Effect of Annealing Temperature on the Microstructural and Mechanical Properties of Wire Rod Steel Annealed Using a Biomass Gasifier

Natural and liquefied petroleum gases are widely used in industrial heat treatment. However, the rising cost of gas, combined with increased demand, has significantly impacted production costs and the environment. The annealing process typically relies on natural or liquefied petroleum gases as the primary heat source. In this study, we aimed to investigate the use of biomass fuel as a replacement for fossil fuels and to evaluate the mechanical properties and microstructure of wire rod steel after annealing using indirect heat from a gasifier. We experimented to examine the effects of annealing temperatures of 650 °C, 700 °C (below the critical temperature Ac1), and 750 °C (above Ac1 but below the upper temperature Ac3). The batch furnace, made of stainless steel, was modified from a traditional wire annealing furnace that originally used CNG and LPG gas burners. It was adapted into a wire annealing furnace connected to a cross-draft gasifier. The furnace’s interior was designed with spiral cooling fins to minimize energy consumption and shorten annealing time. Additionally, it was modified to use biomass as a substitute fuel, reducing environmental pollution. The furnace was coated with thermal insulation, and the biomass gasifier stove was a cross-draft device with primary air feeding at 20 m 3 /h and secondary air supplied at a constant flow rate of 32 m 3 /h, 36 m 3 /h, or 40 m 3 /h. As a fuel source, we used eucalyptus. The mechanical properties of wire rod steel were measured in terms of tensile strength and torsion, following the TIS 138-2562 standard. This standard specifies that the tensile strength must be at least 260 MPa. Regarding torsion, the TIS 138-2562 requirements state that the wire must withstand at least 75 rounds of twisting without breaking. Our results showed that after annealing at 650 °C, 700 °C, or 750 °C, with a soaking time of 30 min and subsequent cooling in the furnace at natural temperature for 24 h, the tensile strength values were 494.82, 430.87, and 381.33 MPa, respectively. The torsion values were 126.92, 125.8, and 125.76 rounds, respectively. Additionally, ferrite grain size increased with annealing temperature, reaching a maximum of 750 °C. The total annealing duration for each batch was 2 h and 40 min at 650 °C, 2 h and 10 min at 700 °C, and 2 h at 750 °C.