EFFECT OF BEVEL ANGLES AND HEAT INPUT ON MECHANICAL AND MICROSTRUCTURAL PROPERTIES OF MILD STEEL WELDMENTS

Abstract

The effect of bevel angles and welding heat input on mechanical and microstructural properties of mild steel weldments was carried out in this work. Two pairs each of 150 x 50 x 10 mm mild steel specimens with bevel angles of 30o, 45o, 60o and 90o, were manually welded with electric arc welding process. The welded specimens were grouped into two sets; one set was annealed, and the other left untreated. The two sets were subjected to microstructural analysis of the weldments and the Heat Affected Zone (HAZ). This was followed by mechanical testing for hardness and tensile strength. Results showed that the heat input for optimum mechanical properties is 60o bevel angle (13.61 KJ/mm). The hardness is maximum for the weldment at bevel angle of 60o (173.2 Hv) untreated sample while for the HAZ and the base plate, maximum hardness was attained at 45o (199.5 Hv and 174.5 Hv) bevel angle untreated sample. 45o bevel angle has the maximum tensile strength (410.92 MPa) at yield for as – welded sample while 60o bevel angle has the maximum tensile strength (308.90 MPa) at yield for the heat treated (annealed) sample. The maximum ductility was found to be at 45o bevel angle untreated sample for the as – welded sample and 60o bevel angle has the maximum ductility for the heat treated (annealed) samples. The maximum ultimate tensile strength was attained at 45o bevel angle untreated while 60o bevel angle has maximum ultimate tensile strength for the heat treated samples. The microstructures indicated the presence of ferrite (α) and pearlite (α + FeC3). The microstructure has finest grain at 45o bevel angle untreated sample as compared with the base metal as – received sample.