106 Journal of Nuclear Materials 179-181 (1991) 706-708 North-Holland Microstructural investigation of 12% Cr martensitic steel for NET by means of small angle neutron scattering G. Albertini ‘, F. Carsughi lT3, R. Coppola 2, F. Rustichelli I, W.A.H.M. Vlak 4 and C. Van Dijk 4 ’ Uniueristci di Ancona, Dipnrtimento Scienre dei Materiali e della Terra, Facolta di Ingegneria, Via Brecce Bianche 60131. Anconu, Italy .’ ENEA-Casaccia, C.P. 2400, 00100 Roma, Italy -’Institut ftir Festkijrperforschung of the KFA, Jiilich, Fed. Rep. Germany 4 ECN, P.O. Box I, 1755 ZG Petten, The Netherlands A microstructural investigation of the modified DIN 1.4914 martensitic steel MANET, developed as a possible structural material zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA for prototype fusion reactors, has been carried out by means of small-angleneutron scattering (SANS) technique. The results of this study concern the presence both of carbides in the tempered material and He bubbles in a sample implanted with a-particles. These results show that the adopted technique can provide useful information on the average size of these microstructural defects. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 1. Introduction The modified martensitic steel DIN 1.4914 (C, 0.17; Cr, 10.5; Ni, 0.85; MO, 0.5; V, 0.25; Nb, 0.20; Si, 0.32; Mn, 0.6; S, 0.005; P, 0.005; B, 0.002; N, 0.003 wt%) (“MANET”) has been developed as a possible candi- date for structural components, such as the first wall in the Next European Torus (NET). It can presently be considered a reference material for the class of low- activation martensitic alloys [1,2]. As shown by previous studies [3-61 the main micro- structural features of MANET are the evolution of the finer martensitic laths (with consequent stress release) and the precipitation of carbides when the tempering temperature is increased. Both these phenomena have relevant effects on the resistance of this steel to the growth of He bubbles, which can be produced by simu- lation techniques, such as the homogeneous implanta- tion of high energy a-particles. This work presents the results of small-angle neutron scattering (SANS) measurements carried out both on tempered MANET samples (containing carbide pre- cipitates) and on a sample of the same steel implanted with a-particles. This technique, which is complemen- tary to Transmission Electron Microscopy (TEM) for such microstructural investigations [7,8], consists in the broadening (0 < 5 o around the incidence direction) of a beam of neutrons having the wavelength h 2: l-10 A when this beam passes through a sample containing chemical or magnetic inhomogeneities of = lo-lo3 A in size. By Fourier transforming the SANS intensity re- corded in a given angular range one can obtain informa- tion on the size and shape of the scattering particles, in addition to their size distribution function averaged over macroscopical volumes up to = 1 cm3. The results presented herein confirm that SANS can also be used in the case of complex materials such as MANET. This work is a part of a wider research programme on MANET and on other materials for fusion technol- ogy carried out by ENEA in collaboration with JRC- Ispra and with other laboratories [8]. 2. Experimental results After some preliminary tests performed at the ECN SANS facility in Petten [9] the SANS measurements were carried out at Lab. Commun. CEA-CNRS Saclay L.L.B., France, by using the PAXY instrument. Wave- lengths of 9 A and 15 A and a sample to detector distance of 2 m were used to study the effect of the tempering temperature; a wavelength of 7 A and a sample to detector distance of 1.07 m were used for the implanted specimen and for the corresponding refer- ence sample. In addition, according to the experimental procedure described in [6], a 14 kG magnetic field was applied in order to saturate the magnetization of the martensitic samples and to suppress as much as possible contribu- tions to SANS arising from magnetic inhomogeneities [7]. The SANS spectra presented here refer to data collected in the parallel direction with respect to the applied magnetic field where the SANS intensity is only of nuclear origin and the magnetic scattering null. The samples used to study the effect of tempering were platelets (10 X 20 X 1 mm3) treated as follows: (a) As cast, (b) austenitization at 1075 o C (30’) + rapid quench (fully martensitic sample), (c) austenitization at 1075 o C (30’) + rapid quench + tempering at 500 o C (2 h), (d) austenitization at 1975 o C (30’) + rapid quench + tempering at 600°C (2 h), (e) austenitization at 1075 o C (30’) + rapid quench + tempering at 700 o C (2 h). 0022-3115/91/$03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland)