Originally Posted by
canid
3lb to 5lb hammer, and for a small poor man's anvil I recommend the head of a large sledge hammer 1/3 burried in a hardwood log section or a pillar of concrete.
HC Rail spikes won't make a wonderful blade, but they'll make a 'knife' near enough for practice's sake. Some people have made some wonderful blacksmith's knives as art objects from them.
To get any worthwhile hardening, they will need to be HC spikes, and will need a pretty aggressive quench. Many people have used brine with some dish soap as a surfactant.