The invention provides mild steel and a friction damper. The friction damper is mainly composed of oval friction plates, mild steel plates, fixing plates, center shaft anchor bolts, center shaft screw holes, fixing plate screw holes, friction plate spring clamping openings, springs and the like. The friction damper is characterized in that the two oval friction plates are arranged in an intersecting mode, two long shafts are perpendicular to each other, the mild steel plates are arranged on the outer sides of the two oval friction plates respectively, and a rectangular energy dissipation body is formed by the two oval friction plates and the two mild steel plates. The friction damper has the advantages that large initial stiffness can be achieved, under the action of wind vibrations and earthquakes, the friction damper can rapidly enter in an energy dissipation state, and moreover good energy-dissipating capacity can still be achieved under large deformation; the entire system is even in stress, stable and saving in material, and it is also guaranteed that the energy dissipation system is steady, effective, simple in structure, economical and practical; the friction damper can be used for the seismic design of novel constructional engineering and also can be used for reinforcement and maintenance of existing engineering.