DESC:PRIORITY STATEMENT
The present application hereby claims priority from Indian patent application with the application number 202341024832, filed on 31 March 2023, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD OF INVENTION
The present invention relates to a method for manufacturing a maraging steel 250. More particularly, it relates to novel method for improving the fracture toughness of Maraging steel 250 higher size forged bar.

BACKGROUND OF INVENTION
Maraging steel 250 is steel with high strength and good fracture toughness. Maraging steel 250 is capable of achieving a fracture toughness of 82MPavm.
Due to its properties, it is widely used in aerospace, marine construction and pressure vessels. However, to meet the aerospace design criteria fracture toughness of 90MPavm is needed. Achieving fracture toughness of 90MPa in higher size forged bars has always been a challenging task due to susceptibility of maraging steels to thermal embrittlement resulting in lower fracture toughness.
It is well known that maraging steel 250 is susceptible to severe thermal embrittlement if exposed to a temperature range 850-950°C while being cooled from higher temperature (around 1200°C) resulting in lower fracture toughness of the material. This phenomenon is usually observed in higher size forged bars where working takes place at 1200°C and slow cooling happens in the embrittlement temperature range due to higher section size of the bars.
With this background, internal trials were carried out to maintain the finish forging temperature above 950°C followed by water quenching to improve the fracture toughness values in higher size forged bars (120mm-200mm dia). However, higher length bars (1.2m) is taking atleast 15 minutes for the forging to be completed, resulting in finish temperature of 850-900°C. Water quenching within 60 seconds when implemented after finish forging did not yield any improvement w.r.t fracture toughness.

OBJECT OF THE INVENTION
The object of the present invention is to provide a novel method for manufacturing maraging steel 250 larger size forged bars.
Another object of the present invention is to disclose a method for forging larger size bar of fracture toughness 80 - 90 MPavm.

SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the disclosure. This summary is neither intended to identify key or essential inventive concepts of the disclosure nor is it intended for determining the scope of the disclosure.
A method for manufacturing maraging steel 250 forged bars of 200 mm diameter, characterized by fractured toughness of 80-90 MPavm, the method comprising the steps of forging MDN 250 at a finish forging temperature ranging between 900°C to 1000°C; reducing the final pass during forging by 50%; cutting the forged bars into lengths ranging from 700mm to 800mm during the final forge reduction to maintain a final finish forging temperature above 950°C; and subjecting the forged bars to water quenching within 55 to 65 seconds.

DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a novel method for manufacturing maraging steel 250 larger size forged bars with improved fracture toughness.
In the present invention, the maraging steel 250 composition in wt% is Nickel (Ni) – 18%, Cobalt (Co) -15%, Molybdenum (Mo) - 6.5%, Titanium (Ti) -1%, Aluminium (Al) and balance being Iron (Fe) with some incidental impurities of C, N and O (composition is in weight percent with an error margin of 10%).
The method discloses a series of steps including forging MDN 250 at a finish forging temperature in the range of 900-1000°C and reducing the final pass by 50%. During final forge reduction, the bars are cut into small lengths of 700 – 800 mm to maintain a final finish forging temperature above 950°C.
In accordance with an embodiment of the present invention, the forged bars are then subjected to water quenching within 55-65 seconds. The implementation of these steps results in a significant improvement in fracture toughness, increasing from 80 to 90. This method can be used to produce high-quality maraging steel 250 for use in critical engineering applications, such as structural materials for spacecraft and aircraft.

ADVANTAGES AND APPLICATION
The method provides several advantages, including Improved fracture toughness: The method results in a significant improvement in fracture toughness, which is essential for critical engineering applications. It was very difficult to produce larger size forged bars with high fracture toughness. The method produces a high-quality product that meets the required specifications for critical engineering applications.
,CLAIMS:Claims:
We Claim
1. A method for manufacturing maraging steel 250 forged bars of 200 mm diameter, characterized by fractured toughness of 80-90 MPavm, the method comprising the steps of:
a. forging MDN 250 at a finish forging temperature ranging between 900°C to 1000°C;
b. reducing the final pass during forging by 50%;
c. cutting the forged bars into lengths ranging from 700mm to 800mm during the final forge reduction to maintain a final finish forging temperature above 950°C; and
d. subjecting the forged bars to water quenching within 55 to 65 seconds.
2. A method as claimed in claim 1, wherein the maraging steel 250 forged bars of 200 mm diameter exhibit an improvement in fracture toughness from 80 to 90 MPavm.
3. The method as claimed in Claim 1, wherein the water quenching is conducted at a temperature between 20°C to 40°C.
4. The method as claimed in Claim 1, wherein the forged bars are subjected to a stress relieving treatment subsequent to water quenching.
5. The method as claimed in Claim 1, wherein the maraging steel 250 forged bars are utilized as structural materials in spacecraft and aircraft applications.