Production of Niobium Carbide Layers on High‐Strength Bainitic Steels by Thermochemical Treatment of Thermoreactive Diffusion Followed by Austempering

Steels with bainitic microstructures show the capacity to fulfil the requirements of high strength and low temperature toughness necessary for plate steels in specialised industrial constructions. The introduction of steels with higher strength allows for weight reductions of steel constructions. This paper investigates the development of hot rolled structural plate steels through laboratory hot rolling simulations of thermo-mechanically controlled processes (TMCP). Specific alloying and microalloying along with an optimised TMCP process has allowed high tensile properties to be achieved in combination with high levels of toughness. Tensile strengths of up to 900 MPa have been achieved with Charpy V-notch toughness greater than 200J at –40°C. Elements such as molybdenum, niobium and boron have been added to low carbon steels to promote the formation of fully bainitic microstructures with much lightened chemical compositions. The presented concepts allow the production of steel grades above S500 up to S690.

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Role of retained austenite on adiabatic shear band formation during high strain rate loading in high-strength bainitic steels

Materials Science and Engineering A ◽

10.1016/j.msea.2020.139118 ◽

2020 ◽

Vol 778 ◽

pp. 139118 ◽

Cited By ~ 3

Author(s):

Min Cheol Jo ◽

Selim Kim ◽

Dong Woo Suh ◽

Sung Suk Hong ◽

Hong Kyu Kim ◽

...

Keyword(s):

High Strain ◽

Adiabatic Shear Band ◽

High Strength ◽

Adiabatic Shear ◽

Shear Band Formation ◽

Band Formation ◽

Bainitic Steels ◽

Adiabatic Shear Band Formation ◽

Strain Rate Loading

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Complex Microstructural Banding of Continuously Cooled Carbide-Free Bainitic Steels

Materials Science Forum ◽

10.4028/www.scientific.net/msf.783-786.980 ◽

2014 ◽

Vol 783-786 ◽

pp. 980-985 ◽

Cited By ~ 2

Author(s):

Lucia Morales-Rivas ◽

Hans Roelofs ◽

Stephan Hasler ◽

Carlos García-Mateo ◽

Francisca García Caballero

Keyword(s):

Volume Fraction ◽

Electron Backscatter Diffraction ◽

High Strength ◽

Gradual Transition ◽

Bainitic Steels ◽

Segregation Of Alloying Elements ◽

Steel Grades ◽

Chemical Segregation ◽

Bainitic Structure ◽

Morphological Differences

Chemical segregation of alloying elements during solidification of steel grades leads to development of a banded microstructure, causing a degree of anisotropy that can be detrimental to the mechanical behavior under service conditions. It is well-known that the presence of strongly orientated martensite bands in carbide-free bainitic microstructures, associated to inhomogeneous Mn redistribution during solidification, leads to a remarkable deterioration in toughness in advanced high strength bainitic steels. In this study, while bands were clearly visible on light optical micrographs of continuously cooled carbide-free bainitic steels, scanning electron microscopy examination revealed only a gradual transition between matrix and bands, both with a granular bainitic structure. Electron backscatter diffraction was used to quantify the bainitic packet size and volume fraction of martensite/austenite constituent between and within the bands, after a process of optimization of the analysis settings in order to minimize the inherent difficulties linked to sub-micrometric and minority phase indexation. The quantitative microstructural results showed negligible morphological differences between bainitic structure bands and matrix, only solute segregation of Cr and Mo was detected by energy-dispersive X-ray spectroscopy within bands, which must be responsible for a stronger resistance against metallographic etching in those regions.

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Investigation of Microstructure and Mechanical Properties of Ultra High Strength Bainitic Steel

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.313-314.77 ◽

2013 ◽

Vol 313-314 ◽

pp. 77-81

Author(s):

M.H. Sheikh Ansari ◽

M. Aghaie-Khafri

Keyword(s):

Mechanical Properties ◽

Alloy Steel ◽

High Strength ◽

Lower Bainite ◽

Good Combination ◽

Bainitic Steel ◽

Low Alloy Steel ◽

Tempered Martensite ◽

Medium Carbon ◽

Bainitic Steels

In this study, medium carbon low alloy steel was used to obtain bainitic structures. The lower bainite and tempered martensite-lower bainite structures were achieved by isothermal austempering and up quenching treatment, respectively. Based on the results obtained these structures showed a very good combination of strength and toughness. Furthermore, it has been shown that austenitization time and temperature, as well as austempering time and temperature play a major role in achieving ultra-high strength bainitic steels.

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