The formal designation of 2304 Stainless is UNS S32304. UNS stands for Universal Number System. It is then classified into a Type 2304. This is listed in the ASTM 276 specification.
EnduraMet 32, as produced by Talley Metals, is a proprietary chemistry but closely allies the XM-28 (UNS S24100) specification in that it is an Austenitic Grade of stainless steel.
From a strictly corrosion resistant standpoint, the chemistries of the Austenitic-Ferritic (Duplex) Grade, seems to be optimal for use in saltwater marine applications and in DOT applications where the reinforced concrete may be exposed to chlorides and other deicing salts. 2304, when compared to 2205, is less expensive and has equal physical properties.
2304 contains 23%(+/-) Chromium and 4%(+/-) Nickel. 2205 contains 22%(+/-) Chromium and 5%(+/-) Nickel.
All Stainless Steel Rebar chemistries have slightly different theoretical weights per lineal foot (per ASTM A955/955M), than does ASTM A615/615M rebar theoretical weights. Generally, however, to simplify the various stainless steel weights per foot, the traditional theoretical weights of ASTM A615/615M may be used.
Generally, all stainless steel rebar, regardless of chemistry, is produced and certified to a Grade 75 with a minimum yield of 75ksi and minimum ultimate tensile of 100ksi. This certification, however, can be done when the 0.2% offset method of testing is only specified or required. The austenitic and austenitic-ferritic grades of stainless steel (316L, XM-28, 2304, and 2205), particularly in larger diameter bars, may however be available only in Grade 60 where the specification requires testing to the 00.35% EUL test method. (ACI 318-14 will be dropping the 00.35% EUL test method in favor of the exclusive use of the 0.2% offset test method for testing ultimate tensiles and ultimate yields for bar grades up to and including GR80 bar and rod.)
The ASTM A955/A955M minimum elongation of an 8” specimen for stainless steel rebar is 20% making stainless considerably more ductile than even ASTM A706/706M low alloy steel. Because of the high yield and tensile strengths created to meet the test method of 00.35% EUL, the elongation of 2304 & 2205 duplex grades of stainless steel rebar, may test at less than 20% but greater than that of the 12% elongation of A706 carbon rebar.
The exceptional ductility of stainless steel rebar makes it an excellent choice for seismic applications.
Pin diameters used in stainless steel rebar fabrication are the same as those used in carbon rebar fabrication.
The high yield and ultimate tensile of GR75 stainless rebar may require less cross sectional area (less weight) of steel in structures originally designed for ASTM A615/615M GR60 carbon rebar. “Less cross sectional area” may also result in less “rebar congestion” and better concrete consolidation. It may even reduce the cost of placing labor.
Stainless steel rebar is generally a weldable material without the need of preheating but subject to standard welding procedures for the chemistry and intended service or end use of the welded stainless steel material.
Testing for corrosion is typically provided by the manufacturer in accordance with ASTM A955/955M Annex A1.
Like carbon steel, stainless steel products are subject to market volatility and are re-priced monthly with an alloy surcharge. Chemistries with greater nickel contents may be subject to the greatest volatility.
There are currently only two active US “domestic melt” mill manufacturers of stainless steel rebar, North American Stainless in Ghent, KY, and Talley Metals in Hartsville, SC. Neither mill stock stainless steel rebar and only rolls to confirmed orders.
Neither North American Stainless nor Talley has the capability to produce bars in straight lengths greater than 40’
Pickling is the process to remove the “hot rolled” mill scale. It involves shot blasting and then immersion into a sulfuric acid solution, a second Nitric plus hydrofluoric acid solution, and then washed and immersed in a water bath to remove any remaining acid.
Passivation is a final process after pickling. The steel is first immersed in a solution of nitric acid and later washed and immersed in a bath to remove any remaining acid. This process is done to further increase corrosion resistance.
Stainless Steel Rebar has excellent physical bond characteristics with concrete.
Dowel bars can be produced in identical chemistries and Types as is stainless steel rebar.
Misconceptions?
There are many misconceptions about stainless steel in general and stainless steel rebar in particular. Most of this misconception is from a previous lack of exposure to the product, the limited past use of stainless steel rebar in the reinforced concrete construction industry, and the lack of any one independent standard for specifying stainless steel rebar. Most people expect stainless steel rebar to arrive as if it were chrome plated. Pickling and Passivation will give the surface appearance of the bar a grey “grainy” look. Fabrication of stainless steel rebar will make the tops of the deformations look polished. This is only because the “etching” effect of the acid baths in pickling and passivation has been altered. In time, and with the introduction of any number of corrosive variables, all stainless steel will exhibit some tendency to corrode. This should not avert the use of stainless since accelerated testing per ASTM A955/A955M has conclusively proven stainless steel rebar to be a very durable long-term material when used to reinforce concrete. Limited surface “freckled” or “patina” discoloration caused by ferrous “cross contamination” should not be a reason for rejection of stainless steel rebar. The stainless has not corroded, only the surface impurities. The passivation process will “heal” the stained area of any corrosion rendering the bar and its surface 100% acceptable for use. (To avoid discolorations from cross contamination that can be cause for concern for the uneducated, stainless steel rebar should only be handled with nylon slings and/or ropes that have been exclusively designated and dedicated for that use. For the same reason, stainless steel rebar should always be kept elevated from a ground level surface with clean dunage.)
Stainless steel rebar has been used extensively and successfully in the smallest of work and in the largest of high profile projects all over the world. Only with the recent concern of US bridge structural conditions and increased interest in life cycle cost of our transportation structures has stainless steel rebar gained the recognition in the US that it has deserved.
Contractors Materials Company/Stainless Steel Rebar Facts and Figures:
- Stocks UNS S32304 and UNS 24100 in #3 through #11 stainless steel rebar. Other chemistries are available but subject to mill rolling lead times and a potential minimum heat tonnage requirement
- Utilizes a machine made specifically and used exclusively for the fabrication of #3 thru #6 stainless steel rebar with minimum 34 Rockwell C hardened rollers and pins. In addition to powered carousels, the equipment uses a straightening system that produces accurate dimensions with reduced cold working of the bar and minimal alterations to rebar deformations.
- Utilizes “straighten and cut” machines for #3 through #11 rebar. These machines are designed specifically and used exclusively to only straighten stainless steel rebar. They also eliminate the stainless steel rebar’s memory and virtually do no damage to the deformations while reducing to a minimum the cold working to the bar. All rollers and wheels are hardened to a minimum 34 Rockwell C hardness.
- Can provide 60’ lengths of #3 through #11 stainless steel rebar
- Can provide in-house mechanical splicing & UNC threading for the Dayton Superior D50 type “connector” splicing system
- Fabricates from a 78,000 SF enclosed and heated concrete “tilt building”
- We have accounts with both North American Stainless and Talley Metals.
- We’ve been visited and/or approved for stainless steel rebar fabrication by The Ministry of Transportation, Ontario & Alberta, Canada; New York State; Vermont; Minnesota; Texas; California; Kentucky; The Illinois Tollway Authority; & Pennsylvania.
- The following are State DOT’s that we have supplied fabricated stainless steel rebar to but have not received “official” approval: The Ministry of Transportation, British Columbia & New Brunswick, Canada; Virginia; North Carolina; Wisconsin; Hawaii; Iowa; Louisiana; Michigan; New Jersey; Colorado; New Hampshire; Oklahoma.
- We have been fabricating stainless steel rebar since 2008 with projects from Hawaii to New England and throughout Canada to the South Eastern part of the US and Texas.
- We have our own in-house detailing and estimating staff.
- We are a 107 year old closely held company with 4th generation ownership.
- We have actively pursued and served the concrete construction industry for thirty plus years with innovation and value added products.
- We are a value added company with an experienced staff that understands all facets of heavy/highway & commercial/industrial concrete construction.
In addition to being a black and stainless steel rebar fabricator, we stock a complete line of concrete construction accessories. - We are a distributor of most major US manufacturers of concrete construction materials and accessories.
- Often we will work with a local fabricator to provide better local response time to change orders and/or potential shortages of stainless steel rebar.
