High density stainless steel product and method for the preparation thereof

Abstract

The invention concerns a method of preparing compacts having a sintered density of above 7.3 g/cm 3. This method comprises the steps of subjecting an annealed, water-atomised, essentially carbon free stainless steel powder, which in addition to iron, comprises at least 10% by weight of chromium, not more than 0.4%, preferably not more than 0.3% by weight of oxygen, not more than 0.05%, preferably not more than 0.02% and most preferably not more than 0.015% of carbon, not more than 0.5% by weight of Si and not more than 0.5% of impurities, to HVC compaction with an uniaxial pressure movement with a ram speed of at least 2 m/s, and sintering the green body.

1 . Method of preparing compacts having a high density comprising the steps of 
 subjecting an annealed, water-atomised, essentially carbon free stainless steel powder, which in addition to iron, comprises at least 10% by weight of chromium, not more than 0.4%, preferably not more than 0.3% by weight of oxygen, not more than 0.05%, preferably not more than 0.02% and most preferably not more than 0.015% of carbon, at most 0.5% by weight of Si and not more than 0.5% of impurities to HVC compaction with a uniaxial pressure movement with an impact ram speed above 2 m/s; and    sintering the green body.    
     
     
         2 . Method according to  claim 1  wherein the annealed powder comprises, by percent of weight 
 10-30% of chromium  
 0-5% of molybdenum  
 0-15% of nickel  
 0-0.5% of silicon  
 0-1.5% of manganese  
 0-2% of niobium  
 0-2% of titanium  
 0-2% of vanadium  
 0-8% of tungsten  
 and at most 0.3% of inevitable impurities, the balance being iron.  
 
     
     
         3 . Method according to any one of the claims  1 - 2  wherein the annealed powder comprises, by percent of weight 
 10-20% of chromium  
 0-3% of molybdenum  
 0.1-0.45% of silicon  
 0.1-0.4% of manganese  
 0-2% of niobium  
 0-0.5% of titanium  
 0-0.5% of vanadium  
 0-8% of tungsten  
 and essentially no nickel the balance being iron.  
 
     
     
         4 . Method according to any one of the claims  1 - 2  wherein the annealed powder comprises comprising, by percent of weight, 
 10-20% of chromium  
 0-3% of molybdenum  
 0.1-0.3% of silicon  
 0.1-0.4% of manganese  
 0-2% of niobium  
 0-0.5% of titanium  
 0-0.5% of vanadium  
 0-8% of tungsten and 7-10% of nickel the balance being iron.  
 
     
     
         5 . Method according to any one of the claims  1 - 4  characterised in that the compaction is performed at a ram speed above 3, preferably above 5 m/s.  
     
     
         6 . Method according to any one of the claims  1 - 5  characterised in that the compaction is performed as warm compaction.  
     
     
         7 . Method according to any one of the preceding claims for the preparation of compacts having a density above about 96%, preferably above 98% of the theoretical density.  
     
     
         8 . Method according to any one of the  claims 1  to  7  wherein the sintering is performed at a temperature between about 1120 and 1250° C. for a period between about 30 and 120 minutes.  
     
     
         9 . Method according to any one of the  claims 1  to  8  characterised in that the sintering is performed in a belt furnace at temperatures below 1250° C., preferably, below 1200° C. and most preferably below 1160° C.  
     
     
         10 . Method according to any one of the  claims 1  to  10  wherein the sintering atmosphere includes hydrogen.  
     
     
         11 . Compacted and sintered stainless steel products, such as flanges, having a sintered density of above 7.25 g/cm 3 , preferably above 7.30 g/cm 3  and comprising at least 10% by weight of chromium, not more than 0.05%, preferably not more than 0.02% and most preferably not more than 0.015% of carbon, and not more than 0.5% by weight of silicon.  
     
     
         12 . Compacted and sintered bodies, according to  claim 11  having a composition, by percent of weight, of 
 10-30% of chromium  
 0-5% of molybdenum  
 0-15% of nickel  
 0-0.5% of silicon  
 0-1.5% of manganese  
 0-2% of niobium  
 0-2% of titanium  
 0-2% of vanadium  
 0-8% of tungsten  
 the balance being iron and at most 0.3% of inevitable impurities  
 
     
     
         13 . Compacted and sintered bodies according to  claim 12  including 
 10-20% of chromium  
 0-3% of molybdenum  
 0.1-0.3% of silicon  
 0.1-0.4% of manganese  
 0-2% of niobium  
 0-0.5% of titanium  
 0-0.5% of vanadium  
 0-8% of tungsten  
 and essentially no nickel, the balance being iron and at most 0.3% of inevitable impurities.  
 
     
     
         14 . Compacted and sintered bodies according to  claim 12  including 
 10-20% of chromium  
 0-3% of molybdenum  
 0.1-0.3% of silicon  
 0.1-0.4% of manganese  
 0-2% of niobium  
 0-0.5% of titanium  
 0-0.5% of vanadium  
 0-8% of tungsten  
 and 7-10% of nickel, the balance being iron and at most 0.3% of inevitable impurities