Eddy-Current Studies of Aging Processes in N26T3 Metastable Austenite Steel

In the N26T3 austenite steel, the eddy-current parameter f ₀ has been measured after one aging cycle at temperatures of 700 and 650°C, and after two aging cycles, one of them at the same temperature and the second at 600 and 550°C. The two-stage aging is conducted by two schemes: (1) preliminary aging at 700 or 650°C, transfer of samples without cooling to the room temperature into a furnace heated to 600 or 550°C, then isothermal aging and cooling to room temperature T _r; (2) the same operations as in the first scheme, but the samples are cooled to T _r after the preliminary aging. The eddy-current parameter f ₀ measured at T _r increases with time after aging at 700 and 600°C owing to isothermal martensite transformation. After the two-stage aging, the isothermal martensite transformation at T _r still takes place, but it is stabilized, i.e., the parameter f ₀ drops with time. The stabilization of the austenite is the more pronounced, the lower the temperature of the second stage of aging, and it is stronger after the two-stage aging by the second scheme.     

Effect of structure of aging metastable austenitic steels on the signal from an eddy-current transducer

Eddy-current parameterf ₀ of the N26T3 steel has been studied as a function of both the aging temperatureT _ag=20–800°C and the time τ of exposure to a constant temperature of 550 and 600°C up to 6h. In the initial state, the steel had two phases: (1) cooling-induced martensite+austenite (α+γ) or (2) strain-induced martensite+austenite (α′+γ). The parameterf ₀ drops monotonically as τ increases, and this drop is the faster, the higherT _ag. The parameterf ₀ changes nonmonotonically with the aging temperature. In addition to the initial two-phase structures, the one-phase γ structure has also been studied. The parameterf ₀ grows monotonically with the plastic cold strain and changes nonmonotonically with the aging temperature (20–800°C). Observed changes inf ₀ have been explained.     

Catastrophic corrosion cracking of Cr-Mn-V aging austenitic steels

Investigations were carried out into the processes of corrosion cracking in a 3.5% aqueous solution of NaCl of 40Kh4G18F and 35Kh12G24F2M austenitic steels hardened by carbide aging, in comparison with Kh12N18T3 and Kh18G20A0.5 austenitic steels subjected to intermetallic and solid solution hardening, respectively. The Cr-Mn-V steels were characterized by a catastrophic reduction of corrosion cracking resistance at loads of=(0.1-0.9) _air associated with weakening of grain boundaries during precipitation of large carbides VC and Cr₂₃C₆. An increase of the grain size is accompanied by a further reduction of corrosion resistance caused evidently by enrichment of the grain boundaries with impurities. The acoustic emission method was used to examine the kinetics of defect formation in examined steels in corrosive medium. The results showed advancing cumulation of microcracks under loading in the aging Cr-Mn-V steels under the effect of salty and distilled water which leads to catastrophic failure in holding for 1–4 h. Microcrack cumulation under loading at = 0.9_air in a 3.5% aqueous solution of NaCl was insignificant in steels with intermetallic (Kh12N18T3) and solid solution (Kh18G20A0.5) hardening because no second phase precipitated at the grain boundaries.Translated from Problemy Prochnosti, No. 1, 51–58, January, 1991.The authors are grateful to E. N. Frizen and A. I. Uvarov for help in the investigations.     

An Eddy-Current Study of Decay of Oversaturated Solid Solution in N32T3 Invar

The eddy-current parameter f ₀ has been studied as a function of temperature and aging time for the N32T3 Invar. Two initial states have been involved: those after quenching and after cold plastic deformation. The rise in the temperature and time of aging reduces the parameter f ₀ owing to the transition of the Invar from the ferromagnetic to paramagnetic state because the oversaturated solid solution decays, and the austenite is depleted of nickel. The parameter f ₀ drops monotonically with the applied strain. In the strained Invar the decay of the oversaturated solid solution reduces f ₀ in the temperature interval of 400 to 600°C.     

Effect of Production Technological Parameters on Corrosion Resistance of Ultralow-Carbon Cold-Rolled IF-Steels

Metallurgist - The influence of production technological parameters on corrosion resistance of cold-rolled ultralow-carbon IF-steels of various compositions (0.003–0.005 wt.% C,...     

A Study of Cellular Decay in Austenite Alloys Using an Applied Eddy-Current Transducer

The eddy-current parameter f ₀ of the N36K10T3 invar has been studied in the range of aging temperatures from 600 to 900°C. The maximal drop in f ₀ has been observed at the temperature T _ag = 800°C, and the drop in this parameter was the larger, the longer the aging process. The drop in this parameter is caused by the cellular decay process in the solid solution, which depletes the austenite of nickel and titanium. The parameter f ₀ increases notably (from 4 to 46 kHz) when crystals of lowtemperature martensite (-phase) are generated in samples of the N26T3 steel with 100% cellular decay. This high value (f ₀ = 46 kHz) persists at T _ag < 400°C and drops by a factor of 4.5 over the interval 400 < T _ag < 600°C because the ferromagnetic -phase transforms to the paramagnetic phase-hardened austenite ( _ph). Aging of the phase-hardened austenite in the steel with cellular decay at T _ag = 700°C increases the parameter f ₀ by a factor of two (from 10 to 20 kHz) because the ferromagnetic -phase is generated when the aged phase-hardened austenite transforms to the martensite (_ph ) as a result of cooling the steel from the aging to room temperature.