400 Series are ferritic and martensitic chromium alloys. The 400 series group of stainless steels has an 11 percent chromium and 1-percent manganese increase, above the 300 series group. 400 Series Ferritic and Martensitic Stainless Steel grades detail are as follow:
Type 405—ferritic for welding applications
Type 408—heat-resistant; poor corrosion resistance; 11% chromium, 8% nickel.
Type 409—cheapest type; used for automobile exhausts; ferritic (iron/chromium only).
Type 410—martensitic (high-strength iron/chromium). Wear-resistant, but less corrosion-resistant.
Type 416—easy to machine due to additional sulfur
Type 420—Cutlery Grade martensitic; similar to the Brearley's original rustless steel. Excellent polishability.
Type 430—decorative, e.g., for automotive trim; ferritic. Good formability, but with reduced temperature and corrosion resistance.
Type 439—ferritic grade, a higher grade version of 409 used for catalytic converter exhaust sections. Increased chromium for improved high temperature corrosion/oxidation resistance.
Type 440—a higher grade of cutlery steel, with more carbon, allowing for much better edge retention when properly heat-treated. It can be hardened to approximately Rockwell 58 hardness, making it one of the hardest stainless steels. Due to its toughness and relatively low cost, most display-only and replica swords or knives are made of 440 stainless. Available in four grades:
Type 440A—has the least amount of carbon making this the most stain-resistant.
Type 440B—slightly more carbon than 440A.
Type 440C—has the greatest amount of carbon of the Type 440 variants. Strongest and considered more desirable in knifemaking than the Type 440A variant[citation needed], except for diving or other salt-water applications. This variant is also more readily available than other variants of Type 440.
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