W.C. Luu

The influence of microstructure on hydrogen transport in carbon steels

An electrochemical permeation technique was performed on mild steel and S45C medium carbon steel. Mild steel shows higher permeation rate and diffusivity than medium carbon steel. The highest permeability and diffusivity for heat treated medium carbon steels are observed in the spheroidized condition and least permeability and diffusivity are in the martensitic condition. Annealed and normalized structures yield intermediate values of permeation rate and diffusivity. A monolayer of AgBr emulsion was coated on the determination site of a specimen to observe hydrogen transport in carbon steel. This hydrogen microprint technique also confirms that the main diffusion path is lattice and carbide/ferrite interfaces in pearlitic and spheroidized steels, and lath interfaces in martensitic steel.

Hydrogen transport and degradation of a commercial duplex stainless steel

Hydrogen embrittlement of 2205 duplex stainless steel has been evaluated using electrochemical permeation measurement, hydrogen microprint technique and tensile test in this study. Due to hydrogen transport in 2205 duplex stainless steel is mainly lattice diffusion in ferritic phase, more hydrogen distribution, higher permeation rate and diffusion in ferritic phase were detected. Brittle fracture was observed in both the ferritic and austenitic phases of hydrogen precharged specimen.

Effect of hydrogen environment on the notched tensile properties of T-250 maraging steel annealed by laser treatment

In the present work, slow displacement rate tensile tests were performed to find out the influence of ageing condition and hydrogen-charging on the notched tensile strength and fracture characteristics of T-250 maraging steel aged at various conditions. The influence of embrittling species in the environment on the notched tensile strength was accessed by comparing the measured properties in air, gaseous hydrogen and H2S-saturated solution. The hydrogen diffusivity, permeation flux and apparent solubility of various specimens determined by electrochemical permeation method, were correlated well with the microstructures and mechanical property. The results indicated that the peak-aged (H900) specimen was highly sensitive to hydrogen embrittlement even in gaseous hydrogen. In contrast, the microstructures of over-aged (H1100) specimen comprising of reverted austenite and incoherent precipitates could trap large amount of hydrogen atoms, resulting in decreased hydrogen permeability and hydrogen embrittlement susceptibility. The solution-annealed specimen had the highest diffusion coefficient and the lowest quantity of trapped hydrogen among the specimens, showing high susceptibility to sulfide stress corrosion cracking. In the presence of notches, hydrogen atoms were prone to segregate and trap at grain boundaries, resulting in the formation of intergranular fracture.

Hydrogen permeation in a submerged arc weldment of TMCP steel

Abstract The effects of the heterogeneous microstructure at the base metal, the heat affected zone (HAZ) and weld metal on hydrogen permeation in thermo-mechanical controlled rolling (TMCP) steel weldments have been investigated. The base metal with equiaxed refined ferrite and scattered fine grain pearlite has the highest permeation rate and effective diffusivity. The HAZ with bainite shows the lowest values of the permeation rate and effective diffusivity. Weld metal yields a higher permeation rate coupled with an intermediate diffusivity value. The hydrogen apparent solubility is low for the base metal, intermediate for the HAZ and high for the weld metal. The mechanisms of hydrogen diffusion path and hydrogen traps are discussed and experimentally confirmed using the hydrogen microprint technique. The high diffusivity paths and the hydrogen trapping site are the grain boundary and the ferrite/carbide interfaces for both the base metal with refined ferrite and the HAZ with bainitic microstructure. The spaces among the basket-weave acicular ferrite, where the martensite and the retained austenite (M/A) constituents present, are the main hydrogen trapping sites for the weld metal.

Effects of sulfide inclusion on hydrogen transport in steels

The electrochemical permeation measurement and hydrogen microprint technique have been used to characterize hydrogen transport and trapping in mild steel and resulfurized low carbon steel. These techniques confirm that the main diffusion path is the lattice and MnS inclusion-matrix interfaces. In resulfurized steel, trapping at MnS inclusion-matrix interfaces is dominant site.

Influence of aluminium content on retarding hydrogen transport in Fe–Al binary alloys

Abstract The electrochemical hydrogen permeation measurement was utilized to determine the effective diffusivity, permeation rate and apparent solubility of hydrogen in a series of Fe–Al binary alloys at 25°C. The experimental results reveal that both the hydrogen effective diffusivity and permeation rate in these alloys are significantly dropped when Al content is more than 15–20 at.%. The hydrogen apparent solubility in these alloys is reduced with the increment of Al content, even though their lattice parameters and strain fields in these alloys are increased. For these Fe–Al binary alloys, the retardation factor of hydrogen is mainly dependent upon Al content. Both oxide film and the degree of structural order are the major retardation factors on hydrogen transport in Fe–Al binary alloys.

Hydrogen transport and environmental embrittlement effects in iron aluminides

Environmental embrittlement types of six iron aluminides have been systematically evaluated using electrochemical hydrogen permeation measurement, hydrogen microprint technique and tensile test in this study. The results of hydrogen permeation and microprint technique show that three α - disordered solid solution structure of binary and ternary iron aluminides (Fe-10Al, Fe-18Al, and Fe-18Al-5Cr) have higher effective diffusivity and permeation rate than B2 ordered structure of binary and ternary iron aluminides (Fe-28Al, Fe-28Al-5Cr, and Fe-40Al). The tensile test of six iron aluminides in air, vacuum treatment and hydrogen precharged were analyzed and concluded. Three α - disordered solid solution structure of iron aluminides suffer in hydrogen environment which are quite different embrittlement mechanisms from those B2 ordered structure of iron aluminides with serious tensile loss in air by moisture induced embrittlement.

Moisture and hydrogen-induced embrittlement of Fe3Al alloys

Abstract Environmental embrittlement types of Fe3Al and Fe3Al–5Cr alloys have been evaluated using hydrogen microprint technique and tensile test in this study. The hot rolled iron aluminides offer better tensile strength and ductility in comparison to the as-cast iron aluminides in all test environments. Due to the fact that hydrogen transport in Fe3Al and Fe3Al–5Cr alloys is mainly lattice diffusion, the cleavage strength is decreased significantly by hydrogen.

Hydrogen permeation through nickel-plated steels

Abstract In order to control the hydrogen embrittlement problems of steels, electrochemical hydrogen permeation experiments and hydrogen microprint technique were performed on nickel plated and electroless nickel (EN) plated steels to evaluate the beneficial effect of the impermeable coating. EN plating which had been annealed at 400 °C for 1 h led to a lowest hydrogen permeation rate and effective diffusivity due to its high hydrogen barrier efficiency. The effective diffusivity of the nickel plating and EN plating layers were calculated from permeation data of coated steels.