100 Year History and Evolutionof Stainless Steels and Welding

– 1913 to 2013Damian J. Kotecki

Damian Kotecki Welding Consultants

105 Barton Lane

Chapel Hill, NC 27516

440-368-4104

Mobile: 440-289-8673

damian@damiankotecki.com

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

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

1924• Irving Langmuir at General

Electric filed a patent application for Atomic Hydrogen Welding

• Predecessor of GTAW for welding stainless

First Constitution Diagram - 1924

• For wrought steel, not weld metal

BennoStrauss

EduardMaurer

Chromium, per cent

• Diagram of Strauss and Maurer, modified by Scherer et al in 1939

• For wrought steel, not weld metal

Schaeffler Diagram – 1949Anton “Tony Schaeffler, Arcos

DeLong Diagram – 1974and AWS A4.2 Standard

William DeLong, McKay Company

WRC-1988 Diagram

ChrisMcCowan, Colorado School of Mines

WRC-1988 vs. DeLong

WRC-1992 Diagram(modified 2000)

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.

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.

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

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)?

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.

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.

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.

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.

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.

2205 Base Metal

22% Cr

6% Ni

3% Mo

0.12% N

2205 Weld Metal

22% Cr

6% Ni

3% Mo

0.12% N

2205 Weld Metal

22% Cr

6% Ni

3% Mo

0.18% N

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.

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.

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.

• 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.

Unintended Consequences – FCAW (continued)

Bi Effect on Stress RuptureTest Temperature 650°CKonosu et al

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.

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.

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.

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.