![]() There are two ways to minimize chrome carbide precipitation, reducing the carbon content e.g. When welding stainless at high temperature, Cr combines with carbon and precipitates chrome carbides at the grain boundaries, significantly reducing corrosion resistance in the heat affected zone (HAZ).Īt high operating temperature this reduced corrosion resistance leads enhanced corrosion and working life in the HAZ, and is also more susceptible to stress fractures. Industrial applications such as chemical, coal and petroleum industries can operate at high temperature and would prefer 321 over 304.ģ04 is widely used in low temperature industry applications like furniture decoration, food, and medical industries. Titanium stabilized steel is the material of choice in applications with working temperatures in the 400 – 900 oC as it has improved stress fracture performance and high-temperature creep resistance, and its stress mechanical properties are superior to 304 stainless steel. Using 304L eliminates the need to anneal weld joints prior to using the completed metal form-saving time, effort, and money.ģ21 stainless steel belongs to the same 300 stainless steel series, and has very similar chemistry to 304 stainless steel with the addition of Titanium at 5 x carbon% value (max 0.7%). The titanium acts as a stabilizer and makes it more resistant to chromium carbide formation. This allows 304L stainless steel to be used in the “as-welded” state, even in severe corrosive environments. If the standard 304H stainless steel were used in the same way, it would degrade much faster at the weld joints than 304L. The 304L alloy’s lower carbon content helps minimize/eliminate carbide precipitation during the welding process. Grade 304L has a slight, but noticeable, reduction in key mechanical performance characteristics compared to grade 304H stainless steel. This means that if you had two stainless steel parts and both parts had the exact same design, thickness, and construction, the part made from 304L would be structurally weaker than the standard 304H part at high temperature (500 to 800 oC or 932-1472F). The low carbon minimizes sensitization, or chromium depletion at the grain boundaries of the material which would otherwise reduce its corrosion resistance. ![]() High carbon or “H” grades are used for higher strength. L-grade stainless steels are typically used for parts which cannot be annealed after fabrication by welding. The “L” grades are used to provide extra corrosion resistance after welding. ![]() In grade 304H, a chromium nickel stainless steel, carbon content is between 0.04 and 0.1% (typically 0.08%), whereas grade 304L stainless steel has a maximum carbon content of 0.03%. Increasing carbon content increases hardness and strength but increases brittleness. The metal’s properties such as weldability and heat or corrosion resistance depend on the carbon content. We focused on analyzing and sorting 304L & 321L from 304H and 321H.* PMI inspection companies know that the work of analyzing pipes and welds and determining their metal composition and carbon equivalency is crucial.Īs we noted in a previous article, the Low carbon 300 series stainless steel (SS) or “L grade”, e.g., 304L, was developed to combat “intergranular corrosion.” Low-carbon stainless steel has a proven resistance to most hostile chemical compounds and is used when the application requires maximum levels of resistance to corrosion and contamination – like in refineries.Ĭarbon works as a hardening agent. I spent a day at an inspection company that delivers Positive Material Identification (PMI) services to refineries.
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