P110 Steel Duplex Structure

In this paper, a kind of P110 casing steel whose carbon content is 0.24% was chosen for study of dual-phase steel. The micro structural features, mechanical properties, and corrosion resistance properties was carefully studied when its microstructure is quarter-phase.After full annealing process, the pearlite-ferrite microstructure was obtained. The microstructure makes P110 steel had a high plasticity so that its elongation was up to 39%. A kind of annealing process was selected as preparation for quenching process according to the uniformity of microstructure.The microstructure of P110 steel was transformed into the martensite-ferrite microstructure by intercritical quenching. Whether quenching medium was salt water or machine oil, the temperature range of such microstructure was 700℃～760℃.The higher quenching temperature was. the rougher martensite's structure was, and the greater volume fraction of martensite was. Hardness obtained by oil quenching was lower than by water quenching. As quenching temperature increased, hardness and strength of P110 steel was rising. but the plastic property first increased and then decreased and obtained the maximum value when temperature is 730℃The quarter-phase microstructure of sorbite (or troostite) and ferrite was obtained by high-temperature (or medium-temperature) tempering after intercritical quenching. Under the same tempering process, how mechanical properties varied along with the quenching temperature increasing was very consistent with only quenching. The selection of quenching temperature among intercritical area could make tempered P110 steel obtain relatively lower yield ratio, higher uniform and total elongation.The corrosion rate of P110 steel in NaCl solution of different concentrations was measured by an electrochemical workstation. The results showed that the pearlite-ferrite and martensite-ferrite structure had no effect on corrosion rate; but the sorbite-ferrite structure made the corrosion resistance properties worse.