Need helping choosing metal

[lukerobert]

I am currently on a project requiring building some pipe bending shoes and rollers that will come in contact with very hot metal. The workpiece blank (low carbon steel) will be heated to about 1600 deg f and then sent thru the bender. It will be in contact with the shoes/rollers for quite some time for the bending process.

I'm thinking 4340, does anyone know what type of steel is generally used for this type of application?

Thanks in advance!

 

[CoryPad]

Definitely not 4340, probably hot work tool steel like H13.

 

[TVP]

Agreed, hot work tool steel. Lots of options, including nitriding of the surface to create improved wear resistance.

 

[EdStainless]

H13 with a Mo or ceramic coating (that will need to be maintained) or one of the H2X grades (like H25).

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Plymouth Tube

 

[ornerynorsk]

"It will be in contact with the shoes/rollers for quite some time"

What does this mean, in terms of seconds, minutes, hours? The hotwork steels are not altogether impervious to the effects of heat. There are limitations. H13 is certainly one of the most commonly used general purpose hot work alloys.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[lukerobert]

The blank will be fed into the bender at roughly 1100 deg F and then sent through the bend process which takes up to 6 minutes. This will be a 90 deg bend on heavy wall pipe using induction heating. It will be held in place by the machine until it cools off to about 250 deg f.

 

[ornerynorsk]

That's the upper limit for tempering on H13. You'll hold somewhere around 38/46 Rc for hardness. It should work.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[EdStainless]

This is a lot like service in glass molding.
There are various other hot work tool steels used in that service.
Hardness retention and resistance to heat checking (cracking) will be the drivers.
Alloys like H24 or H26 may have an advantage in the long run over H11 or H13.
You also do need to consider coatings, a flame spray Mo or ceramic coating will greatly help protect from surface damage.
These coatings could be striped and reapplied at a regular intervals (swapping out with a second set of tooling).
This would greatly extend tooling life.


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Plymouth Tube

 

[lukerobert]

Ed,

Can you tell me more about the Mo coating process? Is it expensive? It will also have to handle hefty amounts of pressure and friction.