Evaluation of PWHT in ASTM A743 steel by analyzing microhardness and metallography data

Abstract

Introduction: ASTM A743 grade CA-6NM stainless steel is used material in the construction of hydraulic turbines due to its excellent mechanical properties, for this reason, its cost is quite high, that is why it is important to resort to repair procedures such as welding to maximize its useful life. Objective: To evaluate the influence of post-weld heat treatment through the analysis of microhardness values ​​obtained in a weld bead, using E410NiMo-15 welding rod as filler material. Methodology: The methodology applied was of an experimental type, the Vickers microhardness test was developed, and the indentations made were every 500µm in the molten zone and every 200µm in the thermally affected zone both in the horizontal and vertical directions with respect to the welding axis. Results: The effect of the thermal treatment was evidenced in the reduction of the hardness with an approximate of 12.68% in the root of the cord and similar values ​​in the other zones of the weld pit, considering the measurements obtained from the test, the width of the thermally affected zone is approximately 2.5mm, while the microstructural analysis shows a reduction in the grain sizes of the tempered martensite in all the zones after the PWHT, with a decrease in the size of the needles of the martensitic matrix. . Conclusion: The effect of post-welding heat treatment was evidenced by analyzing the microstructural changes that occurred, added to this, a homogenization of hardness was obtained in all areas of the weld, however, it is concluded that by subjecting the material to a process of repair by welding its mechanical properties are reduced, shortening its useful life.