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heat treating cold rolled 1018 mild steel


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is it possible or advisable to heat treat cold rolled mild steel?? i just machined an axle for a boom lift and was wondering if it would be needed. the previous axle was ductile iron and snapped clean in half in the middle of the gears and dont really want this to happen again...ive come up with a different hub mounting arrangement to make the weakest point of the axle outside the hub by using large tack welds versus a solid cored axle/hub arrangement...this way i hope that the tacks will break before the axle shaft/gearing....any thoughts or info would be appreciated
Keith

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1018 doesnt have enough carbon in it to respond to heat treating. the 18 means .18 pts of carbon or %0.18 carbon. Generally you dont consider heat treating for steels that have less then 40 pts of carbon. In the absence of other alloying elements, chromium manganese etc, the hardening effect depends on the way the carbon combines with the steel when its chilled rapidly in a quench and forms a kind of crystal called martensite. If there isnt enough carbon the effect will be negligible. The good news is that 1018 is not brittle and might bend or distort but almost surely wont crack.

I would guess - just a guess - that a mild steel bar of the same dia as the CI bar it replaces will give good service.

Case hardening is a process in which carbon is added to the surface of the steel to improve wear but it wouldnt do much for the tensile strength of the shaft.

A member like this boom would typically be made of an alloy steel like 4140 as Wooldridge said. This is an alloy steel (it has chromium and stuff in it ) designed for toughness rather than hardness and is often used in shafting. It can take flexing and twisting without cracking or distorting.

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Cold rolled steel is stronger than hot rolled because it's work hardened. If you try to heat treat it, the first thing that will happen is that it will anneal, and you'll lose that extra strength.

As others have pointed out, 1018 doesn't really have enough carbon to heat treat. It probably will harden a little if you quench it from above critical, but I doubt it would gain back as much strength as you'd lose just by heating it up that first time.

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Generally speaking, 1018 is not heat treated but it can be quenched and lightly tempered. Since it is low carbon, low alloy, you won't get the martensite to go very deep into the part. However, you WILL get a shallow skin of martensite. Martensite expands as it forms and depending on the geometry of the part, you may get compression or tension stresses on the surface of the part. If you get compression stresses, it will keep cracks from propagating. Shafting is often case hardened to improve the fatigue life of rotating parts. If the part has been machined and has any section changes or sharp corners, DO NOT heat treat it. You may crack it even though it is low carbon. I would suggest you put the part into service cold rolled and see how it works. If it fails soon, try quench and tempering it. It might help.

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Cold rolled has a tendency to warp when machined if one part is left stressed from the rolling and another surface is removed by machining. Machining a round shaft should not see this problem though. Normalizing is often done to de-stress the part after machining but as mentioned it changes the work hardened aspect of the metal.

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10xx is for simple carbon steel it also contain some Mn but so do most steels anymore. 51xx is about 0.8 chrome, 92xx is 2% silicon, there are many more and lists are available,

Basically the number system tells the alloy elements includes in that melt of steel.

there is also an alloy steel with Letters and numbers, as well as ANSI grades, and this is only US standards, other countries have their own thing going as well.

Edited by steve sells
typo
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Just don't try to learn everything before you start hammering, there's too much for any dozen people to learn. It's a pick your battles thing. Then when you have a good handle on what you want to do you start discovering all these little details and nuances that make a difference. It never ends. I love that part.

If you'll click on "User CP" at the top of the page and edit your profile to show your location you'll discover the folk who live close enough to get together with for hands on help. It's really helpful, there are folk from more than 50 countries on IFI.

Frosty

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Once again I yield to Quenchcracks educational background. Mild steel today ( new stuff ) may or may not be 100 % scrap. Please correct me if I am wrong. Not my intention to come across as all knowledgable. I have a fair background in forging and steel knowledge. Consider this:

Mild steel ( cold or hot rolled ) will make fine tools or tooling for many shop issues IF the tooling is used for hot mild steel. If I have some better steel, I use it. I make my sizing drifts from mild ( normally hot rolled ). I have a handled top tool ( top fuller ) with the striking head ground to a nice round radius. If you strike it, it will mushroom immediately. It does however make an excellent hammer when struk on sheet ( just another size of ball pien or rounding hammer ). Just use it as a hammer.

If you have no experience, try this. Drill a 3/16 hole in a piece of bar stock ( lets say 1/4 x 1, 2 feet long ). Countersink and drill about an inch from one end. Now, forge the other end the hard way ( making the end 1/4 thick and perhaps 1/2 wide ). No tongs required, simple exercise. Quench ( water ) the forged end after re-heat to some form of red color. Quench cold. Countersink and drill hole on this end. You may or may not find that this end drills harder. Try this exercise again and let the forged end cool normally out of a breeze before drilling. Your control will be the raw stock drilling on the un-forged end. Use drilling fluid if you wish. Use a drill press, hand drill ( electric ) , brace and bit or a breast drill. Also if you have one, use a post drill. Sharp bit in all cases. You will find some differences.

This steel I call manurealloy in that there is no real way to know what is in it. You will now have somewhat of a better knowledge base of smithing. Some in industry think that mild steel may be heat treated to dramatically change it. I think this is hogwash in that subtle changes as Quenchcrack has noted will happen. Even with superquench. Please correct me if I am wrong and you have experience to show me how I am wrong.

Work hardening in the process of cold rolling has been noted. This happens during the removal of hot roll scale and in the process of making the ( shafting for example ) finished goods in tolerance for the need. Cold rolled shafting will be somewhere around - 5 thousandths and plus zero of the assigned dimension. This means that the industry standard bearing will fit the industry standard shafting. When you are crawled up under a machine, this fit will make you happy. This machine may or may not have needs for a harder shaft. If so then the industry will have a spec for the replacement shafting in many cases. You will also perhaps note that standard PTO parts with standard US fittings are a different fit than the same parts of European fittings ( Walterschieb or Bondio-Pavessi ). Points off for me on spelling. This takes the thread in places perhaps not intended perhaps. Sorry for the hijack.

Mild steel will change somewhat yes if quenched. as noted, there is a lot of knowledge that is really un-necessary in learning about smithing. Get the steel hot, forge a point and when you split a few you will learn when to stop hammering and re-heat. When you have production process, you learn to let parts perhaps cool after forging if you have holes to drill. Yes, hot punch is used here and hot filing but on really small holes, hard to punch good clean hole. I have drilled hot steel with no appreciable damage to bit ( on occasion ). Don't mean to sound sage, just have a bit of experience and have made a ton of mistakes. Please convert the measurements to metric if you wish. :)

Edited by Ten Hammers
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I happen to know a smith that lives I guess 20 miles from me. He has a guillotine tool that has several pieces of interchangable tops and bottoms. All mild steel and all superquenched. As I noted before mild steel tooling is fine for hot steel in many cases ( my opinion ). I use other steels ( alloys or 10 series ) for issues I have needs for. Will the mild steel have the properties of a heat treated alloy or 10 series steel with higher carbon ? No. Will the hot rolled tooling suffice in many cases ? Yes.

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I would treat an axle, to make it ductile enough, to absorb the torque applied to it.
Being in a hardened condition, has no advantages here. Even the small amount of carbides the 1018 would produce when hardened has little bearing on the piece functioning as an axle.

If you don't know the condition the steel is in now, I would normalize it.
You can't go wrong doing this. You'll end up with and axle that will flex a little without breaking, because you have produced a ductile grain structure in the steel

Heat the piece to 1450fh[none magnetic] let cool in still air. It only needs to get under a thousand degrees to change structures then back up to none magnetic and let it cool again.

Have a good one, FRed

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