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Welding metallurgy of martensitic advanced high strength steels during resistance spot welding
, Article Science and Technology of Welding and Joining ; Volume 22, Issue 4 , 2017 , Pages 327-335 ; 13621718 (ISSN) ; Pouranvari, M ; Movahedi, M ; Sharif University of Technology
Abstract
The paper addresses the process–microstructure–performance relationships in resistance spot welding of a martensitic advanced high strength steel. Significant softening was observed in the heat affected zone (HAZ) due to allotriomorphic ferrite formation in the inter-critical HAZ and tempering of martensite in sub-critical HAZ (SCHAZ), with the latter plays more important role in mechanical properties of the spot welds. The strain concentration associated with the HAZ softening promotes initiation of pullout failure from the soft SCHAZ. While, the peak load in the interfacial failure mode is governed by the fusion zone size, that of the pullout mode is significantly affected by the HAZ...
Understanding the factors controlling the interfacial failure strength of advanced high-strength steel resistance spot welds: hardness vs. fracture toughness
, Article Science and Technology of Welding and Joining ; Volume 23, Issue 6 , 2018 , Pages 520-526 ; 13621718 (ISSN) ; Sharif University of Technology
Taylor and Francis Ltd
2018
Abstract
The failure of advanced high-strength steels’ spot welds is a critical issue for automotive crashworthiness. This paper deals with understanding the underlying factors of the tensile-shear strength of automotive steels’ resistance spot welds during interfacial failure. It was found that the ratio of the fracture toughness to the hardness of the fusion zone is the critical factor governing the interfacial failure mechanism: ductile shear failure (controlled by the fusion zone hardness) vs. cleavage crack propagation (controlled by the fracture toughness). This clarification could pave the way for more accurate modelling of interfacial failure of advanced steel resistance spot welds and shed...
Duplex stainless steel/martensitic steel dissimilar resistance spot welding: Microstructure-properties relationships
, Article Welding Journal ; Volume 98, Issue 9 , 2019 , Pages 263S-272S ; 00432296 (ISSN) ; Pouranvari, M ; Sharif University of Technology
American Welding Society
2019
Abstract
This paper addresses the phase transformations and mechanical performance of dissimilar resistance spot welds between 2304 duplex stainless steel (DSS) and 1.2-GPa martensitic (MS) advanced high-strength steel (AHSS). The solidification mode and transformation path of the fusion zone (FZ) were analyzed. The key metallurgical feature of the FZ was the formation of a duplex microstructure consisting of delta ferrite and martensite. The FZ size at the sheet/sheet interface was the critical factor controlling the fraction of pullout failure during the partial thickness-partial pullout mode, the load-bearing capacity, and the energy absorption capability of the DSS/MS dissimilar resistance spot...
Welding Metallurgy and Weldability of Martensitic Advanced High Strength Steel and Duplex Stainless Steels during Resistance Spot Welding
, M.Sc. Thesis Sharif University of Technology ; Pouranvari, Majid (Supervisor)
Abstract
Duplex stainless steels and advanced high strength steels are both known as new materials in automobile industry applications. Process of resistance spot welding is the main process in welding of auto-body structures. Hence investigating the welding metallurgy and weldability of similar and dissimilar joints of duplex stainless steels and advanced high strength steel are crucial. The purpose of this study is to analyse the relationship between welding process and geometric characteristic of weld nugget, phase transformations of Weld nugget and heat affected zone, mechanical properties (i.e force bearing capacity and energy absorption capability) and failure mode (interfatial or pullout). in...
Investigation of Microstructure and Fracture Behavior of Similar and Dissimilar Dual Phase Steels and Martensitic Steel Spot Resistance Welding
, M.Sc. Thesis Sharif University of Technology ; Pouranvari, Majid (Supervisor) ; Movahhedi, Mojtaba (Supervisor)
Abstract
The new generation of advanced high-strength steels use in the automotive industry cause resistance spot welding study and their failure characteristics during static and dynamic loading are important. In this study, the relationship among microstructure, failure mode and mechanical properties are investigate during similar and dissimilar DP980 and MS1400 jointing advanced high-strength steels resistance spot welding. To search for micro and macro structural changes, the optical microscope, stereographic microscope and scanning electron microscope were used. Micro-hardness test, tensile shear test and Cross tension test to evaluate the mechanical properties were conducted. As well as...
Improving the Failure Behavior of High Strength and High Hardenable Steels Resistance Spot Welds
, M.Sc. Thesis Sharif University of Technology ; Pouranvari, Majid (Supervisor)
Abstract
Selecting materials is a key stage for designing vehicles. Today, advanced high-strength steels and stainless steels are attractive by the automotive industry. In this study, the improvement of mechanical properties of the martensitic stainless steels (MSS420 with annealed condition) and advanced high strength martensitic steels (MS1400 with quenched condition), which have a different response to mechanical tests, were investigated. The welding of MSS420 steel was carried out in three phases. In the first phase, the MSS420 double pulse welding with variable second pulse times (0.2s-1.8s) with a constant secondary pulse current of 4 kA and in the second phase a double pulse welding with...
Welding metallurgy of stainless steels during resistance spot welding part II –heat affected zone and mechanical performance
, Article Science and Technology of Welding and Joining ; Volume 20, Issue 6 , 2015 , Pages 512-521 ; 13621718 (ISSN) ; Pouranvari, M ; Marashi, S. P. H ; Sharif University of Technology
Maney Publishing
2015
Abstract
Implementation of new materials in automotive body-in-white requires through knowledge of their metallurgical response to welding process thermal cycle. This two-part paper aims at understanding the physical and mechanical metallurgy of stainless steels, as interesting candidates for automotive application, during resistance spot welding. The second part addresses the phase transformations in the heat affected zone of three types of stainless steels including austenitic, ferritic and duplex steels. Failure modes and mechanical properties of stainless steel resistance spot welds are discussed. The peak load and energy absorption of stainless steel resistance spot welds are compared with...
Transient liquid phase bonding of dual phase steels using Fe-based, Ni-based, and pure Cu interlayers
, Article Journal of Manufacturing Processes ; Volume 30 , 2017 , Pages 106-115 ; 15266125 (ISSN) ; Ekrami, A ; Sharif University of Technology
Abstract
Transient liquid phase (TLP) bonding is a joining process which combines benefits of diffusion bonding and brazing. Therefore, this method has widely been used in joining of materials which are sensitive to fusion welding. Interlayer composition, as one of the most important factors of TLP bonding, can affect the bonding region composition, microstructure, and hence mechanical properties of the joint. In this research, Fe-based, Ni-based, and commercially pure Cu interlayers are used to bond low-carbon steel components which are then heat treated to produce dual phase steel. The present work focuses on two main goals. Firstly, drawing a comparison of microstructure and mechanical properties...
Resistance spot welding of MS1200 martensitic advanced high strength steel: microstructure-properties relationship
, Article Journal of Manufacturing Processes ; Volume 31 , 2018 , Pages 867-874 ; 15266125 (ISSN) ; Sobhani, S ; Goodarzi, F ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
This paper addresses the microstructure and tensile-shear mechanical performance of MS1200 Giga-grade martensitic advanced high strength steel resistance spot welds. The key phase transformations in MS1200 welds were lath martensite formation in the fusion zone (FZ) and upper-critical heat affected zone (HAZ), new ferrite formation in the inter-critical HAZ and martensite tempering in the sub-critical HAZ. The MS1200 welds were featured by a near matching hardness in the fusion zone and under-matching hardness in the heat affected zone (HAZ) compared to the base metal. At certain process window a complete nugget pullout and separation was observed with high post-necking tearing energy. The...
Friction stir welding of advanced high strength dual phase steel: Microstructure, mechanical properties and fracture behavior
, Article Materials Science and Engineering A ; Volume 769 , January , 2020 ; Kokabi, A. H ; Goodarzi, M ; Kestens, L. A. I ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
In this study, butt welds of an advanced high strength dual phase steel were fabricated using friction stir welding at a constant rotational speed of 800 rpm and different transverse speeds of 100, 150 and 200 mm/min. It was observed that sound welds can be obtained at transverse speeds of 100 and 150 mm/min. At transverse speed of 100 mm/min, the entire stir zone processed at temperatures higher than Ac3. By increasing transverse speed to 150 mm/min, temperature in the bottom region of the stir zone lied between Ac1 and Ac3, while the middle and the top regions experienced temperatures higher than Ac3. The lower peak temperature in the bottom region of the stir zone resulted in finer and...
The effect of improved cooling on the microstructure and mechanical properties of friction stir-welded advanced high-strength dual-phase steel
, Article Steel Research International ; Volume 92, Issue2 , August , 2020 ; Kokabi, A. H ; Goodarzi, M ; Kestens, L. A. I ; Sharif University of Technology
Wiley-VCH Verlag
2020
Abstract
The heat-affected zone (HAZ)softening is considered one of the most significant challenges during welding of ferrite–martensite dual-phase (DP) steels. In fact, the strain localization in the softened area results in a premature fracture that degrades the mechanical properties of the joint. Herein, the objective is to investigate the effectiveness of improved cooling using a high thermal diffusivity backing plate (BP) to reduce HAZ softening and enhance the mechanical properties of friction stir-welded DP700 steel. Accordingly, friction stir butt welding of DP700 steel was conducted using copper and mild steel BPs. The findings show that the replacement of steel BP with copper significantly...
The effect of improved cooling on the microstructure and mechanical properties of friction stir-welded advanced high-strength dual-phase steel
, Article Steel Research International ; Volume 92, Issue 2 , 2021 ; 16113683 (ISSN) ; Kokabi, A. H ; Goodarzi, M ; Kestens, L. A. I ; Sharif University of Technology
Wiley-VCH Verlag
2021
Abstract
The heat-affected zone (HAZ) softening is considered one of the most significant challenges during welding of ferrite–martensite dual-phase (DP) steels. In fact, the strain localization in the softened area results in a premature fracture that degrades the mechanical properties of the joint. Herein, the objective is to investigate the effectiveness of improved cooling using a high thermal diffusivity backing plate (BP) to reduce HAZ softening and enhance the mechanical properties of friction stir-welded DP700 steel. Accordingly, friction stir butt welding of DP700 steel was conducted using copper and mild steel BPs. The findings show that the replacement of steel BP with copper significantly...