SCIENCE CHINA Physics, Mechanics & Astronomy © Science China Press and Springer-Verlag Berlin Heidelberg 2012 phys.scichina.com www.springerlink.com *Corresponding author (email: wanfr@mater.ustb.edu.cn) Article November 2012 Vol.55 No.11: 2057–2061 doi: 10.1007/s11433-012-4865-8 Mechanical property and irradiation damage of China Low Activation Martensitic (CLAM) steel ZHU YanYong 1,2 , WAN FaRong 1* , GAO Jin 1 , HAN WenTuo 1 , HUANG YiNa 1,3 , JIANG ShaoNing 1 , QIAO JianSheng 1,4 , ZHAO Fei 1,5 , YANG ShanWu 1 , OHNUKI Somei 6 & HASHIMOTO Naoyuki 6 1 Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083, China; 2 Central Iron and Steel Research Institute, Beijing 100081, China; 3 Department of Engineering Physics, University of Wisconsin, WI 53706, USA; 4 China Institute of Atomic Energy, Beijing 102413, China; 5 Department of Material Physics, Guizhou University, Guiyang 550025, China; 6 Faculty of Engineering, Hokkaido University, Sapporo 060, Japan Received March 26, 2012; accepted April 6, 2012; published online September 3, 2012 China Low Activation Martensitic (CLAM) steel is being studied to develop the structural materials for a fusion reactor, which has been designed based on the well-known 9Cr1.5WVTa steel. The effect of tempering temperature on hardness and micro- structure of CLAM steel was studied. The strength of CLAM steel increased by adding silicon, and the ductility remained con- stant. Conversely, while CLAM steel maintained good ductility with the addition of yttrium, its tensile strengths were greatly degraded. Behaviors under electron irradiation of CLAM steel were examined using the high voltage electron microscope. Electron irradiation at 450°C formed many voids in CLAM steel with basic composition, whereas CLAM with silicon steel did not change the microstructure significantly. low activation ferritic/martensitic steel, mechanical property, electron irradiation, irradiation damage, silicon, yttrium PACS number(s): 46.70.De, 81.40.-z, 61.80.-x Citation: Zhu Y Y, Wang F R, Gao J, et al. Mechanical property and irradiation damage of China Low Activation Martensitic (CLAM) steel. Sci China-Phys Mech Astron, 2012, 55: 20572061, doi: 10.1007/s11433-012-4865-8 1 Introduction The development of materials with strong resistance to irra- diation swelling and low induced activation for the first wall and blanket structural components is critical to fusion pow- ers system. The reduced activation ferritic/martensitic (RAFM) steel was considered as candidate materials in this field [1]. Much effort has been made measuring the perfor- mance of RAFM steels in USA, Japan, and in EU. Some RAFMs have been produced and tested, for example, F82H, JLF-1 and EUROFER97 [2,3]. In China, the study of low activation materials is in the preliminary stage. The nominal composition of China Low Activation Martensitic (CLAM) steel, one of the RAFMs, is (wt%) 9.0Cr-0.10C-0.45Mn- 0.003P-0.002S-0.02N-1.5W-0.07Ta-0.01Si-0.006Ti-0.20V- Fe. The main difference between CLAM steel and other RAFMs is tungsten content. The content of tungsten in F82H and EUROFER97 is 2wt% and 1wt%, respectively [2,3]. It was reported that tungsten is an effective element for increasing the yield strength in certain amounts [2]. The application of higher tungsten may lead to the formation of Laves phases during the aging process at higher tempera-