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Abstract

The high temperature corrosion of AISI 4130 steel can be increased by hot-dip aluminizing coating. The aluminized steel specimens with the deposit composition of 100/0, 30/70, 50/50, 70/30, and 0/100 (wt.%) NaCl/Na2SO4 were oxidized at 750 °C for 1-49 h periods. According to a parabolic rate constant (kp) value, the aluminized steel with deposit composition of 70/30 NaCl/Na2SO4 shows the highest kp value (3.71 × 10-11 g2cm- 4s-1), later followed by the kp value of 3.35 × 10-11 g2cm-4s-1 for 100/0 and the lowest kp value is 7.731 × 10-12 g2cm-4s-1 for 0/100. Whereas, the kp value for the aluminized steel without NaCl/Na2SO4 deposit is around 2.23 × 10-13 g2cm-4s-1. The presence of both salts and their mixtures destroyed protective Al2O3 layer on the aluminized steel, leading to the Fe2O3 growth locally. Whereas, the penetration of sulfur into the Al2O3 scale lead to the formation of Al2S3 and FeS in the aluminide coating. Therefore, the kinetics rate was increased. Furthermore, mixtures of 70 wt. % NaCl in Na2SO4 depositing on the aluminized steel produced the highest parabolic rate constant because the aluminide layer on the steel substrate experienced severe corrosion attack, leading to fail in formation of protective Al2O3 layer.

Bahasa Abstract

Korosi Temperatur Tinggi Baja AISI 4130 Lapis Aluminium dengan Komposisi Endapan NaCl/Na2SO4 Berbeda. Ketahanan korosi temperatur tinggi baja AISI 4130 dapat ditingkatkan melalui pelapisan aluminium celup panas. Larutan NaCl/Na2SO4 dengan komposisi 100/0, 30/70, 50/50, 70/30, dan 0/100 (wt.%) diendapkan pada permukaan spesimen baja lapis aluminium dan kemudian dioksidasi pada 750 °C selama 1 sampai 49 h. Berdasarkan nilai konstanta laju parabolik (kp) baja lapis aluminium dengan komposisi endapan 70/30 NaCl/Na2SO4 menghasilkan nilai kp yang tertinggi, yaitu kp = 3.71 × 10-11 g2cm- 4s-1, kemudian diikuti nilai kp = 3.35 × 10-11 g2cm-4s-1 untuk 100/0 dan nilai kp yang terendah adalah 7.731 × 10-12 g2cm-4s-1 untuk 0/100. Sedangkan nilai kp untuk baja lapis aluminium tanpa endapan NaCl/Na2SO4 adalah 2.23 × 10-13 g2cm-4s-1. Keberadaan NaCl, Na2SO4 dan campuran keduanya merusak pembentukan lapisan protektif Al2O3 pada baja lapis aluminium, yang memicu pertumbuhan Fe2O3 secara lokal. Sedangkan, masuknya sulfur ke dalam lapisan Al2O3 memicu pembentukan Al2S3 dan FeS. Oleh karena itu, laju kinetika korosi ditingkatkan. Selanjutnya, endapan campuran 70% NaCl dalam Na2SO4 pada baja lapis aluminium menghasilkan nilai kp tertinggi karena lapisan intermetalik Fe-Al pada substrat baja mengalami serangan korosi yang parah, menghasilkan kegagalan dalam pembentukan lapisan protektif Al2O3.

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