scholarly journals Characterization of Coarse-Grained Heat-Affected Zones in Al and Ti-Deoxidized Offshore Steels

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1096
Author(s):  
Henri Tervo ◽  
Antti Kaijalainen ◽  
Vahid Javaheri ◽  
Satish Kolli ◽  
Tuomas Alatarvas ◽  
...  
Keyword(s):  
Prior Austenite ◽  
Electron Backscatter Diffraction ◽  
Coarse Grained ◽  
Grain Coarsening ◽  
Austenite Grain ◽  
The Matrix ◽  
Backscatter Diffraction ◽  
Prior Austenite Grain ◽  
Deoxidation Practice

Deterioration of the toughness in heat-affected zones (HAZs) due to the thermal cycles caused by welding is a known problem in offshore steels. Acicular ferrite (AF) in the HAZ is generally considered beneficial regarding the toughness. Three experimental steels were studied in order to find optimal conditions for the AF formation in the coarse-grained heat-affected zone (CGHAZ). One of the steels was Al-deoxidized, while the other two were Ti-deoxidized. The main focus was to distinguish whether the deoxidation practice affected the AF formation in the simulated CGHAZ. First, two different peak temperatures and prolonged annealing were used to study the prior austenite grain coarsening. Then, the effect of welding heat input was studied by applying three cooling times from 800 °C to 500 °C in a Gleeble thermomechanical simulator. The materials were characterized using electron microscopy, energy-dispersive X-ray spectrometry, and electron backscatter diffraction. The Mn depletion along the matrix-particle interface was modelled and measured. It was found that AF formed in the simulated CGHAZ of one of the Ti-deoxidized steels and its fraction increased with increasing cooling time. In this steel, the inclusions consisted mainly of small (1–4 μm) TiOx-MnS, and the tendency for prior austenite grain coarsening was the highest.

scholarly journals Local Characterization of Precipitation and Correlation with the Prior Austenitic Microstructure in Nb-Ti-Microalloyed Steel by SEM and AFM Methods

Metals ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 636 ◽  
Author(s):  
Lena Eisenhut ◽  
Jonas Fell ◽  
Christian Motz
Keyword(s):  
Electron Microscopy ◽  
Prior Austenite ◽  
Thermomechanical Processing ◽  
Electron Backscatter Diffraction ◽  
Grain Structure ◽  
Austenite Grain ◽  
Reconstruction Methods ◽  
Local Characterization ◽  
Prior Austenite Grain

Precipitation is one of the most important influences on microstructural evolution during thermomechanical processing (TMCP) of micro-alloyed steels. Due to precipitation, pinning of prior austenite grain (PAG) boundaries can occur. To understand the mechanisms in detail and in relation to the thermomechanical treatment, a local characterization of the precipitation state depending on the microstructure is essential. Commonly used methods for the characterization, such as transmission electron microscopy (TEM) or matrix dissolution techniques, only have the advantage of local or statistically secured characterization. By using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques, both advantages could be combined. In addition, in the present work a correlation of the precipitation conditions with the prior austenite grain structure for different austenitization states could be realized by Electron Backscatter Diffraction (EBSD) measurement and reconstruction methods using the reconstruction software Merengue 2.

Influence of Crystallography on Nucleation of Ferrite Precipitates at Austenite Grain Boundary Corners in a Co-15Fe Alloy

2011 ◽  
Vol 172-174 ◽  
pp. 378-383
Author(s):  
Guo Hong Zhang ◽  
Tomoaki Takeuchi ◽  
Masato Enomoto ◽  
Yoshitaka Adachi
Keyword(s):  
Grain Boundary ◽  
Electron Backscatter Diffraction ◽  
Major Influence ◽  
Austenite Grain ◽  
Electron Backscatter ◽  
The Matrix ◽  
Triple Points ◽  
Individual Grains ◽  
Austenite Grain Boundary ◽  
Backscatter Diffraction

The nucleation of bcc ferrite precipitates at austenite grain corners in a Co-15Fe alloy was studied by serial sectioning coupled with electron backscatter diffraction (EBSD) analysis. Grain corners were identified by recombination of triple points and triangular annihilation, whereas quite a few precipitates were surrounded by more than four matrix grains when twins were counted as individual grains. More than 40% of corners composed all of high angle grain boundaries were vacant at an undercooling of ~60°C from the g/(a+g) phase boundary. All the precipitates had K-S or N-W orientation relationship with at least one grain and a larger proportion of them had the OR with two and three grains. For half of vacant corners a hypothetical precipitate could have the OR with more than one grain. It is likely that not only the misorientations among the matrix grains, but also the orientations of the grain boundary planes have a major influence on nucleation potency even at grain corners.

Microstructure and Toughness Properties of Subcritically, Intercritically and Supercritically Heat Affected Zones in X80 Microalloyed Pipeline Steel

2011 ◽  
Vol 383-390 ◽  
pp. 5886-5893
Author(s):  
Sadegh Moeinifar
Keyword(s):  
Heat Affected Zone ◽  
Prior Austenite ◽  
Charpy Impact ◽  
Impact Testing ◽  
Peak Temperature ◽  
Coarse Grained ◽  
Secondary Peak ◽  
Thermal Cycles ◽  
Austenite Grain ◽  
Prior Austenite Grain

The influence of the real and simulated thermal cycles with different secondary peak temperatures on the properties of the reheated coarse grained heat affected zone (CGHAZ) in the X80 microalloyed steel has been investigated. The four wires tandem submerged arc welding process with different heat input values was used to generate real double passes thermal cycles. The simulated thermal cycles involved heating to the first peak temperature (TP1) of 1400 °C and then reheating to different secondary peak temperatures (TP2) of 700, 800 and 900 °C with cooling rates of 3.75 and 2 °C/s. The toughness of the simulated reheated CGHAZ with different peak temperature was assessed using Charpy impact testing at 0 °C and -50 °C. It is clear that the reheated CGHAZ thermal cycles with different second peak temperatures have a significant effect on morphology of the martensite/austenite (M/A) constituent. The blocky and connected M/A constituent along the prior-austenite grain boundaries as a brittle phase for crack initiation. The Charpy impact results indicated that intercritically reheated coarse grained heat affected zone had less absorbed energy with higher transition temperature and hardness. In the same prior-austenite grain size, cycles 2 and 4 with lower cooling rate (2 °C/s) have larger size of M/A constituents. The M/A constituent size such as mean diameter and length are important factors influencing Charpy impact properties of the simulated reheated CGHAZ.

Impact of Mo content on the microstructure– toughness relationship in the coarse-grained heat-affected zone of high-strength low-alloy steels

2021 ◽  
Vol 112 (2) ◽  
pp. 98-107
Author(s):  
Yuxin Cao ◽  
Xiangliang Wan ◽  
Feng Zhou ◽  
Yu Shen ◽  
Yu Liu ◽  
...  
Keyword(s):  
Heat Affected Zone ◽  
Prior Austenite ◽  
High Strength ◽  
Coarse Grained ◽  
Low Alloy Steels ◽  
Austenite Grain ◽  
Alloy Steels ◽  
Mo Content ◽  
Grain Boundary Pinning ◽  
Prior Austenite Grain

Abstract The present study elucidates the influence of Mo content on the microstructure – toughness relationship in the coarsegrained heat-affected zone of high-strength low-alloy steels. The low-Mo and high-Mo steels were subjected to 100 kJ cm–1 heat input welding thermal cycling. The results indicated that (Ti,Mo)-carbonitrides were formed in high-Mo steel, whereas (Ti,Nb)-carbonitrides were formed in low-Mo steel. The finer and dispersed precipitates in high-Mo steel refined the prior austenite grain in the coarse-grained heat-affected zone based on the grain boundary pinning effect. However, the smaller prior austenite grain and excessive Mo content induced the formation of an entirely bainitic microstructure in high-Mo steel. Furthermore, a higher fraction of martensite –austenite constituents was observed in high-Mo steel. These results could be responsible for the deterioration of the toughness in the coarse-grained heat-affected zone of high-Mo steel.

Microstructural Characterization of Creep Damaged 11Cr-3.5W-3Co Steel

2006 ◽  
Vol 118 ◽  
pp. 475-478 ◽  
Author(s):  
C.S. Kim ◽  
S.I. Kwun ◽  
Bong Young Ahn ◽  
Seung Hoon Nahm ◽  
Seung Seok Lee
Keyword(s):  
Prior Austenite ◽  
Microstructural Characterization ◽  
Martensite Lath ◽  
Square Root ◽  
Petch Relation ◽  
Softening Behavior ◽  
Austenite Grain ◽  
Lath Width ◽  
Prior Austenite Grain

The effects of the precipitate and martensite lath on the softening behavior have been investigated for 11Cr-3.5W-3Co steel during creep at 700. During creep, the precipitate on the PAG (prior austenite grain) boundaries and martensite lath boundaries coarsened. The recovery of dislocation density and an increase of martensite lath width took place. It is shown that the inverse of the size of the precipitates and the inverse of the square root of the martensite lath width have a linear relation with the Vickers hardness, which corresponds to the Hall-Petch relation and particle looping mechanism.

Full Characterization of a Tool Steel Texture and Microstructure by Using Fast Simultaneous EBSD/EDS Measurements

2011 ◽  
Vol 172-174 ◽  
pp. 1290-1295 ◽  
Author(s):  
Daniel Goran
Keyword(s):  
Tool Steel ◽  
Electron Backscatter Diffraction ◽  
Complete Characterization ◽  
Full Characterization ◽  
Multiphase Materials ◽  
Submicron Scale ◽  
Different Types ◽  
The Matrix ◽  
Backscatter Diffraction

The study presents the latest developments in terms of speed and integration of theelectron backscatter diffraction(EBSD) and energy dispersive spectroscopy (EDS) techniques. The microstructural features and texture of a commercially available tool steel have been analyzed by simultaneous EBSD/EDS measurements. The EDS data was used for confirming/correcting the EBSD results as well as for detecting the presence of ultrafine carbide precipitates. The results indicate the formation of two different types of carbides inside a ferritic matrix. Most of the matrix was found to be composed of fully recrystallized grains with average diameters around 10 microns. Zones characterized by finer submicron scale grains could also be identified locally as well as grains containing networks of subgrain boundaries. This study demonstrates that the combination of the two techniques, i.e. EBSD and EDS, results in a powerful tool for a fast, reliable and complete characterization of multiphase materials.

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