An idiots guide to S7

[jdawgnc]

So I have a few lengths of S7 I am planning on making some punches and other hot work tools out of. After a lot of online research, I have what I believe to be the proper way to do this, but I'd like a little more clarification of a few points. The steel I have is from Mcmaster, so is already annealed and in it's ready to work state. For shaped punches, like eyes and such, all I need to do is grind them to shape then heat treat, correct? The heat treating of S7 is where I have found so many different methods that I am a bit confused. To heat treat it, I take my new formed punch, heat it up to a nice red heat (I don't have an accurate thermocouple or thermometer for that high but know it's supposed to be ~1725 and is NOT the non-magnetic Curie point) and then let it air cool (which is technically the quench for S7?) Immediately after is is air cooled (to where I can touch it I guess?) I temper it to around 1000 deg and then what and for how long? What is the best way to temper it without an oven that goes that high? I do have an oxy/acet setup, but have read there can be issues from the oxygen in the mix causing problems when it is used for heating. I'm certainly not building an atomic clock here, but would like my tools to be as good and hard as I can possibly make them. Also the difference in tempering and hardening the whole punch versus the "business end" that will come into contact with the hot metal is a concern to me as well. I see the appeal of both, but would like some opinions there too... What about pieces that I forge out to make chisels out of. After forging it into shape, the whole thing has been subjected to a lot of heat and stress. Do I need to normalize it or re-anneal it, or can I just proceed with the heat treating from there? They are just small tools, so not a ton of mass to deal with... Lastly, but not leastly, I have access to a lot of dry ice here at my shop. I've seen a few things about S7 being one of the tool steels that responds well to dry ice treating. Anyone have any experience with that? Is it even worth my doing it, and how would I go about interacting a hot (or cold) piece of steel with a block of dry ice anyway? 

So for myself and any other novice toolmakers out there here is my step by step plan... please let me know if I've got it right!

1) Take my nice piece of shiny new S7 and grind an eye on the end

2) Place it in my gas forge (don't have a coal one) til the whole thing is a nice red heat, then remove and set aside to air quench

3) Polish up the working edge so I can see the colors move and use my oxy/acet torch to heat it from the middle and watch the colors run out to the working edge til it is just past blue 

4) Once it is at room temp I sit it in the cooler of dry ice for an evening and see how it goes from there

Anything else? Any extra steps for pieces that have been forged?

[Frank Turley]

 I don't know how you grind an eye, because an eye is a hole. Anyway, we punch and drift the eye hot. Forging temp is 1950-2050F (bright orange bordering on lemon). Do not forge below 1700F (bright red). This bright red is above the cherry red ranges. Annealing comes next. You can't normalize, because S7 is air hardening. I have trouble annealing properly in my shop, because the specs say to take the steel to 1500-1550F (bright cherry red) and slow cool it losing 25F/hour down to 1000F (faint or dull red). Then air cool. My shop is too "primitive" to follow those instructions, so instead, I take it to bright cherry red and cool in lime or wood ashes down to room temperature. To harden, go to 1700-1750F (full bright red bordering on orange) and air cool on a non reactive material like a fire brick or a pile of coke down to room temperature. Tempering is done immediately after hardening by heating to at least 400F for a cold work tool. 428F is a light straw surface color, for example. For hot work, temper to 1150F (dark red), an incandescent heat, and cool to ambient temperature on a non reactive material.

*These temperatures  were abstracted from an old Earle M. Jorgensen catalog.

[jdawgnc]

Sorry, the eye I was speaking of is a shaped end. Different ovals to make eyes that are stern, happy, sad, etc... Or leaves, simple rounded ends, or a hot punch even. All different tips I can grind into this already annealed 1/2" S7. For the chisels and hot cuts, do they need to be treated any differently after letting them cool after I forge and hammer the basic shape, then grind it to the final bevel? Can I just go straight to the hardening and tempering then?

 

Thanks for your help!

[Frank Turley]

It comes from the steel maker annealed. If you heat it and forge it, you have undone that anneal, and it needs to be annealed again after forging. The annealing refines the grain structure and makes for a stronger tool in the long run. The order of heat treatments when working hot is 1) forge; 2)anneal; 3)harden; 4)temper.

If you keep asking these basic type of questions, I'll refer you to The Curmugeons.

[Stephen Jones]

On 11/21/2016 at 9:47 AM, jdawgnc said:

4) Once it is at room temp I sit it in the cooler of dry ice for an evening and see how it goes from there

sill question but why would you sit in dry ice?

[Steve Sells]

On 11/23/2016 at 4:29 PM, Stephen Jones said:

sill question but why would you sit in dry ice?

to cool off  ?

[Frosty]

On 11/21/2016 at 4:28 PM, jdawgnc said:

Sorry, the eye I was speaking of is a shaped end. Different ovals to make eyes that are stern, happy, sad, etc... Or leaves, simple rounded ends, or a hot punch even. All different tips I can grind into this already annealed 1/2" S7. For the chisels and hot cuts, do they need to be treated any differently after letting them cool after I forge and hammer the basic shape, then grind it to the final bevel? Can I just go straight to the hardening and tempering then?

Thanks for your help!

The correct terms would be "working end" and "struck end".

Frosty The Lucky.

On 11/23/2016 at 4:29 PM, Stephen Jones said:

sill question but why would you sit in dry ice?

Read up on "Cryogenic" heat treatment.

Frosty The Lucky.

[Bo T]

The dry ice cold treatment is sometimes used to help convert unconverted austenite(RA) to martensite. I am not sure how much RA would be left in quenched S7? I am not sure how much help cryogenic (liquid nitrogen) treatment would help with S7 either. I have some reading lying around somewhere, but the scientists doing that work are probably +/- 10 F on their temperature control. Not necessarily applicable to the present situation. Note: mix your dry ice with acetone. That should get the temperature down to @ -100 C.

[jdawgnc]

Well, had to step away for a minute. I WAS asking a very basic question, and thanks Frank, that was actually the exact response I was looking for. Sorry if it was too basic and not using the proper terminology, but I think a lot of heat treatment varies so much and so many people have their own methods. The advanced books I have assume you have an already extensive knowledge of metallurgy, and the basics seem to vary so much as to be a matter of personal preference at times. All I was looking for was the "normal" steps taken to make and treat a punch or other tool out of a piece of S7 steel. A relatively simple question, that needed a very simple answer...

As for my "cryo" question, it was based off of an earlier thread and is considerably more advanced...

I was just wondering if anyone had any further experience with this. From what I've read, S7, being air hardening, is a prime candidate for cryo treatments of this sort? It's not something I'd be interested in, except that the lab I work in has a virtually limitless supply of dry ice so it is easily sourced and used. I'm not just trying to do something fancy, but to use the tools I have readily available to make the most functional and durable equipment I can. If you have some information or advice I'll gladly listen and learn as much as possible, but if you don't... I know there are a lot of idiots on the internet, don't make the assumption that because I ask basic questions I'm one of them.

On 11/23/2016 at 5:13 PM, Steve Sells said:

to cool off  ?

I needed to cool off after reading this... I thought I was pretty clear about why I was interested in the cryo treatment using dry ice... Maybe if you had read my question instead of just adding a useless 2 cents?

 

On 11/24/2016 at 2:11 AM, Frosty said:

The correct terms would be "working end" and "struck end".

Frosty The Lucky.

Sorry for any misunderstanding there... So for a design punch like I'm wanting to make would you just harden the work end and leave the struck end softer or would you treat the entire punch as one unit? I have read opinions going both ways, and it seems to be a lot of personal preference. To me it seems that having the struck end a bit softer would allow it to mushroom more, but may help it prevent chipping or breaking? Again, this isn't an atomic clock or something my life is going to depend on, so is it REALLY that big a difference?

[Steve Sells]

On 11/30/2016 at 3:08 PM, jdawgnc said:

As for my "cryo" question, it was based off of an earlier thread and is considerably more advanced..

.. I know there are a lot of idiots on the internet, don't make the assumption that because I ask basic questions I'm one of them.

I needed to cool off after reading this... I thought I was pretty clear about why I was interested in the cryo treatment using dry ice... Maybe if you had read my question instead of just adding a useless 2 cents?

 

Tempering and dry ice have no connection. It does have usage in hardening  I wrote a lot on this subject already, much of it is not just a simple answer.   It is pinned at the top of this section, including the use of acetone with dry ice before the tempering stage, because dry ice itself being a hard block wont convect away calories as well or as evenly as crushed ice in acetone does, but if you cant be bothered to read what I already wrote why should I waste my time reposting any of it for a disrespectful person like yourself who refused to read it the first time I wrote it? Why should I care what you think for that matter?  You started this,

Technically " to cool off" is the correct answer to Stephen question,  deal with it, you knew this already as your referenced dry ice thread include mention of it.

[Glenn]

To get a *good* heat treatment on YOUR forged S7, may I suggest the following.

Get back to Mcmaster and ask who manufactured the S7. Contact the manufacture and ask about the proper method for heat treatment of their metal. They are the ones with the knowledge. You may have to supply them with a specific manufacture information, or lot heat number (mix) to be sure to get the right information for that mix.

Contact a professional heat treating company. Ask them to include your tools with the next batch of S7 they run or even do your tools separately. You may have to give then the manufacture information and the lot heat lot numbers (mix) so they can be sure and get it right. 

If this is not acceptable, then I suggest two other options. Go with what Frank Turley has found to work for him, or do some homework and research, and develop your own heat treating method. This may take some trial and error development and some additional trial and error testing. It should give you the best method to meet YOUR specifications for your end product.