Nb/Mo element not only precipitates (Nb,Mo)C in the grains, hindering the movement of dislocations and increases the strength, but also segregates at the austenite/ferrite grain boundary, thus delaying the transformation from austenite to ferrite. In addition, a large amount of nano-scale cementite is retained after cyclic quenching and austenite reverse transformation, which has a positive effect on the proportion of retained austenite in medium Mn steel. Moreover, the carbides with small size and low Mn content are dissolved, and the decomposed C and Mn content are beneficial to the nucleation of austenite during the intercritical annealing process at a temperature of 690 °C.

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