material. The minimum 10.5% chromium in stainless steels provides resistance to approximately , while 16% chromium provides resistance up to approximately . Type 304, the most common grade of stainless steel with 18% chromium, is resistant to approximately . Other gases, such as sulfur dioxide, hydrogen sulfide, carbon monoxide, chlorine, also attack stainless steel. Resistance to other gases is dependent on the type of gas, the temperature, and the alloying content of the stainless steel. With the addition of up to 5% aluminium, ferritic grades Fr-Cr-Al are designed for electrical resistance and oxidation resistance at elevated temperatures. Such alloys include Kanthal, produced in the form of wire or ribbons. Standard finishes Standard mill finishes can be applied to flat rolled stainless steel directly by the rollers and by mechanical abrasives. Steel is first rolled to size and thickness and then annealed to change the properties of the final material. Any oxidation that forms on the surface (mill scale) is removed by pickling, and a passivation layer is created on the surface. A final finish can then be applied to achieve the desired aesthetic appearance. The following designations are used in the U.S. to describe stainless steel finishes by ASTM A480/A480M-18 (DIN): No. 0: Hot-rolled, annealed, thicker plates No. 1 (1D): Hot-rolled, annealed and passivated No. 2D (2D): Cold rolled, annealed, pickled and passivated No. 2B (2B): Same as above with additional pass through highly polished rollers No. 2BA (2R): Bright annealed (BA or 2R) same as above then bright annealed under oxygen-free atmospheric condition No. 3 (G-2G:) Coarse abrasive finish applied mechanically No. 4 (1J-2J): Brushed finish No. 5: Satin finish No. 6 (1K-2K): Matte finish (brushed but smoother than #4) No. 7 (1P-2P): Reflective finish No. 8: Mirror finish No. 9: Bead blast finish No. 10: Heat colored finish – offering a wide range of electropolished and heat colored surfaces Joining A wide range of joining processes are available for stainless steels, though welding is by far the most common. The ease of welding largely depends on the type of stainless steel used. Austenitic stainless steels are the easiest to weld by electric arc, with weld properties similar to those of the base metal (not cold-worked). Martensitic stainless steels can also be welded by electric-arc but, as the heat-affected zone (HAZ) and the fusion zone (FZ) form martensite upon cooling, precautions must be taken to avoid cracking of the