Procedia Engineering 55 ( 2013 ) 226 – 231

1877-7058 © 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license.

Selection and peer-review under responsibility of the Indira Gandhi Centre for Atomic Research.doi: 10.1016/j.proeng.2013.03.247

6th International Conference on Cree

Development of NickeComponents

J. Klöwera∗, RaThyssenKr

bHitachi PowcE.ON New

Abstract

High Temperature Nickel based alloy 617 (A 617) isits combination of creep strength and good fabricabiand privately financed programmes with regard to itsbeen tailored to fit the specific purpose of USC boile617 labeled Alloy 617 B, with creep strength at 700 °step focused on the definition of welding procedures components can be avoided by suitable post-weld heheat-treatment on the mechanical behaviour of Alloy

© 2013 Published by Elsevier Ltd. Selection and/oAtomic Research.

Keywords: Alloy 617B; USC Boilers; fossil power plants; cr

1. Introduction

About 10 years ago, nickel based alloy 617USC 700°C - Boiler projects. This alloy is wideits high creep resistance in combination with goapproved and it has been thoroughly investi("PnP":Prototype Nuclear Process Heat) in the e

Based on data resulting from the PnP-projecincrease in creep strength by about 25 % at 70alloying elements. The increased creep data winitiated within the German funded R&D projec

∗

Corresponding author: E-mail address: jutta.kloewer@thyssenkrupp.com

ep, Fatigue and Creep-Fatigue Interaction [CF-6

el Alloys Based on Alloy 617 for in 700°C Power Plants

.U. Husemannb, M. Baderc

rupp VDM, Werdohl, Germany wer Europe, Duisburg, Germany Build, Gelsenkirchen, Germany

s considered as a candidate material for the 700°C power plantsility. The alloy has been investigated in numerous publicly spos use in USC boilers. Based on the gained experience, the mateers. The first development step resulted in a modified version o°C about 25 % higher than that listed by ASME and VdTÜV. A and heat treatment, demonstrating that crack formation in large eat treatment. This paper will briefly describe the effect of bor617 within the scope of the German USC boiler programmes.

or peer-review under responsibility of the Indira Gandhi Cen

reep strength

7 was selected as material for the first boilers in the Euely used for industrial gas turbines and industrial furnaces od workability and weldability. It is VdTÜV [1] and ASMgated under the German High Temperature Reactor p

eighties [e.g. 3,4,5] ct, the creep data of alloy 617 were re-evaluated. This led00°C for an alloy composition with narrow tolerances ofwere approved in 2003 by VdTÜV with a single appraict MARCKO 700.

6]

s due to onsored erial has of Alloy

second welded ron and

ntre for

ropean due to

ME [2] project

d to an f major isal [6]

Available online at www.sciencedirect.com

© 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license.

Selection and peer-review under responsibility of the Indira Gandhi Centre for Atomic Research.

227 J. Klöwer et al. / Procedia Engineering 55 ( 2013 ) 226 – 231

To meet the extremely high demands for safety, additional development work was carried out to increase cracking resistance of alloy 617B even under extreme conditions. Some of the results are briefly described below. A more detailed overview is given in [7].

2. Experimental details

Alloy 617 and alloy 617 B gain their creep-strength mainly from carbide formation (predominantly M23C6) and solid solution strengthening (Co, Mo). At intermediate temperatures (ca. 550-850°C) additionally ' ((Ni,Ti)3Al) - precipitates form and add to the creep strength of the material [3,4,8].

The chemical composition of alloy 617B in comparison to that of alloy 617 is shown in Table 1. Major differences concern narrower tolerances of alloying elements (Cr, Fe, Co, Al and Ti) and additions of boron to alloy 617B.

Table 1. Typical composition of alloy 617(UNS NO6617) and alloy 617B [1,6].

Element Alloy 617 Alloy 617 B

Ni Bal. Bal.

Cr 20 - 23 21 - 23

Fe < 2 1.5

Mo 8 - 10 8 - 10

Co 10 - 13 11 – 13

Al 0.6 – 1.5 0.8 – 1.3

Ti 0.2 – 0.5 0.25 – 0.5

B 0.002 – 0.005

C 0.05 – 0.10 0.05 – 0.08

Nb < 0.08

Si < 0.7 < 0.3

Mn < 0.7 < 0.3

S < 0.008 < 0.008

P < 0.012 < 0.012

Cu < 0.15

As < 0.01 < 0.01

Pb < 0.007 < 0.007

If not otherwise mentioned, the samples were taken from hot rolled material of industrial heats. They were

prepared by melting in a 20-ton VIM furnace with subsequent ESR (Electro-Slag Remelting) and hot rolling to final thickness of 12 and 30 mm . The sheets were solution annealed at 1160-1175 °C. After heat treatment the microstructure shows some carbides, '– precipitates could not be detected in the solution-annealed condition.

The effect of boron and the effect of heat treatment were investigated on sheets produced by hot-rolling from 100-kg laboratory size ingots at Salzgitter-Mannesmann Research Institute. The preparation of the laboratory ingots is described elsewhere [9].

To investigate the sensitivity to so-called stress relaxation cracking, tensile tests at slow strain rate of 10-5s-1 - 10-6s-1(Slow Strain Rate Test – SSRT or Constant Strain Rate Tests - CSRT)were carried out at 700°C. It should be noted that the sensitivity to "stress relaxation cracking" can only be demonstrated in a Slow Strain Rate Test, not in a standard tensile test.

228 J. Klöwer et al. / Procedia Engineering 55 ( 2013 ) 226 – 231

3. Results and discussion

The 100,000 hour creep strength of alloy 617B in comparison to that of alloy 617 in the relevant temperature range between 600 and 750°C is shown in Table 2. The positive effect of the narrow tolerances in combination with the additions of boron can clearly be seen. The creep strength of alloy 617B is about 25 % higher than that of alloy 617.

Table 2. 100.000 hours creep strength of alloy 617B in comparison to alloy 617 in MPa, (Sources: Alloy 617: VdTÜV data sheet 485,

ASME SB-168, Alloy 617B: VdTÜV single appraisal, ASME Code case under preparation) [1,6].

Alloy 617 Alloy 617 B

T in °C

600 190 265

610 170 249

620 155 233

630 143 218

640 133 202

650 125 187

660 119 172

670 113 158

680 107 145

690 101 132

700 95 119

710 89 108

720 83 97

730 77 87

740 71 77

750 65 69

Fig. 1. Flow stress curves of alloy 617 and alloy 617B, measured in a slow strain rate test at 700°C / 10-6s-1[7].

The positive effect of boron on creep strength was confirmed by Spiegel et al. Laboratory tests carried out on alloy 617 with additions of 0, 30 and 60 ppm B showed that additions of 30 % boron increase the creep strength, while a further increase to 60 ppm boron had no additional effect [9].

The mechanism of boron in alloy 617 is still not fully understood. However, from atom probe tests, it became clear that boron concentrates, (most likely as borides) around carbides and along grain boundaries. The results of this investigation are published elsewhere [10].

229 J. Klöwer et al. / Procedia Engineering 55 ( 2013 ) 226 – 231

Stainless steels and nickel based alloys may be prone to "stress-relaxation cracking" in the temperature range between 500 and 850 °C [11]. The sensitivity to cracking at intermediate temperatures is usually proven in Slow Strain Rate Tests. Figure 1 shows the stress-strain diagrams of alloy 617 and alloy 617 B in comparison. It can be seen that the fracture elongation at 700°C is increased from about 15 % in alloy 617 to more than 50 % in alloy 617B.

According to van Wortel et al., stress relaxation cracking can be prevented by annealing at 980°C for 3 hours prior to exposure [11]. Table 3 shows values for the reduction of area Z for samples before and after annealing for 3 hours at 980°C. In agreement with the results of van Wortel, the ductility increases, if an additional heat treatment at 980 °C is carried out. The major effect of the heat-treatment is relief of residual stresses resulting from cold work, welding and other treatments that induce residual stresses. Furthermore, carbides may precipitate partly within grains during heat treatment at 980 °C and prevent the formation of coarse grain boundary carbides. TEM investigations showed more carbides within the grains after 980°C annealing. However, ' formation could not be found before or after the 980°Cheat treatment [12].

Fig. 2. Effect of cooling rate and stress relief annealing on the Reduction of Area Z of alloy 617B measured in a slow strain rate test at 700

°C, strain rate: 10-6 s-1 [13]. B0-1, B0-W, B0-L, B0-O: w/o Boron

B3-1, B3-W, B3-L, B3-O: with 30 ppm Boron 1: Reference test, W: Water quenched, L: air cooled, O: Furnace-cooled

Table 3. Reduction of area (RA in %) of alloy 617 and alloy 617B before and after stress relief annealing at 980°C, 3 h, measured in a slow strain rate tensile test at 700 °C and 10-6 s-1 [9].

RA in %

w/o stress relief annealing RA in % after stress relief annealed 980°C, 3 hours

Alloy 617 (w/o Boron) 13 %

Alloy 617B (40 ppm Boron) 4.8 41 %

Fig. 2 shows the effect of cooling rate on the reduction of area Z in slow strain rate tests at 700°C. It can be

seen that slow cooling (here: furnace cooling for several hours) has the same effect as additional heat treatment at 980 °C and increases the ductility significantly [13].

05

10152025303540455055606570

B0-1 B0-W B0-L B0-O B3-1 B3-W B3-L B3-O

Red

uct

ion

of

area

Z (

%)

solution annealedstress relief …

230 J. Klöwer et al. / Procedia Engineering 55 ( 2013 ) 226 – 231

The following assessment is given in literatura) Reduction of area: Z < 5% =extremely senb) Reduction of area: Z 5-10% = strongly sec) Reduction of area: Z 10-20% = slightly sd) Reduction of area: Z>> 20% = not signifAccording to this scheme, boron-alloyed 617

3 hours or after slow cooling through the temper

a) Headers and pipes

Fig. 3. Components for 7

4. Summary

Alloy 617B has been tailored for applicationhigher creep strength at 700°C and higher ductishow that cracking under residual stresses canwelding and cold-working. Slow cooling to room

If the peculiarities of this alloy are respectealloy 617B (Fig, 3) and used for 700°C boilers i

Acknowledgements

The authors wish to thank Dr. JulianeMentz aInstitute, Dr. Nicole de Boer, Dr. Martin WGüntherEggeler and Dr. Christoph Sommsen frUniversity of Braunschweig for their contributio

References

[1] VdTÜV-Blatt 485 (VdTÜV Material Data Sheet 485), [2] ASME Standard Specifications B-166 / B-168. [3] Kirchhöfer, Schubert, Nickel: "Precipitation Behavior o

Isothermal Aging", Nuclear Technology, Vol 66, July 1[4] P.P.Schepp, "Mikrostruktur und Kriechverhalten der N

950 °C unter Berücksichtigung aufgekohlterGefügezus

re [14-16]: nsitive

ensitive sensitive ficantly sensitive 7B is not sensitive after appropriate heat-treatment at 980 rature range between 1000 and 800 °C.

b) Superheaters and Re-Heaters

700°C-power plants made of alloy 617 B [7].

n in 700°C USC boilers. Compared to alloy 617, it has aility under creep conditions. Results from Slow-strain rat

n be prevented by a heat treatment at 700°C for 3 hourm temperature has a similarly positive effect on the ductiled, components for 700°C-boilers can easily be producedn USC power plants.

and Dr. Michael Spiegel from Salzgitter Mannesmann Reolf and Dr. Jürgen Tewes from ThyssenKrupp VDM

from Ruhr-University Bochum, and Prof. Joachim Rösleon to this work.

Dec. 2009.

of Ni-Cr-22Fe-18Mo (Hastelloy X) and Ni-Cr-22 Co-12 Mo (Inconel 61984. Nickelbasislegierung Inconel 617 im Temperaturbereich zwischen 850stände", Dissertation Erlangen, D, (1983).

°C for

a 25 % te tests rs after ity. d from

esearch , Prof.

er from

17) after

0°C und

231 J. Klöwer et al. / Procedia Engineering 55 ( 2013 ) 226 – 231

[5] P.J.Ennis and W.J.Quadakkers, "Mechanical Properties and High Temperature Corrosion Resistance of Alloy 617 at 700-1000°C", Proc. Conf. Parsons 2007, 7th Int. Charles Parson Turbine Conf., 11-13 Sept. 2007, Glasgow, UK (2007).

[6] ÜV Rheinland, TÜV Einzelgutachten (Single Material Appraisal) v. 08.07.2003. [7] R.U.Husemann. M.Bader, J.Klöwer, "Metallurgical Aspects during Manufacturing of Nickel Alloy 617B, 9th Int. NIMS-MPa-IfW

Workshop for Advances in High Temperature Materials for High Efficiency Power Plants, 24-26 March 2010, NIMS, Tsukuba, Japan. [8] Q.Wu, "Microstructural Evolution in Advanced Boiler Materials ForUltraSupercritical Coal Power Plants", PhD thesis, University of

Cincinnati, July 2006. [9] M.Spiegel, M.Bader, J.Klöwer, K.H.Tak, H.Tschaffon, U.Zeislmair: "The influence of boron in Alloy 617", 34. Vortragsveranstaltung

FVHT, Düsseldorf, Germany, 2011. [10] D.Tyttko, P.P.Choi, J.Klöwer, A.Kostka, G.Inden, D.Raabe, "Microstructural evolution of a Ni-based superalloy (617B) at 700°C

studied by electron microscopy and atom probe tomography", ActaMaterialia, 60 (2912), 1731-1740. [11] Wortel, J.C.van, "Chemical applications and operational experiences, FDBR Workshop", Düsseldorf, 24-25 Feb. 2005). [12] C.Somsen, G.Eggeler, TEM investigations an alloy 617B, unpublished report, 2010. [13] J.Mentz et al. to be published. [14] J.G.Nawrocki, J.N.DuPont, C.V.Robino, A.R.Marder, Welding Journal, 2001, 80, Welding Research Supplement, pp. 18-s–24-s. [15] A.Dhooge, J.Vekeman, New generation 2 1/4 Cr steels T/P 23 and T/P 24 weldability and high temperature properties,Doc. IIW-1693-

05 (ex. Doc. XI-810-04), Welding in the World, 2005, vol. 49, No. 9/10, pp. 75-93. [16] J.B.Brózda, Welding International, 2004, 18,10. pp. 761-770.