DEVELOPMENT AND COMPARATIVE EVALUATION OF CONTROLLED WATER JET IMPINGEMENT COOLING SYSTEM FOR HOT-ROLLED STEEL PLATES BY MECHANICAL AND METALLURGICAL ASSESSMENTS

Design and development of Water Jet Impingement Cooling System for improving mechanical and metallurgical properties of steel using locally sourced materials was carried out. The modification comprised the 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 the steel mill industry. Comparative performance results revealed an 8% increase in the cooling rate of the improved system over the existing technology. Results further showed that with a test-plate initial temperature at 550oC, a controlled cooling temperature of 160oC was achieved which produced film and nucleate boiling heat extraction effect. This influenced the microstructural properties of the test plates. The plates post treatment examinations of the grain microstructure and mechanical properties revealed good martensite-phase transformation and enhanced "advanced-steel" hardness of Rockwell 59.9 respectively. In addition, the impact energy test showed a good value range of 56 to 63J which compared favorably with AISI standard of 44.3J. This, therefore, gave 53% hardness and 26% to 42.2% impact of improved mechanical and hardened martensite needle-like structure of metallurgical properties thereby saving the high cost of alloying.