11) How is steel classified ?
According to carbon percentage
- Low carbon steel : Less than 0.25% carbon
- Medium carbon steel: 0.25%0.7% carbon
- High carbon steel: 0.7%1.5% carbon
According to percentage of alloying elements
- a. Low alloy steel: Alloying element less than 8%
- b. High alloy steel: Alloying element more than 8%
12) Why is the most of cutting tools made out in H.S.S ?
Because it resist the heat on the cutting edge of tool and it smoothly work in high speed.
13) What do you mean by Stainless Steel ?
It is an alloy steel which contains mainly 8% Nickel and 18% Chromium. Stainless steel main applications in measuring and surgical instruments.
14) Why are the delicate parts quenched in oil ?
To avoid cracks on the part.
15) What are the chemical composition of Gun metal, German silver and Duralumin ?
- Gun metal is an alloy of 88% copper, 10% tin and 2% zinc. It is generally used for casting boiler fittings, bearings ,bushes etc.
- German silver is an alloy of copper, nickel, tin and led. It is used for making utensils and resistances in electrical work.
- Duralumin is the aluminium alloy contains 3.54.5% copper,0.40.7% magnesium,0.40.7% manganese and remaining aluminium .Mainly used for making bars, tubes, rivets, sheets ,forgings and stampings.
16) Write the chemical composition and uses of the following: (1) Babbit metal (2) Bright steel (3) High speed steel
- Babbit metal is a tin base white metal which contains 88% tin, 8% antimony and 4% copper .This is mainly used as a bearing metal.
- Bright steel contains 0.05 to 0.45% carbon and up to 0.2%lead.It is used for making set screws, bolts, pins which withstand high loads at longer time.
- High speed steel is an alloy of 18% tungsten, 4% chromium,1% vanadium,4%cobalt and 0.7% carbon. This is generally used for making machine tools like lathe ,planer, shaper, taps , drills and milling cutters.
17) What are the differences between Brass and Bronze ?
- Brass is an alloy of copper and zinc. Generally brass contains 60% copper and 40% zinc. These are used for making bearings, pump fittings, bushes and utensils.
- Bronze contains copper and tin. It is comparatively hard, surface wear is less, can be remolded into any shape like wires, sheets, rods etc.
18) How will you identify cast iron, mild steel and high carbon steel ?
By spark: When a metal is held against grinding wheel it gives sparks. Cast iron gives thick and short sparks. Mild steel gives medium and dense sparks and High carbon steel gives long and dense sparks. By hammering : When a blow of hammer is given with these metals there will be a deep spot on mild steel, less deep spot on high carbon steel and cast iron may break.
19) What is Heat treatment ?
Heat treatment is an operation involving heating and cooling of metals to change its properties.
20) Why heat treatment of steel is necessary ?
- To improve machinability.
- To obtain desired properties.
- To increase resistance of corrosion.
- To change electrical and magnetic properties.
- To relieve the stresses after cold or hot working.
- To refine the grain size.