REMOVAL OF HEAT TREAT SCALE FROM STAINLESS STEEL
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/process that will remove the Heat Treat Scale without affecting the substrate. The material is 400 series SS.
Thank YouLyndon Tschetter
- Mishawaka, Indiana
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!
Stellar Solutions, Inc.
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 ASTM A380 [link is to "Download ASTM Standards" from ANSI.org] 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.
materials testing laboratory
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
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
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
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
- Toccoa, Georgia
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.
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 can't use it if its shrinks by more than 0.002"Alan Hughes
February 25, 2010
We use a solution called Mirachem to remove heat tint at 3:1 water/Mirachem heated at 100-110 degrees F. It works excellent.James Manning
- West Bridgewater, Massachusetts
February , 2010
Thanks, James. If someone can tell us what it actually is, rather than a supplier name, that would be ideal.
Ted Mooney, P.E. RET
Brick, New Jersey
June 21, 2011
Instead of using complex processes and products to remove scale after heat treatment, it may help to use an effective anti scale compound. The anti scale compound is used by coating on the component before heat treatment and allowed to dry completely. The coated component is heat treated. After heat treatment, scaling is either zero or substantially reduced. The results depend on your heat treatment cycle. However, many users of anti scale compound have reported satisfactory level of scale reduction, if not complete elimination of scale.
A. After many years of trying various chemicals and mechanical methods to remove heavy carbon, smut, and a very tenacious oxide layer, I happened to stumble upon an old military document written by Northrop back in 1952 that really works...
Use an aqueous (distilled water) alkaline solution of 0.5 molar of Potassium Permanganate, 3.75 Molar of NaOH, and 1.5 Molar of Sodium Carbonate (Calcium Carbonate also works good, same amount). Heat up part in this solution to 190 °F for 2 hours, or 150 °F for 4.5 hours (what I do).
If you are not wanting to heat up a bath (especially a large bath), and you don't need such fast results, you can instead use 0.4 molar of Potassium persulfate & 3.75 molar of NAOH. At 70 °F it will take approximately 12 hours. I have not tried this bath method, but according to Northrop you get the same results.
You'll need to google the molecular weight of each of those chemicals, and then use a molar calculator (again, google it)., to figure out the correct amounts to use for the amount of solution you are making.
The next step is to rinse the solution off of your parts. Most carbides & oxides can be wiped off, or (my preference) taken off with a short ultra sonic bath in plain water (fast, very effective).
A quick dip in an inhibited hydrochloric acid bath (3~5 minutes at room temp) will clean up any remaining smut.
Another water rinse, then passivate the surface with either a nitric or citric bath (the surface is "activated" by the HCl bath, so you'll want to passivate it). I have found that it doesn't take as long to passivate an activated surface like this.
Hope this help you (I hope this get posted, unlike the last two times I posted it here).
- Browerville, Minnesota, USA
Ed. note: Excellent posting, Pat, thank you! Apologies for the difficulty. I see several postings from you in 2000, one in 2006, and no others until this one. Sorry, I can't explain why we never received them, but we didn't.