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.

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 Effect of Initial Microstructure on the Toughness of Coarse-Grained Heat-Affected Zone in a Microalloyed Steel

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4760
Author(s):  
Minghao Shi ◽  
Man Di ◽  
Jian Zhang ◽  
Rangasayee Kannan ◽  
Jing Li ◽  
...  
Keyword(s):  
Grain Size ◽  
Base Metal ◽  
Thermal Cycle ◽  
Microalloyed Steel ◽  
Charpy Impact ◽  
Coarse Grained ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Prior Austenite Grain Size ◽  
Prior Austenite Grain

Toughness of the coarse-grained-heat-affected-zone (CGHAZ) strongly depends on the prior austenite grain size. The prior austenite grain size is affected not only by chemical composition, thermal cycle, and dissolution of second-phase particles, but also by the initial microstructure. The effect of base metal microstructure (ferrite/pearlite obtained by air cooling and martensite obtained by water-quenching) on Charpy impact toughness of the CGHAZ has been investigated for different heat inputs for high-heat input welding of a microalloyed steel. A welding thermal cycle with a heat input of 100 kJ/cm and 400 kJ/cm were simulated on the MMS-300 system. Despite a similar microstructure in the CGHAZ of both the base metals, the average Charpy impact energy for the air-cooled base metal was found to be higher than the water-quenched base metal. Through thermo-kinetic simulations, it was found that a higher enrichment of Mn/C at the ferrite/austenite transformation interface of the CGHAZ of water-quenched base metal resulted in stabilizing austenite at a lower A1 temperature, which resulted in a coarser austenite grain size and eventually lowering the toughness of the CGHAZ.

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

2010 ◽  
Vol 154-155 ◽  
pp. 1850-1854 ◽  
Author(s):  
Sadegh Moeinifar
Keyword(s):  
Pipeline Steel ◽  
Charpy Impact ◽  
Initiation Site ◽  
Impact Testing ◽  
Peak Temperature ◽  
Coarse Grained ◽  
X80 Pipeline Steel ◽  
Brittle Phase ◽  
Charpy Impact Testing ◽  
Second Peak

The objective of this paper is to study the influence of second peak temperature during simulated welding on properties of the subcritically (S), intercritically (IC) and supercritically (SC) reheated coarse grained heat affected (CGHAZ) zones. This involved heating to a first peak temperature (TP1) of 1400 °C, then reheating to different second peak temperatures (TP2) of 700, 800 and 900 °C with a constant cooling rate of 3.75 °C/s. Toughness of the simulated reheated CGHAZ regions were assessed using Charpy impact testing at 0 and -50 °C. The blocky and connected M/A particles, along prior-austenite grain boundaries, act as a brittle phase for the initiation site of the brittle fracture. Charpy impact results indicated that IC CGHAZ had less absorbed energy with higher transition temperature and hardness.

The Oxide Inclusion and Heat-Affected-Zone Toughness of Low Carbon Steels

2010 ◽  
Vol 654-656 ◽  
pp. 358-361 ◽  
Author(s):  
Wei Shu ◽  
Xue Min Wang ◽  
Shu Rui Li ◽  
Xin Lai He
Keyword(s):  
Heat Affected Zone ◽  
Prior Austenite ◽  
Oxide Inclusion ◽  
Optical Microscope ◽  
Carbon Steels ◽  
Cooling Time ◽  
Low Carbon ◽  
Low Carbon Steels ◽  
Austenite Grain ◽  
Prior Austenite Grain

The relationship between the oxide inclusions and the Heat-affected-zone (HAZ) toughness of microalloying steels has been investigated. The low carbon steels are smelted with special oxide introduction technique and the properties of HAZ has been studied with thermo-simulation. The optical microscope and SEM were used to analyze the size, composition and distribution of the inclusions, the mechanical properties after thermo-simulation was also analyzed. The results show that the inclusions in steel are mainly Ti and Al oxide with MnS, these complex inclusions are well distributed and the size is less than 3 micron. Microstructure of HAZ consists of intragranular acicular ferrite (IAF), intergranular ferrite and small amount of lath bainite while the cooling time during the phase formation is short. After the thermo simulation with the cooling time between 800°C and 500°C (t8/5) increasing the toughness of HAZ decreased and the size of prior austenite grain increased. Inclusions which located near the prior austenite grain boundary couldn’t induce the nucleation of IAF, only the ones inside the prior austenite grain can promote IAF’s growth.

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