scholarly journals A New Systematic Approach Based on Dilatometric Analysis to Track Bainite Transformation Kinetics and the Influence of the Prior Austenite Grain Size

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 324
Author(s):  
David San-Martin ◽  
Matthias Kuntz ◽  
Francisca G. Caballero ◽  
Carlos Garcia-Mateo
Keyword(s):  
Heat Treatment ◽  
Grain Size ◽  
Prior Austenite ◽  
Bainitic Transformation ◽  
Transformation Rate ◽  
Transformation Kinetics ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Prior Austenite Grain Size ◽  
Prior Austenite Grain

This investigation explores the influence of the austenitisation heat treatment and thus, of the prior austenite grain size (PAGS), on the kinetics of the bainitic transformation, using as A case study two high-carbon, high-silicon, bainitic steels isothermally transformed (TIso = 250, 300, 350 °C), after being austenised at different temperatures (γTγ = 925–1125 °C). A methodology, based on the three defining dilatometric parameters extracted from the derivative of the relative change in length, was proposed to analyse the transformation kinetics. These parameters are related to the time to start bainitic transformation, the time lapse for most of the transformation to take place and the transformation rate at the end of the transformation. The results show that increasing the PAGS up to 70 µm leads to an increase in the bainite nucleation rate, this effect being more pronounced for the lowest TIso. However, the overall transformation kinetics seems to be weakly affected by the applied heat treatment (γTγ and TIso). In one of the steels, PAGS > 70 µm (γTγ > 1050 °C), which weakly affects the progress of the transformation, except for TIso = 250 °C, for which the enhancement of the autocatalytic effect could be the reason behind an acceleration of the overall transformation.

Calibrating Phase Transformation and Grain Growth Models and Measuring Phase Dependent Material Properties for Use in FE Simulations of Welds

2015 ◽  
Author(s):  
Nicholas O’Meara ◽  
Simon D. Smith ◽  
John A. Francis
Keyword(s):  
Grain Size ◽  
Phase Transformation ◽  
Prior Austenite ◽  
Computer Modelling ◽  
Transformation Model ◽  
Transformation Kinetics ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Prior Austenite Grain Size ◽  
Prior Austenite Grain

Computer modelling methods are being used to determine the residual stresses in nuclear reactor pressure vessel welds. It has been found that such models need to simulate the effects of solid state phase transformations. Transformations have an associated transformation strain which can significantly influence the evolution of residual stress. The predicted distribution of phases enables structural simulations to account for the distribution of mechanical properties throughout a weld. Factors such as heating or cooling rate and prior austenite grain size must be considered in order to accurately predict the distribution of phases during a transient thermal cycle since they influence transformation kinetics. In this paper, a model to predict the prior austenite grain size and its effects on phase transformation kinetics is presented and calibrated using free dilatometry data. Validation experiments are conducted using a Gleeble thermo-mechanical simulator and are modelled in a commercial FE package to assess the accuracy of a phase transformation model. Samples have been heat treated to possess specific microstructures and have been tested at different temperatures to establish the properties of the phases that can form during weld thermal cycles.

Homology Analysis of Prior Austenite Grain Size of SAE52100 Bearing Steel Processed by Cyclic Heat Treatment

2013 ◽  
Vol 813 ◽  
pp. 116-119 ◽  
Author(s):  
Kazuaki Nakane ◽  
Katsuyuki Kida ◽  
Koshiro Mizobe
Keyword(s):  
Heat Treatment ◽  
Grain Size ◽  
Retained Austenite ◽  
Prior Austenite ◽  
Cyclic Heat Treatment ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Cyclic Heat ◽  
Prior Austenite Grain Size ◽  
Prior Austenite Grain

Here, we introduce the mathematical methods to quantitatively evaluate the change of the tissue to quenching. SAE 52100 sample was repeatedly quenched and the influence of this cyclic heat treatment was investigated. The repeated quenching process increased the retained austenite content and had little influence on the materials hardness. The prior austenite grain size was decreased and consequently, refinement of the martensitic phase in the material occurred. The higher content of the retained austenite (higher fracture toughness) and the refinement of the microstructure accounted for the higher fatigue properties of the repeatedly quenched material. Here we use mathematical homology to quantify these features.

scholarly journals Exploring the Difference in Bainite Transformation with Varying the Prior Austenite Grain Size in Low Carbon Steel

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 988 ◽  
Author(s):  
Liangyun Lan ◽  
Zhiyuan Chang ◽  
Penghui Fan
Keyword(s):  
Grain Size ◽  
Prior Austenite ◽  
Low Carbon Steel ◽  
Low Carbon ◽  
Bainite Transformation ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Austenite Grains ◽  
Prior Austenite Grain Size ◽  
Prior Austenite Grain

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.

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