×
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!
  • Students Click Here

*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.

Students Click Here

Jobs

Stringers in 722M24 En40B Nitriding Steel

Stringers in 722M24 En40B Nitriding Steel

Stringers in 722M24 En40B Nitriding Steel

(OP)
Hello all,

I'm a newbie to the forum and am in need of some help.
We have a customers crankshaft which we've tested on the Mag bench using the W/C method and we've been finding 'stringers'. Some defects are surface breaking whilst others are not. Some are grouped together but all follow the length of the shaft. How detrimental to the component are these subsurface defects? I've read various articles which would lead me to the conclusion that any of these defects are rejectable even though the customer would like to have a limit on defect size?
Any help would be appreciated.

RE: Stringers in 722M24 En40B Nitriding Steel

Are the stringer defects being detected in the original bar, or in the final crankshaft?  If it is the former, then typical practice is to limit the defect to some detectable size, say 0.13 mm maximum, that will be removed during subsequent machining/grinding.  If it is the latter, then it is typical to reject anything that has a visual appearance during magnetic particle inspection.

RE: Stringers in 722M24 En40B Nitriding Steel

(OP)
Thanks for the reply. It's the final crankshaft so this would mean their rejection rate could be high. If they still insist on using this material is there any safe way of coming up with a limit for this type of defect in the final product?
Thanks.

RE: Stringers in 722M24 En40B Nitriding Steel

The effect of these imperfections on the product depends on their orientation with respect to the principle stresses.  If their lay is parallel to the direction of principle stress, they will have negligible effect, but they are perpendicular to the principle, they can be very detrimental.  In addition, if they are present in a case-hardened layer, they can cause problems regardless of the principle stresses from applied loads because residual stresses can significantly affect the direction of the principle stress in the case hardened layer.

Most of the acceptance criteria I've seen for such stringer imperfections usually address both a size (length) limit and a density (number found within a specified area) limit.  For example, a maximum length of 0.500 inch for any single indication and no more than 3 indications over 0.063 inch in any 1.0 square inch area.

The actual values for the limits have to come from experience and/or trial and error.  In the absence of experience, initial limits could be based on the consequence of failure combined with limits that would reject the worst cases while accepting minor groupings, and adjusting depending on performance.

rp

RE: Stringers in 722M24 En40B Nitriding Steel

(OP)
Thanks for the advice. I think it may be wise to section one and 'see' what is going on. The crank will be going into a very powerful engine so I'll use a bit of caution before setting a limit with the customer.

 

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