304 SS / 304L SS

Type 304L is an extra low-carbon variation of Type 304 with a 0.03% maximum carbon content that eliminates carbide precipitation due to welding.
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탄화물 침전(Carbide Precipitation)
오스테나이트 스테인레스강이 안정화되어 있지 않거나 탄소함량이 낮지 않은 경우 발생한다. 427∼871℃의 온도에서 Cr4C가 경계면으로 석출하여 경계면 근처에 Cr함량이 낮아진다. 심할 경우에 탄화물의 띠가 경계면을 따라 형성되고 부식 및 균열에 대한 저항이 감소하므로 운전 및 정비시 주의가 요구된다.




              <Carbide Precipitation in Stainless Steel>





 Corrosion Resistance
There is usually no difference in corrosion resistance between 304 and 304L.


Heat Resistance
Good oxidation resistance in intermittent service to 870°C and in continuous service to 925°C. Continuous use of 304 in the 425-860°C range is not recommended if subsequent aqueous corrosion resistance is important. Grade 304L is resistant to carbide precipitation and can be heated into this temperature range.


Welding
Heavy welded sections in Grade 304 may require post-weld annealing for maximum corrosion resistance. This is not required for Grade 304L. Grade 321may also be used as an alternative to 304 if heavy section welding is required and post-weld heat treatment is not possible.


“Dual Certification”
It is common for 304 and 304L to be stocked in “Dual Certified” form, particularly in plate, pipe and round bar. These items have chemical and mechanical properties complying with both 304 and 304L specifications. Such dual certified product may be unacceptable for high temperature applications.