heat treating cold rolled 1018 mild steel

[keithh999]

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

[HWooldridge]

You can case harden it but results may be erratic in the home shop especially if you haven't ever done that process before. I'd probably leave it alone - if it breaks again, make one out of 4140.

[Aeneas]

Now, I don't know anything about heat treating (... it's on my list of things to learn ) so this is a legit question ...
Wouldn't heat treating make the axle harder and therefore more brittle?

[metalliferous]

Depending on the heat treatment, a steel can become harder and more brittle or softer and more ductile. With 1018, however, since it is a mild steel, you'll probably see very little difference with any heat treatment. I'd probably just normalize it to relieve any residual stress from machining and let it go.

[maddog]

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.

[Mike BR]

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.

[Quenchcrack]

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.

[kzajko]

Originally Posted by Aeneas

Now, I don't know anything about heat treating (... it's on my list of things to learn ) so this is a legit question ...
Wouldn't heat treating make the axle harder and therefore more brittle?

some detailed information about heat treating can be found here: Low pressure Vacuum carburizing and heat treating

[ThomasPowers]

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.

[minifarmer]

Hi, I'm just learning the blacksmith trade. I'm a retired truck driver and all the years I was driving I always found blacksmithing fastenating,so now I can try my hand at it.