US2752238A

US2752238A - Straight chrome stainless steel pressure vessel

Info

Publication number: US2752238A
Application number: US312511A
Authority: US
Inventors: Carl S Walton
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1952-10-01
Filing date: 1952-10-01
Publication date: 1956-06-26
Anticipated expiration: 1973-06-26

Description

Jun 6, 1956 c. s. WALTON STRAIGHT CHROME STAINLESS STEEL PRESSURE VESSEL Filed 001:. l, 1952 M Kr a mwwmwwm Imam: (4e: 5 14 41 ra/v, fimzw/dw United States Patent STRAIGHT CHROlVIE STAINLESS STEEL PRESSURE VESSEL Carl S. Walton, Sewickley, Pa., assignor to United States Steel Corporation, a corporation of New Jersey Application October 1, 1952, Serial No. 312,511

3 Claims. (Cl. 75-126) This invention relates to straight chrome stainless steels and more particularly to a stainless steel of the 27% chromium grade which is substantially free from embrittlement after prolonged holding at high temperatures.

Straight chromium, ferritic, stainless steel of the so called 27% grade, i. e., containing 24 to 30% chromium has excellent resistance to oxidation up to temperatures of 2000 F. However, this steel cannot be used in many applications which involve protracted heating at temperatures from 1000 to 1300 F. due to embrittlement caused by formation of the intermetallic compound of the iron chromium system known as the sigma phase. While this can be overcome by annealing at temperatures over 1600 F. such annealing is impractical for many articles such as pressure vessels and the like.

It is accordingly an object of this present invention to provide a straight chrome steel of the 27% chrome grade which is free from embrittlement after prolonged heating at temperatures over 1000 F.

The foregoing and further objects will be apparent from the following specification when read in conjunction with the attached drawing, wherein the single figure is a graph depicting the embrittling effect of silicon on 27% chromium straight chromium stainless steel.

Straight chromium stainless steel of the 27% chromium type generally contains 24 to 30% chromium and .35% maximum carbon, along with 1.00% maximum man ganese, .04% maximum phosphorus, .03% maximum sulphur, .25 maximum nitrogen and between about .35 to 1.00% silicon. I have discovered that by formulating the steel With the least possible silicon and preferably less than .17% maximum silicon that the formation of sigma phase and resulting embrittlement when heated for long periods in the 1000 to 1300 F. range can be completely overcome.

In accordance with this invention, a number of long time temperature experiments comprising holding steels of the foregoing composition and along with steels higher silicon contents at temperatures of 1050 and 1200 F. for 10,000 hours were conducted. The results, so far as hardness and the Rockwell scale, were substantially the "ice same at both temperatures so that they are depicted by a single line on the graph of the drawing. This shows conclusively that with silicon contents less than about .17%, no change in hardness results from prolonged heating at 1050 and 1200" F. It is also apparent that increasing the silicon up to about .27% causes a rapid increase in Brinell hardness but thereabove the hardness remains substantially constant.

A typical steel embodying the teachings of this invention contains .12% carbon, .63% manganese, 27.48% chromium and .O9% silicon along with .014% phosphorus, .O1% sulphur and .08% residual nickel.

While I have shown and described a single embodiment of my invention, it will be understood that this embodiment is merely for the purpose of illustration and description and that various other forms may be devised Within the scope of my invention, as defined in the appended claims.

I claim:

1. A pressure vessel of the type subjected in use to prolonged heating in the temperature range of 1000 to 1300 F. formed of ferritic straight chromium stainless steel containing between .03 and 35% carbon, 24 to 30% chromium, 1.00% maximum manganese, and less than .17% silicon, said pressure vessel being characterized by substantially complete freedom from sigma phase embrittlement after being heated for 10,000 hours in the temperature range of 1000 to 1300 F.

2. The method of inhibiting sigma phase embrittlement in pressure vessels subjected to prolonged heating in the temperature range of 1000 to 1300 F. comprising producing straight chromium stainless steel containing between 24 and 30% chromium, .03 to 35% carbon, which type of steel is subject to the formation of sigma phase on prolonged heating in said temperature range and inhibiting the formation of such phase by limiting the silicon content of said steel to less than .17%, forming a pressure vessel therefrom and heating said vessel for 10,000 hours in the range of 1000 to 1300 F., said vessel being characterized after such heating by the substantially complete freedom from sigma phase embrittlement.

3. A pressure vessel of the type subjected in use to prolonged heating in the temperature range of 1000 to 1300 F. formed of ferritic straight chromium stainless steel containing about .12% carbon, about .63% manganese, about 27.48% chromium and about .09% silicon with the balance iron and residual impurities, said pressure vessel being characterized by substantially complete freedom from sigma phase embrittlement after being heated for 10,000 hours in the temperature range of 1000 to 1300 F.

References Cited in the file of this patent Metals and Alloys, vol. 7, August 1936, pages 207-210. Comptes Rendus, vol. 226, June 1948, pages 2150-2151.

Claims

1. A PRESSURE VESSEL OF THE TYPE SUBJECTED IN USE TO PROLONGED HEATING IN THE TEMPERATURE RANGE OF 1000 TO 1300* F. FORMED OF FERRITIC STRAIGHT CHROMIUM STAINLESS STEEL CONTAINING BETWEEN .03 AND .35% CARBON, 24 TO 30% CHROMIUM, 1.00% MAXIMUM MANGANESE, AND LESS THAN .17% SILICON, SAID PRESSURE VESSEL BEING CHARACTERIZED BY SUBSTANTIALLY COMPLETE FREEDOM FROM SIGMA PHASE EMBRIT-