Effect of Weld Thermal Cycles on Microstructure and Properties of Simulated Heat Affected Zone in Thick-Wall X80 Pipe Steels

2016 ◽  
Author(s):  
J. A. Gianetto ◽  
F. Fazeli ◽  
B. Shalchi-Amirkhiz ◽  
J. Li
Keyword(s):  
Electron Microscopy ◽  
Lath Martensite ◽  
Energy Transition ◽  
Cooling Time ◽  
Granular Bainite ◽  
Thick Wall ◽  
Low Carbon ◽  
Pipe Steels ◽  
High Angle ◽  
Electron Backscattered Diffraction

Continuous cooling transformation behaviour of the single cycled grain coarsened heat affected zones (GCHAZs) produced with a peak temperature (Tp) = 1350°C and cooling times, Δt800-500 = ∼ 1 to 100 s was evaluated for three different X80 pipe steels having various content of C, Mn, Ni, Cr, Mo and microalloying elements that include Nb, V and Ti. Optical microscopy was initially used to characterize the simulated GCHAZ, which consisted of a range of coarse prior austenite grains that transformed to different fractions of mainly low carbon lath martensite/fine bainite, mixtures of upper bainite and/or granular bainite as a function of increasing cooling time. A consistent trend of decreasing microhardness with increasing cooling time occurred for the range of GCHAZs formed in the pipe steels. The significant differences in GCHAZ microhardness for Δt800-500 < 15 s is attributable to the respective pipe steel compositions and the resulting microstructures. The GCHAZ microstructures were further characterized by means of scanning electron microscopy with electron backscattered diffraction and transmission electron microscopy with focus to analyze features of the transformation products, fraction of high angle boundaries and the nature of microconstituents, including carbonitride precipitates and inclusions. The simulated GCHAZ Charpy-V-notch impact energy transition curves revealed a consistent upward shift towards higher temperatures with increasing cooling time (Δt800-500 = 6, 15 and 30 s). The primary factors contributing to the variations in impact toughness of the respective GCHAZs were the differences in the microstructure, hardness and detailed features, including fraction of high angle boundaries (packet size), and the presence of various M-A microconstituents.

Microstructure and Toughness of Simulated Grain Coarsened Heat Affected Zones in X80 Pipe Steels

2014 ◽  
Author(s):  
J. A. Gianetto ◽  
F. Fazeli ◽  
Y. Chen ◽  
B. Shalchi-Amirkhiz ◽  
T. Smith
Keyword(s):  
Lath Martensite ◽  
Energy Transition ◽  
Granular Bainite ◽  
Low Carbon ◽  
Pipe Steels ◽  
Thermal Cycles ◽  
Simulation Techniques ◽  
Intermediate Cooling ◽  
Girth Welds ◽  
Cct Diagrams

The objective of this research was to gain a better understanding of the influence of essential welding variables on microstructure and properties of the grain-coarsened heat-affected zone (GCHAZ) regions formed in pipeline girth welds. In this study, thermal simulation techniques were used to provide a detailed evaluation of the GCHAZ microstructure evolution and intrinsic toughness for two different pipe steels subjected to known welding thermal cycles. The continuous cooling transformation (CCT) diagrams for the GCHAZ were determined by means of dilatometric techniques with a peak temperature (Tp) = 1350°C and a range of cooling times (Δt800–500 = ∼1 to 100 s). The transformation start and finish temperatures were used to create GCHAZ CCT diagrams for two X80 pipe steels. To further assist with the interpretation of CCT results both light optical microscopy (LOM) and microhardness surveys were used. The results revealed that transformation to predominantly low carbon lath martensite or fine bainite occurred for short cooling times, while bainite formed at intermediate cooling times and upper or granular bainite was obtained for longer cooling times. Some of the detailed features of these simulated GCHAZ microstructures were characterized by scanning electron and transmission electron microscopy (SEM and TEM) in order to better quantify the phases in selected samples. This analysis clearly indicates that despite similar carbon equivalents (CEs), the response of each steel to given GCHAZ thermal was quite different. The GCHAZ Charpy-V-notch (CVN) impact energy transition curves for the series of single thermal cycles with cooling times, Δt800–500 = 6, 15 and 30 s and were compared against those obtained for the respective pipe steels. The results showed that there were upward shifts in transition temperature for the simulated GCHAZs relative to the respective pipe steels. This overall reduction of notch toughness was attributed to variations in microstructural features for the respective GCHAZs.

scholarly journals Morphological and Crystallographic Characteristics of α Structure in a Low-Carbon Iron–Nickel Alloy

Crystals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 468 ◽  
Author(s):  
Gaojun Mao ◽  
Cyril Cayron ◽  
Xiuli Mao ◽  
Rui Cao ◽  
Roland Logé ◽  
...  
Keyword(s):  
Lath Martensite ◽  
Granular Bainite ◽  
Body Centered Cubic ◽  
Low Carbon ◽  
Electron Backscattered Diffraction ◽  
Dislocation Densities ◽  
Lath Bainite ◽  
Crystallographic Characteristics ◽  
Iron Nickel ◽  
Relationship Of

The features of α (body-centered cubic) structures were investigated in a low-carbon multicomponent alloy from morphological and crystallographic perspectives. In addition to apparent features of granular bainite and lamellar martensite, a morphological similarity can be found between lath martensite and lath bainite. Therefore, it is of interest to explore possible discrepancies between lath martensite and lath bainite from a crystallographic perspective. These microstructures were obtained by various cooling rates (i.e., water quenching, 5 °C/s, and 0.05 °C/s) and then were characterized by a combination of scanning electron microscopy and electron backscattered diffraction techniques. It is shown that: (1) Lath martensite (LM) formed in the samples that were water-quenched, and a mixture of LM and lath bainite (LB) and granular bainite (GB) formed in the samples cooled at rates of 5 °C/s and 0.05 °C/s, respectively; (2) A Kurdjumov-Sachs relationship was mostly found in as-quenched martensite, while a Greninger-Troiano relationship represented the orientation relationship of LB and GB; (3) As the cooling rate decreased, the dislocation densities in corresponding microstructures were reduced, while the tendency of variant grouping was enhanced.

Effect of Aging Temperature on the Microstructure and Mechanical Properties of 1000MPa Grade Low Carbon Bainitic Steel

2012 ◽  
Vol 152-154 ◽  
pp. 376-380 ◽  
Author(s):  
Long Fei Zuo ◽  
Zhan Lei Wei ◽  
Ri Ni ◽  
Ben Ma ◽  
Zi Dong Wang
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Yield Strength ◽  
Aging Temperature ◽  
Granular Bainite ◽  
Bainitic Steel ◽  
Low Carbon ◽  
Microstructure And Mechanical Properties ◽  
Effect On Yield ◽  
Hot Rolled

A kind of 1000MPa low carbon bainitic steel belonged to the Fe-Cu-Nb series was hot rolled and aged, the influence of aging temperatures on the microstructure and mechanical properties of the steel were investigated by using Scanning electron microscopy (SEM) and transmission electron microscopy(TEM). The results show that the microstructure of the low carbon bainitic steel consisted of lath-shaped bainite(LB), granular bainite(GB) and quasi-polygonal ferrite(QF), and the proportion of each kind of microstructure changed with the aging temperatures. The strength of steel with the increase of aging temperature first increased, then decreased, Aging temperatures had distinct effect on yield strength of the tested steel, and less effect on the ultimate tensile strength, we can get the best comprehensive properties yield strength 1011.87 MPa and elongation rate 16.38% of good tough match aged at 450°C. Through analysis it is concluded that the strength of the tested steels aged at 450°C reaches the maximum value, which is attributed to the precipitation of a large amount of fine ε-Cu particles(5~10nm) and a small number of(Nb,Ti)(C,N) precipitates.

Effect of Heat Treatment Process on Microstructure and Properties in Low Carbon Si-Mn Q&P Steel

2011 ◽  
Vol 233-235 ◽  
pp. 1009-1013
Author(s):  
Cai Zhao ◽  
Di Tang
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Heat Treatment ◽  
Retained Austenite ◽  
Treatment Process ◽  
Lath Martensite ◽  
Heat Treatment Process ◽  
Low Carbon ◽  
Transmission Electron ◽  
Partitioning Time

The mechanical properties of Low Carbon Si-Mn Q&P steel are strongly affected by the conditions of heat treatment. Microstructures and mechanical properties of Low Carbon Si-Mn Q&P steel at different partitioning temperature and holding time was investigated. The microstructure was analysed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is shown that the microstructure of Q&P steel is carbon-depleted lath martensite and carbon enriched retained austenite. The retained austenite appear film-type between the laths. Higher partitioning temperature and longer partitioning time can obtain more retained austenite. It is shown that with increasing partitioning time ultimate tensile strength decreases, while elongation increases obviously. Carbon-enriched metastable retained austenite is considered beneficial because the TRIP phenomenon during deformation can contribute to formability and energy absorption.

CHARACTERIZATION OF BAINITIC MICROSTRUCUTRES IN LOW CARBON HSLA STEELS

2008 ◽  
Vol 22 (31n32) ◽  
pp. 5965-5970 ◽  
Author(s):  
JU SEOK KANG ◽  
CHAN GYUNG PARK
Keyword(s):  
Acicular Ferrite ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Bainitic Ferrite ◽  
Carbon Steels ◽  
Granular Bainite ◽  
Low Carbon ◽  
High Angle ◽  
Rate Condition ◽  
Hsla Steels

The austenite phase of low carbon steels can be transformed to various bainitic microstructures such as granular bainite, acicular ferrite and bainitic ferrite during continuous cooling process. In the present study site-specific transmission electron microscope (TEM) specimens were prepared by using focused ion beam (FIB) to identify the bainitic microstructure in low carbon high strength low alloy (HSLA) steels clearly. Granular bainite was composed of fine subgrains and 2nd phase constituents like M/A or pearlite located at grain and/or subgrain boundaries. Acicular ferrite was identified as an aggregate of randomly orientated needle-shaped grains. The high angle relations among acicular ferrite grains were thought to be caused by intra-granular nucleation, which could be occur under the high cooling rate condition. Bainitic ferrite revealed uniform and parallel lath structure within the packet. In some case, however, the parallel lathes showed high angle relations due to packet overlapping during grow of bainitic ferrite, resulting in high toughness properties in bainitic ferrite based steels.

Microstructural Evolution during Warm Compression of Medium Carbon Steel Quenched

2008 ◽  
Vol 47-50 ◽  
pp. 853-856 ◽  
Author(s):  
Xin Zhao
Keyword(s):  
Electron Microscopy ◽  
Carbon Steel ◽  
Microstructural Evolution ◽  
Lath Martensite ◽  
Optical Microscope ◽  
Medium Carbon Steel ◽  
High Angle ◽  
Medium Carbon ◽  
Transmission Electron ◽  
Gleeble 3500

In order to produce nano-structured carbon steel, a 0.45%C steel was quenched and warm-compressed on a Gleeble 3500 Machine. The microstructural evolution during the process was studied by using an optical microscope and a transmission electron microscopy. The starting microstructure was lath martensite with a small amount of flake martensite. A lot of high-angle boundaries between martensite laths were induced after 50% reduction compression at 350°C. The microstructure of the specimen compressed at 600-650°C was nano-carbides + equiaxed ultrafine ferrite grains. The mechanism for grain refinement is incomplete dynamic recrystallization.

scholarly journals Effect of Hot Working Processes on Microstructure and Mechanical Properties of Pipeline Steel

Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 860
Author(s):  
Huiling Ji ◽  
Yiwei Zhang ◽  
Wenzhao Lu ◽  
Bang Wei ◽  
Xiaomin Yuan
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Cooling Rate ◽  
Acicular Ferrite ◽  
Pipeline Steel ◽  
Granular Bainite ◽  
Isothermal Quenching ◽  
Electron Backscattered Diffraction ◽  
Quenching Temperature ◽  
Treatment Conditions

The microstructure and microhardness of X70 pipeline steel were investigated after conducting different processing routes. The microstructure was characterized using optical and electron microscopy. Scanning electron microscopy equipped with electron backscattered diffraction (EBSD) and transmission electron microscopy techniques were applied for investigation of different thermal processing treatment conditions. Mechanical properties were characterized by a microhardness tester. The results show that the microstructure mainly consists of granular bainite, acicular ferrite and a small amount of M/A constituents under hot rolling states. There are many dislocations inside the acicular ferrite. The thermal simulation experiments show that the microstructure becomes homogeneous with the increase in cooling rate. The acicular ferrite morphology becomes fine and uniform, and the content of M/A constituents increases at the same compression amount. The compression gives rise to the accumulated strain and stored energy, which accelerate the transformation of acicular ferrite and refine the microstructure of the pipeline steel. The microhardness rises with the increase in deformation ratio and cooling rate. The microstructure of the pipeline steel subjected to the isothermal quenching process is ultrafine ferrite and M/A islands. When the isothermal quenching temperature reaches 550 °C, a small amount of upper bainite appears in the microstructure. With the increase in isothermal quenching temperature, the microhardness decreases. Acicular ferrite is a better candidate microstructure than ultrafine ferrite for the pipeline steels.

A Study on the Microstructure of Ultra Low Carbon Bainitic Steels by RPC Technique

2007 ◽  
Vol 561-565 ◽  
pp. 2107-2110 ◽  
Author(s):  
Zhi Fen Wang ◽  
Shao Kang Pu ◽  
Y. Guan ◽  
Ping He Li ◽  
Li Xin Wu ◽  
...  
Keyword(s):  
Grain Size ◽  
Bainitic Ferrite ◽  
Granular Bainite ◽  
Low Carbon ◽  
Electron Backscattered Diffraction ◽  
Bainitic Steels ◽  
Transmission Electron ◽  
Effective Grain Size ◽  
Ebsd Technique ◽  
Rolled Condition

The effect of tempering process on the microstructure of ultra low carbon bainitic (ULCB) steel produced by relaxation precipitation controlled phase transformation (RPC) has been investigated by transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). The results showed that the final microstructure mainly contained lath-like bainitic ferrite, granular bainite and martensite-austenite (MA) constituent in ULCB steels. On tempering at 650°C a slight increase was detected in the effective grain size as the strain-induced precipitates pinned up the dislocation walls and subgrains. After tempering at 700°C, bainitic ferrite laths started to coarsen and polygonal ferrite occurred. The effective grain size of ULCB steels in as-rolled condition was 1.5 μm at the tolerance of 10o~15o measured by EBSD technique.

Effect of Final Cooling Temperature on Mechanical Properties of a Water Cooled Mn-Series Low Carbon Bainitic Steel as 8Mn2SiNb

2011 ◽  
Vol 396-398 ◽  
pp. 468-471
Author(s):  
Chun Feng ◽  
Zhi Yong Pan ◽  
Guang Shan Li ◽  
Bing Zhe Bai
Keyword(s):  
Mechanical Properties ◽  
Volume Fraction ◽  
Lath Martensite ◽  
Granular Bainite ◽  
Air Cooling ◽  
Water Cooling ◽  
Bainitic Steel ◽  
Low Carbon ◽  
Cooling Temperature ◽  
Allotriomorphic Ferrite

The effect of final cooling temperature on the mechanical properties of a water cooled Mn-series low carbon bainitic steel as 8Mn2SiNb has been investigated in this paper. The results indicate that the optimum final cooling temperature is 450 °C, followed by air cooling to room temperature. Compared with air cooling, the condition of water cooling to 450 °C increases the tensile strength and yield strength about 13.3% (From 805MPa to 929MPa) and 59.0%(From 464MPa to 741MPa) respectively, remaining 21.5% elongation and 151J toughness. SEM observation reveals that the microstructure of the steel after water cooling to 450 °C is mainly granular bainite +lath martensite +refined grain boundary allotriomorphic ferrite (FGBA). Compared with air cooling, the condition of water cooling to 450 °C increases the volume fraction of strengthening phase (M-A island) from 28.2% to 38.1%.

Experimental Study on the Effect of CGHAZ Microstructure on CTOD of High-Strength Steel EQ56

2011 ◽  
Vol 117-119 ◽  
pp. 1874-1879
Author(s):  
Zi Yu Xia ◽  
Zhang Mu Miao ◽  
Tao Ma ◽  
Gang Chen ◽  
Sheng Peng
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
High Strength Steel ◽  
Lath Martensite ◽  
Microstructural Analysis ◽  
High Strength ◽  
Low Carbon ◽  
Welding Joints ◽  
The Relationship ◽  
Scanning Electron

The CGHAZ Microstructure has great effect on the toughness of welding joints and CTOD. This paper discussed the relationship between the CGHAZ and CTOD .The samples, carried out on high-strength steel EQ56, were observed by scanning electron microscopy. The Microstructural analysis result shows CGHAZ microstructure of EQ56-5, presenting high CTOD with 0.272mm, is low-carbon lath martensite and little M-A constituent, which contribute to the better toughness of EQ56-5. CGHAZ microstructure of EQ56-4, presenting the low CTOD with 0.082 mm, contains M-A constituent. The M-A constituent makes the CGHAZ brittle. The crack would grow easily along the M-A grain boundaries.

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