Using Discarded HC Steel - a lesson learned?

[Steve Anderson]

What do you think...?

The Story
I was given used/discard planer blades that I wanted to anneal and use as raw material for other items (e.g. little knife blades).

They are M2 High Speed Steel. 

I have been reading a lot of information about using scrap steel from this and that--I really like the idea of repurposing material that would otherwise be thrown away.
For example: It apparently use to be true that you could get saw blades from a mill and cut them up to make tools.

After looking into the thermal treatment guidelines for M2 steel I think I would be better off buying an appropriate material.

I am starting to think that the info I've read that questions the wisdom and economics of trying to use "unknown steels" may be more right than I had hoped.
That trying to use "scrap" is likely to be a frustrating, often fruitless, and maybe even dangerous activity. 

I will appreciate your thoughts and experience with using discarded material -- especially as it relates to the Anchorage and The Valley regions of Alaska.

 

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M2 High Speed Steel Thermal Treatments

HEAT TREATING INSTRUCTIONS

HARDENING
Critical Temperature:
Ac1: 1530°F (832°C)    Ac3: 1610°F (877°C)
Ar1: 1430°F (777°C)    Ar3: 1380°F (749°C)
Preheating: To minimize distortion and stresses in large or complex tools use a double preheat. Heat at a rate not exceeding 400°F per hour (222°C per hour) to 1100°F (593°C) equalize, then heat to 1450-1550°F (788-843°C). For normal tools, use only the second temperature range as a single preheating treatment.

Austenitizing (High Heat): Heat rapidly from the preheat.
For Cutting Tools:
Furnace: 2200-2250°F (1204-1232°C)
Salt: 2175-2225°F (1191-1218°C)
To maximize toughness, use the lowest temperature.
To maximize hot hardness, use the highest temperature.
For punches, dies, and tools that require maximum
toughness without hot hardness:
Furnace: 2075-2175°F (1175-1191°C)
Salt: 2050-2150°F (1121-1177°C)

Quenching: Pressurized gas, warm oil, or salt. For pressurized gas, a rapid quench rate to below 1000°F (538°C) is critical to obtain the desired properties. For oil, quench until black, about 900°F (482°C), then cool in still air to 150 -125°F (66-51°C). For salt maintained at 1000-1100°F (538-593°C), equalize, then cool in still air to 150 -125°F (66-51°C).

Tempering: Temper immediately after quenching. Typical tempering range is 1025-1050°F (552-566°C). Hold at temperature for 2 hours, then air cool to ambient temperature. Double tempering is required. For large cross sections, and especially for blanks from which tools will be cut by wire EDM, triple tempering is strongly recommended.

ANNEALING
Annealing must be performed after hot working and before re-hardening.

Heat at a rate not exceeding 400°F per hour (222°C per hour) to 1525-1550°F (829-843°C), and hold at temperature for 1 hour per inch (25.4 mm) of thickness, 2 hours minimum. Then cool slowly with the furnace at a rate not exceeding 50°F per hour (28°C per hour) to 1000°F (538°C). Continue cooling to ambient temperature in the furnace or in air. The resultant hardness should be 248 HBW or lower.

[ThomasPowers]

People still eat mushrooms even though some types are dangerous; People still drive cars even though some types are dangerous.  Because M2 is NOT an alloy suitable for blacksmithing methods does not mean there are no alloys that are suitable.  Part of using recycled metals is learning how to test them for your purposes and then TESTING unknown materials.  We all like to take shortcuts and often we succeed; but when we don't then it's back to first principles---I picked up a stack of 5/8sq stock, looked to be cold rolled, at the scrapyard recently; but then I tried to forge a piece it just laughed at me; so I spark tested it and it had an odd sparktest, more like HSS as it sure wasn't cast iron or wrought iron!!!  It's now waiting on time to do some more in depth testing and though not suitable for camp cooking tripods if may be quite useful for other items.

Or to put it succinctly: when using recycled unknown materials---you win some and you lose some. If the uncertainty is troublesome stick with known new materials and realize that MANY smiths have a tale of an order being messed up by the steel dealer; knowing how to test what you have against what it's supposed to be can be a valuable skill even with new store-bought steel!

[Frosty]

Welcome aboard Steve, glad to have you. I have some planer blades in the shop someone gave me a while back, it looks like I should find something else to do with them. The described heat treatment is beyond the capacity of most home shops to do, mine certainly. If a guy has a ramping kiln it'd be doable.

You were at the meeting today weren't you? I can't see your avatar well enough to be sure. We're going to buy 4140 from the supplier for the hammer workshop for the reason you describe. Using found or scrap is like so much of life, sometimes you're the pigeon sometimes you're the statue.

Frosty The Lucky.

[BIGGUNDOCTOR]

You can still do stock removal knives from them, or reshape them for form cutters. 

I have no issue using scrap materials for most things. Now if I was to make something like a fancy knife for sale, I would want to know exactly what I am working with.

 

[metalmangeler]

I also think that for a knife that you are selling you should use a steel of known material. For personal use just depends, I would use a steel I thought I could heat treat without much trouble. Find out by heat treating a scrap and then try a destructive test. I use quite a bit of scrap for my forging tools, dies, hammers, tongs. I also use known tool steels for these same tools, it depends on the value of the tool and the time I expect it to last, or I expect it to take to make. You don't want to spend lots of time making something that self destructs in the final stage, or when you first try to use it.

[Steve Anderson]

Thank you all for the replies!

I asked the question to see what insight I would gain from the responses. And all your responses

ThomasPowers & metalmangler - You both made a good points about purpose, perspective and also reminded me to focus on what I am trying to get out of this activity. I did a quick test on the planer blades before I even tried to find out what they were -- I cut a blade into three pieces (using an angle grinder), heated the pieces to red hot (with my oxy/ace torch) one at a time, plunged each of the hot pieces into a jar filled with vermiculite for the parts to cool relatively slowly. The pieces showed no sign of softening that I could detect. I was surprised, so it was a good experience to have.

Frosty - I was not able to be at the meeting. I had been following the notice info but I was needed at home. Hammer workshop?! I will need to look into that. :-)

BIGGUNDOCTOR - Thank you for the reminder that I could use them for stock removal projects! I had been focused on one use and had not yet re-opened my mind to other possibilities. Last night I made a 4.5 inch little test knife like object for practice. It is kind of a neat little tool. I used it to cut up the veggies for the pot roast I made today.

[ThomasPowers]

In general I try to avoid the HSS as I do not have the equipment to heat treat them and am too cheap to pay folks that do.  When I get some "accidentally" I usually trade them for stuff I like.  Using them in as is state is a good idea.  Their use case would be for high wear situations but they have to endure quite a bit of force on them too as planer blades.