Interaction between precipitation, normal grain growth, and secondary recrystallisation in austenitic stainless steel containing particles

Padilha, Angelo Fernando; Dutra, Julio Cesar Sampaio; Randlè, Valerie

doi:10.1179/026708399101506850

Cited by 12 publications

(11 citation statements)

References 25 publications

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“…126) However, even after rapid cooling austenite is rarely the only phase present. The most common phases present after the solution annealing heat treatment are Ti(N, C), TiC, Nb(C, N), Ti 4 C 2 S 2 and oxide inclusions containing variable contents of silicon, chromium, niobium, titanium and aluminum.…”

Section: Time-temperature-precipitation Diagramsmentioning

confidence: 99%

Decomposition of Austenite in Austenitic Stainless Steels

2002

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Austenitic stainless steels are probably the most important class of corrosion resistant metallic materials. In order to attain their good corrosion properties they rely essentially on two factors: a high chromium content that is responsible for the protective oxide film layer and a high nickel content that is responsible for the steel to remain austenitic. Thus the base composition is normally a Fe-Cr-Ni alloy. In practice the situation is much more complex with several other elements being present, such as, Mo, Mn, C, N among others. In such a complex situation one almost never has a single austenite phase but other phases invariably form. Those phases are, with few exceptions, undesirable and they can be detrimental to the corrosion and mechanical properties. It is therefore of considerable importance to study the formation of such phases. In this work the decomposition of austenite in austenitic stainless steels is reviewed in detail. First the binary equilibrium diagrams relevant to the system Fe-Cr-Ni are briefly presented as well as other diagrams, such as the Schaeffler diagram, that traditionally have been used to predict the phases present in these steels as a function of composition. Secondly the precipitation of carbides and intermetallic phases is presented in detail including nucleation sites and orientation relationships and the influence of several factors such as composition, previous deformation and solution annealing temperature. Next, the occurrence of other constituents such as nitrides, sulfides and borides is discussed. TTT diagrams are also briefly presented. Finally the formation of martensite in these steels is discussed.KEY WORDS: austenitic stainless steel; precipitation behaviour; carbides; intermetallic compounds; TTT diagram; strain induced martensite. Phase DiagramsPhase diagrams are important to predict the phases present in the austenitic stainless steels. Nevertheless they have limitations due to the complexity of multicomponent thermodynamic calculations and also due to the transformation kinetics that may prevent the attainment of the equilibrium phases. Regarding the first limitation, the number of relevant components is often more than five and published diagrams are rarely found to contain more than four components. As to the second limitation, the diffusion of alloying elements in austenite can be very slow and the precipitation of certain intermetallic compounds can take thousands of hours. Equilibrium DiagramsIn this section the most relevant features of the binary diagrams 3,4) Fe-Cr, Fe-Ni, Cr-Ni, Fe-Mo, Fe-Ti, Ni-Ti, FeNb, Fe-Mn and Fe-Si are considered. Next the Fe-Cr-Ni and Fe-Cr-Mo ternary diagrams and the quaternary FeCr-Ni-Mo diagram are discussed. The individual characteristics of each phase will be presented later in this review.The two main features of the Fe-Cr diagram, shown in Fig. 1, which are relevant to austenitic stainless steels, are the ferrite stabilizing character of Cr and the presence of sigma (s) phase.The Fe-Ni diagram clearly shows the strong ...

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Section: Time-temperature-precipitation Diagramsmentioning

confidence: 99%

Decomposition of Austenite in Austenitic Stainless Steels

2002

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“…Grain growth in the ASSs is significant only over 950°C in the non-stabilized and over 1 050°C in the stabilized ASSs. 38,67,68) In the stabilized steels, the risk of some abnormal grain growth or secondary recrystallization (see Fig. 8) is greater.…”

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confidence: 99%

“…9 shows that between 1 100 and 1 200°C the risk of secondary recrystallization, due to partial dissolution of the MC carbides, is very large. 38,67) Recent work 69) on high purity austenitic stainless steels showed that carbon, even in solid solution, hinders grain growth.Randle and co-authors 37,70,71) showed that small amounts of cold working (2 to 7 %), increase the tendency towards the appearance of coarse grains during annealing in the 900 to 970°C temperature range and attributed the fact of the occurrence of secondary recrystallization due to deformation (strain induced secondary recrystallization). On the other hand, the best interpretation is in terms of primary recrystallization by strain induced grain boundary migration rather than a grain growth phenomenon.…”

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Annealing of Cold-worked Austenitic Stainless Steels.

2003

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This article reviews the phenomena involved during the annealing of cold worked austenitic stainless steels. Initially the cold worked state is discussed, with special emphasis on the formation of deformation induced martensites. Following, the phenomena of martensite reversion, recovery, recrystallization and grain growth are discussed. The interactions between primary recrystallization and precipitation and between precipitate dissolution and secondary recrystallization are dealt with in detail. Finally, the textures resulting from hot and cold working, and from primary and secondary recrystallization, are presented.KEY WORDS: austenitic stainless steels; work hardening; recovery; recrystallization; grain growth; texture.cold working can be correlated to a lower SFE. 39) Deformation twinning is also dependent on SFE and grain size. Low SFE and large grain size favor deformation twinning. Recent work 40) has shown that deformation twin initiation requires a critical deformation (critical dislocation density). The SFE has an indirect effect by increasing dislocation density and strain hardening in low-SFE fcc metals and alloys. 40) Another aspect that must be remembered is that SFE of the ASSs increases with deformation temperature. 41) In summary, depending on the value of the SFE, two different microstructures may be observed in the cold worked ASSs: for a high SFE, a cellular dislocation distribution without DIM and, for a low SFE, a planar dislocation distribution containing DIM. It is worthy of note that deformation bands can be found in both.In terms of recrystallization, the lower is the SFE, keeping all others variables constant, the larger will be the stored energy during deformation and the corresponding driving force for recrystallization. This subject will be discussed later on in greater detail.ASSs are commonly considered to be materials having a low SFE. Actually the SFE of this class of steels are within quite a large range. [42][43][44][45][46][47] Fig. 2(b)). Several interesting features can observed in this figure. Microstructural analysis using optical microscopy, as shown in Fig. 2(a) for a high SFE ASS, does not allow differentiation between high and low SFE austenitic stainless steels after cold working. Furthermore, at the transmission electron microscopy scale deformation bands may be seen eventually (compare Figs. 2(b) and 2(c)). Monteiro and Kestenbach 49) using transmission electron microscopy observed that dislocation substructure is orientation sensitive, i.e., individual grains develop different substructures, according to their specific orientation and the orientation of their neighbours.As previously mentioned, two types of martensite may occur in the ASSs, namely: aЈ-(bcc, ferromagnetic) and e-(hcp, paramagnetic). The typical lattice parameters are: a aЈ ϭ0.2872 nm and a e ϭ0.2532 nm; c e ϭ0.4114 nm Assuming 50) a g ϭ0.3585 nm, we may conclude that the g→aЈ transformation leads to volume increase of about ISIJ International, Vol. 43 (2003) where the contents are in wt%. Since ...

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“…16) A high pinning force is achieved by a large volume fraction of fine particles. Several authors have studied the effect of microalloying on grain size in carbon steels, [17][18][19][20] but only few deal with austenitic stainless steels, 21,22) especially in the instance of ultrafine grain size. Sawada et al 23) studied the effect of V, Nb and Ti additions on the grain size refinement in type 301L 17Cr-7Ni austenitic stainless steel and demonstrated how microalloying can even lead to submicron grain sizes.…”

Section: Effect Of Nb Microalloying On Reversion and Grain Growth In mentioning

confidence: 99%