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Ian B
02-02-2006, 05:21 AM
To my knowledge, stainless steels such as 304, 316 etc can't be hardened by heating to red and quenching.

Can they be case hardened in Kasenit or similar products?

Ian

Rusty Marlin
02-02-2006, 07:01 AM
Short answer, No. They cannot be hardened through heat treat methods. They are desinged for ultimate corosion and chemical resistance not for high strength or wear resistance.
The 300 series of stainlesses can be work hardened by compressing the surface. Shot peening is the most common method. This imparts a hardened case of compressed grains around the softer core. It is generally applied with a slinger wheel of varaiable speed and with steel or glass shot. The speed of the wheel and the size of the shot used give different results, the shot material is also changed depending on the part material. The part is clamped on a rotary table and turned slowly and in a controled manner. Depending on the size and compelexity of the part it may be on a full 5 axis table.

Probably way more information than you wanted.

Wirecutter
02-02-2006, 08:23 AM
Recently, I read (oh, I wish I knew where) that stainless can be hardened and annealed to some extent, but it's opposite of the intuitive.

To anneal it, get it hot and quench it quick.

To harden, get it hot and let it cool slowly.

Or you could always use my tried and true method of "spot" hardening stainless - drill a hole and run the drill fast and feed too aggressively. Stop when the point of the drill glows red hot. Voila! A hard spot! http://bbs.homeshopmachinist.net//biggrin.gif

Rustybolt
02-02-2006, 08:56 AM
<font face="Verdana, Arial" size="2">Originally posted by Wirecutter:

Recently, I read (oh, I wish I knew where) that stainless can be hardened and annealed to some extent, but it's opposite of the intuitive.

To anneal it, get it hot and quench it quick.

To harden, get it hot and let it cool slowly.

Or you could always use my tried and true method of "spot" hardening stainless - drill a hole and run the drill fast and feed too aggressively. Stop when the point of the drill glows red hot. Voila! A hard spot! http://bbs.homeshopmachinist.net//biggrin.gif</font>

Like Rusty said, it all depends on the type of stainless.There are three basic types 400 series martinsitic.400 series ferritic, and 300 series austinitic. Only martisitic has enough carbon to be quench hardened.

PBMW
02-02-2006, 09:59 AM
Then there is 15/5 and 17/4 ....certainly martinsitic
Jim

Ries
02-02-2006, 11:38 AM
Wirecutter- you are half right, for 304 anyway.
One thing to remember about stainless steel, is that there are tons of alloys, and they are all different, and act differently.
But 304, which is the most common in the US, can be annealed with heat. You heat it up to red, quench it, and it will be as soft as it ever is gonna get- which is still pretty hard, but noticeably easier to drill, or bend.

The reverse is not true- no heating and/or quenching operations will get it any harder reliably and accurately- usually only work hardening will do that- beating on it cold, bending it, things like that. You can, as you said, harden a spot by drilling it, but its not the heat per se that does that- its partly the pressure of the drill as well. In fact, I have had success spot annealing halfway drilled holes, by heating with a gas torch, then pouring on some water- you can then drill it again.

If you want to hardern stainless, you use a different alloy- knifemakers seem to like 440, but there are so many different alloys, that you really need to do your homework.

[This message has been edited by Ries (edited 02-02-2006).]

x39
02-02-2006, 04:20 PM
I recently got a hold of some ATS-34 and have been playing around with different hardening methods. As quenched, this stuff gets REAL hard. Not too bad to machine in the annealed state either.

Dawai
02-02-2006, 04:28 PM
Wirecutter:

You are going to laugh, may know this.

To drill stainless, Sharp bit, Press like hell on the drill and just bump the trigger making the drill turn really slow, stop, bump.

You will get a curl unlike ever seeing before. Stainless is kinda soft as recieved, just gummy. It seems to wrap around a sharp tool and heat it up.

I watched two fitters, old guys my age try to drill a stainless box for two days. They went off the dam for lunch, I went over, drilled two holes next to where they hardened it and didn't ever say a word. It was air purge lines, supposed to be my work anyways. (instrument tech)

Rusty Marlin
02-02-2006, 08:21 PM
ATS-34 isn't a 3xx series stainless. Acts more like a 440 but with better edge holding ablilty and higher toughness. It has enough carbon to be hardenable.

400's are generally free machining. The 410 amd 420's that I worked with extensivly gave similar tool life to pre-hard 4140 and generally gave a better machined finish.

Low 300's like 304, 302 and 305 are ****ty to work with. Gummy, stick to the tool, tear out, and generally suck all round. These stainlesses were designed for drawing and blanking operations for decorative trim, sinks, drawer knobs and things like that.

316L is really nice to work with, provided you start a chip and keep under the work hardened layer. Don't ever peck drill this stuff without 1000psi through coolant drills. It'll smoke the end off a HSS drill after the first couple of pecks. Then you're really screwed.

[This message has been edited by Rusty Marlin (edited 02-02-2006).]

wierdscience
02-02-2006, 08:43 PM
Most 304 doesn't have very good carbon controls either,I have seen it arrive at nearly 50rc.It also work hardens in a heartbeat.
316 is what we use most since most of what we make out of stainless is going in saltwater and 304 pits pretty quick in that enviroment.
Don't remember seeing anything that it can be hardened reliably.
I do wonder about hot forging thou,seems 304's work hardening could be used to an advantage.

[This message has been edited by wierdscience (edited 02-02-2006).]

Ian B
02-02-2006, 10:42 PM
Back to my original question; can 304 stainless be case hardened? I also thought (as Rusty said) that 304 doesn't have enough carbon to allow it to be hardened.

That's why I asked about CASE hardening - doesn't this process add carbon (and maybe some nitrogen) to the surface layer, allowing just the surface to harden when quenched from red?

Ian

Harold_V
02-03-2006, 02:26 AM
<font face="Verdana, Arial" size="2">Originally posted by PBMW:
Then there is 15/5 and 17/4 ....certainly martinsitic
Jim</font>

No-----the carbon level of precipitation hardening stainless is way low. It doesn't harden by the familiar carbon cycle. Hardness is achieved through grain growth at relatively low temperatures, thus the name, PH (precipitation hardening).

Harold



[This message has been edited by Harold_V (edited 02-03-2006).]

Rusty Marlin
02-03-2006, 04:42 AM
IanB,
no, 304 cannot be cased by traditional methods; it can only be "case" hardened through cold hammering or shot peening.

Wirecutter
02-03-2006, 08:43 AM
<font face="Verdana, Arial" size="2">Originally posted by David E Cofer:
Wirecutter:

You are going to laugh, may know this.

To drill stainless, Sharp bit, Press like hell on the drill and just bump the trigger making the drill turn really slow, stop, bump.
</font>

David -
Yeah, I found that out, by experience and by the wisdom here. I think of it this way - stainless likes to be "cut" and not "ground" with a drill. If you're getting powder or splinters for chips, slow it way down. It wants a nice, slow, curly chip. Oh yeah, and I learned to keep my fat little fingers away from such chips. They may be fun to watch, but they seem to want to slice me all to ribbons.

I'm still trying to get my head around the way different materials act in the lathe vs the mill vs the saw. I know that cutting involves basic concepts like material, depth of cut, rate of feed, surface feet per minute, etc, but they seem to apply very differently across different machines. It all has to do with how much is happening "where the action is" - that is, right where the cutting is taking place.

Wirecutter
02-03-2006, 08:58 AM
<font face="Verdana, Arial" size="2">Originally posted by Ries:
there are so many different alloys, that you really need to do your homework.</font>

Certainly - really and on a more serious note, that's consistent with what everyone here says about "mystery metal". There are so many variants of the most "popular" metals, like aluminum and stainless. There isn't really one that "does it all". I love 304 for its weldability (even I can make nice welds), but it's a pain to drill or machine. Almost any aluminum is just wonderful to machine, but without a TIG machine, I can pretty much forget welding the stuff. (Yeah, I know there are "tricks", but as I suggested earlier, I'm not a great welder, yet)

I love threads like this. You look at a chart that characterizes metals, and you get the scale of "excellent, good, fair, poor, bad" for things like machinability and weldability. Here you get quotes that really describe how it is, like


<font face="Verdana, Arial" size="2">Originally posted by Rusty Marlin:
Gummy, stick to the tool, tear out, and generally suck all round.</font>

After just a little experience trying to machine 304, I'd say that pretty much sizes it up. No, it's not impossible, but it's a hassle.

Thanks, guys, and sorry for hijacking the thread, Ian B.

-M

INTERPOLATE
02-03-2006, 10:52 AM
We had 316 parts we made for some pumps (gears, cams and a impeller) treated by Bodykote a couple years ago with a process they call Kolsterising. If I remember right when we checked the surface hardness it came in around 65HRC. Everybody was impressed. No dimensional changes (at least none that we could measure). It wasn't cheap, but worked.

[This message has been edited by INTERPOLATE (edited 02-03-2006).]