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Hydrogen Embrittlement Properties of Stainless and Low Alloy Steels in High Pressure Gaseous Hydrogen Environment

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Hydrogen Embrittlement Properties of Stainless and Low Alloy Steels in High Pressure Gaseous Hydrogen Environment ISIJ International, Vol. 52 (2012), No. 2, pp. 234–239 Review Hydrogen Embrittlement Properties of Stainless and Low Alloy Steels in High Pressure Gaseous Hydrogen Environment Tomohiko OMURA and Jun NAKAMURA Corporate Research and Development Laboratories, Sumitomo Metal Industries, Ltd., Amagasaki, 660-0891 Japan. E-mail: [email protected] (Received on June 30, 2011; accepted on September 28, 2011) Recent research on Hydrogen Environment Embrittlement (HEE) susceptibility of stainless and low alloy steels in highly pressurized gaseous hydrogen environments was reviewed from the viewpoint of tensile properties, hydrogen absorption and fatigue properties. HEE susceptibility evaluated by Slow Strain Rate Test (SSRT) in high pressure hydrogen environments strongly depended on steel chemical compositions. Austenitic stainless steels such as type 316L or iron- based superalloy as A286 showed sufficient resistance to HEE, while stainless steels with low levels of alloying elements such as type 304L showed a remarkable ductility loss in high pressure gaseous hydro- gen due to martensitic transformation. Martensitic stainless or low alloy steels also showed a remarkable ductility loss in gaseous hydrogen. Relationship between HEE susceptibility and an amount of hydrogen absorption was investigated. HEE susceptibility and hydrogen embrittlement under cathodic charging in aqueous solution showed the same dependence on the amount of hydrogen absorption, which implies HEE occurs by hydrogen absorption from external gaseous hydrogen environments. Fatigue properties in high pressure gaseous hydrogen environments were evaluated by means of inter- nal or external pressurization tests. Austenitic stainless steels such as type 316L showed little decrease in fatigue life by hydrogen, while metastable stainless steel as type 304 or precipitation hardened superalloy as A286 showed degradation in fatigue life by hydrogen gas. Low alloy steel also showed a decrease in fatigue life in hydrogen, while high strength low alloy steel with much Mo and V showed longer fatigue life than conventional steel. KEY WORDS: hydrogen environment embrittlement; hydrogen gas; SSRT; fatigue; austenitic stainless steel; low alloy steel. In this paper, recent research on HEE is reviewed from 1. Introduction the viewpoint of tensile properties, effect of hydrogen For rapid commercialization of fuel cell vehicles, high absorption and fatigue properties of stainless and low alloy pressure hydrogen systems for storage and transportation of steels. Tensile properties were evaluated by means of Slow hydrogen fuel must be developed in the near future. For the Strain Rate Test (SSRT) in an autoclave pressurized with safety and public acceptance of using compressed high pres- gaseous hydrogen. Relationship between tensile properties sure hydrogen gas, investigating the effect of gaseous and sub-surface hydrogen concentration were discussed. hydrogen on mechanical properties of structural materials Fatigue properties were evaluated by means of internal and used for the hydrogen system is one major subject. It is external pressure fatigue tests to assess fatigue life of tubes widely recognized that gaseous hydrogen decreases mechan- or cylinders used for transportation and storage of hydrogen. ical properties of steels or other metals.1–8) The environmen- tal degradation in gaseous hydrogen is called Hydrogen 2. Tensile Properties Evaluated by SSRT Environment Embrittlement (HEE), or called Hydrogen Gas Embrittlement (HGE) recently, which occurs when a hydro- Tensile tests in gaseous hydrogen are valuable as rapid gen free material is mechanically tested in gaseous hydro- and economical screening tests, which provide a good indi- gen near room temperatures. NASA has carried out many cation of HEE.5,6) Recently, SSRT under extremely low studies on HEE in the 1960’s for the development of fuel strain rates is widely used for assessment of HEE as fol- systems for space shuttles.1–3) Many studies on HEE have lows,10–20) because susceptibility to hydrogen embrittlement been also carried out in Japan.5–8) Additionally, several increases with a decrease in the strain rate. national projects have started and are now continuing to Figure 1 is a schematic illustration of the SSRT appara- select and develop appropriate materials for the high pres- tus. Prior to a test, the autoclave was evacuated and replaced sure hydrogen systems.9–29) with hydrogen gas several times to remove air completely, © 2012 ISIJ 234 ISIJ International, Vol. 52 (2012), No. 2 then filled with hydrogen and pressurized. The purity of es relative effects of alloying elements to Ni on the auste- 30) hydrogen gas was 99.99999%. SSRT was carried out in an nitic stability. Md30 indicates the temperature at which a autoclave pressurized with 45 to 90 MPa gaseous hydrogen 50% martensite structure is produced by a strain of 30%.31) at the temperature range from –40 to 85°C. Many tests were Higher Nieq and lower Md30 values mean higher stability of carried out under the strain rate of 3×10–6 s–1, as there was austenitic phase. Type 420 is a quenched-tempered marten- no remarkable effect of strain rates on HEE susceptibility in sitic stainless steel with the tensile strength of 900 MPa. the range from 3×10–7 to 8×10–5 s–1.7) Fracture elongation SCM435 is a quenched-tempered low alloy steel specified (El.), tensile strength and reduction of area (R.A.) in gas- in JIS (Japanese Industrial Standards) G4053 with tempered eous hydrogen were compared to the values in air or in martensitic microstructure at tensile strength of 800 MPa. nitrogen at the same temperatures. Figure 2 shows examples of fracture surfaces after SSRT Several steels were used as listed in Table 1. They at room temperature in 45 MPa gaseous hydrogen. The frac- include steel sheets or cylinders on the market or modified ture surface of type 304L clearly showed a transgranular laboratory melt steels. Solution-annealed 300 series auste- morphology indicating embrittlement by hydrogen as shown nitic stainless steels, type 304, 304L, 316 and 316L with in Figs. 2(a) and 2(b). In contrast, the fracture surface of various chemical compositions within AISI specifications type 316L revealed a ductile tearing by void formation as were prepared. Tensile cold-works from 30 to 40% were shown in Figs. 2(c) and 2(d). applied to the 316L sheet after the solution heat treatment. Figure 3 summarizes relative fracture El. and relative A286 is a precipitation hardened iron-based superalloy with R.A. evaluated by SSRT in 45 MPa hydrogen at room tem- the tensile strength more than 1 000 MPa. A286 was solu- perature. “Relative” means the ratio of fracture El. and R.A. tion-annealed at 900°C for 1 hr, followed by aging heat in high pressure hydrogen to those in air or in nitrogen at treatment at 720°C for 16 hrs. Nieq and Md30 are parameters ambient pressure. Type 316L showed no degradation. A286 empirically estimated from chemical compositions of steels, and cold worked 316L showed a slight decrease in fracture expressing the stability of austenitic structure. Nieq express- Table 1. Chemical compositions of investigated steels. Chemical compositions (mass%) Nieq Md30 Material ° CSiMnNiCrMoN Ti(%) ( C) 304 0.04 0.40 1.61 9.34 18.27 0.25 0.038 – 23.8 16.6 304L 0.02 0.35 1.36 9.08 18.15 0.23 0.050 – 23.3 28.6 316 (A) 0.06 0.48 0.86 10.43 16.07 2.17 0.029 – 24.4 1.9 316 (B) 0.05 0.48 0.78 11.09 17.34 2.00 0.023 – 25.6 –9.1 316 (C) 0.05 0.57 0.82 11.27 17.49 2.07 0.028 – 26.1 –19.7 316L 0.02 0.53 0.88 12.04 17.82 2.09 0.041 – 27.3 –23.5 A286 0.05 0.38 1.01 25.16 14.75 1.28 0.005 2.18 37.3 –89.0 420 0.20 0.28 0.92 0.12 12.90 0.01 0.027 – 9.9 – SCM435 0.37 0.25 0.77 0.01 1.10 0.26 0.004 – 1.9 – Nieq (%)=Ni+0.65Cr+0.98Mo+1.05Mn+0.35Si+12.6C Fig. 1. SSRT apparatus. Md30 (°C)=413–462(C+N)–9.2Si–8.1Mn–13.7Cr–9.5Ni–18.5Mo –6 –1 Fig. 2. Fracture surface after SSRT. (a) and (b) type 304L, (c) and (d) type 316L, strain rate 3×10 s in 45 MPa H2 at R.T. 235 © 2012 ISIJ ISIJ International, Vol. 52 (2012), No. 2 Fig. 4. Effect of chemical compositions on HEE susceptibilities with strain rate of 3×10–6 s–1 in 45 MPa H . Fig. 3. HEE susceptibilities of investigated steels with strain rate of 2 –6 –1 3×10 s in 45 MPa H2 at R.T. “Relative” means the ratio of fracture El. and R.A. in high pressure hydrogen to those in air or in nitrogen at ambient pressure. El. and R.A. by hydrogen, implying a little effect of the pre- cipitation hardening or the cold work on HEE susceptibility. Ductility losses of type 316 series strongly depended upon their chemical compositions. 316(C) with rich alloying ele- ments such as Cr and Ni, showed no evidence of degrada- tion, while 316(A) and 316(B) showed a remarkable decrease in fracture El. and in R.A. in gaseous hydrogen. The tendency suggests that the chemical composition is one of the important factors affecting HEE, because these steels had quite different HEE susceptibility regardless of the small difference in chemical compositions. Type 304L, type Fig. 5. Effect of the volume fraction of martensite on HEE suscep- 420 and low alloy steel SCM435 showed a remarkable –6 –1 tibilities with strain rate of 3×10 s in 45 MPa H2.
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