Yu. N. Goikhenberg

Strengthening of stainless steels by deformation, the martensitic transformation, and aging

Conclusions1.In austenitic stainless steels with low stacking fault energies the martensitic transformation during plastic deformation occurs by the scheme γ→ɛ→α, in which austenite is directly transformed to ɛ phase, while α marteniste is formed only in bands of ɛ phase.2.With an equal amount of strain martensite, the strengthening is greater in the case where the transformation occurs with formation of intermediate ɛ phase. This is due to the distribution of transformation products in slip lines and the higher dispersity of α martensite.3.Aging of strain martensite in stainless steels at 400–450°C leads to a substantial increase in strength and some decrease of ductility. These changes are greater in steel Kh18N10T.4.In the reverse martensitic transformation in steel 000Kh18N12 the austenite inherits the strengthening acquired by martensite during prolonged aging.

Study of Low-Carbon Pipe Steel Strain Ageing

Strain aging of pipe steels 06G2FB and 07G2MFB with ferrite-pearlite and ferrite-bainite structures is investigated. It is established that a ferrite-bainite structure is more inclined towards strain aging than a ferrite-pearlite structure. The tendency towards strain aging of steel with a ferrite-bainite structure increases with increasing austenitizing temperature. During hot plastic deformation there is development of recrystallization and the tendency towards strain aging decreases.

Strain aging and the Bauschinger effect in low-carbon pipe steel

Strain aging and the Bauschinger effect in low-carbon ferrite–pearlite and ferrite–bainite pipe steel are studied. Steel with ferrite–bainite structure is more susceptible to strain aging and the Bauschinger effect. After alternating loading, strain aging develops, with increase in the yield point. After alternating loading of already aged steel, the Bauschinger effect appears; it is comparable with the effect in unaged steel.

Complex Hardening of Metastable Stainless Austenitic Steels

Corrosion and mechanical properties of austenitic chromium-nickel and chromium-manganese steels are studied after cold plastic deformation accompanied by formation of martensite and after aging. A steel for the production of membranes and casings of high-pulse-pressure gas sensors is chosen and modes for hardening the steel to obtain the combination of properties required for the production are determined. The inverse transformation of strain martensite into austenite is studied and a combined treatment involving a γ ↔ α transformation and elevating the strength properties at preserved austenitic state is suggested.

Structural transformations and tribological properties of amorphous alloys upon wear at room and cryogenic temperatures

The abrasive wear resistance of the Fe64Co30Si3B3, Co86.5Cr4Si7B2.5, Fe73.5Nb3Cu1Si13.5B9, and Fe82.6Nb5Cu3Si8B1.4 commercial amorphous alloys (ribbon 0.03 mm thick and 12 mm wide) has been investigated under the conditions of abrasive and adhesive wear upon sliding friction. The character of fracture of the surface and structural transformations that occur in these materials upon wear have been studied by the metallographic and electron-microscopic methods. It has been shown that at room and cryogenic (−196°C) temperatures of tests the abrasive wear resistance of the amorphous alloys is two-three times lower than that of tool steels Kh12M and U8. A comparatively small abrasive wear resistance of the amorphous alloys is explained by local softening of these materials in the process of wear. Under the conditions of adhesive wear of like friction pairs at room temperature in air and argon, the amorphous alloys are characterized by the rate of wear that is smaller approximately by an order of magnitude than in steels 12Kh13 and 12Kh18N9. It has been established that upon wear the deformed surface layer of the alloys under study retains a predominantly amorphous state but in local sections of this layer nanocrystalline structures that consist of crystals of bcc and fcc phases and borides are formed. The possible effects of this partial crystallization on the microhardness, friction coefficient, and wear resistance of these alloys have been considered.