Engineering Materials

71. Grey cast iron

1. contains 1.7 to 3.5% carbon in free state and is obtained by the slow cooling of molten cast iron
2. is also known as chilled cast iron am is obtained by cooling rapidly. It i: almost unmachinable
3. is produced by annealing process. I is soft, tough and easily machinec metal
4. is produced by small additions o magnesium (or cerium) in the ladle Graphite is in nodular or spheroida form and is well dispersed throughout the material
5. none of the above is true.

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72. Gun metal contains

1. 70% copper and 30% zinc
2. 90% copper and 10% tin
3. 85-92% copper and rest tin with little lead and nickel
4. 70-78% copper and rest tin
5. 85-92% copper and rest zinc.

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73. Hardness of lower bainite (tempered martensite) is about

1. RC 65
2. RC 48
3. RC 57
4. RC 80
5. RC 32.

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74. Hardness of martensite is about

1. RC 65
2. RC 48
3. RC 57
4. RC 80
5. RC 32.

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75. Hardness of steel depends on

1. amount of carbon it contains
2. the shape and distribution of the car-bides in iron
3. method of fabrication
4. contents of alloying elements
5. the quality of ore from which it is made.

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76. Hardness of upper bainite (acicular structure) is about

1. RC 65
2. RC 48
3. RC 57
4. RC 80
5. RC 32.

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77. Heavy duty leaf and coil spring* contain carbon of the following order

1. 0.2%
2. 0.5%
3. 0.8%
4. 1.0%
5. 1.5%.

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78. High carbon steel carries carbon %age c

1. 0.1 to 0.3%
2. 0.3 to 0.6%
3. 0.6 to 0.8%
4. 0.8 to 1.5%
5. 1.5 to 2.5%.

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79. If a refractory contains high content of silicon, it means refractory is

1. acidic
2. basic
3. neutral
4. brittle
5. none of the above.

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80. In grey cast iron, carbon is present in the form of

1. cementite
2. free carbon
3. flakes
4. spheroids
5. nodular aggregates of graphite.

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