Controlled near plane strain deformation was imposed on a super duplex stainless steel. Subsequent characterization involved extensive microtexture measurements, and measurements of general corrosion ...and corrosion behavior (and nature of the passive film) of the individual phases. The general corrosion was controlled by the corrosion performance of the austenite phase, and corresponding microtextural developments. Corrosion resistance in the austenite phase, as well as the general corrosion, improved until a true strain of 0.26 and then dropped. Enhanced corrosion resistance coincided with slip band formation and generation of low-angle boundaries. Beyond a strain of 0.26, shear bands and associated lattice curvatures plus high-angle boundaries led to a clear degradation in the corrosion behavior.
Fully recrystallized commercial Zirconium plates were subjected to uniaxial tension. Tests were conducted at different temperatures (123 K - 623 K) and along two plate directions. Both directions ...were nominally unfavorable for deformation twinning. The effect of the working temperature on crystallographic texture and in-grain misorientation development was insignificant. However, systematic variation in work hardening and in the area fraction and morphology of deformation twins was observed with temperature. At all temperatures, twinning was associated with significant near boundary mesoscopic shear, suggesting a possible linkage with twin nucleation. A binary tree based model of the polycrystal, which explicitly accounts for grain boundary accommodation and implements the phenomenological extended Voce hardening law, was implemented. This model could capture the measured stress-strain response and twin volume fractions accurately. Interestingly, slip and twin system hardness evolution permitted multiplicative decomposition into temperature-dependent, and accumulated strain-dependent parts. Furthermore, under conditions of relatively limited deformation twinning, the work hardening of the slip and twin systems followed two phenomenological laws proposed in the literature for non-twinning single-phase face centered cubic materials.
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Thirty-five ‘apparently’ recrystallized specimens were produced through a combination of cold rolling and recrystallization annealing. They had a range of average grain size (d
av
:18-467
μ
m), grain ...orientation spread (GOS: 0.31 to 1.24 deg) and volume fraction of ND|| (
V
f
N
D
|
|
<
111
>
: 0.15-0.69). The GOS value, for individual grains or for an entire specimen, represented presence of ‘remnant’ cold work – existence of geometrically necessary dislocations and ‘minor’ orientation gradients. The resistance to aqueous corrosion was determined by this ‘remnant’ cold work, and not by average grain size or crystallographic texture. The role of mesoscopic distribution in plastic deformation, and the features of deformed microstructure, were then explored on the resistance to aqueous corrosion. Progressive plastic deformation, through laboratory cold rolling, brought reproducible non-monotonic corrosion responses. In particular, an increase in corrosion resistance (0 to 30 pct rolled) was followed by a drop (30-40 pct) and then an increase (> 40 pct rolling). These changes originated from the evolution in deformed microstructures: formation of near boundary orientation gradients and creation of low and high angle boundaries, respectively. A combination of microtexture and non-contact profilometry clearly established that deformation induced near boundary orientation gradients and grain-interior high angle grain boundaries provided resistance to aqueous corrosion, while low angle boundaries were detrimental.
The applicability of miniaturised small punch tests (SPT) to capture thermal aging degradation of two commonly used low alloy steels (LAS) viz. Mn-Ni-Mo and Cr-Mo-V steels, was investigated. This was ...done by comparing the SPT results to the results of the conventional Charpy V-notch (CVN) tests, fractographic analysis and results of chemical etching test. Both the steels were subjected to accelerated thermal aging at 450 °C (8400 h for Mn-Ni-Mo steel and 5600 h for Cr-Mo-V steel). For both LAS, conventional CVN tests showed reduction in the impact energy and fractographic analysis indicated increase in the percentage brittle fracture with thermal aging. Fractographs indicated intergranular (IG) brittle fracture for the Mn-Ni-Mo steel and transgrannular (TG) brittle fracture for the Cr-Mo-V steel. This was corroborated by the chemical etching tests that showed preferential attack at prior austenitic grain boundaries (PAGBs) for Mn-Ni-Mo steel and conspicuous absence of such IG attack for Cr-Mo-V steel. SPT could clearly capture the embrittlement due to thermal aging for both the LAS as investigated by the conventional CVN testing. However, SPT could not establish the ductile to brittle transition temperature (TSP) as the lower shelf energy was not reached even at the lowest possible test temperature (-196 °C). SPT has been successful in capturing the indications of embrittlement due to thermal aging for both the LAS i.e. it is able to show the loss of ductility and increase in the fraction of brittle fracture. However, the use of SPT, at least in the present form, as an alternative to the most commonly used CVN test, for the materials studied is not recommended.
Twenty different iron ore pellets, consisting primarily of Hematite (Fe
2
O
3
) phase, were subjected to ‘simulated’ reduction studies. A wide range of reduction time periods,
R
t
of 122 to 211 ...minutes, were obtained. Detailed microstructural characterizations were then conducted at different locations of ten selected specimens. The
R
t
did not relate with initial phase mix or chemistry but determined the final iron (Fe) to Wüstite (FeO
1−
x
) ratio. In particular, numerical
R
t
values defined the relative presence of a bright Fe-rich rim. Further, relative density or porosity before the reduction scaled, as expected, with
R
t
. However, this was tenuous. The correlation appeared excellent in the post-reduction-densified specimens. This indicated the role of ‘acquired porosity’ and transformation strain. Several other microstructural parameters also scaled with
R
t
. These included grain size and crystallographic texture and estimated dislocation density. Lower
R
t
specimens had, in general, finer Fe
2
O
3
and coarser Fe grains, but weaker crystallographic textures of Fe
2
O
3
and FeO
1−
x
. However, the most striking correlation appeared between
R
t
and post-reduction dislocation density. The acquired defect density, representing the transformation strain, appeared to be the controlling feature for the reduction of iron ore pellets.
Near eutectoid fully pearlitic wire rod (5.5 mm diameter) was taken through six stages of wire drawing (drawing strains of 0 to 2.47). The as-drawn (AD) wires were further laboratory annealed (LA) to ...re-austenitize and reform the pearlite. AD and LA grades, for respective wire diameters, had similar pearlite microstructure: interlamellar spacing (
λ
) and pearlite alignment with the wire axis. However, LA grade had lower hardness (for both phases) and slightly lower fiber texture and residual stresses in ferrite. Surprisingly, essentially identical tensile yield strengths in AD and LA wires, measured at equivalent spacing, were found. The work hardened AD had, as expected, higher torsional yield strengths and lower tensile and torsional ductilities than LA. In both wires, stronger pearlite alignment gave significantly increased torsional ductility.
In this study, the erosion behaviour of laser clad chromium carbide-Ni rich alloy composite coatings with a wide range of carbide contents at room temperature and 600 °C were investigated. The ...variation in carbide content of the coatings was due to dilution from the substrate and the high cooling rate in the laser cladding process preventing re-solidification of the molten carbides. Erosion rate was observed to be a function of carbide content alone and was significantly higher at 600 °C as compared to room temperature. Erosion wear ratio (E90/E30) was also dependent on carbide content but decreased at higher temperature and higher carbide contents. A comparison of erosion behaviour with detonation and plasma sprayed counterparts showed the superior performance of laser clad coatings at 600 °C. The poor erosion performance of the detonation and plasma sprayed coatings was due to weak splat bonding. Thick oxide layer formed on the steel substrate after pre-oxidation resulted in its poor erosion performance.
•Microstructure was strongly dependent on the processing technique.•Solid particle erosion is a function of carbide content only in laser clad coatings.•In thermal spray coatings splat bonding determines the erosion behaviour.•Increase in temperature increases the erosion rate about five times.•Under oxidising conditions steel undergoes severe erosion affected oxidation.
The effect of surface working operations on the microstructure, electrochemical behavior and stress corrosion cracking resistance of 304L stainless steel (SS) was investigated in this study. The ...material was subjected to (a) solution annealing (b) machining and (c) grinding operations. Microstructural characterization was done using stereo microscopy and electron back scattered diffraction (EBSD) technique. The electrochemical nature of the surfaces in machined, ground and solution annealed condition were studied using potentiodynamic polarization and scanning electrochemical microscopy (SECM) in borate buffer solution. The stress corrosion cracking resistance of 304L SS in different conditions was studied by exposing the samples to boiling MgCl2 environment. Results revealed that the heavy plastic deformation and residual stresses present near the surface due to machining and grinding operations make 304L SS electrochemically more active and susceptible to stress corrosion cracking. Ground sample showed highest magnitude of current density in the passive potential range followed by machined and solution annealed 304L SS. Micro-electrochemical studies established that surface working promotes localized corrosion along the surface asperities which could lead to crack initiation.
► Machining/grinding produce extensive grain fragmentation near the surface of 304L SS. ► Machining/grinding result in martensitic transformation near the surface of 304L SS. ► Machining/grinding drastically reduce the SCC resistance of 304L SS in chloride. ► Machining/grinding make the surface of 304L SS electrochemically much more active. ► SECM study reveal that preferential dissolution takes place along surface asperities.
This study involved hot working, mimicking the first strand of a compact strip production, of grain-oriented (GO) and non-grain-oriented (NGO) electrical steel. The as-cast microstructures, between ...the grades, were similar: large (~ 550
μ
m average diameter and 1 to 7 mm length) columnar grains with ND//〈001〉 fiber texture. However, the developments in hot-worked microstructures were remarkably different. Firstly, the GO had higher carbon (0.06
vs
0.003 weight pct)—which led to the presence of austenite phase at the hot working temperatures. The GO also showed dynamic recrystallization (DRx) and the presence of Goss (110)〈001〉 grains in the hot-worked state. These were absent in the NGO. Further, the majority (~ 95 pct) of the Goss grains, in the hot-worked GO, originated from dynamic recrystallization (DRx) in the ferrite phase, surrounding the harder prior austenite regions. This study thus identified DRx by particle-stimulated nucleation as the primary source of Goss orientation in the hot-worked GO.
