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In the present paper the results of secondary phases determination and quantification in ZERON100 duplex steel, heat treated at 850–1000°C for 180–2400 s, are presented. During the isothermal heat treatments, at 850°C, the ?phase is the only phase to precipitate at a/?boundaries and triple points, while at 900 and 950°C, ?phase is the first phase to precipitate after 180 s, followed by sphase 300 s later. At all the temperatures the total amount of secondary phases is ~3 after <600 s aging.

This paper concerns the phase transformation induced by heat treatment and cold rolling in four duplex stainless steel. In 2205 and 2507 , during the isothermal heat treatments, chi-phase precipitates as small particles at the ferrite/austenite boundaries, followed by sigma precipitation. At the lowest temperature the formation kinetic of chi-phase is favoured, with the increasing of time and temperature a progressive transformation of chi to sigma occurs and the kinetic of sigma is favoured. During continuous cooling, the chi -phase appears at low cooling rates. In low Ni grades the grain boundaries precipitation of chromium nitrides were detected , but no sigma and chi. In 2101 the austenite transforms to martensite both after cold rolling and quenching

The continuous improvement of the applications of duplex stainless steels (DSS) is justified mainly by their excellent corrosion resistance in very aggressive environments and by their mechanical strength, often twice than that of conventional austenitic grades. Therefore more extensive applications have been suggested, like constructions, structural components, automotive applications, etc. However for such not advanced but quantitatively important applications the base cost of the alloy is one of the more constraining features. A way to obtain leaner alloys is to reduce the Ni content and to compensate with manganese and nitrogen additions. In the present paper the structural and mechanical properties of two low Ni duplex grades are analyzed in order to investigate the structural stability of the austenite against its possible transformation to martensite and the secondary phase’s precipitation. The detailed characterization has been performed with SEM-EDS on as received and heat treated (600-850 °C) alloys. A limited precipitation of chromium carbides and nitrides at the grain boundaries has been detected in both grades. The martensite formation has been revealed only in the 2101 grade. With regard to the impact toughness the behaviour of 2101 grade is quite similar to that of the common DSS, while in the 2304 the drastic drop of toughness is avoided. The corrosion behaviour of both grades in aggressive chloride environments is quite similar to that of austenitic AISI 304 grade.

A duplex stainless steel (DSS) containing nominally 22Cr, 5Ni, 3.2Mo and 1.5Mn has been investigated for secondary phases precipitation, after ageing at 780, 850 and 900°C. Selective etching with different reagents, OM and SEM-BSE have been used to quantify ferrite, austenite and secondary phases. A critical discussion of different metallographic techniques (use of OM and/or SEM-BSE) applied to measure intermetallic content is presented, including an attempt to distinguish chi and sigma. The chemical composition of the phases has been determined by means of EDS, the effects on mechanical properties have been studied with a hardness test. The hardness increases with holding time for all temperatures. The rate of secondary phases increases with the holding time. The 850°C treatment is the most effective for increasing hardness and secondary phase precipitation.

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The continuous detonation spray (CDS) process is one of the most recently developed coating processes andallows the production of thick coatings. This paper examines the correlation between process parameters and the properties of WC–17Co coatings deposited by CDS on an austenitic stainless steel substrate. Among the parameters considered the most important are the oxygen and propane flowrates and the ratio between them, and the distance between the torch nozzle and the surface to be coated. The first three affect the amount of process heat generated, while the last affects the interaction between the flame and the sprayed powders, determining the heating rate and final temperature. Coatings were evaluated in terms of porosity, surface roughness, hardness, and wear resistance.

Biological corrosion is one of the most common corrosive processes found in steel, cast iron and other metals placed in soil, sea water and fresh water. We have studied this type of corrosion development process in steel and cast iron pipes. This corrosion process shows tubercular morphology on the inside surface of pipes. Resulting corrosion products have been examined by: chemical analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD) and Mössbauer spectroscopy. In all the samples the following iron compounds were found: α-FeOOH (Goethite), γ-FeOOH (Lepidocrocite), non-stoichiometric Fe3O4and colloidal hydrate oxide Fe(OH)3· 0.9H2O. Small quantities of α-FeOOH and γ-FeOOH compounds were present as small size grain particles (10–20 nm). These particles may be considered responsible for worsening the organoleptic properties of water.

Induction hardening processes with power pulses obtained by means of capacitors-discharge high-frequency generators are discussed. The process is characterized by high-power densities and heating times on the order of some tens or hundreds of milliseconds together with cooling rates obtained by self-quenching without the use of auxiliary means. The possibility of obtaining the most favorable transient temperature distribution in the workpieces by controlling the shape of the pulses and therefore the variable time rate energy supply is examined. The influence of shape of pulses and discharge circuit's electrical parameters on the heating and cooling transients has been analyzed by a thermal model which allows prediction of the depths of hardening. Measurements from hardening tests carried out on steel samples varying the pulse shapes are given in support of the calculation results.

NiAl and Ni3Al were atomised in a sonic nitrogen gas atomiser. The frequency of dendritic or equiaxed morphologies in the powders depends on powder size for NiAl, while it is fairly independent of powder size for Ni3Al. The cooling rates were computed by means of a finite difference code as a function of powder size and related to grain size or secondary dendrite arm spacing for NiAl and Ni3 Al respectively. Nitrogen uptake was determined by a Leco analyser and was found to depend on powder size.