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Sun W.,Shandong Iron and Steel Co. | Hu S.-E.,Shandong Iron and Steel Co. | Li G.,Shandong Iron and Steel Co. | Yu H.,University of Science and Technology Beijing
7th International Conference on High Strength Low Alloy Steels, HSLA Steels 2015, International Conference on Microalloying 2015, Microalloying 2015 and International Conference on Offshore Engineering Steels 2015, OES 2015 | Year: 2015

This paper analyzes precipitation and dislocation strengthening behaviors of a 27mm thick Niobium-bearing Grade X80 steel plate for strain based design line pipe manufacture. The steel is produced by thermal-mechanical processing (TMCP) and is characterized with granular bainite and polygonal ferrite microstructure. Mechanical properties of both the steel and the UOE pipe are briefly introduced. Transmission electron microscope (TEM) is used to investigate the fine grain structure, distribution of the precipitates and dislocations in the steel. Precipitate morphologies, volume fractions of M(C,N), M3C, CaS, A1N and Cu are extensively studied respectively by Electrolytic Chemical Phase Analysis (ECPA) and X-ray Small Angle Diffraction (X-ray SAD). Dislocations in the steel are characterized with Positron Annihilation analysis. The results prove that precipitation hardening reveal a 58.1MPa strengthening contribution by the precipitates less than 20nm in size. Dislocation hardening is approximately 176MPa to the present studied steel and 198MPa to the pipe.

Liu X.,Shandong University | Liu X.,Shandong Iron and Steel Co. | Feng Y.,Shandong Iron and Steel Co. | Yang H.,Shandong University | And 5 more authors.
Jinshu Rechuli/Heat Treatment of Metals | Year: 2015

Phase transformation rule, microstructure and properties of 500 HBW wear-resistant steel were investigated. The results show that when the chemical composition of steel is given, the quenching cooling rates after austenitizing greatly affect on microstructure and the properties of steel. When cooling rate from 3℃/s to 55℃/s, the hardness of the steel changes from 341 HV10 to 596 HV10, the tensile strength varies from 979 MPa to 1690 MPa correspondingly. The hardness and tensile strength increase with increasing of cooling rates. The main cause is due to appearance and increasing of bainite and martensite at higher cooling rate other than ferrite and pearlite at lower cooling rate. ©, 2015, Chinese Mechanical Engineering Society of Heat Treatment. All right reserved.

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