FERRITIC STAINLESS STEEL ALLOY

• US 3,807,991 A
• Filed: 10/29/1971
• Issued: 04/30/1974
• Est. Priority Date: 10/29/1971
• Status: Expired due to Term

• Current Assignee: Allegheny Ludlum Corporation (Allegheny Technologies Incorporated)
• Original Assignee: Eric Gregory, Frederick K. Kies, Ivan A. Franson
• Inventors: Gregory, Eric, Kies, Frederick K., Franson, Ivan A.
• Primary Examiner(s): Bizot, Hyland
• Application Number:
  US05/193,698
• Time in Patent Office: 914 Days
• Field of Search: 75/126C,126J,126F
• US Class Current: 420/69
• CPC Class Codes: C21C 5/005 Manufacture of stainless steel
• CPC Class Codes: C21C 5/5264 Manufacture of alloyed steels including ferro-alloys
• CPC Class Codes: C22C 38/26 with niobium or tantalum
• CPC Class Codes: Y02P 10/20 Recycling

Abstract

A high purity, low interstitial ferritic stainless steel which in the as-welded condition exhibits a combination of improved resistance to intergranular corrosion, good resistance to general corrosion and improved impact resistance. The steel broadly contains by weight from about 20.0 percent to about 35.0 percent chromium, from about 0.75 percent to about 1.20 percent molybdenum, from about 0.10 percent to about 0.30 percent silicon, up to about 0.020 percent phosphorous, up to about 0.020 percent sulfur, up to about 0.0030 percent carbon, from about 0.0050 percent to about 0.0125 percent nitrogen and columbium from about 13 to about 29 times the nitrogen content.

Claims

2. A ferritic stainless steel as defined in claim 1 wherein the chromium content is about 25.0 percent to about 27.5 percent.

3. A ferritic stainless steel as defined in claim 1 in which the total of nickel, copper and cobalt, present as impurities, does not exceed about 0.25 percent.

4. A ferritic stainless steel product having the composition defined in claim 1 and having a DBTT below room temperature after air cooling from 1,800* F.

5. A hot rolled ferritic stainless steel product characterized by its combined toughness and corrosion resistance and characterized further by exhibiting impact strength in the transverse direction substantially equal to the impact strength in the longitudinal direction, said product consisting by weight percent essentially of:

chromium from about 20.0 percent to about 35.0 percent, molybdenum from about 0.75 percent to about 1.20 percent, silicon from about 0.10 percent to about 0.30 percent, phosphorous up to about 0.020 percent, sulfur up to about 0.020 percent, carbon up to about 0.0030 percent, nitrogen from about 0.0050 percent to about 0.0125 percent, columbium from about 13 to about 29 times the nitrogen content, and the remainder substantially all iron.

6. A ferritic stainless steel product as defined in claim 5 wherein the chromium content is about 25.0 percent to about 27.5 percent.

7. A single phase ferritic alloy free of nickel and characterized by high resistance to corrosion, good weldability, and toughness, said alloy consisting essentially of Fe containing by weight 25 to 27.5 percent chromium, 0.75 to 1.20 percent molybdenum, 0.10 to 0.30 percent silicon, and containing as impurities not more than 30 ppm carbon, from about 50 ppm to about 125 ppm nitrogen, not more than 200 ppm sulfur, and not more than 200 ppm phosphorous, and further containing, as an essential element, columbium in an amount of at least 0.05 percent by weight and not more than about 29 times the nitrogen content of the alloy.

8. A ferritic stainless steel consisting, by weight percent, essentially of carbon up to about 0.0030 percent, phosphorous up to about 0.020 percent, sulfur up to about 0.020 percent, silcon from about 0.10 percent to about 0.30 percent, chromium from about 20.0 percent to about 35.0 percent, molybdenum from about 0.75 percent to about 1.2 percent, nitrogen from about 0.0050 percent to about 0.0125 percent, columbium from about 13 to about 29 times the nitrogen content, and the remainder substantially all iron, said steel being ductile in the water quenched condition to less than 0* F and having substantially equivalent transverse and longitudinal impact strength levels, and having an intergranular corrosion rate of less than 400 microns per year.

9. A ferritic stainless steel as defined in claim 8 wherein the chromium content is about 25.0 to 27.5 percent.

10. A ferritic stainless steel as defined in claim 8 in which the total of nickel, copper and cobalt, present as impurities, does not exceed about 0.25 percent.

11. A ferritic stainless steel as defined in claim 9 wherein the DBTT in the air-cooled state after annealing at 1,800* F is below room temperature.