- Email: [email protected]
SS joints conditions for ITER blanket shield
Fusion Engineering and Design 87 (2012) 1461–1465
Contents lists available at SciVerse ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Optimisation of hot isostatic pressing bonded SS/SS joints conditions for ITER blanket shield D. Cédat a , I. Bobin a,∗ , B. Boireau a , P. Bucci b , P. Lorenzetto c a b c
AREVA NP Technical Centre 30, Bld de l’industrie, 71205 Le Creusot Cedex, France CEA DRT/Liten/DTH, 38054 Grenoble, France FUSION FOR ENERGY, Torres Diagonal Litoral, B3, Carrer Josep Pla, 2, 08019 Barcelona, Spain
a r t i c l e
i n f o
Article history: Received 14 September 2011 Received in revised form 13 March 2012 Accepted 13 March 2012 Available online 4 August 2012 With F4E courtesy. Keywords: ITER Blanket Shield 316LN HIP process Powder metallurgy Ultrasonic inspection 3D bent tubes
a b s t r a c t In the engineering design activity of international thermonuclear experimental reactor (ITER), stainless steels are being considered as candidates materials for several module type structures. Hot isostatic pressing (HIP) technique is expected for the fabrication of these modules. Stainless steel powders are simultaneously consolidated as mono-material block or/and joined in bi-material module. This paper reviews the manufacturing stages, non-destructive examination and the developments of the HIP bonded joints of 316L SS (powder and solid) for application to the ITER shield blanket. It is well known that the powder surface oxidation negatively influences the impact toughness of raw material and joints consolidated by this way. In order to get acceptable mechanical properties of materials, a study on the effect of reducing the powder oxygen content has been launched. To evaluate susceptibility to the oxygen content of HIPed joint specimens, tensile and toughness tests have been performed. From this study, optimal conditions of HIP were fitted and the influence of oxygen was mastered to obtain good mechanical properties of the consolidated powder material as well as for HIPed junction. © 2012 Elsevier B.V. All rights reserved.
1. Background/introduction The technologies required to manufacture the ITER shield blanket were under development up to have the design and manufacturing techniques progressing enough to meet/respect the specific cooling requirements of shield blanket, needed in 2003 from the heat fluxes to be sustained. In the frame of the contract EFDA/03.954, the main objectives of the shield blanket module development were listed as: – Developing the technologies required for manufacturing the shield blanket system. – Demonstrating the manufacturing feasibility by fabricating prototypical components. – Demonstrating adequate operational performance of the various blanket system components.
sawing, 3D tube bending. By welding together all the sub-parts, the main part of the water coolant circuit has been erected. Once the water circuit was built; the shield was completed using powder HIPping together with forged block embedding the tubes and their maintaining parts in a final solid part. The powder/solid HIP process was used to minimise the number of seal welds facing the plasma and to increase the reliability of the components during operation. About 300 kg of stainless steel powder was densified together with the forged block. 3D measurement was done before and after the HIP cycle to collect the data to be compared with theoretical model and thus to predict the main distortions of the solid bulk. As main characterisations, ultrasonic examination of the densified powder on the Stainless steel bulk and around the bent tubes was performed as well as metallurgical and mechanical characterisation of the samples HIPed besides. 2. Experimental procedure and results
The manufactured shield was a full scale module obtained from a forged block of 1350 mm × 1300 mm × 450 mm, and main machining steps such as deep drilling (1200 mm), 3D machining and
∗ Corresponding author. E-mail address: [email protected] (I. Bobin). 0920-3796/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2012.03.031
2.1. Materials The austenitic stainless steel 316L(N)-IG type is one of the main structural materials considered for the in-vessel components of ITER. The material shall operate in the temperature range 100–300 ◦ C, under significant irradiation dose. Both traditional
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D. Cédat et al. / Fusion Engineering and Design 87 (2012) 1461–1465
Fig. 1. SS block of the shield machined.
(rolling, forging, casting, etc.) and advanced manufacturing technologies (powder and solid-HIP) are proposed for the ITER components manufacturing. This paper presents the results of investigation performed on 316L(N)-IG steel which the composition is given in Table 1. 2.2. Shield manufacturing steps The shield block is designed as a block of stainless steel with an integrated water cooling system. The obvious approach for manufacture is to start from a solid forged block of steel, to drill the penetration holes and coolant channels from lateral surfaces (as shown in Fig. 1), to close the channels by welding thin plugs without any distortion from the outside, to consolidate by solid/solid HIPing these thin plugs by thick plates and to machine the outer surfaces including the recesses. However, the ITER design called for 3D hydraulic gallery which was impossible to machine or obtain by drilling. It was decided to use 3D bent tubes to be embedded in stainless steel (shown in Fig. 2). Because of this complexity and the need to intimately join tubes and shield body, the alternative route of powder-HIP was explored. The coolant channel geometry needed from cooling requirements, is manufactured as a bent tube gallery. After the tube gallery is placed on the back side of the shield (shown in Fig. 3), a can calculated and designed by CEA Grenoble was manufactured and welded (Fig. 4). Then the can is filled with the steel powder and vibrated to ensure the completeness of the powder filling before seal welding and pumping for gas evacuation.
Fig. 2. Gallery of 3D bent tubes foreseen in the shield coolant system design.
Fig. 3. Can preparation on the backside of the shield.
The assembly with its tooling was put into the 1300 mm diameter HIP facility of Bodycote Surahammar in Sweden, where it has been exposed to a temperature of 1100 ◦ C and a pressure of ∼140 MPa for 4 h (Fig. 5). After removal of the can, the outer surfaces were machined to obtain the last finish with flanges between bent tubes and castellations between drilled holes (Fig. 6).
2.3. Oxygen control It is well known [1] that surface oxides on the powder particles negatively influence mechanical properties and particularly the impact toughness of material and joints consolidated in this way. At a very high HIP temperature, the oxides are at least partly transformed, thereby improving the impact toughness [2]. But in the HIP procedure used in this study, the temperature has been kept at only 1100 ◦ C. In order to get acceptable mechanical properties of materials produced at a low HIP temperature, the oxygen content on the powder surfaces needed to be lowered. The procurement of the metallic powder has been made at a lower content oxygen powder (∼140 ppm) based on previous studies showing a maximum content of oxygen at 150 ppm to insure good mechanical properties. A specification on surface cleaning between steel blocks and tubes has been improved in order to keep a low oxygen content at the surface with powder consolidated material.
Fig. 4. TIG welding of container.
D. Cédat et al. / Fusion Engineering and Design 87 (2012) 1461–1465
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Table 1 Chemical composition of the 316L(N)-IG stainless steel.
Composition of powder SS (wt.%) Composition of forged SS (wt.%)
Fe
Cr
Mo
Ni
C
Mn
Si
Cu
N
S
P
Bal. Bal.
17.7 17.6
2.56 2.46
12.3 12.2
0.023 0.026
1.68 1.83
0.41 0.30
0.23 0.18
0.11 0.07
0.009 0.001
0.025 0.024
Fig. 7. (a) Typical microstructure of forged 316L(N)-IG SS block and SS powderHIPed (b).
Fig. 5. Shield after HIPing.
2.4. Results of investigation 2.4.1. Microstructure examination Microstructure observations have been performed on both 316L(N)-IG forged and 316L(N)-IG powder-Hip material. The micrographies are presented in Fig. 7. It has been observed that the 316L(N)-IG forged stainless steel presented larger grains size (ASTM 1–2) than the steel 316L(N)-IG powder HIPed (ASTM 3–4). 2.4.2. Tensile tests results Samples have been manufactured with same base metal for both 316L(N)-IG solid and 316L(N)-IG powder-HIPed. 10 mm diameter cylindrical specimens have been used for tensile tests.
The tensile properties of the 316L(N)-IG forged and 316L(N)-IG powder-HIPed are presented in Table 2. Specification data for the reference (wrought) steel is also given in the table for comparison. Tensile tests were also carried out on the 316L(N)-IG forged/316L(N)-IG powder junction after HIP. The bonding area is located in the middle of the cylindrical specimens to test the junction. Results of ultimate tensile strength, yield strength and total elongation measured in the present tests are shown in Table 3, at room temperature and at 300 ◦ C. It was observed that the rupture does not occur in the junction but in the 316LN forged material. It means that the junction quality is satisfactory. The localisation of the material distortion could be explained by the grain size which is lower in the 316LN powder than in 316LN forged. 2.4.3. Impact toughness Impact properties do not figure in the conventional design criteria for ductile materials, such as austenitic stainless steel. However, acceptance tests include specification for minimum values of 120 J/cm2 in the as-received state for forged or base metal.
Impact Toughness (J/cm²)
300
forged (ref)
250 200 150 100 50 0 Ra 0,8
Fig. 6. Shield after final machining (rear face).
Ra 1,6
Ra 3,2
Fig. 8. Impact toughness properties at 20 ◦ C, of the 316LN forged /316LN powder HIPed junction for two samples 䊉 and .
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Table 2 Tensile properties (YS, UTS) of 316LN forged and 316LN powder samples after HIP. Samples ref.
Temperature (◦ C)
Yield strength (YS)
Ultimate yield strength (UTS)
Elongation (%)
316LN forged 316LN forged 316LN powder 316LN powder ITER structural design criteria for in-vessel components
20 300 20 300 20 300
277 142 300 190 220 132
550 383 643 524 525 430
60 58 45 37
Table 3 Tensile properties (YS, UTS) of 316LN forged/316LN powder junctions after HIP. Samples ref.
Temperature (◦ C)
Yield strength (YS)
Ultimate yield strength (UTS)
Elongation (%)
316LN forged/316LN powder 316LN forged/316LN powder
20 300 20 300
260 152 220 132
567 443 525 430
35 27
RCC-MR
Fig. 8 graphically presents the results of all tested samples. Compared to the acceptance values proposed for ITER, these values higher than forged material, are acceptable. A study on the roughness effect (Ra = 0,8; 1,6 and 3,2) on the impact toughness has been launched in the same time. The properties showed only small difference, which allows to conclude that it is not an essential parameter, at low roughness.
2.4.4. UT inspection HIP cycle was validated through ultrasonic examinations. A first machining was then realised to level the surfaces, before UT examinations took place. The UT inspection from the surface allowed verification of complete powder densification and localisation of the tubes after HIPing, and before final machining. The recorded data allow the following B-Scan as presented in Fig. 9. No defects have been detected in the bulk or at the junctions. The quality of the tube/base material junction has also to be inspected with ultrasonic examination technique from the inner side of the tubes. Thus, a new inspection tool has been developed (as shown in Fig. 10), which makes it possible to provide a global density map of sintered parts, in particular the tube/powder-HIP bonded. Nevertheless, this improved equipment imposed to master the tube shape. Modelling was then done to master this tubes distortion during HIPing in order to avoid problems when the US probe passed through the cooling circuit for defect examination.
2.4.5. Modelling and simulation It is well known that HIPing part with powder and solid cores results in non negligible shape changes. On the shield, two kinds of problems have been looked at:
Fig. 9. UT examination on the backside of the shield: no defect; localisation of the tubes for final machining between tubes.
– Modelling of the shape changes of the shield to have final overall dimension conformity. – Modelling of problems linked to the tubes embedded in powder while HIPing, to know location of tubes before machining. In the field of modelling powder behaviour during HIP, Areva had benefit of the CEA Grenoble knowledge. The law, used in this study to describe the powder deformation, was the usual Abouaf’s law with slight upgrade in the formulation as the consideration of isotropic hardening. The parameters have been identified from bibliography and experiments.
Fig. 10. UT inspection tool developed for the control from the inner side of the tubes.
D. Cédat et al. / Fusion Engineering and Design 87 (2012) 1461–1465
The behaviours of the tubes, the massive 316LN block, the container in 304 L stainless steel, were assumed to obey a Chaboche’s law. To address the simulation problems, several parts have been analysed through numerical simulations. The model was established and applied for the simulation of a very simplified geometry to adjust the parameters of the law and validated it in order to ensure the relevancy of the calculations. In fact, the location of the tube during HIP cycle has to be controlled precisely, firstly because some post-hip machining has to be done very close to the tube and secondly because the tube shape has to be kept as much circular as possible. 3. Discussion During the manufacture of the blanket modules, 316L(N)-IG is simultaneously consolidated and joined to tubes and blocks of 316L(N)-IG materials by hot isostatic pressing. The tests performed have shown that the proposed HIP cycle is able to get sufficiently high properties for both 316LN powder-HIPed and the junction of 316L(N)-IG forged/316L(N)-IG powder-HIPed, without decrease the wrought steel properties. The UT examination of the shield at the powder/SS solid HIPed junctions (back side, bottom side and top side) does not reveal any indication of lack of bonding. A large part of the tubes have been inspected by the inside, except some tubes due to the complex geometry and the risk to jam the probe in it. The modelling of tubes embedded in powder has confirmed the fact that these tubes turn to be much elliptical after HIP if no special
1465
attention is paid to this aspect. It has permitted to improve the preparation before HIPing to avoid this phenomenon. Although the topology measurements after HIP gave a first good distortion estimation, it also showed that the simulation had to be optimised to give a better mastering of the shield densification. 4. Conclusions This first shield prototype fabricated from forged and powder HIP stainless steel showed that this component which is very complex to manufacture is feasible: – Fabrication operations like deep drilling, slots machining, 3D bending, monitoring of HIP distortions have been successfully anticipated and prepared. – Great progress has been made during this study in understanding the thermal distortion of the shield. The materials and the manufacturing technologies have been assessed. Module prototype have been successfully built and being tested integrally. References [1] L. Arnberg, A. Karlsson, Influence of powder surface oxidation on some properties of a HIPed martensitic chromium steel, International Journal of Powder Metallurgy 24 (2) (1988) 107–112. [2] L. Nyborg, I. Olefjord, Surface analysis of PM martensitic steel before and after consolidation. Part 2. Surface analysis of compacted material, Powder Metallurgy 31 (1) (1988) 40–44.
Contents lists available at SciVerse ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Optimisation of hot isostatic pressing bonded SS/SS joints conditions for ITER blanket shield D. Cédat a , I. Bobin a,∗ , B. Boireau a , P. Bucci b , P. Lorenzetto c a b c
AREVA NP Technical Centre 30, Bld de l’industrie, 71205 Le Creusot Cedex, France CEA DRT/Liten/DTH, 38054 Grenoble, France FUSION FOR ENERGY, Torres Diagonal Litoral, B3, Carrer Josep Pla, 2, 08019 Barcelona, Spain
a r t i c l e
i n f o
Article history: Received 14 September 2011 Received in revised form 13 March 2012 Accepted 13 March 2012 Available online 4 August 2012 With F4E courtesy. Keywords: ITER Blanket Shield 316LN HIP process Powder metallurgy Ultrasonic inspection 3D bent tubes
a b s t r a c t In the engineering design activity of international thermonuclear experimental reactor (ITER), stainless steels are being considered as candidates materials for several module type structures. Hot isostatic pressing (HIP) technique is expected for the fabrication of these modules. Stainless steel powders are simultaneously consolidated as mono-material block or/and joined in bi-material module. This paper reviews the manufacturing stages, non-destructive examination and the developments of the HIP bonded joints of 316L SS (powder and solid) for application to the ITER shield blanket. It is well known that the powder surface oxidation negatively influences the impact toughness of raw material and joints consolidated by this way. In order to get acceptable mechanical properties of materials, a study on the effect of reducing the powder oxygen content has been launched. To evaluate susceptibility to the oxygen content of HIPed joint specimens, tensile and toughness tests have been performed. From this study, optimal conditions of HIP were fitted and the influence of oxygen was mastered to obtain good mechanical properties of the consolidated powder material as well as for HIPed junction. © 2012 Elsevier B.V. All rights reserved.
1. Background/introduction The technologies required to manufacture the ITER shield blanket were under development up to have the design and manufacturing techniques progressing enough to meet/respect the specific cooling requirements of shield blanket, needed in 2003 from the heat fluxes to be sustained. In the frame of the contract EFDA/03.954, the main objectives of the shield blanket module development were listed as: – Developing the technologies required for manufacturing the shield blanket system. – Demonstrating the manufacturing feasibility by fabricating prototypical components. – Demonstrating adequate operational performance of the various blanket system components.
sawing, 3D tube bending. By welding together all the sub-parts, the main part of the water coolant circuit has been erected. Once the water circuit was built; the shield was completed using powder HIPping together with forged block embedding the tubes and their maintaining parts in a final solid part. The powder/solid HIP process was used to minimise the number of seal welds facing the plasma and to increase the reliability of the components during operation. About 300 kg of stainless steel powder was densified together with the forged block. 3D measurement was done before and after the HIP cycle to collect the data to be compared with theoretical model and thus to predict the main distortions of the solid bulk. As main characterisations, ultrasonic examination of the densified powder on the Stainless steel bulk and around the bent tubes was performed as well as metallurgical and mechanical characterisation of the samples HIPed besides. 2. Experimental procedure and results
The manufactured shield was a full scale module obtained from a forged block of 1350 mm × 1300 mm × 450 mm, and main machining steps such as deep drilling (1200 mm), 3D machining and
∗ Corresponding author. E-mail address: [email protected] (I. Bobin). 0920-3796/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2012.03.031
2.1. Materials The austenitic stainless steel 316L(N)-IG type is one of the main structural materials considered for the in-vessel components of ITER. The material shall operate in the temperature range 100–300 ◦ C, under significant irradiation dose. Both traditional
1462
D. Cédat et al. / Fusion Engineering and Design 87 (2012) 1461–1465
Fig. 1. SS block of the shield machined.
(rolling, forging, casting, etc.) and advanced manufacturing technologies (powder and solid-HIP) are proposed for the ITER components manufacturing. This paper presents the results of investigation performed on 316L(N)-IG steel which the composition is given in Table 1. 2.2. Shield manufacturing steps The shield block is designed as a block of stainless steel with an integrated water cooling system. The obvious approach for manufacture is to start from a solid forged block of steel, to drill the penetration holes and coolant channels from lateral surfaces (as shown in Fig. 1), to close the channels by welding thin plugs without any distortion from the outside, to consolidate by solid/solid HIPing these thin plugs by thick plates and to machine the outer surfaces including the recesses. However, the ITER design called for 3D hydraulic gallery which was impossible to machine or obtain by drilling. It was decided to use 3D bent tubes to be embedded in stainless steel (shown in Fig. 2). Because of this complexity and the need to intimately join tubes and shield body, the alternative route of powder-HIP was explored. The coolant channel geometry needed from cooling requirements, is manufactured as a bent tube gallery. After the tube gallery is placed on the back side of the shield (shown in Fig. 3), a can calculated and designed by CEA Grenoble was manufactured and welded (Fig. 4). Then the can is filled with the steel powder and vibrated to ensure the completeness of the powder filling before seal welding and pumping for gas evacuation.
Fig. 2. Gallery of 3D bent tubes foreseen in the shield coolant system design.
Fig. 3. Can preparation on the backside of the shield.
The assembly with its tooling was put into the 1300 mm diameter HIP facility of Bodycote Surahammar in Sweden, where it has been exposed to a temperature of 1100 ◦ C and a pressure of ∼140 MPa for 4 h (Fig. 5). After removal of the can, the outer surfaces were machined to obtain the last finish with flanges between bent tubes and castellations between drilled holes (Fig. 6).
2.3. Oxygen control It is well known [1] that surface oxides on the powder particles negatively influence mechanical properties and particularly the impact toughness of material and joints consolidated in this way. At a very high HIP temperature, the oxides are at least partly transformed, thereby improving the impact toughness [2]. But in the HIP procedure used in this study, the temperature has been kept at only 1100 ◦ C. In order to get acceptable mechanical properties of materials produced at a low HIP temperature, the oxygen content on the powder surfaces needed to be lowered. The procurement of the metallic powder has been made at a lower content oxygen powder (∼140 ppm) based on previous studies showing a maximum content of oxygen at 150 ppm to insure good mechanical properties. A specification on surface cleaning between steel blocks and tubes has been improved in order to keep a low oxygen content at the surface with powder consolidated material.
Fig. 4. TIG welding of container.
D. Cédat et al. / Fusion Engineering and Design 87 (2012) 1461–1465
1463
Table 1 Chemical composition of the 316L(N)-IG stainless steel.
Composition of powder SS (wt.%) Composition of forged SS (wt.%)
Fe
Cr
Mo
Ni
C
Mn
Si
Cu
N
S
P
Bal. Bal.
17.7 17.6
2.56 2.46
12.3 12.2
0.023 0.026
1.68 1.83
0.41 0.30
0.23 0.18
0.11 0.07
0.009 0.001
0.025 0.024
Fig. 7. (a) Typical microstructure of forged 316L(N)-IG SS block and SS powderHIPed (b).
Fig. 5. Shield after HIPing.
2.4. Results of investigation 2.4.1. Microstructure examination Microstructure observations have been performed on both 316L(N)-IG forged and 316L(N)-IG powder-Hip material. The micrographies are presented in Fig. 7. It has been observed that the 316L(N)-IG forged stainless steel presented larger grains size (ASTM 1–2) than the steel 316L(N)-IG powder HIPed (ASTM 3–4). 2.4.2. Tensile tests results Samples have been manufactured with same base metal for both 316L(N)-IG solid and 316L(N)-IG powder-HIPed. 10 mm diameter cylindrical specimens have been used for tensile tests.
The tensile properties of the 316L(N)-IG forged and 316L(N)-IG powder-HIPed are presented in Table 2. Specification data for the reference (wrought) steel is also given in the table for comparison. Tensile tests were also carried out on the 316L(N)-IG forged/316L(N)-IG powder junction after HIP. The bonding area is located in the middle of the cylindrical specimens to test the junction. Results of ultimate tensile strength, yield strength and total elongation measured in the present tests are shown in Table 3, at room temperature and at 300 ◦ C. It was observed that the rupture does not occur in the junction but in the 316LN forged material. It means that the junction quality is satisfactory. The localisation of the material distortion could be explained by the grain size which is lower in the 316LN powder than in 316LN forged. 2.4.3. Impact toughness Impact properties do not figure in the conventional design criteria for ductile materials, such as austenitic stainless steel. However, acceptance tests include specification for minimum values of 120 J/cm2 in the as-received state for forged or base metal.
Impact Toughness (J/cm²)
300
forged (ref)
250 200 150 100 50 0 Ra 0,8
Fig. 6. Shield after final machining (rear face).
Ra 1,6
Ra 3,2
Fig. 8. Impact toughness properties at 20 ◦ C, of the 316LN forged /316LN powder HIPed junction for two samples 䊉 and .
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D. Cédat et al. / Fusion Engineering and Design 87 (2012) 1461–1465
Table 2 Tensile properties (YS, UTS) of 316LN forged and 316LN powder samples after HIP. Samples ref.
Temperature (◦ C)
Yield strength (YS)
Ultimate yield strength (UTS)
Elongation (%)
316LN forged 316LN forged 316LN powder 316LN powder ITER structural design criteria for in-vessel components
20 300 20 300 20 300
277 142 300 190 220 132
550 383 643 524 525 430
60 58 45 37
Table 3 Tensile properties (YS, UTS) of 316LN forged/316LN powder junctions after HIP. Samples ref.
Temperature (◦ C)
Yield strength (YS)
Ultimate yield strength (UTS)
Elongation (%)
316LN forged/316LN powder 316LN forged/316LN powder
20 300 20 300
260 152 220 132
567 443 525 430
35 27
RCC-MR
Fig. 8 graphically presents the results of all tested samples. Compared to the acceptance values proposed for ITER, these values higher than forged material, are acceptable. A study on the roughness effect (Ra = 0,8; 1,6 and 3,2) on the impact toughness has been launched in the same time. The properties showed only small difference, which allows to conclude that it is not an essential parameter, at low roughness.
2.4.4. UT inspection HIP cycle was validated through ultrasonic examinations. A first machining was then realised to level the surfaces, before UT examinations took place. The UT inspection from the surface allowed verification of complete powder densification and localisation of the tubes after HIPing, and before final machining. The recorded data allow the following B-Scan as presented in Fig. 9. No defects have been detected in the bulk or at the junctions. The quality of the tube/base material junction has also to be inspected with ultrasonic examination technique from the inner side of the tubes. Thus, a new inspection tool has been developed (as shown in Fig. 10), which makes it possible to provide a global density map of sintered parts, in particular the tube/powder-HIP bonded. Nevertheless, this improved equipment imposed to master the tube shape. Modelling was then done to master this tubes distortion during HIPing in order to avoid problems when the US probe passed through the cooling circuit for defect examination.
2.4.5. Modelling and simulation It is well known that HIPing part with powder and solid cores results in non negligible shape changes. On the shield, two kinds of problems have been looked at:
Fig. 9. UT examination on the backside of the shield: no defect; localisation of the tubes for final machining between tubes.
– Modelling of the shape changes of the shield to have final overall dimension conformity. – Modelling of problems linked to the tubes embedded in powder while HIPing, to know location of tubes before machining. In the field of modelling powder behaviour during HIP, Areva had benefit of the CEA Grenoble knowledge. The law, used in this study to describe the powder deformation, was the usual Abouaf’s law with slight upgrade in the formulation as the consideration of isotropic hardening. The parameters have been identified from bibliography and experiments.
Fig. 10. UT inspection tool developed for the control from the inner side of the tubes.
D. Cédat et al. / Fusion Engineering and Design 87 (2012) 1461–1465
The behaviours of the tubes, the massive 316LN block, the container in 304 L stainless steel, were assumed to obey a Chaboche’s law. To address the simulation problems, several parts have been analysed through numerical simulations. The model was established and applied for the simulation of a very simplified geometry to adjust the parameters of the law and validated it in order to ensure the relevancy of the calculations. In fact, the location of the tube during HIP cycle has to be controlled precisely, firstly because some post-hip machining has to be done very close to the tube and secondly because the tube shape has to be kept as much circular as possible. 3. Discussion During the manufacture of the blanket modules, 316L(N)-IG is simultaneously consolidated and joined to tubes and blocks of 316L(N)-IG materials by hot isostatic pressing. The tests performed have shown that the proposed HIP cycle is able to get sufficiently high properties for both 316LN powder-HIPed and the junction of 316L(N)-IG forged/316L(N)-IG powder-HIPed, without decrease the wrought steel properties. The UT examination of the shield at the powder/SS solid HIPed junctions (back side, bottom side and top side) does not reveal any indication of lack of bonding. A large part of the tubes have been inspected by the inside, except some tubes due to the complex geometry and the risk to jam the probe in it. The modelling of tubes embedded in powder has confirmed the fact that these tubes turn to be much elliptical after HIP if no special
1465
attention is paid to this aspect. It has permitted to improve the preparation before HIPing to avoid this phenomenon. Although the topology measurements after HIP gave a first good distortion estimation, it also showed that the simulation had to be optimised to give a better mastering of the shield densification. 4. Conclusions This first shield prototype fabricated from forged and powder HIP stainless steel showed that this component which is very complex to manufacture is feasible: – Fabrication operations like deep drilling, slots machining, 3D bending, monitoring of HIP distortions have been successfully anticipated and prepared. – Great progress has been made during this study in understanding the thermal distortion of the shield. The materials and the manufacturing technologies have been assessed. Module prototype have been successfully built and being tested integrally. References [1] L. Arnberg, A. Karlsson, Influence of powder surface oxidation on some properties of a HIPed martensitic chromium steel, International Journal of Powder Metallurgy 24 (2) (1988) 107–112. [2] L. Nyborg, I. Olefjord, Surface analysis of PM martensitic steel before and after consolidation. Part 2. Surface analysis of compacted material, Powder Metallurgy 31 (1) (1988) 40–44.