Aging of a copper bearing HSLA-100 steel

Investigations were carried out on aging of a HSLA-100 steel after varying amounts of cold deformation. Mechanical properties (hardness, tensile properties and toughness) were measured and structural changes were studied using optical, TEM and SEM techniques. As a result of various treatments, the hardness and UTS could be significantly improved, but with drastic fall in ductility and impact strength, especially in peak aged conditions. The parameters affecting impact strength were examined and it was concluded that various microstructural features affected toughness through their influence on tensile properties. In this steel the impact strength could be improved by lowering the UTS and increasing the ductility (pct elongation). The improvement in hardness and UTS was attributed to formation of thick precipitate-dislocation tangles. The aging process caused a slow transformation of lath martensite into acicular ferrite due to occurrence of in situ recrystallization. The concentration of Cu in particles precipitating on aging was followed using EDAX technique.     

Effect of cold work and aging on mechanical properties of a copper bearing microalloyed HSLA-100 (GPT) steel

Investigations have been carried out on the effect of cold work and subsequent aging on mechanical properties of a Cu-bearing HSLA-100 steel microalloyed with Nb and Ti. Aging at 400°C after various degrees of cold work (25–70 pct) exhibits multiple hardness peaks. The treatments cause significant improvement in hardness and tensile strength, but at the cost of impact strength. Cold work also causes deterioration in ductility, which again improves on subsequent aging. The C70A treatment involving 70 pct deformation exhibits maximum response to age hardening giving a hardness of 465 VHN and a UTS of 1344 MPa, but with low values of ductility (5 pct) and impact energy (24 J). C50A treatment involving 50 pct cold work and aging results in an optimum combination of mechanical properties. This treatment in the second hardness peak stage yields a hardness of 373 VHN, UTS of 1186 MPa together with a ductility value of 11 pct and impact energy of 109 J. Scanning electron microscopic studies of fracture surfaces reveal that the impact fracture occurs by formation of dimples and nucleation and growth of voids and cracks. Fracture in tensile specimens is caused by formation of voids and cracks at high density striations. Formation of voids and cracks is also assisted by the presence of precipitated carbide particles.     

Effect of alloy elements on the anticorrosion properties of low alloy steel

Effect of alloy elements on corrosion of low alloy steel was studied under simulated offshore conditions. The results showed that the elements Cu, P, Mo, W, V had evident effect on corrosion resistance in the atmosphere zone; Cu, P, V, Mo in the splash zone and Cr, Al, Mo in the submerged zone.     

Analysis of stainless steel samples by energy dispersive X-ray fluorescence (EDXRF) spectrometry

A simple method for the analysis of stainless steel samples is presented which is based on radioisotope excited energy dispersive X-ray fluorescence (EDXRF) spectrometry and does not require any type-standards. Both absorption and enhancement effects have been taken into account in the fundamental parameter method for quantitative analysis and an iterative approach is followed for calculation of concentrations in steel samples. Non-linear least square fitting (NL-LSF) procedures have been used to determine accurately the fluorescent peak intensities. The method has been tested by analysing several CRM standard reference samples and 304 and 316 steel samples assuming as unknown. The EDXRF results have also been compared with the results of analysis of same samples by vacuum emission spark spectrometry (VES). Obtained values for concentration in steel samples match quite well with their certified values.     

Influence of thermomechanical aging on fatigue behaviour of 2014 Al-alloy

The fatigue behaviour of 2014 Al-alloy has been studied in various thermomechanically aged conditions. It is observed that fatigue properties can be improved by a thermomechanical treatment, which would reduce the concentrations of dispersoids, provide a relatively uniform deformation structure and produce fine distribution of θ’ precipitates. Fine θ’ particles inhibit dynamic recovery and produce uniform deformation structure, which improves fatigue behaviour. Presence of dispersoids and coarse precipitate particles leads to the formation of persistent slip bands (PSBs) and a highly heterogeneous deformation structure, which cause damage to fatigue properties.     

Effect of direct quenching on the microstructure and mechanical properties of the lean-chemistry HSLA-100 steel plates

The influence of direct quenching on structure-property behavior of lean chemistry HSLA-100 steels was studied. Two laboratory heats, one containing Cu and Nb (C:0.052, Mn:0.99, Cu:1.08, Nb:0.043, Cr:0.57, Ni:1.76, Mo:0.55 pct) and the other containing Cu, Nb and B (C:0.04, Mn:1.02, Cu:1.06, Nb:0.036, Cr:0.87, Ni:1.32, Mo:0.41, B:0.002 percent) were hot-rolled into 25 and 12.5 mm thick plates by varying finish-rolling temperatures. The plates were heat-treated by conventional reheat quenching and tempering (RQT), as well as by direct quenching and tempering (DQT) techniques. In general, direct-quench and tempered plates of Nb-Cu heat exhibited good strength (yield strength ∼ 900 MPa) and low-temperature impact toughness (average: 74 J at −85 °C); the Charpy V-notch impact energies were marginally lower than conventional HSLA-100 steel. In Nb-Cu-B heat, impact toughness at low-temperature was inferior owing to boron segregation at grain boundaries. Transmission electron microscopy (TEM) and scanning auger microprobe (SAM) analysis confirmed existence of borocarbides at grain boundaries in this steel. In general, for both the steels, the mechanical properties of the direct-quench and tempered plates were found to be superior to reheat quench and tempered plates. A detailed transmission electron microscopy study revealed presence of fine Cu and Nb (C, N) precipitates in these steels. It was also observed that smaller martensite inter-lath spacing, finer grains and precipitates in direct-quench and tempered plates compared to the reheat quench and tempered plates resulted in their superior strength and good impact toughness.     

Effect of aging on fatigue crack growth behaviour of Cu bearing HSLA-100 steel

Abstract

The effect of aging on fatigue crack growth rate (FCGR) of Cu bearing HSLA-100 steel has been studied. The steel was solution treated, water quenched and aged at various temperatures in the range of 350–700°C. The fatigue crack growth resistance of the steel decreased for the initial stages of aging from 350–500°C. Further aging up to 650°C resulted in an improvement in the crack growth resistance. Beyond 650°C, once again an inferior crack growth resistance was observed. This nature of variation of FCGR behaviour was similar to the trend portrayed by the strength properties with aging treatment. The results are related to the changes in the microstructural constituents owing to the aging treatment.     

Effect of cold work and aging on mechanical properties of a copper bearing HSLA-100 steel

Influence of cold working and aging on the mechanical properties of a Cu-bearing HSLA-100 steel has been studied. The steel was given solution treatment at 1000°C, followed by cold rolling to 25, 50 and 80 pct deformations and aging at 600°C for various durations. Substantial improvement in hardness and UTS was observed in the peak aged condition of various treatments, but at the expense of ductility and impact-energy. Extensive scanning electron microscopic studies carried out on impact and tensile fracture surfaces suggest that poor impact energy and low ductility in peak aged condition could be associated with inhomogeneous deformation caused by the existence of coherent precipitates. Other parameters adversely affecting toughness and ductility in various stages of cold work and aging may include high stress concentration at high density dislocation network and dislocation-precipitate interface. Overaging in various treatments resulted in higher impact energy and ductility, presumably due to existence of incoherent precipitates and reduction in stress concentration at dislocation cell boundaries. It is observed that a good combination of high hardness and UTS with high impact energy and ductility could be obtained by a treatment suitable to cause coexistence of coherent and incoherent precipitates.     

A study on fatigue crack growth in dual phase martensitic steel in air environment

Dual phase (DP) steel was intercritically annealed at different temperatures from fully martensitic state to achieve martensite plus ferrite, microstructures with martensite contents in the range of 32 to 76%. Fatigue crack growth (FCG) and fracture toughness tests were carried out as per ASTM standards E 647 and E 399, respectively to evaluate the potential of DP steels. The crack growth rates (da/dN) at different stress intensity ranges (ΔK) were determined to obtain the threshold value of stress intensity range (ΔK_th). Crack path morphology was studied to determine the influence of microstructure on crack growth characteristics. After the examination of crack tortuosity, the compact tension (CT) specimens were pulled in static mode to determine fracture toughness values. FCG rates decreased and threshold values increased with increase in vol.% martensite in the DP steel. This is attributed to the lower carbon content in the martensite formed at higher intercritical annealing (ICA) temperatures, causing retardation of crack growth rate by crack tip blunting and/or deflection. Roughness induced crack closure was also found to contribute to the improved crack growth resistance at higher levels of martensite content. Scanning electron fractography of DP steel in the near threshold region revealed transgranular cleavage fracture with secondary cracking. Results indicate the possibility that the DP steels may be treated to obtain an excellent combination of strength and fatigue properties.     

Effect of zirconium addition on the recrystallization behaviour of a commercial Al-Cu-Mg alloy

It is well known that the second phase particles have an effect on recrystallization and grain growth behaviour of an alloy. Particularly the bimodal distribution of second phase particles has an effect which is opposite in sense where coarse second phase particles (> 1 μm) stimulate nucleation while fine particles exhibit Zener drag. In the literature, the effect of zirconium addition to aluminium alloys has been well documented in order to produce superplasticity by giving ultra fine grain size to the alloy. Addition of zirconium produces Al ₃ Zr particles which pin the grain boundaries during recrystallization and grain growth. In the present work, zirconium was added to a commercial Al-Cu-Mg alloy and by heat treatment Al ₃ Zr particles were precipitated and after forging, the grain size was an order of magnitude lower than the alloy without zirconium. Transmission electron microscopy was employed to characterize the second phase particles, i.e. Al ₃ Zr particles and found to be rod shaped and identified to be cubic ordered L 1 ₂ phase with a lattice parameter of 0.408 nm. Further, it was observed that fine (100 nm) Al ₃ Zr particles promote only continuous recrystallization which is polygonization of subgrains and subgrain growth. It was found that the fine dispersion of Al ₃ Zr particles inhibits both recrystallization and grain growth in the commercial Al-Cu-Mg alloy.     

Studies on poly (hydroxy alkanoates)/(ethylcellulose) blends

Biodegradable polymers represent one of the most significant area of research today. Among these polymers, poly (β-hydroxy butyrate co β′-hydroxy valerate) i.e. PHBV have received special attention because of their unique combination of properties. They are perfectly biocompatible, biodegradable polymers and can be processed by any conventional technique. In the present study an attempt has been made to develop the biodegradable blends of PHBV by blending them with ethyl cellulose (EC). Ethyl cellulose has been selected to monitor the biodegradation rate of PHBV and also for making the blends cost effective. The blends are thoroughly characterized for their compatibility, by the measurement of viscosity of blends and through FT-IR. Various applications of PHBV/EC blend in agriculture and pharmaceutical industries are being explored. Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore.     

Synthesis and characterization of conducting poly (1-aminonaphthalene), poly (2-aminonaphthalene) and poly (aniline-co-1-aminonaphthalene)

Poly (1&2)-aminonaphthalene and poly (aniline-co-1-aminonaphthalene) have been synthesized in high yields by chemical oxidative polymerization method. The polymers are soluble in polar solvents such as DMSO, NMP etc. In PNA-2 as head-to-tail coupling cannot occur, the electrical conductivity is lower than PNA-1. The copolymer exhibits distinct morphology, higher viscosity, characteristic exciton peak, appreciable thermal stability and electrical conductivity compared to PNA-1.     

Surface studies on as-grown (111) faces of sodium bromate crystals

Single crystals of sodium bromate are grown at various supersaturations ranging from 3% to 8%. Surface studies have been carried out on as-grown and etched (111) faces of these crystals. Typical and systematically oriented growth hillocks are observed almost on all the faces. Further dislocation studies are made to understand the growth history of these crystals. These studies suggest that the crystals grow by 2D-growth mechanism. In addition to this, studies are also conducted on the formation of overgrowths and inclusions in these crystals.     

Corrosion of steel structures in sea-bed sediment

Seabed sediment (SBS) is a special soil that is covered by seawater. With the developments in marine oil exploitation and engineering, more and more steel structures have been buried in SBS. SBS corrosion has now become a serious problem in marine environment and an important issue in corrosion science. In this paper, approach in the field of SBS corrosion is reviewed. Electrochemical and microbial corrosion factors, corrosion mechanism, measurement of metal corrosion rate, corrosion evaluation and prediction of corrosion are also discussed here.     

Preparation of Sm-Ru bimetallic alloy films on Ru(0001) surface by vapour-deposition and annealing

Sm-Ru intermetallic surface alloy films were prepared by vacuum deposition and annealing of rare earth Sm on single crystal Ru(0001) surface. The Ru 3 d and Sm 3 d core level spectra clearly show the formation of surface alloy layers. XPS measurements on surface alloy film revealed an induced peak in the Ru 3 d region at lower binding energy by 1 eV compared to the bulk Ru (elemental) suggesting an electronic effect of alloying and Sm-Ru bond formation. The Sm 3 d _5/2 photoemission peak of Sm film consists of strong features characteristic of Sm(II) with electron configuration 4 f ⁶ (5 d 6 s ) ² and Sm(III) with electron configuration 4 f ⁵ (5 d 6 s ) ³ .It is observed that the Sm(II) feature decreases in intensity upon alloy formation with surface Ru atoms. Oxidation of these films with carbon monoxide indicates alloy breakdown due to the oxidation of Sm atoms selectively. Alloy oxidation also shows a clear shift of Sm 3 d _5/2 feature.     

Study of electrical properties of glassy Se100- xTexalloys

Temperature and frequency dependence of a.c. conductivity have been studied in glassy Se_100- x _Te x(x = 10, 20 and 30) over different range of temperatures and frequencies. An agreement between experimental and theoretical results suggests that the a.c. conductivity behaviour of selenium-tellurium system (Se_100- xTex)can be successfully explained by correlated barrier hopping (CBH) model. The density of defect states has been determined using this model for all the glassy alloys. The results show that bipolaron hopping dominates over single-polaron hopping in this glassy system. This is explained in terms of lower values of the maximum barrier height for single-polaron hopping. The values of density of charged defect states increase with increase in Te concentration. This is in agreement with our previous results obtained from SCLC measurements.     

Effect of penetrants on the aramid Nomex

The response of Nomex sheets to some penetrants has been analyzed. The process of moisture uptake depends on the relative humidity (RH) of the ambient atmosphere and the initial characteristics of the polymer. In the case of common laboratory solvents,the uptake by the polymer shows an inverse dependence on the molar volume of the former. Although the calendered and the uncalendered Nomex sheets exhibit an overall similarity in their response to various penetrants,quantitative comparison reveals distinct differences.     

Effect of plasma ion implantation on the hydrogen embrittlement of Cu strengthened HSLA-100 steel

The effect of low dosage plasma ion implantation on hydrogen embrittlement was studied for an HSLA steel using notched tensile samples. The plasma treatment caused an enhancement in the linear strain to failure under embrittling conditions. This was however not reflected in the fracture surfaces of the treated samples which had similar fractographic features as those of untreated samples. The plasma treatment delayed the process of embrittlement without causing any alteration in the basic mechanism of embrittlement. This was due to introduction of residual compressive stresses as well as reduction in the hydrogen permeation flux. Implantation in pure nitrogen seemed most beneficial while implantation in pure argon caused very little improvement.     

Double stripe reconstruction of the Pt(111) surface

We have studied the reconstruction of the Pt(111) surface theoretically, using a 2D generalization of the Frenkel-Kontorova model. The parameters in the model are obtained by performingab initio density functional theory calculations. The Pt(111) surface does not reconstruct under normal conditions but experiments have shown that there are two ways to induce the reconstruction: by increasing the temperature, or by depositing adatoms on the surface. The basic motif of this reconstruction is a ‘double stripers with an increased surface density and alternatinghcp andfcc domains, arranged to form a honeycomb pattern with a very large repeat distance of 100–300 Å. In this paper, we have studied the ‘double stripe’ reconstruction of the Pt(111) surface. In agreement with experiment, we find that it is favourable for the surface to reconstruct in the presence of adatoms, but not otherwise.     

Investigation of surface modifications in ethylene propylene diene monomer (EPDM) rubber due to tracking under a.c. and d.c. voltages

In the present work, tracking phenomena has been studied with the ethylene propylene diene monomer (EPDM) material under the a.c. and d.c. voltages, with ammonium chloride/acid rain solution as the contaminant. It is noticed that the tracking time depends on the conductivity and flow rate of the contaminant. The physico-chemical analyses viz. wide angle X-ray diffraction (WAXD), thermo-gravimetric differential thermal analysis (TG-DTA) and the differential scanning calorimetry (DSC) studies, were carried out and it was concluded that the tracking process is a surface degradation process. The tracking time is different for a.c. and d.c. voltages.