Bainite

About: Bainite is a research topic. Over the lifetime, 9520 publications have been published within this topic receiving 145305 citations.

High strength microalloyed CMn(V–Nb–Ti) and CMn(V–Nb) pipeline steels processed through CSP thin-slab technology: Microstructure, precipitation and mechanical properties

Abstract: Compact strip production (CSP) technology is an important upcoming processing route to produce low cost microalloyed high strength pipeline steels that meet the API standards. Hot strips of CMn(VNbTi) and CMn(VNb) steel grades with fine-grained ferrite–pearlite microstructure and small volume fraction of lower transformation product (non-polygonal ferrite: acicular ferrite/bainite) were produced using CSP technology with high strength and excellent low-temperature toughness up to −60 °C. For strip thicknesses between 6 and 12.5 mm, yield strength levels of up to 590 MPa and tensile strength levels up to 680 MPa were achieved. The CMn(VNb) steel exhibited outstanding notch-toughness in the range of 200 and 400 J/cm 2 , in spite of its higher yield strength (∼100 MPa or greater) over the CMn(VNbTi) steel. The precipitates present in CMn(VNbTi) and CMn(VNb) steels were characterized in terms of morphology, size and chemistry, and crystallography. The microalloying elements, Ti, Nb, and V form M 4 C 3 type of carbides in the ferrite matrix of both the steels. The multi-microalloying approaches of CMn(VNbTi) and CMn(VNb) results in the formation of duplex and triplex carbonitrides, respectively. The results of the development effort are described.

Deformation-induced martensite formation during cyclic deformation of metastable austenitic steel: Influence of temperature and carbon content

Abstract: To study the influence of the parameters carbon content, temperature and total strain amplitude on the deformation-induced martensite formation in metastable 301 austenitic steel, hollow cylindrical fatigue specimens were carburized and decarburized in methane–hydrogen gas mixtures. Fatigue experiments were carried out in a temperature range between RT and T = −100 °C while monitoring the fraction of deformation-induced martensite versus the number of cycles by means of a magneto-inductive ferrite sensor. The results show that deformation-induced martensite formation leads to pronounced cyclic hardening. A certain amount of accumulated plastic strain is necessary and a threshold value of the plastic strain amplitude must be exceeded to trigger martensitic transformation. The effect of the carbon content and/or the temperature on the formation of α′ martensite is very strong in such a way that high carbon concentrations and elevated temperatures stabilize the austenite phase.

Current Challenges and Opportunities in Microstructure-Related Properties of Advanced High-Strength Steels

Abstract: This is a viewpoint paper on recent progress in the understanding of the microstructure–property relations of advanced high-strength steels (AHSS). These alloys constitute a class of high-strength, formable steels that are designed mainly as sheet products for the transportation sector. AHSS have often very complex and hierarchical microstructures consisting of ferrite, austenite, bainite, or martensite matrix or of duplex or even multiphase mixtures of these constituents, sometimes enriched with precipitates. This complexity makes it challenging to establish reliable and mechanism-based microstructure–property relationships. A number of excellent studies already exist about the different types of AHSS (such as dual-phase steels, complex phase steels, transformation-induced plasticity steels, twinning-induced plasticity steels, bainitic steels, quenching and partitioning steels, press hardening steels, etc.) and several overviews appeared in which their engineering features related to mechanical properties and forming were discussed. This article reviews recent progress in the understanding of microstructures and alloy design in this field, placing particular attention on the deformation and strain hardening mechanisms of Mn-containing steels that utilize complex dislocation substructures, nanoscale precipitation patterns, deformation-driven transformation, and twinning effects. Recent developments on microalloyed nanoprecipitation hardened and press hardening steels are also reviewed. Besides providing a critical discussion of their microstructures and properties, vital features such as their resistance to hydrogen embrittlement and damage formation are also evaluated. We also present latest progress in advanced characterization and modeling techniques applied to AHSS. Finally, emerging topics such as machine learning, through-process simulation, and additive manufacturing of AHSS are discussed. The aim of this viewpoint is to identify similarities in the deformation and damage mechanisms among these various types of advanced steels and to use these observations for their further development and maturation.

Austenite decomposition during continuous cooling of an HSLA-80 plate steel

Abstract: Decomposition of fine-grained austenite (10-µm grain size) during continuous cooling of an HSLA-80 plate steel (containing 0.05C, 0.50Mn, 1.12Cu, 0.88Ni, 0.71Cr, and 0.20Mo) was evaluated by dilatometric measurements, light microscopy, scanning electron microscopy, transmission electron microscopy, and microhardness testing. Between 750 °C and 600 °C, austenite transforms primarily to polygonal ferrite over a wide range of cooling rates, and Widmanstatten ferrite sideplates frequently evolve from these crystals. Carbon-enriched islands of austenite transform to a complex mixture of granular ferrite, acicular ferrite, and martensite (all with some degree of retained austenite) at cooling rates greater than approximately 5 °C/s. Granular and acicular ferrite form at temperatures slightly below those at which polygonal and Widmanstatten ferrite form. At cooling rates less than approximately 5 °C/s, regions of carbon-enriched austenite transform to a complex mixture of upper bainite, lower bainite, and martensite (plus retained austenite) at temperatures which are over 100 °C lower than those at which polygonal and Widmanstatten ferrite form. Interphase precipitates of copper form only in association with polygonal and Widmanstatten ferrite. Kinetic and microstruc-tural differences between Widmanstatten ferrite, acicular ferrite, and bainite (both upper and lower) suggest different origins and/or mechanisms of formation for these morphologically similar austenite transformation products.