High-cr ferritic/martensitic steel having improved creep resistance and preparation method thereof

Abstract

High-Cr ferritic/martensitic steels having an improved tensile strength and creep resistance are provided, which includes 0.04˜0.13 weight % of carbon, 0.03˜0.07 weight % of silicon, 0.40˜0.50 weight % of manganese, 0.40˜0.50 weight % of nickel, 8.5˜9.5 weight % of chromium, 0.45˜0.55 weight % of molybdenum, 0.10˜0.25 weight % of vanadium, 0.02˜0.10 weight % of tantalum, 0.15˜0.25 weight % of niobium, 1.5˜3.0 weight % of tungsten, 0.05˜0.12 weight % of nitrogen, 0.004˜0.008 weight % of boron, and optionally, 0.002˜0.010 weight % of phosphorus or 0.01˜0.08 weight % of zirconium, and iron balance. By regulating the contents of alloying elements such as niobium, tantalum, tungsten, nitrogen, boron, zirconium, carbon, the high-Cr ferritic/martensitic steels with superior tensile strength and creep resistance are provided, and can be effectively used as an in-core structural material for Generation IV sodium-cooled fast reactor (SFR) which is used under high temperature and high irradiation conditions.

1 . A high-Cr ferritic/martensitic steel having an improved tensile strength and creep resistance which includes 0.04˜0.13 weight % of carbon, 0.03˜0.07 weight % of silicon, 0.40˜0.50 weight % of manganese, 0.40˜0.50 weight % of nickel, 8.5˜9.5 weight % of chromium, 0.45˜0.55 weight % of molybdenum, 0.10˜0.25 weight % of vanadium, 0.02˜0.10 weight % of tantalum, 0.15˜0.25 weight % of niobium, 1.5˜3.0 weight % of tungsten, 0.05˜0.12 weight % of nitrogen, 0.004˜0.008 weight % of boron and iron balance. 
     
     
         2 . The high-Cr ferritic/martensitic steel having an improved tensile strength and creep resistance which includes 0.04˜0.13 weight % of carbon, 0.03˜0.07 weight % of silicon, 0.40˜0.50 weight % of manganese, 0.40˜0.50 weight % of nickel, 8.5˜9.5 weight % of chromium, 0.45˜0.55 weight % of molybdenum, 0.10˜0.25 weight % of vanadium, 0.02˜0.10 weight % of tantalum, 0.15˜0.25 weight % of niobium, 1.5˜3.0 weight % of tungsten, 0.05˜0.12 weight % of nitrogen, 0.004˜0.008 weight % of boron, 0.002˜0.010 weight % of phosphorus and iron balance. 
     
     
         3 . The high-Cr ferritic/martensitic steel having an improved tensile strength and creep resistance which includes 0.04˜0.13 weight % of carbon, 0.03˜0.07 weight % of silicon, 0.40˜0.50 weight % of manganese, 0.40˜0.50 weight % of nickel, 8.5˜9.5 weight % of chromium, 0.45˜0.55 weight % of molybdenum, 0.10˜0.25 weight % of vanadium, 0.02˜0.10 weight % of tantalum, 0.15˜0.25 weight % of niobium, 1.5˜3.0 weight % of tungsten, 0.05˜0.12 weight % of nitrogen, 0.004˜0.008 weight % of boron, 0.01˜0.08 weight % of zirconium and iron balance. 
     
     
         4 . A preparation method of the high-Cr ferritic/martensitic steel of one of  claims 1  to  3 , the method comprising steps of:
 mixing and dissolving alloying elements to form an ingot (step 1); 
 hot working such as hot forging, hot extrusion and hot rolling the ingot prepared at step 1(step 2); 
 normalizing the hot worked ingot of step 2 and air cooling the ingot (step 3); and 
 tempering the normalized alloy of step 3 and air cooling the alloy to prepare high-Cr ferrite/martensitic steels (step 4). 
 
     
     
         5 . The preparation method of  claim 4 , wherein the ingot at step 1 is prepared by vacuum inducing melting (VIM) method. 
     
     
         6 . The preparation method of  claim 4 , wherein the hot working at step 2 is performed after a heat treatment at 1100˜1200° C. for 0.5˜2 hours. 
     
     
         7 . The preparation method of  claim 4 , wherein the normalizing at step 3 is performed at 1000˜1100° C. for 0.5˜2 hours. 
     
     
         8 . The preparation method of  claim 4 , wherein the tempering at step 4 is performed at 600˜800° C. for 1˜3 hours. 
     
     
         9 . The preparation method of  claim 4 , after step 4, further comprising additional intermediate heat treatment at 600˜800° C. for 1˜3 hours, 2˜4 times of consecutive cold working, and final heat treatment at 600˜800° C. for 1˜3 hours. 
     
     
         10 . A core device of a Generation IV reactor using the high-Cr ferritic/martensitic steel according to one of  claims 1  to  3 . 
     
     
         11 . The core device according to  claim 10 , wherein the Generation IV reactor is a sodium-cooled fast reactor (SFR). 
     
     
         12 . The core device according to  claim 10 , wherein the core device is one selected from a group consisting of a nuclear fuel cladding tube, a duct and a wire wrap.