Improved design and comparative evaluation of controlled water jet impingement cooling system for hot-rolled steel plates

Abstract

This work focuses on improved design modification and development of Controlled Water Jet Impingement Cooling System for improving mechanical and metallurgical properties of steel using locally sourced materials. The modification comprised introduction of water pump, adjustable impingement gap mechanism and replacement of complicated hydraulic/chain conveyor mechanism with screw conveyor mechanism. The plant was designed, fabricated and instrumented with temperature and flow probes to simulate the actual operating conditions of steel mill industry. Comparative performance results revealed 8% increase in cooling rate of the improved system over the existing technology. Moreover, with a test-plate initial temperature at 550 °C, a controlled cooling temperature of 160 °C was achieved which produced film and nucleate boiling heat extraction effect. This influenced microstructural properties of the test plates. The plates post treatment exanimations of the grain microstructure and mechanical properties revealed good martensite-phase transformation and enhanced “advanced-steel” hardness of Rockwell 59.9, respectively. In addition, impact energy test showed good value range of 56 to 63 J which compared favorably with AISI standard of 44.3 J. This therefore, gave 53% hardness and 26% to 42.2% impact of improved mechanical and desirable hardened martensite needle-like structure of metallurgical properties thereby saving the high cost of alloying.