Heat Treating Steel

[ruffdog]

Wow...1011 steel must be horribly gummy to machine.

 

[3Ts]

Thanks, guys. I appreciate the knowledge and the time you spent typing it up.

I've been looking at a forge for some time and have begun to get serious about one, (maybe next year) so this is helpful. I still have a question on hardening though. The post in the Harbor Freight tools section mentioned trying to harden mild steel and this thread answers that, but what about case hardening powders? Does anyone have some experience with that? Would adding the powder to the Hydraulic press pin actually do anything useful? Also, with a forge using coke does the steel "absorb" any carbon to increase its hardness? Here's a link to one site with the powder.

BROWNELLS SURFACE HARDENING COMPOUND | Brownells

 

[stuckmotor]

So, there's nothing in Zinc that would impart brittleness to mild steel when welded?
My mild steel wasn't as mild as I thought?

 

[ruffdog]

I have used Kasenite before and it will give you a thin case harden.

1LB.CAN #1 SURFACE HARDNING COMPND KASENIT | 81-3-1 | Travers Tool Co., Inc.

We also would send parts out to have the carbonitriding process done to them:

Carbonitriding - Wikipedia

 

[MHarryE]

So, there's nothing in Zinc that would impart brittleness to mild steel when welded?
My mild steel wasn't as mild as I thought?

Never thought much about it but electroplating can cause hydrogen embrittlement. Wikipedia has a good write-up on causes of hydrogen embrittlement and how to prevent it. It’s been so long for me - but donts include welding galvanized, but I cannot remember if it induces hydrogen embrittlement. I can’t think of why it won’t, but getting back into that makes my head hurt. My introduction to it came from plating parts instead of painting to reduce cost (yes, plating small parts can be much less expensive). Then had parts break. Most relate to case I remember is having fasteners with hydrogen embrittlement. Assembly fine at end of line but when loading on rail car, discovered heads popped off some bolts. Suspected over torque but problem turned out to be zinc plating grade 5 hardware without baking afterward. So plating can cause problems but not sure if it is yours.

 

[stuckmotor]

SNIP/So plating can cause problems but not sure if it is yours.

Thank you. It's been a very long time since I welded on the zinc covered straps (I think they were used as braces at the tops of utility poles) and I can't remember exactly how soft they were before being welded.

 

[John_Mc]

Very interesting John. Thanks for taking to time to explain. I have a question on mild steel if that is OK. If you crudely heat a piece to dull red or maybe even orangey/yellow with your torch so that it bends/deforms easily is there any difference in the end product properties if it is left to air cool or is quenched in water?

gg

If you heat it up enough and hold it there for a bit (definitely above 1000˚, cant remember how much above it needs to go to make a difference, but you don't need to go all the way up to austenitizing temperatures) and let it cool slowly you have annealed the steel, which softens it - assuming it wasn't already annealed before you started messing with it.

I'm not sure what happens if you quench it, but I believe with mild (i.e. low-carbon) steel, it will still end up softer than before the heating.

 

[John_Mc]

It is possible to add carbon to the surface of some alloys of steel, which would allow that surface to be case hardened. If I recall, the process was called carburizing. One way of doing this was to expose the steel to a carbon-rich atmosphere while at elevated temperatures. We did not do any of this, so it's not a process I'm familiar with. (Case hardening doesn't really help when you are making spring wire - in fact, it can hurt the cycle life of spring.)

 

[PhysAssist]

The time sensitive parts from the point of view of the heat testing are the initial heat up followed by the quick quench. You can let the part sit around for days after that before heating it back up to temper the blade.

The initial heat up and quench can be dramatic (relatively speaking): glowing steel followed by a dunk in something cold. The reheat is boring: just warm it up, probably well below the temperature where the steel glows. Maybe they don't show it because it doesn't make for good TV?

There are some "contestants" who fail to get properly hardened results, and often it appears either d/t inadequate or incomplete heating, or/also inadequately cooling the piece [sticking it in oil for approx 1 second or less and then bringing it out while it is still hot enough to set the oil on fire [?what kind of oil they are using]- and they then end up doing multiple re-heat/quench cycles. [I think the record was somewhere around 7-9 IIRC].

I have seen only a very few use a magnet to test the steel temp before quenching, and I suspect with the bright [the modern version of Klieg lights] in the studio/"forge", it would be very difficult to gauge the steel heat by color

As a result their blades often warp or develop stress cracks, and more than a few have shattered when dropped on the floor, while being manipulated to straighten a warp, or during the [admittedly over the top] testing phase.

A very small subset of "blacksmiths" on the show will reheat their blades to "normalize" them- but there is no re-quenching associated with this, just using an OA torch/rosebud, and air-cooling- these blades seem to withstand testing somewhat better than the other blades.

 

[John_Mc]

A very small subset of "blacksmiths" on the show will reheat their blades to "normalize" them- but there is no re-quenching associated with this, just using an OA torch/rosebud, and air-cooling- these blades seem to withstand testing somewhat better than the other blades.

There should be no need to re-quench after "normalizing" the steel. (Actually, the term we used at work was "Tempering": you heat, then quench the steel to harden it, the reheat to "temper" the martensite.) It should make no difference in the properties of the steel - at least with any of the alloys I've ever worked with - whether you let it air cool after tempering or whether you dip it in water or oil. We used water for this second cooling in our spring wire, and we didn't call it "quenching". The only reason we did that rather than air cooling is to get it cooled off to where it's easy to handle - plus we wanted it more-or-less room temperature before we wound it back up into a coil at the end of the heat treating process.