39) For case hardening the first stage is carburizing. By carburizing it is meant ?

Increasing the percentage of carbon of the steel piece

Increasing the percentage of carbon of the core of the piece

Increasing the percentage of carbon on the surface

Decreasing the percentage of carbon of the steel piece

Answer is:

Increasing the percentage of carbon on the surface

30 Degree Centigrade to 50 Degree Centigrade above the lower critical point

30 Degree Centigrade to 50 Degree Centigrade above the upper critical point

600 Degree Centigrade to 630 Degree Centigrade

1000 Degree Centigrade to 1030 Degree Centigrade

Answer is:

Sodium carbonate

Sodium sulphate

Sodium cyanide

Barium chloride

Answer is:

slowly in the furnace itself by switching the heat supply off

by removing the piece from the furnace and allowing it to cool in open air

by removing the piece from the furnace and placing it under a blast of air

by removing the piece from the furnace and dipping it in a tank containing water

Answer is: