Effect of plasma beam irradiation on the microstructure and phase composition of high-speed steel R6M5

Abstract

Abstract The present study is devoted to research into the morphology and structural-phase state of an R6M5 high speed steel surface layer after it was affected by a plasma beam. It was discovered, that R6M5 steel is a multi-phase material with an α-phase, γ-phase (retained austenite) and carbide phase just as in the initial state. The main phase component of the R6M5 steel matrix before and after plasma beam processing was an α-phase (γ → α’-martensite): lamellar and lath martensite; but lamellar martensite is dominated by a volume ratio ~90 % gross share α’-martensite. The γ-phase as the second morphological component of the steel matrix (retained austenite) yields within the martensite plates the form of twintype colonies with a volume ratio of ~6 %. It was established that there were М6С -type carbide particles of complex composition (Fe,W,Mo)6C in the material just as in the initial state. It should be said that in its initial state, the dislocation structure, formed under the effect of the plasma beam, is characterized by fairly high value of excess density of dislocations with an average value of ρ± = 2.0 × 1010 cm-2 (in the initial state ρ± = 1.7 × 1010 cm-2) along with scalar density. The depth of torsion curve of the face-centered space lattice in the α’-martensite is χ = 500 cm-1 (in the initial state it is equal to χ ~436 cm-1), the amplitude of the inner long-distance voltage is σ∂ = 280 МPа (in the initial state it is equal to σ∂ = 260 МPа). Thus, the amplitude of shift voltage is equal to σL = 420 МPа (in the initial state it is σL = 350 МPа); nevertheless, σL > σ∂ remains the mean torsion-curve of the fcs-lattice of α’-martensite maintaining its lamellar nature after the effect of the electron beam much as in the initial state.