1018 Steel Elongation

I am currently getting into metallurgy and going through the book I
have I came upon a question that I was unsure on the answer.
There is a piece of 1018 cold drawn steel that is not meeting
elongation, what possible fixes are there?
The only thing I could think of is to re-temper the steel and quinch it
in water. Anyone have any suggestions on this?
Reply to
Chopster
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If by "not meeting elongation" you mean that it's breaking before it's reaching the specified elongation, it could just be steel that isn't meeting spec (too much sulfur or phosphorus in it, etc.). Or it could be over-hardened from cold-working, whether it's rolling or drawing.
You could try re-annealing it. That will increase elongation but it will also decrease strength -- both yield- and ultimate tensile strength. You definitely don't want to quench-harden and re-temper; although, with 1018, all of that will not do much, because 1018 doesn't contain enough carbon to harden noticeably. If it were a higher-carbon steel, quench-hardening would *decrease* the elongation, although it would increase strength.
-- Ed Huntress
Reply to
Ed Huntress
Think about what cold-drawing does to a material.
It orients the grain structure and locks stress into the material.
Take a piece of copper wire, clamp one end in a vise, and pull on the other end (wrap around a hammer handle or whatnot).
The wire becomes harder and more brittle because it's been drawn.
Elongation can be recovered in both cases by heating and allowing slow cooling so the atoms in the material have a chance to thermally 'bounce around' and find happy places to be.
Jim
Reply to
jim rozen
Is this a real life problem or an essay question in the book? If it's a real life problem then if we could get a little more information such as the tensile strength, yield strength and/or perhaps the hardness of the steel then we could suggest a solution.
Assuming this is a test question in the book and no other information is provided then you have to go with the facts that are in the test question. Let's break down the facts and show how you can determine what to do.
Since the questions is specific that this is cold drawn 1018 steel, then you have two "facts":
1) The (SAE or ANSI) 1018 grade gives you the chemistry, which can be looked up in a handbook. This would be a plain carbon steel (as opposed to a medium carbon, high carbon, or alloyed steel). The carbon content is about 0.18% (+/- 0.05%) and the Manganese content would be about 0.30-0.60%. There's nothing else of appreciable quantities in this steel. It is a grade of steel that is NOT designed to be heat treated by quenching and tempering.
2) The "cold drawn" tells us the material was mechanically worked. If the steel is in the form of a sheet the sheet was put through rollers like cookie dough with a rolling pin only on a big scale. Each time the metal thickness is reduced when it goes through the rollers, the grain structure is changed. At an atomic level the atoms move across each other and through this process the tensile strength and hardness is raised, but also through that process the elongation is reduced. If the steel is in the form of barstock the same thing happens, if you start with (for example) a 3 inch diameter bar and pull it (i.e. "draw" it) through rollers that squeeze it into a smaller and smaller diameter, as the diameter is reduced the tensile and hardness go up whilst the elongation goes down.
There are two possible fixes to cause the elongation to be increased. Both involve heat treat.
First choice would be a SUBCRITICAL anneal. In this case the cold drawn steel would be heated up to perhaps 1150 deg F and soaked for a time at that temperature. When the steel is brought out of the furnace and cooled down (and the rate does not matter) the elongation would definitely improve. Where steel mills reduce thicknesses of steel in cold drawing operations, after the steel has undergone a certain percentage of thickness reduction the sucritical anneal must be done to restore toughness to the steel. If it's not donw and the steel is rolled thinner it will crack due to low elongation. The subcritical anneal will cause some grain refining to occur (i.e. small grain size when examined by microscope).
The second choice would be a FULL anneal. Here the steel is heated up ABOVE the critical temperature. I don't have my handbooks avaliable, but for 1018 this might be about 1550 to 1600 degrees F. After soaking the parts at that temperature, so they are through heated, the furnace is turned off and the parts left in the closed furnace. The furnace and parts are cooled to perhaps 400 degrees and taken out. The FULL anneal causes a coarsening of the grain and the steel is returned to it's naturally softest state. Tensile strength, yield strength and hardness go to a minimum and elongation goes to it's maximum (theoretically).
The heat treat you described in your email would be called "HARDENING and QUENCHING" and should be followed by TEMPERING. When you heat a steel up to about 1550-1600 (approx) and quench in water, you need more carbon and manganese in the steel to get it to hardnen. 1018 doesn't have enough in it. After the quench (when you do this to a medium carbon, high carbon or alloyed steel) a tempering process usually follows. The combination of Harden, Quench and Temper will ofter give the optimized or best combination of tensile, yield AND elongation.
Well this is a long answer to your question but if you are getting into metallurgy perhaps this will help.
Mark
Reply to
Mark
Thanks guys for the reply this explained alot. I really appreciate it all the help and thanks to you mark for a indepth look at the problem.
Reply to
Chopster
My pleasure.
Anytime you have a metallurgical question feel free to "PING" me and I'll do my best to give you an answer.
My own alma mater stopped conferring metallurgical engineering degrees some years ago. Now you get a degree in materials science engineering. Glad to see some people interested in metallurgy.
Mark
Reply to
Mark

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