Investigation the effects of heat treatment on mechanical properties and microstructure of low carbon steel joint with ER70s filler metal

Abdul Hamid, Syahrulnaim (2023) Investigation the effects of heat treatment on mechanical properties and microstructure of low carbon steel joint with ER70s filler metal. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

Welding processes like Gas Metal Arc Welding (GMAW) appear to be expanding at the fastest rate, with the most significant growth occurring in the most recent years. However, the process of welding involves rapid heating and cooling, which results in a severe thermal cycle in the vicinity of the weld line region of any metal that becomes submerged in the heating zone. The GMAW welded process which also referred to as Metal Inert Gas (MIG) that using ER70s filler metal was used to joint the low carbon steel. The aim of this study were to investigate the heat treated of low carbon steel in improved its material's physical and mechanical properties. For the purpose of this project, two distinct types of heat treatment processes, namely tempering and annealing, were utilised as parameters. The next step is to carry out the non-destructive test by making use of radiography testing and liquid penetrant inspection. Last but not least, to perform a hardness test and an impact test in order to investigate the effect that heat treatment has on the mechanical and microstructural properties of the material. A Non-Destructive Testing (NDT) method which is liquid or dye Penetrant Testing (PT) that uses capillary forces to detect surfacebreaking flaws and Radiographic Testing (RT) that use gamma rays to examine the internal structure of the specimen has been carried out. After that, the samples were divided into two different types of samples using a abrasive water jet method. For the heat treatment sample is 50 mm x 10 mm x 10 mm and the sample for impact test has dimensions of 55 mm x 10 mm x 10 mm according to ASTM E23. Annealing at a temperature of 950˚ C and tempering at 500˚ C were the two types of heat treatment processes that were utilised in the preparation of the samples. The material characterization was carry out using an optical microscope Scanning Electron Microscope (SEM) and Energy Dispersive X-ray spectroscopy (EDX). The Rockwell and Charpy was used to evaluate the properties of samples that had been treated and those that had not been treated. The Charpy test was used to determine the relative toughness or impact toughness of the sample before it was subjected to the impact test. The result shows after conduct an non destructive test, there is some defect appear at the surface of the weld joint which is porosity and spatter by using liquid penetrant test but there is no internal structure defect occur after performing an radiography test. After performing heat treatment process, the annealing show the best result in microstructures better than tempering as the grain growth normally and it also prove in increasing in the hardness value through the Rockwell hardness test. Next, after performing an impact test it prove that heat-treated samples are better toughness than untreated samples. The value recorded for annealed was the highest among the other sample which 138.761 kJ/m2 at centre of the weld joint and 75.597 kJ/m2 at HAZ. However by performing SEM the structure shows that only at centre of the joint was in ductile condition while at the HAZ was in brittle fracture. Heat treatment is an important process in the oil and gas industry. Through changes in hardness, strength, toughness, ductility and elasticity of materials, it gives the ability to alter the metallurgical characteristics of piping and equipment to better suit their intended applications.

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