Copper Steel - revisited

Proctologically Violated wrote:


I was surfing and came upon this thread from March. The discussion was interesting, but while there was some dicussion of weathering steels such as the COR-TEN types, there really wasn't any mention of copper strengthened medium strength (up to 100ksi) structural steels.
This link: www.intlsteel.com/PDFs/products/spartan.pdf
takes you to a brochure for ISG steel company's medium strength copper strengthened steels. There are 5 grades listed (3 actually with a couple of variations for different thickness ranges). The HPS grade (spartan V) is a 100ksi yield strength bridge weathering steel, the others are 80 and 100 ksi yield strength ship hull steels. None of these steels are "stainless steels".
All of these steels have copper precipitation hardening as their primary strengthening mechanism. The amount of copper far exceeds that needed for weathering. The ship steels aren't considered weathering since that mechanism doesn't work in chloride containing water.
The copper was added specifically to replace carbon for the purpose of significantly improving weldability. While copper is an expensive alloy replacement for carbon strengthening, the improved weldability more than makes up for the increased alloy cost.
The corresponding steels that were replaced had approximately 0.12% to 0.18% (or slightly more) carbon and were quench and temper martensitic strengthened steels. The copper versions have up to 1.75% copper and more complex strengthening mechanisms, but are solution treated, quenched, and aged with most of the strength from copper precipitation. The temperatures and cooling rates for each step are about the same for the old and new alloys, but the metallurgical reactions are differerent, hence the different names. Also the effects of each step are different. The carbon containing steels are very hard and brittle after quenching and then moderate their strength and greatly increase their impact and fracture toughness during tempering. The copper steels are not very hard after quenching, and the strength increases during aging. This is one of the features that makes them more weldable - the weld HAZ hardness doesn't spike like it does in the carbon martensite steels.
The brochure gives some good tables and charts showing how these steels respond to heat treatment.
By the way, the color of the steel looks like steel at this level of copper.
Tom (not associated with ISG)
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snipped-for-privacy@mthtrains.com (Tom) wrote in message

snip
Tom:
Not quite. I did briefly refer to a recent report on this type of steel in a March 20th post.
"The use of copper in steel continues to be researched. See: http://www.iti.northwestern.edu/publications/fine/Fine Steel Final Report.htm"
Pittsbugh Pete
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snipped-for-privacy@mthtrains.com (Tom) wrote in message

snip

Not quite. Actually I referred in a March 20th Post to a report by Fine and Vaynman from last year.
http://www.iti.northwestern.edu/publications/fine/Fine%20Steel%20Final%20Report.htm
"The objectives of the project were:
(a) To develop a high performance 70W steel (tough, strong, improved weldability and weatherability), less expensive that presently used construction steel; (b) To assist in marketing of the steel for infrastructure applications. The starting point was the Navy's HSLA 80 steel, a combined martensitic copper precipitation strengthened steel. Strengthening by copper precipitation plus grain refinement by niobium carbide without employing the martensite transformation was the approach taken. Copper precipitation occurs during air-cooling from hot rolling. Since hardenability during quenching is not a factor the carbon content in the Navy steel was lowered and chromium and molybdenum were omitted. Ni is present to prevent hot-shortness during hot rolling. Nb and Ti are present to control grain size during hot rolling and welding. Because of simplified processing and lean composition the resulting steel is lower in cost than ASTM 709 HPS70, HSLA 80 or other ASTM A710 steels.
The initial development of the steel (chemical composition and processing) was done with nine laboratory heats that were produced at Inland Steel Company and US Steel Research and Technology Center. Then, two commercial 80,000-kg heats were produced at Oregon Steel Mills (OSM) to investigate the steel production under industrial conditions and for use for bridge renovation. Also, slabs previously cast at OSM were hot-rolled at the USS Gary Works and then further processed at North Star Steel Company.
To assist in marketing, we worked with steel producers, steel consumers, the American Iron and Steel Institute/Federal Highway Administration/ US Navy Steering Committee on High Performance Steel Development, Government Agencies (FHWA, IDOT, Ohio DOT), etc. NUCu steel was used for rehabilitation of a bridge in Illinois and is planned for another bridge in the 2003-2004 construction seasons. We worked to include NUCu Steel in the ASTM A710 Standard. and this was accomplished. For technology transfer we published a number of papers and reported results and developments at Conferences and Symposia."
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