Research on Carbide Characteristics and Their Influence on the Properties of Welding Joints for 2.25Cr1Mo0.25V Steel

The carbide characteristics of 2.25Cr1Mo0.25V steel have an extremely important influence on the mechanical properties of welding joints. In addition, hydrogen resistance behavior is crucial for steel applied in hydrogenation reactors. The carbide morphology was observed by scanning electron microscopy (SEM) and the carbide microstructure was characterized by transmission electron microscopy (TEM). Tensile and impact tests were carried out and the influence of carbides on properties was studied. A hydrogen diffusion test was carried out, and the hydrogen brittleness resistance of welding metal and base metal was studied by tensile testing of hydrogenated samples to evaluate the influence of hydrogen on the mechanical properties. The research results show that the strength of the welding metal was slightly higher and the Charpy impact value was significantly lower compared to the base metal. The hydrogen embrittlement resistance of the welding metal was stronger than that of the base metal. The presence of more carbides and inclusions was the main cause of the decreased impact property and hydrogen brittleness resistance of the welding metal. These conclusions have certain reference value for designing and manufacturing hydrogenation reactors.

Influence of thermal strengthening technology on variability of mechanical properties of rolled metal product

Rebars and coiled bar have a tendency to softening over time. After holding at the room temperature the ductility of the rolled products can be partially restored due to the processes of return and relaxation and also deposition of the diffusion-movable hydrogen from the steel. The reverse hydrogen brittleness and ageing are often observed, during production of the thermally strengthening rolled products. The variability of the mechanical properties of rebars and coiled bar of 25G2S, С70D and С82D steels with different diameters has been studied. It has been shown that tendency to softening is decreases during increasing of the strength class of the rebars (steel 25G2S) and it is related to deposition of the hydrogen in different quantities. Dynamics of increase of specific elongation for rebars turns out to be maximum in the first 30 days and growing rapidly (till 4,0…4,5 % abs.) over 90...120 days, then stabilizes and practically does not change over time. After use of the accelerated cooling at the final stage of the deformation heat treatment of the coiled bar of С70D high carbon steel the variability of specific elongation and reduction of area are characterized by a significant increase of ductility indexes within 3 days after primary testing. By research of variability of mechanical properties of coiled bar of С82D steel was established that during initial testing of samples (immediately after rolling) were recorded a low values of specific elongation and reduction of area (7,6…8,4 % and 15…24 % respectively) and while the progress of embrittlement have a tends to growth with increasing diameter. After holding of the coiled bar within 48...72 hours the parameters of the ductility for all diameters of rolled products are grow to 30...34% and stabilize over time. It has been shown that variability of the mechanical properties have a direct relations with the parameters of the structure, the initial hydrogen content in the steel and with degree of deformation processing of blank continuous casting.

Interaction between plastic deformation and hydrogen damage behavior of 30CrMnSiNi2A steel

The interaction between plastic deformation and hydrogen damage behavior of 30CrMnSiNi2A steel was investigated by pre-strain tensile tests and hydrogen charging by electrochemical method. This paper mainly contains two parts. The plastic deformation was restrained by hydrogen-charged, and the effect of hydrogen brittleness damage behavior was accelerated by pre-plastic deformation measure. Tensile pre-strian tests with hydrogen charging at current density from 0 to 50 mA/cm2 for 120 min were performed at room temperature. Both rate of reduction in areaand elongation were decreased due to the transition from ductile to brittle fracture by hydrogen charging, which meant the ability of plastic deformation was reduced by hydrogen. With hydrogen concentration increasing, yield strength also increased indicating that the plastic deformation forming conditions of steel were improved by hydrogen. Hydrogen content increased with pre-strain measured by glycerol gas collection method. Due to the pre-strain measure before hydrogen charging, the reduction of area and elongation were further reduced, while the strength was unexpectedly low. It was because pre-strain promoted the formation of hydrogen-induced crackings (HIC). This proved that the plastic deformation promoted the generation of hydrogen damage.

Research on Nickel-Plated Hydrogen-Absorption Device in Fuel Rod and Performance Testing

The hydrogen may be introduced into the fuel rod during the process of production and manufacture. During the operation in reactor, the irradiated fuel pellets also produce radioactive isotopes of hydrogen and tritium. Under the operating condition in pile, the hydrogen in fuel rod will enter the zirconium alloy cladding tube forming hydride, lead to the hydrogen brittleness of cladding tube, and severe cases can lead to the cladding tube broken. The radioactive tritium inside fuel rod has high activity, and it possibly goes through the cladding tube by diffusion penetration into the reactor coolant. With the reactor in waste water or steam waste emissions to the environment, such as lead to tritium radiation safety problems of environmental pollution. Thus, reduce the hydrogen source and tritium pressure in fuel rod, is the way to reduce the hydrogen absorption effect and the release of tritium to coolant. By conducting the Zr-4 alloy nickel-plated hydrogen-absorption device design research, through nickel plating process on the surface of Zr-4 alloy structure parts, eliminating the influence of the oxide film to maintain its excellent absorbing hydrogen isotope activity. During the design operating temperature conditions of fuel rods, the reaction of zirconium hydride has lower hydrogen balance pressure, while the gas cavity kept low pressure hydrogen isotope, can significantly reduce the hydrogen pickup of fuel rod zirconium alloy cladding tube and reduce the tritium permeation emissions by cladding tube. Through nickel-plated hydrogen-absorption device structure design, manufacture, performance testing, analysis and evaluation, demonstrates that the flat plate and cross nickel-plated hydrogen-absorption device can meet the expected effect.