The effect of heat treatment on mechanical properties and microstructure of low carbon steel welded joint with ER70s filler metal

Ab Radzak, Nur Aliya Alina (2022) The effect of heat treatment on mechanical properties and microstructure of low carbon steel welded joint with ER70s filler metal. Project Report. Melaka, Malaysia, Universiti Teknikal Malaysia Melaka. (Submitted)

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Abstract

Welding process such as GMAW appears to be growing the fastest, with recent years showing the greatest growth. However, the process during welding, rapid heating and cooling takes place which produce severe thermal cycle near weld line region of any metal that gets submerged in the heating zone. Gas Metal Arc Welding (GMAW), sometimes known as metal inert gas (MIG) welding, is a type of welding method in which an electric arc is produced between a consumable wire electrode and the workpiece metal(s), heating, melting, and joining them. The main objective of this study were to study the welded joint of low carbon steel joint with filler metal ER70s. Next, to carry out the non-destructive test by using radiography testing and liquid penetrant inspection. Last but not least,to study the effect of heat treatment on the mechanical and microstructure properties by performing hardness and impact test. Radiography and liquid penetrant test were conducted to investigate the surface defects on the sample. After that, the sample were cut into 9 samples with the dimension of 55mm x 10mm x 12mm using abrasive water jet. The samples were prepared through two types of heat treatment process which is annealing with the temperature of 900˚C and tempering 450˚C. Next, the material characterization were confirmed through optical microscope and Scanning Electron Microscope (SEM/EDX). The macro hardness test were done by using Rockwell machine to evaluate the microhardness behaviour of treated and untreated samples. Meanwhile, for the impact test, the Charpy test were used to determine the relative toughness or impact toughness of the sample. The impact test results showed similar value of three samples with value 49.885J for untreated sample, 49.860J for tempered sample and 49.884J for annealed were tough and strong enough to break at the welded connection, however at the HAZ area, the annealed sample with value 49.884J is stronger than the tempered which have 48.860J and untreated samples with 47.885J. At annealed sample, the result of the graph showed that the line pattern of each area were in average compared to graph of untreated and tempered sample. Even though the line pattern of annealed sample were in average, but the annealed sample have the lowest value of hardness at HAZ and weld joint compared to tempered and untreated sample. Next, by performing SEM, it shown the presence of Iron (Fe) in the welded joint with 94.95% at untreated sample meanwhile after performing a heat treatment test, it showed that the structure has changed by showing the presence of manganese in the welded join area with 97.56% at tempered sample and 92.72% at annealed sample.

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