Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The eff...Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The effective grain size and the fraction of high angle grain boundaries in the pipeline steels were investigated by electron backscatter diffraction analysis. It is found that the low temperature toughness of the pipeline steels depends not only on the effective grain size, but also on other microstructural factors such as martensite-austenite （MA） constituents and precipitates. The morphology and size of MA constituents significantly affect the mechanical properties of the pipeline steels. Nubby MA constituents with large size have significant negative effects on the toughness, while smaller granular MA constituents have less harmful effects. Similarly, larger Ti-rich nitrides with sharp corners have a strongly negative effect on the toughness, while fine, spherical Nb-rich carbides have a less deleterious effect. The low temperature toughness of the steels is independent of the fraction of high angle grain boundaries.展开更多
In order to learn the variation laws of shear strength of side fillet weld post high temperatures, the tension tests were conducted after the double-strapped side fillet welded joints which were cooled down from diffe...In order to learn the variation laws of shear strength of side fillet weld post high temperatures, the tension tests were conducted after the double-strapped side fillet welded joints which were cooled down from different high temperatures with different cooling patterns. The tests indicate that specimens appear brittle fracture at the side fillet weld during the tension tests after cooling down. The fracture su（face is located in the welding throat. The maximum temperatures undergone and the cooling pattern are major factors influencing shear strength of side fillet welded joint post high temperatures. The shear strength reduces by 24% at most within 900 ~C. Based on the experimental results, the calculation formulas of shear strength of side fillet weld post high temperatures were proposed. Conclusions supply references for evaluation damage and reinforcement of steel structure post fire.展开更多
High strength low alloy steel with 16 mm thickness was welded by using high power laser hybrid welding. Microstrueture was characterized by using optical microscopy, scanning electron microscopy （ SEM ） , transmissi...High strength low alloy steel with 16 mm thickness was welded by using high power laser hybrid welding. Microstrueture was characterized by using optical microscopy, scanning electron microscopy （ SEM ） , transmission electron microscopy （TEM） and selected area electron diffraction （SAED）. Low temperature impact toughness was estimated by using Charpy V-notch impact samples selected from the upper part and the lower part at the same heterogeneous joint. Results show that the low temperature impact absorbed energies of weld metal are （202,180,165 J） of upper samples and （178,145,160 J） of lower samples, respectively. All of them increase compared to base metal. The embrittlement of HAZ does not occur. Weld metal primarily consists of refined carbide free bainite and a little granular bainite since laser hybrid welding owns the character of low heat input. Retained austenite constituent film ＂locates among the lath structure of bainitie ferrite. Refined bainitic ferrite lath and retained austenite constituent film provide better low temperature impact toughness compared to base metal.展开更多
This paper introduces the research and development of high strength A517Q developed by Baosteel for platform rack,with micro-alloying adding suitable quenching and tempering process,trial thickness of 127 - 178 mm hig...This paper introduces the research and development of high strength A517Q developed by Baosteel for platform rack,with micro-alloying adding suitable quenching and tempering process,trial thickness of 127 - 178 mm high-strength A517Q.The trial plate crossing thickness has a uniform mechanical properties, yield strength greater than 700 MPa,tensile strength than 790 MPa,the Charpy impact than 90 J at -40℃, aging impact than 69 J,has high strength and excellent low temperature impact toughness,While the plate has excellent resistance to crack tearing ability of low-temperature,NDT is less than -45℃.The Developing heavy plates had been used for manufacturing racks of 200-foot jack-up offshore platform,the performance meeting the requirements of the ABS,CCS classification societies.展开更多
文摘Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The effective grain size and the fraction of high angle grain boundaries in the pipeline steels were investigated by electron backscatter diffraction analysis. It is found that the low temperature toughness of the pipeline steels depends not only on the effective grain size, but also on other microstructural factors such as martensite-austenite （MA） constituents and precipitates. The morphology and size of MA constituents significantly affect the mechanical properties of the pipeline steels. Nubby MA constituents with large size have significant negative effects on the toughness, while smaller granular MA constituents have less harmful effects. Similarly, larger Ti-rich nitrides with sharp corners have a strongly negative effect on the toughness, while fine, spherical Nb-rich carbides have a less deleterious effect. The low temperature toughness of the steels is independent of the fraction of high angle grain boundaries.
基金The research is supported by the China Postdoctoral Science Foundation （No. 2011M501428）.
文摘In order to learn the variation laws of shear strength of side fillet weld post high temperatures, the tension tests were conducted after the double-strapped side fillet welded joints which were cooled down from different high temperatures with different cooling patterns. The tests indicate that specimens appear brittle fracture at the side fillet weld during the tension tests after cooling down. The fracture su（face is located in the welding throat. The maximum temperatures undergone and the cooling pattern are major factors influencing shear strength of side fillet welded joint post high temperatures. The shear strength reduces by 24% at most within 900 ~C. Based on the experimental results, the calculation formulas of shear strength of side fillet weld post high temperatures were proposed. Conclusions supply references for evaluation damage and reinforcement of steel structure post fire.
文摘High strength low alloy steel with 16 mm thickness was welded by using high power laser hybrid welding. Microstrueture was characterized by using optical microscopy, scanning electron microscopy （ SEM ） , transmission electron microscopy （TEM） and selected area electron diffraction （SAED）. Low temperature impact toughness was estimated by using Charpy V-notch impact samples selected from the upper part and the lower part at the same heterogeneous joint. Results show that the low temperature impact absorbed energies of weld metal are （202,180,165 J） of upper samples and （178,145,160 J） of lower samples, respectively. All of them increase compared to base metal. The embrittlement of HAZ does not occur. Weld metal primarily consists of refined carbide free bainite and a little granular bainite since laser hybrid welding owns the character of low heat input. Retained austenite constituent film ＂locates among the lath structure of bainitie ferrite. Refined bainitic ferrite lath and retained austenite constituent film provide better low temperature impact toughness compared to base metal.
文摘This paper introduces the research and development of high strength A517Q developed by Baosteel for platform rack,with micro-alloying adding suitable quenching and tempering process,trial thickness of 127 - 178 mm high-strength A517Q.The trial plate crossing thickness has a uniform mechanical properties, yield strength greater than 700 MPa,tensile strength than 790 MPa,the Charpy impact than 90 J at -40℃, aging impact than 69 J,has high strength and excellent low temperature impact toughness,While the plate has excellent resistance to crack tearing ability of low-temperature,NDT is less than -45℃.The Developing heavy plates had been used for manufacturing racks of 200-foot jack-up offshore platform,the performance meeting the requirements of the ABS,CCS classification societies.
基金Acknowledgement： The authors appreciate the support of the National Science Foundation of China （No. 50778025） and Hunan Provincial Natural Science Foundation of China （No. 07JJ6090）.
