Effect of solution annealing on weldability of aged alloy 800/25Cr–35Ni steel dissimilar welds

Abstract

Dissimilar welding of the aged alloy 800 and the as cast 25Cr–35Ni (wt-%) heat resistant steel was investigated. Microstructures, mechanical properties and weldability of the dissimilar welds were characterised using optical microscopy, scanning electron microscopy and transition electron microscopy equipped by energy dispersive X-ray spectroscopy, and Varestraint test. Since such dissimilar welding was susceptible to crack formation in the heat affected zone of the aged part, the effects of a preweld solution annealing, heat input, interpass temperature and type of filler metal on the weldability of two alloys were investigated. It was found that during the solution treatment, the precipitates produced in the service stage were decomposed and that TiC was formed. In addition, tensile strength and hardness were reduced, but ductility and toughness increased. It was concluded that the most important step to improve weldability and to reduce cracking susceptibility was solution annealing. A suitable annealing treatment was then proposed. The best weldability was found under conditions of solution annealing, low heat input, low interpass temperature and using Inconel 82 or 617 for filler metals.     

Effects of strain aging on the structure and mechanical properties of PM 92·5W–5Ni–2·5Fe heavy alloys

Abstract

This paper describes the effects of strain aging on the mechanical properties and the microstructure of forged 92·5W–5Ni–2·5Fe and its heavy alloys microalloyed with cobalt. The investigation was performed on cold rotary forged rods deformed 15, 20 and 30% and strain aged at temperatures from 673 to 1273 K for 1·8–32·4 ks. The results show that for these alloys, there is a temperature range from 773 to 873 K in which maximum ultimate strength and hardness can be attained. Furthermore, the strain aged alloys have shown strength and hardness increase at a temperature of 973 K in a time period of 10·8 ks. The fracture analysis has shown the presence of predominant transgranular fracture of the tungsten phase and γ-phase in the strain-aged alloys in comparison with the forged alloys. The results indicate that interface and tungsten phase strengthening are predominant mechanisms of strain aging.     

Thermal aging of 16Cr – 5Ni – 1Mo stainless steel Part 2 – Mechanical property characterisation

Abstract

Mechanical property characterisation has been carried out on specimens of 16Cr - 5Ni - 1Mo stainless steel, subjected to various aging cycles. The heat treatment cycles involved solution treatment at 1050 ° C for 1 h followed by heating in the temperature range 400 - 750 ° C for different holding times (1 - 16 h). After heat treatment, tensile, hardness, impact, and creep tests were conducted. Specimens aged at 475 ° C exhibited maximum values of tensile strength and hardness with minimum values of ductility and impact toughness, while specimens aged at 625 ° C had maximum values of impact toughness and ductility. The results were correlated with the microstructural data presented in Part 1 of this study. Softening of the martensitic matrix at 625 ° C occurs as a result of the elimination of internal stresses, the decrease in the dislocation density, and the high volume fraction of austenite which lead to the drop in values of tensile strength and hardness. The results of the study reveal that aging at 550 ° C for 4 h gives the optimum combination of strength, hardness, ductility and toughness for this steel.     

The role of additional silane coupling agent treatment in oxygen plasma-treated UHMPE fiber/vinylester composites

Ultra-high modulus polyethylene (UHMPE) fiber was treated with oxygen plasma and a silane coupling agent in order to improve the interfacial adhesion between the UHMPE fiber and vinylester resin. The oxygen plasma and γ-methylmethacryloxypropyltrimethoxysilane (γ-MPS)-treated UHMPE fiber/vinylester composites showed a slightly higher interlaminar shear strength than the oxygen plasma-treated UHMPE fiber/vinylester composites. The interfacial adhesion of the oxygen plasma-treated UHMPE fiber/vinylester composites in this study is mainly due to mechanical interlocking between the micropits formed by the oxygen plasma treatment and the vinylester resin. The γ-MPS molecules adsorbed onto the UHMPE fiber surface neither affected the morphology of the UHMPE fiber surface, nor reduced the extent of mechanical interlocking. The improved interfacial adhesion by the γ-MPS treatment is due to enhanced wettability and chemical interaction through the chemically adsorbed γ-MPS molecules, as detected by Fourier-transform infrared (FT-IR) spectroscopy. The γ-MPS molecules adsorbed onto the ultra-high molecular weight polyethylene (UHMWPE) plate surface also reduced the aging effect of the oxygen plasma-treated UHMWPE surface.     

Comparison of microwave and thermal cure of unsaturated polyester resin

Abstract

A commercial unsaturated polyester resin, Beetle R 8592 from BIP Chemical Limited has been cured using a microwave oven. Thermal curing was also carried out as a comparative study. The cured resins were compared using differential scanning calorimetry, Fourier transform infrared spectroscopy, dynamic mechanical analysis, scanning electron microscopy, solid state NMR spectroscopy, and flexural properties. The DSC analysis showed that microwave curing was much faster than thermal curing. However, within the limits of experimental error, it was found that the shear modulus, the number average molecular weight M _c, flexural modulus and strength were not significantly different. Solid state NMR also showed similar spectra for both microwave and thermal cured samples, which suggests that the same curing reactions took place in each case.     

Sol–gel derived nanostructure hydroxyapatite powder and coating: aging time optimisation

Abstract

The aim of this work was to evaluate the effect of aging time on the formation and phase purity of nanostructure hydroxyapatite powder and coating. Hydroxyapatite powder and coating were prepared by sol–gel method using calcium nitrate and phosphorous pentoxide as starting materials. Precursor sols were dip coated onto the pure titanium substrates. The coated plates were aged in different aging times and dried. Finally, samples were calcinated at 600 and 700°C. Thermal behaviour, phase formation, surface morphology and interfacial coherency were investigated by thermogravitometry analysis, X-ray diffraction and scanning electron microscope. Results showed that a solution aging time of at least 24 h was required to achieve monophasic nanostructure hydroxyapatite powder and coating. Hydroxyapatite structure of coating was obtained at 600°C, and a β-tricalcium phosphate phase was formed at 700°C. The effect of sintering temperatures on crystallite size of the coatings was not significant.     

A method for screening adhesive materials for small displacements during environmental aging

This paper discusses the use of etalons fabricated from prepared glass slides to quantify the dimensional stability of two adhesive materials in damp environments. This technique facilitated the screening of adhesives for a kinematically demanding application. In addition to describing the etalon technique, additional data are provided on the performance of the device with the selected adhesives. One of the adhesives is simply identified as a cationic cured adhesive, while the other adhesive was Loctite 3615. A range of adhesive bond gaps from 50 to 500 μm was examined for the adhesive that showed the least displacement resulting from environmental aging. The results of this testing were applied to a kinematically sensitive device for verification of the adhesives use in this geometry.     

Relationship between chemical structure of imidazoline inhibitors and their effectiveness against hydrogen sulphide corrosion of steels

Abstract

Seven homologous imidazoline type inhibitors were synthesised, all being derivatives of cyclopentyl- and cyclohexylnaphthenic acids. The protective effectiveness of these compounds was investigated by applying the potential sweep method to the carbon steel St3S and austenitic steel 1H18N9T in a 2% solution of sodium chloride in contact with a hydrocarbon phase and saturated with hydrogen sulphide gas. It was found that the inhibitors investigated and their mixtures present high protective effectiveness at a concentration of 25 ppm, reaching values of 99% for carbon steel and 80% for austenitic steel at 40°C. This protective effectiveness was improved by increasing the length of the substituent chain. Consequently, the least effective compounds were those with the shortest chain substituted at the imidazoline ring. Inhibitors under study were chemisorbed on the electrode surface of the steel and this chemisorption process obeyed the Frumkin adsorption isotherm. Values of the Gibbs free energy of adsorption of inhibitors were determined, and also the equilibrium constants of adsorption and constants of attraction.     

Influence of Trace Additions of Silver on the Stress Corrosion of an Al–4% Zn–3% Mg Alloy

Abstract

Direct measurement of the magnesium solute distributions occurring around grain boundaries in aged Al–4% Zn–3% Mg alloy with and without trace additions of silver has shown that the segregation behaviour of the magnesium is not influenced by the presence of the silver. It has been shown that reported improvements in the stress corrosion resistance of the ternary alloy resulting from trace additions of silver are not due to any effect on either the magnesium segregation or the distribution of silver itself. Microanalysis was performed using the technique of combined electron microscopy and electron energy analysis with a spatial resolution of < 100Å.     

X-ray diffraction and TEM analysis of Fe–Al alloy layer in coating of new hot dip aluminised steel

Abstract

The phase structure in the Fe-Al alloy layer of a new hot dip aluminised steel has been researched by means of electron probe microanalysis, X-ray diffraction and TEM, etc. The test results indicated that the Fe-Al alloy layer of the new aluminised steel was composed of Fe₃Al, FeAl, a few Fe₂Al₅ and α-Fe (Al) solid solution. There was no brittle phase containing higher aluminium content, such as FeAl₃ (59.18 wt-%Al) and Fe₂Al₇ (62.93 wt-%Al). The tiny cracks and brittlement, formerly caused by these brittle phases in the conventional aluminium coated steel, were effectively eliminated. There was no microscopic defect (such as tiny cracks, pores or loose) in the coating. This is favourable for resisting high temperature oxidation and corrosion of the aluminised steel.