scholarly journals Residual Stress Formation Relating to Peak Temperature- and Austenite Grain Size-based Phase Transformation of S355 Steel

2014 ◽  
Vol 56 ◽  
pp. 1343-1352 ◽  
Author(s):  
Fabian Klaproth ◽  
Frank Vollertsen
Keyword(s):  
Residual Stress ◽  
Grain Size ◽  
Phase Transformation ◽  
Peak Temperature ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Stress Formation

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.

Mesoscopic Simulation of the Ferrite Nucleation on Austenitic Grain Boundary for Nanograined Steel

2015 ◽  
Vol 817 ◽  
pp. 731-735
Author(s):  
Peng Yu ◽  
Lin Zhang ◽  
Lin Xiu Du ◽  
Jun Hu
Keyword(s):  
Grain Size ◽  
Phase Transformation ◽  
Nucleation Process ◽  
Austenite Grain Size ◽  
Mesoscopic Simulation ◽  
Thermodynamics And Kinetics ◽  
Austenite Grain ◽  
Austenite Grains ◽  
Ferrite Nucleation ◽  
Kinetics Of

We use the cellular automaton (CA) modeling to investigate the ferrite nucleation on the austenite grains. On the basis of the thermodynamics and kinetics of phase transformation from austenite to ferrite, the CA modeling demonstrates that the size of nucleated ferrite grains is increased with increasing of cooling rates, and nucleation process is finished instantly at a given cooling rate. The initial austenite grain size plays an important role in the obtained ferrite nucleation number, and the potential nucleation cells are increased.

On the Thermo-Mechanical Behaviour of SA508 Grade 4 Ferritic Steel

2014 ◽  
Author(s):  
Hamidreza Abdolvand ◽  
John A. Francis ◽  
Feridoon Azough ◽  
Joanna N. Walsh ◽  
Christopher M. Gill ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Residual Stress ◽  
Phase Transformation ◽  
Ferritic Steel ◽  
Structural Integrity ◽  
Fe Modelling ◽  
Austenite Grain Size ◽  
Stress Development ◽  
Grain Sizes ◽  
Austenite Grain

The development of residual stresses in the Heat Affected Zone (HAZ) during welding of a ferritic steel can be critical to weld structural integrity. The Prior Austenite Grain Size (PAGS), the thermo-mechanical properties of the phases that develop during phase transformation, and the transformation strains are some of the key parameters that can alter residual stress development during welding. Understanding the trend in variation of these parameters is crucial for Finite Element (FE) modelling of residual stress development in weld. In this study, the effect of PAGS on the phase transformation in SA508 grade 4 was determined. For this purpose, samples were heated up to 900, 1050, 1250, and 1350°C and held for various time intervals to produce different austenite grain sizes. The measured austenite grain sizes were then used to fit parameters in an exponential equation implemented in an FE User MATerial subroutine (UMAT) for the modelling of welds. With performing various free dilatometry experiments, it is shown that the only phase that austenite transforms to upon cooling is martensite. In addition, the mechanical properties of as-received material, austenite, and martensite as a function of temperature were measured. Also, various uni-axial loads were applied during cooling cycles, and before the onset of phase transformations, to measure the evolution of transformation strain to generate an empirical formulation for numerical modelling.

Nanocrystallization of Bulk Steels through γ/α Transformation

2007 ◽  
Vol 539-543 ◽  
pp. 4687-4691
Author(s):  
Lin Xiu Du ◽  
Ming Xian Xiong ◽  
Xiang Hua Liu ◽  
Guo Dong Wang
Keyword(s):  
Grain Size ◽  
Phase Transformation ◽  
Microalloyed Steel ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Austenite Grains

A method of obtaining nanocrystallized bulk steels through phase transformation was investigated. Firstly, the austenite grain size of a microalloyed steel was refined to 1~3μm through repeatly heating and quenching; secondly, the samples with ultrafined austenite grains were heavily deformed at different temperature, and the uniform microstructures with some 0.1~0.3μm equiaxed ferrites were obtained.

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