Process and plant for manufacturing fine iron and steel powders, fine iron and steel powders and use of powders manufactured by the process

Abstract

A process for manufacturing fine iron or steel powders includes the steps of providing an iron based, fragmented raw material, finely divided when applicable, providing a brittle material by transforming raw material to nitride by means of ammonia gas, milling the nitridic material to particle sizes desired, when applicable, and denitriding to a fine iron or steel powder. Also disclosed is a plant for manufacturing fine iron or steel powders, fine iron or steel powders and use of powders manufactured thereby.

1 - 29 . (canceled)  
   
   
       30 . Process for manufacturing fine iron based powders comprising the steps of: 
 (a) providing an iron based, fragmented raw material, finely divided when applicable;    (b) transforming raw material to nitride by means of ammonia gas to provide a brittle nitridic material;    (c) milling the nitridic material to particle sizes desired, when applicable; and    (d) denitriding the milled nitridic material to a fine iron based powder.    
   
   
       31 . Process according to  claim 30 , wherein the raw material is chosen from at least one of the material groups consisting of iron, iron powder, sponge iron, iron oxide powder, steel, steel powder and steel turning scrap.  
   
   
       32 . Process according to  claim 30 , wherein the transformation to nitride is carried out in a temperature range between about 400° and 800° C.  
   
   
       33 . Process according to  claim 32 , wherein the transformation to nitride is carried out in a temperature range between about 500° and 700° C.  
   
   
       34 . Process according to  claim 30 , wherein the nitridic material has a nitrogen content of about 3% to 20% by weight.  
   
   
       35 . Process according to  claim 34 , wherein the nitrogen content is more than 6% by weight.  
   
   
       36 . Process according to  claim 30 , wherein the milling step is performed by milling equipment for milling materials down to micron sizes.  
   
   
       37 . Process according to  claim 36 , wherein the milling equipment is chosen from the group consisting of ball milling equipment and jet milling equipment.  
   
   
       38 . Process according to  claim 30 , wherein the milling step is performed batchwise.  
   
   
       39 . Process according to  claim 30 , wherein the milling step is performed continuously.  
   
   
       40 . Process according to  claim 30 , further including the step of separating a fraction of powder particles of the milled nitridic material within a desired particle size interval.  
   
   
       41 . Process according to  claim 40 , wherein the separation step is chosen from the group consisting of sieving and elutriation techniques in a batchwise or continuous separation procedure.  
   
   
       42 . Process according to  claim 40 , wherein the milling and separation steps are performed dry.  
   
   
       43 . Process according to  claim 40 , wherein the milling and separation steps are performed wet.  
   
   
       44 . Process according to  claim 40 , wherein, during the separation step, too coarse, separated particles of the milled nitridic material are recirculated from the separation step to the transformation step.  
   
   
       45 . Process according to  claim 40 , wherein, during the separation step, nitride powder is produced as an alloying substance for sintering purposes.  
   
   
       46 . Process according to  claim 40 , further comprising the step of using a portion of the powder particles of the milled nitridic material as an alloying substance in sintered steel production.  
   
   
       47 . Process according to  claim 30 , wherein the transformation to nitride and milling steps are performed in an integrated process step by providing milling bodies in a rotating tube furnace.  
   
   
       48 . Process according to  claim 30 , wherein denitriding step is performed by hydrogen gas.  
   
   
       49 . Process according to  claim 48 , wherein the denitriding step is performed in a temperature range between about 250° to 400° C.  
   
   
       50 . Process according to  claim 47 , wherein the denitriding step is performed in a temperature range between about 300° to 350° C.  
   
   
       51 . Process according to  claim 30 , wherein the fine iron based powder produced by the denitriding step has a mean particle size of about 1 to 50 μm.  
   
   
       52 . Process according to  claim 51 , wherein the fine iron based powder produced by the denitriding step has a mean particle size of about 3 to 25 μm.  
   
   
       53 . Process according to  claim 30 , further comprising the step of using the fine iron based powder as material for metal injection molding.  
   
   
       54 . Process according to  claim 30 , further comprising the step of using the fine iron based powder in a sintering process.  
   
   
       55 . Process according to  claim 54 , wherein the fine iron based powder is a steel powder.  
   
   
       56 . Fine iron based powder produced by the process according to  claim 30 .  
   
   
       57 . Plant for manufacturing fine iron based powders comprised of: 
 (a) means for containing a fragmented iron based raw material;    (b) transformation means for providing ammonia gas to said raw material to transform the raw material substantially totally to nitride to provide a brittle nitridic material;    (c) milling means, when applicable, for milling the nitridic material to particle sizes desired; and    (d) means for denitriding the milled nitridic material to a fine iron based powder.    
   
   
       58 . Plant according to  claim 57 , wherein said transformation means operates in a range of about 400° to 800° C.  
   
   
       59 . Plant according to  claim 58 , wherein said transformation means operates in a range of about 500° to 700° C.  
   
   
       60 . Plant according to  claim 57 , wherein said transformation means provides a nitrogen content in a range of about 3% to 20% by weight.  
   
   
       61 . Plant according to  claim 60 , wherein said transformation means provides a nitrogen content over 6% by weight.  
   
   
       62 . Plant according to  claim 57 , wherein said milling means is chosen from the group consisting of ball milling equipment and jet milling equipment for milling materials down to micron sizes.  
   
   
       63 . Plant according to  claim 57 , wherein the milling means is arranged for batchwise milling.  
   
   
       64 . Plant according to  claim 57 , wherein the milling means is arranged for continuous milling.  
   
   
       65 . Plant according to  claim 57 , further comprising separation means for obtaining a fraction of powder particles of the milled nitridic material within a desired particle size interval.  
   
   
       66 . Plant according to  claim 65 , wherein the separation means is chosen from the group consisting of sieving and elutriation means arranged for batchwise or continuous operation.  
   
   
       67 . Plant according to  claim 65 , wherein the milling and separation means are intended to be operated dry.  
   
   
       68 . Plant according to  claim 65 , wherein the milling and separation means are intended to be operated wet.  
   
   
       69 . Plant according to  claim 65 , wherein the separation means separates too coarse particles to be recirculated back to the transformation means.  
   
   
       70 . Plant according to  claim 57 , wherein the transformation and milling means are a rotating tube furnace provided with milling bodies.  
   
   
       71 . Plant according to  claim 57 , wherein the transformation and milling means are integrated.  
   
   
       72 . Plant according to  claim 71 , wherein the integrated transformation and milling means are a rotating tube furnace provided with milling bodies.  
   
   
       73 . Plant according to  claim 71 , further comprising separation means for obtaining a fraction of powder particles of the milled nitridic material within a desired particle size interval.  
   
   
       74 . Plant according to  claim 73 , wherein the separation means separates too coarse particles to be recirculated back to the transformation means.  
   
   
       75 . Plant according to  claim 57 , wherein the denitriding means provides hydrogen gas for denitriding the nitride powder.  
   
   
       76 . Plant according to  claim 57 , wherein the denitriding means is intended to be operated in a temperature range from about 250° to 400° C.  
   
   
       77 . Plant according to  claim 76 , wherein the denitriding means is intended to be operated in a temperature range from about 300° to 350° C.  
   
   
       78 . Plant according to  claim 57 , wherein the raw material is chosen from at least one of the material groups consisting of iron, iron powder, sponge iron, iron oxide powder, steel, steel powder and steel turning scrap.