StainlessSteels.pptVIP

Chapter 16 – Stainless Steels Gateway Arch in St Louis – 304 series SS F-35 Joint Strike Fighter (JSF) Lightning II, built by Lockheed Martin – airframe 17-7 PH – 600 series SS Key Points: Alloy steels containing at least 10% Cr are SS. Contain sufficient amount of Cr that they are considered high alloy. Corrosion resistance is imparted by the formation of a passivation layer characterized by: Insoluble chromium oxide film on the surface of the metal - (Cr2O3) . Develops when exposed to oxygen and impervious to water and air. Layer is too thin to be visible Quickly reforms when damaged Susceptible to sensitization, pitting, crevice corrosion and acidic environments. Passivation can be improved by adding nickel, molybdenum and vanadium. Where Used? Food industry (cookware, flatware, food transport and storage tankers) due to its corrosion resistance and antibacterial properties. Surgical equipment Aerospace High end automotive, industrial, etc. Also: strong, tough, high operating temperatures, thermal conductivity = 1/3 that of carbon steels, difficult to machine, more expensive than carbon steel ($5/lb vs $0.5/lb). Key Points: SS can also be classified by crystal structure (austenitic, ferritic, martensitic) Best corrosion resistance (CR): Austenitic (25% Cr) Middle CR : Ferritic (15% Cr), Least CR: Martensitic (12% Cr), but strongest Key Points: Over 150 grades of SS available, usually categorized into 5 series containing alloys w/ similar properties. AISI classes for SS: 200 series = chromium, nickel,manganese (austenitic) 300 series = chromium, nickel (austenitic) 400 series = chromium only (ferritic) 500 series = low chromium 12% (martensitic) 600 series = Precipitation hardened series (17-7PH, 17-7 PH, 15-5PH) 200/300 Series SS (Austenitic): Most common SS (roughly 70% of total SS production) Used for flatware, cookware, architecture, automotive, etc. 0.15% C (max), 16% Cr (min) and Ni or Manganese Austenitic, High strength, best corrosion resistance.