A stainless steel surface of 0.25 mm thickness at 800 ± 10ºC initial temperature was quenched by the jetimpingement cooling method. The transient surface heat flux was determined during surface quenchingwith three different jet diameter The flow of water at 22 ± 1ºC temperature was regulated to maintain thejet Reynolds number in a range of 5000–24 000. The observations were made form the stagnation pointto the 12 mm downstream spatial location. The quenching performance of the horizontal test surface wasevaluated on the basis of maximum surface heat flux obtained during transient cooling.It was observed that the maximum surface heat flux increases with the rise in jet diameter and becamethe highest for the largest jet diameter at Re = 24 000. The correlations developed to determine the max-imum surface heat flux was able to predict the experimental data well within the error band of ±15%.