Behavior of Tempered Surface Nanocrystalline Structures Obtained by Mechanical-Pulse Treatment

The influence of tempering on the structure, phase composition, and mechanical properties of the surface nanocrystalline (NCS) layer on 40Kh (0.4С-1Cr) steel obtained by mechanical-pulse treatment (MPT) was studied. It was revealed that tempering in the temperature range of 200–500 °C did not have any effect on the phase composition of the strengthened NCS layer contained from α-Fe, but it essentially influenced on its microhardness, grain size, and value of relative stresses in ferritic lattice. All carbon in the NCS surface layer was in atomic state at grain boundaries, since no martensite and cementite in the phase composition of the surface layer was detected by X-ray analysis. The specimens made of 40Kh steel treated by MPT and tempered at 300 °C with minimal grain size was characterized by the highest wear resistance despite the reduced microhardness in comparison with the other specimens tempered at another temperatures.