*        "The New American Machinist's Handbook" shows the Hardening (i.e. quenching) Temperature for 1050 to be 1475F/802C to 1550F/843C. I heat the small pieces to 1500F/815C  but something like a breast plate or a helmet I heat to 1550F/843C.  This is because large pieces it will cool off somewhat in the time it takes for me to grab it with a pair of tongs (sometimes two pairs of tongs) and quench it. If you heat them to 1600F/871C like I used to do they are much more likely to warp.

*       The electric kiln that I use for heat treating is a Paragon HT-22D (shown at the bottom of the page).

*        I'm sure there are better alloys then 1050, the reason I picked 1050 was because it was the closest to the period 15th century steel  used for armour.

*        There are three times during the heat treating process that plates can warp. The first is when it's heated to 1500-1550F  /  802-843C it can warp under is own weight under some circumstances. For larger pieces such as breast plates I would said that you should build a frame to keep the piece from warping. The second is when you pick it up with the tongs to quench it, the pressure from the tongs can easily warp the plate if you grip it the wrong way.  The third is when you quench the piece. Having the piece go into the water in such a way that it is symmetrical side to side seems to help eliminate warping. I've found that when I quench in transmission fluid or oil that plates don't seem to warp during quenching (unless it happened earlier in the process). However I been geting much better results with water quenching then transmission fluid or oil.
 
 

Relatively Soft Temper for 1050 spring steel (deforms instead of cracking):

        Heat the pieces to 1500F/815C and quench them in water (around 60-70F /  16-21C). Then reheated them to 660F/ 349C for 30 minutes to temper them. Test plates heat treated using this method have a hardness around Rc38 and seemed to have the same dent resistance as mild steel plates 80% thicker.

(The following chart shows my best guess of what the dent resistance of 1050 spring steel heat treated with this method is relative to mild steel.)

0.035"  / 20 gauge  / ~0.9mm   =     0.063" / ~16 gauge / ~1.6mm
0.050"  / 18 gauge  / ~1.3mm   =     0.090" / ~13 gauge / ~2.3mm
0.062"  / 16 gauge  / ~1.6mm   =     0.111" / ~12 gauge / ~2.8mm
0.075"  / 14 gauge  / ~1.9mm   =     0.135" / ~10 gauge / ~3.4mm
 
 
 

Moderate Temper for 1050 spring steel (will usually deform instead of cracking *):

* If a plate with this temper is bent to the point of deforming it and straightened repeatedly it will crack after doing this a few times.

        Heat the pieces to 1500F/815C and quench them in water (around 60-70F / 16-21C). Then reheated them to 600F/316C for 30 minutes to temper them. Test plates heat treated using this method have a hardness around Rc44-45 and seemed to have the same dent resistance as mild steel plates 100% thicker.

(The following chart shows my best guess of what the dent resistance of 1050 spring steel heat treated with this method is relative to mild steel.)

0.035"  / 20 gauge  / ~0.9mm   =     0.070" / ~15 gauge / ~1.8mm
0.050"  / 18 gauge  / ~1.3mm   =     0.100" / ~12 gauge / ~2.6mm
0.062"  / 16 gauge  / ~1.6mm   =     0.124" / ~11 gauge / ~3.2mm
0.075"  / 14 gauge  / ~1.9mm   =     0.150" / ~  9 gauge / ~3.8mm
 
 
 

Hard Temper for 1050 spring steel (will crack under some circumstances *) :

* If a plate is bent to the point of deforming it may crack when straightened again.

        Heat the pieces to 1500F/815C and quench them in water (around 60-70F/16-21C). Then reheated them to 570F/299C for 30 minutes to temper them. Test plates heat treated using this method have a hardness around Rc48 and  seemed to have the same dent resistance as mild steel plates 200% thicker. If a flat plate is bent back and forth to a 90 degree angle after a couple of bends it will crack.

(The following chart shows my best guess of what the dent resistance of 1050 spring steel heat treated with this method is relative to mild steel.)

0.035"  / 20 gauge  / ~0.9mm   =     0.105" / ~12 gauge / ~2.7mm
0.050"  / 18 gauge  / ~1.3mm   =     0.150" / ~  9 gauge / ~3.9mm
0.062"  / 16 gauge  / ~1.6mm   =     0.186" / ~  7 gauge / ~4.8mm
0.075"  / 14 gauge  / ~1.9mm   =     0.225" / ~  5 gauge / ~5.7mm
 
 
 

Very Hard Temper for 1050 steel (plates will crack in half if bent to far):

* If a plate is bent to far it will probably crack instead of deforming.

        I heat treated a few test plates using the following method. Heat the pieces to 1500F/815C and quench them in water (around 60-70F/16-21C). Then reheated them to 550F/287C for 30 minutes to temper them. Test plates heat treated using this method have a hardness around Rc50. When I put the test pieces on my anvil and hit them with a ball peen hammer about 5 times or so pieces of the plate cracked off. With another test piece I clamped one 4 inch end of the 8 inch by 4 inch plate in a vise and grabbed the other with a pair of tongs to see how far it would bend before breaking. The plate broke in half at about a 70 to 80 degree bend.
 
 

        All the fire scale comes off when you quench in brine unlike quenching in water. The dent resistance after tempering the plates seemed about the same as with a water quench. Using Brine didn't seems like it was worth the effort.
 
 

        After talking to a number of other armourers and knife makers that do heat treating it sounded like I could get better results using an oil or transmission fluid quench.  So I bought quenching oil (low-viscosity, straight mineral oil) from McMaster-Carr. The plates plates that I quenched but didn't temper bent much easier then test plates that had been water quenched and tempered to 600F/315C or even 660F/348C. The quench took much longer in the oil then in water and far longer then in fast moving (stirred) brine. The plates seemed much less likely to warp during the quench. Quenching in the oil cleaned off the fire scale similar to quenching in brine. I not sure if this is due to some special property of the quenching oil or if quenching in any mineral oil does this.
 
 

        I heat treated a few test plates by quenching them in transmission fluid. The plates that I quenched (but didn't temper) resisted denting about the same as test plates quenched in water and tempered to 660F/348C. However unlike the plates quenched in water the untempered plates quenched in transmission fluid cracked after 5 to 10 or so hard hits with a ball peen hammer in the same area.
       If the plates quenched in transmission fluid had been tempered they would be less likely to crack. However they would still be easier to dent then even a water quenched plate with a 660F/348C temper.
 
 

Precision Steel Warehouse, Inc.  (Best prices I've found for orders of 130 pounds or more per size)
Admiral Steel LLC  (Good for small orders)
 
 

All Fired Up / Kiln Doctor   Best prices I've seen on Olympic and Paragon kilns. Be sure to tell him I sent you and ask about discounts on Olympic kilns. For heat treating you will need a front loading electric kiln with an automatic temperature controller.
 
 
 

Pictures of my kiln:

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Copyright 2006   Craig W. Nadler   All rights reserved