Shielded Metal Arc Welding

Abstract

The welded two pieces steel was done by shielded metal arc welding (SMAW) using E-6013 electrode. The welded sample is characterized by different microstructures as seen in the images. This microstructural difference in the welded joint caused variation on the hardness of the welded metal. The objective of this research work was to investigate these differences in hardness using Rockwell hardness test in relation with microscopic observations of the welded sample while considering the effects of annealing and quenching media.

Introduction

Welding is a process in which materials of the same fundamental type or class are brought together and caused to join (and become one) through the formation of primary (and, occasionally, secondary) chemical bonds under the combined action of heat and pressure.

Producing welds is fundamentally a simple process: Just cause large numbers of atoms of the base materials comprising joint elements to come together to equilibrium spacing. The result will be one piece from many, with continuity of structure and properties at both a microscopic and macroscopic level. In reality, the situation is complicated by the presence of asperities on the surfaces of real parts that limit the points of intimate contact, as well as by the presence of intervening layers of contaminants in the form of oxide or tarnish layers, adsorbed gases or moisture, or paint, grease, oil, or dirt. The two principal means to overcome these impediments are to employ heat and pressure in some combination, from one extreme to the other. When done well, welding offers several advantages over other methods of joining, but, as for all things in life, not without some limitations and sacrifices. [Ref. 1]

Methodology

During the experiment two steel samples were used. They were laid parallel to each other. The metal pieces were joined together by arc welding. The electrode was evenly deposited evenly from one end of the joint to the other. After welding, the sample was quenched using ice cold water. Then the sample was taken from the pail of ice cold water and was cut into pieces perpendicular to the weld to reveal the cross section. The pieces of metal were grinded using SiC paper with increasing grit size, polished with the polishing wheel using alumina and etched for microstructural analysis. Three samples were used for hardness test. Areas starting from the center of the weld proceeding away towards the periphery were tested for hardness.

Results and Discussion

In its broadest context, welding is a process in which materials of the same

fundamental type or class are brought together and caused to join (and become one) through the formation of primary (and, occasionally, secondary) chemical bonds under the combined action of heat and pressure (Messler, 1993). The definition found in IS0 standard R 857 (1958) states, “Welding is an operation in which continuity is obtained between parts for assembly, by various means.”

In welding, materials are made one by establishing continuity. A weld can be made homogeneous, as when two parts made from the same austenitic stainless steel are joined with a filler of the same alloy, or they can be made to be intentionally dissimilar (heterogeneous), as when two parts made from gray cast iron are joined with a bronze filler metal. In short, the key is achieving continuity of structure by forming chemical bonds, and this limits possibilities to like types even if not identical compositions of materials. It is this goal that often places additional constraints and demands on the welding process as it is selected and applied. Creating a weld between two materials requires producing chemical bonds by using some combination of heat and pressure. How much heat and how much pressure are partially dictated by the inherent nature of the materials being joined. But, how much heat and how much pressure also depend on the nature of the actual parts or physical entities being joined.

Shielded metal arc welding process (SMAW) is also known as the stick welding process. This process involves metal coalescence which is produced by the heat from an electric arc that is maintained between the tip of flux-coated, stick electrode and the surface of the base metal being welded. A core wire conducts the electric current from a constant current power supply to the arc and provides most of the filler metal to the joint. Some portion of the arc heat is lost to the electrode by conduction, and some source power is lost as heat. The covering, coating, or flux ...