Bainite

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

High-strength line-pipe steel having low yield ratio and excellent low-temperature toughness

Abstract: An ultrahigh-strength and low-yield-ratio line-pipe steel being excellent in HAZ toughness and field weldability and having a tensile strength of at least 950 MPa (exceeding the API Specification 100). The steel comprises a low-C-high-Mn-Ni-Mo-Nb-trace Ti steel, further selectively contains if necessary B, Cu, Cr and V, and has as the microstructure a hard-soft two-phase mixed structure comprising martensite/bainite and 20-90 % of ferrite, the ferrite containing 50-100 % of worked ferrite and having a grain diameter of 5 νm or less. It has thus become possible to produce an ultrahigh-strength and low-yield-ratio line-pipe steel (exceeding the API Specification 100) excellent in low-temperature toughness and field weldability. As a result, it has become possible to improve the pipeline safety remarkably and to improve the pipe-lining performance and conveying efficiency largely.

New insights into the mechanism of cooling rate on the impact toughness of coarse grained heat affected zone from the aspect of variant selection

Abstract: In this article, the authors tried to establish a direct correlation between crystallographic variants and impact toughness, and provided some novel insights into the mechanism of cooling rate on the impact toughness of coarse grained heat affected zone (CGHAZ) of offshore engineering steel by means of electron back-scattering diffraction (EBSD) analysis. The results showed that variant selection becomes stronger with an decrease in the cooling rate, resulting in the decline of high angle grain boundaries (HAGBs) and thus lower the impact toughness. Moreover, the variation in impact toughness is mainly correlated to the crystallographic block size. The larger the block size, the lower the impact toughness. By visualizing the crystallographic features, it has been clarified that the transition from Bain zone grouping to close-packed plane grouping with the increase of cooling rate, while the corresponding microstructure changes from granular bainite to lath bainite. Furthermore, it has been found that ~ 25% (number fraction) reconstructed prior austenite grains in simulated CGHAZ present a twin-related structure (austenitic twin), which can enhance the variant selection and displays a negative effect on the formation of HAGBs.

Microstructural and mechanical characterization of C–Mn–Al–Si cold-rolled TRIP-aided steel

Abstract: Retained austenite characteristics and tensile properties in a 021C–177Mn–12Al–0283Si, high strength cold-rolled TRIP steel were investigated The microstructure of this steel is comprised of ferrite, bainite and retained austenite, which is obtained by controlled cooling from the intercritical annealing temperature to the isothermal bainitic holding temperature The effects of cooling rate from intercritical annealing temperature to isothermal transformation temperature, as well as effect of isothermal transformation time on microstructure and mechanical properties, were studied using optical microscopy, SEM, TEM, XRD, dilatometry and mechanical testing These studies revealed that the microstructure of the steel mainly consisted of bainitic ferrite lath matrix, blocky martensites and stable retained austenite films of 7–8 vol% When austempered at temperatures above M S temperature, the steel possessed high tensile strength of 600 MPa, total elongation of 28–32% and n -value 02 The present paper deals with the effect of heat treatment on microstructure and mechanical properties of C–Mn–Al–Si cold-rolled TRIP steel