REMOVAL OF HEAT TREAT SCALE FROM STAINLESS STEEL

Letter 5089

REMOVAL OF HEAT TREAT SCALE FROM STAINLESS STEEL

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One of our products uses a threaded fastener that, by print, requires an Oil Quench Heat Treat prior to passivation. After Heat Treat the fasteners have a scale residue that is not affected by our cleaners or Passivation Processes. We have prescribed a mechanical removal but this is both expensive and difficult to monitor.

Is there a product or process that will remove the Heat Treat Scale without affecting the substrate. The material is 400 series SS.

Thank You

Lyndon Tschetter
- Mishawaka, Indiana

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Lyndon: If neither nitric acid or hot CitriSurf formulations remove the scale, you probably have to go to nitric/HF solutions or Potassium Permanganate solutions. The hot KMnO4 is safer to use, but can be very messy. Of course, you can remove it with electropolishing. Good luck!

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

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It sounds like you will have to acid pickle to remove the scale prior to passivation. The process that you should use will depend on the specific stainless steel alloy, its condition, and the nature of the scale. The residue may be oxide from the thermal process and/or from the oil quench. Start by referring to ASTM A380 [link is to spec at TechStreet] for as a standard guide for cleaning and passivation.

The ASM Handbook Volume 5 also has excellent information about surface cleaning and passivation. It may take some experimentation to get the best method with the safest chemicals and minimum damage to your parts.

Larry Hanke
materials testing laboratory
Minneapolis, Minnesota

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In response to the Question of "Removal of heat treat scale from stainless steel", I find the quickest and the most logical method would be a form of electropolishing. With a small power supply, a hand held wand and less than a liter of electropolishing solution, the problem can be solved within a matter of seconds.

This is not to be confused with electropolishing,but, rather weld stain clean-up or heat treat scale removal. The true advantages of this method is it's portability, selectiveness of the area to be cleaned up and the time it takes to achieve the required results. This is a proven method that is user friendly with little waste.

J. D. Stanley
- Cleveland, Ohio

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Lyndon, Have you tried using inhibited HCl in conjunction with ultrasonic ? This method has worked for me in the past. Good Luck,

Mark Kruzel
- El Cajon California

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There is a specialty foil and foil baggie that you can put SS parts in that will significantly reduce oxidation (scale) on your parts and they can still be oil quenched with similar results as to what you are doing now. Do not know what the cost benefit tradeoff would be for your particular parts. On tight tolerance parts, it worked for me as we did not have to regrind them.

James Watts
- Navarre, Florida

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Lyndon: There is a new type of passivation now available that we call Selective Abstraction Passivation. It is a non nitric/HF formulation that is electrolytic. SAP will remove heat treat scale, weld residues, etc. and give you a passive surface second only to electropolishing. This process is environmentally friendly and can be used by OEM's that do not have waste treatment or ventilation equipment. It is NOT a citric chelant product by the way.

Dan Weaver
Team Metal Finishing

Toccoa, GA

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Lyndon: Is the quench oil in good condition? Excessive scale can be eliminated or greatly reduced if the proper quench oil is used and maintained correctly. I prefer the Potassium permanganate method of removal of scale after the quench has been looked at.

Regards,

Tom Walen
Heatbath Corporation

Springfield, Mass.

September 16, 2009

Is it possible to descale stainless steel (304 and 316) without stripping some of the surface away?. We have a process where we have a small diameter rod (0.035") that are single use only because of the scale that builds up during our process. We've tried electropolishing but to no avail? Will any of the above methods affect the diameter of the rod our tolerance is not strictly defined but i reckon we cant use it if its shrinks by more than 0.002"

Alan Hughes
- Ireland

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