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 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.

scholarly journals Continuous Cooling Transformation Diagram, Microstructures, and Properties of the Simulated Coarse-Grain Heat-Affected Zone in a Low-Carbon Bainite E550 Steel

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 939 ◽  
Author(s):  
Yun Zong ◽  
Chun-Ming Liu
Keyword(s):  
Impact Toughness ◽  
Cooling Rate ◽  
Vickers Hardness ◽  
Heat Affected Zone ◽  
Granular Bainite ◽  
Coarse Grain ◽  
Low Carbon ◽  
Transformation Diagram ◽  
Lath Bainite ◽  
Continuous Cooling Transformation Diagram

In order to provide important guidance for controlling and obtaining the optimal microstructures and mechanical properties of a welded joint, the continuous cooling transformation diagram of a new low-carbon Nb-microalloyed bainite E550 steel in a simulated coarse-grain heat-affected zone (CGHAZ) has been constructed by thermal dilatation method in this paper. The welding thermal simulation experiments were conducted on a Gleeble-3800 thermo-mechanical simulator. The corresponding microstructure was observed by a LEICA DM2700M. The Vickers hardness (HV) and the impact toughness at −40 °C were measured according to the ASTM E384 standard and the ASTM E2298 standard, respectively. The experimental results may indicate that the intermediate temperature phase transformation of the whole bainite can occur in a wide range of cooling rates of 2–20 °C/s. In the scope of cooling rates 2–20 °C/s, the microstructure of the heat-affected zone (HAZ) mainly consists of lath bainite and granular bainite. Moreover, the proportion of lath bainite increased and granular bainite decreased as the cooling rate increasing. There is a spot of lath martensite in the microstructure of HAZ when the cooling rate is above 20 °C/s. The Vickers hardness increases gradually with the increasing of the cooling rate, and the maximum hardness is 323 HV10. When the cooling time from 800 °C to 500 °C (t8/5) is 5–15 s, it presents excellent −40 °C impact toughness (273–286 J) of the CGHAZ beyond the base material (163 J).

EBSD Study of the Effect of Hot Deformation on Low Carbon Bainitic Structure

2020 ◽  
Vol 993 ◽  
pp. 513-519
Author(s):  
Xin Li Wen
Keyword(s):  
Grain Size ◽  
Thickness Reduction ◽  
Granular Bainite ◽  
Low Carbon ◽  
Remarkable Effect ◽  
Lath Bainite ◽  
Effective Grain Size ◽  
Bainitic Structure ◽  
Ebsd Technique ◽  
The Given

The effect of deformation temperature (DT) and thickness reduction on the bainitic structure was investigated under various test conditions by using hot compression on a Gleeble-1500 thermo-mechanical simulation machine, and electron back scattering diffraction (EBSD) technique. In the case of the bainitic structure consisting of granular bainite (GB), lath bainite (LB) and a little ferrite (AF) under the given deformation conditions, DT and thickness reduction have remarkable effect on the transformation kinetics, starting temperature (B) of bainite fast transformation, and the type of bainitic structure. With the decreasing of DT from 810 °C to 730 °C, the starting temperature of transformation B increase from 585 °C to 595 °C. When the thickness reduction was 0 % and 20 %, the microstructure consists of GB, LB and a little AF, whereas as the thickness reduction increase to 40 %, large grain size of LB and GB disappear, and only AF and M/A remained. With the thickness reduction increases from 0 % to 40 %, the effective grain size decreases from 4 μm to 2 μm, and the fraction of HGB increases from 48 % to 57 %.

Microstructure and Property Research of T91 and T23 Heat-Resisting Steel Welding Joint

2011 ◽  
Vol 328-330 ◽  
pp. 1471-1474
Author(s):  
Guang Feng Wu ◽  
Xiao Bin Zhang ◽  
Hui Bin Xu
Keyword(s):  
Fusion Zone ◽  
Base Metal ◽  
Lath Martensite ◽  
Granular Bainite ◽  
Experimental Result ◽  
Micro Structure ◽  
Corrosion Properties ◽  
Chemical Corrosion ◽  
Welding Joint ◽  
Lath Bainite

Microstructure in the welding zone, mechanical and electro-chemical corrosion properties of high matching T91/T23 heterology heat-resisting steel welding joint were investigated. Experimental result shows that good welding joint was made by high matching and argon tungsten arc process. Micro-structure of the weld metal was tempering lath martensite with coarsing crystal grain. Microstructure in the HAZ of T23 steel side was mainly granular bainite and lath bainite; micro-structure of HAZ at T91 steel side was mainly tempered sorbite and tempered martensite. Hardness nearbynearby the fusion zone of T91 steel was the highese, and weak carbon migration were found nearby the fusion zone of T23 steel side weld junction. Corrosion resistance properties by turns of from large to small were: welded joint, T91 base metal , T23 base metal.

scholarly journals The Effect of Nickel Contents on the Microstructure Evolution and Toughness of 800 MPa Grade Low Carbon Bainite Deposited Metal

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 709
Author(s):  
Jingwu Liu ◽  
Jian Sun ◽  
Shitong Wei ◽  
Shanping Lu
Keyword(s):  
Microstructure Evolution ◽  
Gas Metal Arc Welding ◽  
Lath Martensite ◽  
Control Unit ◽  
Low Carbon ◽  
Ni Content ◽  
Metal Arc Welding ◽  
Deposited Metal ◽  
Lath Bainite ◽  
Low Carbon Bainite

In this work, three deposited metals with different nickel (Ni) contents were produced by active gas metal arc welding (GMAW) in order to explore the influence of Ni on the microstructure evolution and toughness of 800 MPa grade low carbon bainite deposited metal. The results showed that microstructure of the deposited metals mainly consisted of lath bainite, lath martensite, coalesced bainite (CB), and retained austenite (RA), and that the toughness was closely related to two factors: CB and RA. RA in deposited metal could improve the toughness, while the CB would deteriorate the toughness of deposited metal. As the Ni content increased, a large amount of CB was generated in the deposited metals. The RA content increased from 1.5% to 5.7% with the content of Ni increasing from 5.5% to 6.5%. However, the RA content did not increase when the Ni content increased from 6.5% to 7.5%. Additionally, the smallest control unit of toughness in 800 MPa grade low carbon bainite deposited metals is the Bain Packet (BP) from the perspective of crystallography characteristics. This work provided a reference for the chemical composition design of 800 MPa grade steel welding consumables and showed that the toughness of the deposited metal could be improved effectively by increasing the RA content while suppressing the formation of CB.

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.

Development of Low Carbon Bainitic Cr-B Steel with High Strength and Good Toughness

2010 ◽  
Vol 146-147 ◽  
pp. 937-940
Author(s):  
Xiang Dong Huo ◽  
Zhang Guo Lin ◽  
Yu Tao Zhao ◽  
Yu Qian Li
Keyword(s):  
High Strength ◽  
Polygonal Ferrite ◽  
Steel Plates ◽  
Granular Bainite ◽  
High Yield ◽  
Low Carbon ◽  
Experimental Steel ◽  
Large Size ◽  
Final Microstructure ◽  
Lath Bainite

In order to develop low carbon bainitic Cr-B steel, experimental procedures including melting, thermal simulation study and laboratory hot rolling were adopted. The dynamic CCT diagram was established, microstructure and properties of experimental steel were also analyzed. The transformation temperature of experimental steel lies between 650～400°C and final microstructure changes fromquasi-polygonal ferrite, granular bainite to lath bainite as cooling rate increases from 0.2 to 50°C.s-1. The microstructure of steel plates, air cooled or water cooled to 530°C then air cooled, is mainly composed of granular bainite and quasi-polygonal ferrite, and the large size islands in granular bainite are responsible for the low strength and poor toughness. However, steel plate with lath bainite, water cooled to roomtemperature, boasts high yield strength (672MPa) and superior impact toughness (127J at -20°C). Therefore, it is feasible to produce low carbon bainitic Cr-B steel with high strength and good toughness through controlling cooling parameters.

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.

Effects of Final Cooling Temperature on Microstructure Transformation and Properties of Q550 Low Carbon Bainite Steel

2020 ◽  
Vol 993 ◽  
pp. 550-558
Author(s):  
Zeng Qiang Man ◽  
Wei Yu ◽  
Huan Yang ◽  
Wen Gao Chang ◽  
Yun Fei Cao
Keyword(s):  
Great Influence ◽  
Granular Bainite ◽  
Low Carbon ◽  
Continuous Cooling Transformation ◽  
Cooling Temperature ◽  
Continuous Cooling ◽  
Bainite Steel ◽  
Lath Bainite ◽  
Transformation Curve ◽  
Low Carbon Bainite

The mechanical properties of low carbon bainite steel are closely related to the microstructure and proportion after phase transformation. The microstructure of the deformed austenite of low carbon bainite steel after isothermal transformation and continuous cooling transformation was studied by thermal simulation test. The metallographic structure was observed by optical microscopy (OM) and scanning electron microscopy (SEM). The metallographic and microhardness were used to judge the microstructure type, and the CCT (continuous cooling transformation) curve and TTT (time-temperature-transformation) curve of the test steel were drawn. It was found that at 700-430 °C isothermal, undergo a variety of medium-temperature microstructure transformations appeared for the test steels, such as ferrite, pearlite, granular bainite and lath bainite. The cooling rate and final cooling temperature have great influence on the type and performance of the final microstructure. The final cooling temperature was controlled at about 515°C. The mixed microstructures of granular bainite (GB) and fine martensite-austenite (M-A) island, a small amount of acicular ferrite and lath bainite were obtained. The yield and tensile strengths of this type of microstructure reached 639 MPa and 750 MPa respectively, the shrinkage rate reached 17%, and the better low-temperature impact performance was realized.

scholarly journals Effect of Welding Heat Input on Microstructure and Impact Toughness in the Simulated CGHAZ of Low Carbon Mo-V-Ti-N-B Steel

Metals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1997
Author(s):  
Mingliang Qiao ◽  
Huibing Fan ◽  
Genhao Shi ◽  
Leping Wang ◽  
Qiuming Wang ◽  
...  
Keyword(s):  
Impact Toughness ◽  
Heat Input ◽  
Acicular Ferrite ◽  
Granular Bainite ◽  
Equivalent Diameter ◽  
Low Carbon ◽  
Welding Heat Input ◽  
Lath Bainite ◽  
Gleeble 3500 ◽  
The Impact

Welding thermal cycles with heat inputs ranging from 25 to 75 kJ/cm were performed on a Gleeble 3500. The impact energy improved significantly (from 10 to 112 J), whereas the simulated coarse-grain heat-affected zone (CGHAZ) microstructure changed from lath bainite ferrite (LBF) and granular bainite ferrite (GBF) + martensite/austenite (M/A) to acicular ferrite (AF) + polygonal ferrite (PF) + M/A as the heat input increased. Simultaneously, the mean coarse precipitate sizes and the degree of V(C,N) enrichment on the precipitate surface increased, which provided favorable conditions for intragranular ferrite nucleation. The Ar3 of CGHAZ increased from 593 °C to 793 °C with increasing heat inputs; the longer high-temperature residence time inhibited the bainite transformation and promoted the ferrite transformation. As a result, acicular ferrite increased and bainite decreased in the CGHAZ. The CGHAZ microstructure was refined for the acicular ferrite segmentation of the prior austenite, and the microstructure mean equivalent diameter (MED) in the CGHAZ decreased from 7.6 µm to 4.2 µm; the densities of grain boundaries higher than 15° increased from 20.3% to 45.5% and significantly increased the impact toughness. The correlation of heat input, microstructure, and impact toughness was investigated in detail. These results may provide new ideas for the development of high welding heat input multiphase steels.

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