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■■■■■■■■■■■■■■■■■■■ 川崎製鉄技報 KAWASAKI STEEL GIHO Vol.11 (1979) No.1 ■■■■■■■■■■■■■■■■■■■ |
| 20％NaCl+1％ Na2Cr2O7･2H2O 水溶液中における高Cr-Moフェライトステンレス鋼の孔食および応力腐食割れ Pitting Corrosion and Stress Corrosion Cracking of High Cr-Mo Ferritic Stainless Steels in 20%Na2Cr2O72H20 宮脇 哲雄(Tetsuo Miyawaki) 木下 昇(Noboru Kinoshita) 小野 寛(Yutaka Ono) 大橋 延夫(Nobuo Ohashi) |
| 要旨 : 高Cr-Moフェライトステンレス鋼およびオーステナクトステンレス鋼の20％NaCl+1％Na2Cr2O7･2H2O, 水溶液中における孔食および応力腐食割れを調べた。沸とう水溶液中では，オーステナイト鋼およびC+N >160ppm かつNiを2〜4％含むフェライト鋼は応力腐食割れを起こすが，C+N <110ppm またはNiを含まないフェライト鋼は起こさない。加熱過程中の電極電位の変化から，鋼はオーステナイト鋼（液温の上昇とともに不動態→孔食の発生・停止→孔食の発生・成長），C+N <110ppm のフェライト鋼（不動態→孔食の発生・停止），C+N >160ppm のフェライト鋼（不動態→孔食の発生・成長）の3種に分類される。この孔食挙動の機構および応力腐食割れとの関係について検討した。 |
| Synopsis : The susceptibility to stress corrosion cracking (SSC) and pitting corrosion of austenitic stainless and high Cr-Mo ferritic stainless steels has been investigated in a 20% NaCl+1% Na2Cr2O7･2H2O solution. SCC at boiling temperature (107℃) occurrs not in the ferritic steels containing C+N below 110 ppm or free of Ni, but in the austenitic steels and also in the ferritic steels having C+N above 160ppm and 2〜4%Ni. Using electrode potential temperature (time) curves obtained by heating the solution, pitting behavior of the steels consists of two or three of the following three regions; (1) the metal is passivated, (2) pits successively nucleate but immediately cease to grow and (3) one or a few pits nucleate and grow. By their pitting behavior, the steels are classified into three groups; austenitic steels (TypeT), the ferritic steels containing C+N below 110ppm (TypeU) and ferritic steels having C+N above 160 ppm (TypeV). The TypeT exhibits a curve composed of all the three regions, the TypeU shows a curve composed of the regions 1 and 2, and the TypeV gives a curve composed of the regions, 1 and 3. The mechanism of these pitting behaviors and the differences in the susceptibility to SCC of these steels is discussed on the basis of polarization characteristics. |
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