Yukitaka Murakami

A New Nonmetallic Inclusion Rating Method by Positive Use of Hydrogen Embrittlement Phenomenon

A new inclusions rating method using hydrogen embrittlement of a tensile test specimen is proposed. This method is essentially based on the statistics of extremes for inclusion rating where the maximum inclusion size is determined by simple tensile testing of a hydrogen-precharged (H-precharged) specimen. Tensile tests were conducted using two bearing steels (SAE52100 HV 346, HV 447, HV 559, HV 611, HV 678 and ASTM-A485-1 HV 706, HV 715) and one spring steel (SAE5160, HV 651). Fatigue tests were conducted using SAE52100 bearing steel (HV 682). All H-precharged tensile specimens (SAE52100, ASTM-A485-1 and SAE5160) were fractured from internal inclusions except the SAE52100 tensile specimens with a Vickers hardness of HV 346. It was confirmed that the distribution of extreme values of inclusion sizes obtained by SAE52100 tensile testing with H-precharged specimens coincided with those obtained by SAE52100 fatigue testing. From these results, it is presumed that the inclusion rating method by fatigue testing can be replaced by simple tensile testing with H-precharged specimens. The proposed method is more convenient and reliable than other existing inclusion rating methods, i.e., fatigue testing and optical microscopy. The proposed method can be applied to specimens with a Vickers hardness of higher than HV 447.

Highly sensitive detection of net hydrogen charged into austenitic stainless steel with secondary ion mass spectrometry.

Secondary ion mass spectrometry (SIMS) is used to detect local distributions of hydrogen in various materials. However, it has been well-known that it is extremely difficult to analyze net hydrogen (H(N)) in metals with SIMS. This was because hydrogen, which is originated from moisture (H(2)O), hydrocarbon (C(x)H(y)) or other organic materials (C(x)H(y)O(z)) existing on a sample surface or in the SIMS chamber, is simultaneously detected in the SIMS measurement of the H(N), and the H(N) and the background-originated hydrogen (H(BG)) cannot be distinguished in a SIMS profile. The effective method for reductions and determinations of the H(BG) in hydrogen measurements of metallic materials with the SIMS method has not been established. The present paper shows an effective method for reduction and estimation of H(BG) in SIMS analyses of hydrogen charged into type 316 L austenitic stainless steel, and an accurate estimation method of the net charged hydrogen. In this research, a silicon wafer is sputtered by a primary ion beam of a SIMS near an analyzed area (silicon sputtering method) to reduce H(BG). An uncharged type 316 L sample was prepared for estimation of H(BG) in SIMS measurements of the hydrogen-charged sample. The gross intensities of hydrogen between the hydrogen-charged sample and the uncharged sample were compared. The gross intensities of hydrogen of the uncharged sample (26.8-74.5 cps) were much lower than the minimal gross intensities of hydrogen of the hydrogen-charged sample (462-1140 cps). Thus, we could reduce the H(BG) enough to estimate the hydrogen charged into the type 316 L sample. Moreover, we developed a method to determine intensities of H(BG) in the measurement of the hydrogen-charged sample by estimating the time-variation of hydrogen intensities in the measurements of the uncharged sample. The intensities of the charged hydrogen can be obtained by subtracting the estimated intensities of the H(BG) from the gross intensities of hydrogen of the hydrogen-charged sample. The silicon sputtering method used to reduce H(BG) and the determination method for H(BG) in this research can be applied to the accurate hydrogen analysis for other various metallic materials.