Six Reasons to Consider Rolled Threads

drop forging creates the sane grain structure

What effect (if any) would the roll forming process have on corrosion resistance (In particular, hydrogen embrittlement) as compared to cut threads?

The smoother flanks and greater radii of a rolled thread would minimize the parts' susceptibility to corrosion attack compared to rough / torn flanks and sharp features on a cut thread where corrosion cells could set up.

Neither cutting threads nor rolling threads per se contribute to Hydrogen pick up.

If the material has high levels of hydrogen and has not been properly baked out then the loss of ductility could cause the material to fail if you were to then try to cold roll the thread into that material.

Hope this helps.

Milo

Thanks Milo,

Your answer supports what I have observed for the use of various grades of stainless for both rolled and cut studs.

These studs are exposed to acid mine water, under tension, a tough application in anyones book.

Observation is a great teacher.

Milo

Milo -- I'm troubled by unredundant's observations as they run contrary to what I would have thought. I'm assuming here that the stainless steel fasteners he refers to are common 304 or 316 Stainless. So I'm groping here for a learned explanation.

I've always held to the belief that to the extent that you convert the austenitic structure of chrome nickel stainless by work hardening you reduce its corrosion resistance as well as increase its magnetic properties. The latter is easily observable. But corrosion resistance is a complex subject. And common corrosion tables and data tabulations generally do not cover alternate hardness conditions of the test samples.

Is there a reasonably easy answer to this or are there a topics in the area of corrosion of austenitic stainless steel that I should spend some time studying? I have access to ASM Metals Handbooks.

Ed Weldon

Ed we once replaced the standard carbon bolts/nuts with stainless steel fasteners to assemble the boat dock . We figured the stainless would allow us to easily disassemble the dock sections in the fall (better than trying to undo rusty carbon bolts/nuts). What we found was the stainless bolts/nuts galled and broke when we disassembled them. Need to use "Never Seize" to prevent this. A problem we have found with threaded stainless pipe and fittings is we needed to mark and match fittings and pipe once we threaded the pipe. If not the fittings did not make up properly and we had a number of leaks as a result. Threads in stainless is a tough one.

Ed, I think that what I am saying and he observed is that given a cut thread vs a rolled thread of similar stainless analysis, the cut thread will be the one to corrode faster. I attribute this to the roughness of surface finish on the cut thread, allowing for a much higher frequency of galvanic cells to be created.

So if (I SAID IF< I'm NOT AN NACE CERTIFIED CORROSION ENGINEER) there was a hierarchy of conditions to be considered as contributing to corrosion, I am saying that the relative surface finish of a stainless item is of higher importance than one thinks, as the use of rolled (smoother) vs cut (orn and or rougher) creates differences ion opportunity for corrosion cells to be created.

A rough surface on an otherwise low reactive material can create conditions that "trump" that material's usual behavior.

Milo

Milo -- Surface finish, a very interesting consideration for threaded stainless steel fastenings in salt water service. This looks like one of those areas where the difficulty of analysis, metrology and controlled testing pushes such approaches into the back seat behind proven experience for most real world situations.

You've got a lot of credibility over here on my side of the mountain. Many thanks for your comments. .... Ed Weldon

Think of it like, well, "Guts," Captain Eddie.

We've only got a couple meters of intestines, but we have hundreds of square meters of surface area because of all of the surface irregularities and features. Same with machined surfaces- and remember that pits and pockets have different chemical properties because of the fdifference in relative abundance of available ions therein...

Check out this cool illustration:

http://www.vendian.org/envelope/dir2/lungsout.html

Now think about all of the ups and downs that a rough surface finish adds to a surface on a thread flank.

Thanks for the comeback.

Milo

I use long rolled stainless threaded rods in my little CNC machines.

I have found that they vary considerably in diameter over their length, which means that I have to run a die down them to try and get a consistent diameter.

You would be shocked to see just how much material I have usually have to remove .......and these are the DIN Dies that are fixed, not variable ones with a slit.....I even bough other more expensive dies, they were exactly the same.....

Re cutting a meter of stainless threaded rod can take several hours due to the heating effects of the cut and needing to wait and let things cool down........also, I have to polish the threads at the end for a good finish....

Variation between the upper and lower limits is probably not a problem for most applications, but I need to control the amounts of slack in the mechanics a lot tighter than most people......

Once I have used up my stock of stainless, I am going to normal steel as I find re cutting normal steel is a hell of a lot easier and better than stainless.....the lubrication will keep the rust at bay!!!

I found the information here to be of particular interest for me, many thanks for the post.

So there is no down side to thread rolling?

Anthony@alno

Hi Anthony.

Thread rolling requires different tooling and horsepower compared to cutting threads. Quantitiy needed is usually the determinant on whether or not a rolled thread is economically available or not.

The point of our post was to present the reasons that one could consider when evaluating the threaded joint that they are trying to design. We are trying to create a means of "knowledge retention" of some of the aspects of our metalworking craft that might not be easily available on the web. This was one such piece.

Thanks for sharing a link to your website. It looks like you will be a contributor of some merit to our discussions here on CR4. I am looking forward to your sharing your experiences!

Milo

Good clear post.

One of the common and dangerous mistakes made when "reverse engineering" of machine parts is not to specify the method of creating threads. You may end up with an item that "looks" the same, but is certainly not.

I have witnessed the aftermath of a broken piston rod on a large reciprocating compressor in hydrocarbon service. Root cause was simple - reverse engineered piston rod had cut threads instead of the specified rolled threads.

I have had vendors of these "pirate" parts assure me that there is no difference between cut and rolled threads - they do not remain vendors for long.