The effect of vanadiumand niobium on the restoration behavior after hot deformation in mediumcarbon spring steels was investigated by use of a thermomechanical processing simuiator. It
A b + g coincidence positron lifetime spectrometer equipped with two electromagnetic lenses was constructed. The electromagnetic lens was used to have energy selected positron beam. It accomplished a time resolution of 385 ps (FWHM) for the total system with a Pilot U plastic scintillator. By using a silicon avalanche diode instead of Pilot U plastic scintillator to initiate start timing signals, the time resolution was improved to 345 ps (FWHM). With this method, in situ positron lifetime measurements at high temperatures or under high stresses can be attained easily.
This paper presents the results of the research activities of the subcommittee on Hydrogen Embrittlement of the Japan Pressure Vessel Research Council (JPVRC). The combined effect of temper embrittlement and hydrogen embrittlement in Cr-Mo steels is discussed. It has been recognized that Cr-Mo steels used widely in the refining and petrochemical industry are quite susceptible to temper embrittlement. Although the synergetic relation between temper embrittlement and hydrogen embrittlement is a matter of major concern, studies regarding this subject are rarely encountered. Task group VIII (TG8) of the JPVRC conducted fracture toughness tests for three kinds of 2.25Cr-1Mo steels and 2.25Cr-1Mo-0.3V steel. These steels were prepared by subjecting them to normalizing, tempering and post-weld heat treatments which simulated actual conditions. Some specimens were embrittled by step cooling (Socal −1 treatment). It was found that the threshold for hydrogen-induced fracture was lowered when the specimen was exposed to pressurized hydrogen gas (15MPa) for 48 hours at 450 °C and there was no marked indication of the synergetic action concerning this embrittlement.
In the field of offshore structure, the strength and the toughness required for steel plates used for oil resource development become higher as the installation areas of the structures move into arctic and deep water areas. High strength steel plates for offshore structures, which meet the low temperature specification, have been developed. Excellent properties of the steel plates have been achieved by micro-alloying, the latest controlled rolling and accelerated cooling technology. Excellent properties of weld joints have been also achieved by advanced metallurgical techniques, which are grain-refinement of the coarse grain heat affected zone (CGHAZ), reduction of Martensite-Austenite (M-A) constituent in inter-critically CGHAZ (ICCGHAZ), and improvement of the matrix toughness. These steels are designed for excellent weldability due to low weld cracking parameter (PCM) value up to 550 MPa class in yield stress, and also up to 101.6 mm in thickness with 420 MPa class in yield stress, and satisfying −40°C of crack tip opening displacement (CTOD) temperature specification for offshore structure.
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