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Abstract Effect of tempering time on fatigue crack behavior of China Low Activation Martensitic (CLAM) steel was studied at room temperature in air. The fatigue crack growth rates subjected to the tempering time range of 90–9000 min were investigated. The results showed that the fatigue crack growth decelerated in the near-threshold region as the tempering time increased. The fatigue crack growth rate after tempering for 9000 min was approximately one-third of that of the specimen tempered for 90 min with ΔK of 14 MPa m0.5. The improved fatigue crack growth resistance could be explained by the influence of variation in microstructure, i.e., martensitic laths and precipitates. This study suggested that the effective driving force for fatigue crack growth was reduced in the near-threshold region by the activated roughness-induced crack closure mechanism as a result of rougher fracture surface caused by coarsened martensitic laths and precipitates. [ABSTRACT FROM AUTHOR]

Abstract Blanket is the key energy conversion component of a fusion reactor, it is designed with a large number of complex embedded cooling channels to remove the high nuclear heat deposition. Due to the complex inner-channeled structure, the fabrication of the blanket components has been one of the key issues of the blanket technical development. In this study, the selective laser melting (SLM) additive manufacturing (AM) processing was employed to fabricate small scale test blanket module with China low activation martensitic (CLAM) steel, and the hot isostatic pressing (HIP) was applied to improve the microstructure and mechanical properties. The microstructure and mechanical properties of the SLM built CLAM at the as-built, standard heat treatment (SHT) and HIP&SHT status were investigated and evaluated. The results showed that the relative density at the as-built status compared to the hot-rolled CLAM steel reached 99.7%. The tensile strength of the as-built status was 966.2 MPa and 829.1 MPa in the directions vertical and parallel to the building direction, respectively. After the HIP&SHT, the orientation of the microstructure and the difference in strength in different directions decreased. The strength values in the directions vertical and parallel to the building direction were similar, which were equivalent to that of the hot-rolled CLAM steel with SHT. Moreover, the impact absorbed energy in the directions vertical and parallel to the building direction was increased from 21.02 J to 9.18 J at the as-built status to 54.48 J and 18.83 J at the HIP&SHT status, respectively. Meanwhile, micro-defects were drastically decreased with the help of HIP. It could be concluded that the dislocation migration and recrystallization in HIP process is effective to improve the microstructure and mechanical properties of the SLM built CLAM steel. [ABSTRACT FROM AUTHOR]

Tungsten inert gas (TIG) welding was considered as one of the candidate technologies to achieve the box structure of test blanket module (TBM). In this paper, the effects of heat input on the microstructure and mechanical properties of multilayer TIG butt-welded China Low Activation Martensitic (CLAM) steel were investigated by microstructure observations, Vickers hardness, tensile and Charpy impact tests. The results showed that the microstructure of the weld metal (WM) were coarse quenched martensite and residual delta-ferrite. When the heat input value increased from 1.73 kJ/mm to 2.41 kJ/mm, the width of martensite laths increased slightly and the delta-ferrite content decreased firstly then increased. Moreover, the increasing heat input resulted in remarkable tempering effect on the previous layer of the WM by the following deposited layers. The transverse hardness distribution of the joints showed that softening occurred in the heat-affected zone (HAZ), and the hardness of WM decreased slightly as the heat input increased. The ultimate tensile strength values of the joints with various heat input were all higher than 630 MPa, and the rupture position located at the HAZ. Charpy impact toughness of the as-welded joints met the toughness criteria for the welded joint (≥27 J) of creep resistant 9Cr steel according to the standard of ISO-3580. [ABSTRACT FROM AUTHOR]