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.

Cavitation control in steels of high residual element content

1980 ◽  
Vol 295 (1413) ◽  
pp. 305-305 ◽  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Prior Austenite ◽  
Low Alloy Steels ◽  
Boundary Zone ◽  
Austenite Grain ◽  
Alloy Steels ◽  
Austenite Grain Boundary ◽  
Prior Austenite Grain ◽  
Transverse Boundary

The cavitational mode of failure of prior austenite grain boundaries in bainitic creep-resisting low alloy steels is now well established as a principal factor in the high incidence of cracking problems which has developed on modern power plant in recent years. The microstructural features dominating the cavitation process at the reheat temperature in a ½CMV bainitic steel of high classical residual level have been determined. The prior austenite grain boundaries become zones of comparative weakness ca . 1 pm thick at 700 °C and are incapable of sustaining significant shear loads. Deformation is therefore initiated by a relaxation of load, through a process of prior austenite grain boundary zone shear, from inclined to transverse boundaries such that a concentration of normal stress develops across the latter. The overall deformation is thereafter determined by cavitation of the transverse boundary zones, the necessary inclined boundary displacements being accommodated by further grain boundary zone shear. Transverse boundary cavitation is shown to be an essentially time-independent process of localized ductile microvoid coalescence resulting from the plastic deformation of the boundary zone.

The critical influence of La content on the microstructure-toughness relationship in the simulated coarse-grained heat-affected zone of high-strength low-alloy steels

2021 ◽  
Vol 118 (2) ◽  
pp. 212
Author(s):  
Yuxin Cao ◽  
Xiangliang Wan ◽  
Feng Zhou ◽  
Hangyu Dong ◽  
Kaiming Wu ◽  
...  
Keyword(s):  
Heat Affected Zone ◽  
Acicular Ferrite ◽  
High Strength ◽  
Coarse Grained ◽  
Low Alloy Steels ◽  
Fine Grained ◽  
Welding Thermal Cycle ◽  
Alloy Steels ◽  
High Fraction ◽  
The Impact

The present study was envisaged to investigate the role of La content on the particle, microstructure and toughness in the simulated coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steels. Three steels with La content of 0.016 wt.%, 0.046 wt.% and 0.093 wt.% were prepared and simulated in a 100 kJ/cm heat input welding thermal cycle. Subsequently, the particle and microstructure of selected specimens were characterized and the impact absorb energy was measured at −20 °C. The results indicated that the La2O2S inclusions in 0.016 wt.%-La steel were gradually modified to LaS-LaP in 0.046 wt.%-La steel and to LaP in 0.093 wt.%-La steel. A higher fraction of acicular ferrite was obtained in the simulated CGHAZ of 0.016 wt.%-La steel, since the inclusion of La2O2S was more powerful to induce the formation of acicular ferrite. Furthermore, the fraction of M-A constituents in the simulated CGHAZ increased with increasing La content. The impact toughness in the simulated CGHAZ of 0.016 wt.%-La steel was the highest, owing to the high fraction of the fine-grained acicular ferrite and low fraction of M-A constituent.

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.

Effect of Nb on Microstructure Evolution of Coarse-Grained Heat-Affected Zone with Large Heat Input Welding

2011 ◽  
Vol 284-286 ◽  
pp. 1174-1179 ◽  
Author(s):  
Xue Li Tao ◽  
Kai Ming Wu ◽  
Xiang Liang Wan
Keyword(s):  
Grain Boundary ◽  
Heat Affected Zone ◽  
Heat Input ◽  
Acicular Ferrite ◽  
High Strength ◽  
Coarse Grained ◽  
Granular Bainite ◽  
Low Alloy Steels ◽  
Alloy Steels ◽  
Grain Boundary Ferrite

The effect of Nb microalloying on microstructure transformation of coarse-grained heat-affected zone of high strength low alloy steels were investigated utilizing different heat input welding simulation. For the low-Nb steel, the microstructures of coarse-grained heat-affected zone mainly consisted of acicular ferrite, bainite and grain boundary ferrite for small heat input welding; the amount of acicular ferrite decreased whereas grain boundary ferrite, polygonal ferrite and pearlite increased with increasing heat input. In constrast, for the high-Nb steel, granular bainite was the dominant microstructure. The formation of granular bainitic microstructure was associated with the solid solution of Nb, which suppressed ferrite transformation and promoted the formation of granular bainite. The hardness of coarse-grained heat-affected zone increased with increasing Nb content, and decreased with decreasing heat input, which was attributed to the microstructural change.

scholarly journals Effect of Ce Content on Microstructure-Toughness Relationship in the Simulated Coarse-Grained Heat-Affected Zone of High-Strength Low-Alloy Steels

Metals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 2003
Author(s):  
Yuxin Cao ◽  
Xiangliang Wan ◽  
Feng Zhou ◽  
Yong Wang ◽  
Xinbin Liu ◽  
...  
Keyword(s):  
Heat Affected Zone ◽  
Energy Levels ◽  
High Strength ◽  
Coarse Grained ◽  
Low Alloy Steels ◽  
Moderate Degree ◽  
Treated Steel ◽  
Alloy Steels ◽  
The Impact ◽  
Ce Content

The study aimed to identify a moderate degree of Ce addition to improve the toughness in the simulated coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steels, based on the effect of the Ce content on particle characteristics, microstructure and impact toughness. Three steels with 0.012 wt.%, 0.050 wt.% and 0.086 wt.% Ce content were subjected to 100 kJ/cm heat input in their thermal welding cycles. The particles and microstructures in the simulated CGHAZ of each steel were characterized and the impact-absorbance energy levels were measured at −20 °C. The results indicated that Ce2O2S inclusion compounds were gradually modified to CexSy-CeP and CeP with the increasing of the Ce content. A higher fraction of acicular ferrite was formed in the 0.012 wt.%-Ce-treated steel due to the lower mismatch between Ce2O2S and α-Fe. Furthermore, a lower fraction of M-A constituent was obtained in the 0.012 wt.%-Ce-treated steel. As a result, superior toughness and a typical amount of ductile fracture were detected in the simulated CGHAZ of the 0.012 wt.%-Ce-treated steel. Compared with the 0.012 wt.%-Ce-treated steel, a smaller prior austenite grain was observed in the 0.086 wt.%-Ce-treated steel because of the segregation of CeP at the grain boundary. However, the larger size and density of CeP led to poor toughness in the CGHAZ of the 0.086 wt.%-Ce-treated steel.

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