in this investigation, continuous cooling transformations and microstructures have been studied in detail in a low carbon ti-nb bearing microalloyed steel by means of dilatometry, metallography and hardness measurements. the results indicate that when the cooling rate is greater than 1˚c/s, the dilatation curve is associated with a major dilatation at relatively low transformation temperatures,...

The microstructure characterization of tempered nanocrystalline bainitic steel is investigated in the present study. It is found that two types of plastic relaxation, dislocation debris and nanotwin, occurs in the displacive transformation due to relatively low transformation temperature and high carbon content. Because most carbon atoms trap in the dislocation, high dislocation density can be ...

Bainitic steels are now at the forefront of new and exciting developments in steel technology. This paper discusses how phase transformation theory is being exploited in the systematic design of every aspect of the new alloys, emphasising the immense influence that Professor Wayman has had on the development of the subject [1]. Technology of Bainitic Steels Gone are the days when industry could...

Bainitic transformation at low transformation temperatures leads to a microstructure involving fine plates of bainitic ferrite and thin films of retained austenite. This microstructure has shown ultimate tensile strength of about 2.2 GPa, noticeable uniform elongation in the range of 5 to 30%, hardness values of about 600 to 670 HV and impact toughness in the range of 30 to 40 MPa m1/2. With ca...

In this work, three low-carbon bainitic steels, with different Mo contents, were designed to investigate the effects of Mo addition on microstructure and mechanical properties. Two-step cooling, i.e., initial accelerated cooling and subsequent slow cooling, was used to obtain the desired bainite microstructure. The results show that the product of strength and elongation first increases and the...

In situ three-dimensional (3-D) X-ray diffraction experiments have been performed at a synchrotron source on low-alloyed multiphase TRIP steels containing 0.25 wt.% Si and 0.44 wt.% Al and produced with different bainitic holding times, in order to assess the influence of the bainitic transformation on the thermal stability of individual austenite grains with respect to their martensitic transf...

The kinetics and mechanism of bainite transformation have been studied in Fe-Cr-Mo-V-Ti-C steel high speed dilatometry backed by thermodynamic analysis. The complete transformation of austenite, however, has not occurred at any reported temperature. Obtained results confirm the incomplete reaction phenomenon with the cessation of the bainite transformation well before the paraequilibrium is ach...

New developments with bainite have resulted in a steel with an ultimate tensile strength of 2500 MPa, a hardness of 600-670 HV and a toughness in excess of 30-40 MPa m [1]. The novel microstructure is generated in a high carbon (0.98 wt.%) high silicon (1.46 wt.%) steel austenitized for 15 min. at 1000 oC, and then isothermally transformed at temperatures of ∼200 oC. Iron does not diffuse durin...

For several decades, the question of carbon supersaturation in bainitic ferrite has attracted the attention of physical metallurgists. Originally, this was associated with excess carbon due to the displacive nature ofphase transformation and its subsequent trappingatdefects inbainitic ferrite. The development of advanced experimental techniques, such as atom probe tomography and in situ synchro...

A bainitic microstructure with fine ferrite plates (20 to 40 nm) in a matrix of high-carbon retained austenite, obtained by isothermal transformation at 200°C, was characterized with an energy-compensated optical position-sensitive three-dimensional atom probe. The average carbon concentration in the austenite was found to be 8.0±1.6 at.% and in the bainitic ferrite 1.1±0.7 at.%. The latter con...