Effect of Heat Imput on Microstructure and Toughness of High Strength Bridge Steel

2011 ◽  
Vol 194-196 ◽  
pp. 255-258
Author(s):  
Kun Ning Jia
Keyword(s):  
Grain Size ◽  
Crack Propagation ◽  
Heat Affected Zone ◽  
High Strength ◽  
Thermal Simulation ◽  
Granular Bainite ◽  
Coarse Grain ◽  
Bridge Steel ◽  
Lath Bainite

The coarse grain heat affected zone(CGHAZ) at different parameters t8/5 of high-strength bridge steel Q460q were simulated with thermal simulation machine. the microstructure of CGHAZ and the effect of granular bainite on the toughness were analyzed in this paper.The results show that: When t8/5<60s, lath bainite and granular bainite intertwine, and the quantity of strip M-A constituents in granular bainite decreased, so toughness is higher.When t8/5>60s, the quantity of eutectoid ferrite and granular bainite increased, coarse M-A constituent resulting in the grain size of effective crack propagation becoming coarser and toughness decreased significantly.

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).

Microstructure and mechanical properties of high strength TMCP steel hybrid disk laser-MAG welded joint

2019 ◽  
Vol 34 (01n03) ◽  
pp. 2040063
Author(s):  
Zheng Lei ◽  
Zongtao Zhu ◽  
Xiaoyi Yang ◽  
Yishuai Jiang ◽  
Hui Chen
Keyword(s):  
Fusion Zone ◽  
Heat Affected Zone ◽  
Acicular Ferrite ◽  
Welded Joint ◽  
Base Material ◽  
High Strength ◽  
Energy Criterion ◽  
Granular Bainite ◽  
Hybrid Laser Arc Welding ◽  
Lath Bainite

Hybrid laser-arc welding (HLAW) was carried out on high strength thermo-mechanical controlled process (TMCP) steel of 14 mm thickness using single-pass welding (SPW) and multi-pass welding (MPW) processes. Well-formed weld joints with good performance were successfully obtained. The results showed that the microstructure of weld was pre-eutectoid ferrite, acicular ferrite and some granular bainite. There were mainly lath bainite, granular bainite and acicular ferrite in the heat-affected zone. The grain sizes of SPW were thicker than MPW, and the bainite content of MPW was higher than SPW. The average hardness value of the fusion zone was lower than that of the Heat affected zone, but higher than that of the base material. The weld was divided into upper arc domain zone (ADZ) and lower laser domain zone (LDZ). The ADZ was harder than the LDZ. The average absorbed energy of SPW and MPW in the fusion zone at −40[Formula: see text]C was 125.5 and 92 J/cm2, respectively. The influences of microstructure on impact toughness were summarized by analyzing the hardness distribution and microstructure of the welded joint. The brittle transition temperatures of the two processes obtained by the energy criterion and the morphology criterion were close to each other.

scholarly journals Effect of Welding Peak Temperature on Microstructure and Impact Toughness of Heat-Affected Zone of Q690 High Strength Bridge Steel

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2981
Author(s):  
Yue Zhang ◽  
Jun Xiao ◽  
Wei Liu ◽  
Aimin Zhao
Keyword(s):  
Impact Toughness ◽  
Heat Affected Zone ◽  
Lath Martensite ◽  
Testing Machine ◽  
High Strength ◽  
Peak Temperature ◽  
Granular Bainite ◽  
Fine Grain ◽  
Bridge Steel ◽  
The Impact

The effect of peak temperature (TP) on the microstructure and impact toughness of the welding heat-affected zone (HAZ) of Q690 high-strength bridge steel was studied using a Gleeble-3500 thermal simulation testing machine. The results show that the microstructure of the inter critical heat-affected zone (ICHAZ) was ferrite and bainite. The microstructure of fine grain heat-affected zone (FGHAZ) and coarse grain heat-affected zone (CGHAZ) was lath bainite (LB) LB, lath martensite (LM), and granular bainite (GB), but the microstructure of FGHAZ was finer. With the increase in peak temperature, the content of LB and GB decreased, the content of LM increased, and the lath bundles of LM and LB gradually became coarser. With the increase in peak temperature, the grain size of the original austenite increased significantly, and the impact toughness decreased significantly. When the peak temperature was 800 °C, the toughness was the best. For CGHAZ, the peak temperature should be less than 1200 °C to avoid excessive growth of grain and reduction of mechanical property.

Microstructure and Mechanical Properties of X80/X100 High Deformability Pipeline Steel

2011 ◽  
Vol 399-401 ◽  
pp. 139-143
Author(s):  
Dian Xiu Xia ◽  
De Liang Meng ◽  
Shou Yong An ◽  
Yong Lin Kang
Keyword(s):  
Pipeline Steel ◽  
Large Strain ◽  
High Strength ◽  
Longitudinal Direction ◽  
Granular Bainite ◽  
Dual Phase ◽  
Cooling Process ◽  
Bainite Structure ◽  
Lath Bainite ◽  
High Deformability

In the present study, X80 and X100 grade high deformability pipeline steels have been processed by using TMCP and followed two-stage cooling process. The microstructures of the X80HD (HD, high deformability) and X100HD steels were both characterized by ferrite-bainite dual phase. The grains sizes of ferrite were mostly less than 5μm and the volume fractions were about 20~25% in X80HD and 10~15% in X100HD steel. The bainite structure in X80HD steel was granular bainite (GB); while in X100HD steel large amounts of lath bainite (LB) were also formed besides GB, and bainite grains were much finer. Ferrite-bainite dual phase microstructure has large strain hardenability that resulting high strength and high deformability combination. Both the steels exhibit high strength/toughness in transverse direction and high deformability in longitudinal direction. The X100HD steel with more volume of LB and less volume of PF has higher strength but lower deformability than that of X80HD steel.

scholarly journals Morphology and Crystallography Analyses of HSLA Steels with Hardenability Enhanced by Tailored C–Ni Collocation

Metals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 32
Author(s):  
Zhipeng Liu ◽  
Yishuang Yu ◽  
Jie Yang ◽  
Zhiquan Wang ◽  
Hui Guo ◽  
...  
Keyword(s):  
Driving Force ◽  
Nickel Content ◽  
High Strength ◽  
Transformation Strain ◽  
Steel Plates ◽  
Granular Bainite ◽  
Variant Selection ◽  
High Hardenability ◽  
Hsla Steels ◽  
Lath Bainite

High hardenability is of great importance to ultra-heavy steel plates and can be achieved by tailoring the composition of steel. In this study, the continuous cooling transformation (CCT) curves of two high-strength low-alloy (HSLA) steels (0.16C-0.92Ni steel and 0.12C-1.86Ni steel) were elucidated to reveal the significance of C–Ni collocation on hardenability from the perspective of morphology and crystallography. At a low cooling rate (0.5 °C/s), the 0.12C-1.86Ni steel showed higher microhardness than 0.16C-0.92Ni steel. The microstructure in 0.16C-0.92Ni steel was mainly granular bainite with block-shaped martensite/austenite islands (M/A islands), while that in 0.12C-1.86Ni steel was typically lath bainite with film-shaped M/A islands, denoting that the 0.12C-1.86Ni steel is of higher hardenability. Moreover, the 0.12C-1.86Ni steel exhibited a higher density of block boundaries, especially V1/V2 boundaries. The higher density of block boundaries resulted from the weakened variant selection due to the larger transformation driving force and more self-accommodation of transformation strain induced by the reduced carbon and increased nickel content.

scholarly journals Numerical and Experimental Investigation of the Heat Input Effect on the Mechanical Properties and Microstructure of Dissimilar Weld Joints of 690-MPa QT and TMCP Steel

Metals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 355 ◽  
Author(s):  
Francois Njock Bayock ◽  
Paul Kah ◽  
Pavel Layus ◽  
Victor Karkhin
Keyword(s):  
Heat Affected Zone ◽  
Heat Input ◽  
Lath Martensite ◽  
High Strength ◽  
Primary Recrystallization ◽  
Coarse Grain ◽  
Dissimilar Weld ◽  
Thermal Fields ◽  
Relative Value ◽  
Experimental Comparisons

The study evaluates numerically and experimentally the effect of welding heat input parameters on the microstructure and hardness of the heat-affected zone (HAZ) of quenched and tempered (QT) and thermo-mechanically controlled process (TMCP) 690-MPa high-strength steel. Numerical analyses and experimental comparisons were applied using three heat input values (10, 14, and 17 kJ/cm) in order to predict the thermal fields during welding. Experimental analysis was carried out of the microstructure and microhardness behavior in different HAZ areas. The numerical values indicate that the maximum respective values of temperature measured in QT steel and TMCP steel were about 1300 and 1200 °C for a heat input of 10 kJ/cm, 1400 and 1300 °C for a heat input of 14 kJ/cm, and 1600 and 1450 °C for a heat input of 17 kJ/cm. The cooling times resulted, for a heat input of 10 kJ/cm, in numerical t8/5 (14.5 s) and experimental (18.84 s) increases in hardness in the coarse-grain heat-affected zone (CGHAZ) of the QT steel (317 HV0.1), due to the formation of bainite and lath martensite structures with grain growth. Decreased hardness in the CGHAZ of TMCP steel (240 HV0.1) was caused by primary recrystallization of the microstructure and the formation of more equilibrium products of austenite decomposition. Increasing the heat input (14 to 17 kJ/cm) led to numerical t8/5 (29 s) and experimental (36 s) decreases in hardness in the CGHAZ of QT steel (270 HV0.1) due to the full austenite (thermal weld cycle), and maintained the relative value of TMCP steel (235 HV0.1).

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 %.

scholarly journals Impact Toughness of Gas Metal Arc Welded HY-80 Steel Plate at Sub-zero Temperatures

2019 ◽  
Vol 269 ◽  
pp. 06003
Author(s):  
Herry Oktadinata ◽  
Winarto Winarto
Keyword(s):  
Impact Toughness ◽  
Weld Joint ◽  
Heat Affected Zone ◽  
High Strength Steel ◽  
Steel Plate ◽  
Gas Metal Arc Welding ◽  
High Strength ◽  
Coarse Grain ◽  
Fracture Appearance ◽  
The Impact

Various welding methods are widely applied in large fabrication of high strength steel. However, commonly the problem occurs where a coarse grain is formed near fusion zone causing reduce the impact toughness due to the weld joint become brittle. Ductility and toughness in a coarse grain heat affected zone (CGHAZ) is low due to the formation of coarsening grain size. The objective of this research is to investigate the microstructure evolution, impact toughness and fracture appearance at sub-zero temperatures of the high strength steel arc welded. The steel that used in this experiment is a HY-80 steel welded by gas metal arc welding (GMAW) with a mixture of argon and carbon dioxide (90%Ar and 10%CO2) and ER100S solid wire. Microstructure observation and Charpy V-notch (CVN) tests were performed on the weld joint which consist of base metal (BM), heat affected zone (HAZ), and weld metal (WM). The CVN tests on the HY-80 steel plate at various temperatures (20, -20, -60 and -80 °C) show impact toughness decrease when the test temperature decrease. The CVN tests on the HY-80 weld joint at a temperature of 80 °C show the lowest impact toughness was measured at WM (61 J) and followed fusion line-FL (101 J) with brittle fracture appearance.

scholarly journals Effect of the Interpass Temperature on Simulated Heat-Affected Zone of Gas Metal Arc Welded API 5L X70 Pipe Joint

2021 ◽  
Author(s):  
Paulo Henrique Grossi Dornelas ◽  
João da Cruz Payão Filho ◽  
Victor Hugo Pereira Moraes e Oliveira ◽  
Diogo de Oliveira Moraes ◽  
Petrônio Zumpano Júnior
Keyword(s):  
Heat Affected Zone ◽  
Welded Joints ◽  
Oil And Gas ◽  
Thermodynamic Simulation ◽  
Gas Metal Arc Welding ◽  
High Strength ◽  
Simulation Software ◽  
Coarse Grain ◽  
Metal Arc Welding ◽  
Pipe Joint

Abstract Welding costs associated with the laying of pipes for deepwater oil and gas extraction can be reduced using high interpass temperatures (ITs). However, a high IT can decrease the mechanical properties of the heat-affected zone (HAZ) of welded joints. With the use of high strength-toughness stees, this decrease may be an acceptable trade-off. Therefore, it is necessary to evaluate the influence of high ITs on the HAZ. The influence of the IT on the coarse grain HAZ (CGHAZ) and intercritically reheated coarse-grain HAZ (ICCGHAZ) of an API 5L X70 pipe joint welded by gas metal arc welding was investigated. The welding was numerically simulated using finite element method software. The microstructure of the HAZ was predicted using thermodynamic simulation software. The CGHAZ and ICCGHAZ were also physically simulated and evaluated via optical microscopy and scanning electron microscopy, dilatometry, and Vickers microhardness and Charpy V-notch (CVN) impact tests. The increase in IT led to a decrease in CGHAZ microhardness, but did not affect the ICCGHAZ. The CVN energies obtained for all ITs (CGHAZ and ICCGHAZ) were higher than that set by the DNVGL-ST-F101 standard (50 J). These results show that increasing the IT is an interesting and effective method to reduce welding costs. In addition, thermodynamic simulation proved to be a valid method for predicting the phases in the HAZ of API 5L X70 pipe welded joints.

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