Home Effect of thermo-mechanical parameters on the mechanical properties of Eurofer97 steel for nuclear applications
Article Open Access

Effect of thermo-mechanical parameters on the mechanical properties of Eurofer97 steel for nuclear applications

  • Andrea Di Schino EMAIL logo , Claudio Testani and Luciano Pilloni
Published/Copyright: October 26, 2018
Become an author with De Gruyter Brill

Abstract

Eurofer97 steel has been recognised in Europe as the reference steel for nuclear application under high radiation density. Following to this a detailed knowledge of microstructure evolution is required for such steel after thermo-mechanical processing. In this paper the effect of thermo-mechanical parameters on the mechanical behavior of Eurofer97 was investigated by hot rolling and heat treatment on pilot scale. Results show a strong effect was found of reheating temperature before rolling on the material hardness, due to an increase of hardenability following the austenite grain growth. A minor effect was found of the hot reduction and the tempering temperature in the total investigated deformation range. A loss of impact energy was found coupled with the hardness increase.

1 Introduction

In Europe EUROFER97 has been recognised as reference steel [1] for the nuclear costructions under high radiation density for first wall of a fast breeder reactors as well as in other high stressed primary structures such as the divertors, blanklet and vessels, [2, 3, 4, 5, 6, 7]. One of the main reason for this selection are the EUROFER97 steel high mechanical properties at service temperatures coupled with the low or reduced activation (RAFM) characteristic under radiation with the result of low mechanical properties loss. This material behavior has been reported in many literature studies and important initiatives are still ongoing [8, 9, 10]. The reduced activation ferritic/martensitic steels differ from conventional Cr-Mo steels because of W presence instead of Mo. With this respect EUROFER 97 steel is essentially a low carbon steel with 9 Cr (% wt) with controlled Ta and V (favoring grain refinement and enhancing precipitation state) content that can have an important influence on resulting final mechanical properties in carbon and stainless steels [11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21]. EUROFER 97 reference chemical composition is reported in Table 1.

Table 1

EUROFER 97 chemical composition (mass, %) (Ni, Mo, Cu, Nb, Al, B, Co: as low as possible (ALAP), S = 20 ppm, P = 100 ppm)

CMnCrVTaWNAs+Sn+Sb+Zr
0.110.49.00.20.071.0-2.00.030ALAP, 0,05

Moreover, other elements such us Mo, Nb, Ni, Cu and N, are maintained as low as possible. The irradiation tests carried on EUROFER 97 show that the resulting radioactivity levels over two orders of magnitude under those recorded for conventional Cr steels [22, 23, 24], with low affected mechanical and physical properties [9, 10]. Low activation steels have a fully austenite structure when are austenitized in the temperature range from 850C to 1200C. Austenite phase transforms to martensite phase during air cooling or rapid cooling (quenching) to room temperature, and then steels are tempered to obtain a good combination of strength, ductility, and toughness. However, the use of these materials during long-time at high temperatures (thermal ageing) can produce microstructural changes (new precipitates, grain growth, segregation, etc.) which can significantly affect their mechanical properties (tensile, Charpy-V, fracture toughness, low cycle fatigue, etc.) [23, 24, 25]. For these reasons, an exhaustive knowledge of the metallurgical characteristics of these steels before and after thermal ageing is considered essential. In RAFM steels the desirable properties (low sensibility to radiation damage) are controlled by mean of the martensitic transformation thermal cycle design, and in particular are due the microstructure refinement (increase of the low and high angle boundaries) with clear advantages for applications in nuclear reactors [1]. The martensitic transformation occurs in steels by mean of a non-diffusional transformation when the material is cooled from above Ac1 to a sufficiently lower temperature (Ms) with cooling rate higher than the “critical cooling-rate”: in these condition the transformation is lead from the energy decrease due to the metastable face-centered cubic (FCC) phase arrangement in the new stable body-centered cubic (BCC) phase [2]. The conventional EUROFER 97 thermal treatment consists in normalization at 980C/30 minutes + temper at 760C/90’/air-cooling [12].

In this work the effect of thermo-mechanical treatment on the microstructure is analyzed, aimed to achieve higher tensile properties in order to evaluate its feasibility as possible structural material for fusion applications. In particular, the effect of thermo-mechanical and tempering treatment at T = 750C and 720C is analyzed in comparison with standard tempering condition for improving fusion applications ranges.

2 Methods

Starting from a EUROFER 97 rolled plate with the steel chemical composition reported in Table 1, the effect of reheating temperatures (before hot rolling) and rolling temperatures is analyzed. The plate was hot rolled on a pilot scale (diameter of working roll = 450 mm) adopting two different reheating temperatures (1075C and 1175C for 60 minutes), together with two finish rolling temperatures (750C and 650C) and two different total reductions (30% and 40%). Reductions were in all cases given in 3 passes. The plate was air-cooled (cooling rate about 5C/s). The effect of tempering treatment after hot rolling is also analyzed (in the temperature range 720C-760 C). Hardness and Charpy-V impact tests at −20C are carried out on transverse specimens. Microstructure is analyzed by light microscopy after Vilella etching.

3 Results and discussion

A limited effect was found following to the variation of rolling temperature, reheating temperature and reduction in the considered range (Figure 1).

Figure 1 Effect of thermo-mechanical parameters on EUROFER 97 hardness (a: 30% hot reduction, b: 40% hot reduction)
Figure 1

Effect of thermo-mechanical parameters on EUROFER 97 hardness (a: 30% hot reduction, b: 40% hot reduction)

The effect of tempering following the hot rolling as a function of thermo-mechanical parameters is reported in Table 2. Results show that higher hardness values are found after re-heating at higher temperature (1175C).

Table 2

Effect of tempering after hot rolling

Specimen nReheating (C) TRolling (C) THot reduction, (%)Tempering T (C)
720760
HV10HV10
175030278225
2107540267225
365030271228
440270234
575030284251
6117540290246
765030298254
840306259

This is due to an improvement of hardenability following an increase of austenite grain size. In Figure 2 the microstructure evolution is reported for specimens 1–8 after tempering at T = 720C. Results show a clear effect of reheating temperature on austenite grain growth. Average grain size was about 20 μm in the case of specimens austenitised at 1075C and about 200 μmafter austenitisation at 1175C. The same effect is independent and effective also in the case of specimens after tempering at T = 760C.

Figure 2 (a) Microstructure evolution of EUROFER 97 after thermo-mechanical processing according to Table 2 (Final rolling temperature = 750∘C; (b)Microstructure evolution of EUROFER 97 after thermo-mechanical processing according to Table 2 (Final rolling temperature = 650∘C
Figure 2

(a) Microstructure evolution of EUROFER 97 after thermo-mechanical processing according to Table 2 (Final rolling temperature = 750C; (b)Microstructure evolution of EUROFER 97 after thermo-mechanical processing according to Table 2 (Final rolling temperature = 650C

At the same time larger austenitic grain size (due to higher austenitization temperature) leads to an intense decrease of impact toughness behavior. In Table 3 the effect of austenite grain size on impact energy is reported: a decrease of CVN energy is found as hardness is increased, as expected, following to an increase of critical cleavage stress [26, 27].

Table 3

Effect of reheating temperature on Charpy-V notch toughness

Reheating T = 1075 C

HV10 = 267
Reheating T = 1175 C
HV10 = 306
CVN-Test T= -20C ASTM A673 fullCVN-Test T = −20C ASTM A673-
size - specimenfull size specimen
mean Value (J) (three tests)Dispersion (J)Mean Value (J) (three tests)Dispersion (J)
63+/− 159+/− 2
Fracture appearance = 100%Fracture appearance = 100%
ductilebrittle

4 Conclusions

The effects of thermo-mechanical parameters on the mechanical behavior of EUROFER 97were investigated by hot rolling and tempering heat treatment on pilot scale. Results show that EUROFER 97 is a high sensitive material to the thermo-mechanical process and thermal post process cycle. In fact, a strong effect was found of reheating temperature before rolling on the material hardness, due to an increase of hardenability following the austenite grain growth. Apoor effect of the hot reduction and of the following tempering temperature was detected in the total thickness reduction range: 30-40%. An intense loss of CV-N impact energy is found coupled with the hardness increase when the reheating temperature is increased from 1075C up to 1150C.

Acknowledgement

The present paper summarise some of the research results obtained under EUROFUSION funded activities.

References

[1] Rieth M., Dafferner B., Rohrig H.D., Wassilew C., Charpy impact properties of martensitic 10.6 Cr steel after neutron exposure, Fusion Engineering and Design, 1995, 29, 365-37010.1016/0920-3796(95)80043-WSearch in Google Scholar

[2] Zilnyk K.D., Oliveira V.B., Sandim H.R.Z., Möslang A., Raabe D., Martensitic transformation in eurofer-97 and ODS-eurofer steels: A comparative study, J. Nucl. Mater., 2015, 462, 360-36710.1016/j.jnucmat.2014.12.112Search in Google Scholar

[3] Möslang A., IFMIF: the intense neutron source to qualify materials for fusion reactors Comptes Rendus Physique, 2008, 9, 457-46810.1016/j.crhy.2007.10.018Search in Google Scholar

[4] S.J. Zinkle, Was G.S., Materials challenges in nuclear energy, Acta Mater., 2013, 61, 735–73810.1016/j.actamat.2012.11.004Search in Google Scholar

[5] Guerin Y., Was G.S, Zinkle S.J., Materials Challenges for Advanced Nuclear Energy Systems, MRS Bulettin, 2009, 34, 10-14Search in Google Scholar

[6] Marcus G.H., Progress in Nuclear Energy, Innovative Nuclear Energy Systems and the Future of Nuclear Power.2008, 50, 92-9610.1016/j.pnucene.2007.10.009Search in Google Scholar

[7] Ehrlich K., Konys J., Heiinheimo L., Recent progress in research on tungsten materials for nuclear fusion applications in Europe, J. Nucl. Mater., 2004, 327,140-14710.1016/j.jnucmat.2004.01.020Search in Google Scholar

[8] Klueh R.L., Donald D.R. Harries, High Chromium Ferritic and Martensitic Steels for Nuclear Applications, ASTM Stock number, 200110.1520/MONO3-EBSearch in Google Scholar

[9] Tan L., Hoelzer L., Busby J.T., Sokolov M.A., Klueh R.L., Microstructure control for high strength 9Cr ferritic–martensitic steels, J. Nucl. Mater., 2012, 422, 45-5010.1016/j.jnucmat.2011.12.011Search in Google Scholar

[10] Tan L., Ren X., Allen T.R., Corrosion behaviour of 9-12% Cr ferritic martensitic steels, Corrosion Science, 2010, 52, 1520-152810.1016/j.corsci.2009.12.032Search in Google Scholar

[11] Dulieu D., Tupholme K., Butterworth G.J., J. Nucl. Mater., 1986, 141-143, 1097-110110.1016/0022-3115(86)90148-0Search in Google Scholar

[12] Was G.S., Fundamentals of Radiation Materials Science. Metals and Alloy (Second editon), Springer, Berlin, 2016 10.1007/978-1-4939-3438-6Search in Google Scholar

[13] Declan B., Nuclear power energy Nature, 2004, 429, 238-24010.1038/429238aSearch in Google Scholar PubMed

[14] Kvačkaj T., Bidulský R., Kováčová A., Ileninová J., Bidulská J., Analysis of metallic materials for iter with emphasis on Cu alloys, Acta Metallurgica Slovaca, 2014, 20, 397-40410.12776/ams.v20i4.438Search in Google Scholar

[15] Di Schino A., Di Nunzio P.E., Metallurgical aspects related to contact fatigue phenomena in steels for back-up rolls, Acta Metallurgica Slovaca, 2017, 23, 62-7110.12776/ams.v23i1.852Search in Google Scholar

[16] Hilger L., Boulnat X., Hoffman J., Testani C., Bergner F., Ferraro F., Ulbricht A., Fabrication and characterization of oxide dispersion strengthened (ODS) 14Cr steels consolidated by means of hot isostatic pressing, hot extrusion and spark plasma sintering, J. Nucl. Mater., 2016, 472, 206-21410.1016/j.jnucmat.2015.09.036Search in Google Scholar

[17] Gabrel J., Coussement C., Verelst L., Blum R., Chen Q., Testani C., Superheater materials testing for USC boilers: Steam side oxidation rate of 9 advanced materials in industrial conditions, Materials Science Forum, 2001, 369-372, 931-93810.4028/www.scientific.net/MSF.369-372.931Search in Google Scholar

[18] Di Schino A., Analysis of heat treatment effect on microstructural features evolution in a micro-alloyed martensitic steel, Acta Metallurgica Slovaca, 2016, 22, 266-27010.12776/ams.v22i4.815Search in Google Scholar

[19] Di Schino A., Di Nunzio P.E., Niobium effect on base metal and heat affected zone microstructure of girth welded joints, Acta Metallurgica Slovaca, 2017, 23, 55-6110.12776/ams.v23i1.836Search in Google Scholar

[20] Di Schino A., Richetta M., Evaluation of metallurgical parameters effect on tensile properties in austenitic stainless steels, Acta Metallurgica Slovaca, 2017, 23, 111-121.10.12776/ams.v23i2.841Search in Google Scholar

[21] Di Schino A., Richetta M., Effect of microalloying on quenching behaviour of steels for back-up rolls, Acta Metallurgica Slovaca, 2017, 23, 105-11010.12776/ams.v23i2.898Search in Google Scholar

[22] Garrison L.M., Katoh Y., Snead L.L., Byun T.S., Reiser J., Rieth M., Fusion mateials research, J. Nucl. Mater., 2016, 481, 134-14610.1016/j.jnucmat.2016.09.020Search in Google Scholar

[23] Allen T.R., Gan J., Cole J.I., Miller M.K., Busby J.T, Radiation response of a 9 Cr ODS steel to heavy ion irradiation, J. Nucl. Mater., 2008, 375, 26-3710.1016/j.jnucmat.2007.11.001Search in Google Scholar

[24] Yamashita S., Oka K., Ohnuki, Akasaka S. Ukai, S,: Mechanical behaviour of ODS steels, J. Nucl. Mater., 2002, 307-311, 283-28810.1016/S0022-3115(02)01077-2Search in Google Scholar

[25] Di Schino A., Kenny J.M, Barteri M., High temperature resistance of a high nitrogen and low nickel austenitic stainless steel, J.Mat. Science Letters, 2003, 22, 691-69310.1023/A:1023675212900Search in Google Scholar

[26] Di Schino A., Barteri M., Kenny J.M., Barteri M., Fatigue behaviour of a high nitrogen austenitic stainless steel as a function of its grain size, J.Mat. Science Letters, 2003, 22, 1511-151310.1023/A:1026155215111Search in Google Scholar

[27] Di Schino A., Guarnaschelli, C., Effect of microstructure on cleavage resistance of high strength quenched and tempered steels, Materials Letters, 2009, 63, 1968-197210.1016/j.matlet.2009.06.032Search in Google Scholar

Received: 2017-10-17
Accepted: 2017-11-17
Published Online: 2018-10-26

© 2018 Andrea Di Schino et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

Articles in the same Issue

  1. Regular Article
  2. Real-scale comparison between simple and composite raw sewage sampling
  3. 10.1515/eng-2018-0017
  4. The risks associated with falling parts of glazed facades in case of fire
  5. Implementation of high speed machining in thin-walled aircraft integral elements
  6. Evaluating structural crashworthiness and progressive failure of double hull tanker under accidental grounding: bottom raking case
  7. Influence of Silica (SiO2) Loading on the Thermal and Swelling Properties of Hydrogenated-Nitrile-Butadiene-Rubber/Silica (HNBR/Silica) Composites
  8. Statistical Variations and New Correlation Models to Predict the Mechanical Behavior and Ultimate Shear Strength of Gypsum Rock
  9. Analytic approximate solutions to the chemically reactive solute transfer problem with partial slip in the flow of a viscous fluid over an exponentially stretching sheet with suction/blowing
  10. Thermo-mechanical behavior simulation coupled with the hydrostatic-pressure-dependent grain-scale fission gas swelling calculation for a monolithic UMo fuel plate under heterogeneous neutron irradiation
  11. Optimal Auxiliary Functions Method for viscous flow due to a stretching surface with partial slip
  12. Vibrations Analysis of Rectangular Plates with Clamped Corners
  13. Evaluating Lean Performance of Indian Small and Medium Sized Enterprises in Automotive Sector
  14. FPGA–implementation of PID-controller by differential evolution optimization
  15. Thermal properties and morphology of polypropylene based on exfoliated graphite nanoplatelets/nanomagnesium oxide
  16. A computer-based renewable resource management system for a construction company
  17. Hygrothermal Aging of Amine Epoxy: Reversible Static and Fatigue Properties
  18. The selected roof covering technologies in the aspect of their life cycle costs
  19. Influence of insulated glass units thickness and weight reduction on their functional properties
  20. Structural analysis of conditions determining the selection of construction technology for structures in the centres of urban agglomerations
  21. Selection of the optimal solution of acoustic screens in a graphical interpretation of biplot and radar charts method
  22. Subsidy Risk Related to Construction Projects: Seeking Causes
  23. Multidimensional sensitivity study of the fuzzy risk assessment module in the life cycle of building objects
  24. Planning repetitive construction projects considering technological constraints
  25. Identification of risk investment using the risk matrix on railway facilities
  26. Comparison of energy parameters of a centrifugal pump with a multi-piped impeller in cooperation either with an annular channel and a spiral channel
  27. Influence of the contractor’s payment method on the economic effectiveness of the construction project from the contractor’s point of view
  28. Special Issue Automation in Finland
  29. Diagnostics and Identification of Injection Duration of Common Rail Diesel Injectors
  30. An advanced teaching scheme for integrating problem-based learning in control education
  31. A survey of telerobotic surface finishing
  32. Wireless Light-Weight IEC 61850 Based Loss of Mains Protection for Smart Grid
  33. Smart Adaptive Big Data Analysis with Advanced Deep Learning
  34. Topical Issue Desktop Grids for High Performance Computing
  35. A Bitslice Implementation of Anderson’s Attack on A5/1
  36. Efficient Redundancy Techniques in Cloud and Desktop Grid Systems using MAP/G/c-type Queues
  37. Templet Web: the use of volunteer computing approach in PaaS-style cloud
  38. Using virtualization to protect the proprietary material science applications in volunteer computing
  39. Parallel Processing of Images in Mobile Devices using BOINC
  40. “XANSONS for COD”: a new small BOINC project in crystallography
  41. Special Issue on Sustainable Energy, Engineering, Materials and Environment
  42. An experimental study on premixed CNG/H2/CO2 mixture flames
  43. Tidal current energy potential of Nalón river estuary assessment using a high precision flow model
  44. Special Spring Issue 2017
  45. Context Analysis of Customer Requests using a Hybrid Adaptive Neuro Fuzzy Inference System and Hidden Markov Models in the Natural Language Call Routing Problem
  46. Special Issue on Non-ferrous metals and minerals
  47. Study of strength properties of semi-finished products from economically alloyed high-strength aluminium-scandium alloys for application in automobile transport and shipbuilding
  48. Use of Humic Sorbent from Sapropel for Extraction of Palladium Ions from Chloride Solutions
  49. Topical Issue on Mathematical Modelling in Applied Sciences, II
  50. Numerical simulation of two-phase filtration in the near well bore zone
  51. Calculation of 3D Coordinates of a Point on the Basis of a Stereoscopic System
  52. The model of encryption algorithm based on non-positional polynomial notations and constructed on an SP-network
  53. A computational algorithm and the method of determining the temperature field along the length of the rod of variable cross section
  54. ICEUBI2017 - International Congress on Engineering-A Vision for the Future
  55. Use of condensed water from air conditioning systems
  56. Development of a 4 stroke spark ignition opposed piston engine
  57. Development of a Coreless Permanent Magnet Synchronous Motor for a Battery Electric Shell Eco Marathon Prototype Vehicle
  58. Removal of Cr, Cu and Zn from liquid effluents using the fine component of granitic residual soils
  59. A fuzzy reasoning approach to assess innovation risk in ecosystems
  60. Special Issue SEALCONF 2018
  61. Brush seal with thermo-regulating bimetal elements
  62. The CFD simulation of the flow structure in the sewage pump
  63. The investigation of the cavitation processes in the radial labyrinth pump
  64. Testing of the gaskets at liquid nitrogen and ambient temperature
  65. Probabilistic Approach to Determination of Dynamic Characteristics of Automatic Balancing Device
  66. The design method of rubber-metallic expansion joint
  67. The Specific Features of High-Velocity Magnetic Fluid Sealing Complexes
  68. Effect of contact pressure and sliding speed on the friction of polyurethane elastomer (EPUR) during sliding on steel under water wetting conditions
  69. Special Issue on Advance Material
  70. Effect of thermo-mechanical parameters on the mechanical properties of Eurofer97 steel for nuclear applications
  71. Failure prediction of axi-symmetric cup in deep drawing and expansion processes
  72. Characterization of cement composites based on recycled cellulosic waste paper fibres
  73. Innovative Soft Magnetic Composite Materials: Evaluation of magnetic and mechanical properties
  74. Statistical modelling of recrystallization and grain growth phenomena in stainless steels: effect of initial grain size distribution
  75. Annealing effect on microstructure and mechanical properties of Cu-Al alloy subjected to Cryo-ECAP
  76. Influence of heat treatment on corrosion resistance of Mg-Al-Zn alloy processed by severe plastic deformation
  77. The mechanical properties of OFHC copper and CuCrZr alloys after asymmetric rolling at ambient and cryogenic temperatures
Downloaded on 5.11.2025 from https://www.degruyterbrill.com/document/doi/10.1515/eng-2018-0040/html
Scroll to top button