Showing papers on "Carbon steel published in 2001"

Dilatometric analysis of phase transformations in hypo-eutectoid steels

Abstract: Dilatometry is a useful technique to obtain experimental data concerning transformation kinetics in ferrous alloys. This technique is commonly used in cooling experiments to study the austenite decomposition of hypo-eutectoid steel grades. In the standard analysis of the dilatation signal there are two factors that are normally neglected. During the pro-eutectoid ferrite formation the austenite enriches in carbon, resulting in a non-linear temperature dependence of the specific austenitic volume. Furthermore, the specific volume of the formed ferrite is considerably different from that of the formed pearlite. In total not taking into account these two effects can lead to an error in the determined fraction ferrite of up to 25%. A method is presented that takes into account the two above-mentioned factors. In order to determine both the fraction ferrite and the fraction pearlite, in the analysis the temperature range of the transformation is divided into a ferrite-formation range and a pearlite-formation range. Two possible criteria for this division are discussed, and it is shown that the choice does not have an essential influence on the results.

The use of electrochemical techniques to study the corrosion behaviour of organic coatings on steel pretreated with sol-gel zirconia films

Abstract: The two main features of a protective organic coating are its adhesion and corrosion protection. In order to improve both, chemical pretreatments have been used. The use of chromates was very popular, but recently they have been highly restricted because of their toxicity, so that chromate-free pretreatments have been developed and tested. An interesting alternative seems to be the deposition on the metallic surface of thin layers of zirconia by the sol-gel process. In this study thin films of amorphous zirconia on low carbon steel sheets have been obtained by the dip-coating technique, using two different complexing reagents. Control of the hydrolysis allowed the formation of ZrO 2 films suitable as pretreatments, promoting the adhesion of organic coatings. The behaviour of these samples was compared with steel samples pretreated in conventional phosphatation baths. The adhesion of a polyester organic coating was evaluated by the pull-off technique, by measuring the detachment of cross-scratched samples after salt fog chamber testing, or by swelling the organic coating in methyl pyrrolidone. According to the results, the samples pretreated with zirconia layers showed promising performance, in comparison with commercial chemical treatments (tricationic phosphate and iron phosphate). The organic coating adhesion on zirconia films was found to depend strongly on the process parameters, e.g. concentration of the precursors solutions and chelating agents, which determine the thickness and the amount of organic residuals of the amorphous zirconia. Electrochemical impedance spectroscopy (EIS) was also used in sodium sulphate solutions to evaluate adhesion and the corrosion behaviour of these materials. No barrier properties of the zirconia films were observed. Resistance to delamination was studied by using samples where an artificial defect was made by mechanical tools of different diameter. The information obtained by EIS was in good agreement with the data obtained by salt fog chamber tests.

Influence of machining by finishing milling on surface characteristics

Abstract: The aim of this study is to analyse the evolution of residual stresses, microstructure, microhardness and roughness in relation to the different parameters of milling. For finishing milling, parameters are cutting speed and feed. The hole drilling strain gage technique was used to determine the residual stresses. These are measured from the surface to the bottom of the treated workpiece. Two different materials were used in this study: a carbon steel (CS) and a duplex stainless steel (DSS). The latter belongs to a high strength stainless steel family with high corrosion resistance properties. In this study, we have used the experimental system method to analyse the evolution of different surface characteristics in connection with cutting phenomena which are cutting forces, chip geometry and cutting temperature. We have noted that a high value of cutting speed used with a small value of feed improves the quality of the machined surface.

On the thermo-mechanical events during friction surfacing of high speed steels

Abstract: This paper is concerned with the friction surfacing of high-speed steels, BM2, BT15 and ASP30 onto plain carbon steel plate. The events that the matrix and carbides experience as the coating material pass from the coating rod to the substrate, in forming the coating, is described. The coating is observed to harden automatically within a few seconds of being deposited onto the cold substrate. This autohardening is observed to be an inherent feature of the friction surfacing process and the only post-coating heat treatment required is tempering, as with traditionally hardened high-speed steels. The mechanism of autohardening is discussed in terms of the mechtrode/coating/substrate thermal system.

Coating system for high temperature stainless steel

Abstract: A method for protecting carbon steel and stainless steel, and particularly high temperature stainless steel, from coking and corrosion at elevated temperatures in corrosive environments, such as during ethylene production by pyrolysis of hydrocarbons or the reduction of oxide ores, by coating the steel with a coating of MCrA1X or MCrA1XT in which M is nickel, cobalt, iron or a mixture thereof, X is yttrium, hafnium, zirconium, lanthanum, scandium or combination thereof, and T is silicon, tantalum, titanium, platinum, palladium, rhenium, molybdenum, tungsten, niobium, or combination thereof. The coating and substrate preferably are heat-treated at about 1000 to 1200 °C for at least about 10 minutes, preferably about 20 minutes to 24 hours, effective to metallurgically bond the overlay coating to the substrate and to form a multiphased microstructure. The coating preferably is aluminized by depositing a layer of aluminum thereon and subjecting the resulting coating to oxidation at a temperature above about 1000 °C for a time effective to form an alumina surface layer. An intermediary aluminum-containing interlayer may be deposited directly onto the substrate prior to deposition of the overlay coating and is heat-treated with the coating to form a protective interlayer between the stainless steel substrate and coating to disperse nitride formation at the substrate/coating interface. Also, the coating may be deposited onto and metallurgically bonded to the substrate by plasma transferred arc deposition of atomized powder of MCrA1XT, obviating the need for a separate heat treatment. Alternatively, a blended powder composition to produce a desired MCrA1XT alloy may be applied to the substrate.

Microbiologically Influenced Corrosion of Carbon Steel Exposed to Anaerobic Soil

Abstract: Microbiologically influenced corrosion (MIC) of plain carbon steel in anaerobic soil was investigated using field survey, the electrochemical polarization technique, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), a thin-film electrical resistance (ER) probe, and galvanic current measurement. The field survey revealed that the risk of MIC could be predicted by the analysis of environmental parameters such as soil resistivity, water content, the content of total organic carbon, reduction-oxidation potential, and the content of sulfate with the consideration of the effectiveness of cathodic protection (CP). From the results of conventional electrochemical experiments, it is evident that the presence and therefore the activity of sulfate-reducing bacteria (SRB) alter the corrosion mechanism of steel by the production of hydrogen sulfide (H2S) and iron sulfide (FeS) film on the steel surface, which reduces the polariz...

Cavitation erosion-corrosion behaviour of laser surface alloyed AISI 1050 mild steel using NiCrSiB

Abstract: A Ni-based hardfacing alloy NiCrSiB (Ni–16.5%Cr–15.5%Fe–3.5%Si–3.8%B–1%C) was surface alloyed on AISI 1050 mild steel (Fe–0.2%Cr–0.4%Mn–0.5%C) specimens using a two-step process. NiCrSiB powder was preplaced on the substrate by flame spraying and then remelted by a 2 kW continuous wave Nd:YAG laser to achieve surface alloying. The cavitation erosion–corrosion characteristics of the surface alloyed specimens in 3.5% NaCl solution at 23°C were determined by means of a 20 kHz ultrasonic vibrator at a peak-to-peak amplitude of 30 μm and a potentiostat. At a dilution ratio of 12% (corresponding to a laser scanning speed of 25 mm s −1 ), the overall cavitation erosion–corrosion resistance of the alloyed surface was 8.9 times that of the as-received AISI 1050 specimen. The corrosion resistance was also improved as reflected by a reduction in the current density of least one order of magnitude as compared with the as-received specimen at the same potential. The improvement in cavitation erosion resistance could be attributed to the superior mechanical properties of the NiCr-alloyed matrix formed and the presence of borides and boro-carbides which increased the hardness. The improvement in corrosion resistance was due to the increase in Cr and Ni content in the alloyed layer. The relative contributions of pure mechanical erosion, electrochemical corrosion, and synergism between erosion and corrosion to the overall cavitation erosion–corrosion were also determined.

The anaerobic corrosion of carbon steel and cast iron in artificial groundwaters

Abstract: In Sweden, high level radioactive waste will be disposed of in a canister with a copper outer and a cast iron or carbon steel inner. If the iron insert comes into contact with anoxic geological water, anaerobic corrosion leading to the generation of hydrogen will occur. This paper presents a study of the anaerobic corrosion of carbon steel and cast iron in artificial Swedish granitic groundwaters. Electrochemical methods and gas collection techniques were used to assess the mechanisms and rates of corrosion and the associated hydrogen gas production over a range of conditions. The corrosion rate is high initially but is anodically limited by the slow formation of a duplex magnetite film. The effects of key environmental parameters such as temperature and ionic strength on the anaerobic corrosion rate are discussed.

Room temperature creep and strain-rate-dependent stress-strain behavior of pipeline steels

Abstract: Creep deformation and the effect of strain-rate on stress-strain behavior of X-52, X-70 and X-80 pipeline steels at room temperature were studied using round tension test specimens. Depending on its chemical composition and the processing condition (as-received or fully annealed), a pipeline steel may exhibit a stress-strain curve with or without a yield point. The as-received and the annealed steels with both type of yielding behavior were creep tested at a constant stress either below or past the yield point / 0.2% offset yield strength. Independent of yielding behavior, significant post-yield creep deformation was observed in all the steels. The pre-yield creep, however, is strongly dependent on the yielding behavior. In the presence of a yield point, only a minor deformation was detected in the steels subject to the pre-yield creep. In the absence of a yield point, pre-yield creep deformation occurred to a relatively large extent. For the latter case, an annealing treatment further enhanced creep deformation. A strain-rate-dependent stress-strain behavior was also observed in all thesteels that show significant creep deformation. Dislocation mechanisms responsible for the creep behavior observed in the study are also provided in the paper.