will hammering of metals brings about magnetic field around it?

If you take a piece of steel, line it up North-South, then hit it with a hammer a few times you will indeed make it in to a magnet. It won't be terribly strong, but it will certainly be enough to act as a compass needle. Pieces of steel can also have magnetism induced in them by heating them and letting them cool whilst aligned in a North / South direction, or if they're put in an existing strong magnetic field. For example, a piece of steel might pick up a magnetic field if it were placed near a large electromagnet, part of a running electric motor, etc.