The invention concerns a low pressure for the preparation of an iron-based, optionally alloyed powder comprising the steps of preparing a raw powder essentially consisting of iron and optionally at least one alloying element selected from the group consisting of chromium, manganese, copper, nickel, vanadium, niobium, boron, silicon, molybdenum and tungsten; charging a gas tight furnace with the powder in an essentially inert gas atmosphere and closing the furnace; increasing the furnace temperature; monitoring the increase of the formation of CO gas and evacuating gas from the furnace when a significant increase of the CO formation is observed and cooling the powder when the increase of the formation of CO gas diminishes.