Hank Rearden

  Points on Forge and Tempering Tool Steel

1. Use a good, clean, deep, coke fire for heating tool steel and heat it slowly and evenly.

2. Heating in a poor shallow fire, or heating too rapidly, is likely to cause uneven heating, which results in unequal expansion, which in turn may cause internal flaws or cracks.

3. Proper hammering of tool steel at the proper temperature refines it, making the grain size smaller.

4. Do riot hammer tool steel unless it is at least at a dark-red heat, and heated uniformly clear through.

5. Hammering below a red heat is likely to cause cracking and splitting.

6. Hammering when not heated clear through may cause the outer parts to stretch away from the inner parts and cause internal flaws or cracks.

7. Light hammering should be avoided even when the steel is well heated, because of danger of drawing the outer surface without affecting the inner parts.

8. Never heat tool steel above a bright-red or low-orange heat, and then only for heavy hammering.

9. For moderate hammering, as in finishing and smoothing a job, do not heat above a dark red.

10. Tool steel is ruined if it gets white hot.

11. In case tool steel is accidently overheated somewhat, allow it to cool slowly and then reheat, being careful not to overheat it again; or heat it to a bright-red or low-orange heat and forge by heavy hammering to restore the fine grain size.

12. After a tool is forged, it should be annealed by heating to a uniform low red and placing it in dry ashes or similar material to cool slowly.

13. In quenching a tool like a cold chisel, move it about rapidly-up and down and around-to prevent a sharp line of demarcation between the hot and cold parts.

14. Tempering colors should move slowly so they may be easily seen. If they move too fast, dip the tool quickly into water for an instant.

15. In the final quenching of a tool like a cold chisel, cool the end quickly but dissipate any, heat left in the shank very slowly. Otherwise the shank may be hard and brittle.

16. In case a tool is found to be too hard, retemper it and allow the temper colors to go out a little further before final quenching.

17. In case the tool is too soft, quench before the colors go so far.

code[Maglio.gif]  Keep the fires burning hot!
2020 ABANA Conference in Sarasota New York. June 3rd. through June 6th. Plan now!
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Hank Rearden
This is an excellent primer on the understanding of tempering steel.

code[Maglio.gif]  Keep the fires burning hot!
2020 ABANA Conference in Sarasota New York. June 3rd. through June 6th. Plan now!
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Interesting video.  I would make a couple of suggestions for anyone working with this stuff for the first time.  First, use a magnet to determine his "red" heat.  Judging the proper heating color for hardening is next to impossible.  Remember, if the material isn't hot enough it wont fully harden and if it is too hot grain growth will occur weakening the material.  For me the proper heating color looks more yellow/orange than red.  Also differences in ambient light can change things, full sun vs shop lighting.  When simple carbon tool steels get to the proper temperature for hardening the magnet will quit being attracted.  At that point quench in oil.  Never quench knife blades in water.  Even steels like W-1 can crack with a water quench.

Second point, on tempering.  Use an oven.  I keep a big toaster oven in my shop with a thermometer to help judge the temps along with the tempering colors he mentioned.  You may use a torch on simple carbon steels but note that the tempering colors are a lagging indicator and you may have over heated before the oxide form so take it slow and easy.  He suggested dumping your tool in water to keep it from over heating.  Never do this with knife blades as the rapid cooling at tempering temperatures may cause cracking.

Finally, these procedures are only applicable to simple carbon steels.  High alloys and stainless steels require complex heat treating procedures that cannot be obtained with a torch or forge.

Rule #10;  "I can make that" translates to; "I'm to cheap to buy it new."

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