Corrosion Resistant Metallurgical Powder Compositions

Abstract

Provided are corrosion resistant metallurgical powder compositions, corrosion resistant compacted articles prepared from metallurgical powder compositions, and methods of preparing the same. Corrosion resistant metallurgical powder compositions include as a major component, an iron-based powder and, as a minor component, alloy additives that include chromium, and carbon. Upon compaction and sintering, the iron-based powder and alloy additives form a dual phase alloy system. The dual phase alloy system is denoted by an admixed martensite and ferrite microstructure. This unique microstructure results in beneficial physical properties, such as for example, high strength, hardness, and ductility, impact energy, and fatigue endurance, while maintaining resistance to corrosion.

1 . A method of preparing corrosion resistant compacted articles comprising the steps of:
 (a) providing a metallurgical powder composition comprising:
 (i) as a major component, an iron-based powder, 
 (ii) as a minor component, alloy additives comprising:
 about 5.0 to about 30.0 weight percent chromium, and 
 about 0.001 to about 0.1 weight percent carbon, 
 
   (b) compacting the metallurgical powder composition in a die at a pressure of at least 5 tsi;   
       wherein the metallurgical powder composition achieves a dual phase microstructure of martensite and ferrite upon sintering. 
     
     
         2 . The method of preparing corrosion resistant compacted articles of  claim 1  wherein the metallurgical powder composition further comprises molybdenum, copper, nickel, sulfur, phosphorus, silicon, manganese, titanium, aluminum, or combinations thereof. 
     
     
         3 . The method of preparing corrosion resistant compacted articles of  claim 1  wherein the metallurgical powder composition comprises a prealloyed powder. 
     
     
         4 . The method of preparing corrosion resistant compacted articles of  claim 1  wherein the ferrite factor of the metallurgical powder composition is from about 6 to about 20 and ferrite factor (K m ) is defined by the formula:
     K   m =(weight percent Cr)−40(weight percent C+weight percent N)+4(weight percent Mo)−5(weight percent Cu)−4(weight percent Ni)−20(weight percent P)+6(weight percent Si)−2(weight percent Mn)+8(weight percent Ti)+2(weight percent Al).
 
 
     
     
         5 . The method of preparing corrosion resistant compacted articles of  claim 1  wherein the iron based powder is a water-atomization powder. 
     
     
         6 . The method of preparing corrosion resistant compacted articles of  claim 1  further comprising the step of sintering the compacted article to form a dual phase microstructure of martensite and ferrite. 
     
     
         7 . The method of preparing corrosion resistant compacted articles of  claim 1  wherein the compacted article exhibits a density of greater than about 6.6 g/cm 3 . 
     
     
         8 . The method of preparing corrosion resistant compacted articles of  claim 6  wherein the sintered compact comprises from about 1.0 to about 20.0 volume percent of ferrite in a martensite matrix. 
     
     
         9 . The method of preparing corrosion resistant compacted articles of  claim 6  wherein the sintered compact exhibits a sintered density of from about 7.15 g/cm 3  to about 7.38 g/cm 3 .