100 Year History and Evolution of Stainless Steels and Welding – 1913 to 2013

1. 100 Year History and Evolutionof Stainless Steels and Welding – 1913 to 2013 Damian J. Kotecki Damian Kotecki Welding Consultants 105 Barton Lane Chapel Hill, NC 27516 440-368-4104 Mobile: 440-289-8673 damian@damiankotecki.com

2. Before the First 100 Years • 1797 – Discovery of Chromium by Klaproth and Vauquelin • 1871 – Woods and Clark patent “weather resistant” alloys of iron with 5 to 30% chromium • 1900 – Holtzer and Co. exhibit “rustless steels” at the Paris Exposition • 1905 – Léon Guillet publishes a book entitled Stainless Steel in Paris

3. 1913 • August 20 – Harry Brearly, at Firth Brown in Sheffield, England, pours the first commercial heat of what we now know as stainless steel (essentially Type 410 martensitic steel) • Eduard Maurer and Benno Straus produce first austenitic stainless steel at Friedrich A. Krupp Works in Essen, Germany

4. 1924 • Irving Langmuir at General Electric filed a patent application for Atomic Hydrogen Welding • Predecessor of GTAW for welding stainless

5. First Constitution Diagram - 1924 Benno Strauss • For wrought steel, not weld metal Eduard Maurer Chromium, per cent

6. Diagram of Strauss and Maurer, modified by Scherer et al in 1939 • For wrought steel, not weld metal

7. Schaeffler Diagram – 1949Anton “Tony Schaeffler, Arcos

8. DeLong Diagram – 1974and AWS A4.2 Standard William DeLong, McKay Company

9. WRC-1988 Diagram Chris McCowan, Colorado School of Mines

10. WRC-1988 vs. DeLong

11. WRC-1992 Diagram(modified 2000)

12. Stainless Refining for 6 Decades • If Cr was added to furnace charge, most Cr was oxidized to the slag. • To achieve < 0.03% C, it was necessary to add expensive low carbon ferrochrome after melting. • Large cost differential between low carbon stainless and non-low carbon stainless. • Non-low carbon stainless required annealing and quenching after welding.

13. Sensitization - If Weld is not Annealed and Quenched • M23C6 precipitates on grain boundaries in the HAZ. • Region adjacent to grain boundary is depleted in Cr. • Cr-depleted zones are preferentially corroded.

14. Argon Oxygen Decarburization • Conceived in 1955 by blowing argon-oxygen mixes over surface of molten steel – not successful on large scale. • Joslyn Steel injected Ar-O2 at the bottom of the refining vessel (October 24, 1967). • Joslyn achieved 0.008% C, 97% Cr recovery. • Spread to other mills in 1970. William Krivsky, Linde

15. Unintended Consequence of AOD – Variable Penetration • Automatic autogenous GTAW of tubing began to produce unpredictable penetration. • Low penetration was specific to certain heats of steel. • Many investigators thought the effect was due to trace elements, but which one(s)?

16. Marangoni Effect • Heiple and Roper (1982) demonstrated that variable penetration was caused by surface tension driven fluid flow in the weld pool. • Very low S and/or addition of small amount of Al cause decreasing surface tension with increasing temperature. • Increased S causes increasing surface tension with increasing temperature. • AOD is very efficient at reducing S.

17. Marangoni Effect • Decreasing surface tension with increasing temperature causes outward fluid flow along pool surface. • Increasing surface tension with increasing temperature causes inward fluid flow along pool surface.

18. Marangoni Effect • S < 0.005% tends to cause outward fluid flow along the weld pool surface. • S > 0.010% tends to cause inward fluid flow along the weld pool surface. • 0.005% < S <0.010% causes unpredictable fluid flow. • Tinkler et al (1983) recommend S > 0.010% as a purchase specification for stainless steel tubing for automatic autogenous GTAW.

19. Unintended Consequence of AOD – Addition of Nitrogen • In AOD refining of stainless steel, nitrogen has been considered an inert gas, interchangeable with argon. • This led to injection of some air in the AOD process, causing an increase in nitrogen in the stainless steel. • Duplex stainless steels, invented in the 1930s, were considered unweldable through the 1960s, unless annealed after welding.

20. Unintended Consequence of AOD – Addition of Nitrogen • Use of AOD for refining duplex stainless steel introduced nitrogen into the steel. • When nitrogen was specified as a necessary part of the composition, the as-welded properties improved. • Ogawa and Koseki (1989 and 1990) demonstrated that nitrogen addition increases the rate of austenite formation in the weld metal and HAZ, causing the as-welded improvement.

21. 2205 Base Metal 22% Cr 6% Ni 3% Mo 0.12% N

22. 2205 Weld Metal 22% Cr 6% Ni 3% Mo 0.12% N

23. 2205 Weld Metal 22% Cr 6% Ni 3% Mo 0.18% N

24. Definition of 2205 Duplex Stainless • Originally composition was defined in ASTM by UNS S31803 (0.08 to 0.20% N). • Work of Ogawa and Koseki caused ASTM to redefine 2205 as UNS S32205 (0.14 to 0.20% N) in year 2000. • At higher N level, HAZ properties are much less sensitive to welding heat input.

25. Unintended Consequences - FCAW • 1980s saw a major shift in FCAW of stainless from large diameter self-shielded to small diameter gas shielded electrodes. • Key feature of this shift was the patent of Godai et al describing addition of a “low melting oxide” to produce clean easy slag removal with a high SiO2 slag system.

26. Unintended Consequences – FCAW (continued) • Oxides of Pb, Bi and Sb were included. • Bi was the principal oxide, many copies of these wires were produced. • In the early 1990s, reports surfaced of in-service cracking at temperatures above 700°C. Investigations followed. • Failed welds contained about 200 ppm Bi.

27. Unintended Consequences – FCAW (continued) • Nishimoto et al reported reheat cracking above 700°C in self-restrained cracking test in weld metal of 200 ppm Bi. • Konosu et al reported reduced stress rupture properties at 200 ppm Bi.

28. Bi Effect on Stress Rupture Test Temperature 650°C Konosu et al

29. Late 1990s IIW Commission IX Round Robin of Bi Analysis • Nominally Bi-free electrodes produced weld metal analyzed at 20 ppm Bi or less. • Commercial Bi-containing electrodes produced weld metal analyzed at about 200 pp Bi. • Requiring 0 Bi is not feasible, but requiring < 20 ppm Bi for FCAW weld metal for service above 550°C is feasible.

30. State of the Art of Stainless FCAW • Most manufacturers of 1.6 mm and smaller gas-shielded FCAW electrodes produce both nominally Bi-free electrodes and electrodes of about 200 ppm Bi. • 200 ppm Bi has no adverse effect for service below 550°C – such electrodes dominate the market because they are more welder friendly.

31. State of the Art of Stainless FCAW • 20 ppm Bi maximum should be specified for high temperature exposure. • AWS A5.22 now requires reporting Bi on material certificates.

32. Conclusions • The foregoing are my very personal views about landmark events in the history of welding stainless steels. • The list is certainly not all-inclusive – others can offer their own views.