scholarly journals The Effect of Martensitic Phase Transformation Dilation on Microstructure, Strain–Stress and Mechanical Properties for Welding of High-Strength Steel

Crystals ◽  
2018 ◽  
Vol 8 (7) ◽  
pp. 293 ◽  
Author(s):  
Xizhang Chen ◽  
Pengfei Wang ◽  
Qiuhong Pan ◽  
Sanbao Lin
Keyword(s):  
Residual Stress ◽  
Phase Transformation ◽  
Transformation Temperature ◽  
Weld Zone ◽  
Welding Process ◽  
Martensitic Phase ◽  
Martensitic Phase Transformation ◽  
Granular Bainite ◽  
Residual Tensile Stress ◽  
The Impact

The application of low transformation temperature (LTT) wire can effectively reduce residual stress, without the need for preheating before welding and heat treatment after welding. The mechanism reduces the martensitic transformation temperature, allowing the martensite volume expansion to offset some or all of the heat-shrinking, resulting in reduced residual stress during the welding process. In this paper, commercial ER110S-G welding wire and LTT wire with chemical composition Cr10Ni8MnMoCuTiVB were developed to solve the problem of stress concentration. The microstructure of the LTT joint is mainly composed of martensite and a small amount of residual austenite, while the microstructure of the ER110S-G joint is mainly composed of ferrite and a small amount of granular bainite. The micro-hardness and tensile strength of the LTT joint is higher than that of ER110S-G joint; however, the impact toughness of the LTT joint is not as good as that of the ER110S-G joint. The martensitic phase transformation of LTT starts at 212 °C and finishes at around 50 °C, and the expansion caused by phase transition is about 0.48%, which is much higher than that of the base metal (0.15%) and ER110S-G (0.18%). The residual tensile stress at the weld zone of the ER110S-G joint is 175.5 MPa, while the residual compressive stress at the weld zone of LTT joint is −257.6 MPa.

Analysis of Welding Process for Automotive Rear Cradle

2015 ◽  
Vol 1091 ◽  
pp. 97-101
Author(s):  
Hak Jae Seol ◽  
Kyoung Teak Lee ◽  
Chang Soo Park ◽  
Kwan Bong Yoo
Keyword(s):  
Residual Stress ◽  
Phase Transformation ◽  
Temperature Distribution ◽  
Transformation Temperature ◽  
Thermal Deformation ◽  
Welding Process ◽  
Phase Transformation Temperature ◽  
Side Member ◽  
Cross Member ◽  
Total Model

A rear cradle as one of the suspension system takes a role to connect a tie rod, suspension arm, transmissions and rubber bush. It consists of the side member and cross member which are joined by welding process. However, the rear cradle may be distorted due to thermal deformation during welding process, which cause dimensional tolerance problem when assembling. So, it is necessary to predict the thermal deformation and the optimal welding conditions should be suggested to reduce the dimensional tolerances. In this paper, MAG(metal active gas) welding process was applied in the simulation model using the SYSWELDR, commercial S/W for welding simulation. And then, It should be predicted on the results about the gap and thermal deformation of main cylinder and derived the phase transformation, temperature distribution, residual stress and thermal deformation of total model shape.

Capability of martensitic low transformation temperature welding consumables for increasing the fatigue strength of high strength steel joints

2020 ◽  
Vol 62 (9) ◽  
pp. 891-900
Author(s):  
Jonas Hensel ◽  
Arne Kromm ◽  
Thomas Nitschke-Pagel ◽  
Jonny Dixneit ◽  
Klaus Dilger
Keyword(s):  
Residual Stress ◽  
Phase Transformation ◽  
Fatigue Strength ◽  
High Strength Steel ◽  
Transformation Temperature ◽  
Fatigue Cracks ◽  
High Strength ◽  
Filler Material ◽  
Phase Transformation Temperature ◽  
Filler Materials

Abstract The use of low transformation temperature (LTT) filler materials represents a smart approach for increasing the fatigue strength of welded high strength steel structures apart from the usual procedures of post weld treatment. The main mechanism is based on the effect of the low start temperature of martensite formation on the stress already present during welding. Thus, compressive residual stress formed due to constrained volume expansion in connection with phase transformation become highly effective. Furthermore, the weld metal has a high hardness that can delay the formation of fatigue cracks but also leads to low toughness. Fundamental investigations on the weldability of an LTT filler material are presented in this work, including the characterization of the weld microstructure, its hardness, phase transformation temperature and mechanical properties. Special attention was applied to avoid imperfections in order to ensure a high weld quality for subsequent fatigue testing. Fatigue tests were conducted on the welded joints of the base materials S355J2 and S960QL using conventional filler materials as a comparison to the LTT filler. Butt joints were used with a variation in the weld type (DY-weld and V-weld). In addition, a component-like specimen (longitudinal stiffener) was investigated where the LTT filler material was applied as an additional layer. The joints were characterized with respect to residual stress, its stability during cyclic loading and microstructure. The results show that the application of LTT consumables leads to a significant increase in fatigue strength when basic design guidelines are followed. This enables a benefit from the lightweight design potential of high-strength steel grades.

Numerical simulation of the effect of ultrasonic impact treatment on welding residual stress

2021 ◽  
pp. 2150175
Author(s):  
Tao Mo ◽  
Jingqing Chen ◽  
Pengju Zhang ◽  
Wenqian Bai ◽  
Xiao Mu ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Residual Stress ◽  
Compressive Stress ◽  
Welded Joints ◽  
Welding Process ◽  
Residual Compressive Stress ◽  
Welding Residual Stress ◽  
304 Stainless Steel ◽  
Residual Tensile Stress ◽  
Ultrasonic Impact Treatment

Ultrasonic impact treatment (UIT) is an effective method that has been widely applied in welding structure to improve the fatigue properties of materials. It combines mechanical impact and ultrasonic vibration to produce plastic deformation on the weld joints surface, which introduces beneficial compressive residual stress distribution. To evaluate the effect of UIT technology on alleviating the residual stress of welded joints, a novel numerical analysis method based on the inherent strain theory is proposed to simulate the stress superposition of welding and subsequent UIT process of 304 stainless steel. Meanwhile, the experiment according to the process was carried out to verify the simulation of residual stress values before and after UIT. By the results, optimization of UIT application could effectively reduce the residual stress concentration after welding process. Residual tensile stress of welded joints after UIT is transformed into residual compressive stress. UIT formed a residual compressive stress layer with a thickness of about 0.13 mm on the plate. The numerical simulation results are consistent with the experimental results. The work in this paper could provide theoretical basis and technical support for the reasonable evaluation of the ultrasonic impact on residual stress elimination and mechanical properties improvement of welded joints.

Influence of Cr Alloying (1.5 to 5 at.%) on Martensitic Phase Transformation Temperatures in Co-Ni-Ga-Cr Thin Films

2019 ◽  
Vol 5 (1) ◽  
pp. 106-112 ◽  
Author(s):  
Peer Decker ◽  
Jill Fortmann ◽  
Steffen Salomon ◽  
Philipp Krooß ◽  
Thomas Niendorf ◽  
...  
Keyword(s):  
Thin Films ◽  
Phase Transformation ◽  
Martensitic Phase ◽  
Martensitic Phase Transformation ◽  
Transformation Temperatures
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