Corrosion Wear of Alloy Tool Steel (SKD 11) Coated with VC and Precipitation Hardening Stainless Steel (SUS 630) in Sodium Chloride Aqueous Solution Toshiyuki TANAKI*, Makoto YUASA** and Isao SEKINE*** We studied corrosion wear of alloy tool steel (SKD 11) coated with VC and precipitation-hardened stainless steel (SUS 630) in NaCl aqueous solution. SUS 630 lost more weight than SKD 11 coated with VC, except where SUS 630 was used as a rotor at a load region below 9.8 ~ 10-1 MPa. VC film appeared externally sound overall. Sample edges revealed galvanic corrosion of the substrate and partial disappearance of the VC film, and SUS 630 was plastically deformed under high load. The polarization curve indicated that VC film and SUS 630 form a galvanic couple with SKD 11 in NaCl solution, and that VC film and SUS 630 behave cathodic and SKD 11 anodic. Pinhole defects were detected in VC-coated SKD 11 using optical and scanning electron microscopy by anodic polarization in deaerated 0.5kmol E m-3 H2SO4 solution. Pinhole defects averaged 2 `4 per cm2 Key Words : Corrosion Wear, Alloy Tool Steel, Stainless Steel, VC Film, Pinhole Defect Tokyo Metropolitan Ind. Tech. Center (13-10, Nishigaoka 3-chome, Kita-ku, Tokyo 115) Fac, of Sci, and Tech., Science Univ, of Tokyo (2641, Yamazaki, Noda-shi, Chiba 278) Inst. of Colloid and Interface Sci., Science Univ. of Tokyo (1-3, Kagurazaka, Shinjuku-ku, Tokyo 162)
Vol.47,No.6,1996 Stator Rotor Fig. 1 Dimension of specimen (mm).
Fig. 2 Relation between load and weight loss in NaCI solution determined for SKD 11 coated with VC. (Cl- 10'ppm, 308K) (Test period : 5h) (Slip velosity : 0.136m/s) Fig. 4 Scanning electron micrograph of surface appearance of SKD 11 coated with VC after corrosion wear test. (Stator, Load 9.8MPa) (NaCI solution ; Cl- 10'ppm, 308K, 5h, 0.136m/s) A B Fig. 3 Optical micrographs of cross section of SKD 11 coated with VC after corrosion wear test. A) Stator, Load 4.9 x 10-' MPa B) Stator, Load 9.8MPa (NaCI solution ; Cl- 10'ppm, 308K, 5h, 0.136m/s)
Vol.47,Na6,1996 Fig. 5 Relation between load and weight loss in NaCl solution determined for SUS 630 (Stator) and SKD 11 coated with VC (Rotor). (Cl-10'ppm, 308K) (Test period : 5h) (Slip velosity : 0.136m/s) Fig. 6 Relation between load and weight loss in NaCl solution determined for SKD 11 coated with VC (Stator) and SUS 630 (Rotor). (Cl- 10'ppm, 308K) (Test period : 5h) (Slip velosity : 0.136m/s) A B Fig. 7 Optical micrographs of cross section of SUS 630 after corrosion wear test. A) Stator, Load 4.9x10-`MPa B) Stator, Load 9.8MPa (NaCI solution : Cl- 10'ppm, 308k, 5h, 0.136m/s)
Fig. 8 Cathodic polarization curves for sintered VC and SUS 630 in aerated NaCI solution and anodic polarization curve for SKD 11 in deaerated NaCI solution. (Cl- 104ppm, 308k Sweep rate 20mV/min) Fig. 9 Anodic polarization curves for SKD 11, SKD 11 coated with VC and sintered VC in deaerated sulfuric acid (0.5kmol/m3 H2SO4, 303k, Sweep rate 20mV /min).
Vol.47,Na6,1996 A B C Fig. 10 Scanning electron micrographs of surface appearance of sintered VC and SKD 11 coated with VC before and after anodic polarization test. A) Sintered VC before anodic polarization test B) Sintered VC at 1000mV (vs Ag/AgCI) C) SKD 11 coated with VC at 100mV (vs Ag/AgCI) (0.5kmol/m' H2SO., 303k)
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