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Abstract: Surface hardening of 17-4PH was achieved by laser transformation hardening using 5kW continuous wave CO2 laser system. The microstructure of the laser-quenched sample was investigated by optical microscopy, transmission electron microscope and 57Fe Mössbauer spectrometer. The hardness profile was determined by a Vickers hardness tester. The hardened layer with a thickness of 1.75mm was formed, and it was composed of classic lath martensite, coarse NbC and a lot of finer fcc copper-rich phases which were similar to ɛ-Cu precipitates. The maximal hardness value of hardened zone is 446HV which is 50HV higher than that of the substrate (386–397HV). The higher hardness in laser transformation layer of the 17-4PH steel could be attributed to the following aspects: the matrix with a high dislocation density; the fine microstructure; the finer fcc copper-rich phases that were similar to the ɛ-Cu precipitates as well as the transforming of retained austenite into lath martensite. [Copyright &y& Elsevier]

Hydrogen transportation by pipelines gradually becomes a critical engineering route in the worldwide adaptation of hydrogen as a form of clean energy. However, due to the hydrogen embrittlement effect, the compatibility of linepipe steels and associated welds with hydrogen is a major concern when designing hydrogen-carrying pipelines. When hydrogen enters the steels, their ductility, fracture resistance, and fatigue properties can be adversely altered. This paper reviews the status of several demonstration projects for natural gas-hydrogen blending and pure hydrogen transportation, the pipeline materials used and their operating parameters. This paper also compares the current standards of materials specifications for hydrogen pipeline systems from different parts of the world. The hydrogen compatibility and tolerance of varying grades of linepipe steels and the relevant testing methods for assessing the compatibility are then discussed, and the conservatism or the inadequacies of the test conditions of the current standards are pointed out for future improvement. [Display omitted] • Summarized projects of pure-hydrogen and natural gas-hydrogen blending pipelines. • Discussed the factors affecting hydrogen compatibility of pipeline. • Reviewed the testing methods for assessing hydrogen-steel compatibility. • Presented a new proposal for toughness test for pipeline slow loading condition. • Several challenges facing the high-pressure hydrogen pipelines are outlined. [ABSTRACT FROM AUTHOR]