The size of the heat-affected zone of LBW-made weldment is also relatively smaller than that of GTAW-made weldment ( Lee et al., 2014).Īlthough some investigations on the giga-cycle fatigue behavior of 316L base metal and weldment have been done ( Carstensen et al., 2002 Naoe et al., 2015, 2018 Xiong et al., 2019b), the fatigue data of 316L, especially of the 316L weldment, is still insufficient. And the fine grains are usually formed in the weld seam, leading to high hardness ( Xiong et al., 2019a), which is different from the much lower hardness distributed in the weld seam induced by the much coarse grains in the case of GTAW ( Xiong et al., 2019b). For example, in the case of LBW, it is difficult to completely eradicate the pore due to the metal evaporation caused by the high energy density and protection gas captured by high cooling rate ( Errico et al., 2020). In general, the microstructure and mechanical properties of the weld seam are closely related to welding methods. So far, there are many kinds of commercial welding methods, such as Laser Beam Welding (LBW), Gas Tungsten Arc Welding (GTAW), Submerged-Arc Welding, and so on. The reduction in the fatigue strength is caused by the existence of welding defects and a soft zone along with the welds ( Deng et al., 2016 Hong and Sun, 2017 Zhang et al., 2018). The fatigue cracks usually initiate from subsurface or internal detects caused by welding in the giga-cycle fatigue regime. It is proposed that the characteristics of weld microstructures have a significant influence on the fatigue behavior of weldments ( Ko, 1989 Yoshihisa and Raman, 2000 Iwata et al., 2006 Basu et al., 2013). A typical feature of giga-cycle fatigue, that is the so-called fish-eye, can be observed on the fracture surface. In the giga-cycle fatigue regime, the conventional fatigue limit disappeared and the fatigue cracks initiate from the internal defect (such as pores, inclusions, and so on) due to the localized stress or strain concentration. It has been reported that the fatigue behavior in the giga-cycle regime is different from that in the high-cycle fatigue regime ( Ping et al., 2015 Su et al., 2017). The study of giga-cycle fatigue behavior of the 316L weldments is then necessary for the operation and lifetime management of the nuclear plants. Therefore, the knowledge of the fatigue properties of these weldings is very important to the design of components in the nuclear industry. These components usually suffer from giga-cycle loading during their service life, which can lead to catastrophic nuclear accidents after a certain period of time ( Naoe et al., 2015 Han et al., 2016). The fatigue failure mode of the GTAW-made specimens is the same as that of LBW-made specimens in the high-cycle fatigue regime but different in the giga-cycle fatigue regime.ĭue to its excellent corrosive resistance, irradiation resistance, and mechanical properties, 316L austenitic stainless steel (316L) is widely used in the fabrication of nuclear components, which are usually connected by welding. For the GTAW-made specimens, the quality requirement of the weld seam has to be more strict to prevent fatigue strength from decreasing. However, an obvious decrease in fatigue life was not observed in such cases. For the LBW-made specimens, the LBW-induced internal pores with a diameter range of about 89–270 μm were observed in the fracture surface. The results indicate that the fatigue strength of LBW-made weldments is almost the same as that of GTAW-made weldments even though the microstructure and mechanical properties of the weldments are different.
![sam the ultimate mechanism designer crack sam the ultimate mechanism designer crack](https://s3-ap-northeast-1.amazonaws.com/peatix-files/pod/8143065/cover-artas-sam-61crack.jpeg)
Therefore, the giga-cycle fatigue behavior of 316L weldments, which are fabricated by Laser Beam Welding (LBW) and Gas Tungsten Arc Welding (GTAW), were investigated using an ultrasonic fatigue testing system.
![sam the ultimate mechanism designer crack sam the ultimate mechanism designer crack](https://1.bp.blogspot.com/-eUeb2Ed8EHc/VqFKeEJpQGI/AAAAAAABWE4/gltA8ihglkE/s400/UWT.jpg)
Some components made of 316L stainless steel in nuclear reactors are connected by welding, and these are under giga-cycle fatigue loading.
![sam the ultimate mechanism designer crack sam the ultimate mechanism designer crack](https://www.mdpi.com/energies/energies-14-04713/article_deploy/html/images/energies-14-04713-g019-550.jpg)
School of Industrial Automation, Beijing Institute of Technology, Zhuhai, China.Zhihong Xiong, Engao Peng, Lianghua Zeng* and Qirong Xu