The influence of repeated ???-transformations on the structure of iron-nickel alloys

Volosevich, P. Yu.; Gіrzhon, V. V.; Danil'chenko, V.E.

doi:10.1007/bf00700057

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“…Electron microscope research have shown [ 17 ] that, after the first γ-α-γ transformation, dislocation density in reverted austenite increases by three orders and reaches the value of 5 × 10 11 cm -2 , which fully agrees with [ 18 ]. Repeated γ-α-γ transformations slightly increase dislocation density achieved after the first cycle.…”

Section: Resultssupporting

confidence: 75%

“…It is known that dislocation density increases by three orders after the first γ-α-γ transformation. With increased number of such cycles, dislocation density remains almost unchanged although the total length of additional subboundaries significantly increases [ 17 , 18 ]. The up-to-date ability to create ultrafine and nanocrystalline structures of metallic materials opens new prospects for further intensification methods of chemical and thermal treatment (carburizing, nitriding, metallization) due to a significant acceleration of diffusion.…”

Section: Resultsmentioning

confidence: 99%

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The effect of multiple martensitic transformations on diffusion of Fe and Ni atoms in Fe-31.7%Ni-0.06%C alloy

2014

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Diffusion characteristics of iron and nickel atoms were investigated using radioactive isotopes method in phase-hardened metastable iron-nickel Fe-31.7%Ni-0.06%C alloy with nanofragmented structure. It has been found that diffusion mobility of nickel and iron atoms in reverted austenite of Fe-31.7%Ni-0.06%C alloy significantly increases as the result of multiple γ-α-γ martensitic transformations. The diffusion coefficients of nickel and iron in the austenite at 400°C corresponded to the stationary diffusion coefficients at the temperatures above 900°C. The revealed diffusion acceleration at low temperatures is caused by high-density dislocations and additional low-angle subboundaries of disoriented nanofragments of reverted austenite and deformation twin subboundaries formed during multiple γ-α-γ cycles.

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Section: Resultssupporting

confidence: 75%

Section: Resultsmentioning

confidence: 99%

The effect of multiple martensitic transformations on diffusion of Fe and Ni atoms in Fe-31.7%Ni-0.06%C alloy

2014

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Microstructure of phase-hardened iron?nickel alloys

Gіrzhon¹,

Danil'chenko²

1994

Met Sci Heat Treat

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Thermal cycling treatment (TCT), including martensitic transforTrmtion, is an effective method for improving alloy properties. The set of properties for phase-hardened alloys is mainly governed by their structure which in turn dependsStructural changes in iron-nickel alloys after y -+ c~ --, "),-transformation have been studied in detail [1, 2]. There are less data for the effect of repeated TCT in the martensitic transformation range on the structure of steels and alloys and mainly their mechanical properties have been studied [3][4][5].Alloys 50N25 (0.48% C; 25.4 % No) and N30 (0.05% C, 29.7% Ni) have been studied which have an austenitic structure at room temperature. The alloys were melted in a HFC furnace in a protective atmosphere of argon. The charges are used were carbonyl iron, nickel N-I, and spectrally pure graphite. Direct martensitic 3' ~ o~-transformation was accomplished by immersing specimens in liquid nitrogen for -1.5 min. Reverse o~ --, B-transformation was accomplished by soaking for -1.5 rain in a salt bath of the composition 50% NaNO 3 + 50% NaNO 2 at a temperature exceeding A r for the given alloy by 5-10°C. The thermal cycling temperature range was determined magnetometrically. Metallographic analysis of specimen structure was performed in an EPIQUANT light microscope. The structure of mechanically polished specimens was revealed by short-term (1-2 sec) chemical etching in freshly-prepared reagent containing equal parts of hydrogen peroxide and concentrated nitric acid.The microstructure of steel 50N25 in the original condition (n = 0) and after TCT is shown in Fig. 1. It can be seen that the structure of this steel in the original condition is coarse equiaxed grains of austenite with clearly defined boundaries (Fig. la). According to data in [6] the dark areas close to grain boundaries and within crystals are graphite globules.Formation of a typical coarse lamellar structure of reversed austenite after heating to A t-at a rate of 60°C/sec points to the preferred martensitic nature of reverse c~ --, 7-transformation (Fig. lb). Here the grain boundaries and graphite particle distribution differ little from the original.After five cycles of phase transitions the structure of reversed austenite is much refined. In individual boundary areas there is formation of fine grains and the boundaries thicken. A further increase in the number of 3' "-" c~-transformations causes an increase in the number of fine formations both within grains and along their boundaries. The size of the formations is about two order of magnitude less than in the original grains. Boundary continuity is disrupted (Fig. lc) and in a number of cases the boundaries are a network of partly merged fine particles.Repeated thermal cycling (n = 200) leads to formation of specific fiber structure without boundary resolution. Fibers form along the alloy flow direction which proceeds with much shape change for thermally cycled specimens (Fig. ld). There is an increase in the density and fineness of graphite globules in a microsection....

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The influence of repeated ???-transformations on the structure of iron-nickel alloys

Cited by 2 publications

References 1 publication

The effect of multiple martensitic transformations on diffusion of Fe and Ni atoms in Fe-31.7%Ni-0.06%C alloy

The effect of multiple martensitic transformations on diffusion of Fe and Ni atoms in Fe-31.7%Ni-0.06%C alloy

Microstructure of phase-hardened iron?nickel alloys

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