Analysis of impact toughness and the critical stress intensity factor KIc in ferrite-austenite welded joints with different heat input

Introduction/purpose: Constructions always have several critical points that can be sources of possible defects. All these critical places must be taken into account in safety assessment where the most unfavorable exploitation factors are considered and the local safety of a joint is assessed. Today, joints of various compositions are becoming more frequent in metal constructions. Due to the requirements of economy and ecology, welded joints of microalloyed ferritic steels with high-alloyed austenitic steels are increasingly encountered during the construction of power plants, chemical facilities, etc. Tests of such welded joints have been performed on tanks for oil derivatives, where parts of the tank shell are made of microalloyed ferritic\ud steel and the roof structure is made of high-alloyed austenitic steel. Methods: In the paper, an experimental analysis of crack propagation in an austenitic-ferritic welded joint was performed. The welding was performed by the MIG welding process with two different heat inputs, and the same filler material MIG 18/8/6 was used. Two types of welded plates were tested. The characteristics of the base, filler and auxiliary materials and welding technologies are given. Notched test specimens with an initiated crack-type fracture were made in order to determine the impact properties and fracture mechanics parameters. The results: The research carried out within this study aimed to compare the obtained results of the impact toughness and fracture toughness at flat deformation in a ferrite-austenitic welded joint. An evaluation of the results obtained during the testing of the experimental plates welded with different amounts of heat input is also given. Conclusion: These test results established the dependence of the geometry of a propagating crack and the stress conditions for further crack propagation. It is possible to determine the values of the parameters that describe the behavior of the material, both in linear-elastic and in elastoplastic fracture mechanics

Influence of pin geometry on mechanical and structural properties of butt friction stir welded 2024-T351 aluminum alloy

The aim of this work was to investigate the combined effect of small difference in pin geometry, together with rotation and welding speed on the weldability, mechanical and structural properties of FSW 2024-T351 Al plates. The only difference in tool pin design was the shape of thread: regular and rounded. Specimens were welded using rotation rate of 750 rev/min and welding speeds of 73 and 93 mm/min. In all four cases, specimens were defect free, with good or acceptable weld surface. Modification in pin design showed strong influence on macro structure and hardness distribution. Weak places are identified as low hardness zone, close to the nugget zone and are in good agreement with fracture location in tensile testing. Weld efficiency, as a measure of weld quality, are better in case of 310 tool, while UTS values can differ up to 13% for the equal welding parameters. Therefore, it can be assumed that small modification in tool design, particularly in pin geometry, can have great influence on weld formation and mechanical properties