Assuming the steel is en9 - which is fairly common for hammers then I would quench it at 820-840 , no need to soak it for ages although a couple of normalising cycles from the same temperature would probably help. Warm Oil is safer to quench in, although water should be fine as well , and I would temper at 200- 240. If you don't have a thermocouple for the HT then get it to non-magnetic then heat it slowly until you see a slight change in colour this should see you in the right temperature range.