My company is a manufacturer's agent that specializes in finishes for stainless steel (type 304/316). What may be the root cause and how can I redeem the surface from being stained over the course of my heat treatment? This stuff is not letting me sleep at night. I have used analytics grade purity reactants and it still seems to have those impurities causing the dirty final look. I have also tried this procedure without the acid etching, with different machining process (turning 2 mm off the metal surface to make sure i've reached a clean layer) and even with different furnaces. Unfortunately, the sample comes out with sharp edged brown stains. I turned the furnace off and left the sample overnight to cool down slowly I turned on the furnace and let it reach destined temperature over the course of 1 hour to avoid uneven heatingġ2. I put the tube into a clean muffle furnace with PID temperature control with tested setup that avoids overheating through oversteer.ġ1. I put the tube to a vacuum dryer at 100 mbar and 60 ☌ (140 ☏) for 5 hoursġ0. I rinsed the tube in deionised water againĩ. I seasoned the tube in 75% phosphoric acid for 24 hoursĨ. I cut out the tube on a lathe and transferred to a tank containing isopropyl alcohol, without touching the surfaceĦ. Wiped out the surface clean with a dustless wipe and demineralised waterĥ. Polished the surface again with 1000 grade sandpaperĤ. Polished the surface on a lathe with 400 grade sandpaper using isopropyl alcohol as a medium (also tried with regular coolant and water to the same effect)ģ. However, there's an issue with the finish, as the surface is usually covered with sharp edged brown stains, which ruins the finish. I have found, that at the temperature of 500 ☌ (930 ☏ for American friends), those alloys are turned beautiful golden color. I want to achieve aesthetic browning of AISI 316L and AISI304L steel by using a furnace. Browning/Blackening stainless steel: black oxide, chemical dip, PVD, electroplating? Plating, anodizing, & finishing Q&As since 1989

Does 304 stainless steel rust