The steel specimens of nominal composition 0.3C-1.0Cr-1.0Mn-2.0Si-1.0Ni- 0.04 Nb were quenched and tempered or isothermally quenched from various temperatures. It is found that the steel quenched and tempered with a...The steel specimens of nominal composition 0.3C-1.0Cr-1.0Mn-2.0Si-1.0Ni- 0.04 Nb were quenched and tempered or isothermally quenched from various temperatures. It is found that the steel quenched and tempered with a tensile strength of 1 500-1 600 MPa has a K ISCC (critical stress intensity factor) value below 15.0 MPa·m 1/2 . The steel isothermally quenched with a tensile strength of 1 350-1 750 MPa has a K ISCC value about 20.0 MPa·m 1/2 . In addition, with increase of isothermal quenching temperature, the tensile strength decreases greatly and K ISCC value does not pronouncedly change. The microstructure of isothermally quenched specimens is composed of bainite and retained austenite. The delayed fracture resistance is dependent on the stability of austenite, which is in turn related to the retained austenite volume fraction and carbon content in austenite.展开更多
ERH end-quenching method was used to determine the hardenability of four kinds hot-forging die steels with deep-hardening and hence the order of their hardenability was given.The tempering hardness of the steels was m...ERH end-quenching method was used to determine the hardenability of four kinds hot-forging die steels with deep-hardening and hence the order of their hardenability was given.The tempering hardness of the steels was measured and the tempering resistance was studied.It was approved that ERH method is effective for the determination of hardenability of deep-hardening steel and the beginning of hardness drop in the ERH specimen is caused by bainite occurring.展开更多
Polycrystalline samples of the new superconductor MgB_(2) are prepared by solid state reaction using Mg and B powders.The resistance measurement shows that the onset transition temperature and zero resistance transiti...Polycrystalline samples of the new superconductor MgB_(2) are prepared by solid state reaction using Mg and B powders.The resistance measurement shows that the onset transition temperature and zero resistance transition temperature are Tonsetc=43.8 K and Tc0=37 K,respectively.The Tc0 depends on measuring current strongly.The diamagnetic transition temperature of~38 K is obtained by the ac susceptibility measurement.X-ray powder diffraction spectra of MgB_(2) can be indexed using hexagonal structure with space group P6/mmm and lattice parameters a=0.30864 and c=0.35212 nm.A second phase,probably MgO,is also found.展开更多
基金Item Sponsored by Provincial Natural Science Foundation of Inner Mongolia of China(9610E22)
文摘The steel specimens of nominal composition 0.3C-1.0Cr-1.0Mn-2.0Si-1.0Ni- 0.04 Nb were quenched and tempered or isothermally quenched from various temperatures. It is found that the steel quenched and tempered with a tensile strength of 1 500-1 600 MPa has a K ISCC (critical stress intensity factor) value below 15.0 MPa·m 1/2 . The steel isothermally quenched with a tensile strength of 1 350-1 750 MPa has a K ISCC value about 20.0 MPa·m 1/2 . In addition, with increase of isothermal quenching temperature, the tensile strength decreases greatly and K ISCC value does not pronouncedly change. The microstructure of isothermally quenched specimens is composed of bainite and retained austenite. The delayed fracture resistance is dependent on the stability of austenite, which is in turn related to the retained austenite volume fraction and carbon content in austenite.
基金Project sponsored by Research Fund for Doctoral Program of Higher Education(9514509)
文摘ERH end-quenching method was used to determine the hardenability of four kinds hot-forging die steels with deep-hardening and hence the order of their hardenability was given.The tempering hardness of the steels was measured and the tempering resistance was studied.It was approved that ERH method is effective for the determination of hardenability of deep-hardening steel and the beginning of hardness drop in the ERH specimen is caused by bainite occurring.
基金Supported by the Ministry of Science and Technology of China(NKBRSF-G1999064602)the National Natural Science Foundation of China under Grant No.59872043the Fundamental Research Bureau,Chinese Academy of Sciences.
文摘Polycrystalline samples of the new superconductor MgB_(2) are prepared by solid state reaction using Mg and B powders.The resistance measurement shows that the onset transition temperature and zero resistance transition temperature are Tonsetc=43.8 K and Tc0=37 K,respectively.The Tc0 depends on measuring current strongly.The diamagnetic transition temperature of~38 K is obtained by the ac susceptibility measurement.X-ray powder diffraction spectra of MgB_(2) can be indexed using hexagonal structure with space group P6/mmm and lattice parameters a=0.30864 and c=0.35212 nm.A second phase,probably MgO,is also found.
