Patent Publication Number: US-2019169721-A1

Title: Martensitic steel with delayed z-phase formation, and component

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to PCT Application No. PCT/EP2017/058861, having a filing date of Apr. 12, 2017, based off of German application No. 102016206370.7 having a filing date of Apr. 15, 2016, the entire contents of both of which are hereby incorporated by reference. 
    
    
     FIELD OF TECHNOLOGY 
     The following relates to a martensitic steel having delayed Z-phase formation and a component made of this. 
     BACKGROUND 
     As a function of the use condition, forged rotor disks have hitherto been produced from various forging steels. Thus, a steel based on NiCrMoV is used for compressor disks and a steel based on CrMoWVNbN is used for turbine disks. The use conditions and the design requirements are decisive for the selection of the forging material. 
     When choosing the forging material, it is always necessary to ensure an equilibrium between strength and toughness in order to meet the desired requirements. 
     The material having the highest use temperature is at present a steel based on CrMoWVNbN and a steel based on CrMoCoVB. Both materials are unsuitable in the 800-900 MPa strength class for use above 773K and 823K, respectively. 
     For higher use temperatures, nickel materials are at present being discussed. 
     Unfortunately, the components have disadvantages, which have to be taken into consideration for use: 
     very high costs compared to a disk made of steel, 
     new design concepts have to be developed, 
     longer working times in manufacture. 
    
    
     SUMMARY 
     An aspect relates to solving the abovementioned problem. 
     The alloy composition of martensitic steels has hitherto been restricted by the formation of the Z-phase. 
     The following relates to an alloy which comprises at least (in % by weight):
     Carbon (C): 0.01%-0.10%,   Silicon (Si): 0.02%-0.7%,   Manganese (Mn): 0.3%-1.0%,   Chromium (Cr): 8.0%-10%,   Molybdenum (Mo): 0.1%-1.8%,   Cobalt (Co): 0.8%-2.0%,   Nickel (Ni): 0.008%-0.2%,   Boron (B): 0.004%-0.01%,   Nitrogen (N): 0.03%-0.06%,   Vanadium (V): 0.1%-0.3%,   Niobium (Nb): 0.01%-0.06%,   optionally   Tungsten (W): 2.0%-2.8%,   balance iron (Fe),   in particular consisting of these elements.   

     1st working example (in % by weight):
     Carbon (C): 0.03%,   Silicon (Si): 0.36%,   Manganese (Mn): 0.49%,   Chromium (Cr): 9.12%,   Molybdenum (Mo): 0.15%,   Tungsten (W): 2.4%,   Cobalt (Co): 1.8%,   Nickel (Ni): 0.01%,   Boron (B): 0.006%,   Nitrogen (N): 0.05%,   Vanadium (V): 0.2%,   Niobium (Nb): 0.05%, balance iron (Fe).   

     2nd working example (in % by weight):
     Carbon (C): 0.08%,   Silicon (Si): 0.05%,   Manganese (Mn): 0.82%,   Chromium (Cr): 9.32%,   Molybdenum (Mo): 1.47%,   Cobalt (Co): 0.96%,   Nickel (Ni): 0.16%,   Boron (B): 0.0085%,   Nitrogen (N): 0.04%,   Vanadium (V): 0.17%,   Niobium (Nb): 0.02%,   balance iron (Fe).   

     Apart from the use as forged disk in the gas turbine, further applications are conceivable.
     These include gas turbine compressor blade, steam turbine blade or steam turbine forged parts.   

     The inventive step lies in the development and validation of new Z-phase-delaying alloys for primary use as rotor disk in gas turbines. 
     The advantages are: 
     widening of the use range of inexpensive iron-based alloys compared to expensive nickel-based materials, 
     faster workability of the rotor components based on iron (9%-12% Cr) compared to nickel-based materials, 
     experiences from construction, manufacture and production of the high-alloy iron-based alloys can largely be carried over. This assists, for example, in all probabilistic approaches (e.g. fracture mechanics=&gt;minimized risk), 
     use temperature can be increased and therefore makes power and performance increases for the machine possible without external cooling being necessary. 
     Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. 
     For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements. 
     Martensitic Steel with Delayed Z-Phase Formation, and Component 
     The invention relates to a martensitic steel having delayed Z-phase formation and a component made of this. 
     As a function of the use condition, forged rotor disks have hitherto been produced from various forging steels. Thus, a steel based on NiCrMoV is used for compressor disks and a steel based on CrMoWVNbN is used for turbine disks. The use conditions and the design requirements are decisive for the selection of the forging material. 
     When choosing the forging material, it is always necessary to ensure an equilibrium between strength and toughness in order to meet the desired requirements. 
     The material having the highest use temperature is at present a steel based on CrMoWVNbN and a steel based on CrMoCoVB. Both materials are unsuitable in the 800-900 MPa strength class for use above 773K and 823K, respectively. 
     For higher use temperatures, nickel materials are at present being discussed. 
     Unfortunately, the components have disadvantages, which have to be taken into consideration for use: 
     very high costs compared to a disk made of steel, 
     new design concepts have to be developed, 
     longer working times in manufacture. 
     It is therefore an object of the invention to solve the abovementioned problem. 
     The object is achieved by an alloy as claimed in claim  1  and a component as claimed in claim  2 . 
     The alloy composition of martensitic steels has hitherto been restricted by the formation of the Z-phase. 
     Further advantageous measures which can be combined with one another in any way in order to achieve further advantages are listed in the dependent claims. 
     The invention relates to an alloy which comprises at least (in % by weight):
     Carbon (C): 0.01%-0.10%,   Silicon (Si): 0.02%-0.7%,   Manganese (Mn): 0.3%-1.0%,   Chromium (Cr): 8.0%-10%,   Molybdenum (Mo): 0.1%-1.8%,   Cobalt (Co): 0.8%-2.0%,   Nickel (Ni): 0.008%-0.2%,   Boron (B): 0.004%-0.01%,   Nitrogen (N): 0.03%-0.06%,   Vanadium (V): 0.1%-0.3%,   Niobium (Nb): 0.01%-0.06%,   optionally   Tungsten (W): 2.0%-2.8%,   balance iron (Fe),   in particular consisting of these elements.   

     1st working example (in % by weight):
     Carbon (C): 0.03%,   Silicon (Si): 0.36%,   Manganese (Mn): 0.49%,   Chromium (Cr): 9.12%,   Molybdenum (Mo): 0.15%,   Tungsten (W): 2.4%,   Cobalt (Co): 1.8%,   Nickel (Ni): 0.01%,   Boron (B): 0.006%,   Nitrogen (N): 0.05%,   Vanadium (V): 0.2%,   Niobium (Nb): 0.05%,   balance iron (Fe).   

     2nd working example (in % by weight):
     Carbon (C): 0.08%,   Silicon (Si): 0.05%,   Manganese (Mn): 0.82%,   Molybdenum (Mo): 1.47%,   Cobalt (Co): 0.96%,   Nickel (Ni): 0.16%,   Boron (B): 0.0085%,   Nitrogen (N): 0.04%,   Vanadium (V): 0.17%,   Niobium (Nb): 0.02%,   balance iron (Fe).   

     Apart from the use as forged disk in the gas turbine, further applications are conceivable.
     These include gas turbine compressor blade, steam turbine blade or steam turbine forged parts.   

     The inventive step lies in the development and validation of new Z-phase-delaying alloys for primary use as rotor disk in gas turbines. 
     The advantages are:
         widening of the use range of inexpensive iron-based alloys compared to expensive nickel-based materials,   faster workability of the rotor components based on iron (9%-12% Cr) compared to nickel-based materials,   experiences from construction, manufacture and production of the high-alloy iron-based alloys can largely be carried over. This assists, for example, in all probabilistic approaches (e.g. fracture mechanics=&gt;minimized risk),   use temperature can be increased and therefore makes power and performance increases for the machine possible without external cooling being necessary.