Influence of Thermomechanical Control Process on the Evolution of Austenite Grain Size in a Low-Carbon Nb-Ti-Bearing Bainitic Steel

The simulation welding thermal cycle technique was employed to generate different sizes of prior austenite grains. Dilatometry tests, in situ laser scanning confocal microscopy, and transmission electron microscopy were used to investigate the role of prior austenite grain size on bainite transformation in low carbon steel. The bainite start transformation (Bs) temperature was reduced by fine austenite grains (lowered by about 30 °C under the experimental conditions). Through careful microstructural observation, it can be found that, besides the Hall–Petch strengthening effect, the carbon segregation at the fine austenite grain boundaries is probably another factor that decreases the Bs temperature as a result of the increase in interfacial energy of nucleation. At the early stage of the transformation, the bainite laths nucleate near to the grain boundaries and grow in a “side-by-side” mode in fine austenite grains, whereas in coarse austenite grains, the sympathetic nucleation at the broad side of the pre-existing laths causes the distribution of bainitic ferrite packets to be interlocked.

Download Full-text

Coupling Effect of Prior Austenite Grain Size and Inclusion Characteristics on Acicular Ferrite Formation in Ti-Zr Deoxidized Low Carbon Steel

Metallurgical and Materials Transactions B ◽

10.1007/s11663-020-01785-0 ◽

2020 ◽

Vol 51 (2) ◽

pp. 480-491

Author(s):

Yongkun Yang ◽

Dongping Zhan ◽

Hong Lei ◽

Yulu Li ◽

Guoxing Qiu ◽

...

Keyword(s):

Grain Size ◽

Carbon Steel ◽

Prior Austenite ◽

Coupling Effect ◽

Low Carbon Steel ◽

Low Carbon ◽

Austenite Grain Size ◽

Austenite Grain ◽

Prior Austenite Grain Size ◽

Prior Austenite Grain

Download Full-text

Evaluation of Austenite Grains Growth in High Nb and Low Nb HSLA Steel

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1000.404 ◽

2020 ◽

Vol 1000 ◽

pp. 404-411

Author(s):

Eddy S. Siradj

Keyword(s):

Grain Size ◽

Grain Growth ◽

Oil And Gas ◽

Hsla Steel ◽

Large Diameter ◽

Low Carbon ◽

Austenite Grain Size ◽

Austenite Grain ◽

Reheating Process ◽

Austenite Grain Growth

This study was presented due to the increasing demand of High Strength Low Alloy (HSLA) steel, such as demand for thinner-walled and large diameter pipes in oil and gas industries. In order to meet the imposed economic restrictions, the high standard of all kinds of steel properties is required and can be achieved by controlling the steel microstructure. The austenite grain size influences the microstructure and properties of steel significantly, in which fine austenite grain size leads to higher strength, better ductility, and higher toughness. Studying the behavior of steel grain growth during the reheating process is still being a fascinating subject. P.R. Rios and D Zollner [1] mentioned that grain growth is the most important unresolved issue that has been a topic of research for many years. In this research, the behavior of austenite grain growth at a high niobium-low carbon (High Nb-low C) and low Nb-high C HSLA steel was evaluated, and the result was compared with other investigation. The results found that the austenite grain growth at high Nb-high C steel was slower than the growth at a low Nb-low C steel. The activation energy of austenite grain growth and both constant A and exponent n ware determined close agreement was obtained between the prediction of the model and the experimental grain size value.

Download Full-text

Austenite Grain Structures in Ti and Nb-Containing HSLA Steel during Slab Reheating

Materials Science Forum ◽

10.4028/www.scientific.net/msf.783-786.669 ◽

2014 ◽

Vol 783-786 ◽

pp. 669-673

Author(s):

Debalay Chakrabarti ◽

S. Roy ◽

Dinesh Srivastava ◽

Gautam Kumar Dey

Keyword(s):

Grain Size ◽

Hsla Steel ◽

Size Variation ◽

Inhomogeneous Distribution ◽

Low Carbon ◽

Cast Slab ◽

Austenite Grain Size ◽

Intermediate Temperature Range ◽

Austenite Grain ◽

Grain Structures

Spatial distribution of microalloy precipitates have been characterized in a low carbon microalloyed steel containing Nb, Ti and V. Micro-segregation during casting resulted in an inhomogeneous distribution of Nb (and also Ti) precipitates in the as-cast slab. Austenite grain growth has been investigated in the above mentioned steel, using different reheating temperatures between 1000°C and 1250°C for 1 h. Inhomogeneous distribution of Nb-rich precipitates created austenite grain size bimodality after reheating to an intermediate temperature range (1150-1200°C). Uniformly fine and uniformly coarse grain structures were found after reheating at lower- (≤ 1075°C) and higher-reheating temperatures (≥ 1250°C). A model has been proposed for the prediction of austenite grain size variation in the reheated steel.

Download Full-text