Thickness and microstructure effect on hydrogen diffusion in creep-resistant 9% Cr P92 steel and P91 weld metal

Martensitic 9% Cr steels like P91 and P92 show susceptibility to delayed hydrogen assisted cracking depending on their microstructure. In that connection, effective hydrogen diffusion coefficients are used to assess the possible time-delay. Limited data on room temperature diffusion coefficients reported in literature vary widely by several orders of magnitude (mostly attributed to variation in microstructure). Especially P91 weld metal diffusion coefficients are rare so far. For that reason, electrochemical permeation experiments had been conducted using P92 base metal and P91 weld metal (in as-welded and heat-treated condition) with different thicknesses. From the results obtained, diffusion coefficients were calculated using to different methods, time-lag, and inflection point. Results show that, despite microstructural effects, the sample thickness must be considered as it influences the calculated diffusion coefficients. Finally, the comparison of calculated and measured hydrogen concentrations (determined by carrier gas hot extraction) enables the identification of realistic diffusion coefficients.

Study on Hydrogen Content in Cord Steel by Carrier gas hot extraction

Cord steel has very strict requirements on the content of impurities. Hydrogen is a harmful gas element in steel and is the cause of hydrogen embrittlement. In this work, the Carrier gas hot extraction method is used to measure the hydrogen content of 77A steel. It was found that the measured value of hydrogen content was related to cooling capability of the mold. It is found that with the increasing of cooling speed of the mold, the hydrogen content increases. The measured hydrogen content can roughly reflect the hydrogen content in the liquid alloy by using the cast iron mold with faster cooling speed.

Determining the Nitrogen Content in (Oxy)Nitride Materials

Nitrogen (and also oxygen) determination has become an important parameter to characterize (oxy)nitride materials for many properties and applications. Analyzing such anions with accuracy is still a challenge for some materials. However, to date, a large panel of methodologies is available to answer this issue with relevant results, even for thin films. Carrier gas hot extraction techniques and electron probe microanalysis with wavelength dispersive spectroscopy (EPMA-WDS) look attractive to analyze bulk materials and thin films, respectively. This paper gathers several techniques using chemical and physical routes to access such anionic contents. Limitations and problems are pointed out for both powders and films.

Design and application of a versatile gas calibration for non-metal determination by carrier gas hot extraction

Versatile gas calibration: flexible in composition and signal form by use of a gas mixing pump and an automated syringe.