Jump to content

Hardening Screwdriver Blade


jdrichard

Recommended Posts

I debated whether to post this, it’s verbose and sounds like a lecture.  But I see the subject wrestled with all the time and thought a summary from someone who has done lots of it might help you - and the next guy.  Here’s imo pretty much all you need to know to get some successful results from DIY heat treating:

1)  Drill rod IS tool steel IS Silver steel.  The name silver steel is the common name in the UK, drill rod in North America.  Also called carbon tool steel.

2) you HAVE to know what tool steel the drill rod is:   O1 (oil hardening) or W1 (water hardening).  Don't buy drill rod without knowing what it is.  Another common tool steel is A2 (air hardening).  It’s more expensive so less likely to what he drill rod is at the local outlet

3) Why do you have to know?  The quench is different - oil for O1, water for W1, air for A2

4) Why the different quenches?  Different fluids (Water, air, oil, ice cold brine) have different quench speeds suitable for different tool steel alloys

5) What happens if I quench O1 in water, and vice versa?  Water is too fast a quench for O1, you risk cracking it.   Oil is too slow for W1, it won't harden as much as it could/should.

6)  Which tools steel is best?  W1 is the cheapest.   Most imo prefer O1, it machines well and is less likely to distort or crack in the quench than W1

7) What oil to use?  Doesn't much matter.  I use a mineral oil I keep after draining a machine tool’s gearbox.  For the size of parts watchmakers deal with, just get a quart of hydraulic oil from the hardware/auto store (Canadian Tire for us canucks).  Hydraulic oil is just very pure mineral oil without all detergent and additives in motor oil (which you could also use, used or new).  Use a tin can, not a glass jar or plastic container.  Ideally the oil should be warmed on a hotplate (slower quench for O1), but I confess I don’t usually bother without ill results (cracking)

8) is the quench dangerous?  no, for the size of stuff we’re doing.  It takes a lot of heat to ignite oil.  You'll get a small plume of smoke that smells and that's about it.  There are special quench oils with a high flash point available; they make less smoke; I’ve never bothered

9) Where to get O1?  Any industrial supply place.  In Canada, metal supermarkets, Fastenal, Granger, Brafasco, KBC - heck even some hardware stores.   Catalogue houses, KBC, McMaster Carr, MSC and so on.  It’s so common it should be like picking up milk on the way home lol

I would avoid ebay and offshore mail order, while metallurgy and controls have only gotten better, the same hasn't necessarily happened to QC in the developing world.   I think the last time I bought small dia O1, its was $3 or $4 for a 3' piece of 1/8" O1 from KBC.  imo its not worth going to a less than mainstream source....the mainstream vendors mostly sell to industry and that's your QC, business and toolmakers won't put up with crappy tool steel.

10)  What is heat treatment?  If the steel has enough carbon (is a tool steel), you can change its state by heat treating.  This is usually done to harden the material.  Three words to know:  Hardened, Annealed and Tempered

11)  Hardened.   The steel has been brought up to its critical temp (1500F or bright red in sunlight) held for a bit then quenched.  When above the critical temp, the molecules arrange themselves in a structure (austenite) that gets "locked in" when its quenched.  After a proper quench the steel is as hard as it can get, and also brittle.

12) Tempering.  After hardening, the steel temp is raised again, slightly, to let it down or remove some of the brittleness at the expense of hardness.  How much its let down is (mostly) a function of temp and it so happens these temps correspond well to some colours.   light straw through blue etc.  You temper to a higher temp, say blue, around 600F, for something like a screwdriver - you want it somewhat hard, but not brittle.  A cutting tool you'd temper less.  When tempering you can quench to stop the tempering or heat flowing, but it’s not necessary for the tempering to work

Polish a bit of the hardened steel so you can see the tempering colours, heat slowly, they change rapidly

13) Annealing or annealed steel.  Steel in its soft state, unhardened.   Except for special examples like watchmakers blued steel (which will be O1 or W1)  tool steel is sold annealed so it’s ready to be machined into whatever

14) how is annealing done?  Kind of the opposite a rapid cool (quench).  Heat to critical temp and then slowly cool.  Slowly as in overnight (a steel box full of ashes works well – use extra thermal mass if the part is small).  With a proper anneal the stress in the metal will be removed and it will be soft.  You'll hear of guys talking about annealing in much short time frame; what’s really happening is it’s a partial anneal - they've softened it enough for what they need.  Residual stress may remain which could lead to cracking on subsequent quenches (if necessary)

15)  Casehardening.  By soaking a non tool steel in an environment (a bath or packed with carbon around it in a steel box) where it can absorb carbon for a period of time, you can get it such that the out layer has enough carbon to then be heat treatable.  It’s then quenched.  It is not usually (ever?) tempered.  The idea is it’s an advantage having a dead hard skin and ductile core.  The skin depth might be 1 -2 thou using casehardening compound, 5-10 thou with long pack hardening and 50 thou with an overnight soak at a commercial heat treaters.  It’s good for wear parts, not so good for most tools

16)  HSS – high speed steel.  High speed steel is another group of tool steels we see, drills, lathe tools etc.  Its great advantage is it holds its hardness at high temps, unlike say O1 that starts to anneal at a few hundred degrees.  This matters as where one molecule meets another when cutting, temps can go very high.  HSS cannot be heat treated by the likes of us, there is a very narrow band of tolerance on the temperatures and cycles required

 

 

 

Edited by measuretwice
  • Like 2
  • Thanks 1
Link to comment
Share on other sites

I debated whether to post this, it’s verbose and sounds like a lecture.  But I see the subject wrestled with all the time and thought a summary from someone who has done lots of it might help you - and the next guy.  Here’s imo pretty much all you need to know to get some successful results from DIY heat treating:
1)  Drill rod IS tool steel IS Silver steel.  The name silver steel is the common name in the UK, drill rod in North America.  Also called carbon tool steel.
2) you HAVE to know what tool steel the drill rod is:   O1 (oil hardening) or W1 (water hardening).  Don't buy drill rod without knowing what it is.  Another common tool steel is A2 (air hardening).  It’s more expensive so less likely to what he drill rod is at the local outlet
3) Why do you have to know?  The quench is different - oil for O1, water for W1, air for A2
4) Why the different quenches?  Different fluids (Water, air, oil, ice cold brine) have different quench speeds suitable for different tool steel alloys
5) What happens if I quench O1 in water, and vice versa?  Water is too fast a quench for O1, you risk cracking it.   Oil is too slow for W1, it won't harden as much as it could/should.
6)  Which tools steel is best?  W1 is the cheapest.   Most imo prefer O1, it machines well and is less likely to distort or crack in the quench than W1
7) What oil to use?  Doesn't much matter.  I use a mineral oil I keep after draining a machine tool’s gearbox.  For the size of parts watchmakers deal with, just get a quart of hydraulic oil from the hardware/auto store (Canadian Tire for us canucks).  Hydraulic oil is just very pure mineral oil without all detergent and additives in motor oil (which you could also use, used or new).  Use a tin can, not a glass jar or plastic container.  Ideally the oil should be warmed on a hotplate (slower quench for O1), but I confess I don’t usually bother without ill results (cracking)
8) is the quench dangerous?  no, for the size of stuff we’re doing.  It takes a lot of heat to ignite oil.  You'll get a small plume of smoke that smells and that's about it.  There are special quench oils with a high flash point available; they make less smoke; I’ve never bothered
9) Where to get O1?  Any industrial supply place.  In Canada, metal supermarkets, Fastenal, Granger, Brafasco, KBC - heck even some hardware stores.   Catalogue houses, KBC, McMaster Carr, MSC and so on.  It’s so common it should be like picking up milk on the way home lol
I would avoid ebay and offshore mail order, while metallurgy and controls have only gotten better, the same hasn't necessarily happened to QC in the developing world.   I think the last time I bought small dia O1, its was $3 or $4 for a 3' piece of 1/8" O1 from KBC.  imo its not worth going to a less than mainstream source....the mainstream vendors mostly sell to industry and that's your QC, business and toolmakers won't put up with crappy tool steel.
10)  What is heat treatment?  If the steel has enough carbon (is a tool steel), you can change its state by heat treating.  This is usually done to harden the material.  Three words to know:  Hardened, Annealed and Tempered
11)  Hardened.   The steel has been brought up to its critical temp (1500F or bright red in sunlight) held for a bit then quenched.  When above the critical temp, the molecules arrange themselves in a structure (austenite) that gets "locked in" when its quenched.  After a proper quench the steel is as hard as it can get, and also brittle.
12) Tempering.  After hardening, the steel temp is raised again, slightly, to let it down or remove some of the brittleness at the expense of hardness.  How much its let down is (mostly) a function of temp and it so happens these temps correspond well to some colours.   light straw through blue etc.  You temper to a higher temp, say blue, around 600F, for something like a screwdriver - you want it somewhat hard, but not brittle.  A cutting tool you'd temper less.  When tempering you can quench to stop the tempering or heat flowing, but it’s not necessary for the tempering to work
Polish a bit of the hardened steel so you can see the tempering colours, heat slowly, they change rapidly
13) Annealing or annealed steel.  Steel in its soft state, unhardened.   Except for special examples like watchmakers blued steel (which will be O1 or W1)  tool steel is sold annealed so it’s ready to be machined into whatever
14) how is annealing done?  Kind of the opposite a rapid cool (quench).  Heat to critical temp and then slowly cool.  Slowly as in overnight (a steel box full of ashes works well – use extra thermal mass if the part is small).  With a proper anneal the stress in the metal will be removed and it will be soft.  You'll hear of guys talking about annealing in much short time frame; what’s really happening is it’s a partial anneal - they've softened it enough for what they need.  Residual stress may remain which could lead to cracking on subsequent quenches (if necessary)
15)  Casehardening.  By soaking a non tool steel in an environment (a bath or packed with carbon around it in a steel box) where it can absorb carbon for a period of time, you can get it such that the out layer has enough carbon to then be heat treatable.  It’s then quenched.  It is not usually (ever?) tempered.  The idea is it’s an advantage having a dead hard skin and ductile core.  The skin depth might be 1 -2 thou using casehardening compound, 5-10 thou with long pack hardening and 50 thou with an overnight soak at a commercial heat treaters.  It’s good for wear parts, not so good for most tools
16)  HSS – high speed steel.  High speed steel is another group of tool steels we see, drills, lathe tools etc.  Its great advantage is it holds its hardness at high temps, unlike say O1 that starts to anneal at a few hundred degrees.  This matters as where one molecule meets another when cutting, temps can go very high.  HSS cannot be heat treated by the likes of us, there is a very narrow band of tolerance on the temperatures and cycles required
 
 
 

As a fellow Canadian, thanks for the great advice. I bought 5 rods of O1 and 2 rods of W1. Tonight I made a drill bit with the W1. Ground it down in a lathe. One thing I noticed as I was spinning it in the lathe and using a dremel tool to grind it is that it warped a bit. Anyway, first shot. I then heated it up to bright red for a minute and water quenched it. Then I tried it on a screw just for fun and the tip cracked....so that part worked. I then shaped it into a screwdriver again (very small one) and heated it up to bright red for 10 seconds. Then I let it air cool. Tried it on a screw again and it seemed to work and not twist or crack. The tip looks a bit crappy, however, it works and is my first shot at this.6c3a0efc073ca67877e5e1389c93a9e6.jpg3670fc21c2819aa31d3eed022ff1a8bf.jpg


Sent from my iPhone using Tapatalk Pro
  • Like 1
Link to comment
Share on other sites

An easy test to see if it has enough carbon in it to harden is the 'spark test.
Its not fool proof but it will definitely let you know if its not carbon steel.
If you have a grinder just grind a bit of it and watch the sparks, carbon steel will have sparks explode off the sparks like little fireworks, mild still will have just straight sparks, look here for a better explanation
https://en.wikipedia.org/wiki/Spark_testing.
 

Thanks btw

Sent from my GT-N5110 using Tapatalk

Link to comment
Share on other sites

Update. Just picked up a WEN drill press and am going to make another blade as the first one warped a bit when I was grinding it down. Figure I will put the O1 steel rod in the drill press and use it with my dremel tool to grind it down. Then I will pick up some transmission oil for quenching the bit. Question I have, is how long to heat up the bit the second time when annealing it. It turns red almost immediately under a torch due to its small diameter.

Sent from my GT-N5110 using Tapatalk

Link to comment
Share on other sites

1 hour for each of material thickness is the rule of thumb,  but I've always found a few minutes for really thin/small stuff seems to work well.  You're not annealing it the second time, you are tempering it, (12 + 13 above).    Again a minute or two works however If you don't have a heat treat oven, it can be difficult to hold at exactly say 600 for 5 minutes, so just take it to the colour you want it and remove the heat.  (technically you could leave it on a oven for hours at a lower temp and get the same temper, tempering is  actually dependent on time and temp, but as a practical matter, take to the colour and call it done)

Edited by measuretwice
Link to comment
Share on other sites

Update! Moved the mess to my workshop and used a new drill press vs the lathe, then finished it off on the lathe. Annealed it for 60 seconds and quench it in oil; then tempered it for around 29 seconds and let it air cool. Looks good and I think it is tough enough. Here is a video I made. Still not completely convinced on the time needed to make the blade less brittle.





Sent from my iPhone using Tapatalk Pro
Link to comment
Share on other sites

7 hours ago, jdrichard said:


This is the second heating, to soften it a bit, correct?


Sent from my iPhone using Tapatalk Pro

Well, this is for both softening (annealing), and for hardening.

You must observe the colour change when tempering unless you have a temperature controlled oven. This is why you polish the steel before tempering so that you can see it easily. It helps to coat the steel in soap (soap bar) before hardening as it forms a protective skin when heating which is easy to polish off.

For screwdriver blades, temper to brown or blue (or anywhere in between!). For larger bits you can get away with straw. If tempering in free air (not in brass filings or any other medium) then you can apply the heat to the middle of the screwdriver blade for a more gradual tempering towards the tip.

Link to comment
Share on other sites

Well, this is for both softening (annealing), and for hardening.
You must observe the colour change when tempering unless you have a temperature controlled oven. This is why you polish the steel before tempering so that you can see it easily. It helps to coat the steel in soap (soap bar) before hardening as it forms a protective skin when heating which is easy to polish off.
For screwdriver blades, temper to brown or blue (or anywhere in between!). For larger bits you can get away with straw. If tempering in free air (not in brass filings or any other medium) then you can apply the heat to the middle of the screwdriver blade for a more gradual tempering towards the tip.

Big thanks. I think i saw the blue color when annealing the blade and I did start in the middle so the tip would not turn cherry red. What I was wondering is How Long do you apply the heat when annealing (softening) the steel for the last step...to toughen the blade end.

Sent from my GT-N5110 using Tapatalk

Link to comment
Share on other sites

The last step is tempering the blade to a colour (hardness). For small parts like ours, you can take as long as you want, but you have to do it slowly otherwise you'll overbake it. You can do it in stages, for example let it cool down at one colour and then heat more to move to another colour. Sometimes the colour will continue even if you remove the heat. It can help to immediately plunge in water/oil if this happens.

It's a bit like scrambling eggs.

Link to comment
Share on other sites

Just to re-cap:

You anneal the steel to soften it by bring to cherry red for a minute or two and slowly cool. Some metal is supplied already annealed.

You machine the metal to whatever shape you want.

You cover it in soap and bring to cherry red again for a minute or two before suddenly quenching in water/brine/oil. The metal is now glass-hard and will scratch glass. You can test it by rubbing it against a sharp file; the file will not bite and will just jangle across it.

You remove the crust from the surface of the glass-hard metal and polish to reveal the white colour.

You finally slowly temper the metal to soften it slightly by monitoring the colour of the metal which indicates its hardness.

Link to comment
Share on other sites

Just to re-cap:
You anneal the steel to soften it by bring to cherry red for a minute or two and slowly cool. Some metal is supplied already annealed.
You machine the metal to whatever shape you want.
You cover it in soap and bring to cherry red again for a minute or two before suddenly quenching in water/brine/oil. The metal is now glass-hard and will scratch glass. You can test it by rubbing it against a sharp file; the file will not bite and will just jangle across it.
You remove the crust from the surface of the glass-hard metal and polish to reveal the white colour.
You finally slowly temper the metal to soften it slightly by monitoring the colour of the metal which indicates its hardness.

Perfect, thanks and no more questions. I will practise now.


Sent from my iPhone using Tapatalk Pro
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.



×
×
  • Create New...