PSI - Issue 79

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

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Table 1. Heat treatment conditions.

Material

Type of Heat Treatment

Heat Treatment Conditions

S45C (Carbon steel)

2) Quenching and Tempering

1) Quenching

Quenching: Heated to 850 o C for 1h, then oil cooling Tempering: Heated to 635 o C for 1h, then water cooling

SCM435 (Low alloy steel)

2) Quenching and Tempering

1) Quenching

FC200 (Cast iron)

2) Quenching and Tempering

Quenching: Heated to 900 o C for 1h, then oil cooling Tempering: Heated to 600 o C for 1h, then water cooling

1) Quenching

SUS304 (Austenitic stainless steel)

Solution Heat Treated

Heated to 1000 o C for 1h, then water cooling

3. Experimental results Table 2 lists the results of the Vickers hardness measurements. The data indicate a significant increase in hardness within the bulk of each material. By contrast, the SUS304 steel showed minimal change in hardness, because it did not undergo martensitic transformation. Fig. 1 shows the TDA profiles of SCM435 coated specimens after heat treatment: (a) quenched and (b) quenched and tempered. Hydrogen desorption occurred primarily below 300 °C, corresponding to diffusible hydrogen relevant to hydrogen embrittlement (Takai et, al., 2003). For the coated specimens, the hydrogen content decreased from 0.72 to 0.10 mass ppm in (a) quenched specimens and from 0.25 to 0.05 mass ppm in (b) quenched and tempered specimens. The lower hydrogen content observed in the quenched and tempered specimens compared to that in the quenched specimens was likely due to the reduction in the dislocation density and internal strain during tempering, which decreased the number of hydrogen trap sites. Although these results indicate that the coating effectively prevented hydrogen ingress, the hydrogen cut ratio was not perfect. Table 3 summarizes the hydrogen content and hydrogen cut ratio for all the materials, and Fig. 2 shows a comparison of the hydrogen cut ratio among the various materials. SCM435 steel exhibited prevention rates of 86.1% for the quenched specimens and 80.0% for the quenched and tempered specimens. FC200 steel showed a prevention rate exceeding 91.7%, and SUS304 steel exhibited a high prevention rate of 97.3%. For the S45C steel, the quenched specimens showed a prevention rate of 0%, whereas the quenched and tempered specimens showed a prevention rate of 42.1%, indicating a substantial reduction compared with the preheat treatment rate of 100%.

Table 2. Vickers hardness test results

Material

As-coated material

Hardness after Quenching (HV)

Hardness after Quenching and Tempering (HV)

S45C(Carbon steel)

169 163 205

665 445 615

252 292 221

SCM435 (Low alloy steel)

FC200 (Cast iron)

Material

As-coated material

Hardness after Solution treating (HV)

SUS304 (Stainless steel)

188

177