Patent EP-1927580-A1 (EP)
Inventor: RUTHNER MICHAEL J
IPC: C21B13/00
Filed: 2006-12-01
Abstract: The process for making iron powder or microalloyed steel powder suitable for powder metallurgy, comprises reducing a spray roasted iron (III) oxide powder, which is obtained from a spent pickling liquor, at elevated temperatures with gaseous reducing agents and then cooling the reduced powder. The spray roasted iron (III) oxide with a specific surface over 2.0 m 2>/g and a remaining chloride content over 440 ppm Cl -> is used as a raw material. After reduction of the chloride content and the specific surface, the iron oxide is reduced as pre-sintered granulates on a bulk weight of 1200 g/dm 3>. The process for making iron powder or microalloyed steel powder suitable for powder metallurgy, comprises reducing a spray roasted iron (III) oxide powder, which is obtained from a spent pickling liquor, at elevated temperatures with gaseous reducing agents and then cooling the reduced powder. The spray roasted iron (III) oxide with a specific surface over 2.0 m 2>/g and a remaining chloride content over 440 ppm Cl -> is used as a raw material. After reduction of the remaining chloride content and the specific surface in two stages, the iron oxide is reduced as pre-sintered granulates on a bulk weight of 1200 g/dm 3>. The remaining chloride contents of the iron oxide are reduced to less than 100 ppm Cl -> and the specific surfaces of the pre-sintered granulates are reduced to a value of 0.1-2.0 m 2>. The raw material is brought into a slurry by adding a neutralization agent to a pH value of 7.0+- 1.0 and then reduced with respect to the iron oxide on a remaining content around greater than 70%. The iron oxide hollow ball granulates are milled and micronized with the remaining chloride content. Magnetic iron oxide components are removed from the iron oxide suspension, which is mixed with bonding agents and surfactants and then processed with spray drying to green micro granulates of 5-300 mu m. The green micro granulates are treated for the further dismantling of the chloride content at 1000-1350[deg] C for few seconds thermally within the radiation area. A ceramic bonding of the iron oxide particles carries out and the remaining chloride content is lowered on less than 100 ppm Cl ->. The green micro granulates are temporarily sintered under oxidizing conditions at 900- 1350[deg] C. The specific surface of the pre-sintered granulates is stabilized on a value of 0.1-2 m 2>/g. The pre-sintered micro granulates of the iron oxide at temperature of 1050[deg] C are reduced with hydrogen. The oxidizing thermal treatment of the green micro granulates and the reducing treatment of the pre-sintered micro granulates are carried out in a heat. After the reduction of the pre-sintered micro granulates, a classification of iron or micro-alloyed steel powder is carried out to grain fractions. The iron or microalloyed steel powder is cooled in reducing or inert atmosphere, is pressed directly with pressing tools and is processed to mold by pressing. The iron or micro-alloyed steel powder is mixed with carburizers, crystal growth inhibitors, metallic powders, metal alloys, microalloying constituents or alloy form, and is processed with a metallic powder spraying procedure under additive of soluble thermoplastic plastics.