Abstract: Seamless tubes are manufactured, as it is well known, via continuous mandrel rolling
process. A billet is first pierced, then the hollow is reduced and rolled with mandrel at temperatures
higher than 1000oC. After mandrel extraction, the hollow can either cool down to room temperature
or be directly charged in an intermediate furnace for re-austenitization. Finally, the tube is finished
in a stretch-reducing mill to several gauges. The thermomechanical process is complex allowing
little flexibility along the line. The aims of this paper are a) to describe the industry schedule in
terms of simple process variables and b) to simulate this process via numerical and physical models.
The latter uses torsion testing as experimental technique. It is shown that good agreement is
obtained between industry results and predictions from the numerical model. Torsion experiments
have produced somewhat larger predictions for ferrite grains sizes, however. This is mostly
attributed to the necessary simplifications made to the mechanical testing experiments due to
restrictions in maximum strain rates and shortest dwell times achievable with thermomechanical
Abstract: This work presents a unique approach for the modelling of the austenitisation of martensite in dual-phase
steels within the phase-field method. Driving forces for nucleation and growth are derived from thermodynamic
databases. Routines for nucleation are based on a discretisation of the classical nucleation theory. Validation is given via
Abstract: The orientation relationships that apply to phase transformations in high-performance
TRIP and TWIP steels were characterised by orientation imaging and EBSD techniques. The results
are presented in the fundamental zones of Rodrigues-Frank space that correspond to the specific
phase transformation under consideration (cubic to cubic or cubic to hexagonal). The use of
Rodrigues-Frank space enables straightforward comparison to be made with orientation
relationships proposed in the literature. The observations indicate that the active slip systems in the
parent phase play important roles in variant selection.
Abstract: Deformations at temperatures 900 °C, 860 °C, 810 °C and 780 °C in the consecutive
amounts 24%, 20%, 19% and 18.5% were applied to low carbon HN5MVNb bainitic steel using hot
compression testing in dilatometer Bähr 805 followed by continuous cooling. The results show
clearly that the kinetics of the austenite decomposition were depended on local equilibrium
conditions between recovery, recrystallization and phase transformation processes for a given
cooling rate. Bainite transformation was accelerated when sample was cooled after deformation at
cooling rate 60 °C/s. At lower cooling rates than 5 °C/s down to 0.5 °C/s, bainite transformation was
postpone when comparing its kinetics with those for non deformed steel. The bainitic
transformation cannot be fitted to a single transformation mechanism owing to the formation of
carbides. Different behavior was observed for austenite to ferrite transformation. Usually it was
accelerated with consecutive deformations of the steel for all cooling rates used in experiments.
Abstract: The first step in the heat-treatment processes for a vast majority of commercial steels is
austenitization. There is much less research put in this field comparing to the cooling
transformation, but the interest is continuously increasing especially in view of the development of
TRIP and Dual-phase steels.
The microstructural evolution during continuous heating experiments has been studied for a
series of C-Mn steels with carbon contents in the range 0.35-0.45 wt. % using optical and
scanning electron (SEM) microscopy. It is shown that the formation of the austenitic phase is
possible in pearlitic as well as in ferritic regions, although in the former it proceeds at a much
faster rate due to the shorter diffusion distances. Thus a considerable overlap in time of the ferriteto-
austenite and the pearlite-to-austenite transformations is likely to occur.
Another observation that was made during the experiments is that depending on the heating
rate, the pearlite-to-austenite transformation can proceed in either one or two steps. At low
heating rates (0.05 °C/s) ferrite and cementite plates transform simultaneously. At higher heating
rates (20 °C/s) it is a two-step process: first ferrite transforms to austenite within pearlite grains
and then the dissolution of the cementite lamellae takes place.
Abstract: In order to develop an economical production method of high Si steel sheet, 6%Si (by weight
percent, unless specified otherwise) steel was prepared by a combined process of conventional casting and
hot- and cold-rolling. Tension and nano-hardness tests and TEM analysis were carried out to examine the
effects of ordered phases, Si-content, and testing temperature on cold workability. By optimizing the
successive processes of casting, hot-rolling, heat treatment, and cold-rolling, 0.5 mm thick 6%Si steel sheet
was successfully produced without crack formation. As Si content increased from 3% to 6%, core loss
(W10/50) of the 0.5 mm thick Si steel sheet decreased from 1.36 W/kg to 0.89 W/kg.
Abstract: Fe and Fe-C based alloys present the exceptional feature that the processing route can be
adapted to lead to various phases that present antagonist mechanical properties ranging from soft
ferrite to high strength martensite. Among the different deformation mechanisms that can be
exhibited by these phases, the TRIP effect brings about large enhancements of the work-hardening
rate. The current TRIP-assisted multiphase steels present a ferrite-based matrix with a distribution
of islands of bainite and retained austenite obtained at the end of specific thermal or
The present study aims at characterising the interactions occurring between ferrite recrystallisation
and austenite formation during the intercritical annealing of cold rolled Nb-added TRIP-aided steels.
It is shown that the addition of niobium retards the ferrite recrystallisation during heating. As a
consequence, ferrite may not be completely recrystallised before the nucleation and growth of the
austenite grains. Strong interactions between these phenomena can then be observed, i.e. a strong
hindering of the ferrite recrystallisation due to the austenite formation. Furthermore, the heating rate
from room temperature to the intercritical temperature range influences the thermodynamic
conditions prevailing at the ferrite / austenite interface and dictates the phase proportions.
Abstract: A novel concept of two-step austempering in a magnetic field has been conceived by this investigator. This twostep
process involves first quenching the alloy to a lower temperature after austenitizing and then immediately
rising the temperature of the quenching media to a higher temperature and the whole austempering process is
carried out in the presence of a high magnetic field. In this investigation, Austempered Ductile Iron (ADI) was
processed by this novel two-step austempering process in a high magnetic field of 20 Tesla. The microstructure
and the mechanical properties of the ADI processed in a magnetic field has been characterized and compared
with ADI processed by conventional process.
The results of this investigation indicate significant improvement in the mechanical properties of ADI
when Austempered in a high magnetic field. Both yield and tensile strengths were higher in the samples
processed in the presence of a magnetic field. Very fine grain ferrite and austenite was obtained in the
microstructure. The ferrite content was also significantly higher.