Microstructure And Mecha Nical Properties Of Dispersion Strengthening 20 Steel By Tio₂ Particles

The aim of this work is to strengthen 20 low-carbon steel by introducing the admixture of TiO₂ particles and iron powder using the mediun frequency induction melting furance. The 20 low-carbon steel by 0.48Vol%TiO₂ particles dispersion strengthening sample was prepared. The microstructural transformation of the cast, normalized and quenched original 20 steel and strengthened 20 steel was observed by using the optical microscope, the Vickers hardness with different heat treatments was measured by Vickers hardness testing system, and the mechanical properties was tested by the Instron5982 type universal testing machine.The TiO₂ particles dispersion strengthening steel was rolled at 850℃,900℃and 950℃with deformation 20%,25% and 30%, respectively. Subsequently, the stress-relief annealing was carried out at 570℃, 600℃and 630℃. The microstructural characteristics of the dispersion stengthened steel are analyzed by optical microscope after rolling normalized, quenched and rolled state, and then compared with the No.20 steel unstrengthened. The results showed that: After 910℃, 15min followed by air cooling the normalizing heat treatment and 925℃, 15min after the salt bath quenching heat treatment, compared with 20 low carbon steel, the grain sizes of the dispersion strengthened steel have different degree of reduction, in which the grain size of the dispersion strengthened steel after quenching is smaller and more uniform; for the untreated, the hardness of the 20 low-carbon steel, compared with the dispersion strengthening steel which containing 0.48Vol%TiO₂ particles, the average hardness, increases 52.6% from the 117.36Mpa to 179.15MPa; in the normalizing condition, the average hardness increases from the 130.76MPa to 206.81MPa, increases 58.16%; in the quenched condition, the average hardness increases from the 174.57MPa to 241.77MPa, increased 36.5%. At the room temperature, the mechanical properties both before and after rolling was measured under different conditions by the tensile tests. The results shows that before rolling, the mechanical properties of the dispersion strengthened steel increased compared with the 20 low-carbon under different heat treatment. At different rolling temperatures and deformations, then annealing also at different temperature, the mechanical properties of the dispersion strengthened steel has been also improved compared with the original steel, the yield strength increased up to 33%, and the good plasticity of the dispersion strrengthened steel is still maintained.The test results show that the 20 low-carbon steel strengthened by the TiO₂ dispersion obtained good mechanical properties.