With the non-staggered grids,a three-dimensional quasi-state laser remelting problem,considering heat transfer and fluid flow,is numerically simulated.A modified momentum interpolation scheme is used to solve momentum equations associated with SIMPLE algorithm.Numerical results show the important effect of surface tension temperature coefficient ∂γ/∂T on the fluid flow pattern.For ∂γ/∂T being -3.5×10^-6,there is a first flow loop along clockwise in the melted pool;For ∂γ/∂T being -3.5×10^-4,there is a secondary flow loop induced by the first flow loop.On the contrary,the first flow loop along anti-clockwise exists when ∂γ/∂T is+3.5×10^-4.Laser surface phase transformation hardening (including laser remelting) experiments on HT200 cast iron blocks were carried out using a continuous wave CO₂ laser.The width and depth of the phase transformation hardened zone were measured.The numerical results are compared with experimental data.