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The effect of quenching-partitioning (Q&P) and quenching-tempering (Q&T) treatments on the stability of austenite and mechanical properties of cold-rolled medium-manganese TRIP steel (0.2% C – 8.5% Mn – 3.0% Al – Fe) is studied. It is shown that the Q&T treatment provides an ultimate tensile strength σr = 1160 MPa and an elongation δ = 53%; the value of σr × δ = 61 GPa · %, which is lower than after the Q&P treatment (σr = 910 MPa, δ = 47% and σr × δ = 43 GPa · %). The elevated mechanical properties of the steel after the Q&T treatment are explained by the higher content of austenite in the structure and the more manifested TRIP effect during the deformation process. [ABSTRACT FROM AUTHOR]

Within the presented research, effect of annealing on nature of corrosion damages of medium-nickel austenitic nodular cast iron castings, containing 5.5% to 10.3% Ni, was determined. Concentration of nickel, lower than in the Ni-Resist cast iron, was compensated with additions of other austenite-stabilising elements (manganese and copper). In consequence, raw castings with austenitic matrix structure and gravimetrically measured corrosion resistance increasing along with nickel equivalent value EquNi were obtained. Annealing of raw castings, aimed at obtaining nearly equilibrium structures, led to partial austenite-to-martensite transformation in the alloys with EquNi value of ca. 16%. However, corrosion resistance of the annealed alloys did not decrease in comparison to raw castings. Annealing of castings with EquNi value above 18% did not cause any structural changes, but resulted in higher corrosion resistance demonstrated by smaller depth of corrosion pits.

Abstract The medium Mn-TRIP steels usually exhibited excellent strength and elongation at 25 °C. However, the early plastic instability occurred when the deforming temperature increased to 100 °C due to the lack of work hardening in ultrafine grains and deformation induced martensitic transformation. In this study, an intermediate temperature annealing heat treatment was suggested to inhibit the plastic instability at 100 °C without markedly decreasing the mechanical properties. The results showed that two scenarios happened during the annealing process: i) austenite decomposed into M 23 C 6 and ferrite, ii) C-Mn clusters formed in the austenite. It is revealed that such microstructural evolutions can increase the hardening effect by pinning the dislocations, decreasing the stability of austenite and promoting the TRIP effect during the tensile test. [ABSTRACT FROM AUTHOR]

A novel lean duplex stainless steel with the composition of Fe-0.11C-21.8Cr-4.52Mn-1.16Ni-0.40Mo-0.16 N has been developed, which can be easily deformed during hot rolling without forming edge cracks. It has been found that the volume fraction of austenite was decreased with the increase of heat treatment temperatures. After having been annealed at 1050 ℃ for 5 min, the cold rolled and annealed band exhibited an excellent combination of strength and ductility, with the ultimate tensile strength and elongation having been measured to be 860 MPa and 63%, respectively. Its yield strength and pitting corrosion potential are higher than those of SUS304 by more than 100% and 60%, respectively. As compared to the conventional LDX 2101, the present steel possesses lower deformation resistance and higher ductility with higher fraction of ferrite during the hot deformation, and exhibits more excellent combination of strength and plasticity with slight decrease in corrosion resistance. The behavior of plastic deformation was studied, in which the effect of transformation induced plasticity (TRIP) had been observed with the orientation relationships between α´-martensite and austenite matrix being close to the K-S and N-W relationships. The stability of austenite for the present steel was found to be increased with increasing annealing temperature, resulting in slower strain induced martensite (SIM) transformation. [ABSTRACT FROM AUTHOR]

We investigated the effect of deformation temperature and gain size on the tensile behaviors of a new medium Mn-TRIP steel processed by batch and continuous annealing. It was found that the tensile strength decreased when the testing temperature increased from −20 to 300 °C. The total elongation firstly increased, reaching the maximum at 25–100 °C, and then decreased when the temperature was higher than 100 °C. The results can be explained by (i) the influence of temperature on chemical driving force for martensitic transformation and (ii) the grain size effect on the stability of austenite. To achieve optimal mechanical properties, the stability of austenite should be tailored so that the transformation-induced plasticity effect occurs under continuous deformation. Also, ferrite should have appropriate grain sizes so that work hardening of ferrite can coordinate the deformation of austenite. [ABSTRACT FROM AUTHOR]

Deformation-induced martensitic transformation is a key phenomenon to manage both high strength and large ductility in low alloy multi-phase steels. Significant enhancement of strain hardening ability could be achieved by the phase transformation from soft austenite to hard martensite during deformation, which is known as transformation induced plasticity (TRIP) effect. The occurrence of TRIP effect can be controlled by austenite characteristics like carbon content, grain size and morphology. Additionally, the mechanical interaction with other phases surrounding each austenite grain during deformation would affect the stability of austenite, which has not been clarified. The current study has clarified how surrounding phases affect the mechanical stability of austenite against deformation-induced martensitic transformation. Two types of multi-phase microstructures composed of three different phases, i.e., ferrite (α) + austenite (γ) + martensite (M) and two phases of ferrite (α) + austenite (γ) were fabricated in Fe-1.6Mn-1.4Si-1.0Ni-0.5Al-0.2C, maintaining the characteristics of retained austenite nearly the same. It was found that the α+γ+M specimen exhibited slower rate of deformation-induced martensitic transformation during tensile deformation than the α+γ specimen, indicating higher austenite stability in the α+γ+M specimen. The in-situ synchrotron XRD measurements during tensile deformation revealed that there was significant stress partitioning between austenite and adjacent phases (ferrite, martensite and deformation-induced martensite), which influenced the phase transformation rate of austenite into deformation-induced martensite. Furthermore, it was also clarified by the in-situ synchrotron XRD that the austenite in the α+γ+M specimen always had higher stress than that in the α+γ specimen due to higher dislocation density in austenite introduced by martensitic transformation to form pre-existing martensite, so that higher stress was required for deformation-induced martensitic transformation in the α+γ+M specimen during tensile deformation than the α+γ specimen. [ABSTRACT FROM AUTHOR]

The phase recrystallization of medium-carbon steel with the initial structure of lamellar pearlite in the process of short-term heating to different temperatures above Ac and subsequent cooling has been studied. The structure of steel formed under the nonequilibrium conditions corresponding to the decomposition of supercooled austenite has been described. It has been shown that the changes in the structure and phase composition that arise during this treatment have a noticeable effect on the characteristics of the deformation behavior of the material determined based on the results of dynamic indentation. [ABSTRACT FROM AUTHOR]

Two twinning-induced plasticity steels have been investigated for their high-strain-rate deformation behaviour. The stability of austenite is low at lower strain rates, but high when high-strain-rate deformation is used. The stability has been attributed due to the temperature rise during high-strain-rate deformation leading to dynamic recrystallization in the material. [Copyright &y& Elsevier]

Solution nitriding was applied to a metastable austenitic stainless steel plate (Fe–18Cr–8Ni alloy) to stabilize the austenite near the plate surface. After cold rolling, the interior austenite almost entirely transformed to martensite, but the stabilized surface austenite remained unchanged. The interior deformation-induced martensite contributes to the material’s high strength and the surface stable austenite-layer plays an important role in preventing hydrogen permeation. As a result, the resistance to hydrogen embrittlement was significantly improved for the cold-rolled specimen. [ABSTRACT FROM AUTHOR]