This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Melting of Steel and Stainless Steel”.
1. How is much amount of chromium (in percent) normally added in steel to be called as stainless steel?
a) 1-2 %
b) 2-5 %
d) 10-30 %
Explanation: Stainless steels mainly contain 10-30 % of chromium besides other elements such as carbon, manganese, silicon, sulphur etc. Chromium produces corrosion resistance property in steel, that’s why the material is known as stainless steel as no any kind of stains are occur on the surface of the steel.
2. Which of the following types of stainless steels contain maximum amount of chromium in it?
a) Duplex stainless steels
b) Martensitic stainless steels
c) Austenitic stainless steels
d) Precipitation hardenable stainless steels
Explanation: Duplex stainless steels contain approximately 25 % of chromium while rest of the stainless steels contain less than that of duplex stainless steels. All the stainless steel materials contain chromium and carbon besides other elements. In production of stainless steels, controlling of carbon and chromium content should be proper.
3. In the manufacturing of stainless steel, oxidation of carbon and chromium cannot be possible.
Explanation: In the manufacturing of stainless steel, both chromium and carbon can be oxidized due to decarburization of molten casting. Carbon oxidation in comparing with chromium oxidation may occur at temperature above 1220 ⁰C in the pure state conditions. But experimentally, carbon oxidation can occur at temperature above 1800 ⁰C than that of chromium.
4. Which of the following materials is required in a technique of decarburizing the molten steel?
a) Calcium carbonate
b) Sodium chloride
c) Carbon ferrochrome
d) Sodium ferrochrome
Explanation: Decarburization technology uses high carbon ferrochrome to decarburize the molten steel at lower temperatures. If carbon oxidizes first with respect to chromium at low temperatures, then the reduction in pressure from atmosphere to a lower value will be required. Reduction in pressure is mostly done by vacuum oxygen decarburization (VOD) method.
5. In argon oxygen decarburization (AOD) method, whole process is carried out in a converter type of vessel.
Explanation: The argon oxygen decarburization (AOD) process is mainly carried out in a converter type of vessel which is generally lined up with magnesite bricks. Then a combination of argon and oxygen is filled by the application of tuyeres located on the side of the converter vessel. Then the melt of steel is charged into the vessel for further processing.
6. Preheating of scrap material in steel making process can increase the overall productivity.
Explanation: The energy required for steel making in the electric vessel is mainly for the melting down of scrap material. Preheating of scrap material can reduce the energy requirement which further reduces the time in making of steel that can directly increase the overall productivity. Other advantages include decrease in electrode consumption and the refractory wear.
7. The dust produced from electric furnaces in steel making procedure is directly thrown out to the atmosphere via chimney.
Explanation: In steel making, dust is produced in the electric furnace during melting of steel. The produced dust is carried away in the off-gases which basically contains iron and some non-ferrous materials like zinc and lead. So not only environmental considerations but also for the economic considerations, the dusts are collected and recovery of valuable materials is done.
8. Obsolete scrap is the scrap which is relatively pure and its chemical composition is known.
Explanation: Obsolete scrap generally contains iron and steel parts which are rejected due to end of their service life. It is often mixed with other metals like copper, zinc and tin to form other steel alloys. And home scrap is known as the scrap which is relatively pure and chemical composition is known.
9. Steel yield is highest in continuous casting method which significantly reduces scraps.
Explanation: It is always aimed to have higher steel yield in steel industries through attributes of equipment and technologies used in steel making. The steepest decrease in the amount of scraps is mainly achieved by the application of continuous casting method which has highest casting or steel yield.
10. Copper cannot be removed from steel scraps by the method of conventional refining.
Explanation: It is not possible to remove copper from steel scraps by the method of conventional refining. It can be removed by treating steel scraps with sulphide fluxes and also by treating it at reduced pressure of the gas phase which basically includes vapourization of copper from the steel scraps.
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