The critical pitting temperature, which is an indicator of corrosion resistance in aqueous chloride media, may be reduced from 60 to 40°C for a type 316 stainless steel weld in 0.1% NaCl solution with an applied potential of +300 mV SCE. To ensure the highest standard in quality, Accredited Fabricators belong to the ASSDA Accreditation Scheme, an ASSDA initiative that is intended to achieve self regulation of the industry, for the benefit of both industry members and end users. The colors formed are similar to the ‘temper colors’ seen on other steel surfaces following heat treatment and range from pale straw hues to dark blue. The rainbow stain on stainless steel is what we call "heat tint." This is particularly important where the root bead is thin and is nearly re-melted by the second bead. A technician electrochemically cleans a circumferential weld joint on a rolled section of stainless steel to ensure complete passivation occurs. Change ), Misconception: More the Hardness, More is the wear resistance. The color combination depends largely on the amount of heat used during welding – darker colors (brown, blue, and purple) are usually formed at higher temperatures (> 370 °C or 698 °F). Tests performed in various corrosive environments have shown that susceptibility to pitting and crevice corrosion is greater when the surface is heat-tinted, and the colour of the heat-tint is an indicator of the degree of susceptibility to corrosion. When heat tint scale forms, chromium diffuses outward from the base metal in the heated zone. THIS INFORMATION MUST BE USED WITH CARE WHEN INTREPETING THE HINT TINT COLOURS OBSERVED ON STAINLESS STEEL SURFACES AS THE HEATING CONDITIONS ARE NOT SPECIFIED. The oxygen content of the atmosphere is normally sufficient to create and maintain this passive layer. While it is possible to paint or tint stainless steel, the only ways to permanently alter the color are through chemical changes or heat. Argon/nitrogen backing gases produce good results when welding highly alloyed stainless steels, such as duplex and super-austenitic stainless steels. See more information about Materials and Corrosion Management or please contact us. Contact Us. Oxidation of the root bead and adjacent HAZ during welding of stainless steels is commonly called heat-tint. naDesign FIGURE 1 >i»>>he dark heat tint formed alongside welds during welding of stainless steel (55)-theheat-affected zone (HAZ)-isa thicker chromium oxide scale with a mixture of iron, nickel, and other oxides. Mechanical means can be sand blasting or grinding or abrading. Because of the change in the metallurgical structure caused by carbide precipitation, the heat affected zones are more susceptible to corrosion because of the chrome and carbon being drawn to the surface. ( Log Out /  Most specifications require that the back purge be maintained until the root and hot pass, and sometimes the first few fill passes, are completed or until the temperature of the root region is below about 250°C. In order to restore corrosion resistance, the scale and the Cr-depleted layer must be removed by post-weld cleaning. Heat tints are often seen in heat affected areas of welded stainless steel fabrications, even where good gas shielding practice has been used (other weld parameters such as welding speed can affect the degree of heat tint color formed around weld bead). Topic Welding Industry / Technical Discussions / Stainless steel discoloration By apiguy Date 06-19-2002 16:16 Does anyone know where I can obtain a chart that would describe the heat tint discoloration of stainless steels. Dip a soft cloth in vinegar and rub over the surface of the stainless steel. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. Heat tint is the result of the thickening of the naturally occurring transparent oxide layer on the surface of the steel. It steel is protected from corrosion by a thin, impervious, invisible surface layer – the passive layer-that consists mainly of chromium oxide. This discoloration is called heat tint. As heat tints are formed on the stainless steel chromium is drawn to the surface of the steel, as chromium oxides forms more readily … Facebook; ... with a stainless steel brush, or sand blasting may also be used but are less effective because they generally do … For example, purple-blue oxides are generally the most susceptible to corrosion attack. However, it may be beneficial to reduce the gas flow pressure slightly after the root pass to stop an over-pressure build up. 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