High nitrogen steel powder and methods of making the same

Abstract

Provided are methods and devices for forming high nitrogen steel. The processes include heating a steel precursor to a temperature that transforms the steel into an austenite of FCC wherein the heating is in a nitrogen containing atmosphere. After an optional nitrogen uptake time, the precursor is further heated to a temperature above the TγN of the steel yet below the melting point of the steel thereby preserving a solid and creating a solid solution of nitrogen. The second temperature is optionally maintained for a nitride conversion time, optionally wherein the nitride conversion time is too short to result in sintering of the steel. The process further includes rapid quenching of the precursor powder to maintain the nitrogen solid solution and prevent nitride formation thereby forming a high nitrogen steel with little to no nitride content and including nitrogen in solid solution.

1 . A process of forming a high nitrogen steel powder comprising:
 providing a precursor steel, the precursor steel optionally in the form of a precursor powder, the precursor steel comprising iron at 50 weight percent or greater;   heating the precursor powder to a first temperature for a nitrogen uptake time, the first temperature above a T N  of the precursor powder;   heating the precursor powder to a second temperature for a nitride conversion time, the second temperature above a T γN  of said precursor powder and below a melting temperature (Tm) for said precursor powder; and   quenching the precursor powder at a quenching rate, the quenching rate sufficient so as to prevent nitride formation within said procurer powder so as to form the high nitrogen steel powder.   
     
     
         2 . The process of  claim 1 , wherein first temperature is above the T N  of the precursor powder and below a T γ  of the precursor powder. 
     
     
         3 . The process of  claim 1 , wherein the first nitrogen uptake time is equal to a time heating the precursor powder between T N  and T γ  of the precursor powder. 
     
     
         4 . The process of  claim 1 , wherein the nitrogen uptake time results in uptake of an amount of N substantially equivalent to that of the high nitrogen steel powder. 
     
     
         5 . The process of  claim 4 , wherein the second temperature is sufficient to convert substantially all N in the precursor powder to a solid nitrogen solution. 
     
     
         6 . The process of  claim 1 , wherein the nitride conversion time is less than 10 minutes. 
     
     
         7 . The process of  claim 1 , wherein the nitride conversion time is sufficient to convert substantially all nitrides in said precursor powder into dissolved nitrogen. 
     
     
         8 . The process of  claim 1 , wherein the step of quenching is at a quenching rate of 1° C./s to 100° C./s within the precursor powder. 
     
     
         9 . The process of  claim 1 , wherein said precursor powder is agitated during said nitrogen uptake time. 
     
     
         10 . The process of  claim 1 , wherein said precursor powder is consistently maintained below the Tm. 
     
     
         11 . The process of  claim 1 , wherein said nitrogen uptake time is in an atmosphere comprising a reducing gas comprising nitrogen. 
     
     
         12 . The process of  claim 11 , wherein said reducing gas further comprises hydrogen, argon, anhydrous ammonia, or combinations thereof. 
     
     
         13 . (canceled) 
     
     
         14 . The process of  claim 1 , wherein said high nitrogen steel powder is substantially free of nitride compound precipitates. 
     
     
         15 . The process of  claim 1 , wherein said substantially all N in the high nitrogen steel powder is in solid solution. 
     
     
         16 . The process of  claim 1 , wherein nitrogen is present in the alloy at 0.05 weight percent to 6.0 weight percent. 
     
     
         17 - 23 . (canceled) 
     
     
         24 . The process of  claim 1 , wherein the alloy is free of BCC structure. 
     
     
         25 - 27 . (canceled) 
     
     
         28 . A high nitrogen steel alloy that is substantially free of nitride compound precipitates. 
     
     
         29 . The process of  claim 1 , wherein the precursor powder is in a rotary hot tube comprising a plurality of baffles or in a fluidized bed reactor. 
     
     
         30 - 31 . (canceled) 
     
     
         32 . The alloy of  claim 28 , wherein nitrogen is present in the alloy at 0.05 weight percent to 6.0 weight percent. 
     
     
         33 . The alloy of  claim 28 , wherein nitrogen is present in the alloy in excess of 0.4 weight percent, optionally in excess of 0.9 weight percent. 
     
     
         34 . The alloy of  claim 28 , wherein the alloy includes Mn, the Mn optionally present at >0 weight percent to 35 weight percent. 
     
     
         35 . The alloy of  claim 28 , wherein the alloy comprises Ni, optionally at >0 wt % to 20 wt %. 
     
     
         36 . The alloy of  claim 28 , wherein the alloy comprises C, optionally at >0 wt % to 0.2 wt %. 
     
     
         37 . The alloy of  claim 28 , wherein the alloy comprises an austenite metal alloy. 
     
     
         38 . The alloy of  claim 28 , wherein the alloy has an FCC structure, the FCC structure defining 50% or greater the structure of the alloy. 
     
     
         39 . The alloy of  claim 38  wherein the FCC structure is 95% FCC structure or greater. 
     
     
         40 . The alloy of  claim 28 , wherein the alloy is free of BCC structure. 
     
     
         41 . The process of  claim 1 , wherein the precursor comprises ferrite (α) phase, austenite (γ) phase, or a mixture of α+γ phase. 
     
     
         42 . The all of  claim 28 , wherein the high nitrogen steel alloy comprises a single phase structure.