Is this steel bar considered mild unhardened steel?

If I recall correctly, Hillman is hardware store steel. Probably hot rolled 1018 or A36. Gummy and definitely not hard!
 
It is "hardenable" but not all the way through. You will need to do a case hardening on something like that. On youtube is Chris, from "Clickspring". He built a clock, then started the Antikythera device build. I haven't seen videos for a good while from him on it, but one of those videos he branches out to a side topic where he "hardens" mild steel. It might be of interest.

 
Thanks Silverhawk. The reason I am asking is because I broke two taps today on that 1/8" material. I had the correct pilot hole and was very careful. Either the HSS steel in the tap was inferior or the steel was harder than I wanted. I thought it was be a non hardened mild steel. But I am not a machinist and don't know all that much about the various steels.
 
I've broken more taps in plastic than I have in steel. It's a tendency to think it's softer without realizing the chips still need to be cleared. The mild stuff is just as bad as the semi hard stuff in that the chips don't break as easily when tapping a turn and then backing out. I've had to remove the tap completely multiple times. Use your senses - if it's starting to bind, back it all out, blow things clear, and add tapping fluid. If you don't have any, the closest you might encounter would be WD-40 (actually better than tapping fluid if you are using aluminum in my opinion).
 
Thanks for your help I do have some tapping fluid and did use it. The tough thing about this is that the taps I broke were my last two 12-20s and they are impossible to find right now, Victor Machinery has sold them in the past but they were bought out by another company and the 12-20 tap and dies are in limbo or on terminal back order from China.
 
Tozguy said:
Might I ask what size pilot hole you used? Sometimes with less than perfect taps, a slightly larger hole will solve the binding problem.
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Hi Ken thanks for the response. I am tapping with a 12-20 HSS tap (Chinese made) (old thread for Stanley hand planes) I started with an 11/16" hole. It did feel a little tight and then I broke off a few threads on the tap. I then drilled out to 3/16" and tried again with my second and only remaining 12-20 tap and damaged that one as well. So now both of my extremely hard to find taps are damaged. (hence my other current post about asking if anyone can make a tap like that in this group) I was making a threaded "tree" for bead blasting the screws. As shown below. I ground the taps down past the damage and tapered the ends a little and was able to finish what I was doing. But the 1/8" material just seemed hard. (I don't have a lot of experience with metal work so I don't have a lot of experience determine hardness, other than the skittering file For future "trees" I was looking for something a little softer than this Hillman material I just used. Maybe I just need a bigger hole. Thanks again
 

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There is a big difference in performance between your Gran'daddy's taps, Hardware store taps, and ground machine taps. I've found that even dirt cheap imported taps that are ground for use by machinists far out perform Irwin brand or similar hardware store taps. The entirety of the cutting occurs on the tapered edge of the first 3-5 threads, so the relief angle and sharpness there makes a tremendous difference in the tap cutting or plowing through the material. Tapping oil helps, but only to a point. There are special taps for hard materials (6-8 flutes, very sharp).
 
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