Grade and State of Stainless Steel Rulers

[pawilkes]

I am a mechanical engineer and entrepreneur working on a new product. I've used stainless steel rulers (with the cork backing removed) that are 0.020" thick for my prototypes and need to figure out what grade and state the stainless used in these rulers are so that I can order material for production.

One website (

https://secure.mycart.net/catalogs/store.asp?pid=177300)

states that they use 301 stainless but I do not know what hardness they use. The materials are pretty springy so I assume it is fully hardened but it could be half hardened, I'm not sure. I'm hoping someone who deals with stainless sheet could give me their expert advice on what hardened state these rulers are typically made of. Thanks for the help

phil

 

[EdStainless]

You really want me to put hardness test dimples into one of my rulers?
Actually you will need to do a tensile test to find out.
ASTM A666 does not use hardness (thank God) but actual strength.
I doubt that it is full hard. 1/4 hard is strong stuff.

I am not sure that either of mine are a 300 series alloy, they could be 410.

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Plymouth Tube

 

[arunmrao]

Ed, I quite agree with you. I always believed they were 410,as it would be the most economical,and the edges could remain straight and sharp despite any abuse.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[EdStainless]

Use either 201 or 301. Unless strength is critical I would go with 1/4 hard.

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Plymouth Tube

 

[pawilkes]

Thanks for the thoughts. I am not as much worried about strength as I am springy-ness, so I suppose I am worried about the yield strength. I had some cut out of annealed 304 and they were like limp noodles, totally useless. I'll try to find somewhere that will send me small pieces at a reasonable price.

 

[pawilkes]

It's been a long time since I've had to deal with a tensile testing machine. The set up, as I recall, would be pretty simple though. Just clamp the sample in the upper and lower jaws(?) of the machine, look at the readout to find the elastic and ultimate strengths and then divide those by the cross sectional area of the sample, right?

 

[EdStainless]

Right. You can prob find a local lab that would pull a couple for you for a reasonable cost.

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Plymouth Tube

 

[pawilkes]

I was looking around for places to get small samples pieces of 301 and looking at McMaster (

http://www.mcmaster.com/#type-301-stainless-steel-bars/=hvhbss)

I noticed they listed strength and Rockwell hardness for the various states. While it may not be the best method to determine exact strength, I think using a hardness test would allow for identification (assuming it is 301). I might be able to have a friend do this for me at work.

 

[Guest102023]

Start with a tool no metallurgist should ever be without - a magnet. Strongly magnetic and it is 400 series; however I don't think that 400 would be sufficiently corrosion resistant to stay as bright and clean as my cork-backed ruler does. You should present it to a PMI tester to get an approximate idea.

My guess is they are made from very plain vanilla 301 or 304.

 

[pawilkes]

They are reasonable magnetic, so that means it's not 301?

 

[swall]

301 will exhibit various degrees of magnetism, depending on how severely it has been cold rolled. Spring temper 301 will exhibit a permeability in excess of 30, according to my SMI spring design book.

 

[Guest102023]

Compare the magnetic force to a similar thickness piece of carbon or alloy steel. 301/304 at the thickness of a ruler will likely be work hardened and be slightly ferromagnetic.

 

[EdStainless]

200 and 300 alloys are meta-stable and will be magnetic enough when heavily cold worked that you won't be able to tell them from CS without instrumentation.
I did PMI one of mine and it is sort of 301. My guess is that it is off-chemistry material.

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Plymouth Tube

 

[pawilkes]

Ed - Thanks for doing the PMI on your ruler, that info is super helpful. I ordered some 0.24" 1/4 hardened 301 from McMaster on Thursday, hopefully I'll be able to determine if it will be an appropriate material even though I want to use 0.020".

 

[btrueblood]

You couldn't find .02" thick material on McMaster? Try searching for "stainless steel shim stock" - you should be able to get hard, 1/2 hard, or annealed 301/304 materials, in or near .02" thick.

 

[EdStainless]

http://www.starrett.com/metrology/product-detail?k=667-20

but not stainless, heat treated med carbon steel.

It will tell you if the thickness and strength are right.
Commonly available for a couple of bucks each.

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Plymouth Tube

 

[pawilkes]

I miss typed in my last post. I purchased 0.024" 1/4 hard 301 from McMaster. They have 0.020" but only in fully hardened rolled strip which doesn't really work for me. The problem isn't ultimate strength but the tensile strength, really more the "springyness" of it. The 1/4 hard doesn't seems springy enough and forms easier than the rulers. The 20% extra thickness should make it stiffer, therefor more springy and harder to form. Based on this, I suspect that the rulers are 1/2 hard. To back up this thought I poked around the internet and found that Azom.com suggests that "Grade 301 enables it to retain sufficient ductility in conditions up to 1/2 hard conditions to be roll or brake formed".

 

[mcguire]

It's not hard to bend it around a known radius until it deforms and then calculate the yield strength. 410 would not be good because of warping during quench. Either 201,301 or 304 can be made sufficiently hard by cold rolling.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[btrueblood]

"They have 0.020" but only in fully hardened rolled strip which doesn't really work for me. "

Don't understand - you don't want rolled material, or you don't want full hard? If the former, they also stock sheets to 24x24" of full hard stock, and strips.

Not wanting full hard material doesn't make much sense - from MIL-HDBK-5H, AISI 301 full hard has 9% elongation minimum. This is equivalent to the elongtation for aluminum 5052 H32, in 1/8" section. You may need to control the bend radius, but it has plenty of formability. Springs are wound every day from "spring hard" type 301 and 302 wire, higher tensile than strip and lower elongation - again, the trick is controlling the bend radius.

 

[pawilkes]

I did a little experiment with a piece of 0.020" ruler and a piece of the 0.024" 301 1/4 hard. They were the same length and roughly the same width and clamped identically to a block. I then bent the free ends down an equal distance, released and measured the permanent deformation. The ruler was bent at 19 degrees and the 301 1/4 was 26 degrees. The ruler has a lower I value than the 301 1/4 based on the thicknesses. Since the ruler had less permanent deformation even though it had a lower I value, I conclude that it must have a higher tensile strength. Does this make sense or am I missing something obvious?

McGuire - I'm not sure how to go about calculating the yield strength based on bending around a radius. I'd love a brief explanation of the process though. Perhaps I got get a better estimation of the ruler's yield strength.

btrueblood - My final part has large flat areas so working with flat sheet is desirable. Also, I think that fully hardened will be too brittle and would be more prone to cracking. I don't have much equipment so controlling bend radius isn't always possible. Basically I have go the design and process down with rulers and I am trying to figure out their material so I don't need to redesign it.