316 Stainless

I have been trying to machine 316 stainless bar stock using carbide tooling.

I don't have any flood cooling it just gets extremely hot and now I think its case hardened itself. My carbide tools are not touching it. I have gone through several carbides I think I need to find another material for my project.

I need something that is strong and fairly hardwearing any ideas.

Stainless steel is a relatively poor conductor of heat. You need to keep the speed down to control the heat build up. This is a particular problem with drilling, where you need to withdraw the drill frequently. It is a good idea to use coolant, even if all you can do is squirt it on from a plastic bottle.

John

I machine a fair bit of 303, 304 and 316 stainless.

I use a small amount of Rocol RTD liquid **LINK**

If you are using insert tooling, you may not be taking a deep enough cut.

Slow and steady is the way to go.

I tend to use silversteel for hard wearing items (either hardened or in its natural state).

Jim

I have made a few items in 316 stainless steel and never had any problems using carbide insert tooling. As John says, reduce the speed and make sure you have a sufficient depth of cut and a high enough feed rate. If the tool just rubs the 316 will workharden. I use a plastic bottle to squirt a few drops of thin oil on the cutting area.

Thor

Are you using bar or plate?? The reason I ask is because, at least up here in 'Straya, 316 plate is assumed by the steelmaker to be used on weldments, and due to a lack of (I think) Sulphur it behaves exactly as you described. The steel makers add sulphur to the melt when making bar and as a result it becomes almost free machining.

cheers

Bill

316 steel or any ss material to cut, you need correct type of carbide tools. The hardness of the tool has to be atleaset 65Rc . Mind you that Tungsten carbide has different grades to suit different materials to machine.

Tungsten carbide in micro particles mixed with Cobolt is suitable for cast iron, but addition of Titanium Carbide makes it more suitable for steels. However I found that the first grade with Cobolt and Tungsten carbide only, does not fracture easily at heat and shock loading. I do not use any coolant but slow speeds and a medium depth of cut helps.

If you are using tip changing tools ,then of course you have to go at 6000 RPM with low depth of cut ( .05 mm), medium high feed will do the trick. CBN tools will also help at high speed without any appreciable wear,

How confident are you that it is 316? Was the material from a reasonably-trusted source?

Stainless does not case harden. It does work harden, mainly due to allowing the tools to rub and not cut. Small depths of cut, high speeds and low feed rates are ideal conditions for rubbing. Do not dwell at the end of the cut.

You might need to be a bit more specific than simply 'carbide'. Are they name-brand inserts of standard geometry?

Please ignore totally the advice given by another poster viz: "If you are using tip changing tools, then of course you have to go at 6000 RPM with low depth of cut ( .05 mm)". If you really want to work harden your material, this is the ideal recipe.

I machine 316L all the time at work. I have never had problems with the material hardening, we use standard indexable tips and for some special cases HSS tools. Flood coolant is is used except when tapping or reaming then we use Rocol. The only thing we do different is keep the speed and feed down and for tapped holes drill a little bigger than the standard drill size.

I sometimes take very light cuts with no problems, if you want a decent finish coolant needs to be used. That said 316L is a very nice material to work with and it's easy to get a very good surface finish.

It's only when we machine exotic metals do we problems with work hardening.

Phil.

Oh and I forgot to mention in the above post when machining 316 at home (offcuts from the scrap bin) I don't have flood coolant I just drip or brush it on, again it will not harden.

Phil.

In my early days of making hot air motors I required a stainless hot cap 3" long by 1 3/4" dia bore. I went to the local stainless supplier and told them what I was trying to do, the onlt bit suitable was 2 14" dia bit of 316 but they warned me that it wasn't free cutting and might prove difficult to bore out all that metal, and more suited to making a prop shaft for a boat. I'll admit that it wasn't that easy because of the miles of hot swarf. I used back gear and a good deep cut with plenty of feed, and undiluted soluble cutting oil. The finished item is in the heated area .010", Made in 1994 and still going. The tools used were all HSS.

It's the bit in the furnace as the r/h end.

Ian S C

Edited By Ian S C on 04/08/2019 12:21:37

I used to machine, and fabricate and weld the 300 series stainless steels a lot. it work hardens very quickly, so you need to push on and not let the tool rub or it will become a nightmare to work.

I give it up as a bad job no matter what speed I run it at the carbides end up glowing red and I struggle to remove any material. I binned it and turned it out of mild steel.

Edited By Dave Harding 1 on 04/08/2019 17:50:28

I doesn't sound like you were trying to machine 316 then.

Phil.