Patent Publication Number: US-2019169722-A1

Title: Martensitic steel having a z-phase, powder and component

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to PCT Application No. PCT/EP2017/056363, having a filing date of Mar. 17, 2017 based off of German application No. 102016206371.5 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 comprising Z-phase, powder and a component made therefrom. 
     BACKGROUND 
     As a function of the use condition, forged rotary 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 selection of the forging material. 
     When choosing the forging material, it is always necessary to ensure an equilibrium of strength and toughness in order to meet the design 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 773 K and 823 K, respectively. 
     For higher use temperatures, nickel materials are at present under discussion. Nevertheless, present studies indicate that iron alloys can be utilized up to 873 K. 
     Unfortunately, the components have the following disadvantages which have to be taken into consideration for use: 
     very high costs compared to a disk made of steel,
 
new fracture mechanics concepts have to be developed,
 
longer working times in manufacture.
 
    
    
     SUMMARY 
     An aspect relates to soliving the above mentioned problem. 
     The alloy composition of martensitic steels has hitherto been restricted by the formation of the Z-phase within the period of use of the component. 
     The alloy of embodiments of the invention comprise at least (in percent by weight):
     carbon (C): 0.08%-0.12%, preferably 0.10%   silicon (Si): 0.04%-0.08%, preferably 0.06%   manganese (Mn): 0.08%-0.12%, preferably 0.10%   chromium (Cr): 9%-11%, preferably 10%,   molybdenum (Mo): 0.4%-1.0%, preferably 0.7%,   tungsten (W): 1.6%-2.4%, preferably 2.0%,   cobalt (Co): 2.5%-3.5%, preferably 3.0%,   nickel (Ni): 0.10%-0.24%, preferably 0.17%,   boron (B):0.006%-0.01%, preferably 0.008%,   nitrogen (N): 0.002%-0.01%,   titanium (Ti): 0.008%-0.03%,   vanadium (V): 0.15%-0.25%, preferably 0.20%,   niobium (Nb): 0.03%-0.07%, preferably 0.05%,   optionally   copper (Cu): 1.25%-2.25%, preferably 1.75%,   aluminum (Al): 0.04%-0.10%, in particular 0.07%,   balance iron (Fe),
 
in particular consisting of these elements.
   

     The limit can be shifted by new concepts: 
     a) shifting of the formation of the Z-phase in the direction of 200 000 hours,
 
b) formation of the Z-phase before commencement of the period of use of the future GT forged component.
 
     As a result, the mechanical properties no longer change over the period of use due to formation of the Z-phase. Instead, the characteristics are very much more constant due to the formation of the Z-phase. Design of the components is possible. 
     1 st  working example (in % by weight)
     carbon (C): 0.1%   silicon (Si): 0.06%   manganese (Mn): 0.1%   chromium (Cr): 10%   molybdenum (Mo): 0.7%   tungsten (W): 2%   cobalt (Co): 3%   nickel (Ni): 0.17%   copper (Cu): 1.75%   boron (B): 0.008%   nitrogen (N): 0.003%   titanium (Ti): 0.01%   vanadium (V): 0.2%   niobium (Nb): 0.05%   balance iron   

     2 nd  working example (% by weight)
     carbon (C): 0.1%   silicon (Si): 0.06%   manganese (Mn): 0.1%   chromium (Cr): 10%   molybdenum (Mo): 0.7%   tungsten (W): 2%   cobalt (Co): 3%   nickel (Ni): 0.17%   boron (B): 0.008%   nitrogen (N): 0.008%   titanium (Ti): 0.025%   aluminum (Al): 0.07%   vanadium (V): 0.2%   niobium (Nb): 0.05%   balance iron.   

     Apart from use as forged disk in a gas turbine, further applications are conceivable, e.g. gas turbine compressor blades, steam turbine blade or as steam turbine forged part. 
     The advantages are:
         widening of the use range of “inexpensive” iron-based alloys compared to “expensive nickel-based materials”,   quicker workability of the rotor components based on iron (9%-11% of Cr) compared to nickel-based materials,   experience from construction, manufacture and production of high-alloy iron-based alloys can largely be carried over; this assists, for example, in all probabilistic approaches (e.g. fracture mechanics⇒minimized risk),   use temperature can be increased and therefore allows an increase in power and performance of the machine 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.