THERMAL INFLUENCE ON THE MICROSTRUCTURE AND THE MICRO HARDNESS OF A CARBON STEEL WELD PROBES

During welding, the heat produced during the process can affect the microhardness and the microstructure of the material. The change in the microstructure and the microhardness can be discovered by carrying out a microhardness test on the welded sample and compare changes in the three different zones i.e the base, the weld and the Heat affected zone or by carrying out a micro structural examination on the welded sample and see the grain dispersion in relation to their sizes. In this work, weld quality of manual arc welded samples of low-carbon steel St3spdestined for bridge construction to be used in Cameroon has been investigated. After a chemical analysis of the material, a micro hardness test and a micro structural examination was also done. Results show that a composition of pearlite and ferrite was seen with the print of the id enter of the micro hardness test. The formation of pearlite and ferrite in base metalis composed of 20/80 respectively. For weld zone and HAZ it changes due to thermal processes. So the microstructure analysis shows that the base metal is a ferrite and pearlite having a grain size of 11-12 on a scale corresponding to an average grain diameter ≈ 7 microns. The structure of the weld metal is also made up of ferrite and pearlite with columnar crystals of cast metal. The HAZ is made up of Widmanstätten. The width of the HAZ zone is about 1,5 mm. In different areas of heat affected zone is observed fine-grained ferrite-pearlite structure with a high degree of dispersion.