Uniaxial hot compression tests performed on a HDS-20 Hot Deformation Simulator were utilized to compare the influence of niobium amount on hot flow stresses of these steels. For both steels, the temperature range from 700 °C to 1200 °C in combination with the nominal strain rate range from 0.1 s-1 to 100 s-1 were investigated. A unique computing method was employed to correct the shape of the experimentally obtained hot flow stress curves influenced by the barrel-like shape of the test samples at high strains. Decrease in temperature led to an increase in hot flow stress. The same influence had an increase in strain rate. The hot flow stress of the steel S355J2H is almost at each temperature higher when compared to the steel P355NH. Nevertheless, different flow stress behavior was observed at small strain rates.Keywords: HSLA steel, uniaxial hot compression test, flow stress curves, peak stress
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