Jump to content
I Forge Iron

Stainless and how it works?

Recommended Posts

My wife brought home a 2' long by 5/8" round. It was laying out in the dirt somewhere. It cleaned up easily, spotless and was not magnetic. So I assumed stainless, 300 series.

Wanted to make two hooks to hang from the chain link fence around the pool for holding pool tools. With the water and chlorine I thought ss would do well.

So had to forge 5/8" round down to roughly 1/4" square then went to octagon. OMG was this a lot of work! Way WAY more than CS would have been. NOw I heard that you should not heat SS too hot. So my heats were lighter. It seemed like it cooled faster. Though with lighter heats this is expected. I'm looking for advice on working SS. Here are some observations or beliefs that perhaps people could respond to.

Should you work stainless at lower heat than CS. HOw low? What color of heat?

If you need a lower heat... Why?

Is SS pretty darn hard to move (Move metal) or is it more a function of lighter heat required? or both?

As I observed the fire it seemed like I could see some very small but possibly numerous little/tiny sparks coming up though the fire. Like when you are doing a forge weld on CS you can see the bigger sparks come up when you hit the high temp. Not sure if this was a SS thing or some sort of coal dust in the fire or just me being overly observant due to trying to forge a different metal. Does this mean anything to anyone?

My hook came out grey. I guess that wil slough off but I brushed it pretty hard. Does that mean anything?

I added a twist and it looked like part of that twist started to crack or tear perhaps. Is SS more prone to this?

One last thing. As I hammered it seemed that I could more easily see visible heating of the metal at the hammer points. Something I don't see with CS though I know it happens. Once again maybe this is me being more observant working a different material.

After some reasearch on IFI with google it looks like I need to passivate too. Not sure what this is all about?

Link to comment
Share on other sites

Stainless is tougher than CRS. At the same temp, it will be harder to forge. So you were feeling the effects of two things: the top heat wasn't as high as mild, and tougher at the same time.

Stainless also starts to crack at a higher temp than mild. That's why you got the crack from your twist (or could be, since I didn't see the crack). So there's a narrower window of working temps.

Regarding passivation, I'm still not clear on the technical definition, but there are two issues you face with forged stainless: the grey scale, and the reduced resistance to corrosion. I think you can take care of both by pickling in a 10% citric acid solution. 10% being defined as 10g citric acid to 1liter of distilled water. Your stainless should be stainless again, and will take a polish.

Link to comment
Share on other sites

I heat stainless hot, like near welding heat hot, and it still is hard to move. I haven't had any problems from the slightly magnetic stock I have used (long bolts, 1/4 or 3/8 inch) but my experience is quite limited. I have a couple bars from somewhere that are sitting.

Passivization is removing free iron from the surface, and creating a solid chrome oxide layer. Chlorine bearing acids and agents will strip the chrome oxide layer. Citric acid and nitric acid are used in industry. Citric acid can be purchased in small quantity at some grocery and vitamin stores, or ordered online.

Heating to forging temperature and cooling is another option. The material will be grey after cleaning or pickling.

If you use a new sanding belt to clean the material the stainless will remain unprotected but passive. Follow up with stainless steel polish.


Link to comment
Share on other sites

Whether it's hot short or not depends on the alloy and there're more alloys than there are letters available to ID them. Experiment with your forging temps till you find what works best. It's going to be harder to move, it's generally tougher than hard so the molecules don't slide around very easily.

Passivation is returning a layer of clean, clear chromium to the surface. Using acid as said already works well. Please use PPE and proper disposal methods.

You can electro polish stainless too and that's really pretty cool. I'd have to play with my battery charger and electrolites to give you specifics but I can lay the basics on ya. Positive ground the piece to be polished and hook the negative pole to the polishing element. This can be in a tank like electrolytic rust removal or a sponge or paint brush. Wet the polishing element with the electrolite, I THINK salt water will work but don't quote me, apply a couple amps or DC power and brush it over the area to be polished. As I recall someone was using an airbrush to good effect but again don't quote me.

Frosty The Lucky.

Link to comment
Share on other sites

It's the citric acid in the orange clean, I think. When I was doing a bunch of searching about stainless, I came across that. You might try some stronger citric acid on your stove to see how it does.

I found that the best deal on citric acid was through Amazon.com. (Beeswax, too, if you're making a wax finish.) You can buy a 5lb bag of granulated acid for..... I don't remember, but it was cheaper than I found elsewhere.

Link to comment
Share on other sites

My wife brought home a 2' long by 5/8" round. It was laying out in the dirt somewhere. It cleaned up easily, spotless and was not magnetic. So I assumed stainless, 300 series.

Curious. Could it still be considered Steel if it has no magnetic properties? It is the iron content after all, not the carbon, that makes the steel magnetic.

Perhaps, your wife actually found a bar of platinum. Ok, I wanted to add a smiley face here, but it doesn't seem to be an accessible feature of iPad.

Link to comment
Share on other sites

There are several alloys of stainless steel that become non-magnetic. They ARE steel, primarily iron, and they are very specific grades of steel. A few points difference on the alloy elements and a magnet sticks!

I stopped with the Orange Clean on the stove because the Orange Clean worked, and I haven't had a problem since! I am fairly sure there is a good citric acid load in that stuff too.


In my reading last night I discovered that the annoys are non-magnetic in their annealed state, and become slightly magnetic if work hardened. They are austenitic grades including 300 series.


Link to comment
Share on other sites

For about a decade I was the Manufacturing Engineer in an Auto Parts manufacturing plant.

We forged about 15,000 Exhaust Valves every day, from a non-magnetic stainless alloy.

Valves are forged in 2 consecutive strokes of the press.

The 500 to 1,000 ton Press, "extrudes" the roughly 1.125" dia. billet, into what we called the "onion".

( Basically, a "stem" with a "bulb" on the end. )

The onion" is then transferred into the "coining die", which flattens the "bulb" into the familiar valve head shape.

As a general rule, the billet enters the first stage of the die at 2100 degrees Fahrenheit, and about 7 seconds later, is ejected from the Coining Die, at approximately 1900 degrees F.

The next step is an 8 hour "soak" at 1400 degrees F, ... for the purpose of Stress Relief, ... before being allowed to cool to ambient.

And yes, ... all un-machined surfaces, remain a dull gray color.

As stated elsewhere, there are more than a Brazillion :P different Stainless Alloys, ... so, ... as always, ... "results may vary". ;)


Link to comment
Share on other sites

Phil which steels are non magnetic and primarily iron?

Stainless Steel essentially breaks into 5 general categories and the following is an excerpt from some of my work training notes:

  • Austenitic: These types have sufficient nickel and/or manganese to remain austenitic at room temperatures. These are the 2XX and 3XX series of stainless steels. They are nonmagnetic and can only be hardened by cold working. In the annealed condition, they have relatively low strength, but exhibit good toughness at all temperatures, including cryogenic. Austenitic stainless steels have generally low resistance to chloride induced stress corrosion cracking.
  • Martensitic: These types are normally alloyed only with chromium, and possibly small amounts of nickel or molybdenum. These are part of the 4XX series of stainless steels. They are magnetic and can be hardened by conventional heat treatments, such as quenching and tempering. Depending upon the hardness (strength) level, these types are susceptible to hydrogen embrittlement. Because these steels can be heat treated, a wide variety of strength and toughness levels can be obtained.
  • Ferritic: These types are also normally alloyed only with chromium, and possibly small amounts of nickel and molybdenum. In comparison to the martensitic grades, however, they have higher chromium contents and lower carbon contents. These are also part of the 4XX series of stainless steels. They are magnetic, but cannot be hardened by heat treatment, although they can be hardened by cold working. These types generally have higher tensile properties in the annealed condition than austenitic stainless steels, however, they do exhibit deceased toughness as the temperature decreases. These types are very immune to chloride induced stress corrosion cracking.
  • Duplex: These types are alloyed with chromium, nickel, and normally other elements to produce a mixed microstructure of austenite and ferrite. Duplex stainless steels are normally identified only by brand names, but may have UNS numbers, especially in ASTM specifications. Duplex stainless steels combine many of the positive attributes of austenitic and ferritic stainless steels, including higher strength and stress corrosion cracking resistance of the ferritic types and improved corrosion resistance of the austenitic types.
  • Precipitation Hardening: These types can be hardened by a low temperature (generally 900 to 1150 °F) aging process. Therefore, they can normally be machined to finish size before aging with minimal distortion or dimensional changes. The mechanical properties can be varied depending upon the aging temperature to properties similar to the martensitic grades, but with corrosion resistance similar to the austenitic grades. Therefore, they are commonly used when high strength and good corrosion resistance are required. These types are alloyed with chromium and nickel, along with elements that can be dissolved during the solution treatment and can be subsequently precipitated during the aging process, including copper, niobium, tantalum, and aluminum. These types are commonly identified by brand names, but are designated as Type 6XX in ASTM specifications.

The magnetism of the stainless steels is dependent on the microstructure (as previously stated), and the microstructure is varied by heat treatment and chemistry. I thought the general grade info may be useful for reference.
Link to comment
Share on other sites

I am in the pertrochemical business and one thing we do is called PMI (positive material Indentification). This requires taking a nuclear deveice or other such device to "shoot" a given piece of pipe, tube, plate, valve or welds etc for material composition. Many materials look similar and in certain service you must not have the wrong material or very bad things can happen. Thus the need for PMI in some services. This is something we do in the field or in the warehouse to absolutely verify what we have.

Fortunately where I work we have a good bit of what I'll call plain carbon steel and some 304L/316L stainless. A poor mans PMI machine is a magnet. IF magnetic (meaning it sticks to the magnet) then probably CS. If not magnetic then not CS and probably stainless. Not a very accurate PMI machine by any means. And somtimes the SS can be just a bit magnetic, especially the welds. For what most of us find laying around will probably be one of these two most of the time. Unless you have acces to people who use and throw away more exotic stuff or of course the various tool steels.

Back to SS... I also was having a lot of trouble seeing the metal at higher heats. It squared up pretty easily (in that I could see or feel it easy enough..) but when I went for octagon it was very hard to see the corners. My belief is this is due to there being very little scale. But maybe it's something else. Anyone else have this trouble? I found myself really struggling to get just the right angle to see the piece while hot. As it cooled it became easier to see.

Link to comment
Share on other sites

Per the ASM's Source Book on Stainless Steels, the non-magnetic 300 series should be forged 1700F to 2000F or more. Actual ranges depend on actual alloy, of course. I'm told that is a salmon-to-orange range. (I don't forge by color because I suck at judging color. I forge by brightness.)

And, yes, forging stainless will make a man out of you if you survive the experience. :huh:

Link to comment
Share on other sites

We forge literally tons of stainless every week in the austentic, martensitic, precipitation hardening and duplex types. forge temps vary by family and carbon content but the austenitics are worked up to 2300 F, the duplex at 2200 F and the martensitic and precipitation hardening types between 2100 and 2200 for an upper limit depending on carbon content. 2300 F is the standard max temp for carbon and alloy steels when carbon does not exceed 0.50%. Reduced temps are needes with some grades because carbon has a signifcant role on the melting temperature. Other elemnets do to some degree as well and since we don't want to melt the steel, we need to keep the temps lower. Note that in heavy forge work, the movement of the metal generates heat due to friction so when selecting a forge temp, it is wise to make sure you don't go to near the melting point. (This is primarily of concern only with very heavy industrial forging).

As Thomas pointed out, the magnetism or lack thereof is a function of the phase present. Austenite is non-magnetic at all temperatures, therefore it you can keep autenite present at room temp, that material will be non-magnetic. Nickel, manganese and molybdenum are all austenite stabilizers. Chrome is the element that makes stainless stainless. Nickel can enhance and improve corrosion resistance but since it stabilizes austenite at low temps you may not want that in a steel intended to be used in the martensitic state.

Monel is a nickel/copper alloy and is NOT a steel at all.
Nickel superalloys have lots of nickel and other elements. I'm not sure they still are majority iron or not, but they are so far removed from the steels in alloy content and behavior that they are considered there own family.

Solution annealing is a common practice with the stainless grades that hasn't been mentioned yet. This is the practice of heat back up to usually around 1950 and quenching. This is done do dissolve chromium carbides which can reduce the corrosion resistance and also to dissolve other preciptating compounds which can affect corrosion resistance and toughness


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.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  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...