US2504453A - Alloy steels for use at elevated temperatures - Google Patents

Description

PatentelApr. 18, 1950 ALLOY STEELS FOR USE AT ELEVATED TEMPERATURES Dronfield, and Charles Sykes, Sheffield, England, assignors to Thos. Firth & John Brown Limited, Sheffield, Eng- Leonard Rotherham,

land, a British company No Drawing. Application January 23, 1948, Se-

rial No. 4,074. In Great Britain November 18,

Section 1, Public Law 690, August 8, 1946 Patent expires November 18, 1966 1 Claim.

This invention relates to alloy steels and to their use in th manufacture of power plant (or parts thereof) and other apparatus which in service is or may be required to operate in a range of temperature extending up to 850 C., and moreover may be subjected during such operation to considerable stress.

U. S. Patent No. 2,402,814 describes and claims alloy steels having a high resistance to creep at temperatures up to 800 and 850 C. The alloys described in this specification possess a very high degree of resistance to creep, but they fail eventually by a typical intergranular type of brittle creep failure.

It has now been found that alloy can be produced, which have much improved resistance to the brittle type of failure, and which show a considerable ductility, as measured by the reduction of area of a specimen fractured under creep conditions at high temperatures.

The alloys havin these improved properties form the subject of the present invention, and have the following range of composition:

Per cent Carbon upto 1.5 Silicon up to 2.0 Manganese 1.0-10.0 Chromium 12.0-20.0, Nickel 15.0-35.0 Molybdenum 1.5- 6.0 Columbium 1.0- 5.0 Cobalt 4.0-40.0

Iron, remainder The preferred range of composition is as fol- Iron, remainder After suitable solution and precipitation heattreatments, an alloy with a composition within the preferred range of analysis gave the followmg extension after testing at 650 C. at a stress of tons/sq. in.:

0.1% in 1000 hrs.

As an example of the increased ductility, an alloy with a composition within the preferred range which was fractured in 633 hours under a load of 14.0 tons/sq. in. at 650 C. gave a. reduction of area at the point of fracture in excess of 40%. There was also complete freedom from the characteristic intergranular creep cracks even in the necked portion of the test piece.

From the above figures it wi11 be seen that alloys within the range of composition according to the invention have a high resistance to creep with a high ductility, and are particularly suitable for the blades, rotors or other highly stressed components of gas turbine or other power plant or mechanical parts, particularly in those cases where the shape of the component necessitates the use of stress-raising changes of section such as sharp fillet radii or re-entrants or other notches.

We claim:

A creep-resisting alloy steel having a composition within the following ranges:

Iron, remainder.

LEONARD ROTHERHAM. CHARLES SYKES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,141,389 Hatfield Dec. 27, 1938 2,373,490 Mohling Apr. 10, 1946 2,397,034 Mohling Mar. 19, 1946 2,408,771 German Oct. 8, 1946 2,423,738 Thielemann July 8, 1947