Showing papers on "Carbon steel published in 2002"

Control of intermetallic compound layers at interface between steel and aluminum by diffusion-treatment

Abstract: The toughening of Fe–Al intermetallic compound coating formed by aluminizing of carbon steel was investigated. The growth mechanism, morphology and mechanical properties of Fe–Al intermetallic compound layers on the surface of carbon steel were systematically evaluated for specimens diffused at temperatures ranging from 873 to 1323 K after hot dip aluminizing. Fe2Al5 was mainly formed on the specimen surfaces at the usual diffusion temperatures from 873 to 923 K. However, FeAl and Fe3Al layers having relatively high fracture resistance and oxidation resistance properties were preferentially formed in the specimens diffused at temperatures greater than 1273 K. The activation energies required for the growth of the FeAl and Fe3Al layers were QFeAl=180 and QFe3Al=260 kJ mol−1, respectively. It was identified that the formation and growth of Fe–Al intermetallic compound layers is controlled by the diffusion of Fe atoms into the intermetallic compound layers.

Influence of the pack thickness of the boronizing mixture on the boriding of steel

Abstract: Boronizing, which involves diffusion of boron atoms into steel substrate to form iron borides, is a well-known diffusion coating process and numerous studies have demonstrated the outstanding tribological properties of boronized steel vis-a-vis carburized or nitrided steels However, the high cost of the boronizing process has severely limited its applications One way to bring down the cost of the boronizing process is to reduce the thickness of the boronizing mixture to be packed around the component (called pack thickness) to the minimum required level without compromising on the properties of the boride coating The present study attempts to estimate the optimum pack thickness required to form boride coating of adequate thickness and property in the case of a low carbon steel boronized at 940°C for 2 h Low carbon steel samples have been boronized with varying pack thickness in the range 2-25 mm and the resulting boride coatings have been examined for thickness, microstructure, microhardness profile and abrasion resistance An analysis of the results obtained indicated that a pack thickness of 10 mm is sufficient to obtain boride coatings of adequate thickness and optimum properties

Anaerobic electrochemical corrosion of mild steel in the presence of extracellular polymeric substances produced by a culture enriched in sulfate-reducing bacteria.

Abstract: The corrosion of mild steel in a seawater medium containing extracellular polymeric substances (EPS) produced by sulfate-reducing bacteria (SRB) was studied by electrochemical experiments and atomic force microscopy (AFM). Under anaerobic conditions, the corrosion of mild steel increased up to 5-fold in the presence of a 1% (w/w) EPS solution but in the absence of SRB. The enhanced corrosion is mainly due to the oxidizing power of EPS with a reduction potential of E1/2 at −0.54 V (saturated calomel electrode), which is 0.4 V above that of hydrogen reduction. The electrochemical reduction of EPS provides a couple to iron oxidation, as demonstrated by H-shaped cell experiments in which the steel sample and EPS are not in physical contact but are ionically connected via the solution and electronically connected through an external wire. Fourier transformation infrared spectroscopy and X-ray photoelectron spectroscopy showed that EPS derived from SRB are comprised of 60% proteins, 37% polysaccharides, and 3% ...

Modeling and real time mapping of phases during GTA welding of 1005 steel

Abstract: Evolution of the microstructure in AISI 1005 steel weldments was studied during gas tungsten arc (GTA) welding experimentally and theoretically. The experimental work involved real-time mapping of phases in the heat-affected zone (HAZ) using a synchrotron-based spatially resolved X-ray diffraction (SRXRD) technique and post weld microstructural characterization of the fusion zone (FZ). A three-dimensional heat transfer and fluid flow model was used to calculate the temperature and velocity fields, thermal cycles, and the geometry of the FZ and the HAZ. The experimental SRXRD phase map and the computed thermal cycles were used to determine the kinetic parameters in the Johnson–Mehl–Avrami (JMA) equation for the ferrite to austenite transformation during heating in the HAZ. Apart from providing a quantitative expression for the kinetics of this transformation, the results are consistent with a decreasing nucleation rate of austenite from a ferrite matrix with time. In the FZ, the volume fractions of microconstituents were calculated using an existing phase transformation model and the computed thermal cycles. Good agreement was found between the calculated and experimental volume fractions of allotriomorphic and Widmanstatten ferrites in the FZ. The results indicate significant promise for understanding microstructure evolution during GTA welding of AISI 1005 steel by a combination of real time phase mapping and modeling.

Ferrite/pearlite band formation in hot rolled medium carbon steel

Abstract: The influence of the microsegregation of Mn, Si, and Cr on the austenite decomposition during isothermal transformations in hot rolled medium carbon steel has been studied by neutron depolarisation, electron probe microanalysis (EPMA), and optical microscopy. Eight specimens of the same alloy were held at 1173 K for 30 min and were rapidly cooled to different isothermal transformation temperatures. Two-dimensional EPMA maps of the specimen annealed at 1013 K showed that microsegregation of alloying elements in hot rolled steel is strongly related to the ferrite/pearlite band formation. The local variations in alloying element concentration lead to variations in local transition temperatures, which were calculated with the thermodynamic database MTDATA. Similar EPMA maps for the specimen transformed at 953 K demonstrate the presence of microchemical bands, while optical microscopy reveals the absence of microstructural bands. It is shown that the formation of microchemical bands is a prerequisite f...

Analysis of residual stress in carbon steel weldment incorporating phase transformations

Abstract: The welding process, incorporating rapid heating and cooling, generates distortion and residual stress in weldments Welding distortion and residual stress in welded structures can result in problems such as dimensional inaccuracies during assembly and raise concerns regarding safety during service Therefore, accurate prediction and reduction of residual stress are critical in improving the quality of a weldment In the present paper a new method of analysis is proposed to predict welding residual stress by considering solid phase transformations during the welding process This method is applied to two cases, involving medium carbon steel and low carbon steel respectively The analysis of medium carbon steel revealed the presence of compressive residual stress due to martensite formation when phase transformation was considered However, in low carbon steel the residual stress obtained considering the effect of phase transformation did not differ significantly from that obtained when phase trans

Tungsten-inert gas surface alloying of a low carbon steel

Abstract: In the present study, SAE 1020 steel surface was alloyed with preplaced graphite, chromium and high-carbon-ferro-chromium powders by using a tungsten-inert gas (TIG) heat source, separately. The effects of thickness of the preplaced powder layer on the microstructure, hardness and wear resistance of the alloyed surfaces were investigated. Following the surface alloying, conventional characterization techniques, such as optical microscopy, scanning electron microscopy (SEM), energy dispersive spectrograph (EDS) and X-ray diffraction were employed for studying the microstructure of the alloyed surface. Hardness measurements were performed across the alloyed zone and wear properties of the surfaces were evaluated by a pin-on-disc abrasive wear testing method. The results indicated that different amounts of chromium, carbon and chromium with carbon could be obtained on the surface of the SAE 1020 steel, changing the thickness of the preplaced powder layer. The alloyed surfaces showed an increase in hardness and wear resistance and this was attributed to harder phases. However, the highest hardness and wear resistance surface was obtained for the high-carbon-ferro-chromium powder layer with a 2.4-mm layer. This was attributed to a higher volume friction of carbides (Cr 7 C 3 ) in the microstructure. As a result, TIG arc heat source can be used effectively for surface alloying with a preplaced powder to improve resistance of the surface of the SAE 1020 steel to wear.

Deformation enhanced transformation and dynamic recrystallization of ferrite in a low carbon steel during multipass hot deformation

Abstract: Multipass hot deformation with an industry-acceptable pass reduction has been investigated by hot compression. A fine ferrite grain size can be achieved by carefully controlling the interaction of the deformation-enhanced transformation and dynamic recrystallization of ferrite. By the development of a ferrite grain size of 3–5 μm, the yield strength of Q235 grade plain carbon steel can be doubled, without significant loss of ductility, compared with material produced by conventional processing.

Oxidation of Low-Carbon, Low-Silicon Mild Steel at 450–900°C Under Conditions Relevant to Hot-Strip Processing

Abstract: The oxidation behavior of a low-carbon, low-silicon mild steel was investigated in ambient air at 450–900°C to simulate steel strip oxidation during finishing hot rolling and coiling. Oxide scales developed at 880–900°C for a very short time (12 sec) had a structure similar to that formed on pure iron, but with a greater thickness ratio between the magnetite and wustite layers. However, the scale structure after oxidation for a longer period (200 sec) at 900°C deviated significantly from that reported for pure iron. This difference was attributed to the loss of scale–steel adhesion at some locations. Oxide scales formed in the range of 580–700°C after oxidation for more than 2 hr also differed from those reported for pure iron. The scale structures were irregular, comprising mainly hematite and magnetite with no or very little wustite, while the thickness ratio of these two layers differed considerably at different locations. The scale formed at 450–560°C was relatively uniform with a two-layered (hematite and magnetite) structure; however, the thickness ratio of these two scale layers varied for different oxidation temperatures and different oxidation durations. It was also found that limited oxygen supply (zero air flow) improved the scale–steel adhesion, and substantially reduced the relative thickness of the hematite layer. Continuous-cooling experiments proved that significant growth of the hematite layer, as well as the entire scale layer, may occur if the steel is cooled slowly through the temperature range 600–660°C, and even more significantly through the range 660–720°C.

Annealing behavior of submicrometer grained ferrite in a low carbon steel fabricated by severe plastic deformation

Abstract: The annealing behavior of submicrometer grained ferrite in a low carbon steel processed by equal channel angular pressing (ECAP) was investigated. In particular, the effect of the ECAP strain on the annealing behavior of submicrometer grained ferrite was studied by examining the microstructural changes of the samples processed by two different ECAP strains, 4 and 8, during static annealing. Contrary to the general belief that more severely worked materials exhibit faster kinetics of microstructural evolution related to annealing, i.e. recovery, recrystallization and grain growth, the steel subjected to higher ECAP strain exhibited more sluggish recovery and recrystallization kinetics. The more sluggish recovery and recrystallization kinetics with increasing the ECAP strain is associated with the carbon dissolution from pearlitic cementite during ECAP. The grain growth kinetics of submicrometer grained ferrite was analyzed by the non-ideal grain growth law. The grain growth exponent was about 0.2 and the apparent activation energy for grain growth was 170–180 kJ mol−1. Neither value was influenced by the ECAP strain.

Anaerobic Corrosion of Carbon Steel and Cast Iron in Artificial Groundwaters: Part 1—Electrochemical Aspects

Abstract: In Sweden, high-level radioactive waste will be disposed of in a canister with a copper outer container and a cast iron or carbon steel insert. If the iron insert comes into contact with anoxic geological water, anaerobic corrosion will occur. This paper presents a study of the electrochemical aspects of anaerobic corrosion of carbon steel in artificial Swedish granitic groundwaters. The electrochemical measurements confirm that anaerobic corrosion will lead to the generation of hydrogen, but the rate of corrosion will be anodically limited by the formation of a corrosion product film. The corrosion rate was unaffected by hydrogen pressures up to 100 atm.

Grain refinement and formation of ultrafine-grained microstructure in a low-carbon steel under electropulsing

Abstract: High current electropulsing was applied to a low-carbon steel in the solid state. The relationship between grain size and experimental conditions was revealed. It was found that the ultrafine-grained (UFG) microstructure could be formed when electric current density, heating rate, and cooling rate all were high. The UFG samples prepared by applying electropulsing were free of porosity and contamination, and had no large microstrain. Also, their tensile strength was dramatically enhanced over that of their coarse-grained counterparts, without a decrease in ductility. The mechanism for grain refinement and formation of the UFG microstructure was discussed. It is proposed that the effect of a decrease in thermodynamic barrier and enhancement of nucleation rate in a current-carrying system cannot be neglected.

Effect of martensite content, its dispersion, and epitaxial ferrite content on Bauschinger behaviour of dual phase steel

Abstract: Dual phase microstructures were produced in a low carbon steel, in which the martensite volume fraction was kept constant at two levels, of 18 and 25%, while the epitaxial ferrite content was varied independently. The microstructures were produced with two dispersions of martensite, a relatively coarse dispersion by intercritical annealing of a ferrite/pearlite starting microstructure and a finer dispersion from an initial martensitic microstructure. Bauschinger tests were conducted using prestrains in both tension and compression of 0.4, 1, and 2.2%. Prestrain direction had no measurable effect on plastic flow behaviour after strain reversal. Mean back stresses increased with increasing strain and martensite content, and were higher for the finer martensite dispersion. They decreased significantly with increasing epitaxial ferrite content in the case of the finer dispersion, but less significantly in the coarser dispersion. These effects of microstructure are discussed in terms of stress transfer...

Effect of Temperature on the Marine Immersion Corrosion of Carbon Steels

Abstract: Theoretical and laboratory studies indicate that the corrosion of mild and low-alloy steels should be a function of temperature. In practice, however, it is usually held that this cannot be discerned from actual field corrosion data, being confounded by many other influences. The present study considers data from a recent ASTM-sponsored field study, which reported observations for more than 5 years for the immersion corrosion at 14 different sites around the world for copper-bearing carbon steel (UNS K01501). It also considers data reported historically in the literature, both for copper-bearing steel and for structural-grade steel. For these steels, general or uniform corrosion is the main interest because pitting is usually limited. When data is restricted to conditions that might be expected to prevail at sea and is carefully scrutinized and supplemented by information about (the likely) environmental conditions, it can be arranged to suggest that there is a clearly defined effect of temperatu...

The production of ultrafine ferrite in low-carbon steel by strain-induced transformation

Abstract: An investigation into the production of ultrafine (1 µm) equiaxed ferrite (UFF) grains in low-carbon steel was made using laboratory rolling, compression dilatometry, and hot torsion techniques It was found that the hot rolling of thin strip, with a combination of high shear strain and high undercooling, provided the conditions most suitable for the formation of this type of microstructure Although high strains could be applied in compression and torsion experiments, large volume fractions of UFF were not observed in those samples, possibly due to the lower level of undercooling achieved It is thought that ferrite refinement was due to a strain-induced transformation process, and that ferrite grains nucleated on parallel and linear deformation bands that traversed austenite grains These bands formed during the deformation process, and the undercooling provided by the contact between the strip and the work rolls was sufficient to drive the transformation to homogeneous UFF grains