anneal stainless steel 1

[terruscam]

I need to fully anneal, for machining, some 304 stainless bar. What is a good temperature to set my oven, heat and then turn off for the night to cool?
terruscam

 

[EdStainless]

Are you trying to change the microstructure or are you only concerned with residual stresses?
In this 304L (low carbon) material?
Will grain growth hurt you? (are you concerned about fatigue life or surface finishes)

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[NickE]

slow cooling doesnt solution anneal stainless. it sensitizes it.

 

[arunmrao]

How often I hear this "Your stainless steel casting is not annealed properly".
"You cool it very fast probably hence the dificulty in machining".

I encountered this statement just today. I just grinned and walked off.

 

[Flesh]

One listed aerospace practice: heat to 1065 C, hold , then quench in water. Parts under 2.5mm thick can be air cooled. Hold time at temperature depends on thickness.

 

[TVP]

terruscam,

When you say oven, do you mean a proper heat treating furnace? As Flesh points out, the solution annealing temperature is quite high for austenitic stainless steels like Type 304.

 

[EdStainless]

If you have low carbon material (0.02% or less) you can furnace cool with no issues.
If you are just trying to relive stresses then stay low, say 1850F. Let the part cool out of the furnace in still air. When it gets to the point that you cannot see any glow (about 1500F) it will be strong enough that you can force cool it without causing much residual stress or deformation.
If you need to fix the microstructure then you need to anneal hotter (about 2050F). This will increase grain size.

If you do any of this in the open air you will need to remove the oxides formed. This needs to be done by either machining off material or by acid pickling.

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Rust never sleeps
Neither should your protection

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[TEV]

Why do you need to anneal for machining? We actually prefer strain hardened stainless for machining, as we get less stringy chips, better surface finish, and reduced tearing (with form tools). For some of our machined products, we actually specify fairly strongly strain hardened barstock and anneal following machining, as we need the reduced mechanical properties of the annealed stainless for product performance.

It's important that you source barstock specified for machining, also. Such barstock will have about 0.025% sulfur and about 0.035% phosphorous, which will aid machinability, although at a slight loss of corrosion resistance.

 

[EdStainless]

There are some better machining grades of stanless that don'e have reduced corrosion resistance. The ones that I have worked with are the Prodec grades from Outokumpu.

Yes, TEV, We have many customers that buy cold finished tube for machining. It isn't that hard (Rc in the low 30's) and you get a lot better surface. If hte application doesn't require an annealed material you just leave it hard.

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Rust never sleeps
Neither should your protection

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