S. A. Gerasimov

EFFECT OF PRIOR HEAT TREATMENT ON THE STRUCTURE AND PROPERTIES OF NITRIDED STEELS

Conclusions1.The hardness of the nitrided layer decreases with the elevation of the temperature and time parameters of prior tempering due to coarsening of the nitrides.2.We have suggested a hypothesis that nitrides form in the nitriding process on segregations of the alloying elements formed in prior tempering. With the growth in the tempering parameters (the temperature and the time) the size of the segregations increases, which causes coarsening of the nitrides.

The Influence of High-Pressure Gas Nitriding on the Properties of Martensitic Steels

The influence of high-pressure gas nitriding on the structure and properties of martensitic steels VKS-5, VKS-7, 20Kh3N3MFB, and 25Kh5M is investigated. It is shown that the high-pressure nitriding increases the thickness of the diffusion zone at substantial reduction of the process time as compared to the traditional gas-phase nitriding. Increase of the post-treatment cooling rate above 30 K/min favors the formation of diffusion layers with greater hardness.

Physical fundamentals of criterial estimation of nitriding technology for parts of friction units

Characteristics of the structure and properties of surface layers of nitrided structural steels and alloys, which affect the level of surface fracture under friction, are studied. A generalized structural parameter for optimizing the nitriding process and a rapid method for estimating the quality of the surface layer of nitrided parts of friction units are developed.

Effect of nitriding on wear resistance of iron alloys with various lattice types

The paper considers the characteristics of the formation of the wear-resistant structure of nitrided model alloys with bcc and fcc lattices: Fe-Mo, Fe-Cr, Fe-Al, Fe-Ni-Cr, Fe-Ni-Al, Fe-Ni-Ti, and Fe-Ni-Cr-Al-Ti. The relationships between the structure characteristics of the nitrided layer and the wear resistance of the alloys are found. The maximal wear resistance of the alloys with the bcc lattice of the matrix is shown to be attained when incoherent particles of nitrides of the alloying elements appear; the maximal hardness corresponds to the alloy that contains coherent nitrides. In the alloys with the fcc lattice, the maximal hardening under nitriding and the maximal wear resistance are achieved at the stage that precedes the rupture of the coherent bond between the nitride and the matrix. The relationships between the structure characteristics of the nitrided layer and the wear resistance are discussed from the viewpoint of the formation of a wear-resistant structure state of the alloys.