PSI - Issue 79

Hiroshi Nishiguchi et al. / Procedia Structural Integrity 79 (2026) 517–523

521

0 ％ ↓ Hydrogen cut ratio, R H,C (%)

Quenched Quenched & Tempered

Quenched Quenched & Tempered

Solution-treated

Quenched Quenched & Tempered

S45C

SCM435 steel

FC200

JIS-SUS304

Fig. 2. Hydrogen cut ratios of various materials and heat treatment conditions.

↓ Interface

↓ Interface

↓ Interface

↓ Interface

R H,C = 86.1% (b-1) Quenched

R H,C = 80.0% (b-2) Quenched and Tempered

R H,C = 0%

R H,C = 42.1% (a-2) Quenched and Tempered

(a-1) Quenched

(a) S45C steel

(b) SCM435 steel

Fig.3 Cross-sections of coating part.

To clarify the causes of the observed reduction in the hydrogen cut ratio, cross-sections of the coatings were examined. Fig. 3(a) shows cross-sectional micrographs of the S45C steel for the (a-1) quenched and (a-2) quenched and tempered specimens. In the quenched specimens, delamination was observed at the interface between the base material and coating, whereas delamination was observed only in localized regions in the quenched and tempered specimens. These observations suggest that one factor contributing to the reduction in hydrogen permeation prevention is the interfacial condition between the coating and the base material. Fig. 3(b) shows cross-sectional micrographs of SCM435 steel for the (b-1) quenched and (b-2) quenched and tempered specimens. In both cases, minimal delamination was observed and delamination was nearly nonexistent in the quenched and tempered specimens. Fig. 4 shows EDS and SEM images of SCM435 steel for (a) as-coated and (b) quenched specimens. The upper layer of the coating exhibited voids in the heat-treated coatings. Furthermore, aluminum was found to have diffused further into the substrate. This result suggests that aluminum diffused out of the upper Al layer during heat treatment, creating voids, and underwent secondary diffusion from the aluminum-rich layer into the substrate. Yamabe et al. (2015) reported that in coatings produced by the hot-dipping method, hydrogen permeation prevention was primarily governed by the interface between the Al layer and the Al/Fe intermetallic layer, as confirmed by secondary ion mass spectrometry (SIMS). Therefore, the reduction in hydrogen-blocking efficiency