Bainite

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

Transformation kinetics, microplasticity and aging of martensite in fe-31 ni.

Abstract: : The effects of testing temperature and volume fraction of martensite on the microplastic response of unaged Fe-31 Ni martensite-austenite aggregates have been determined. These results, supplemented by other experimental studies, show that two unusual mechanisms of plastic deformation give rise to the apparent softness of the quenched structures. The transformation of retained austenite to martensite during the application of stress gives rise in specified conditions to large microplastic strains. The other strain component, which dominates the microdeformation above the temperature range where transformation occurs, is attributed to stress-assisted relaxation of internal stresses. The measured changes in elastic modulus and internal friction (at 80 kHz) during aging of Fe-31 Ni after quenching cannot be explained by the diffusion of point defects to dislocations. It is suggested that this aging effect is instead due to the motion of dislocations which occurs in order to decrease the internal stress. Experimental results pertaining to the kinetics of the austenite to martensite phase transformation show that no distinguishable athermal component of transformation exists in the Fe-31 Ni alloy. A model for martensitic kinetics is developed which treats the propagation of the interface as analogous to plastic deformation. This model and reconsideration of the implications of dislocation motion in the kinetics of embryo formation both lead to the conclusion that martensitic kinetics should be of a 'fast isothermal' character. (Author)

Microstructural evolution at the initial stages of continuous annealing of cold rolled dual-phase steel

Abstract: The performance of cold rolled dual-phase (DP) steels depends on their microstructure, which results from the thermomechanical processing conditions, involving hot rolling, cold rolling, and continuous annealing. The knowledge on the influence of each annealing stage on the microstructure formation is essential for manufacturing high-quality DP steels. In the present work, the effects of some intercritical annealing parameters (heating rate, soaking temperature, soaking time, and quench temperature) on the microstructure and mechanical properties of a cold rolled DP steel (0.08% C–1.91% Mn) were studied. The microstructure of specimens quenched after each annealing stage, simulated on a Gleeble, was analyzed using optical, scanning, and transmission electron microscopy. The tensile properties, determined for specimens submitted to complete annealing cycles, are influenced by the volume fractions of martensite, bainite, martensite/austenite (MA) constituent, and carbides, which depend on annealing processing parameters. The results obtained showed that the yield strength (YS) increase and the ultimate tensile strength (UTS) decrease with the increasing intercritical temperature. This can be explained by the increased formation of granular bainite associated with the increased volume fraction of austenite formed at the higher temperatures. The experimental data also showed that, for the annealing cycles carried out, UTS values in excess of 600 MPa could be obtained with the steel investigated.

High-strength steel sheet and process for production thereof

Abstract: Disclosed are an ultra-high-strength steel sheet having both a tensile strength of as high as 1400MPa or above and excellent formability and an advantageous process for manufacturing the same. A high-strength steel sheet having both a composition which contains by mass C: 0.12 to 0.50%, Si: 2.0% or less, Mn: 1.0 to 5.0%, P: 0.1% or less, S: 0.07% or less, Al: 1.0% or less, and N: 0.008% or less with the balance being Fe and unavoidable impurities, and a structure which comprises, in terms of area fraction, autotempered martensite: 80% or more, ferrite: less than 5%, bainite: 10% or less, and retained austenite: 5% or less and in which the average number of precipitated iron carbide particles of 5nm to 0.5[mu]m in the autotempered martensite is 5OE04 or above per mm2.