Effect Of Warm Deformation And Annealing Treatment On The Microstructure And Properties Of SCRAM Steel

Reduced-activation ferritic/martensitic (RAFM) steels are currently considered as oneof the realistic structural materials for fusion blanket systems owing to their high thermalconductivity, low thermal expansion coefficient, good resistance to irradiation inducedswelling and helium embrittlement, good compatibility with tritium breeding and coolant.The SCRAM (Super-clean Reduced Activation Martensitic) steel was developed byHuazhong University of Science and Technology was experimented in this research. Inorder to improve the comprehensive mechanical properties and the resistance to radiationof SCRAM steel, the SCRAM steel was processed by warm deformation and annealingtreatment in this research. The effect of warm deformation and annealing treatment on themicrostructure, mechanical properties and irradiation properties of SCRAM steel wasinvestigated. The main results are as follows:Warm deformation can effectively refine martensitic lath width, promote precipitatesand greatly increase dislocation density in the SCRAM steel. With the strain increasing,the packet of lath martensite tended to orderly align and the size became small andhomogeneous. Dislocation configuration gradually evolved from low-density patternsincluding dislocation lines, networks and pile-ups to higher density patterns includingheavy dislocation tangles and dislocation cells. The ultimate tensile strength and yieldstrength of the SCRAM steel strongly increased while the reduction of area and totalelongations continually decreased with the strain increasing. Fracture surface morphologyobservation shows that dimples became smaller and shallower, and tear ridges drasticallygrew up.After annealing treatment, the martensitic lath width increased from0.48um to0.65um and the dislocation density decreased from6.4×1015m-2to2.8×1015m-2in SCRAMsteel. Free dislocation progressively decreased and gathered to grain boundaries with theannealing temperature increasing. The specimen exhibited high reduction of area and totalelongations when the annealing temperature was up to600oC. The tensile fracture surfaceobservation indicated that dimples became more uniform and deeper and cleavage fracture traces disappeared with the annealing temperature increasing.The irradiation-induced helium bubbles were observed in all the specimens.Furthermore, the bubbles were preferentially nucleated and aggregated at dislocations andvarious boundaries. With the deformed strains increasing, the bubbles became smaller andmore numerous. However, the helium bubbles became larger but less when the annealingtemperature increased. The irradiation-induced hardening was generated in all heliumimplanted specimens. The untreated (undeformed, unannealed) sample exhibited themaximum nano-indentation variation (ΔH) and the sample of ε=0.5(unannealed)exhibited the minimum ΔH. The ΔH gradually increased with annealing temperatureincreasing, but the ΔH of the annealing specimens was still lower than the untreated(undeformed, unannealed) ones.