PDF《Alloy 690 Base Metal》

Alloy

690 Base Metal Strategy

1 Alloy

690 Base Metal Alloy

690 Base Metal Issues &

Strategy Issues &

Strategy Peter Andresen and Martin Morra GE Global Research Center John Hickling, Al Ahluwalia &

John Wilson EPRI / NRC Meeting July

2008 Alloy

690 Base Metal Strategy

2 Introduction and Philosophy Introduction and Philosophy ? The industry has made a huge investment in moving to the more SCC resistant Alloy

690 and its weld metals ? Vulnerabilities will be understood and resolved, and specs developed to prevent problem conditions/microstructures ? One vulnerability is related to a synergy among: ? inhomogeneous microstructures, ? directional deformation and ? crack plane orientation relative to structure &

deformation ? Cracks find the problem areas, so we must evaluate these problem areas without just focusing on ugly material.

Alloy

690 Base Metal Strategy

3 Inhomogeneities Inhomogeneities ? Inhomogeneity results from melting &

processing: ? dendritic segregation during solidification is inherent ? more pronounced in highly alloyed (Nb,C): 690,718… ? single melting C vs. double or triple melt ? air melting gives more inclusions &

perhaps loss of Cr ? not achieving critical strains of ~70% during processing ? Inhomogeneities can include: ? compositional banding C gives rise to gs &

MC banding ? large variation in carbide content, including gb carbides ? stringers or sheets of oxide or C,N inclusions ? large variation in grain size ? Processing causes uneven deformation &

poor properties ? SCC and toughness are both affected Alloy

690 Base Metal Strategy

4 Thermo Thermo- -Mechanical Processing Mechanical Processing Steps used to melt and Thermo-Mechanical-Process (TMP) Ni-Fe base superalloys from ingot to billet Segregation and inhomogeneities are much bigger issues in high Cr,Nb alloys like Alloys

690 and (esp.)

718 Alloy

690 Base Metal Strategy

5 Processing of an ESR Ingot Processing of an ESR Ingot Large ESR ingot (left) after heating for drawing operation (right) Alloy

690 Base Metal Strategy

6 Metal Specifications Metal Specifications Good specifications should eliminate inhomogeneities and banding without adding to cost. Processing Alloy

690 is not complex or poorly understood, but some forms (e.g., plate) are more prone to inhomogeneities. Vendors work to the spec, so it must address compositional banding and related inhomogeneities, including large or banded grain size, MC carbides, gb carbide decoration, etc. Macro-etching of full cross-sections or center-mid-edge sampling will identify banding. Alloy

690 Base Metal Strategy

7 Technical Background Technical Background Factors that enhance SCC growth rates include: ? Water chemistry C high Cr

690 is very resistant here ? Yield strength C all materials seem to suffer at high YS ? Stress Intensity Factor C often higher in high YS materials Weld HAZ affects microstructure and imposes high residual ε ? EBSD is very effective in quantifying/mapping strain YS increases CGR by ~10X. Additional ~10X effect of: ? Inhomogeneous microstructures + ? Directional deformation + ? Crack plane orientation relative to structure &

deformation Alloy

690 Base Metal Strategy

8 Effects of Yield Strength / Cold Work Effects of Yield Strength / Cold Work Nickel alloys &

stainless steels are not fundamentally different Roughly 10X increase from

15 C 30% cold work in most cases 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 Corrosion Potential, Vshe Crack Growth Rate, mm/s Alloy 182, Alloy