Introduction to Stainless Steel Series Grades -- 303

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303 stainless steel has the best machinability among austenitic stainless steels. It is mainly used in situations where the production process involves a large amount of automated screw cutting operations. The machinability rating (compared to B1212) is approximately 78%. 303 also comes in a “Ugima” grade, which offers better machining properties and is superior to the standard 303 grade. The improved machinability and wear resistance of 303 stainless steel are due to the addition of sulfur, which also reduces its corrosion resistance, making it lower than that of 304 stainless steel. Like other austenitic stainless steels, 303 stainless steel possesses excellent toughness, although sulfur slightly reduces it. 303Se (UNS S30323) contains selenium instead of sulfur; compared to 303, it exhibits improved cold and hot formability, a smoother machined surface, as well as a slightly reduced machining speed. Corrosion resistance: It exhibits good corrosion resistance in mildly corrosive environments; however, due to the presence of sulfur, its corrosion resistance is significantly lower than that of 304 stainless steel, with sulfide inclusions acting as initiation points for pitting. 303 stainless steel should not be used in marine or similar environments, as such environments cause rapid pitting corrosion. Since the sulfide inclusions in 303 are mainly arranged along the rolling direction, the reduction in corrosion resistance across the cross-section is particularly noticeable. Like other common austenitic stainless steels, 303 is susceptible to stress corrosion cracking in chloride environments above about 50°C. It has good heat resistance and excellent oxidation resistance; it can withstand temperatures of up to 760°C when used intermittently, and up to 870°C when used continuously. 303 usually has a high carbon content, making it prone to sensitization, which can lead to intergranular corrosion. Due to carbide precipitation, continuous use in the temperature range of 425–860°C is generally not recommended. Processing: In addition to reducing corrosion resistance, the sulfur added to 303 also leads to a decrease in weldability and formability (compared to grade 304). 303 is not suitable for bending operations with a small radius. A compromise solution might be to use a grade of 304 with improved cutting properties – although its machinability is inferior to that of 303, it offers better formability, excellent weldability, and significantly improved corrosion resistance. Heat treatment: Solution treatment (annealing) – heating to 1010–1120°C and rapid cooling. This grade cannot be hardened through heat treatment. Welding is generally not recommended, but if it is unavoidable, 308L or 309 welding rods should be used. The welds must be annealed to achieve optimal corrosion resistance; however, even this leads to a decrease in mechanical and corrosion-resistant properties. Machining: Many bar products are available in the 303 grade, which features improved machinability; it even offers better machinability than standard 303, with very high machining speeds and less tool wear. If extremely high machining speeds are required, special grades such as Ugima 303UX can be used. In addition to typically containing a high level of sulfur and employing steelmaking processes to improve cutting performance, it also contains copper to reduce the rate of work hardening. Typical applications: nuts and bolts, bushings, shafts, components of electrical switching equipment, gears. Generally, this grade can be used for any component that requires extensive machining, as well as in applications where the corrosion resistance and manufacturing properties of 303 meet the requirements. The performance data specified in the standard specifications: ASTM A582M specifies the properties of long products (rods). For other products such as wires and forgings of corresponding specifications, similar but not necessarily identical properties are specified.