Ni-Cr-Fe alloy and Ni-Cr-Fe alloy pipe having resistance to carburization and coking
View Patent ↗A stainless steel pipe includes a base metal containing 20-35 mass % of Cr, and a Cr-depleted zone is formed in the surface region of the pipe. The Cr concentration in the Cr-depleted zone is at least 10%, and the thickness of the Cr-depleted zone is at most 20 micrometers. A Cr-based oxide scale layer having a Cr content of at least 50% and a thickness of 0.1-15 micrometers may be provided on the outer side of the Cr-depleted zone. An Si-based oxide scale layer with an Si content of at least 50% may be provided between the Cr-based oxide scale layer and the Cr-depleted zone. The pipe is particularly suitable for use in petroleum refineries or petrochemical plants, such as for use as a pipe of a cracking furnace of an ethylene plant.
1. A Ni—Cr—Fe alloy for use in a carburizing gas atmosphere comprising a base metal having a chemical composition comprising in mass %, C: 0.01-0.6%, Si: 0.1-5%, Mn: 0.1-10%, P: at most 0.08%, S: at most 0.05%, Cr: 22-55%, Ni: 23-70%, N: 0.001-0.25%, O: oxygen: at most 0.02%, and a remainder of Fe and impurities, the base metal having in its surface region a Cr-depleted zone with a Cr concentration of at least 10 mass % but less than a concentration of Cr in the base metal, and a thickness of at most 20 micrometers, said surface of the base metal formed by removing an oxide scale generated by heating of the base metal.
2. A Ni—Cr—Fe alloy as claimed in claim 1 wherein the base metal further comprises, in mass percent, at least one material selected from the following (i)-(viii)
(i) Cu: 0.01-5%,
(ii) Co: 0.01-5%
(iii) at least one of Mo: 0.01-3%, W: 0.01-6%, Ta: 0.01-6%, Re: 0.01-6%, and Ir: 0.01-6%
(iv) at least one of Ti: 0.01-1% and Nb: 0.01-2%
(v) at least one of B: 0.001-0.1%, Zr: 0.001-0.1%, and Hf: 0.001-0.5%
(vi) at least one of Mg: 0.0005-0.1%, Ca: 0.0005-0.1%, and Al: 0.01-1%
(vii) at least one of Y: 0.0005-0.15%, and Ln series elements: 0.0005-0.15%
(viii) at least one of Pd: 0.005-1%, Ag: 0.005-1%, Pt: 0.005-1%, and Au: 0.005-1%.
3. An alloy pipe comprising a Ni—Cr—Fe alloy as claimed in claim 2 and having surface irregularities on the inner surface of the pipe.
4. An alloy pipe comprising a Ni—Cr—Fe as claimed in claim 1 and having surface irregularities on the inner surface of the pipe.
5. A Ni—Cr—Fe alloy for use in a carburizing gas atmosphere comprising a base metal having a chemical composition comprising in mass %, C: 0.01-0.6%, Si: 0.1-5%, Mn: 0.1-10%, P: at most 0.08%, S: at most 0.05%, Cr: 22-55%, Ni: 23-70%, N: 0.001-0.25%, O: oxygen: at most 0.02%, and a reminder of Fe and impurities, the base metal having in its surface region a Cr-depleted zone with a Cr concentration of at least 10 mass % but less than a concentration of Cr in the base metal, and a thickness of at most 20 micrometers, said base metal further including a Cr-based oxide scale layer with a Cr content of at least 50 mass % on the outer side of the Cr-depleted zone, wherein the Cr-based oxide scale layer has a thickness of 0.1-15 micrometers.
6. A Ni—Cr—Fe alloy as claimed in claim 1 , including an Si-based oxide scale layer with an Si content of at least 50 mass % between the Cr-based oxide scale layer and the Cr-depleted zone.
7. An alloy pipe comprising a Ni—Cr—Fe alloy as claimed in claim 6 and having surface irregularities on the inner surface of the pipe.
8. A Ni—Cr—Fe alloy as claimed in claim 6 , where in the base metal further comprises, in mass percent, at least one material selected from the following (i)-(viii)
(i) Cu: 0.01-5%,
(ii) Co: 0.01-5%,
(iii) at least one of Mo: 0.1-3%, W; 0.01-6%, Ta: 0.01-6%, Re: 0.01-6%, and Ir: 0.01-6%,
(iv) at least one of Ti: 0.01-1% and Nb: 0.01-2%,
(v) at least one of B: 0.001-0.1%, Sr: 0.001-0.1%, and Hf: 0.001-0.5%,
(vi) at least one of Mg: 0.0005-0.1%, Ca: 0.0005-0.1% and Al: 0.01-1%,
(vii) at least one of Y: 0.0005-0.15%, and Ln series elements: 0.0005-0.15%,
(viii) at least one of Pd: 0.005-1%, Ag: 0.005-1%, Pt: 0.005-1%, and Au: 0.005-1%.
9. An alloy pipe comprising a Ni—Cr—Fe alloy as claimed in claim 8 and having surface irregularities on the inner surface of the pipe.
10. An alloy pipe comprising a Ni—Cr—Fe alloy as claimed in claim 5 and having surface irregularities on the inner surface of the pipe.
11. A Ni—Cr—Fe alloy as claimed in claim 5 , where in the base metal further comprises, in mass percent, at least one material selected from the following (i)-(viii)
(i) Cu: 0.01-5%,
(ii) Co: 0.0 1-5%,
(iii) at least one of Mo: 0.1-3%, W; 0.01-6%, Ta: 0.01-6%, Re: 0.01-6%, and Ir: 0.01-6%
(iv) at least one of Ti: 0.01-1% and Nb: 0.01-2%,
(v) at least one of B: 0.001-0.1%, Sr: 0.001-0.1%, and Hf: 0.001-0.5%,
(vi) at least one of Mg: 0.0005-0.1%, Ca: 0.0005-0.1% and Al: 0.01-1%,
(vii) at least one of Y: 0.0005-0.15%, and Ln series elements: 0.0005-0.15%,
(viii) at least one of Pd: 0.005-1%, Ag: 0.005-1%, Pt: 0.005-1%, and Au: 0.005-1%.
12. An alloy pipe comprising a Ni—Cr—Fe alloy as claimed in claim 11 and having surface irregularities on the inner surface of the pipe.