Effect of Phosphorus on hardening
Effect of Phosphorus on hardening
(OP)
Here's the problem. I've got a failed 25mm diameter pin from a clevis joint (it's case hardened). It's 'broken straight through corresponding to the centre of the male end of the clevis.
The quoted material specification is 16MnCr5 (1.7131),
C 0.14-0.19, Mn 1.00-1.30, Si 0.4 max, S 0.035 max, P 0.35 max, Cr 0.80-1.10
Lab report gives,
actual analysis C 0.17, Mn 1.35, Si 0.26, S,0.01, P 0.063, Cr 1.12
Surface hardness 640 Hv, core hardness 350 Hv, grain size 4.5 to ASTM E112, case depth 1.1mm
Lab report says ".. reason for cracking is probably the high P content."
I'm not familiar with the effect of phosphorus on the hardening of steels. Any illumination would be appreciated.
The quoted material specification is 16MnCr5 (1.7131),
C 0.14-0.19, Mn 1.00-1.30, Si 0.4 max, S 0.035 max, P 0.35 max, Cr 0.80-1.10
Lab report gives,
actual analysis C 0.17, Mn 1.35, Si 0.26, S,0.01, P 0.063, Cr 1.12
Surface hardness 640 Hv, core hardness 350 Hv, grain size 4.5 to ASTM E112, case depth 1.1mm
Lab report says ".. reason for cracking is probably the high P content."
I'm not familiar with the effect of phosphorus on the hardening of steels. Any illumination would be appreciated.





RE: Effect of Phosphorus on hardening
RE: Effect of Phosphorus on hardening
"Microstructure consists of coarse tempered martensite in a core, with retained austenite at the surface. Intergranular cracking was observed at the surface. The structure shows that heat treatment was not done optimally."
Does this help?
RE: Effect of Phosphorus on hardening
What is the stress level on the pin? Without addressing these items, it is premature to speculate on the role of an out of spec chemistry.
RE: Effect of Phosphorus on hardening
http://
This one is particular describes the mechanism in case hardened steels, from one of the foremost experts on physical metallurgy of carburized steels:
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Not to discount swall's comments regarding the necessity for a thorough metallurgical failure analysis, but I would be very extremely concerned about a case hardened part that has a P content of ~ 0.060 % by mass. Anything over ~ 0.030 has significant negative effects on grain boundary fracture in case carburized steels.
RE: Effect of Phosphorus on hardening
There are many things you could blame, but the phosphorus content seems really out of range. This really isn't something that a steel mill would make a mistake on; their practices typically don't allow for a phosphorus level even half this. Could the surface have been phosphate coated and contaminated the sample thereby affecting the result?
If you take the phosphorus out of the analysis, I think you still have problems that could lead to a failure, so I think stopping at the phosphorus content in the failure analysis is a little premature.
rp
RE: Effect of Phosphorus on hardening
The batch of pins were manufactured in India.
At least I now know a bit more on the effect of phosphorus, thank you.