ISO 16573-2 pdf download – Steel – Measurement method for theevaluation of hydrogen embrittlement resistance of high-strength steels —Part 2: Slow strain rate test.
e) To assure the reliability, at least 3 specimens shall be tested with the same cross head speed.
f) Alter the slow strain rate test, measure diffusible hydrogen contents of the specimen immediately. If it is impossible to measure diffusible hydrogen content iust after the test, specimens should be preserved below -50 °C. preferably In liquid nitrogen, to prevent hydrogen release from the fractured surface. Freezer or dry ice box where the temperature is controlled under -50°C shall be used to preserve the specimens. In such cases, maximum preservation period should he one week. Alternatively, the thermal desorption analysis of pre-charged but not stressed samples allows the quantification of the initial diffusible hydrogen content.
8.3 Presentation of the results
a) Several examples of the results obtained by the slow strain rate test are shown in FiguresA, 5 and . Results shall be displayed in the form of curves in which the horizontal axis represents the diffusible hydrogen content and the vertical axis represents the susceptibility to hydrogen embrittlcment through the property chosen for representing it. Figures shall be drawn in log-log coordinates. Results shall also be expressed as coefficients a and b where log(Y) = a loglo(X) + b. Curves generally contain at least 5 measured values. Those measured data shall be regularly distributed. The ratio of diffusible hydrogen contents of maximum value and minimum value should be at least 10,
h) In EigureA. the horizontal axis indicates the diffusible hydrogen content of the specimens and the vertical axis represents either fracture strength in the smooth specimen or notched fracture strength in the notched specimen. In Figure 5. the horizontal axis should be the diffusible hydrogen content, and the vertical axis represents notch tensile strength. In the case of smooth specimen, the vertical axis may represent ductility such as reduction of area or elongation to fracture as shown in FIgure 6.
c) In Eigirej.4 to , the vertical axis shall be replaced by the parameter such as fracture strength! tensile strength, and/or the horizontal axis shall be replaced by current density (mA/mm2).
d) It shall he concluded that the susceptibility of hydrogen embrittlement is severe if the vertical axis parameter of a material Is lower than that of the competitive material at the specific diffusible hydrogen content, or at the specific current density.
e) As an additional evaluation method, local hydrogen concentration and local stress may be calculated by numerical method for comparing the results of specimens with different stress concentration factors[2].
10 Hydrogen thermal desorption10.1 General
Diffusible hydrogen is generally calculated by integrating the first peak of the curve of thermaldesorption analysis. In the case of tempered martensitic steel, when several peaks are observed atlow temperature (i.e. below 400 C), diffusible hydrogen may be calculated by integrating peaks below400 C of the curve of thermal desorption analysis. in the case of drawn pearlite steel, calculation isnecessary by integrating the hydrogen desorption curve having a peak in the vicinity of 100 °C only. Ifpeaks at i00·Cand 300 Coverlap, measure from the room temperature to the lowest point between thetwo peaks. In the range of the heating rate of up to 200 °C/h, the heating rate does not have a significanteffect on the test results. The 100C/h heating rate is recommended. When the heating rate is over200 C/h, hydrogen desorption will not end with up to 400 °C.Then,make a calculation by integratingthe range until the appropriate hydrogen desorption is terminated.The heating rate shall be reported.10.2 Experimental apparatus (gas chromatograph)
The equipment for thermal desorption analysis consists of three parts: heating, gas sampling, anddetecting.When the specimens are heated, hydrogen inside of the specimens diffuses out and flowsinto the gas chromatography column with carrier gas (high purity Ar or He gas). The heating rate wasfixed at any value of up to 200 °C/h, and the specimen is heated up to 400 °C.The 100 C/h heating rateis recommended. Gases can be separated by ‘an adsorption column. For the accurate measurement ofhydrogen content, measuring the background is recommended.
ISO 16573-2 pdf download – Steel – Measurement method for theevaluation of hydrogen embrittlement resistance of high-strength steels —Part 2: Slow strain rate test
