×
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

Possible TME Failure??
2

Possible TME Failure??

Possible TME Failure??

(OP)
I have just read Thread 330-248132 on Temper Embrittlement and have some questions regarding a failure that I am currently analyzing.

The component is supposed to be 4147 but is 4140 deoxidized with silicon and grain refined with aluminum.  The mechanical properties of one failure are TS 184 ksi, YS 121 ksi and Elongation 12%. The second failure has TS 216 ksi, YS 137 ksi and Elongation 2%.  The mechanical values are well below the typical. Hardness readings however were quite high (52-55 HRC) I have submitted samples for Charpy testing but do not have the results yet.  Microstructure is nonhomogeneous with tempered martensite, untempered martensite, bainite and pearlite.  The fracture morphology is intergranular across the majority, microvoid coalesence across the remainder. What phenomenon could be causing the low mechanical properties? Is it possible TME? Poor steel quality? A mistake in heat treatment? The print states a minimum tempering temperature of 600F, hardness range 47-53 HRC.

Any thoughts would be appreciated.  

RE: Possible TME Failure??

nlj;
Did you confirm the chemical composition and presence of tramp elements?

RE: Possible TME Failure??

(OP)
The chemical compositions are as follows:

Carbon            0.388    0.395
Manganese       0.82    0.86
Phosphorus      0.0062 0.012
Sulfur            0.0036    0.0084
Silicon            0.283    0.243
Chromium    0.86    0.96
Nickel            0.129    0.112
Molybdenum    0.193    0.178
Copper            0.135    0.234
Aluminum    0.023    0.029
Niobium            <0.0040    <0.0040
Vanadium    0.0064    0.0074
Titanium    <0.0010    <0.0010
Tin            0.0083    0.0079
Boron            0.0007    0.0010
 

RE: Possible TME Failure??

One additional comment - your statement above

Quote:

Microstructure is nonhomogeneous with tempered martensite, untempered martensite, bainite and pearlite.

Was the microstructure you observed and mentioned above throughout the failed part? You should be observing a consistent tempered martensite microstructure with other phase constituents introduced further away from the quenched surface because of hardenability limitations with this alloy. What was the thickness of the failed part and heat treatment practice?
 

RE: Possible TME Failure??

(OP)
The non-homogeneous structure is throughout the entire part.  It is machined from a 2.25" bar, machined to approximetaly 1.5" I do not know the details of the heat treatment other than oil quench and temper. Temper set to a minimum of 600F.

RE: Possible TME Failure??

(OP)
I am going to re-run chemistry to find antimony, arsenic, and tin content. I will re-post.  

RE: Possible TME Failure??

While the subject matter is 5160 hot coiled, quenched and tempered springs, a passage from the 1993 edition of the SMI spring design manual may hold some relevance for your situation:
"It should be noted that as hardness increases above Rockwell C 48, ductility and toughness of the steel fall off rapidly..." "...springs made to a hardness of Rockwell C 53, for example, have been known to shatter under a constant load."

You may just be dealing with a brittle component because of the hardness range you are at.

RE: Possible TME Failure??

(1) Non-homogeneous microstructure is a definite problem.  It appears that the heat treating process was significantly off, especially the quenching phase.

(2) Yes, tempered martensite embrittlement is a possibility.  Because the steel was presumably tempered at 600 F, this is right in the TME range (400-600 F, 205-370 C).  Tempering in this range causes films of cementite to cover the prior austenite grain boundaries, which reduces the tensile strength, fracture strain (elongation), and fracture toughness.

(3) Low yield strength could be due to decarburization or other defects at the surface.

RE: Possible TME Failure??

I don't know why people want to use Temper Embrittlement as a failure mechanism.  It is not.  Perhaps the failure is due to low toughness (probably so), but the failure would have occured regardless of whether the low toughness was due to temper embrittlement or just plain poor heat treatment (as seems the case here).

Look at the yield to tensile ratios, 66% and 63%.  Any highly loaded part should have a Y:T ratio of at least 80%.

The substitue of 4140 for the 4147 is a poor choice.  4147 has much higher carbon and manganese, both contribute strongly to the hardenability.  With the reported mixed microstructure, the hardenability is most certianly an issue, as a higher hardenability steel would have developed more martensite on quenching, improved the yeild to tensile ratio, and would have much improved mechanical properties.

Temper embrittlement is a red herring.  Much more important is the failure occured because of a poor transformation during heat treatment (quenching), and a lower-hardenability steel was substituted for what was originally called for.

rp  

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