Martensittc steel and method of manufacturing a martensitic steel

Abstract

A martensitic steel, consisting of, in % in weight: C: 0.30 to 0.80%, Si: 2.50 to 4.50%, Mn: 1.00 to 2.50%, Al: 0.40 to 1.50%, Cr: 0.1 to 2.00%, V: 0.01 to 0.40%, Ti: 0.005 to 0.35%, and optionally one or more of Nb: less than 0.35%, Zr: less than 0.35%, Ta: less than 0.35%, P: less than 0.25%, S: less than 0.25%, Co: less than 0.50%, Mo: less than 0.90%, W: less than 0.90%, Ni: less than 0.50%, Cu: less than 0.50%, N: less than 0.050%, Ca: less than 0.10%, Mg: less than 0.10%, Ce: less than 0.10%, La: less than 0.10%, B: less than 0.10%, the balance Fe and impurities, and comprising one or more intermetallic phases based on an Al—Fe—Mn—Si system.

1 . A martensitic steel consisting of, in % in weight:
 C: 0.30 to 0.80%,   Si: 2.50 to 4.50%,   Mn: 1.00 to 2.50%,   Al: 0.40 to 1.50%,   Cr: 0.10 to 2.00%,   V: 0.01 to 0.40%,   Ti: 0.005 to 0.35%,   and optionally one or more of   Nb: less than 0.35%,   Zr: less than 0.35%,   Ta: less than 0.35%,   P: less than 0.25%,   S: less than 0.25%,   Co: less than 0.50%,   Mo: less than 0.90%,   W: less than 0.90%,   Ni: less than 0.50%,   Cu: less than 0.50%,   N: less than 0.050%,   Ca: less than 0.10%,   Mg: less than 0.10%,   Ce: less than 0.10%,   La: less than 0.10%,   B: less than 0.10%,   the balance Fe and impurities, and comprising one or more intermetallic phases based on an Al—Fe—Mn—Si system.   
     
     
         2 . The martensitic steel of  claim 1 , fulfilling at least one of the following requirements:
 C: 0.40 to 0.60%,   Si: 3.00 to 4.00%,   Mn: 1.30 to 1.80%,   Al: 0.70 to 1.20%.   
     
     
         3 . The martensitic steel of  claim 1 , fulfilling at least one of the following requirements:
 V: 0.01 to 0.15%,   Ti: 0.05 to 0.25%,   Nb: less than 0.15%.   
     
     
         4 . The martensitic steel of  claim 1 , fulfilling at least one of the following requirements:
 Mo: less than 0.10%,   W: less than 0.10%,   Ni: less than 0.05%,   Cu: less than 0.10%.   
     
     
         5 . The martensitic steel of  claim 1 , fulfilling the following requirement:
 Cr: 0.30 to 0.80%.   
     
     
         7 . The martensitic steel of  claim 1 , wherein the one or more intermetallic phases of the Al—Fe—Mn—Si system comprise at least one ternary Al—Mn—Si intermetallic phase, in particular Al 2 Mn 2 Si 3 . 
     
     
         8 . The martensitic steel of  claim 1 , wherein the one or more intermetallic phases of the Al—Fe—Mn—Si system comprises one or more intermetallic phases of the group consisting of Al 4 Mn 1 Si 2 , Al 4 Mn 1 Si 1 , Al 9 Mn 3 Si 1 , Al 2 Mn 2 Si 3 , Al 17 Fe 3.2 Mn 0.8 Si 2 , α-Al 8.36 Mn 2 Si 1.14 , α-Al 4.01 Mn 1.0 Si 0.74 . 
     
     
         9 . The martensitic steel of  claim 1 , wherein the steel is substantially free of V- and/or Ti- and/or Nb-secondary hardening carbides, in particular substantially free of any secondary hardening carbide. 
     
     
         10 . The martensitic steel of  claim 1 , wherein the steel has an impact toughness equal to or higher than 120 J/cm 2  or 140 J/cm 2  or 160 J/cm 2  or 200 J/cm 2  or 250 J/cm 2 . 
     
     
         11 . A method of manufacturing a martensitic steel, the method comprising:
 providing a hardened and quenched steel having a composition of, in % in weight:   C: 0.30 to 0.80%,   Si: 2.50 to 4.50%,   Mn: 1.00 to 2.50%,   Al: 0.40 to 1.50%,   Cr: 0.10 to 2.00%,   V: 0.01 to 0.40%,   Ti: 0.005 to 0.35%,   and optionally one or more of   Nb: less than 0.35%,   Zr: less than 0.35%,   Ta: less than 0.35%,   P: less than 0.25%,   S: less than 0.25%,   Co: less than 0.50%,   Mo: less than 0.90%,   W: less than 0.90%,   Ni: less than 0.50%,   Cu: less than 0.50%,   N: less than 0.050%,   Ca: less than 0.10%,   Mg: less than 0.10%,   Ce: less than 0.10%,   La: less than 0.10%,   B: less than 0.10%,   the balance Fe and impurities, and comprising one or more intermetallic phases based on an Al—Fe—Mn—Si system; and   tempering the hardened and quenched steel.   
     
     
         12 . The method of  claim 11 , wherein tempering heat treatment is performed at a temperature in a range between 100° C. and 600° C., in particular between 100° C. and 300° C. 
     
     
         13 . The method of  claim 12 , wherein an upper limit of the temperature range is 500° C. or 450° C. or 400° C. or 350° C. or 300° C. 
     
     
         14 . The method of  claim 11  to  13 , further comprising:
 coating the hardened, quenched and tempered steel by physical vapor deposition or chemical vapor deposition or by forming a diffusion layer via nitriding, in particular gas nitriding, plasma nitriding, carbonitriding, oxidation followed by nitriding or nitriding followed by oxidation. 
 
     
     
         15 . The martensitic steel of  claim 1 , machined to form a knife or a saw or a mold or a die or a valve, each part respectively for hot or cold work applications.