Slack quenching
Slack quenching
(OP)
I have been always told that if you get proof failure one of the main reasons can be slack quenching.
my questions are:
- is this true?
- what else can be involved?
- can we explain the reasons scinetifically (by dislocation theory or...)?
thank you evryone for your help.
my questions are:
- is this true?
- what else can be involved?
- can we explain the reasons scinetifically (by dislocation theory or...)?
thank you evryone for your help.





RE: Slack quenching
As a generalization, no. A slack quenched microstructure can be a contributor to failure. It depends on the type of failure, material and conditions of service.
One major factor unrelated to a slack quenched microstructure which can cause failure is poor design.
Unclear what you are asking.
RE: Slack quenching
material is low alloy steel and it is hardened and temepred and as i mentioned it is 0.2% proof stress failure.
the location of the test is fixed and sometimes we get test failure on these parts not always, so we rule out the design issue.
what i am looking for, is scinetific explanation for correlation between slack quench and 0.2% proof stress failure.
RE: Slack quenching
Thanks for the follow-up. If you are observing failures related to inadequate strength of the material after heat treatment, a slack quenched microstructure could be the cause.
Have you performed a metallurgical evaluation of one or more of the failed test parts to confirm slack quenching? It would be wise to confirm if the heat treated low alloy steel contains phase constituents other than tempered martensite.
RE: Slack quenching
Maui
www.EngineeringMetallurgy.com
RE: Slack quenching
RE: Slack quenching
Maui
www.EngineeringMetallurgy.com
RE: Slack quenching
Maui
www.EngineeringMetallurgy.com
RE: Slack quenching
In my opinion, this is false. At least, the "one of the main reasons" part. What I understand "slack quenching" to mean is "removal from the quench medium before the parts have fully cooled to the temperature of the quenching medium". While this may result in low yield strength, there are many cases where it does not (and it can be useful in prevention of cracking). Not only that, but there are many other reasons for low yield strength.
There are a lot of reasons, some mentioned above:
Low austenitizing temperature
Short austenitizing time
Surface condition of the material (ie, heavy forging scale)
Too large section
Poor quench agitation
Wrong quenchant (ie, slow oil when a fast oil should have been used)
Poor steel chemistry
Too large a quenching load
Too long delay after leaving austenitizing furnace before quenching
and many others...
The fact the UTS is within range but the Yield Strength is not COULD suggest that inadequate transformation to martensite occurred during quenching, however, there are other reasons as well. But, even then, slack quenching is only one reason for inadequate transformation to martensite.
rp