Mechanisms of Salt Corrosion Resistance Alterations of Refractory Steels Irradiated by Intense Pulsed Electron Beams

determination of the surface layer physical and chemical state of these objects was carried out by electron Auger spectroscopy (chemical composition), X-ray analysis (phase composition and residual stresses), scanning electron microscopy (surface topography), exo-electron emission and optical metallography. Besides, such characteristics as the surface roughness (R_a) and microhardness (H_m) were also determined.

The electron beam treatment was performed with the use of «GESA-1» accelerator [3] at the rotation of targets under the beam. The irradiation conditions were as follows [3]: accelerating voltage of 100–120 kV, pulse duration of 15–20 ms, electron beam energy density of 20–24 J/cm², beam cross-section area of 40–55 cm² and pulse number of 5. After irradiation the part of targets was annealed under vacuum (10^–3 Pa) for 6 hours at the following temperatures: EP866sh — 67⁰ C and EP718ID — 690⁰ C (optimal regimes of irradiation and annealing). Initial, irradiated and annealed samples and blades were tested for the salt corrosion resistance at the presence of Cl^- ions under the thermal cycling condition from the operating temperature to the room temperature (cooling in sea water).

Specimens and blades fractured or damaged during the tests were studied by electron Auger spectroscopy, X-ray analysis, optical and electron fractographic methods.

Results and discussion

Some salt corrosion test results of patterns and compressor blades are given in Table 1 and Figures 1, 2. The test results show that the corrosion resistance of samples, subjected to electron beam irradiation with the post-process vacuum annealing at the operating conditions, could be increased by 500 %. The study results of samples and blades after irradiation, heat treatment and tests (Tables 2, 3 and Figures 3–6) can be summarized as follows:

TABLE 1. Corrosion test results of EP866sh and EP718ID steel specimens: number of cycles — 150; heating up to 600⁰ C (650⁰ C); cooling in seawater — 25⁰ С.

Steel

Irradiating regime

Annealing regime

Specific mass gain

W, J/cm²

N, pulses

T, ⁰C

τ, hours

±0,03 mg/mm²

EP866sh

—

—

—

—

1.98

EP866sh

20–22

5

670

6

0.33

EP866sh

20–22

5

—

—

2.11

EP866sh

26-28

5

670

6

1.39

EP718ID

—

—

—

—

1.89

EP718ID

22–24

5

—

—

2.06

EP718ID

22–24

5

690

6

0.41

EP718ID

34–36

5

690

6

1.56