Satya V. Ravikumar

Ultra Fast Cooling and Its Effect on the Mechanical Properties of Steel

The objective of this work is to study about the ultrafast cooling of a hot static 6 mm thick steel plate (AISI-1020) by air assisted spray cooling. The study covers the effect of air flow rate and the water impingement density on the cooling rate. The initial temperature of the plate, before the cooling starts, is kept at 900 °C. The spray was produced from a full cone high mass flux and low turn down ratio air atomizer at a fixed nozzle to plate distance. The cooling rate shows that low turn down ratio air atomized spray can generate ultra fast cooling (UFC) rate for a 6 mm thick steel plate. After cooling, the tensile strength and hardness of the cooled steel plate were examined. The surface heat flux and surface temperature calculations have been performed by using INTEMP software. The result of this study could be applied in designing of fast cooling system especially for the run-out table cooling.

Effect of Oxide Layer in the Ultra Fast Cooling of a Steel Plate

This study deals with the effect of oxide layer during ultra-fast cooling of a hot plain carbon steel plate. In the current research, the hot plain carbon steel plates were cooled from an initial surface temperature of 900°C by using air atomized spray at different air pressures. The heat transfer analysis illustrates that during high pressure air atomized spray cooling, the average surface temperature is almost unaffected by the presence of an oxide layer. For better understanding, the plain carbon steel cooling data have been compared with the data obtained during the cooling of a stainless-steel plate.

Heat Transfer from a Hot Moving Steel Plate by Air-Atomized Spray Impingement

Air-atomized spray cooling of a hot moving AISI 304 steel plate of 6 mm thickness has been investigated experimentally by varying water flow rate and plate velocity at a fixed nozzle-to-plate distance. It is found that the heat transfer coefficient is a non-linear function of surface temperature. The result shows that the cooling rate increases with an increase in the water flow rate. The highest cooling rate has been found for the static plate, whereas for a moving plate, an increasing cooling rate trend has been observed with increasing plate velocity.

Jet Impingement Cooling of a Hot Moving Steel Plate: An Experimental Study

In the current study, a hot moving steel plate of 6 mm thickness with an initial temperature of 900°C has been considered for jet impingement cooling. The experiment has been designed with the help of Design of Expert software to optimize the process parameters based on the highest cooling rate. The various subsurface transient temperature histories have been measured during the cooling process. The surface heat flux and surface temperature were calculated with the help of a commercial inverse heat transfer solver called INTEMP. The experimental result has been presented in terms of cooling rate and critical heat flux.

Ultrafast cooling of medium carbon steel strip by air atomised water sprays with dissolved additives

Abstract Ultrafast cooling is a newly developing heat treatment technique that can be used for the production of advanced high strength steels. Conventional laminar jet cooling is generally fitted in the runout table; however, it cannot provide the higher cooling rates necessary, and air atomised spray cooling can be the best alternative for ultrafast cooling rates. As water is the commonly used coolant, it is beneficial to know the effect of surface active or volatile additives on the cooling characteristics for high heat flux applications. Thus, this study examines the two aspects of the use of enhancement of air atomised water spray cooling process with a mixture of ethanol and surfactant additives. First, additive based cooling of stainless steel strip was evaluated to optimise the cooling rate, then these optimum parameters were used to study the improvement in mechanical properties and microstructure of medium carbon steel compared to pure water ultrafast cooling. The cooling experiments were carried out at a temperature above the Leidenfrost point of the hot strip. A commercial inverse solver called INTEMP was used for the calculation of surface temperature and heat fluxes. It was observed that the addition of surfactants and alcohol enhanced the cooling rate and critical heat flux of the test strip and has higher impact on martensite phase evolution.