An exact solution was developed for a quasi-steady-moving-interface heat transfer problem in laser transformation hardening by a beam customized to a flat-top rectangular shape. The absorption and release of the latent heat were taken into account. The solution provided the body temperature, heating rate, and subsequent cooling rate. Using the IT and CCT diagrams, the rapid austenitization and pearlitic/martensitic phase transformation were determined for prediction of the hardening effect. In the experimental study, a diffractive optical kinoform (130K) was used to customize a conventional Gaussian laser spot beam to a flat-top rectangular beam. A reasonable agreement between the theoretical predictions and the experimental measurements was obtained. (c) 2007 Elsevier Ltd. All rights reserved.