A brass billet is to be excluded from its initial diameter of $$100mm$$ to a final diameter of $$50mm$$. The working temperature is $${700^ \circ }C$$ and the extrusion constant is $$250$$ $$MPa.$$ The force required for extrusion is

Cold working of steel is defined as working

With a solidification factor of $$0.97 \times {10^6}s/{m^2},$$ the solidification time (in seconds) for a spherical casting of $$200$$ $$mm$$ diameter is

Hardness of green sand mould increase with