Abstract. The hot deformation behavior of HSLA steel was investigated by using a MMS-200 thermal mechanical machine at different conditions and with deformation temperature of 800-1100 o C and strain rate of 0.1-10 S -1 . FEM was analyzed the deformation characteristics of hot compression through Deform-3D software. It was discovered that the flow stress increases with increasing strain rate and decreasing temperature. The activation energy and stress exponent during hot deformation were calculated using hyperbolic sine constitutive equations. The result from the experiment represents the activation energy and stress exponent during hot compression of 222.256 kJ/mol. and 10.84. The prediction of distribution stress values from the constitutive equation in Deform-3D can be matched with the experimental results. IntroductionHigh strength low alloy steel (HSLA) is a type of steel widely used for structural construction. Steels with low carbon content and very small additions of strong carbide or carbonitride forming elements such as Nb, V, and Ti to strengthening precipitation and grain refinement are called microalloyed or high strength low alloy steel [1]. These steels are much stronger and tougher than ordinary carbon steels, more ductile, highly formable, weldable and highly resistant to corrosion. Nowadays, HSLA steel has been improved with suitable chemical composition and thermo mechanical treatment in order to reinforce its application in heavy industries and automotive. Recently, HSLA steel has been investigated for several features, including its hot deformation behaviors. Hot deformation process is necessary to improve the effectiveness of HSLA steel. With the increasing use of FEM (finite element method) to simulate the specimen behavior under the various parameter of compression test. The relationships between the constitutive equation and the relating process variables such as strain rate and temperature to the flow stress of the deforming material is required, and it is important to calculate the flow stress [2]. Flow stress can be defined as the resistance of a material against plastic deformation and it is expressed as a function of temperature, strain, and strain rate. Hence, FEM technique provides an effective approach for evaluating and determining the distribution and variation of thermo mechanical parameters in deformed specimens during hot working [3,4]. In this paper, the influence of characteristic hot deformation behavior of HSLA steel during compression test at different temperature and strain rate will be investigated. The general constitutive equations were used to determine the hot deformation constants of the material from experimental