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Mechanical Engineering Objective Questions { Material science }

204. For better fluidity, the following is added in blast furnace
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205. Case hardening of steel
A.Is the saturation of the surface of steel with carbon by heating it at a high temperature
B.Is the saturation of the surface of steel with any element by its diffusion from the surrounding medium at a high temperature
C.Is the hardening of the casing or surface of steel by proper heat treatment
D.Involves diffusion of carbon and nitrogen in the surface of steel above the critical temperature on heating
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206. The hardest known material is
B.High speed steel
D.Cemented carbide
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207. The significance of the white flame during the operation of the bessemer converter is
A.That air is burning out the silicon and manganese resulting in high increase in temperature and scrap steel needs to be added to control temperature
B.That silicon has burned out and carbon has started burning
C.That the converter must be tilted and air turned off, otherwise iron would oxidise
D.White flame does not occur during the operation of the bessemer converter
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208. Blast furnace uses the following as fuel
D.Liquid oxygen
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209. The property of corrosion resistance of chromium stainless steels is due to
A.Predominating nature of chromium present in stainsteel
B.The formation of a thin film of oxygen and moisture absorbed from the atmosphere
C.The formation of a thin oxide film of Cr2O3 on the surface of steel
D.Super-fire finish of stainless steel which gives no opportunity for any atmospheric constituent to penetrate into the surface
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210. Presence of sulphur makes steel brittle. Its effect can be reduced by adding
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