Abstract: Large amount of nitrogen addition into an austenitic stainless steel can improve the
mechanical properties and corrosion resistance remarkably as far as the nitrogen is in solid solution.
However, once the nitrogen precipitates as nitride, it results in deteriorations in the properties of the
high nitrogen austenitic stain steel. During welding, a high nitrogen austenitic stainless steel is
ready to precipitate rapidly immense amounts of chromium nitride in the heat affected zone (HAZ),
as intergranular or cellular morphologies at or from grain boundaries into grain interiors. The nitride
precipitation reduces seriously the local mechanical properties and corrosion resistance. The present
authors have demonstrated that a thermomechanical-processing as grain boundary engineering
(GBE) inhibited intergranular chromium carbide precipitation in the HAZ of a type 304 austenitic
stainless steel during welding and improved the intergranular corrosion resistance drastically. In the
present study, the thermomechanical-processing was applied to a high nitrogen austenitic stainless
steel containing 1 mass% nitrogen to suppress the nitride precipitation at or from grain boundaries
in the HAZ during welding by GBE. GBE increases the frequency of coincidence site lattice (CSL)
boundaries in the material so as to improve the intergranular properties, because of strong resistance
of CSL boundaries to intergranular deteriorations. The optimum parameters in the
thermomechanical-processing brought a very high frequency of CSL boundaries in the high
nitrogen austenitic stainless steel. The GBE suppressed the intergranular and cellular nitride
precipitation in the HAZ of the high nitrogen austenitic stainless steel during welding.
Abstract: Investigation into the effect of carbon and nitrogen contents of steels with an addition of
chromium, nickel and manganese on their structure and properties after thermoplastic treatment has
been carried out within the present study. For the physical modeling of thermoplastic treatment
processes, a DIL 805A/D dilatometer with a deformation capability and a Gleeble 3800 simulator
were used. The effect of carbon and nitrogen contents and the sum of these elements (C+N) on the
hardening of the material during hot plastic working. The softening of the material depends on the
C/N element ratio. The influence of the constituents under analysis on the dynamics of removal of
cold work effects is different; C speeds up, while N slows down this process. The influence of the
sum of the elements C and N depends on the type of nonmetallic phase precipitates. The structure
and properties of such steels are determined by quenching and tempering cycles.
Abstract: We produced low carbon and high nitrogen martensitic stainless steels that contain less than
0.1 mass% C and more than 0.45 mass% N, through the pressurized induction melting process, in which
nitrogen is introduced from a pressurized N2 atmosphere. The hardness and corrosion resistance of these
steels were investigated under various heat treatment conditions.
The hardness of these steels after spheroidal annealing treatment is approximately 95HRB and the cold
workability is superior to that of AISI440C. The hardness of these steels after quenching and sub-zero
treatment is from 53 to 56HRC. In the tempering process, however, high nitrogen steels show secondary
hardening at approximately 4 points in HRC compared with the quenched hardness after subzero
treatment and have the maximum tempered hardness of 56 to 60HRC around 723K. The corrosion
resistance of quenched and tempered materials under 723K is better than AISI304 evaluated by the pitting
potential in 3.5% NaCl aqueous solution. Both remnant Cr2N in hardening and precipitated Cr2N in
tempering degraded the corrosion resistance of high nitrogen martensitic stainless steels. The best
balanced developed steel has a hardness of 60HRC and better corrosion resistance than AISI304 under
optimal heat treatment conditions.
Abstract: The influence of shot peening on the fatigue properties of duplex stainless steel
reinforcing bars manufactured using both hot and cold rolled processes was studied. From
determination of the S-N curves, the experimental results show that shot peening improves the
fatigue behaviour of the re-bars, but that the improvement is much greater for the hot rolled
bars. A more severe peening action capable of promoting greater plastic deformation of the
bar surface needs to be used to improve the fatigue resistance of cold rolled corrugated bars.
Abstract: Internal friction of nitrogen in α iron has known as Snoek peak of N atom resolv
ed in the octahedral interstitial site of bcc. When M atom ( Mn, Mo, Si, et.al)
which has the affinity bigger than Fe were added ,another peaks due to the jump
of N from Fe-Fe site to Fe-M site appear in the upper temperature side and
complicate the Snoek peak curve of N.
In this paper, the Snoek peak curve was studied in Fe-0.4wt%Nb-0.02wt%N alloys.
This alloy showed no other peaks in the upper side to 373K and had only the
single peak of N in Fe-Fe site. Internal friction measured by torsion pendulum
method at about 1 Hz. After that this alloy was cooled from 373K to room
temperature and reheated to 373K, but Snoek peak of N which showed on the first
measurement just after nitriding disappeared completely and internal friction was
only background. One of the reasons of it is the precipitation of Fe16N2 under
heating and resolved N atoms disappeared. So these specimens were reheated to
873K and quenched, but Snoek peak of N was not measured. This shows the
disappearance of N atom from Fe-Fe site.
The mixture gas of a few % NH3 and H2 was used in this study. Therefore after
nitriding much of H atoms were resolved in α iron alloys. Because the diffusion
rate of H atom in α iron is bigger than N atom , it expected that H atoms can
combine with Nb atoms before coming N atoms. And the appearance of Snoek
peak of N in these alloys is considered. After that, in the heating to 373K H atom
leave Nb and go away from the surface, and N atoms combine with Nb in place
of H atoms. Nb has the very strong affinity with N, so these alloys have no peaks.
When they reheated to the nitriding temperature N atoms can not diffuse from
Fe-Nb site to Fe-Fe site. Then Snoek peak of N can not appears again in these
alloys. Therefore, when Fe-Nb alloys were nitrided in NH3 and H2 mixture gas H
atom plays very important part and it needs that the interaction of N-H atoms will
be considered in these nitrided Fe-Nb alloys.
Abstract: Measurements of conduction electron spin resonance (CESR) in steel allow to separate
the contributions from free electrons which provide the metallic character of interatomic bonds and
from localized electrons involved in the covalent bonds. The data of the CESR study carried out on
austenitic CrMn steels alloyed with carbon, nitrogen or carbon+nitrogen are presented. It is shown
that, in contrast to carbon, nitrogen enhances the metallic character of atomic interactions with a
maximum of the concentration of free electrons at some critical content of nitrogen (about 2 at.%).
The combined alloying with carbon+nitrogen leads to two effects: (i) a larger concentration of free
electrons and (ii) a shift of the critical content of interstitials towards higher values. The
experimental data are supported by theoretical ab initio calculations of the electron properties of
austenitic CrMn steels alloyed with carbon, nitrogen or carbon+nitrogen. Using the full-potentialfull-
electron-linearized-augmented-plane-wave (FLAPW) method, the total energy per primitive
crystal cell, the density of the electron states (DOS) and the distribution of the electron density over
the crystal lattice were calculated by means of the computational program WIEN-2k. The total
electron energy decreases due to alloying in the sequence of carbon→nitrogen→carbon+nitrogen,
which suggests a corresponding increase in the thermodynamic stability of the austenite. The
obtained results of the theoretical and experimental studies of the electron structure were used for
the development of super-high–strength stainless austenitic steels.
Abstract: This paper overviews our recent investigations on the processing of net-shaped Fe-based
nanoparticulate materials and their related material properties such as mechanical and corrosion
properties. The key-process for fabricating fully densified net-shaped nanopowder by pressureless
sintering is an optimal control of agglomerate size of nanopowder. Enhanced mechanical property
of powder injection molded Fe-Ni nanopowder could be explained by grain refinement and
uniformity of microstructure.
Abstract: Nanoscale studies of four important phenomena – in-situ development of high
temperature (HT) wear resistant nanostructured surface glaze, the initial stages of oxidation of TiAl
intermetallics, the high temperature degradation of DLC coatings and the property change promoted
by nano-patterning of a TiO2 surface are described.
Abstract: Copper sheet samples composed of nanometer scale lamellar twins was produced by
electrodeposition. The coherent lamellar twin boundaries were within 20˚ of being parallel to the
sheet plane in more than 60% of the grains. The electrodeposited sample was cold rolled to 30 and
85% reductions in thickness and the structural evolution during cold rolling was examined by
transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Extensive activity of
partial dislocations along twin boundaries and of perfect dislocations within twins (in particular in
coarse twins >100nm) were identified. Moreover, it was found that shear banding occurred, which
locally destroyed the lamellar twin structure. A dislocation structure developed within the shear
bands, and such a structure evolved with strain and gradually replaced the lamellar twin structure.
After 85% deformation, a large volume fraction of the lamellar twin structure was replaced by a
lamellar dislocation structure characteristic of high strain rolling where the lamellar dislocation
boundaries are almost parallel to the rolling plane. It was also found that the structural scales are
coarser in the lamellar dislocation structure than in the initial lamellar twin structure.
Abstract: The radiotracer technique was applied to measure self- (Fe, Ni) and solute- (Ag) grain
boundary diffusion in nanocrystalline Fe-40wt.%Ni alloy. The nanocrystalline material was
prepared by pressureless sintering of the nanoalloy powders. The nano-sized crystallites were
found to be clustered in micrometer-large agglomerates. Two types of internal interfaces with
fundamentally different properties exist in the nanomaterial: the grain boundaries between the
nanocrystallites and the interfaces between the agglomerates. A complete and consistent model of
the diffusion processes in such material is elaborated. Whereas the nanocrystalline boundaries
reveal diffusivities, which are similar to those in coarse-grained material, diffusion along interagglomerate
interfaces occurs faster by orders of magnitude. This behavior is explained by a nonrelaxed
structure of the inter-agglomerate interfaces.