×
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

Rock-Candy Fracture

Rock-Candy Fracture

Rock-Candy Fracture

(OP)
Who can give us some data about the steel casting defect called "Rock-Candy" Fracture.

Thanks !

RE: Rock-Candy Fracture

The ASM Handbook series would be helpful for you.  The term "rock candy" appears 20 times throughout.  For castings, the handbook has a table of casting defects (originally created by the American Foundry Society) and lists conchoidal or rock candy as defect number C 411 and defines it as "Separation along grain boundaries of primary crystallization".

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Rock-Candy Fracture

When excess Al is added to the melt for killing the bath, aluminium nitride is formed which results in classic rock candy fracture. You can take a small(20 lb)  sledge hammer and knock off the feeders and gates easily.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

RE: Rock-Candy Fracture

(OP)
What is the max values of AL in the steel casting ?

RE: Rock-Candy Fracture

Refer to ASTM A 216 Gr WCB ,for residual Aluminium content.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

RE: Rock-Candy Fracture

stanislasdz;
I don't have my copy of the Physical Metallurgy Handbook with me today. The Handbook is an excellent resource book for metallurgical engineers, and is not too expensive. As also mentioned by CoryPad, I would investigate an on-line subscription service with ASM.

RE: Rock-Candy Fracture

stanislasdz;
I checked in the Physical Matallurgy Handbook by Sinha,  and the aluminum nitride embrittlement that can result in the "rock candy" fracture appearance in castings. The minimum amount of AlN to cause intergranular fracture (aka rock candy appearance), in carbon steel is 0.002% and for alloy steels is 0.004%.

To reduce the susceptibility to this embrittlement;

Additions of Ti,Zr,B,S,Mo,Ni or Cu to the steel
Use of the lowest possible amount of nitrogen (0.005% or less), aluminum (0.015 to 0.030%)
Increased cooling rate after solidification
Faster cooling rate in the range of 2100-1290 deg F after solutionizing to control the amount and size of AlN.

RE: Rock-Candy Fracture

Aluminum nitride embrittlement, which is typified by a rock candy fracture surface, is dependent on (among other things):  Al level, N level, and section size.  There are some curves available that show the safe levels of Al for a given N and section size, but they aren't necessarily accurate particularly at large section sizes.  The Steelfounders' Society of America (www.sfsa.org) has a Special Research Report #12, which can be purchased, that covers the topic.

RE: Rock-Candy Fracture

While browsing my files I got this reference on rock candy fracture. Hope you find it useful.


Avoiding Aluminum Nitride Embrittlement in
Steel Castings for Valve Components
V-Rep 84-

By
William C. Banks,
Senior Metallurgical
Engineer
Materials Engineering
Department
Flow Control Division,
Rockwell International
First Published 1984

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

RE: Rock-Candy Fracture

to follow metengr, substitution of Ti for Al usually works well for lowering susceptibility.  I have seen empirically (not sure if it is in texts or not) that AlN formation follows a trend of the Al X N product.  They form on gamma grain boundaries and can often be remedied with re-austentizing. hope this helps.

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