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[신간서적 안내] 재료과학과 공학 (Fundamentals of Materials Science and Engineering)

プロテク (PROduction TECHnology) 研究会

Materials: engineering, science, processing and design

Principles of Solidification and Materials Processing

Effect of manganese, silicon and chromium additions on microstructure and wear characteristics of grey cast iron for sugar industries applications

Welding as a fabrication process is one of the vital production routes for most manufacturing industries. Several factors are involved in the choice of welding process for specific applications; notable among these are compositional range of the material to be welded, the thickness of the base materials and type of current. Most metals oxidize rapidly in their molten state, and therefore, the weld area needs to be protected from atmospheric contamination; this is achieved in gas tungsten arc welding GTAW by a shielding gas (argon, helium, nitrogen). GTAW technique is one of the major processes for joining austenitic stainless steels (ASS) and ferritic stainless steel (FSS) fabrication. However, the microstructural change that occurs during welding and at weld joint is still a major challenge today as it affects both the corrosion resistance and the mechanical properties. Therefore, this present paper reviews past research findings on GTA welding of ASS and FSS. Results of the findings have confirmed that, depending on the amount of heat input, which can be controlled by welding parameters (welding speed, voltage and current), welded joints particularly, heat affected zones (HAZs) of both grades of steels can undergo mechanical failure and can be susceptible to corrosion attack if the joints are produced with a less ideal combination of welding parameters.

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Review of GTAW Welding Parameters

In this study, effects of sawdust, coal dust and iron filling additives at varied proportions on some selected properties of moulding sand were investigated. Consequently, cylindrical specimens with different percentages of additives were prepared based on standard procedures. The prepared specimens were subjected to basic moulding sand testing including moisture content, bulk density, porosity, permeability, green compression strength and green shear strength using standard methods and equipment. From the obtained test results, all the experimental additives were found to improve the selected moulding properties of the base (silica) sand. Moulding sand specimen with sawdust additive revealed a relatively better compaction as compared to moulding sand specimens with coal dust and iron filling additives respectively. The moisture absorbing strength of the moulds was also found to increase with increasing percentage of sawdust. Addition of coal dust to the moulding sand was found to improve sand porosity and permeability which results in less casting defects, and due to improved moisture absorbing strength of sawdust, moulding sand specimens that contained sawdust were equally found to exhibit good compaction with maximum green compressive strength of 108.99 kPa. Also, the combination of 25% sawdust, coal dust and iron filling in the moulding sand was found to produce mould with optimum green shear strength value of 54.49 kPa.

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Effects of Additives on Some Selected Properties of Base Sand

Effect of heat treatment on the corrosion of welded low-carbon steel in 0.3 M and 0.5 M of hydrochloric acid and sodium chloride environments at ambient temperature (25oC) has been investigated. Arc welded low-carbon steel sample of known composition were subjected to the corrosion reagents for 21 days (504 hours). pH and weight loss values were taken at interval of 3 days. Thereafter, weight loss method was used to measure therate of corrosion attack on the heat treated samples at ambient temperature. Results obtained showed that at low concentration, the annealed sample exhibits better corrosion characteristic as compared to the normalized and quenched samples. However, at higher concentration the normalized sample exercised better service performance over the annealed and quenched samples. Thequenched sample was found to have relatively low corrosion performance over the annealed and normalized samples at both low and high concentrations of the media.

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Effect of Heat Treatments on Corrosion of Welded Low-Carbon Steel in Acid and Salt Environments

Modificarea grafitizanta (inocularea) in forma (aliaje Ca-FeSi si Sr-FeSi) are un efect puternic asupra solidificarii fontelor tratate cu magneziu. In procesul de solidificare, cei mai reprezentativi parametrii ai analizei termice au fost imbunataţiţi prin inoculare, precum temperaturi eutectice ridicate, subraciri scazute si valori ridicate ale temperaturii la sfârsitul solidificarii. A fost considerata eficienţa relativa a modificatorilor grafitizanţi, prin intermediul careia a fost gasit faptul ca sistemele Ca,Ba-FeSi si Ca,RE,S,O-FeSi sunt foarte performante. Aliajul Ca,RE-FeSi ce include si S si O poate fi o soluţie pentru producerea pieselor turnate din fonta cu grafit nodular cu pereţi subţiri, deoarece procesul de solidificare este influenţat benefic pe intreaga sa durata. Late in-mould inoculation (Ca-FeSi and Sr-FeSi alloy systems) appears to have a very strong effect on subsequent solidification of Mg-treated irons. As for solidification pattern, the most representative parameters of thermal analysis were improved by inoculation, such as higher eutectic temperatures, lower undercooling and higher temperature at the end of solidification. The inoculant’s relative performance was considered which further confirm that Ca,Ba-FeSi inoculant and Ca,RE,S,O-FeSi inoculant give a very high performance. S and O bearing Ca,RE-FeSi alloy appears to be a solution for thin wall ductile iron castings production, as solidification pattern is beneficially influenced on entire eutectic solidification range.

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Thermal analysis of inoculated ductile irons

This research was conducted to formulate a refractory lining recipe for lining diesel fired rotary furnace from locally sourced kaolin, using locally sourced potter’s clay as binder. Six samples (A-F) of kaolin clay mined locally from Apata II area, Ondo road, in Ile-Ife,Nigeria, were roasted at 1200oC held for 8 hours, mixed with different percentages of raw kaolin and appropriately made into briquettes using potter’s clay of good plasticity as binder. The samples were tested for various refractory properties. The result showed that sample mixes A (100% chamotte), B (80% chamotte, 20% rawkaolin) and C (60% chamotte, 40% raw kaolin) are considered to have good properties. However, the optimum material-mix for the refractory bricks lining, with particular reference to the highest thermal shock resistance was found to be 80% chamotte mixed with 20% raw kaolin.

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Saliu Ojo Seidu

Papers

Review of GTAW Welding Parameters

Effects of Additives on Some Selected Properties of Base Sand

Effect of Heat Treatments on Corrosion of Welded Low-Carbon Steel in Acid and Salt Environments

Thermal analysis of inoculated ductile irons

Production of Refractory Lining for Diesel Fired Rotary Furnace, from Locally Sourced Kaolin and Potter’s Clay