Nitrided mo alloy worked material having high corrosion resistance, high strength and high toughness and method for production thereof

Abstract

The present invention provides an innovative material which has properties which cannot be achieved with conventional materials, i.e., having satisfactory high corrosion resistance and high strength in very severe corrosive conditions, for example, a 75% sulfuric acid (H 2 SO 4 ) aqueous solution (180° C.) in addition to high strength at high temperatures and high toughness at low temperatures, and provides a method for effectively manufacturing the innovative material. A worked molybdenum-alloy material, subjected to nitriding, which has high corrosion resistance, high strength, and high toughness, includes fine nitride particles formed by subjecting a nitride-forming-metal element dissolved to form a solid solution in an untreated worked molybdenum-alloy material to internal nitriding, the fine nitride particles being dispersed inside the worked molybdenum-alloy material subjected to nitriding; and a molybdenum nitride layer formed by subjecting a worked structure or a recovered structure at the surface of the untreated worked molybdenum-alloy material to external nitriding, the molybdenum nitride layer being provided at the surface of the worked molybdenum-alloy material subjected to nitriding. A method for manufacturing a worked molybdenum-alloy material subjected to nitriding includes the steps of subjecting an untreated worked alloy material in which at least any one of titanium, zirconium, hafnium, vanadium, niobium, and tantalum is dissolved to form a solid solution to multi-step internal nitriding treatment including a stepwise increase of the treatment temperature, and then subjecting the worked alloy material to external nitriding treatment.

1 . A worked molybdenum-alloy material, subjected to nitriding, which has high corrosion resistance, high strength, and high toughness, comprising: fine nitride particles formed by subjecting a nitride-forming-metal element dissolved to form a solid solution in an untreated worked molybdenum-alloy material to internal nitriding, the fine nitride particles being dispersed inside the worked molybdenum-alloy material subjected to nitriding; and a molybdenum nitride layer formed by subjecting a worked structure or a recovered structure at the surface of the untreated worked molybdenum-alloy material to external nitriding, the molybdenum nitride layer being provided at the surface of the worked molybdenum-alloy material subjected to nitriding.  
   
   
       2 . The worked molybdenum-alloy material subjected to nitriding according to  claim 1 , wherein the molybdenum nitride layer at the surface of the worked molybdenum-alloy material subjected to nitriding comprises at least any one of δ-MoN, γ-Mo 2 N, and β-Mo 2 N.  
   
   
       3 . The worked molybdenum-alloy material subjected to nitriding according to  claim 1  or  2 , wherein a layer between the molybdenum nitride layer and the matrix in the inside of the worked molybdenum-alloy material subjected to nitriding has a worked structure or recovered structure.  
   
   
       4 . The worked molybdenum-alloy material subjected to nitriding according to  claim 1  or  2 , wherein the inside of the worked molybdenum-alloy material subjected to nitriding has a recrystallized structure.  
   
   
       5 . A method for manufacturing a worked molybdenum-alloy material subjected to nitriding according to  claim 1  or  2 , comprising the steps of: subjecting an untreated worked alloy material in which at least any one of titanium, zirconium, hafnium, vanadium, niobium, and tantalum is dissolved to form a solid solution in a molybdenum matrix to multi-step internal nitriding treatment including a stepwise increase of the treatment temperature, and then subjecting the worked alloy material to external nitriding treatment.  
   
   
       6 . The method for manufacturing a worked molybdenum-alloy material subjected to nitriding according to  claim 5 , wherein the internal nitriding treatment is performed with a nitrogen gas, and then the external nitriding treatment is performed with an ammonia gas.