Microstructural and corrosion aspects of alloy 690

Abstract

Undissolved particles in alloy 690 were identified as titanium nitrides with a hexagonal crystal structure. On subsequent thermal treatment of the alloy these inclusions were found to act as preferred sites for the precipitation of chromium carbide. The alloy in three heat treated conditions (solution annealed and solution annealed followed by thermal treatment at 700°C for 4 or 16 h) displayed active–passive–transpassive behaviour in H₂ SO₄ solution. Passivation of the alloy in H₂ SO₄ solution was found to be adversely affected by the presence of discrete chromium carbide precipitates at the grain boundaries. In HCl solution, the alloy displayed unstable passivation in all three heat treated conditions. Microscopic studies revealed that the TiN inclusion/matrix interface may provide a preferential site for pit initiation in alloy 690.

Get full access to this article

View all access options for this article.

References

Crum

J. R.

: Corrosion, 1986, 42, 368.

Harrod

D. L.

, GOLD

R. E.

, LARSSON

, and BJOERKMAN

: Proc. 5th Int. Symp. on ‘Environmental degradation of materials in nuclear power systems — water reactors’, California, 1991, American Nuclear Society, TMS, NACE, 849.

Smith

A. J.

and STRATTON

R. P.

: Proc. 5th Int. Symp. on ‘Environmental degradation of materials in nuclear power systems — water reactors’, California, 1991, American Nuclear Society, TMS, NACE, 855.

G. R

and Yao

H. C.

: Corrosion, 1990, 46, 391.

Kai

J. J.

, YU

G. P.

, TSAI

C. H.

, LIU

M. N.

, and YAO

S. C.

: Metall. Trans. A, 1989, 20A, 2057.

Norring

, STILLER

, and NILSSON

J.-O.

: Proc. 5th Int. Symp. on ‘Environmental degradation of materials in nuclear power systems — water reactors’, California, 1991, American Nuclear Society, TMS, NACE, 482.

Sakai

, SENJUH

, AOKI

, SHIGEMITSU

, and KISHI

: Proc. 5th Int. Symp. on ‘Environmental degradation of materials in nuclear power systems — water reactors’, California, 1991, American Nuclear Society, TMS, NACE, 764.

Yamanaka

: Proc. 5th Int. Symp. on ‘Environmental degradation of materials in nuclear power systems — water reactors’, California, 1991, American Nuclear Society, TMS, NACE, 773.

Choi

and WAS

G. S.

: Corrosion, 1990, 46, 100.

10.

Marcus

and GRIMAL

J. M.

: Corros. Sci., 1992, 33, 805.

11.

LA MALFA

and Quaranta

: in ‘Alloy 800’, (ed. Betteridge

et al), 71; 1978, Amsterdam, North-Holland.

12.

Villagrana

R. E.

and KAAE

J. L.

: in ‘Alloy 800’, (ed. Betteridge

et al), 175; 1978, Amsterdam, North-Holland.

13.

Burke

M. G.

, MAGER

T. R.

, and WILSON

I. L. W.

: Proc. 5th Int. Symp. on ‘Environmental degradation of materials in nuclear power systems — water reactors’, California, 1991, American Nuclear Society, TMS, NACE, 287.

14.

Heck

K. A

: Proc. Int. Symp. on ‘Superalloys 718, 625, 706 and various derivatives’, (ed. Loria

E. A.

), 393; 1994, Warrendale, PA, TMS.

15.

Mitchell

, SCHMALZ

A. J.

, SCHVEZOV

, and COCKCROFT

S. L.

: Proc. Int. Symp. on ‘Superalloys 718, 625, 706 and various derivatives’, (ed. Loria

E. A.

), 65; 1994, Warrendale, PA, TMS.

16.

Mitchell

: Proc. Int. Symp. on ‘Superalloys 718, 625, 706 and various derivatives’, (ed. Loria

E. A.

), 109; 1994, Warrendale, PA, TMS.

17.

Pearson

W. B.

: ‘Handbook of lattice spacings and structures of soft metals and alloys’, Vol. 2; 1967, Oxford, Pergamon.

18.

Okamoto

and SHIBATA

: in ‘Passivity of metals’, (ed. Frankenthal

R. P.

and Kruger

), 646; 1978, Princeton, NJ, The Electrochemical Society.

19.

Dutta

R. S.

, MADANGOPAL

, GADIYAR

H. S.

, and BANERJEE

: Br. Corros. J., 1993, 28, 217.

20.

Galvele

J. R.

: in ‘Passivity of metals’, (ed. Frankenthal

R. P.

and Kruger

), 285; 1978, Princeton, NJ, The Electro-chemical Society.

21.

Eklund

: in ‘Localised corrosion’, (ed. Staehle

R. W.

et al), 477; 1974, Houston, TX, NACE.