FIELD OF THE INVENTION

This invention in general relates to the field of metallurgy. More particularly, the invention relates to the formation of an alloy with Cobalt as its main constituent and imparting specialized required properties which are desired in the areas of its application. Furthermore, the invention describes the specific conditions and processes to which the base metal viz., cobalt and other constituent elements are subjected to while achieving the end product i.e., the alloy which has the desired properties necessary for its applications especially in the Aerospace sector for manufacture of component like springs, rotors, jet and liquid engine parts which are operated in high temperatures.

BACKGROUND OF THE INVENTION

Cobalt (Co) based alloys with Nickel (Ni), Chromium (Cr) and Tungsten (W) as constituent elements exhibit properties such as exhibiting excellent strength and resistance to oxidation effects with excellent mechanical properties at elevated temperatures upto 1000° C.

One of the drawbacks existing in the conventional metallurgical processes used for obtaining this alloy has been maintaining of the grain sizes of the obtained alloy at optimum levels. Because, it is required that the grain sizes along the entire microstructure of the alloy to exhibit the fineness and uniformity to achieve better mechanical properties and at the same time, grain size should not be very fine so that desired creep properties can be achieved. Thus, there arises the need for controlling and maintaining of the grain sizes of this alloy in a very narrow range.

Another problem faced in the present metallurgical processes of manufacturing this alloy is to achieve the desired elongation values for the components manufactured using the alloy for the applications in which they are needed. It is desired that the components should exhibit minimum elongation values of 30%.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a Cobalt based alloy which has properties that make the components [manufactured from this alloy desirable for Aerospace applications such as possessing good mechanical properties at elevated temperatures.

Another object of this invention is to provide a Cobalt based alloy which exhibits a narrow range of grain size in its entire microstructure so that an equilibrium between creep and tensile properties can be maintained.

A further object of this invention is to provide components made of Cobalt based alloy, which have an elongation values of minimum of 30%.

The invention discloses a cobalt based alloy with improved mechanical properties as well ,as uniform grain size throughout within its microstructure, comprising of constituent elements, Chromium (Cr) in the range of 19 to 21 %, Tungsten (W) in the range of 14 to 16 %, Iron (Fe) in the range of 3 % (maximum), Nickel (Ni) in the range of 9 to 11 %, Sulphur (S) in the range of 0.03 % (maximum), Phosphorus (P) in the range of 0.04% (maximum), Manganese (Mn) in the range of 1 to 2 %, Carbon (C) in the range of 0.15 % (maximum) and Cobalt (Co) forming the remaining major constituent element of the alloy. The cobalt based alloy of the invention has Ultimate Tensile stress values in the range of 1050 to 1070 MPa. The Cobalt based alloy of the invention possesses elongation values in the range of 30 % to 42 %, hardness values in the range of 267 to 269 BHN and micro-structural grain sizes in the range of 4 to 6 ASTM number.

Further, the invention discloses a method of manufacturing the Cobalt based alloy
with improved mechanical properties as well as uniform grain size throughout within its microstructure. The method according to this invention comprises of solution annealing process at a temperature of about 1070° C for a period of 3/2 hours.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the invention will now be explained further. However, it will be apparent to a person of ordinary skill in the art that the disclosed embodiments are merely exemplary and that the invention may be embodied in various forms. The following description is not to be construed as limiting. Numerous specific details are described to provide a thorough understanding of the invention, as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention. However, in certain instances, well-known or conventional details may not be described in order to maintain clarity.

'SuperCo 605' is a solid solution strengthened Cobalt based alloy. Solid solution hardening of the alloy is achieved by addition of 15% Tungsten (W) which acts as principal strengthener, and in addition to that adding of M6C also contributes to imparting of strength to the alloy. The alloy can be further hardened by cold working. Here, Nickel is used as the austenite stabilizer. This alloy is used for all components and parts working at elevated temperature under high stress conditions. It is mainly used in the form of plates and rings.

Table 1 shows the typical requirements for components to be manufactured using the Cobalt based alloy for application in the Aerospace sector.

Table 1

From observations it was found out that the process of solution annealing of Superco 605 which was usually carried out at 1175 - 1250° C and ail the carbides were added into the solution at this temperature. It was revealed that addition of carbides into the solution resulted in getting coarse grains in the microstructure of the end product i.e., the alloy and it also possessed high creep rupture properties. This in turn reduces the elongation property.

Thus to overcome these undesired properties, and to achieve finer grains in the microstructure of the alloy the constituent materials of the alloy was hot worked to obtain fine-grained forging. Also, the temperature in which the process of solution annealing was carried out was reduced by around 10 %.

(1100 ° C) and the process was carried out for 2 hours to achieve the optimum mechanical properties as well as desired micro structural grain sizes.

The obtained components by this process using the constituent elements of the alloy were tested for the desired properties. But, even after this improved treatment, it was found out that the microstructure of the alloy components was showing unrecrystallized grains in. the range of 2-3 (ASTM No) along with fine recrystastallized grains of 5 land 6 (ASTM No) Thus, the difference between average coarse and finer grain sizes of the microstructure of the alloy was found to be high. Also the percentage elongation values of the components made out of the alloy were found out to be lower i.e., 20 % to 28 % than that of the desired limit of 30 % minimum.

Based on further analysis and studies, it was concluded that the conduct of operations of final forging of the alloy components at higher hot working window and insufficient time period of annealing of the component were responsible for not achieving the desired properties (controlled levels of difference in grain sizes and percentage of Elongation at lower levels than the desired values)

Finally, a controlled hot working at lower temperature followed by annealing at 1050
- 1060 ° C, at optimum levels for 3 '/2 hours and when they were checked for the
properties, they were found to be possessing the fine grained recrystallised
microstructure with grains between ASTM No. 4-6 and also with good mechanical
properties such as percentage of elongation being greater than 30 %, the minimum
required value.

Table2 shows the improved mechanical properties as well as grain sizes of the components made out of the constituent materials of the alloy by adopting the method of optimal heat treatment.

The following sequence of operations describe in detail regarding the process involved in forging of the 'SuperCo 605' Component

To make the rings of Superco 605 T, Ingots of alloy material which have basic sizes
of 350 millimetres (mm) in diameter, are heated at a temperature of 1210° C for 4
hours and forged to get their diameters reduced to 260 millimetres (mm) diameter.
The work pieces are further ground and cut and subjected to heat for 1210° C for 4
hours followed by upsetting. This is followed by heating at 1180° C and then
punching action is carried on them followed by heating at 1150° C for 3 hours.
Finally the components are hot rolled at 1150 ° C followed by finishing at a
temperature of around 900 C with minimum 20% reduction to achieve the Cobalt
alloy components at the desired mechanical properties as well as required micro
structural grain sizes after annealing.

TERMINOLOGY & UNITS INVOLVED

MPa ---> Mega Pascals

BHN -> Brinell Hardness Number

ASTM Number-> American Society for Testing and Materials Number

CLAIMS

What is claimed is:

1. A cobalt based alloy with improved mechanical properties as well as uniform
grain size throughout within its microstructure, the cobalt based alloy comprising of constituent elements,

- Chromium (Cr)-l9 to 21 %

- Tungsten (W)-14 to 16%

- Iron (Fe) - 3 % (maximum)

- Nickel (Ni)-9 to M %

- Sulphur (S) - 0.03 % (maximum)

- Phosphorus (P) - 0.04% (maximum)

- Manganese (Mn) - 1 to 2 %

- Carbon (C) —0.15 % (maximum) and

- Cobalt (Co) forming the remaining major constituent element of the alloy.

2. The cobalt based alloy as claimed in claim 1, wherein the alloy has Ultimate Tensile stress values in the range of 1050 to 1070 MPa.

3. The cobalt based alloy as claimed in claim 1, wherein the alloy possesses
elongation values in the range of 30 % to 42 %.

4. The cobalt based alloy as claimed in claim 1, wherein the alloy possesses hardness values in the range of 267 to 269 BHN.

5. The cobalt based alloy as claimed in claim 1, wherein the alloy possesses micro-structural grain sizes in the range of 4 to 6 ASTM number.

6. A method of manufacturing a cobalt based alloy with improved mechanical properties as well as uniform grain size throughout within its microstructure, the method comprising final hot working at lower temperature and of solution annealing process at a temperature of about 1070° C for a period of 31/2 hours.

7. A cobalt based alloy and a method of manufacturing the cobalt based alloy
substantially described above with reference to the accompanying
metallurgical process and methodology.