heat treating 410- Water, oil, or air quench. Temper or not?

[Gaston de Clermont]

Perhaps my higher temp is a caution borne from working with other alloys. The temper curves I've seen say 350F doesn't do much, though 410 tends to be pretty crack resistant without tempering at all. I'd be curious to compare pieces with and without the 350F tempering step. I don't think you're going to experience the shattering like we've seen on some of the helmet failures lately, but you might be more likely to see small cracks form at articulation points or from exceptional weapon strikes. It's all a probability game, really. You could temper it dead soft and still crack it under the right conditions. You just want to make that unlikely, and get the right balance between cracking, denting and price. Every end user is going to pick a different point where those balance for them.

[Craig Nadler]

Tonight I brought some test pieces over to the Knight's Hall in Nashua, NH and had Jaye Brooks test them with a sword and a two handed ax. The two round plates have holes in them so that they can be nailed to the pell for testing. The round plate on the upper left is 0.035"/20ga. that has been heated to 1950F and quenched in water, then tempered to 350F for 30 minutes. The round plate on the upper right is the test control plate that is made from 0.078"/14ga. 304 stainless steel. The helmet half is made from 0.090"/13ga. annealed 1050 carbon steel, it was NOT hardened at all.

Please note that after the two round plates had been tested with equal numbers of blows the 20ga. 410 stainless steel plate then received a fair amount of extra testing.

The 14ga 304 stainless steel test plate seemed slightly stronger than the hardened 20ga. 410 stainless steel. Based on this test it would appear that the hardened 20ga. 410 stainless steel test plate resisted dent as well as 15ga./0.070" 304 stainless steel.

Jaye only hit the helmet half once with the two handed ax. The dent was about 3/8" deep.

The most interesting part of the testing is that we retested some of the 0.035"/20ga, 1050 spring steel test plates that we have laying around at the Knights Hall. The 1050 test plates had been heated to 1600F and quenched in water and then tempered for 30 minutes at 650F. The 1050 spring steel test plates significantly outperformed the hardened 410 stainless steel test plates. It looks like my figures for the dent resistance of 1050 spring steel were very low. The 0.035"/20ga. 1050 spring steel test plates resisted dent significantly better than the 14ga. 304 stainless steel test plate.

I'm going to build another batch of 410 stainless steel test plates for some more testing tomorrow night.

[Craig Nadler]

Even at a 350F temper I'm still getting 410 stainless steel test plates to crack sometimes. If you clamp a test plate in a vise and hit it with a 2 pound rubber mallet 6" to 8" above the vise the plate will either crack at the point when it's bent to a 90 degree angle or when you try to straighten it afterwards.

[Halberds]

I enjoyed your heat treat and test demo at the Texas armour in.
The bend test was what we used to do in a lab years ago with special tools, equipment and chart recorders.

I think what you are doing will produce usable results for the intended need.
Thanks for the great in progress pics.

Hal

PS: Perhaps a little more draw back temp and time.

[Sean Powell]

Looks like good info. I want to look at some yield strength/ultimate strength numbers for the times and temps you posted. We have gone beyond basic number comparison into energy absorbtion. The point at which the materials just barely start to dent may be less important then how much energy is left to cause deformation and how far that energy will deform the plate.

If you got a splitting maul head on a long shaft you could set up a pendulum to control the impact energy more then "Jaye who is a bid dude hit it hard." Eventually we can come up with an energy conversion of 1 Jaye = 1462 ergs.

Sean

[Craig Nadler]

Sean Powell:

I agree that a more scientific repeatable method would be better in general. The purpose of the Jaye test is a worst case scenario sort of test.

[Craig Nadler]

Tonight I brought some 0.035"/20ga. 410 stainless steel test plates with a 400F temper over to the Knight's Hall in Nashua, NH and had Jaye Brooks test them with a sword and a two handed ax. These test plates preformed very well with no cracking at all. Jaye's option was that the 0.060"/16ga. 304 stainless steel plate was much easlier to dent than the 0.035"/20ga. 410 stainless steel with a 400F temper and the 0.078"/14ga. 304 stainless steel test plate was somewhat easlier to dent than the 0.035"/20ga. 410 stainless steel with a 400F temper.

[Craig Nadler]

After reviewing a few different spec sheets again I desided to go with a 2 hour temper at 400F. Most of the spec sheets say 1 to 4 hours for the tempering step so I'm going to go with the middle of the range.