1018 vs ASTM A36

[Glenn]

There has been some discussion between 1018 and A 36 and the differences, It is time to go to the references and get the facts.

Ref onlinemetals
1018 Mild Steel
Alloy 1018 is the most commonly available of the cold-rolled steels. It is generally available in round rod, square bar, and rectangle bar. It has a good combination of all of the typical traits of steel - strength, some ductility, and comparative ease of machining. Chemically, it is very similar to A36 Hot Rolled steel, but the cold rolling process creates a better surface finish and better properties.



1018 Mild (low-carbon) steel
Minimum Properties
Ultimate Tensile Strength, psi 63,800
Yield Strength, psi 53,700
Elongation 15.0%
Rockwell Hardness B71


Chemistry
Iron (Fe) 98.81 - 99.26%
Carbon © 0.18%
Manganese (Mn) 0.6 - 0.9%
Phosphorus (P) 0.04% max
Sulfur (S) 0.05% max


A36 Mild Steel
ASTM A36 steel is the most commonly available of the hot-rolled steels. It is generally available in round rod, square bar, rectangle bar, as well as steel shapes such as I-Beams, H-beams, angles, and channels. The hot roll process means that the surface on this steel will be somewhat rough. Note that its yield strength is also significantly less than 1018 - this means that it will bend much more quickly than will 1018. Finally, machining this material is noticeably more difficult than 1018 steel, but the cost is usually significantly lower.



ASTM A36 Mild (low-carbon) steel
Minimum Properties
Ultimate Tensile Strength, psi 58,000 - 79,800
Yield Strength, psi 36,300
Elongation 20.0%


Chemistry
Iron (Fe) 99%
Carbon © 0.26%
Manganese (Mn) 0.75%
Copper (Cu) 0.2%
Phosphorus (P) 0.04% max
Sulfur (S) 0.05% max

For more detailed information go to ASTM.org

[Quenchcrack]

OK all you "but metallurgists", you know, the "I'm not a metallurgist but....", why does the 1018, with only .18% carbon have a yield strength of 53,700 psi but the A36, with a carbon of .26% have a yield strength of only 36,000 psi?

Edited April 13, 2009 by Quenchcrack

[Charlotte]

Quench if someone asked me at a demonstration I'd reply one specification 1018 is a specification for composition.

A36 is a specification for performance. The specifed properties can be achieved in an number of different ways. When you buy A36 you are buying a puppy that you have no Idea who the father is. A Saint Bernard or a pekinese..

I remember vividly an afternoon demo of nail making. One of better smiths was making nails and cursing a blue stream. After taking a break he came by my little rivet forge and saw that I was getting along OK. He borrowed some of the 1/4 in rod I was using. No more complaints, no more cussing just nail after nail hitting the slack tub.

The specs were the same and, it turned out later, from the same dealer.
It just happened the my 1/4 hot rolled was a year newer.

I've often suspected that the variable response to "Super Quench" was the result of different lots of material more than anything else.

Edited April 13, 2009 by Charlotte
spelling

[Glenn]

I am not sure that it is a Saint Bernard or a pekinese issue, but one of meeting the specs of 4 feet and fur. As long as the ASTM A 36 specifications are met it can be labeled A 36, otherwise it is something else and can not carry the A 36 label.

The full spec sheet will give the standards and properties to which the steel must comply.

We keep hearing about differences in batches, etc, and I do not doubt the reports. It would be interesting to get an analysis on one of those hard spots and compare it to the ASTM A 36 specs.

[Ed Thomas]

Several factors help, including the surface finish and the homogenous alloy composition, but the most significant contribution to the increase in yield strength for cold-rolled is the strain-hardening caused by the process itself. That is to say: the dislocation density is nano-scopically increased and there is irreversible microscopic crystal deformation, with subsequent decrease in plasticity and ductility caused by (respectively) the resistances to further nucleating dislocations and increased pinning point impediments.

Essentially, smushing the alloy cold makes it harder.

[HWooldridge]

A36 is a relatively wide spec material because it is generally composed of melted down cars and other scrap. 1018 is a narrow spec material that you might see on an engineering print for machined or forged parts but it is unlikely to see A36 specified for anything other than structural work. Hot rolled often has seams and cold shuts but I have also seen it (recently) in premium steels such as 12L14 and 4140. Might have something to do with the "global market" and "economic supply and demand" or whatever...

I have frequently experienced hard spots in A36 - some hard enough to make drilling a chore. In fact, you can likely grab a piece of material in any convenient size and bend it cold - you'll likely see kinks and not a smooth curve. A36 makes a pretty decent material for replacement springs on post vises, just forge to size, heat to cherry and quench in Super Quench without tempering. Makes a great spring that typically won't break or take a set.

BTW, I was given some 1008 a few months ago - that stuff forges like butter and welds pretty easily. It's worth trying if you can find it.

[Mark Emig]

Speaking of the problems with A36, I was talking with a major steel distributor in Albany, and was told that when you buy steel, if you just ask for "hot rolled" you can get almost anything. I was told that a bunch of hot roll that is out there is actually A992 (I think that was the ID) which is a structural steel which is WAY harder and tougher. If you want to be sure to get A36, you need to ask for certs, or you don't know what you'll get. Also, the specs that you see are "MINIMUM",which means that what you get can have considerably MORE carbon and such in it. I know that the "forgeability with different loads of hot roll I get varies greatly-and it sure doesn't seem like it is getting ang softer-it just seems to be getting harder and harder.
Mark

[Thomas Dean]

OK all you "but metallurgists", you know, the "I'm not a metallurgist but....", why does the 1018, with only .18% carbon have a yield strength of 53,700 psi but the A36, with a carbon of .26% have a yield strength of only 36,000 psi?

Totally a guess...but could the copper content in the A36 give it more elongation?

[bigfootnampa]

As a consideration for smithing work it seems to me that the greater yield strength of the 1018 would be overwhelmed by the work hardening and grain alterations inherent in the forging processes... not to mention any quenching effects. The extra carbon in the A36 might well be lost in the forging cycles but the 1018 might also lose some and having less to begin with end up softer rather than stronger. I would typically favor the 1018 for an axle for a small wagon/cart where I would use the steel as bought (without forging or heating/quenching cycles)... for general forged items I tend to buy the A36, which is slightly cheaper, as I feel that I would get little gain from the nicer surface or the higher yield strength where these properties will be so thoroughly impacted by my forging and heat treatments.

[Quenchcrack]

OK, Ed Thomas was the first to post what I believe to be the correct answer: cold finished rod is indeed work hardened. It loses that strength the first time you heat it up to forging temperature because you re-crystalize the microstructure. That relieves all the strain done in cold working. The lesson is simple: don't buy expensive cold finished stock if you don't need the closer shape tolerances. Also, when steel scrap is melted, it is carefully sorted and blended to achieve a close match to the desired final product. It is melted, analyzed, alloyed, cast and possibly treated in a Ladle Metallurgy Furnace where they add the final trim to the alloys and add the Silicon, Aluminium, etc. Don't think that just because a mill melts scrap, that they just scoop up a load of junk, melt it and cast it. It is very carefully melted under the same controls that are used when making virgin steel in a BOF. If we did not re-cycle scrap steel, our landfills would be overflowing with rusty junk.....unless there were a few blacksmiths living close by.......

[ThomasPowers]

BigFoot unless you are hammering your steel cold there is no work hardening "inherent in the forging processes" as forging is done at a temp above dislocation climb temp.

[CRAFTBENDER]

Over a ten year period I bought a lot of cold rolled 1018 steel 1/4 x 1.0 and 3/8 x 1.0. The minimum tensile strength in the book was 85,000 pounds per square inch. Also bought and cold bent a huge amount of hot rolled steel. Cold rolled will almost always break when bending cold but hot rolled can be bent readily in the cold condition. The only way to bend cold rolled at room temp. is to heat it first to barely red and let it cool.

This is a picture of some cold rolled vs hot rolled 1/4 thick bent cold on a 3/16 radius.

[bigfootnampa]

Well actually Thomas, I do hammer my steel as it cools when I am refining my shapes and in specific areas (like hook curves) where I desire some work hardening. However I also find that MY metal gets stiffer after being worked even when I haven't intentionally forged into the black heats. Maybe this is not theoretically predicted but it happens when I am working and I generally find it useful.

[Don A]

Do you think the .2% CU in the hot-rolled has any effect on the steel's ability to be forge welded?

I've sworn that I could tell a difference, but perhaps the power of suggestion has something to do with that.

It also seems to me that in a piece of work that has endured multiple heats, the 1018 is not as prone to be "scale pitted" (for lack of a better description). Seems that the 1018 will finish up with a smoother surface.

And stress cracks... like in small, highly worked pieces (tines of a fork, for example)... seems like the A-36 is more prone to get those stinkin' cracks in the transition areas.

Maybe I'm imagining these things; maybe there is some merit to it. We can say for sure that industry standards for structural integrity have little to do with how it preforms when we "heat it and beat it". Perhaps this calls for the lot of us to do some legitamate comparison testing and see what we come up with.

One thing I do know... when I happen to be able to use 1018, I don't have to work at getting that ugly mill-scale off of any unhammered areas of a finished piece.

My $.02

Don

[ThomasPowers]

Don I go through a lot of HR 1/4" sq stock teaching a beginner's class and I have noticed great variability in the cracking department. Some stuff will crack all over doing a simple twist, other stuff won't crack even if you twist it off (well except for the one...). I ascribe it to varrying alloy content of the steel.

[Dodge]

I agree with Ed T. I worked in a factory that made steel light poles primarily from A36. This material, after forming into a tapered tube was then cold worked on a mandrel in a machine called a burnisher which in effect, cold rolled the steel. This process not only made the tubes rounder, but also increased the tensile strength as much as, if not more than 10,000 psi. From my experience, cold working hot rolled steel will make it stronger.

[Quenchcrack]

Working steel at a black heat will certainly make it feel stiffer. It is. That's why we like to forge at higher heats. The recrystalization temperature of steel is 900F-1100F so if you really want to cold work it, do it below 900F. This applies to CD or HR steel equally.

[Bam Bam]

This is a tad off topic, but here is a picture of two pieces of steel that we drilled for a bracket.   In the back is a typical piece of 1018 hot rolled flat bar.   In the front is a piece of flat bar that the mill sheared off of a piece of A36 plate.   Both of the plates are 1/4" thick and both were drilled under a power feed drill with the same drill bit, at the same down feed and the same rotational speed, one right after the other.   Note the volcanic burrs on the A36 piece while the 1018 has virtually no burr.   I am guessing this malformation is due to the differences in yield strength that allows the A36 to deform rather than cut.

 

[JNewman]

Hot Rolled is not always A36.  I have bought lots of hot rolled 1018.  To be sure you need the Certs.   In round bar I have had to buy over 1.5"  dia to get 1018. 

 

Here in Canada a lot  of the structural steel  is 44W which has a minimum tensile and yield higher than A36 and meets the specs for A36. 

[John Larson]

I drill A-38 all the time and never see such large burrs. Something else is amiss here.

[anvil]

quenchcrack & Ed T give the correct answer.

[Ten Hammers]

one hot rolled, one cold.  The ONLY reason I use cold (for 99 % of my needs ) would be sharper corners on square leading to nicer twists.  Otherwise no need to waste the money on anything but hot rolled.