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

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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Microstructure and Toughness of Weld CGHAZ Under Different Heat Input for X90 High Strength Pipeline Steel

Volume 3: Operations, Monitoring and Maintenance; Materials and Joining ◽

10.1115/ipc2016-64665 ◽

2016 ◽

Cited By ~ 1

Author(s):

Liuqing Yang ◽

Yongli Sui ◽

PeiPei Xia ◽

Die Yang ◽

Yongqing Zhang

Keyword(s):

Impact Toughness ◽

Impact Energy ◽

Heat Input ◽

Pipeline Steel ◽

Charpy Impact ◽

Optical Microscope ◽

Granular Bainite ◽

Alloy Content ◽

Welding Heat Input ◽

The Impact

Two kinds of industry trial X90 pipeline steel which had different chemical composition were chosen as experimental materials, and the grain coarsening, microstructure evolution characteristics and the variation rules of low-temperature impact toughness in weld CGHAZ of this two steel under different welding heat input were studied by physical thermal simulation technology, SEM, optical microscope and Charpy impact test. The results show that microstructure in weld CGHAZ of 1# steel is mainly bainite ferrite (BF) and most of the M/A constituents are blocky or short rod-like; the grains of 2# steel are coarse and there is much granular bainite (GB), meanwhile M/A constituents become coarse and their morphology is changing from block to elongated laths; alloy content of X90 pipeline steel under different welding heat input has great effect on the grain size of original austenite, and when heat input is lower than 2.0KJ/mm, Charpy impact toughness in CGHAZ of lower alloy content pipeline steel is good; as heat input increases, impact toughness in CGHAZ of 1# steel is on the rise, and it is high (between 260J and 300J) when heat input is between 2.0KJ/mm and 2.5KJ/mm and the scatter of impact energy is small; impact toughness of 2# steel decreases gradually and the impact energy has obvious variability.

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Effect of Heat Input on Toughness of Coarse-Grained Heat-Affected Zone of an Ultra Low Carbon Acicular Ferrite Steel

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.538-541.2003 ◽

2012 ◽

Vol 538-541 ◽

pp. 2003-2008 ◽

Cited By ~ 2

Author(s):

Zheng Hai Xia ◽

Xiang Liang Wan ◽

Xue Li Tao ◽

Kai Ming Wu

Keyword(s):

Electron Microscopy ◽

Impact Toughness ◽

Heat Affected Zone ◽

Heat Input ◽

Acicular Ferrite ◽

High Heat ◽

Coarse Grained ◽

Low Carbon ◽

Ferrite Steel ◽

The Impact

The effect of heat input on toughness of coarse-grained heat-affected zone of an ultra low carbon acicular ferrite steel were investigated when the welding was conducted with high heat input. Microstructural observations, energy dispersive X-ray spectroscopy analyses were conducted using optical microscopy, scanning electron microscopy and transmission electron microscopy, respectively. The microstructures of coarse-grained heat-affected zone consist of predominantly bainitic microstructure and a small proportion of acicular ferrite grains. The bainitic microstructures become coarsened with increasing heat input. The impact toughness of coarse-grained heat-affected zone remained at a higher level when the heat input ranged from 42 to 55 kJ/cm. It became not stable and dropped to a lower level when the heat input increased to 110150 kJ/cm. The enhancement in impact toughness was attributable to the MnS precipitation on the pre-formed Ti oxides as well as the formation of intragranular ferrite. When specimens were welded with higher heat input, the deterioration of impact toughness was caused by the coarsening of austenite grains.

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

Metals ◽

10.3390/met9090939 ◽

2019 ◽

Vol 9 (9) ◽

pp. 939 ◽

Cited By ~ 1

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).

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Effects of Zirconium on Impact Toughness for the Hull Structure Steel Plate

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.644-650.4932 ◽

2014 ◽

Vol 644-650 ◽

pp. 4932-4935

Author(s):

Tie Li Qi

Keyword(s):

Impact Toughness ◽

Impact Energy ◽

Heat Input ◽

Steel Plate ◽

Sharp Decline ◽

Large Size ◽

Welding Heat Input ◽

Hull Structure ◽

Large Heat ◽

The Impact

The Gleeble3500 combined with SEM, TEM and other experimental methods are employed in this paper to investigate the effects of zirconium content on impact toughness of heat affected zone (HAZ) of hull structure steel plate during the large heat input welding. The results showed when 0.01% zirconium were added in the steel, the impact energy reached 224 J at-60°C experienced 150 kJ/cm welding heat input. But the large-size rectangular inclusions are found in CGHAZ when 0.02% zirconium were added in the steel, the impact energy fell to 38 J at-60°C experienced 150 kJ/cm welding heat input, the large-size inclusions, especially rectangular inclusion, were the main cause for the sharp decline of low temperature toughness after welding.

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Study in Simulated Heat-Affected Zone of Ship Steel

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.228-229.1196 ◽

2011 ◽

Vol 228-229 ◽

pp. 1196-1200

Author(s):

Wen Yan Liu ◽

Ji Bin Liu ◽

Cong Mao Zhu ◽

Hui Wang

Keyword(s):

Impact Toughness ◽

Heat Affected Zone ◽

Heat Input ◽

Physical Simulation ◽

Wide Range ◽

Lath Bainite ◽

Quench Hardening ◽

Impact Energies ◽

The Impact ◽

Cct Diagrams

The experiments were carried out upon the determination of simulated heat-affected zone continuous cooling transformation (SH-CCT) diagrams, the characteristics of microstructure and Vickers hardness of SH-CCT specimens, and impact toughness in simulated coarse grain heat-affected zone (CGHAZ) of ship steels under different heat input based on physical simulation. The SH-CCT diagram reveals that bainite is always obtained in a wide range of cooling rates. When the maximum cooling rate reaches 100 °C/s (t8/5=3 seconds), the maximum fraction of martensite (8%) is obtained and the microstructures mainly consist of lath bainite and the hardness is only 255 HV. This demonstrates that the steel has a low quench-hardening tendency and excellent resistance to cold cracking. There are no obvious hardening and softening phenomena in simulated CGHAZ. Test results of impact toughness under different heat input in simulated CGHAZ show that the impact energies reach over 30 J at -40 °C when t8/5 is less than 20 s, meeting the stipulated requirements of ship steel (≥22 J at -40 °C) but no great allowance. Thus, to meet the requirement of properties during welding, it is proposed to choose t8/5 ranging from 5 to 20 s, correspondently the line energies ranging from 14 to 37 KJ/cm for 30 mm thick plate.

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Effect of Ferritic Morphology on Yield Strength of CGHAZ in a Low Carbon Mo-V-N-Ti-B Steel

Metals ◽

10.3390/met11111863 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1863

Author(s):

Leping Wang ◽

Huibing Fan ◽

Genhao Shi ◽

Qiuming Wang ◽

Qingfeng Wang ◽

...

Keyword(s):

Yield Strength ◽

Heat Input ◽

Low Carbon Steel ◽

High Heat ◽

Coarse Grained ◽

Granular Bainite ◽

Low Carbon ◽

Fine Grained ◽

High Heat Input ◽

The Impact

For investigating the impact of ferritic morphology on yield strength (YS) of the high-heat-input welding induced coarse-grained heat-affected zone (CGHAZ) of a low carbon Mo-V-N-Ti-B steel, a group of particular welding heat inputs were designed to obtain different ferritic microstructures in CGHAZ. The tensile properties were estimated from typical samples with ferritic microstructures. The mixed microstructures dominated by the intragranular polygonal ferrite (IGPF), the intragranular acicular ferrite (IGAF), and the granular bainite (GB) were obtained at the heat inputs of 35, 65, 85 and 120 kJ/cm, respectively. When the main microstructure changed from IGPF to IGAF and GB, YS increased first and then decreased. The microstructure consisting mainly of IGAF possessed the maximum YS. As the main microstructure changed from IGPF to IGAF and GB, the contribution of grain refinement strengthening to YS was estimated to be elevated remarkably. This means the strength of CGHAZ in a low-carbon steel subjected to the high-heat-input welding could be enhanced by promoting the fine-grained AF and GB formation.

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Microstructure, Mechanical Properties, and Corrosion Behavior of Ultra-Low Carbon Bainite Steel with Different Niobium Content

Materials ◽

10.3390/ma14020311 ◽

2021 ◽

Vol 14 (2) ◽

pp. 311

Author(s):

Yun Zong ◽

Chun-Ming Liu

Keyword(s):

Impact Toughness ◽

Electrochemical Impedance ◽

Charge Transfer Resistance ◽

Granular Bainite ◽

Low Carbon ◽

Transfer Resistance ◽

Niobium Content ◽

Maximum Charge ◽

Low Carbon Bainite ◽

The Impact

Four types of ultra-low carbon bainite (ULCB) steels were obtained using unified production methods to investigate solely the effect of niobium content on the performance of ULCB steels. Tensile testing, low-temperature impact toughness testing, corrosion weight-loss method, polarization curves, electrochemical impedance spectroscopy (EIS), and the corresponding organizational observations were realized. The results indicate that the microstructure of the four steels comprise granular bainite and quite a few martensite/austenite (M/A) elements. The niobium content affects bainite morphology and the size, quantity, and distribution of M/A elements. The elongation, yield strength, and tensile strength of the four types of ULCB steels are above 20%, 500 MPa, and 650 MPa, respectively. The impact toughness of the four types of ULCB steels at −40 °C is lower than 10 J. Steel with Nb content of 0.0692% has better comprehensive property, and maximum charge transfer resistance in 3.5 wt.% NaCl solution at the initial corrosion stage. The corrosion products on the surface of steel with higher niobium content are much smoother and denser than those steel with lower niobium content after 240 h of corrosion. The degree of corrosion decreases gradually with the increase of niobium content at the later stage of corrosion.

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Significant Influence of Welding Heat Input on the Microstructural Characteristics and Mechanical Properties of the Simulated CGHAZ in High Nitrogen V-Alloyed Steel

High Temperature Materials and Processes ◽

10.1515/htmp-2020-0003 ◽

2020 ◽

Vol 39 (1) ◽

pp. 33-44

Author(s):

Jing Zhang ◽

Wenbin Xin ◽

Guoping Luo ◽

Ruifen Wang ◽

Qingyong Meng

Keyword(s):

Mechanical Properties ◽

Impact Toughness ◽

Heat Input ◽

Prior Austenite ◽

Alloyed Steel ◽

Coarse Grained ◽

High Nitrogen ◽

Microstructural Characteristics ◽

Welding Heat Input ◽

The Impact

AbstractThe microstructural characteristics and mechanical properties of the simulated coarse grained heat affected zone (CGHAZ) in high N V-alloyed steel have been conducted under different welding heat input, characterized by the cooling time taken from 800°C to 500°C (t8/5). The experimental results show that the microstructure is dominantly composed of lath bainite (LB) and granular bainite (GB) at t8/5 30 s– 90 s. The content of LB decreases with t8/5 increasing, and that of GB increases. When t8/5 further increases to 120 s and 180 s, the microstructure mainly consists of intragranular polygonal ferrite (IPF) and acicular ferrite (IAF). The higher t8/5 leads to the increased content of intragranular ferrite (IGF). Meanwhile, the prior austenite grain size (PAGS) progressively increases from 56 ± 6.0 μm to 148 ± 9.9 μm as t8/5 increases from 30 s to 180 s. Besides, EBSD analysis indicates that the fraction of high angle grain boundaries (HAGBs) is 0.570, 0.427 and 0.624, respectively, corresponding to t8/5 30, 90 and 180 s. Moreover, the impact toughness decreases as t8/5 increases from 30 s to 90 s caused by the increased PAGS and GB content, and then sharply increases with t8/5 exceeding 90 s due to the increased formation of IGF, especially IAF. Furthermore, the high nitrogen content accelerates V(C,N) precipitation, which not only inhibits the coarsening of prior austenite grains, but promotes the formation of IGF, resulting in the increased number of HAGBs and raising impact toughness.

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Transformation of M/A Constituents during Tempering and Its Effects on Impact Toughness of Weld Metals for X80 Hot Bends

Advances in Materials Science and Engineering ◽

10.1155/2019/6429045 ◽

2019 ◽

Vol 2019 ◽

pp. 1-10 ◽

Cited By ~ 1

Author(s):

Gui-ying Qiao ◽

Xiu-lin Han ◽

Xiao-wei Chen ◽

Xu Wang ◽

Bo Liao ◽

...

Keyword(s):

Impact Toughness ◽

Weld Metal ◽

Acicular Ferrite ◽

Tempering Temperature ◽

Factors Affecting ◽

Weld Metals ◽

Gleeble 3500 ◽

The Impact ◽

Carbide Particles

Impact toughness of the weld metal is one of the important factors affecting the quality of hot bends, which is strongly dependent on the microstructure transformation during hot bending and tempering. In this study, three kinds of weld metals with different Ni contents were selected, and then the effects of tempering temperature on the microstructure impact toughness of weld metals for hot bends were investigated by simulation conducted on a Gleeble-3500 thermal simulator. The results show that the nonmetallic inclusion particles in weld metals can become the nuclear core of acicular ferrite like in as-welded metal. So, the overlapping acicular ferrite microstructure is obtained in the weld metal after direct cooling from the reheating temperature. During tempering, the overlapping acicular ferrite microstructure is degenerated, and martensite/austenite (M/A) constituents in the acicular ferrite microstructure decompose into ferrites and carbides. The resulting carbide particles mainly distribute along the acicular ferrite grain boundaries. With the increase of the tempering temperature, the carbide particles coarsen, which decreases the impact toughness of the weld metal of hot bends. Addition of Ni to weld metals can refine the acicular ferrite and improve the impact toughness.

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Research on Influential Mechanism of HAZ Impact Toughness for Shipbuilding Steel with Mg Addition

Metals ◽

10.3390/met8080584 ◽

2018 ◽

Vol 8 (8) ◽

pp. 584 ◽

Cited By ~ 4

Author(s):

Hui-rong Li ◽

Li-gen Sun ◽

Li-guang Zhu ◽

Yun-song Liu ◽

Yun-gang Li

Keyword(s):

Impact Toughness ◽

Heat Input ◽

Steel Plates ◽

Heat Affect Zone ◽

Shipbuilding Steel ◽

Welding Heat Input ◽

Large Heat ◽

Mg Addition ◽

The Difference ◽

The Impact

The welding performance of shipbuilding steel under large heat input could be improved greatly by the addition of Mg to the steel, but the impact toughness of the heat affect zone (HAZ) is not stable. According to the three different thickness steel plates obtained in the industrial experiment, the large heat input welding was carried out by different heat input, and the impact toughness analysis, impact fracture analysis, metallographic microstructure analysis and inclusions analysis were carried out. The results showed that, the HAZ of three kinds of thickness plates induced much intragranular acicular ferrite (IAF); with Mg addition, the inclusion dimension had been reduced effectively, and the IAF-induced ability of the inclusions had also been improved. The difference of HAZ impact toughness with different welding heat input and different impact temperature is significant; considering the influence of welding heat input and metallographic microstructure on the impact toughness of HAZ, the welding heat load had a far greater effect than the metallographic microstructure on ductile–brittle transition temperature. At the same time, if the original metallographic microstructure of steel was coarse, the pinning effect of the inclusions would be reduced significantly, and the microstructure of HAZ would be coarsened and the impact toughness of HAZ would be decreased, so there is a certain matching relationship between the metallographic microstructure and the inclusion dimension.

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