INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

(OP)
Hello

I have some thinwall parts made of inco718. Part diameter is about 6 mm and wall thickness is about 1 mm. The problem is hardness value after heat treatment process. Heat treatment process that i did is conventional inco 718 heat treatment (solution heat treatment between 930-1010 C - min 1 hour - air cooling, 2 step aging 720 C/620 C - 8 hours/8 hours - air cooling). I changed solution temperature, cooling rates, cooling media everything that spec allows me. But i have never found a part has hardness lower than 44.5 HRc. This makes me crazy. Please help me.

Thank you.

RE: INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

First, how are you conducting the hardness test to verify heat treatment compliance? Do you have access to a metallurgical test lab? What other examinations have you performed on the heat treated material???

RE: INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

Even though in theory you are above the min thickness for HRC 45, you are too close for my comfort.
I would go to 30N or 45N.
The next question is are you testing ID or OD? what are you using for curvature correction factor?
If you are testing on the ID using HRC your readings will be high by 3-4 points due to the curvature.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

(OP)
metengr;

Yes ı have access to metallurgical lab. I checked the microstructere and grain size. It wasnt homogenous and grains were really small.(something between ASTM 8-9)


EdStainless;

Actually i always find the hardness between 45-46 HRc. I didnt understand your questıon because i dont know what is ID or OD. But i have never tested heat treated parts in rockwell machine because of the wall thickness. It is about the same size with indenter. Generally, i test it in Microvickers machine then i convert it to HRc ( 0.3 Hv, 40x ).

(Note : Sorry about my english, it not my native language. My grammer could be hard to understand)

RE: INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

Ahh, in that case I wonder about your conversion. You need to HT a larger sample (a piece of the raw material) of flat material and test it in multiple hardness scales to verify your conversions. The ones that are published are not for these alloys and are very approximate. I would test HV at multiple loads and in various Rockwell scales, build your own reference. I have had to do this for cold worked stainless steels since many are too thin for the standard tests, and in many cases the published conversions were off by 3-5 points.
You said that the part had a diameter, so I presumed that you were testing on a curved surface.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

(OP)
I had two experiement, first one is oil quenching after solution and the other one is air cooling after solution. I checked the grain size for all the parts. I fıgured out an interesting thing, bigger the grain size higher the hardness. The minimum hardness value that i measured from the parts has minimum grain size (ASTM 10). I couldnt find any proper explanation for this situation. I am really confused.

RE: INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

This is a precipitation hardened alloy, the size and distribution of the secondary phase is what governs your measured hardness.
The smaller the indenter and lighter the load the more impact the size and distribution will have.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

Contact Special Metals and discuss your issue/concerns with them. I know several of the metallurgists at Special Metals, they are helpful, know their product line and can better assist you.

RE: INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

(OP)
Thanks for your help guys. Both of you were really helpful. I am going to contact with them. I will let you know in this post if i can find a solution.

RE: INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

(OP)
I did the process at 930 C for 2 hours. Then i cooled it with water (10 C water). Results were awesome. Hardness values are between 42.5-43.0 .

RE: INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

For a small size part like this, is there any reason you can't machine it from heat treated bar stock? 718 Inconel at Rc 42-43 is not that difficult to machine, unless the part has some complicated features.

RE: INCO718 thinwall parts heat treatment - maximum hardness 44.5 hrc

(OP)
Actually i dont know because i always do heat treatment process to machined parts. But i think it is because of hardness and complexity of the parts.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close