Empirical Investigation of Carbon Equivalent and Weldability of Rebar Steels Produced by Induction Furnace Mills in South West Nigeria

This study conducts an empirical investigation of the carbon equivalent (CE) values and weldability characteristics of reinforcement bar steels produced by induction furnace rolling mills in the South West geopolitical zone of Nigeria. The weldability of rebar is increasingly important as welded reinforcement couplers gain usage in Nigerian construction practice, yet systematic weldability data for locally produced rebar are absent from the published literature. Rebar samples of 12 mm and 16 mm diameter are collected from ten induction furnace mills in Lagos, Ogun, and Osun States through direct mill sampling. Chemical composition is determined by optical emission spectroscopy. Carbon equivalent is calculated using the International Institute of Welding (IIW) formula and the Pcm formula for low carbon steels. Controlled thermal analysis Bead-on-plate HAZ hardness tests are performed at standard preheat (none) and with 100 and 150 degrees Celsius preheat, following the Tekken (y-groove) weld cracking test modified for rebar geometry. HAZ microhardness traverses are made across transverse weld sections. Findings reveal CE values ranging from 0.41 to 0.68 across the ten mills, with six mills producing rebar with CE above the 0.43 threshold beyond which preheat is recommended for weldability. HAZ hardness peaks above 350 HV are recorded in high CE specimens without preheat, indicating cold cracking risk. Keywords: carbon equivalent, weldability, induction furnace rebar, South West Nigeria, HAZ hardness.