原子力用含Bステンレス鋼の特性

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B bearing 18Cr-9Ni stainless steel is used for the neutron absorption material of nuclear power plant.Some investigations on the effects of B addition on the 18Cr-9Ni stainless steel have been made and the following results are obtained.(1) The crystal structure of boride is Cr2B type. More than 2.1% addition of B induces coarse primary crystals of borides.(2) Cr content of boride is much higher than that in matrix. Cr content in matrix decreases to about 13% when 1.55% B is added.(3) At the high temperature, deformation resistance is higher than that of 18Cr-9Ni alloy, but reduction in area does not change so much. When heating over 1200°C, reduction in area decreases rapidly for the partial remelting by eutectic reaction.(4) By the addition of B, tensile strength rises but toughness decreases. Forged material has higher impact value than cast material, for example impact value of 1.55%B bearing steel is about 4kg·m/cm2.(5) By the addition of B, corrosion resistance for nitric acid goes down. And corrosion resistance for hydrochloric acid and sulfuric acid goes down by the addition of 0.5%B but changes little by more addition of B.(6) Welded joint by TIG welding is small in ductility, but has no welding defects. Joint efficiency of 1.27%B bearing steel is 84%.(7) Drilling machinability with no lubricant is about 1/10 in tool life of the base 18Cr-9Ni alloy.
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