Manufacturing Technology Today

S. Rasool Mohideen ¹, K. Angamuthu ¹, G. Thanigaiyarasu ¹, R. Rajendran ¹

Affiliations
1 Department of Mechanical Engg., B. S. A. Crescent Engg. College, Chennai, IN

Abstract

Toughness property evaluation of a weldment is art important step in the analysis of welded structures. Many techniques are being employed for the improvement of welded joints' performance and their properties. This paper discusses the influence of cryogenic treatment on the improvement of toughness of weldments. Deep cryogenic treatment was given to the material and its effect on the toughness was studied by a notch tensile test. To investigate its influence, notched tensile test was conducted on the cryogenically treated weldments and post weld heat-treated weldments and the results were compared. Numerical analysis using finite element method was carried out to support the experimental results. Thermo-mechanical coupled field analysis was performed using ANSYS finite element code. It was found that the cryogenic treatment improved the toughness ofthe weld metal arid the heat affected zone (HAZ). The same result was also observed in the finite element analysis even though there was about 8% error between the experimental and finite element analysis.

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S. Mohamed Nazeer ¹, M. Murugan ¹, S. Rasool Mohideen ¹, Y. V. N. Narasimma Moorthy ²

Affiliations
1 Dept of Mechanical Engg., BSA Crescent Engg. College, Chennai, IN
2 BHEL R&D Ltd, Hyderabad, IN

Abstract

Cryogenic treatment is a process of treating materials, at temperatures well below 0°C to achieve improved mechanical properties. Cryogenic treatment was observed to enhance the mechanical properties of various materials like tool steels, bearing materials, carbon fiber composites and copper resistance welding electrodes. Application of cryogenic treatment as a post weld treatment to weldments is a new area to be studied. In the present investigation, 2.25 Cr 1 Mo low carbon low alloy steel weldments were cryogenically treated and their mechanical behavior evaluated. Changes in microhardness, Charpy V notch toughness and changes in the microstructure were studied. The performance of as welded, tempered, long cycle cryogenic treated and tempered and long cycle cryogenic treated weldments were compared. J-integral as a measure of fracture toughness of the weldments was computed and compared. The long cycle cryogenic treatment was found to result is substantial increase in impact toughness with the marginal reduction in micro hardness. At the micro structural level, that formation of acicular ferrite, grain refinement and precipitation of alloying elements were found to be the basic mechanisms responsible for the increased impact toughness.

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