Microstructure and Mechanical Characterization of Austempered AISI 1018 Steel

AISI 1018 mild steels are widely used for engineering applications in machine components and for structural purposes. These materials suffer mechanical damages especially when used under critical conditions of extreme load. In this study, the effect of austempering heat-treatment on the hardness, tensile strength, impact energy and the microstructure of AISI 1018 steels were evaluated. The steel specimens were subjected to austempering heat-treatment by austenitizing at a temperature of 830°C, maintained at this temperature for a period of 1 hour 30 minutes, before rapidly cooled down in a NaNO3 salt bath maintained at 300°C for isothermal transformation for a further 50 minutes before finally cooled down to room temperature. Microstructural analysis using Scanning Electron Microscope (SEM) shows transformation from ferrite/pearlite to bainite microstructure. The tensile strengths of the specimen increased from 400 MPa to 500 Mpa; hardness increased from an average value of 140Rc to 162Rc; while impact energy increased from 15.6 Joule to 30.6 Joule by the austempering heat-treatment. Keywords—Austempering, hardness, tensile strength, impact energy, microstructur

Mechanical and Structural Responses of Low Carbon Steel to Cold Rolling and Stress Relief Anneal Treatments

This study investigated the effect of deformation by cold rolling and stress relief anneal on the mechanical and structural properties of low carbon steel. The as-received steel samples were cold rolled at 20% – 40 % degrees of deformation using Buhler rolling machine in Metallurgical and Materials engineering department University of Lagos, Nigeria. Additionally, some of the cold rolled samples were annealed at a temperature of 650° C and soaked for 1 hour in a muffle furnace. The results revealed that the ultimate tensile strength (UTS), percent elongation, hardness and impact strength of the cold rolled low carbon steel improved significantly after stress relief anneal due to the elimination of induced strain hardening caused by cold rolling. The micrographs show that cold rolled + stress relief anneal caused significant recrystallization of ferrite-austenite phase to refine martensite with reduction of dislocations. Therefore, the low carbon steel can be used effectively for structural purposes in machines and equipment

Effects of zinc powder addition to Villa Gloss and Silka Lux marine enamel paints on corrosion resistance of mild steel

The anti - corrosion properties of paints can be optimised when adequate proportion of the paint constituents are used. Effect of zinc powder addition to Villa Gloss and Silka Lux Marine Enamel paints on corrosion resistance of mild steel was studied. Quantitative Analysis and Potentiodynamic Polarisation Technique were used to evaluate the samples. The results indicate that zinc powder addition between 15 and 25 % signifi cantly reduced the corrosion rate. The corrosion rate stabilized at approximately 0.10 mmpy when zinc powder added was above 15%, independent of the exposure time. Potentiodynamic anodic polarization curves of the samples immersed in seawater showed that sample with 25% zinc powder addition exhibited highest corrosion potential and the least corrosion current density . Microstructural analysis of the samples also revealed the presence of pitting corrosion at the surfaces of the samples and their geometry, v olume fraction and distribution vary with the zinc powder addition.Keywords: zinc powder, inhibition efficiency, potentiodynamic, weight loss, corrosion rate, pit corrosio

Evaluation of Inhibitive Performance of Some Plants Extracts on Low Carbon Steel Corrosion

The corrosion inhibitive potential of Plumeria Alba, Blighia Sapida and Secamone Afezeli plants extracts on heat-treated and non-heat-treated mild steel samples immersed in different concentrations of hydrochloric acid (HCl) were investigated using weight loss technique. The mild steel samples were cut and prepared for the corrosion test in the acid media mixed with the plant extracts obtained by natural drying, grinding and chemical extraction using hexane. The plants were collected from the botanical garden of University of Lagos, Nigeria. Samples of the mild steel were weighed before immersion and at regular interval of 7 days for a period of 56 days after immersion. The experiment was repeated using 0.1 M and 0.2 M of an inorganic inhibitor. Results obtained showed that the extract of Blighia Sapida exhibited the highest inhibitive power, while annealed samples have the least corrosion rate in the Hcl solution

Electrolytic Co-deposition of Zn-ZnO and Zn-ZnO-CaCO3 Composite Substrates on Low-Carbon Steel

Conventionally employed zinc-rich paints and coatings for marine corrosion protection of steel still comprise environmentally unfriendly compounds such as zinc phosphate. This paper is focused on developing eco-friendly zinc ternary composite coatings of Zn-ZnO-CaCO3 utilizing CaCO3 additives derived from tympanotonus fuscatus (periwinkle) shell and calcareous eggshell respectively on low-carbon steel using electrodeposition technique. This is aimed at improving not only the surface corrosion resistance of steel structures in marine environment but also the sustainability of raw materials and minimal environmental pollution. Corrosion studies of uncoated and coated steel samples in simulated marine environment were done using linear polarization technique. Results obtained suggested that CaCO3 (i.e., calcareous eggshell) additive in the composite coating significantly improved the corrosion performance of the substrate. Steel coated with calcareous eggshell additive displayed superior corrosion performance having highest polarization resistance, Rp (156090 Ω), lowest corrosion rate, CR (0.01 mm/year) and highest coating efficiency, Ceff (97%) as against those of uncoated, zinc oxide, and tympanotonus fuscatus shell additives after 30 minutes deposition time. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS) results of selected developed coatings indicated presence of a homogeneous surface morphology and a significant amount of calcium in the calcareous eggshell coating

Corrosion Behaviours of Aged Haynes 282 and Inconel 718 in Acidic and Alkaline Environments

Haynes 282 and Inconel 718 are superalloy materials originally designed and used in aero- and land-based gas turbine engines. However, they are being considered and used in challenging environments such as nuclear power plants, chemical, and petrochemical plants due largely to their high creep strength and corrosion resistance at low and high temperatures. Recently, there is quest for their uses in the oil and gas refineries. This work examines the corrosion behaviour of these two materials in acidic and alkaline environments; similar to that in the petroleum refinery. The samples were cut, aged, and electrochemically characterized using VersaSTAT 3 model potentiostat with graphite counter electrode and Ag-AgCl SCE. The Linear polarization corrosion test conducted revealed that the corrosion rate, break down potential(Ecorr) and the corrosion current(Icorr)  of the aged Haynes 218 are 0.05mmpy, 0.198V, 5.032µA in dilute HNO3 ; 0.145mmpy,16.23V,13.48 µA in dilute NaOH while those of aged Inconel 718 are 0.068mmpy,96.5V,63.56 µA in the dilute HNO3  and 0.026mmpy,0.41V,2.478 µA in the dilute NaOH respectively. These results showed that aged Haynes 282 has a higher corrosion resistance than aged Inconel 718  in the acidic medium ,but, the reverse in the alkaline medium .However better corrosion  passivation was obtained in HNO3 for the two materials than in NaOH.Keywords- Superalloys, Haynes 282, Inconel 718, Tafel  Extrapolation Method

Effects of Welding Power Input on the Microstructure and Impact Toughness of the Heat Affected Zone of 304L Austenitic Stainless Steel

The effects of welding power input on the microstructural characteristics and impact behaviour of the Heat Affected Zone (HAZ) of type 304L austenitic stainless steel were investigated. This is with a view to optimize the welding process and ensure high weldment integrity of the heat affected zone.  Chemical analysis of the as-received 304L austenitic stainless steel was determined using an Optical Emission Spectrometry AR 4 30 metal analyzer. Thereafter, 30 samples of the as-received 304L austenitic stainless steel plate with dimensions  of 70 mm length, 45 mm breadth and 8 mm thickness  were cut and labeled into A, B and C each of 10 numbers. The grouped samples were further cut into two equal halves with hacksaw and welded using Gas Metal Arc Welding (GTAW) process and 304L electrode to produce butt joint HAZ square geometry samples. The obtained HAZ and as-received samples were machined to standard charpy impact test specimens.  Also, the HAZ and as-received specimens were prepared for microscopy studies using optical microscopy. Results obtained showed that the microstructures are composed majorly of mixture of austenite and ferrite phases, also variations in volume fraction and grain size of the phases were observed under varied range of power input. In addition, chromium carbide formation and precipitation due to sensitization was seen at the grain boundaries. Optimum impact toughness (IT) of 42 J was obtained for HAZ sample at power input of 12.0 KW while the least IT of 39 J was obtained from sample welded using power input of 4.6 KW as compared with the as-received with IT of 58 J.Keywords - 304L austenitic stainless steel; gas metal arc welding; impact toughness; microstructures

The Suitability of Seashell, Animal Bone and Sodium Carbonate as Energizers in Case Carburization of Mild Steel

This work examines the suitability of using seashell (Oyster shell), animal bone and Na2CO3 materials as energizers for case hardening of mild steel. A carburizer consisting of charcoal was used for research with sea shell, animal bone and Na2CO3 as energizers. Samples were carburized in fabricated rectangular stainless steel boxes using different percentages of energizers (10, 20, 30, 40, and 50%) respectively. The samples were covered completely in each of the boxes with the mixture of carburizer and energizer placed in the chamber of the furnace. The process was carried out at carburizing temperature of 9500C, soaked for 4, 6, and 8hours and quenched in oil. Twenty samples were further tempered at 2000C for 1hour to relieve the stress built up during quenching. Hardness test, chemical analysis and impact test were carried out on the samples. The hardness values of the carburized mild steel were measured with a micro hardness tester. The results of the study showed that hardness values of the untempered mild steel samples were slightly improved than the tempered samples at carburizing temperature of 9500C and carburizing time of 4, 6 and 8hours. The Impact results revealed that samples carburized at 9500C in seashell energizer for 8hours have the highest impact values of 184 Joules for the tempered samples which are higher than the untempered samples due to increase in toughness resulting from tempering. The results also showed that seashell and animal bones are potential energizers in case carburization of mild steel

The Suitability of Seashell, Animal Bone and Sodium Carbonate as Energizers in Case Carburization of Mild Steel

This work examines the suitability of using seashell (Oyster shell), animal bone and Na2CO3 materials as energizers for case hardening of mild steel. A carburizer consisting of charcoal was used for research with sea shell, animal bone and Na2CO3 as energizers. Samples were carburized in fabricated rectangular stainless steel boxes using different percentages of energizers (10, 20, 30, 40, and 50%) respectively. The samples were covered completely in each of the boxes with the mixture of carburizer and energizer placed in the chamber of the furnace. The process was carried out at carburizing temperature of 9500C, soaked for 4, 6, and 8hours and quenched in oil. Twenty samples were further tempered at 2000C for 1hour to relieve the stress built up during quenching. Hardness test, chemical analysis and impact test were carried out on the samples. The hardness values of the carburized mild steel were measured with a micro hardness tester. The results of the study showed that hardness values of the untempered mild steel samples were slightly improved than the tempered samples at carburizing temperature of 9500C and carburizing time of 4, 6 and 8hours. The Impact results revealed that samples carburized at 9500C in seashell energizer for 8hours have the highest impact values of 184 Joules for the tempered samples which are higher than the untempered samples due to increase in toughness resulting from tempering. The results also showed that seashell and animal bones are potential energizers in case carburization of mild steel