Characterization of bainite-ferrite structures formed on the heat-affected zone of a dissimilar welds of high-strength steel (S700MC/S960QC) and their dependency on cooling time

Modern steel structures and joints must satisfy various increasingly demanding requirements such as high yield strength, improved cross section to mass ratio, and desirable ductile-to-brittle transition properties. Consequently, joining different types of high-strength steels has become an attractive option from the cost perspective and for weight and corrosion reduction. In dissimilar welding, however, there remains a need for better understanding of discrepancies in microstructure formation resulting from asymmetric heat distribution. In this study, a characterization of the transformation of bainite, ferrite, and martensite in the microstructure of the heat affected zone (HAZ) formed by a cooling time of 10 kJ/cm of heat input was carried out for dissimilar high-strength joint steels (S700MC/S960QC). The characterization was performed by scan electron microscopy (SEM) sampling, the images of which were analyzed by ImageJ Pro and evaluated by volume fraction of block - like granular bainite (GB). The alloy elements composition close to the fusion line of both materials was then assessed using energy dispersive X-ray spectroscopy (EDS). The results showed a strong presence of GB, which had about 70% volume fraction in S700MC at 615 °C, and which comprised formations of lower bainite and retained austenite (RA) at 420 °C. The presence of 55% block GB was observed at 470 °C in S960QC, which was caused by the formation of tempered martensite (TMA) at 400 °C. Presence of 1.3Ni, 0.4Mo, and 1.6Mn in the coarse grain heat affected zone (CGHAZ) of S700MC confirmed the risk of brittle failure on the S700MC side due to the high presence of carbide and ferrite in the GB.

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Effect of Heat Input and Undermatched Filler Wire on the Microstructure and Mechanical Properties of Dissimilar S700MC/S960QC High-Strength Steels

Metals ◽

10.3390/met9080883 ◽

2019 ◽

Vol 9 (8) ◽

pp. 883 ◽

Cited By ~ 1

Author(s):

Francois Njock Bayock ◽

Paul Kah ◽

Belinga Mvola ◽

Pavel Layus

Keyword(s):

Mechanical Properties ◽

Cooling Rate ◽

Heat Affected Zone ◽

Heat Input ◽

Volume Fraction ◽

Base Material ◽

Welding Process ◽

High Strength Steels ◽

High Strength ◽

Microstructure And Mechanical Properties

The effect of heat input on the microstructure and mechanical properties of dissimilar S700MC/S960QC high-strength steels (HSS) using undermatched filler material was evaluated. Experiments were performed using the gas metal arc welding process to weld three samples, which had three different heat input values (i.e., 15 kJ/cm, 7 kJ/cm, and 10 kJ/cm). The cooling continuous temperature (CCT) diagrams, macro-hardness values, microstructure formations, alloy element compositions, and tensile test analyses were performed with the aim of providing valuable information for improving the strength of the heat-affected zone (HAZ) of both materials. Micro-hardness measurement was conducted using the Vickers hardness test and microstructural evaluation by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The mechanical properties were characterized by tensile testing. Dissimilar welded samples (S700MC/S960QC) with a cooling rate of 10 °C/s (15 kJ/cm) showed a lower than average hardness (210 HV5) in the HAZ of S700MC than S960QC. This hardness was 18% lower compared to the value of the base material (BM). The best microstructure formation was obtained using a heat input of 10 kJ/cm, which led to the formation of bainite (B, 60% volume fraction), ferrite (F, 25% volume fraction), and retained austenite (RA, 10%) in the final microstructure of S700MC, and B (55%), martensite (M, 45%), and RA (10%), which developed at the end of the transformation of S960QC. The results showed the presence of 1.3 Ni, 0.4 Mo, and 1.6 Mn in the fine-grain heat-affected zone of S700MC. The formation of a higher carbide content at a lower cooling rate reduced both the hardness and strength.

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Effects of Heat Affected Zone Softening Extent on the strength of Advanced High Strength Steels Resistance Spot Weld

10.31224/osf.io/e2679 ◽

2018 ◽

Author(s):

Hassan Rezayat ◽

Hassan Ghassemi-Armaki ◽

Sudarsanam Suresh Babu

Keyword(s):

Finite Element ◽

Base Metal ◽

Heat Affected Zone ◽

Volume Fraction ◽

Load Capacity ◽

High Strength Steels ◽

High Strength ◽

Stress Strain ◽

Resistance Spot ◽

Advanced High Strength Steels

Resistance spot welds made from Advanced High Strength Steels (AHSS) exhibit Heat Affected Zone (HAZ) softening due to the tempering of pre-existing martensite phase and the consequent decomposition into a mixture of ferrite and cementite. Despite the high strength level for the base metal, the occurrence of HAZ softening may lead to inferior joint strength during Tension-Shear (TS) and Cross-Tension (CT) testing. In this work, we investigated the effects of the HAZ softening on the global loading response for AHSS steels with three different volume fractions of martensite. Microhardness mapping was used as a measure of martensite tempering and extent of softening. Based on the data, the softening was identified in the sub-critical heat affected zone. Hardness drop with the magnitude of 6%, 18%, and 42% was observed in steels with 16%, 52% and 100% of martensite volume fraction (MVF), respectively. In order to model the welded joint loading response using finite element methods (FEM), there is a need to represent the softening in terms of stress-strain relationships. In this work, local stress-strain curves for different weld zones were obtained by scaling the base metal constitutive properties with local hardness ratio. Finite element (FE) simulations of Tension-Shear tests showed that HAZ softening can affect the Tension-Shear load capacity of specimens more significantly when the base metal tensile strength is above 1000 MPa. The paper will discuss the validity of the above finite element approach for describing experimental results and future directions.

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Design of Low-Cost and High-Strength Titanium Alloys Using Pseudo-Spinodal Mechanism through Diffusion Couple Technology and CALPHAD

Materials ◽

10.3390/ma14112910 ◽

2021 ◽

Vol 14 (11) ◽

pp. 2910

Author(s):

Chaoyi Ding ◽

Chun Liu ◽

Ligang Zhang ◽

Di Wu ◽

Libin Liu

Keyword(s):

Diffusion Couple ◽

Titanium Alloys ◽

High Throughput ◽

Volume Fraction ◽

Raw Materials ◽

Low Cost ◽

High Strength ◽

High Yield ◽

Α Phase ◽

Cr System

The high cost of development and raw materials have been obstacles to the widespread use of titanium alloys. In the present study, the high-throughput experimental method of diffusion couple combined with CALPHAD calculation was used to design and prepare the low-cost and high-strength Ti-Al-Cr system titanium alloy. The results showed that ultra-fine α phase was obtained in Ti-6Al-10.9Cr alloy designed through the pseudo-spinodal mechanism, and it has a high yield strength of 1437 ± 7 MPa. Furthermore, application of the 3D strength model of Ti-6Al-xCr alloy showed that the strength of the alloy depended on the volume fraction and thickness of the α phase. The large number of α/β interfaces produced by ultra-fine α phase greatly improved the strength of the alloy but limited its ductility. Thus, we have demonstrated that the pseudo-spinodal mechanism combined with high-throughput diffusion couple technology and CALPHAD was an efficient method to design low-cost and high-strength titanium alloys.

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Fatigue and Burst Analysis of Hy-140(T) Steel Pressure Vessels

Journal of Engineering for Industry ◽

10.1115/1.3427696 ◽

1970 ◽

Vol 92 (1) ◽

pp. 11-16 ◽

Cited By ~ 1

Author(s):

J. M. Barsom ◽

S. T. Rolfe

Keyword(s):

Yield Strength ◽

Pressure Vessel ◽

Low Cycle Fatigue ◽

High Strength Steels ◽

High Strength ◽

Fatigue Tests ◽

Pressure Vessels ◽

High Yield ◽

Corrosion Properties ◽

Burst Analysis

Increasing use of high-strength steels in pressure-vessel design has resulted from emphasis on decreasing the weight of pressure vessels for certain applications. To demonstrate the suitability of a 140-ksi yield strength steel for use in unwelded pressure vessels, HY-140(T)—a quenched and tempered 5Ni-Cr-Mo-V steel—was fabricated and subjected to various burst and fatigue tests, as well as to various laboratory tests. In general, results of the investigation indicated very good tensile, Charpy, Nil Ductility Transition Temperature (NDT), low-cycle fatigue, and stress-corrosion properties of HY-140(T) steels, as well as very good burst tests results, in comparison with existing high-yield strength pressure-vessel steels. The results also indicate that the HY-140(T) steel should be an excellent material for its originally designed purpose, Naval hull applications.

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Favourable Steel Structures using High Strength Steels

ce/papers ◽

10.1002/cepa.1452 ◽

2021 ◽

Vol 4 (2-4) ◽

pp. 1530-1536

Author(s):

Fengyan Gong ◽

André Dürr ◽

Jochen Bartenbach

Keyword(s):

High Strength Steels ◽

Steel Structures ◽

High Strength

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Carbon Redistribution and Microstructural Evolution Study during Two-Stage Quenching and Partitioning Process of High-Strength Steels by Modeling

Materials ◽

10.3390/ma11112302 ◽

2018 ◽

Vol 11 (11) ◽

pp. 2302 ◽

Cited By ~ 2

Author(s):

Yilin Wang ◽

Huicheng Geng ◽

Bin Zhu ◽

Zijian Wang ◽

Yisheng Zhang

Keyword(s):

Retained Austenite ◽

Volume Fraction ◽

High Strength Steels ◽

High Strength ◽

Simulation Method ◽

Low Carbon ◽

Two Stage ◽

Quenching And Partitioning ◽

Carbon Redistribution ◽

Carbon Martensite

The application of the quenching and partitioning (Q-P) process on advanced high-strength steels improves part ductility significantly with little decrease in strength. Moreover, the mechanical properties of high-strength steels can be further enhanced by the stepping-quenching-partitioning (S-Q-P) process. In this study, a two-stage quenching and partitioning (two-stage Q-P) process originating from the S-Q-P process of an advanced high-strength steel 30CrMnSi2Nb was analyzed by the simulation method, which consisted of two quenching processes and two partitioning processes. The carbon redistribution, interface migration, and phase transition during the two-stage Q-P process were investigated with different temperatures and partitioning times. The final microstructure of the material formed after the two-stage Q-P process was studied, as well as the volume fraction of the retained austenite. The simulation results indicate that a special microstructure can be obtained by appropriate parameters of the two-stage Q-P process. A mixed microstructure, characterized by alternating distribution of low carbon martensite laths, small-sized low-carbon martensite plates, retained austenite and high-carbon martensite plates, can be obtained. In addition, a peak value of the volume fraction of the stable retained austenite after the final quenching is obtained with proper partitioning time.

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Metallurgical Study of Friction Stir Welded High Strength Steels for Shipbuilding

Materials Science Forum ◽

10.4028/www.scientific.net/msf.783-786.2798 ◽

2014 ◽

Vol 783-786 ◽

pp. 2798-2803 ◽

Cited By ~ 1

Author(s):

Marion Allart ◽

Alexandre Benoit ◽

Pascal Paillard ◽

Guillaume Rückert ◽

Myriam Chargy

Keyword(s):

Cubic Boron Nitride ◽

High Strength Steels ◽

High Strength ◽

High Yield ◽

Friction Stir ◽

Polycrystalline Cubic Boron Nitride ◽

Recent Developments ◽

Metallurgical Study ◽

Welding Processes ◽

Pcbn Tools

Friction Stir Welding (FSW) is one of the most recent welding processes, invented in 1991 by The Welding Institute. Recent developments, mainly using polycrystalline cubic boron nitride (PCBN) tools, broaden the range of use of FSW to harder materials, like steels. Our study focused on the assembly of high yield strength steels for naval applications by FSW, and its consequences on the metallurgical properties. The main objectivewas to analyze the metallurgical transformations occurring during welding. Welding tests were conducted on three steels: 80HLES, S690QL and DH36. For each welded sample, macrographs, micrographs and micro-hardness maps were performed to characterize the variation of microstructures through the weld.

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