Abstract
The paper is focused on testing the weld of the S960MC steel produced at the micro-jet cooling under static and fatigue loading at critical parameters. This kind of material was in the form of a sheet with a thickness equal to 2 mm. The joint was obtained using three different types of welding wires: EDFK 1000, Union NiMoCr and Union X96 at the same parameters of the process. The joints were examined using non-destructive and destructive tests. The results from non-destructive experiments enable us to assess the quality of the welds directly before the joining process. In contrast, the destructive one allows following welds behavior under different loading conditions with their critical parameters. The bending experiments confirmed the good plastic properties of the weld, expressed by no cracks in the region tested in many variants of the joint manufactured. The results from static tests indicated a significant reduction of mechanical parameters of the weld in comparison to the base metal, expressed by 50% differences. Fatigue data have enabled us to follow the welding behavior at the increasing amplitude of axial stress up to fracture at constant amplitude value covering the following values of stress 650 MPa–100 MPa. Variations of total energy are presented at different values of several cycles up to fracture. Fracture regions are collected for analysis of the joint region features under cyclic loading. They have indicated differences in weld cracking depended on the stress level. Finally, the Wöhler S-N curve of the weld was determined, indicating the value of the fatigue limit of the weld tested, i.e., 100 MPa. The weld at the Union NiMoCr welding wire was indicated as the joint having the highest resistance on static and fatigue loadings.
Highlights
High-Strength Steels (HSS) belong to modern metals used in a lot of branches of the industry concerning their mechanical properties, such as ultimate tensile strength and yield stress, which are higher compared to typical structural materials [1,2]
The S960MC steel is very difficult for welding processes even when high technology is used, such as the micro-jet cooling method, and when different welding wires are applied because the weld’s mechanical properties can be lowered by 50%;
The following welding parameters are recommended for MAG-welding sheet metal with a thickness of 2 mm: U = 19 V, I = 101 A, V = 300 mm/min and a mixture Ar-18% CO2 as shielding gas;
Summary
High-Strength Steels (HSS) belong to modern metals used in a lot of branches of the industry concerning their mechanical properties, such as ultimate tensile strength and yield stress, which are higher compared to typical structural materials [1,2]. The following material types can be indicated: Strenx [1,3], Docol [4,5], Amstrong Ultra [6] and Optim QC [7] Their application is very wide, and it is selected based on comparing the value of stress due to operational conditions and mechanical parameters at microstructure features [1,2]. Typical applications are represented by advanced lifting devices such as mobile cranes and lighter transport solutions and components [3,6] They indicate the steel and their joints can be subjected to various types of loading, including: static and cyclic, which influence mechanical parameters important for engineering practice and inspection stages for a correct designing and service life, respectively. They have presented a fatigue curve at stress value close to data shown in [18], indicating good agreement between the method and experimental efforts
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