ISO 898 Phosphorus Layer Prohibition
ISO 898 Phosphorus Layer Prohibition
(OP)
I am reading a hydrogen embrittlement research paper put out by Republic Steel (it is a reprint of a Kobe paper) and there is a section on phosphate wire rod coatings causing embrittlement in heat treated bolts made from said rod. There is a photomicrograph purporting to show a 12 micron phosphorus rich layer on the surface of the sample. And, the paper cites ISO 898-1-1988 as prohibiting a white phosphorus enriched layer on heat treated bolts.Anyone ever heard of this?





RE: ISO 898 Phosphorus Layer Prohibition
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: ISO 898 Phosphorus Layer Prohibition
RE: ISO 898 Phosphorus Layer Prohibition
CoryPad must have overlooked it, because there is a footnote h) that appears in Table 2 of ISO 898-1 that reads as follows:
h A metallographically detectable white phosphorous enriched layer is not permitted for property class 12.9 on surface subjected to tensile stress.
I have read a couple of different papers that discuss this issue of incomplete phosphate coating removal leading to a white layer and possible embrittlement. One such reference is "Reduction of Hydrogen Embrittlement in High-Strength Precision Fasteners" by Rainer Rink in the February 2000 issue of Fastener Technology International. The following is an excerpt:
"...if any phosphate or sulfur containing lubricant remains on the surfaces of these fasteners, they diffuse into the steel and form delta ferrite, which in turn increases the hydrogen pickup and causes embrittlement. In view of this, the pre-washing before heat treatment is very important."
RE: ISO 898 Phosphorus Layer Prohibition
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: ISO 898 Phosphorus Layer Prohibition
RE: ISO 898 Phosphorus Layer Prohibition
I have encountered this problem twice since I retired on continuos heat treating lines for fasteners, lines where the furnace belts come straight our of the rinse tank to a dryer then to a continuos furnace. If your cleaning and rinsing isn’t set up correctly the problem will manifest itself in the lost or breaking of the high dollar furnace chain.
Nearly all wire and small bar that we used in house had phosphate coating for lubrication when we were cold forming it. A phosphate coating is either used as the lubricant or surface modification to improve the adhesion of additional lubricants to improve the formability and save wear and tear on the tooling.
I have never seen a white phosphorous coating on the samples that I have crossed sectioned and analyzed.
CoryPad the only white layer I've seen on bolting is from decarb. The other white layer is from gaseous nitriding which I don't thing will be seen on bolting. One of these lines made fasteners for the auto industry. They were breaking so many belts that they didn’t get many bolts into the pipeline. Like I stated I never seen this problem affect bolts.