reamer metallugy - Cu additions 2

[LanaCarrie]

I'm analyzing a reamer bit that failed in in a spiral path, with a flat fracture face, in a brittle manner. I cannot identify the manufacturer of the bit (the only markings are HSS Poland) and consequently have no mill certs for the chemistry to check the material against. I sparked the reamer and got the following chemistry:
0.67 C
.27 Si
0.62 Mn
0.21 Cr
0.024 Mo
0.13 Ni
0.029 Al
0.21 Cu

I have not been able to identify the material yet but am thinking this may be a carbon steel similar to 1065 but with Cu additions. However, the HSS marking had me originally thinking I would find the material to be a high speed tool steel. My question is this - I know that Cu can be used for secondary hardening, however, is this typical for tooling? This seems like a strange composition for a bit, but I'm not that familiar with tooling. I've searched the internet and my reference books and have not been able to find any references to the use of copper additions in tool steels. Can anyone offer some insight?

 

[Metalguy]

If you don't find W or lots of Cr and Mo, it's going to get soft at moderate temps., and it isn't a HSS. I don't think the Cu does anything good. This alloy sounds like a real oddball.

 

[unclesyd]

I have never seen Cu called out as an alloying agent for H.S.S. But it is there none the less and the old max was .35% Cu in alloy steels and .15 % in H.S.S. Copper is very detrimental as it tends to segregate very easily and cause problems in the manufacture of steel.

Reamers tend to break in the manner you describe. Are there any other cracking evident?

Is there any other indications on the fracture surface, Discoloration or markings?

Is this a one time failure are is it a continuing problem?

 

[LanaCarrie]

Unclesyd - Using wet flourescent MPI I did find one other small crack at the tip of a spline coming from the fracture face. I'm having the area mounted right now so I can take a better look. One other area away from the fracture face was mounted and I haven't had a chance to examine the microstructure yet but I've been told there are numberous orange colored inclusions in the unetched condition - sounds like the segregation you mentioned. There is some darkening on one edge of the fracture face, however, this area was covered in blood so that may have been the cause.

This is a one time failure. The part had only been used to ream 3 holes prior to failure. However, the reamer bit was modified (welded to a nut to allow it to accomodate a using an impact gun istead of a reamer drill) causing it to be misaligned. Though I believe tool mods to be generally poor practice, it is apparently something that is commonly done to these reamers where I work.

I believe the modification to be the cause of the failure (misalignment plus reverse torque imposed by the impact gun), however, I wanted to check the chemistry, microstructure and mechanical properties so that the failure could not be blamed on a "bad" reamer. I was hoping the metallurgy, etc would check out so it would be easier to convince people that it was the way the tool was used and not the tool itself that caused the problem. But, now that I'm faced with this wonky chemistry the failure could be more complex than we originally thought.

 

[swall]

I think you just have 1065 carbon steel with high residuals (i.e. the Cr,Ni and Cu are not intentiional).

 

[unclesyd]

Based on what you are saying I would look no further than the nut being welded to the reamer and driving it with an impact wrench.

There are so many safety and common sense rules being violated that it's hard to believe or understand. Just the welding is bad enough and depending on where the ground was attached it's amazing that it worked at all. Driving with an impact!

I would recheck the chemistry as a one shot deal might be in error. Check it against a standard close the your first analysis. The failure is more than likely going to be a torsion and low cycle high stress fatigue type.

If you read the rules for reaming holes on of the things they will tell you is that driving off center will break tools. Impact forces will break tools. Everything that was done to and with the reamer is a prelude to a catastrophic failure.
They are reamer designs that are made to take much higher loads.

Yu mention blood, I sure hope the operator didn’t get hurt too bad.

 

[LanaCarrie]

Unclesyd - I hear ya on the lack of common sense on this tool mod. I realize the whole cause of failure seems incredibly cut and dry. It's just hard to convince people that this is such a bad practice because they've been modifying these reamers to use them with impact guns in the field for something like 10 years. The classic "we've been doing it this way for 10 years and we've never had any problems before..." That's why I was hoping I'd be able to conclusively say it wasn't a defective bit, but that it was the fact that it is being operated completely outside its design parameters and intended function. I better stop now before this turns into a rant

No - the operator wasn't hurt too badly - a few stiches to the inside of his wrist. But obviously it could have been a whole lot worse.

 

[unclesyd]

I think if you check around you will find that a lot more have been broken, it's just that no one was wounded.

We had this problem some years ago in what seemed like a campaign to modify every tool in site. We had an accident with a modified tool that hurt two mechanics and when we presented the plant manager with the incident investigation and our conclusions he immediately made it company policy that any tool modification not cleared through engineering would be grounds for dismissal.
We had an OSHA audit of our site and one of the things mentioned in the critique was the absence of modified and worn tools. Evidently one of the inspectors had this on his agenda.

I think that metallurgical analysis of the broken reamer is a good exercise as it may contribute something down the road. As you mentioned not finding this material by the analysis, I looked at my information and could find nothing either. If your analysis is good the material is definitely “tramp metal”

I doubt you will find specific information as to the material in the reamer other than H.S.S. You might find a makers mark unless it was covered by the modifications. I might bang on the supplier of the reamer for more information, doubt you’ll get any, but worth a try.

I would look and see if clamping while welding left an arc strike or hot spot. A lot of welders will ground through the stationary part of a vise. Check the tip of the reamer also.

Was the break close to the weld or at the entrance of the hole being reamed?

Good luck in getting rid of thre attitude that modifying tools is ok just because it has been done.

You might look at this site for a few of the available options.

http://www.yankeereamer.com/Special_Reamers/special_reamers.html

 

[LanaCarrie]

Thanks for the response. Our company policy is that tools should not be modified but obviously this is not being enforced.

I'm pretty sure the chem. analysis is good as we did a quick PMI with a nuclear analyzer to confirm the results of the spark test and the results matched. I'll have a look for evidence of an arc strike - thanks for the tip. The bit broke basically in half - a good 5" from the weld so I'm not concerned about the actually welding being the cause.

Now my newest bit of info - the hardness is over 850 Hv! Seems incredibly high to me. Original readings were done with microvickers (500g load) so I had them test on the macrovickers machine (30kg load) to confirm and the results matched. Seems crazy hard to me.

Thanks for everyone's help on this. Better get back at it!

 

[unclesyd]

Wait until you get a good cross section as the material my have had a surface treatment. I don’t think they could have gotten it hot enough when welding to quench it. A lot of low alloy drills and reamers are tempered a low temperatures 350°F to 450°F.

It looks like the reamer would have failed in the weld area, the weld acting as a overload device. It looks like the shear pin was too far from the load and being that hard there was no windup. As you stated that hardness value is somewhat high though not that much as I have drill bits that are 62-63 HRc.
Do you have an unused reamer to compare against?

Have you analyzed the weld area, MT, Macro, and Micro?

Just for curiosity was size and type of reamer was it?

Keep everyone informed.

 

[LanaCarrie]

I don't have an unused reamer to compare this one two as we can't figure out who supplied us with it and can't find any others that are the same as this one in the tool crib. The reamer is a helical tapered pin reamer and is 12" in total length. It has left hand helical flutes for an 8" section. The reamer failed approximately 5" from the reamer tip. I have not analyzed the welded area since the fracture was so far from it that I don't believe heat effects from the welding could have contributed to the failure. Micros also do not show any evidence of a surface treatment.

The reason the hardness surprised me so much was that looking in the metals handbook (4.59, Fig 1), for .65 C I would expect this to be 100% martensite. I assume this hardness would reflect an untempered condition. I would have expected a tool to be tempered back a bit to increase the toughness.

I'll let you know if I find anything else this afternoon. Thanks for all the advice.

 

[LanaCarrie]

I made a mistake - this is a SPIRAL not a helical reamer.

 

[unclesyd]

Like is stated they do temper at lower temperatures. I'm like you, you can’t get there from here with 1065 material and the alloying elements aren’t high enough to have much of affect on the hardness.
You didn’t by chance see any Tungsten or Vanadium in the sample? If this were a W tool steel it could be tempered at 350°F with a resulting hardness of Rc 64 which is very close to you hardness values.

Appreciate the update

 

[LanaCarrie]

Thank you everyone for your help with this. I was confident that the reamer broke because it was placed under loading conditions for which it was not designed. However, I wanted to discount the possibility that it was a flawed bit so I could hammer the point home that we shouldn't be modifying tools. I issued my findings a while ago but thought I post an update just to tie up loose ends:

-chemistry = 1065 CS with lots of tramp elements (all below acceptable maximums)
-hardness = 65.5 HRC - through hardened
-microstructure = spherodized carbides (not homogenized)
-fracture morphology = stepped cracking - demonstrated that it did have adequate toughness and "fought back"

Overall - not what you'd consider a top of the line tool in terms of chemistry and heat treatment but it did the job it was supposed to do. I concluded the metallurgy and fabrication of the reamer to be suitable for the application. Thanks again everyone - your advice is always appreciated.

 

[unclesyd]

LanaCarrie
I think all that were interested greatly appreciate you bring us up to speed. I think your conclusion was a very good one and as you stated the tool fought back. As we all get ratched up at times we can only hope the marks are very small, so we'll last a little longer.

So often one never hears the outcome of effort put into the resolution of problem or the answer to question.

This type posting adds another blade to windmills.

Again thanks for the update.

unclesyd