Ohmaloy® 30 and Ohmaloy® 40 alloys are moderately magnetic, ductile stainless steels having extremely high electrical resistivity. In addition to imparting high electrical resistivity, the aluminum content in these iron-13% chromium-aluminum resistance alloys also provides oxidation resistance. These alloys are capable of resisting oxidation for continuous duty at temperatures up to 1800°F (982°C), and are satisfactory for intermittent heating in temperatures from 1800°F (982°C) to 1900°F (1038°C). These Ohmaloy resistance alloy are classified as UNS K91470 and K91670. These are covered in ASTM B603 as Types IV and III, respectively.

Ohmaloy® 30 and Ohmaloy® 40 alloys are used in many applications requiring dissipation of electrical energy. Some examples are grid resistors for mine locomotives, crane starters and, the largest application, braking resistors for railroad diesel locomotives. These alloys are used where the application demands heavy-duty resistors with a small surface-to-volume ratio. They can also be used in applications where resistance heating is required.