DOI: 10.36347/sjet.2018.v06i04.004

Pages: 127-138

Cooling of the steel on the run-out table system was done through impingement water jets on the top of hot steel plates to study microstructural phase transformation of the final product and its hardness .Controlled accelerated cooling system was designed and developed for this target in order to achieve the desired mechanical properties of the final steel products. In order to achieve this goal, the microstructural and hardness test of the workpiece before and after was conducted. The examinations of microstructural phase transformation of pipe diameters, D, of 20mm, 25mm, 32mm and 45mm, and impingement gaps, H, of 40mm and 70mm from austenite temperature of 9200C and exposed to surface temperatures of 4380C and 4700C were investigated. The cooling was controlled at 2000C. The control sample had 39.9 hardness number before heating. However, after heating and impingment cooling, the examinations revealed hardened phase transformed needles of marensitie with hardness number 59.5 from control of 39.9, for pipe diameter, D, of 20mm and H = 70mm. Moreover, the examinations also revealed hardened phase transformed needles of martensite with hardness number 70 from control of 39.9, for pipe diameter, D, of 45mm and, H, of 70mm. The results suggested that better advanced steel grades occurred with marensitic phase with hardness number 59.5 that falled within RHN range.