Mechanical properties refer to the mechanical characteristics of materials under different environments when they bear various external loads (tensile, compression, bending, torsion, impact, etc.). The mechanical properties of bridge steel castings mainly include tensile properties and impact properties, which are tested by microcomputer controlled electro-hydraulic servo universal testing machine and impact testing machine respectively.
Tensile properties include tensile strength, lower yield strength, reduction of area and elongation after fracture. Tensile strength is the critical value of metal from uniform plastic deformation to local concentrated plastic deformation, and it is also the maximum bearing capacity of metal under static tension; yield strength is the yield limit of metal material when yielding phenomenon occurs, that is, the stress resisting micro plastic deformation. The lower yield strength is the minimum stress in the yield stage without considering the initial instantaneous effect. In the tensile test, the percentage of the length increased by the gauge length to the original gauge length after the specimen is broken is called the elongation; the ratio of the reduced area to the original area is called the reduction of area.
Impact properties, namely impact toughness, mainly include room temperature impact toughness and low temperature impact toughness. Temperature has a great influence on metal materials. Long term use in high temperature, low temperature or large temperature difference environment will lead to abnormal damage of metal materials. When iron and steel materials are used at low temperature, the impact toughness of steel materials decreases significantly when the temperature is lower than a certain temperature. The critical temperature is called ductile brittle transition temperature. There is no obvious ductile brittle transition temperature for austenite in fcc lattice, while the increase of BCC lattice, such as ferrite, pearlite and martensite, will show obvious low temperature brittleness below the ductile brittle transition temperature.
In recent years, with the extensive construction of iron main bridge, the service environment of bridge bearing is more severe, especially in cold areas, such as the service environment of main bridge bearing of China and Russia is – 40 ℃, so the impact toughness of steel for bridge bearing is required to be higher.
