FIELD OF THE INVENTION:
This invention relates to a method for manufacturing a 9Cr-Oxide Dispersion Strengthened (ODS) steam turbine blade.
This invention also relates to the ODS blade manufactured by the method, having a distinct morphology and mechanical properties.
BACKGROUND OF INVENTION:
Oxide dispersion strengthened steels are the class of materials with exceptional characteristics and provide opportunity for step change in performance of existing and new plant components. The 9Cr ODS alloys with Tungsten, Titanium and yitria exhibit excellent creep strength at high temps and have exceptional resistance to high temp degradation. Therefore, Oxide Dispersion- Strengthened (ODS) alloys have excellent potential for use in next-generation high-temperature applications where superior creep strength and oxidation resistance compared to current alloys is required. For increasing and retaining the high temperature strength of metals and alloys, high number density of very fine second phase particles are dispersed in them. Such materials are termed as oxide dispersion strengthened (ODS) materials. One example of second phase strengthened material is 'Y2O3 dispersed in steels'. The ODS steels have emerged as a new class of materials endowed with excellent high temperature strength, creep resistance and

resistance to oxidation. Therefore, establishment of manufacturability of first stage moving blades from 9Cr Oxide Dispersion strengthened steels was proposed. Also, the new ODS blade material may have some of the same benefits as more expensive Ni based alloys but at a much cheaper cost.
JP5636532B2 teaches the method for producing the oxide dispersion strengthened steel which includes: blending raw material powder in such a manner that excess oxygen content in the steel falls within the prescribed range, the raw material powder being composed of, by mass%, 0.05-0.25% C, 8.0-12.0% Cr, 0.1-4.0% W 0.1-1.0% Ti, 0.1-0.5% Y2O3 and the balance Fe with inevitable impurities; solidifying the raw material powder after subjecting to mechanical alloying treatment; and hot-rolling the solidified raw material powder at a temperature of Ar3 transforming point or higher, then cooling the hot-rolled material in the prescribed cooling speed range.
US20150252458A1 discloses a ferritic/martensitic oxide dispersion
strengthened steel with increased high temperature creep resistance, including 0.02 to 0.2 wt % of carbon (C), 8 to 12 wt % of chromium (Cr), 0.1 to 0.5 wt % of yttria (Y2O3), 0.2 to 2 wt % of molybdenum (Mo), 0.01 to 0.5 wt % of titanium (Ti), 0.01 to 1 wt % of manganese (Mn), 0.01 to 0.3 wt % of vanadium (V), 0 to 0.3 wt % of zirconium (Zr), 0 to 0.5 wt % of nickel (Ni), and the remaining content of iron (Fe), and a method of manufacturing the same. The ferritic/martensitic oxide dispersion strengthened steel may be useful as

a material for core structural components of a nuclear power system, ultra supercritical pressure steam generator components of a thermal power plant, or engine components of an airplane due to a high tensile strength at 700°C and excellent creep resistance.
JP2015168883A related to ODS which contains carbon (C) of 0.02 to 0.2 wt.%, Chromium (Cr) of 8 to 12 wt.%, yttria (Y2O3) of 0.1 to 0.5 wt.%, molybdenum (Mo) of 0.2 to 2 wt.%, titanium (Ti) of 0 01 to 0.5 wt.%, manganese (Mn) of 0.01 to 1 wt.%, vanadium (V) of 0.01 to 0.3 wt.%, zirconium (Zr) of 0 to 0.3 wt.%, nickel (Ni) of 0 to 0.5 wt.%, and the balance iron (Fe), has excellent tensile strength and creep resistance at high temperature, especially 700°C, and is suitably used as reactor core structural components of a nuclear power system such as a sodium cooling fast reactor (nuclear cladding coated tube, duct, wire, end cap, or the like), components of an ultra super critical pressure steam power generator for thermal power generation (rotor, shaft, or the like) and materials of engine components for aircraft (disk, nozzle, or the like).
In JP5339503B2, the oxide dispersion strengthening type alloy steel is produced by applying a mechanical alloying treatment to powers, with which into Fe powder, as the ratio to the total weight, 13.0-23.0% Cr powder, 3.5-5.0% Al powder and 0.25-0.45% Y2O3 powder, 0.02-0 05% C powder and at least one side of 0.2-0.7% Hf powder and 0.4-1.0% Zr powder, are mixed.

Among those powders, Hf or/and Zr are prevented from the agglomeration of the oxide with Al, and since the distribution of the oxide becomes fine and high density, such as 9Cr ODS steel, the high temperature strength is improved. Further, Hf or/and Zr are formed as the carbide or the oxide in the crystal grain boundary, and thus, the high temperature strength is improved by restraining the grain-boundary slipping.
In EP1528113B1 teaches, a method of manufacturing an oxide dispersion strengthened ferritic steel excellent in high-temperature creep strength having a coarse gram structure. The method comprises mixing alloy powders and an Y2O3 powder, subjecting the mixed powder to mechanical alloying treatment, solidifying the alloyed powder by hot extrusion, and subjecting the extruded solidified material to final heat treatment involving heating to and holding at a temperature of not less than the Ac3 transformation point and slow cooling at a rate of not more than a ferrite-forming critical rate which comprises, 0.05-0.25%C, 8.0-12.0% Cr, 0.1-4.0% W, 0.1-1.0% Ti, 0.1-0.5% Y2O3 by weight, with the balance being Fe. In this method, by using a TiO2 powder as a Ti, component to be mixed at the mechanical alloying treatment or by adding a Fe2O3 powder, the bonding of Ti with C is suppressed, and the C concentration in the matrix does not decrease.

OBJECTS OF THE INVENTION:
It is therefore an object of this invention to propose a method for producing oxide dispersion strengthened (ODS) Ferritic/Martensitic steam turbine blade.
It is a further object of this invention to propose a method for producing oxide dispersion strengthened (ODS) Ferritic/Martensitic steam turbine blade, which has a highly stable microstructure.
Another object of this invention is to propose a method for producing oxide dispersion strengthened (ODS) Ferritic/Martensitic steam turbine blade with improved mechanical properties.
Yet another object of this invention is to propose a method for producing oxide dispersion strengthened (ODS) Ferritic/Martensitic steam turbine blade, for the production of ODS blade material, which has the same benefits as more expensive Nickel based alloys.
These and other objects of the invention will be apparent to a reader on reading the ensuing description, in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE INVENTION
This invention relates to a method of producing Oxide Dispersion
Strengthened (ODS) steam turbine blade with composition: Fe - 9 wt. % Cr -
0.13 wt. % C - 2 wt. % W - 0.2 wt. % Ti - 0.35 wt. % Y2O3 through powder
metallurgy route which comprising the steps of:
Subjecting the powder ingredients to mechanical alloying,
Subjecting the mechanically alloyed powder to extrusion of rods,
Subjecting the extruded rods to upset forging and closed die forging to ODS
blade shape,
Subjecting the forged ODS blade to initial machining and heat treatment,
Subjecting the heated ODS blade to final machining and vibrotumbling
thereafter,
Subjecting the ODS blades to various test evaluation like microstructure,
hardness, tensile strength and impact strength.
The invention will be explained in greater details with the help of the following description when read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1: Flow chart and chemical composition of powders

Figure 2: Left: SEM pictures of atomised steel powder and right TEM of Yttria
powder
Figure 3: SEM images of milled powder
Figure 4: TEM of milled powders
Figure 5: Powder feeding facility, canning facility and sealed cans
Figure 6: 9Cr-ODS rods
Figure 7: HP 500MW first stage moving blade from ODS rods
Figure 8: Mechanical properties of X12CrMoWVNbN10-1-1 as per HW 10663
Figure 9: 0.35-0.37% Y2O3 strengthened 8.8-9.2%Cr-W-Ti Steel (ODS)
microstructure at 1000X
DETAILED DESCRIPTION OF THE INVENTION
Thus according to this invention is provided a method for manufacturing a 9Cr – Oxide Dispersion Strengthened (ODS) steam turbine blade.
In accordance with this invention, I provided a method of producing Oxide Dispersion Strengthened (ODS) steam turbine blade with composition: Fe - 9 wt. % Cr - 0.13 wt. % C - 2 wt. % W - 0.2 wt. % Ti - 0.35 wt. % Y2O3 through powder metallurgy route which comprising the steps of: Subjecting the powder ingredients to mechanical alloying, Subjecting the mechanically alloyed powder to extrusion of rods,

Subjecting the extruded rods to upset forging and closed die forging to ODS blade shape,
Subjecting the forged ODS blade to initial machining and heat treatment, Subjecting the heated ODS blade to final machining and vibrotumbling to produce the blades. Thereafter, the ODS blades are subjected to various tests of for evaluation of microstructure, hardness, tensile strength and impact strength. A flow chart for manufacturing the blade from oxide dispersion strengthened steel is given in fig. 1. Raw material consists of atomized steel powder (Fe-9Cr-0.1C-2W-0.2Ti) and Nano Yitria (Y2O3) powder. The SEM and TEM photographs of atomized steel powder and Nano Yitria powder are shown in Fig.2. Pure elemental powders of iron (99.5 mass%, 45-100 µm), carbon (99.7 mass%, 5 µm), chromium (99.9 mass%, under 250 µm), tungsten (99.9 mass%, 4.5-7.5 µm), and titanium (99.7 mass%, under 150 µm) were mechanically alloyed (MA) together with Y2O3 powder (99.9 mass%, 35 nm) in an argon gas atmosphere using a high energy mil. Powders are mechanically alloyed using high energy Mill for mechanical alloying with 4kg capacity for each batch. The standard chemical composition of mechanical alloyed powders produced is Fe-9Cr-0.13C-2W-0.2Ti-0.35Y2O3 (mass%). The excess oxygen (Ex.O) was measured to be 80ppm contained in Y203 from the total oxygen content; this amount of oxygen is inevitable for the formation of a Y–Ti complex oxide. Fig.3 shows SEM Images of milled powder. Milling time is considered as four hours for steady state particle of 60microns. Fig. 4 shows TEM of milled powders. After one hour milling Y2O3 is distributed

between two fragmented layers during milling. After four hours of milling, TEM shows no evidence of Y2O3 and a very fine precipitate of Y-Ti-0 is formed. Milled powder was filled in and degassed at 450°C and sealed. Fig. 5 shows powder feeding, canning facilities and sealed cans. Extrusion trails trials were carried out at 1050, 1100 and 1150°C to optimise the extrusion temperature. After initial trials the sealed cans were upset and extruded at 1150°C with a load of 10T/cm2. Hot extrusion at 1150°C was carried out in extrusion press to produce ODS rods for manufacturing. Initially, 30mm diameter rod was produced from extrusion. In view of the higher diameter requirement of the blades, trials were made to produce 40mm diameter rod and finally process was established for 50mm diameter rod extrusion successfully. ODS rods of diameter 50mm and length of 400mm are given in Fig.6. Since the blade is made though powder metallurgy route having high strength due to nano strengthening, number of trials were made in upset forging and closed die forging for establishing parameters.
During initial trials one rod went through upsetting and other two rods cracked while straightening. It was decided to increase the soaking temperature to 1125°C and also straightening was to be avoided completely. In view of the strength, number of passes were increased to six. It was also suggested to make a trial in 403Cb steel and then make a trial on ODS rods. After completing the trials on the 403Cb steel, die modifications were carried out. Subsequently upset forging was carried out on ODS rods with new dies

with modified heat treatment to get 165mm length and 58/62 diameter rods. These rods were used for closed die forging at 1125°C. The forging is hardened at 1150°C for one hour followed by air cooling and tempered at 750°C for one hour followed by Air cool. The heat treated forging is final machined and given finish with vibrotumbling.
Manufacturing process involved (a) mechanical alloying of powder via ball milling (with parameters: milling energy: 14Kg-m/mm2, milling time: 4 hours, milling atmosphere: Argon gas) and canistering, (b) Extrusion of the rods, (c) Upset forging of extruded rods to 58 to 62mm diameter and 165 mm length at temperature 1125 Deg. C using a series of dies, (d) Closed die envelope forging, (f) machining, (g) heat treatment, (h) final machining and (i) vibrotumbling.
Subsequent to the manufacturing, the ODS blade material was subjected to its properties evaluation tests like microstructure, hardness, tensile strength and impact strength. The forged blade material is found to have a highly stable microstructure with a fine nano distribution of Y-Ti-O dispersoides in tempered martensite matrix, hardness from 322 to 343 HV10 (32 to 35 HRc), tensile strength from 850 to 885MPa, yield strength from 980 to 1032MPa and impact strength from 100 to 120J.

Fig.7 gives 500MW first stage moving blade produced from 9Cr Oxide
dispersion strengthened alloys through powder metallurgy route. The stress
levels, testing and also acceptance criteria for creep and fatigue are being
worked out separately.
Following Fig.8 gives room temperature mechanical properties requirements for X12CrMoWNbn 10-1-1 steel. Detailed NDT test such as Phased Array Ultrasonic testing, MPI, Eddy current testing revealed no cracks in all ODS blades. Tensile and impact samples were made from manufactured blade. Tensile test report show, at room temperature, yield strength from 850 to 885MPa and tensile strength from 980 to 1032MPa. Impact test, at room temperature, shows impact strength value from 100 to 120J. Tensile and impact properties evaluated for room temperature are significantly better than that of X12CrMoWNbn 10-1-1 steel. Addition of titanium to Y2O3 strengthened ODS steel, has the ability to refine the Y-Ti-O dispersoid size to 2-6 nm and at the same time increase the number density of the dispersoids substantially. It has also been shown that the Y-Ti-O nano dispersoid strengthened steel exhibits a higher elevated temperature strength and improved creep compared to Y2O3 dispersed steels without Ti addition. Y-Ti-O nano dispersoids are stable (i.e. no coarsening) up to 800°C, explaining their outstanding creep resistance up to the above temperature. The 'W' content imparts solution hardening effect. In the present study, macrostructures of Oxide (0.35-0.37%Y2O3) Strengthened 8.8-9.2%Cr-1.9-2.1%W-0.19-0.22%Ti

Steel have been evaluated through optical microscopy technique. The sample for metallographic examination was cut from blade and was polished first using emery papers of grit sizes 60,120,180, 220, 320 and 600 and finally with diamond polishing. The sample was etched with Viella's Reagent (5cc HCl + 2gr Picric acid + 100cc Ethyl alcohol) for 30 seconds. Microstructure of polished and etched sample was analyzed under Leica make microscope at 1000X magnification. The microstructure in Fig. 9 shows the uniform distribution of fine dispersoids in the matrix of equiaxed as well as elongated tempered martensite grains with ferrite content in it. Fine distribution of the dispersoids in Y2O3 ODS steels imparts the dislocation pinning effect and reduces grain boundary sliding thereby increases the tensile as well as creep strength of the material. Since, higher creep strength steels consist of a proper mixture of hard grains (elongated grains) and soft grains (equiaxed grains) which is ensured by Ti addition up to 0.35%. Mixture of equiaxed as well as elongated tempered martensite grains along with ferrite morphology demonstrates the expected effect of Ti addition (0.19-0.22%) in the present Y2O3 ODS steel.

WE CLAIM:
1. A method for producing oxide dispersion strengthened (ODS) steam turbine blade having a composition: Fe - 9 wt. % Cr - 0.13 wt. % C - 2 wt. % W - 0.2 wt. % Ti - 0.35 wt. % Y2O3, comprising the steps of subjecting powder ingredients of Iron (Fe), Chromium (Cr), Carbon (C), Tungsten (W), Titanium (Ti) and Yttria (Y2O3) to mechanical alloying by ball milling, to produce a milled powder, feeding the milled powder into cans for extrusion into ODS rods, subjecting the extruded rods to upset forging and closed die forging to ODS blades, subjecting the forged ODS blade to initial machining and heat treatment, followed by subjecting the heat treated ODS blade to final machining and vibrotumbling, to produce the ODS blades.
2. The process as claimed in claim 1, wherein powder ingredients selected for mechanical alloying includes pure elemental powders of iron (99.5 mass%, 45-100 µm), carbon (99.7 mass%, 5 µm), chromium (99.9 mass%, under 250 µm), tungsten (99.9 mass%, 4.5-7.5 µm), titanium (99.7 mass%, under 150 µm) and Y2O3 powder (99.9 mass%, 35 nm).
3. The process as claimed in claim 1, wherein milling is conducted at a milling energy of 14 kg-m/mm2, milling time of 4 hours in an atmosphere of Argon gas.
4. The process as claimed in claim 1, wherein extrusion is carried out at a temperature of 1150°C at a load of 10T/cm2.
5. The process as claimed in claim 1, wherein upset forging of extruded rods is carried out using a series of dies, at temperature of 1125°C to produce rods of 58 to 62 mm diameter and 165 mm length.

6. The process as claimed in claim 1, wherein heat treatment comprises the steps of a) Normalizing: Heat @ 100 to 125 Deg. C/hour till 1150 Deg. C, hold at 1150 ± 10 Deg. C for 1 hour and air cool to room temperature and b) Tempering: Heat @ 100 tol25 Deg. C/hour till 750 Deg. C, hold at 750 ± 10 Deg. C for 1 hour and air cool to room temperature.
7. An Oxide Dispersion Strengthened (ODS) steam turbine blades having a composition: Fe - 9 wt. % Cr - 0.13 wt. % C - 2 wt. % W - 0.2 wt. % Ti - 0.35 wt. % Y2O3, with a uniform distribution of highly thermal stable fine Y-Ti-0 dispersoids in the matrix of equiaxed as well as elongated tempered martensite grains with some ferrite content in them.
8. The steam turbine blades as claimed in claim 7, wherein the hardness in
heat treated condition ranges from 322 to 343 HV10 (32 to 35 HRc).
9. The steam turbine blades as claimed in claim 7, wherein, at room temperature, the yield strength and tensile strength of the ODS blade material ranges from 850 to 885MPa and 980 to 1032MPa respectively.
10. The steam turbine blades as claimed in claim 7, wherein at room temperature, impact strength of the ODS blade material ranges from 100 to 120J.