Heat treatment

[rb88]

1. How important are the following steps in the heat treat process of steel(6150)? What if these steps of the heat treat are missed?:

Annealing, Subcritical Annealing, Pre-hardening stress relieving, and post tempering stress relieving.

2, If the material was hardened too high during the temper can the temper be reperformed to a higher temp in order to get a lower hardness without ill effects.

Thanks

 

[NickE]

I have to say this looks like homework to me.

How about some more info on what shape and size the part is.

Nick
I love materials science!

 

[rb88]

The part is actually a landing gear leg and is a 1" dia rod approximately 30" long that has a 112 degree bend in it. Material is 6150 with a desired hardness of 43-46 HRC. It was first tempered to 775 F with a hardness of 48 and then retempered to 825 F back in the acceptable hardness range.

 

[EdStainless]

I presume that this part was extenstivly tested to qualify it. The heat treatment should have been fixed at that time and any deviation is unacceptable.
While re-tempering is a minor sin, there are a lot of ways with different heat treatments to reach similar hardness that result is significantly different fatigue resistance and toughness.

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

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

 

[TVP]

rb88,

I agree with EdStainless that this part likely involves significant testing for qualification, which can make process changes difficult to accept/implement. Having said that, my answers to your questions are as follows:

1. Annealing and sub-critical annealing are performed in order to increase the formability of the steel and to decrease the forces needed for deformation. A low-ductility grade like 6150 is difficult to deform without cracks, etc. unless it is annealed. The sub-critical anneal is a recrystallization step after some intermediate forming that is needed in order to complete the final shape. Pre-hardening stress-relieving is done in order to reduce the tensile stresses that are present on the surface and to reduce the amount of distortion that will occur after hardening. Post-tempering stress relieving is likely performed after chromium plating or some similar process. It will be difficult to eliminate any of these without a thorough evaluation of the entire manufacturing process.

2. This is unlikely to be a significant problem, provided that the microstructure is good (100% martensite transformation, no decarburization, etc.).

 

[rb88]

Thanks for all the responses.

 

[NickE]

I apologize, I remember a question like that off a test in school. Other than that, what they said.