grain or inclusion pull-out in turned steel??

[gearHTr]

I am looking for possible explanations and reference material related to pits found in steel parts after turn operation. Customer keeps rejecting as corrosion, but they are being found as they come off the machine.

Material is forged steel, German grade WL 1.6722, vac.arc remelted, quenched and tempered approx 30-34 HRC. Cert. chemistry is .17 Carbon, .25 Si, .43 Mn, .005 P, .0008 S, 1.22 Cr, .25 Mo, 3.95 Ni, .13 Cu, .007 Sn, .044 Al.

Typical photo attached, 40X mag.

Thanks

 

[swall]

Looks like electrical pitting from a ground fault in the turning machine.

 

[Gem1]

I'd agree that they could be electrical arc pits. They are more irregular than arc pits I've seen before, but that is probably just conditions. Have you looked for melting beads in the pits at higher magnification?

photo attached is from a steel surface which was covered in pitting corrosion, but also had some arc pits. the smooth edged, round pit in the middle is the arc pit.

 

[metengr]

gearHTr;
If this problem is resulting in rejection of components, this is costing you money and time. Here is my advice have a proper metallurgical analysis to first determine what is the source of the surface pits to allow you to correct the problem. The cost of the metallurgical analysis will more than pay back if you can get to the root cause and prevent it from re-occurring.

 

[gearHTr]

thanks guys, I'm waiting to see what maintenance has to say regarding the machine ground.

metengr - can you recommend a couple labs who are knowledgeable in this area? NADCAP preferred but not required.

 

[CoryPad]

Regarding labs, is location important to you?

High quality ones would include:

Stork

http://www.storksmt.com/

Westmoreland

http://www.wmtr.com/

Exova

http://www.exova.ca/

 

[tbuelna]

metengr,

Excellent advice. Methodically diagnose the situation. Then formulate a corrective action that addresses the problem, not the symptom.

Regards,
Terry