Will heating S/S make it brittle?

[Baldini]

Fitting Stucchi xover to Ti kitted bike: I need to bend either the connector pipe or xover exit pipe to get a decent run for the silencer. If I heat w/gas torch enough to get it to bend will stainless become prone to fracture?

 

...and ... how can I keep pipe section round & stop it kinking whilst bending it?

 

Thanks, KB

[Steve G.]

Yes!

Ciao, Steve G.

[Guest davidb]

It will kink. SS tubing is bent on a mandrel. SS can take a good amount of heat before it cracks. It will crack over time with reputition heating and cooling in the 1000 degree range.Our Waukesha enginators had exhaust expansion joints that would last about 3 years. the rest of the SS exhaust lasted the life of the engines. In your case, I would insert a long solid round in the crossover and heat the crossover joint ,then bend it to fit. If it cracked there, and I doubt it will, it will be easy to weld at the joint.

[Guest davidb]

Unless Guzzi bought some cheap ass chinese stainless steel with a dirt and rice alloy.

[Keith Foster]

If I heat w/gas torch enough to get it to bend will stainless become prone to fracture?

 

Thanks, KB

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For 12 years I was process engineer for a company that produced small diameter SS tubing. 300 series, 304, 316, 321, some Inconel's. We heated treated thou. of pounds every day. To bright anneal this grade of SS you heat the tubing in a hydrogen atmosphere to 1850 +\- and cool rapidly in the same, getting it below the 1000 deg. area in a certain time, I forget the time deal, like less than 2 minutes I think.(no, it doesn't go "boom" unless you have enough oxygen present) This made the tubing soft and able to be drawn to smaller sizes.

 

I think key to your question will be to know what grade of SS our exhausts are produce from. A lot of automotive SS exhaust is made from 400 series, the heat treatment of these I don't have any experience with, hopefully someone else can offer some insight. I don't think heating an area would make that area more prone to cracking, but this is based on my experience with the 300 sreies and not knowing what grade the MG exhaust is. My $0.02

[Guest Nogbad]

You don't need to worry about the effect of short term heating and bending on the material. The biggest difficulty you will have is in achieving a neat bend without kinking the pipe. One method is to fill the tubing tightly with fine zircon sand to support it as it bends. It is inevitable that you will get wrinkling on the inside of the bend.

 

With or without sand try this: Heat the area of the bend to a dull red, then heat a stripe on the inside of the bend a bit hotter to encourage the material to flow more in that area. Bend slightly, then transfer the hotter area over a bit and bend a bit more and so on. With skill, you can get a decent bend with a series of small corrugations on the inside.

 

Avoid overheating the outside of the bend, as you really want the material to thicken on the inside rather than stretch and thin out on the outside.

 

I all depends how far you need to bend it. A small correction is easy. 90° might be tricky.