scholarly journals Role of Reversed Austenite Behavior in Determining Microstructure and Toughness of Advanced Medium Mn Steel by Welding Thermal Cycle

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2127 ◽  
Author(s):  
Yunxia Chen ◽  
Honghong Wang ◽  
Huan Cai ◽  
Junhui Li ◽  
Yongqing Chen
Keyword(s):  
Grain Size ◽  
Impact Toughness ◽  
Significant Role ◽  
Heat Affected Zone ◽  
Martensite Transformation ◽  
Thermal Cycle ◽  
Retained Austenite ◽  
Coarse Grained ◽  
Reversed Austenite ◽  
Austenite Transformation

Reversed austenite transformation behavior plays a significant role in determining the microstructure and mechanical properties of heat affected zones of steels, involving the nucleation and growth of reversed austenite. Confocal Laser Scanning Microscope (CLSM) was used in the present work to in situ observe the reversed austenite transformation by simulating welding thermal cycles for advance 5Mn steels. No thermal inertia was found on cooling process after temperature reached the peak temperature of 1320 °C. Therefore, too large grain was not generated in coarse-grained heat-affected zone (CGHAZ). The pre-existing film retained austenite in base metal and acted as additional favorable nucleation sites for reversed austenite during the thermal cycle. A much great nucleation number led to the finer grain in the fine-grained heat-affected zone (FGHAZ). The continuous cooling transformation for CGHAZ and FGHAZ revealed that the martensite was the main transformed product. Martensite transformation temperature (Tm) was higher in FGHAZ than in CGHAZ. Martensite transformation rate was higher in FGHAZ than in CGHAZ, which is due to the different grain size and assumed atom (Mn and C) segregation. Consequently, the softer martensite was measured in CGHAZ than in FGHAZ. Although 10~11% austenite retained in FGHAZ, the possible Transformation Induced Plasticity (TRIP) effect at −60 °C test temperature may lower the impact toughness to some degree. Therefore, the mean absorbed energy of 31, 39 and 42 J in CGHAZ and 56, 45 and 36 J in FGHAZ were exhibited at the same welding heat input. The more stable retained austenite was speculated to improve impact toughness in heat-affected zone (HAZ). For these 5Mn steels, reversed austenite plays a significant role in affecting impact toughness of heat-affected zones more than grain size.

Microstructure and Properties of HAZ in Low-Carbon Bainite E550 Steel during Double-Pass Welding Thermal Cycle

2018 ◽  
Vol 913 ◽  
pp. 317-323 ◽  
Author(s):  
Yun Zong ◽  
Chun Ming Liu
Keyword(s):  
Impact Toughness ◽  
Heat Affected Zone ◽  
Thermal Cycle ◽  
Coarse Grained ◽  
Granular Bainite ◽  
Low Carbon ◽  
Microstructure And Properties ◽  
Welding Thermal Cycle ◽  
Low Carbon Bainite ◽  
The Impact

Investigations on the microstructure and properties of the Coarse-Grained Heat-Affected Zone (CGHAZ) and intercritical reheated Coarse-Grained Heat-Affected Zone (ICCGHAZ) of a low-carbon bainite E550 steel were carried out using thermal simulation technology in this paper.Double-pass welding thermal cycle were performed on Gleeble-3800 thermal simulator, tempering heat treatment of the critical coarse crystal zone carried out in a box resistance furnace, low impact energies at -40 °C and Vickers hardness determined, and the microstructure were observed. The experimental results show that the microstructure of CGHAZ (Tp1 is 1320 °C) was dominated by coarse granular bainite and Lath bainite Ferrite, the impact toughness of CGHAZ was poor. The toughness of the CGHAZ was improved after second welding heat cycle except intercritical two-phase heating. When the peak temperature of the second thermal cycle(Tp2) was 650 °C, martensite-austenite (M-A) constituent of original CGHAZ wasdecomposed and refined, impact toughness and hardness were all higher than that of CGHAZ; When Tp2 is 750 °C, there was a ” necklace” distribution of massive M-A constituent in this ICCGHAZ, the impact energy at -40 °C prominently decreased and Hardness went up; When Tp2 was in the temperature range of 850 °C ~1100 °C, the microstructure was mainly finer granular bainite, the toughness of CGHAZ could be effectively improved; When Tp2 was over 1100 °C, M-A constituents become coarse, the toughness declined slightly . The changing of hardness was the opposite of toughness but the hardness fluctuation was comparatively small. After tempering at different temperature (520 °C~640 °C) , the grain boundary "necklace" structure of ICCGHAZ was still obvious, some of the M-A constituent were decomposed, the hardness decreased, the lowest hardness was obtained in 610 °C.

Effect of Welding Processes with High Heat Input on the Microstructure and Toughness of Coarse-Grained Heat-Affected Zone of a High-Strength High-Toughness Steel

2018 ◽  
Vol 937 ◽  
pp. 61-67
Author(s):  
Yu Jie Li ◽  
Jin Wei Lei ◽  
Xuan Wei Lei ◽  
Oleksandr Hress ◽  
Kai Ming Wu
Keyword(s):  
Low Temperature ◽  
Impact Toughness ◽  
Heat Affected Zone ◽  
Heat Input ◽  
High Strength ◽  
High Heat ◽  
Coarse Grained ◽  
Low Temperature Impact Toughness ◽  
The Impact ◽  
Welding Processes

Utilizing submerged arc welding under heat input 50 kJ/cm on 60 mm thick marine engineering structure plate F550, the effect of preheating and post welding heat treatment on the microstructure and impact toughness of coarse-grained heat-affected zone (CGHAZ) has been investigated. The original microstructure of the steel plate is tempered martensite. The yield and tensile strength is 610 and 660 MPa, respectively. The impact absorbed energy at low temperature (-60 °C) at transverse direction reaches about 230~270 J. Welding results show that the preheating at 100 °C did not have obvious influence on the microstructure and toughness; whereas the tempering at 600 °C for 2.5 h after welding could significantly reduce the amount of M-A components in the coarse-grained heat-affected zone and thus improved the low temperature impact toughness.

Microstructure and Properties of Heat-Affected Zones in X100 Steel Grade Line Pipes

2009 ◽  
Author(s):  
Chuanjing Zhuang ◽  
Na Li ◽  
Shipeng Wang ◽  
Weiping Lin ◽  
Jicheng Ren
Keyword(s):  
Heat Affected Zone ◽  
Thermal Cycle ◽  
Deleterious Effect ◽  
Ferrite Matrix ◽  
Steel Grade ◽  
Peak Temperature ◽  
Coarse Grained ◽  
Microstructure And Properties ◽  
The Relationship ◽  
Second Peak

The relationship between microstructure and properties of weld heat-affected zones in X100 grade pipeline steels was studied. It was found that the intercritically reheated coarse-grained heat-affected zone (IRCGHAZ) of experimental steels has the lowest toughness values when the second peak temperature is at the intercritical (α + γ) region during multi-pass welding. The local embrittlement is attributed to the morphology, amount, and size of the M-A constituent. It is also found that the microstructural inheritance at IRCGHAZ has a deleterious effect on toughness. On the basis of the experimental results, it is suggested that the local embrittlement could be prevented by using pre-heating or post-heating thermal cycle. Pre-heating thermal cycle would eliminate the microstructural inheritance and meliorate M-A constituent. Furthermore, the use of a post-heating thermal cycle will improve the morphology, amount and size of the M-A constituent, and improve the conformation of ferrite matrix.

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.

Investigation of CGHAZ Simulations of Low-Carbon Bainitic Steels

2021 ◽  
Vol 1016 ◽  
pp. 1869-1874
Author(s):  
Tun Tun Nyo ◽  
Antti Kaijalainen ◽  
Jaakko Hannula ◽  
Jukka I. Kömi
Keyword(s):  
Impact Toughness ◽  
Heat Affected Zone ◽  
Base Material ◽  
Strength Properties ◽  
Coarse Grained ◽  
Low Carbon ◽  
Bainitic Steels ◽  
Produce Steel ◽  
Welding Procedure ◽  
Nb Alloying

The effect of ten different combinations with various amounts of niobium (0-0.6 wt.%) and chromium (1-4 wt.%) on weldability and mechanical properties of thermomechanically rolled and direct-quenched low-carbon (0.035 wt.%) microalloyed bainitic steel were investigated. Two compositions were alloyed with boron to increase the hardenability, and two with titanium to improve the toughness properties in heat affected zone. The target of the study was to produce steel with 700 MPa yield strength combined with good impact toughness. Coarse grained heat affected zone (CGHAZ) simulations were performed using the Gleeble 3800 thermomechanical simulator to evaluate the weldability of the investigated steels using cooling time from 800 °C to 500 °C (t8/5) of 5 s and 15 s to simulate different heat inputs in actual welding procedure. Microstructures were characterized using light optical microscopy, and hardness profiles of simulated heat affected zones were determined as well as Charpy-V impact toughness at-40 °C and-60 °C. Shorter t8/5 time (5 s) produced generally better impact toughness properties compared to longer t8/5 -time (15 s). Steels with 4 % Cr had the highest impact energies. Generally, more softening occurred with longer t8/5-time (15 s). However, Cr and Nb alloying decreased the amount of softening in the CGHAZ region, especially with longer t8/5 -time. These results indicate that even with higher t8/5 -time, it is possible to achieve strength properties equivalent to the base material in the CGHAZ region by Cr and Nb alloying.

Carburizing

1999 ◽  
Author(s):  
Geoffrey Parrish
Keyword(s):  
Grain Size ◽  
Wear Resistance ◽  
Impact Toughness ◽  
Fracture Strength ◽  
Retained Austenite ◽  
Nonmetallic Inclusions ◽  
Print Version ◽  
The Core ◽  
Carburized Steel ◽  
Fatigue And Fracture

Carburizing: Microstructures and Properties explains how to recognize and address problems associated with case carburizing treatments for steels. It examines the nature of internal oxidation, decarburization, free carbides, and retained austenite and their effect on fatigue and fracture strength, wear resistance, impact toughness, hardness, and other properties. It discusses the influence of grain size, microcracking, microsegregation, and nonmetallic inclusions and explains how composition and cooling rate determine the core properties of carburized steel parts and how alloy and carbon content largely determine the depth and hardness of the case. It also discusses the effect of tempering, refrigeration, grinding, roller burnishing, and shot peening, and makes extensive use of images, graphs, charts, and examples throughout. For information on the print version, ISBN 978-0-87170-666-9, follow this link.

Mechanical Behaviour of Intercritically Reheated Coarse-Grained Heat Affected Zone in High Strength Line Pipe Steels

2018 ◽  
Author(s):  
Madhumanti Mandal ◽  
Warren J. Poole ◽  
Thomas Garcin ◽  
Matthias Militzer ◽  
Laurie Collins
Keyword(s):  
Impact Toughness ◽  
Heat Affected Zone ◽  
Welding Process ◽  
Charpy Impact ◽  
High Strength ◽  
Coarse Grained ◽  
Fracture Mechanisms ◽  
Line Pipe ◽  
Secondary Cracks ◽  
The Impact

Multipass welding of high strength steels used for fabrication and joining of transmission pipelines presents a number of metallurgical challenges. A key concern is both the strength and toughness of the heat affected zone (HAZ) adjacent to both seam and girth welds. In this work, a systematic study has been conducted on regions of the heat affected zone in the base metal where the first welding pass produces a thermal excursion which results in a coarse-grained heat affected zone (CGHAZ). The subsequent weld pass involves intercritical annealing of this region, i.e. a microstructure associated with intercritically reheated coarse grain heat affected zone (ICCGHAZ). The small ICCGHAZ region is often identified as being particularly susceptible to crack initiation. This work was undertaken to understand microstructure development in this zone and how the ICCGHAZ may affect the overall performance of the HAZ. Gleeble thermomechanical simulations have been conducted to produce bulk samples representative of different welding scenarios. Charpy impact tests and tensile tests have been performed over a range of temperatures. It was found that when a continuous necklace of martensite-austenite islands form on the prior austenite grain boundaries (i.e. for a M/A fraction of ≈10%), the Charpy impact toughness energy is dramatically decreased and the ductile brittle transition temperature is significantly raised. Detailed studies on the secondary cracks have been conducted to examine the fracture mechanisms in the different microstructures. The results show that the lower bainite microstructures obtained after the 1st thermal treatment, representative of CGHAZ have excellent impact properties. The impact toughness of the microstructures typical of ICCGHAZ is strongly dependent on the composition as well as morphology and spatial distribution of the resulting martensite-austenite (M/A) islands transformed from inter-critically formed austenite. This zone can play a significant role in fracture initiation and thus needs to be considered in alloy and welding process designs.

scholarly journals Comparison of Impact Toughness in Simulated Coarse-Grained Heat-Affected Zone of Al-Deoxidized and Ti-Deoxidized Offshore Steels

Metals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1783
Author(s):  
Henri Tervo ◽  
Antti Kaijalainen ◽  
Vahid Javaheri ◽  
Mohammed Ali ◽  
Tuomas Alatarvas ◽  
...  
Keyword(s):  
Impact Toughness ◽  
Heat Affected Zone ◽  
Electron Backscatter Diffraction ◽  
Cooling Time ◽  
Coarse Grained ◽  
X Ray Diffraction ◽  
X Ray ◽  
Electron Backscatter ◽  
Backscatter Diffraction ◽  
The Impact

The presence of acicular ferrite (AF) in the heat-affected zone (HAZ) of steels used offshore is generally seen as beneficial for toughness. In this study, the effects of varying fractions of AF (0–49 vol.%) were assessed in the simulated, unaltered and coarse-grained heat-affected zones (CGHAZ) of three experimental steels. Two steels were deoxidized, with one using Ti and the other using Al. The characterization was carried out by using electron microscopy, energy-dispersive X-ray spectrometry, electron backscatter diffraction and X-ray diffraction. The fraction of AF varied with the heat input and cooling time applied in the Gleeble thermomechanical simulator. AF was present in one of the Ti-deoxidized steels with all the applied cooling times, and its fraction increased with increasing cooling time. However, in other materials, only a small fraction (13–22%) of AF was present and only when the longest cooling time was applied. The impact toughness of the simulated specimens was evaluated using instrumented Charpy V-notch testing. Contrary to the assumption, the highest impact toughness was obtained in the conventional Al-deoxidized steel with little or no AF in the microstructure, while the variants with the highest fraction of AF had the lowest impact toughness. It was concluded that the coarser microstructural and inclusion features of the steels with AF and also the fraction of AF may not have been great enough to improve the CGHAZ toughness of the steels investigated.

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