Evolution of the residual stress state in a duplex stainless steel during loading

Reverted austenite in PH 13-8 Mo maraging steels

Precipitate evolution and strengthening behavior during aging process in a 2.5 GPa grade maraging steel

The load sharing between phases and the evolution of micro- and macrostresses during cyclic loading has been investigated in a 1.5-mm cold-rolled sheet of the duplex stainless steel SAF 2304. X-ray ...

Load sharing between austenite and ferrite in a duplex stainless steel during cyclic loading

Materials with submicron to nanometer-sized grains by virtue of their high grain boundary area to grain size ratio provide valuable tools for studying deformation behavior in ultrafine-grained structures. In this regard, the well-known strain-induced martensite transformation and its reversal to the parent austenite phase were used to produce nanograins/ultrafine grains via controlled annealing of heavily cold-worked metastable austenite. The results of the electron microscopy study of phase-reversion-induced microstructure and deformation behavior of nanograined/ultrafine-grained (NG/UFG) austenitic stainless steel during tensile straining are described here. The phase-reversion-induced structure was observed to depend on the cold rolling reduction and temperature-time annealing cycle. The optimized structure consisted of nanocrystalline (d < 100 nm), ultrafine (d ≈ 100 to 500 nm), and submicron (d ≈ 500 to 1000 nm) grains and was characterized by a high yield strength (800 to 1000 MPa)–high ductility (30 to 40 pct) combination. Austenite nucleation during phase-reversion annealing occurred in the form of thin plates or as equiaxed grains along the martensite laths. Twinning and dislocation glide were identified as the primary deformation mechanisms, where twinning had a varied character. However, the high elongation seems to be associated with the gradual transformation of metastable austenite, with twinning having only a minor contribution.

Microstructure and Deformation Behavior of Phase-Reversion-Induced Nanograined/Ultrafine-Grained Austenitic Stainless Steel

Changes in the lattice parameter of martensite phase in a maraging steel is measured as a function of ageing temperatures. A decrease in the lattice parameter is observed when aged between 400–650°C which is attributed to the depletion of alloying elements in the martensite matrix as a consequence of precipitation and austenite formation. An increase in the lattice from 650 to 710°C was characteristic of enrichment of alloying elements in the martensite matrix due to dissolution of austenite phase. A minimum value of the lattice parameter of martensite is observed at 650 °C which coincides with the maximum vol % of retained austenite. Electrical resistivity, hardness measurements, andin situ high temperature dilatometry was also carried out to delineate various precipitation reactions that occur in this steel.[/p]

Lattice changes in the martensitic phase due to ageing in 18 wt% nickel maraging steel grade 350

Austenite reversion was studied in 18% Ni 350 grade maraging steel. The samples were heat treated from room temperature to the austenite phase field and, without holding, they were cooled again to ambient temperature. The reverted austenite which was retained after this heat treatment was examined using a scanning transmission electron microscope equipped with an energy dispersive spectroscopic system. Two morphologies of the austenite were observed. The first forms at the martensite lath boundaries and the other nucleates inside the martensite laths in the form of Widmanstatten plates. These Widmanstatten plates mostly appear as coupled twins. The coupled twins have a distinct midrib which was found parallel to (1 1 1)γ and (1 1 0)α planes. The latter morphology of austenite appeared only after the formation of Ni3Ti precipitates. Growth of Fe2Mo precipitates was not observed in this heat-treatment cycle. Both Nishyama–Wassermann and Kurdjumo–Sachs orientation relationships were found between the austenite and martensite phases. On the basis of these results, it can be suggested that intra-lath-reverted austenite is formed on or by the local dissolution of Ni3Ti precipitates. © 1998 Kluwer Academic Publishers

The formation of reverted austenite in 18% Ni 350 grade maraging steel

Alkaline-earth stannates having the general chemical formula MSnO3 (M = Ca, Sr and Ba) have been projected as potential electronic ceramics. In view of the information gaps in the reported research, a vigorous and systematic investigation on these exotic materials has been carried out. In this communication, the synthesis of CaSnO3, SrSnO3 and BaSnO3 via sol-gel technique is reported. Infrared spectroscopy and X-ray analyses of various gel samples with different thermal history helped in identifying the reaction pathways and the stage where amorphous gel to crystalline phase transition occurred. Grains of submicron size with narrow size distribution and spherical morphology, were the most noticeable characteristics of sintered calcium metastannate derived by sol-gel method. In the case of barium analogue, a fascinating ‘sugar cube’ structure (akin to that observed in solid-state reaction and the self-heat-sustained reaction derived samples) having improved density characteristics evolved at low sintering temperatures. This gradually transformed into a more familiar spherical granular motif with improved density characteristics as the sintering profiles were varied from 1200 °C/24 h to 1500 °C/2 h. This seems to be an inherent feature of this system, irrespective of the method of synthesis.

http://www.eng.utoledo.edu/~aazad/pdf/MSnO3-solgel.pdf

Phase evolution and microstructural development in sol-gel derived MSnO3 (M = Ca, Sr and Ba)

Long lengths of Bi-2223 conductors doped with Ag, Nb and B were fabricated. The recrystallization of the glasses during various heat treatments was studied by differential thermal analysis (DTA), differential scanning calorimetry, X-ray diffraction and resistivity measurements. Activation energies and frequency factors for crystallization were determined by non-isothermal DTA, employing different models. It was found that both the peritectic transition and the reaction rate were dependent on the ambient atmosphere. Kinetic studies under different atmospheres revealed that the thermal stability of Bi-2223 was greatly enhanced under an oxygen atmosphere. Jc measurements at 77 K showed an increase on silver addition. Furthermore it was found that the silver addition does not destroy the superconductivity. © 1998 Chapman & Hall

Fabrication and transport properties of long-length doped Bi1.7Pb0.3Sr2Ca2-xMxCu3Oy conductors (M=B, Nb or Ag)

Remanit dual-phase stainless steel in the annealed state was studied after 20% tensile deformation in 0, 45 and 90 ° with respect to the rolling direction and subsequent ageing at 475 and 850 °C for 3 h, and water quenched for texture development in ferrite and austenite phases by ODF analysis. It is concluded that 20% tensile deformation leads to deformation of both ferrite and austenite phases. The degree of deformation of the respective phases is dependent upon the deformation direction. Furthermore, the texture for the ferrite phase changes distinctly after ageing at 475 or 850 °C, but the texture for the austenite phase remains unaffected. Thus it may be concluded that ageing treatment leads to change predominantly of the ferrite phase.

A. Ul Haq

Papers

Lattice changes in the martensitic phase due to ageing in 18 wt% nickel maraging steel grade 350

The formation of reverted austenite in 18% Ni 350 grade maraging steel

Phase evolution and microstructural development in sol-gel derived MSnO3 (M = Ca, Sr and Ba)

Fabrication and transport properties of long-length doped Bi1.7Pb0.3Sr2Ca2-xMxCu3Oy conductors (M=B, Nb or Ag)

Influence of ageing on the texture development of tensile-deformed duplex steel