Tim,
I've got the ASTM Book before me and A-572 is defined as "High strength, low alloy, columbium-vanadium steels of structural quality".
On the other hand, SAE 1018 is a low carbon steel with a carbon content of 0.18 %, with no alloying element whatsoever. So, in this case, I'd say that you shouldn't use it in lieu of A-572.
While the mechanical properties of ASTM steels, such as yield point and tensile strength, are a requirement set forth by the standard and must be guaranteed by the steel mill, in SAE steels the only requirement is the chemical composition. The mechanical properties are stated just for information, with no guarantee from the steel mill. When The Engineer (with capital letters) uses a SAE steel to withstand a given mechanical stress, like when The Ford Motor Company uses a SAE steel to make the crankshaft of their motors, he (The Engineer) does it based on his experience and under his responsibility. The steel mill can not be blamed because the material failed, because the mill didn't give any warranty on the mechanical properties of the steel.
As for ASTM A-36, it's a low carbon steel of structural quality, with a carbon content of 0.25 % in the thicknesses you mention.
Could you use SAE 1018 instead of A-36? From a purely engineering point of view, no, for the reasons stated above.
Now, we must take into account that there's an acute shortage of steel all over the world, prices are sky rocketing, delivery is astronomically long etc. etc. etc. By the way, here in Brazil, when you buy steel nowadays, the price invoiced is not the price stated on the purchase order but the price of the steel at the moment of shipping. Is it also so in the USA?
So, we must be reasonable, and I've been reasonable my whole life.
What I would do if I were you is the folllowing: take the necessary quantity of specimens off the lot of SAE 1018 steel your supplier has offered and submit them to the mechanical test stated on ASTM standard A-36, which is a tensile test. Impact and bend apply only if required on the purchase order.
If the tests are OK, you can safely assume that the lot of SAE 1018 steel your supplier has offered behaves in an equal manner than ASTM A-36, and you can use it with no problems.
I insist on the tests because the change will be made under your responsibility. If something goes wrong the one who will be blamed is you, or as we say in Brazil, the head under the guillotine will be yours.
Keep me aware of your decision.
Giovanni S. Crisi
Sao Paulo - Brazil
In addition to the machanical tests mentioned, I would also ask for a chemical analysis of the C1018 steel. Structural steels have limits on certain alloy elements to ensure its weldability. C1018 has no such requirements and so it may not be as readily weldable as A36 or A572 steels
Thank you for your replies.
Last Friday I presented this question to an Engineering consultant and his reply was as follows:
"I have reviewed the composition of SAE 1018 and ASTM A36 and 992. The compositions are similar. However, the specification in the AISC Manual of Steel Construction, Allowable Stress Design, Ninth Edition, restricts the use of steel materials to certain steel grades. SAE 1018 is not included as an acceptable grade of steel under the specifications.
I cannot recommend the 1018 steel as a substitute for other approved steels due listing of specific steel grades that are acceptable for use under the structural design specifications.
The 1018 steel grade may perform well under your application. However it has not been tested or approved for this application. If there was ever a problem with the steel, there would be no literature available to suggest that it was a proper application for this grade."
So much for that bright idea...
Yes Mr. Crisi, the steel market in the US is the same. Purchasing steel during the last year has been an enormous challenge, as our salesmen have not been adding the necessary fine print concerning steel prices in their bids. They come to me with a PO for a job to be built with steel that was quoted a month or two earlier and expect me to procure the steel at or preferably under the previously quoted amount. This has forced me to do a lot of scrounging to find what I need. One thing I have done is to get my Vendors to go through their A36 material MTR's and pick out heat numbers that the test reports show a 50 KSI yield or greater as I can purchase this steel cheaper than A572 gr50. On my last purchase, a Vendor offered the 1018 plates I need at 25% of the cost of the A572, so I was trying to figure out a way to use it. However, I'll not be risking the sacrifice of structural integrity no matter how cheap the steel is.
Thanks again for your replies and listening to me vent.
Tim Gary
Tim:
I have a client who uses these spec. materials regularly, particularly overseas where simple A 36 is like gold and hard to find. We had to qualify numerous procedures using 1018 and 1020 materials. The RDP for the designer told me once that 1018 is the same as A36 and therefore it is prequalified. I asked him to put that in writing which he did reluctantly. A week or two later I received a letter from the former AWS D1.1 chairperson who noted any material not listed in Table 3.1 is not prequalified and requires testing per section 4. Lot's of PQR's.
The 2004 edition Table 3.1 now includes ASTM A 1008, A 1011 and A 1018. While numerous steels can be similar to A 36, or many other specifications, if it ain't A 36... That multigrade steel used to be called dual-grade here, but now these materials comply with so many specs. they can be A 36, A 572 gr. 50, A 992, A 709 and a few more I can't remember off the top of my head. There are also situations where the designer wants "soft steel" in specific locations of the structure, and the multigrade materials are unacceptable. That problem has for the most part diminished due to the availabilty (or lack thereof) of A 36.
If as others say 1018 is similar to and often exactly a-36 perhaps the supplier can either through history of the batch or by testing cause this steel to be truthfully designated a-36. The cost might easily be absorbed if the required amount is large.
(How's that for a run-on sentence?)
Bill
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