Material Choice for 1300F Mandrel 3

[mewhg]

We have a situation in our plant and I would like to ask advice on material choice.

We have a forming machine that wraps red hot steel bar around a 40mm diameter cylindrical mandrel to form a spring. About 15,000 springs are made off each mandrel per day. Due to the heat pick-up from the spring steel the mandrel rises to 1300F and stays there for 2 shifts.

We have been experiencing pitting and spalling of the mandrel and this causes the size of the formed spring to change over time.

Our current material is M2 at 62 HRC. the dimensions of the mandrel are 40mmx165mm long with an M20 drilled and tapped hole in one end.

We could water cool the mandrel but this adds a lot of complexity to the machine.

So far we have tried spraycoated mandrels (the coating flaked off) and a solid carbide mandrel (lasted 1 day). Currently, we get 3 days of use out of each M2 mandrel.

Is there any other steel we might try that would decrease the pitting and spalling? I am looking at Carpenter X-750 and 718 alloys but I am not sure if these might be good choices. I called into Carpenter and got the run around when I tried to get technical assistance.

Thanks in Advance.

 

[EdStainless]

Have you tried CPM 9V or H-19? These are hot work tool steels with good high temp properties.
At temperature any alloy will be fairly soft. These alloys can bot be surface trated (nitride) to improve surface hardness.
The Ni based aircraft alloys have strength, but I am not sure that the really high cost will be offset by the properties. I don't think that they will be strong enough to resist wear.

How do you cool the mandrel? Cooling internally with hot oil would be nice. You don't want to run the risk of thermal shock, but you do need some cooling.
I might also suggest a light mist on the OD of the tooling with some Boron Nitride. This will provide some lubrication and fend off the metal adhesion issues. This could be refreshed every so often (30-50 parts?)

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[TVP]

I am thinking along the same lines as EdStainless, i.e. using a tool steel with higher strength/hardness at elevated temperature rather than going to a nickel-based alloy like 718. I propose changing to a super HSS grade like Type M48 (JIS SKH57, DIN 1.3207, EN ISO S10-4-3-10). It has substantial tungsten and cobalt additions to improve hot hardness, while the molybdenum and vanadium additions create wear-resistant carbides. This grade is available from a number of manufacturers around the world (Crucible REX 76, Cartech Micro-Melt M48, Böhler S700, Hitachi XVC5, Daido MH8), so there should not be a significant problem with availability. You can obtain datasheets from the respective producers websites.

Another option would be to use a lower-carbon hot-work tool steel like Type H21 (JIS SKD 5, DIN 1.2581, EN ISO X30WCrV9-3) and then have it nitrided. Nitriding of warm/hot forging tools is commonly done in order to improve their resistance to wear at elevated temperatures. A typical depth would be ~ 90 micrometers. I think both of these options would be a significant improvement over the current M2. I also agree with Ed's recommendation of a boron nitride lubricant/release agent. Fuchs Lubritech and Klüber are two providers of this type of lubricant.

 

[mewhg]

The mandrel is not cooled at all except for conduction heat transfer into the machine body. I know this does not help things at all but the added complexity on this minimally maintained machine would drive the maintenance mechanics nuts.

Thanks for the replys and suggestions. I have a call into Crucible and will discuss Rex 76 with them. Will also consider the nitrited H21.

Spoecifically TVP thanks for the lubricant suppliers. I was wondering where I would find tha boron nitride at.

 

[EdStainless]

and another source

http://www.bn.saint-gobain.com/

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[mewhg]

I spoke to Crucible. They recommended the Rex 76 and CPM 1V. I'll have mandrels made from both and post back on results.

 

[unclesyd]

For your Boron Nitride you want to checkout ZYP. They have some very sharp techical people.

http://www.zypcoatings.com/

 

[StoneCold]

Here is a crazy idea. How about a ceramic sleeve over the top of the mandrel?

Regards
StoneCold

 

[EdStainless]

Saint Gobain and Fuchs invented industrial BN.

I decided agains suggesting ceramic because of the thermal shock issues.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[Compositepro]

How about water mist or spray cooling from the outside of the mandrel. It is what I see in steel rolling mills. You will need ventillation to remove steam.

 

[arunmrao]

I produce cast mandrels used in steel industry. These are cast in the grade 28NiMo17(sorry I do not have AISI equivalent).

The chemistry of this is as follows :
C-0.2-0.3%, Cr 0.3-0.5%, Ni 4.2-4.7% , Mn 0.2-0.4%, Si 0.15-0.35%, Mo 1.15-1.25, Va 0.15-0.2%, W 0.25-0.3%,S 0.05%max, P 0.03% max.

This is oil quenched and tempered to a hardness of RC 48-52.
Hope this helps.

 

[unclesyd]

Once you solve your mandrel problem you might take a look at the forging lubricants, either the graphite or the non-graphite based materials.

I've had excellent results using this type lubricant forming wire at 1100F-1200F. Though I'm a big fan and long time user of BN these lubricant materials are considerably cheaper than BN and in most cases easier to handle.

http://www.achesonindustries.com/process_lubricants/forgedata.asp

 

[TVP]

I also agree with unclesyd regarding forging lubricants vs. BN. I had gone so far as to include the same Acheson link in my previous post, but then thought that was a significant deviation from the current practice and therefore deleted it. The forging lubricants will be much easier to handle, but the graphite-based ones still can be quite messy. Water-based lubricants may be an issue with respect to local cooling gradients, and can lead to thermal shock issues for the tools, so this needs to be carefully evaluated. BN should be easier to implement from this perspective.