Effect of shielding gas on the properties and microstructure of melted steel surface using a TIG torch

Abstract

This version is available at https://strathprints.strath.ac.uk/49507/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output. Abstract. A surface engineering technique based on a Tungsten Inert Gas (TIG) torch was used to melt single tracks on the surface of a micro-alloyed steel with a hardness of 150 HV. The influence of three shielding gases, argon, helium and nitrogen, on the microstructure and hardness of the resolidified surfaces was analyzed. Effect of Shielding Gas on the Properties andIn all melting techniques, the heat generated by the source is normally conducted to the substrate ahead of the torch, and has been described as 'preheat'. This leads to a gradually higher substrate temperature, from the start to the finish of a melted surface track. The aim of this research was to analyze any inhomogeneities in the microstructure, due to 'preheat', which is rarely considered in the published literature. Three thermocouples were located along the melted track in order to record the temperature at three different points. An energy input of ~ 840J/mm was used in each experiment and the results show that the maximum temperature recorded by the last thermocouple, N o three (subjected to the preheat), for argon, helium and nitrogen gas was 590 ºC, 1120º C and 740 ºC respectively, where a difference of 150 ºC and 200 ºC was registered between the first and third thermocouples when using helium and nitrogen respectively. The corresponding hardness values were 170 HV, 162 HV and 225 HV, and the corresponding surface roughness values were 6 µm, 12 µm and 25µm. A decrease of almost 60% in the roughness value was observed between the initial and last stage of the melted track, when using argon as shielding gas.

Silicon carbide particulates incorporated into microalloyed steel surface using TIG: Microstructure and properties

“…However, in the present work, substantial increases in the microhardness were recorded. Initially, this result was not entirely unexpected, as previous work with lasers and TIG employing higher energy inputs than the present work but with similar volumes of SiC powder, reported SiC particles along with iron silicides, contributing to an increased hardness [26,[28][29][30][31].…”

“…A modified surface of hardness >1000Hv to a depth ≥1.4mm was developed. This study was expanded by Muñoz-Escalona et al [31], who found that substituting helium for argon as the shielding gas in single track TIG processing, reduced the melt zone hardness due to the significantly higher temperatures recorded in the parent microalloyed (MA) steel. Changes in heat input, shielding gas, and alloying powder composition, volume fraction and size, can also influence the surface roughness.…”

Effect of silicon carbide particle size on microstructure and properties of a coating layer on steel produced by TIG technique

“…3, in general there are higher values of temperature registered at the end of the melted track, where an average increase of ~50C was obtained between the start and the end of the melted track. This small increase is associated to a pre-heat process [18][19]. As observed, the temperature increased when SiC particles were incorporated.…”

“…In a study by Patel et al [18], ~5µm SiC was dissolved into a microalloyed steel using a TIG torch, with argon as the shielding gas, to produce a modified surface of hardness >1000Hv to a depth ≥1.4mm. Muñoz-Escalona et al [19], found that substituting helium for argon as the shielding gas in single track TIG processing, reduced hardness, due to the significantly higher temperatures recorded in the parent steel. Changes in heat input, shielding gas, and alloying powder composition, volume fraction and size, can also influence the surface roughness.…”

Comparison of empirical and predicted substrate temperature during surface melting of microalloyed steel using TIG technique and considering three shielding gases

“…Both techniques require a gaseous shielding atmosphere, usually 2, Ar, He, CO2 or mixture of these gases. The shielding gas protects the metal transfer stream and the molten weld pool from contamination resulting from dissolution from the atmosphere of nitrogen, oxygen and water vapour , which often have a deleterious effect on the mechanical properties of the modified surface ] [13][14][15][16][17]. Shielding gases also provide a medium for the electrical current to flow in the plasma jet between workpiece and electrode.…”