The deformation twinning leads to a reduction of the coefficient of strain hardening, i.e. twinning plays an important role in deformation of steel. The contribution of twinning to the total deformation is significant (up to 1/3 of the overall deformation). The final effect of twinning on strain hardening rate depends on the number of factors introduced by the twinning itself in the process of sliding. Calculated Schmid factors for slip systems operating in the matrix and in the twin. The analysis of the twinning geometry in particular grains showed that twinning is primarily developed for systems with the highest Schmid factor. However, twinning was also observed with a minimum and even zero Schmid factor. The obtained results indicate the importance of the orientation of slip planes in the newly formed micro-twins and Schmid factors for twinning. The important role of crystallographic texture in the physics of strain hardening was also shown.