scholarly journals Dependency of phase transformation on the prior austenite grain size and its influence on welding residual stress of S700 steel

2018 ◽  
Vol 62 (4) ◽  
pp. 699-712 ◽  
Author(s):  
J. Ni ◽  
J. Vande Voorde ◽  
J. Antonissen ◽  
M. Abdel Wahab
Keyword(s):  
Residual Stress ◽  
Grain Size ◽  
Phase Transformation ◽  
Prior Austenite ◽  
Welding Residual Stress ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Prior Austenite Grain Size ◽  
Prior Austenite Grain

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.

Field Girth Weld HAZ Toughness Improvement: X80/Grade 550

2010 ◽  
Author(s):  
Christopher Penniston ◽  
Laurie E. Collins
Keyword(s):  
Grain Size ◽  
Phase Transformation ◽  
Prior Austenite ◽  
Phase Transformation Temperature ◽  
Austenite Grain Size ◽  
Lower Phase ◽  
Austenite Grain ◽  
Prior Austenite Grain Size ◽  
Haz Toughness ◽  
Prior Austenite Grain

Field welding and field weld rework can be a significant cost in the construction of pipelines. Heat affected zone (HAZ) material adjacent to a weld is of particular concern because the base material microstructure has been altered significantly. In instances where Engineering Critical Assessment (ECA) is used for defect acceptance, optimizing and/or improving the base material for field weldability will reduce repair welding rates, which in turn improves project economics. Several alloys of X80/Grade 550 were assessed. All materials were robotically welded to simulate a typical mechanized field weld. Two of the alloys were also welded using a field mechanized welding system. These welds were subjected to tests assessing field weldability. Weldability is a broad term used to summarize various material properties related to the level of conduciveness to welding. For the purposes of this paper, the term field weldability is used to describe the level of HAZ toughness of a material subjected to field welding conditions. Charpy V-notch (CVN) and crack tip opening displacement (CTOD) tests were utilized to assess the toughness of the welded material. Optical microscopy was employed to characterize the HAZ microstructures. In addition, all materials were subjected to HAZ thermal processing in a Gleeble thermo-mechanical simulator. Gleeble dilatometry curves were constructed to characterize phase transformation behavior, and tested materials were used to characterize HAZ microstructures using optical microscopy. Gleeble HAZ CVN specimens were processed in order to assess the toughness of a uniform, idealized HAZ microstructure. It was found that HAZ toughness was better for material chemistries that promote lower phase transformation temperatures. Lower phase transformation temperatures caused the formation of favorable microstructural phases, with finer coarse grain HAZ (CGHAZ) prior austenite grain size, as well as fine packet size. Phase transformation temperature and prior austenite grain size were found to be most dependant on the carbon and carbon equivalent content of the material. The steel containing the lowest amount of carbon displayed the highest phase transformation temperature, coarsest CGHAZ prior austenite grain size, and lowest HAZ toughness, as measured by CTOD and CVN tests.

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.

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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