Manganese is too brittle to be of much use as a pure metal. It is mainly used in alloys, such as steel.
“Ordinary” steel can contain about 1% manganese, to increase the strength and also improve workability and resistance to wear. “Manganese steel” contains about 13% manganese (Manufacture Of Manganese Steel (1908)).
Manganese steel is is extremely strong and is used for railway tracks (Manufacture Of Manganese-Steel Rails Or Shapes (1905)), safes (Improvements in Safes (1915)), bullet proof materials and prison gratings (Prison Safe-Custody Room Grating Comprizes Edge Reinforcement At Room Opening Anchored In Building Wall And Held In Manganese Steel Box Frame For Maximum Resistance (2000)).
Food cans are made of manganese alloy to improve resistance to corrosion (Thickness-Reduced Draw-Formed Can (1993)). With aluminium, and carbon for example, manganese forms highly magnetic alloys (Method For Making Manganese-Aluminium-Carbon Ternary Alloys For Permanent Magnets (1968)).
Manganese(IV) oxide is used as a catalyst (Preparation Of Manganese Dioxide Catalyst (1961)), and a rubber additive to enhance, for example, tyre properties (Rubber Composition For Tire Sidewall And Rubber Insert Comprising Silica With Manganese Dioxide Catalyst For Decomposing Ozone And The Tire Using The Rubber Composition (2015)).