Grade 303Se stainless steel is a modified version of the basic grade 303, where selenium is substituted for sulfur to enable machining. Grade 303Se offers excellent machinability, good strength, and corrosion resistance. It has the capacity to resist scaling at temperatures up to 871°C (1600°F). This stainless steel is commonly used in parts requiring cold forming after machining.

The machinability of grade 303Se can be performed at excellent speeds and feeds. Selenium gives this material a very brittle chip. Welding at high temperature is not recommended as the selenium in this material tends to precipitate at the weld boundary causing weak and brittle joints; however welding can be performed at low temperatures with the AWS E/ER312 as the recommended filler metal.

Annealing of the grade 303Se can be performed at 1010-1066°C (1850-1950°F) followed by rapid cooling. Cold working can be used to raise the hardness and strength characteristics of this material. Hot working treatments such as forging and upsetting can be performed when the material is well heated to 1149-1260°C (2100-2300°F). Hot working below 927°C (1700°F) is not advisable. Rapid cooling after working enhances corrosion performance.