Novel method for refinement of retained austenite in micro/nano-structured bainitic steels

Hu, Feng; Wu, Kaiming; Wan, Xiangliang; Rodionova, I. G.; Shirzadi, A. A.; Zhang, F. C.

doi:10.1080/02670836.2017.1291165

Cited by 10 publications

(3 citation statements)

References 22 publications

(31 reference statements)

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“…Thus, finally the microstructure will consist of partially carbon-supersaturated plates of bainitic ferrite, α b , and C enriched austenite (γ + ), the latter as thin films between ferrite plates and submicron blocks between sheaves of bainite [5,6]. This microstructure has a high hardness and strength, owing to the combined influence of several types of obstacles to dislocation motion, such as interfaces and dislocations, and also to solid solution strengthening and to the interaction between carbon and defects [3,[7][8][9][10][11][12][13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Quantitative Assessment of the Time to End Bainitic Transformation

Santajuana

Eres-Castellanos

Ruiz-Jimenez

et al. 2019

Metals

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Low temperature bainite consists of an intimate mixture of bainitic ferrite and retained austenite, usually obtained by isothermal treatments at temperatures close to the martensite start temperature and below the bainite start temperature. There is widespread belief regarding the extremely long heat treatments necessary to achieve such a microstructure, but still there are no unified and objective criteria to determine the end of the bainitic transformation that allow for meaningful results and its comparison. A very common way to track such a transformation is by means of a high-resolution dilatometer. The relative change in length associated with the bainitic transformation has a very characteristic sigmoidal shape, with low transformation rates at the beginning and at end of the transformation but rapid in between. The determination of the end of transformation is normally subjected to the ability and experience of the “operator” and is therefore subjective. What is more, in the case of very long heat treatments, like those needed for low temperature bainite (from hours to days), differences in the criteria used to determine the end of transformation might lead to differences that might not be assumable from an industrial point of view. This work reviews some of the most common procedures and attempts to establish a general criterion to determine the end of bainitic transformation, based on the differential change in length (transformation rate) derived from a single experiment. The proposed method has been validated by means of the complementary use of hardness measurements, X-ray diffraction and in situ high energy X-ray diffraction.

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Section: Introductionmentioning

confidence: 99%

Quantitative Assessment of the Time to End Bainitic Transformation

Santajuana

Eres-Castellanos

Ruiz-Jimenez

et al. 2019

Metals

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“…These thin foils were ground down to 50 µm thickness, and then electropolished at 50 V using a twin-jet unit using an electrolyte solution of 5% perchloric acid, 15% glycerol, and 80% methanol. Meanwhile, thickness of martensite laths (t) was determined by the mean lineal intercept (L = π t/2) using TEM with at least 10 micrographs [13].…”

Section: Methodsmentioning

confidence: 99%

Influence of Partial Replacement of Si by Al on Microstructure and Properties of Nanostructured Martensitic Steel

Zheng

Zhou

et al. 2019

Materials

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Nanostructured martensitic steels comprising nanoscale-martensite and retained austenite were obtained by quenching–partitioning–tempering (Q–P–T) treatment. The influence of partial replacement of Si by Al on the microstructure and properties were studied. Results showed that with partial replacement of Si by Al, except nanoscale-martensite and retained austenite, a little ferrite was also clearly observed. By contrast, with partial replacement of Si by Al, although the ultimate tensile strength (1392 MPa against 1215 MPa) was slightly lower, the elongation after fracture (16.7% against 19.9%) and the toughness (equivalent to the area under the stress–strain curve) (43.1 × 106 against 37.1 × 106 J/m3) were relatively higher. This was because the retained austenite in the steel with partial replacement of Si by Al had higher carbon content, similar volume fraction of film-like morphology, lower volume fraction of blocky morphology and was surrounded by ferrite, which played significant role in the transformation-induced plasticity (TRIP) effect.

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“…The microstructural dependence, for example the grain size [10,12], retained austenite [9,13,14], of the response to deformation can help optimise the mechanical properties of Q&P steels. In all the studies, uniaxial tension test has been adopted for the study of the deformation response, although in practice, other tests, such as multiaxial tensile, shear strain and bending deformation [15,16], are applied to study the complex deformations applied to a vehicle body.…”

Section: Introductionmentioning

confidence: 99%

Bending deformation and fracture characterisation in quenching and partitioning steel

Jiang

et al. 2018

Materials Science and Technology

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The bending deformation recorded and fracture characterisation seen during the process of quenching and partitioning (Q&P) steel are investigated as a function of bending angle. According to experimental results, the mechanically induced martensitic transformation of the retained austenite occurred heterogeneously in the direction of thickness. Results from electron backscattered diffraction and finite element analysis confirmed that the heterogeneous phase transformation was caused by the stress difference in the direction of thickness. The results prove fracture behaviour is dominated by martensite cracking. The results provide a new insight into deformation characterisation of the Q&P steel under bending, which allows the design and optimisation of mechanical properties.

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Novel method for refinement of retained austenite in micro/nano-structured bainitic steels

Cited by 10 publications

References 22 publications

Quantitative Assessment of the Time to End Bainitic Transformation

Quantitative Assessment of the Time to End Bainitic Transformation

Influence of Partial Replacement of Si by Al on Microstructure and Properties of Nanostructured Martensitic Steel

Bending deformation and fracture characterisation in quenching and partitioning steel

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