Method for producing mold steel, mold steel, method of producing pre-hardened mold material, and pre-hardened mold material

Abstract

A method of producing a mold steel, the method including a first process of preparing a molten steel A that is obtained after vacuum refining and has a component composition including from 0.005% to 0.1% by mass of C, from 1.0% to 5.0% by mass of Ni, from 3.0% to 8.0% by mass of Cr, more than 0% but less than or equal to 2.0% by mass of Mo, more than 0% but less than or equal to 3.5% by mass of Cu, and more than 0% but less than or equal to 2.0% by mass of Al, in which an amount of O is 0.005% by mass or less and an amount of N is 0.03% by mass or less; a second process of reducing the amount of O and the amount of N in the molten steel A, by slag refining the molten steel A, to obtain a molten steel B; and a third process of casting the molten steel B, is provided.

1 . A method of producing a mold steel, the method comprising:
 a first process of preparing a molten steel A that is obtained after vacuum refining and has a component composition comprising from 0.005% to 0.1% by mass of C, from 1.0% to 5.0% by mass of Ni, from 3.0% to 8.0% by mass of Cr, more than 0% but less than or equal to 2.0% by mass of Mo, more than 0% but less than or equal to 3.5% by mass of Cu, and more than 0% but less than or equal to 2.0% by mass of Al, wherein an amount of O is 0.005% by mass or less and an amount of N is 0.03% by mass or less;   a second process of reducing the amount of O and the amount of N in the molten steel A, by slag refining the molten steel A, to obtain a molten steel B; and   a third process of casting the molten steel B.   
     
     
         2 . The method of producing a mold steel according to  claim 1 , wherein the molten steel B comprises more than 0% but less than or equal to 0.05% by mass of S. 
     
     
         3 . The method of producing a mold steel according to  claim 1 , wherein, in the molten steel B, the amount of O is 0.001% by mass or less and the amount of N is 0.01% by mass or less. 
     
     
         4 . The method of producing a mold steel according to  claim 1 , wherein the molten steel B comprises more than 0% but less than or equal to 0.05% by mass of S, and the molten steel A comprises more than 0% but less than or equal to 2.0% by mass of Mn. 
     
     
         5 . The method of producing a mold steel according to  claim 1 , wherein, in the second process, the molten steel B is obtained by adding S to the molten steel A after the slag refining. 
     
     
         6 . The method of producing a mold steel according to  claim 1 , wherein, in the first process, the molten steel A is prepared by adding Al to a molten steel in which an amount of O and an amount of N have been reduced to 0.005% by mass or less and 0.03% by mass or less, respectively, by vacuum refining such that an amount of Al in the molten steel A is more than 0% but less than or equal to 2.0% by mass. 
     
     
         7 . The method of producing a mold steel according to  claim 1 , wherein an amount of O in the molten steel A is more than 0.0010% but less than or equal to 0.005% by mass, and an amount of O in the molten steel B is 0.0010% by mass or less. 
     
     
         8 . The method of producing a mold steel according to  claim 1 , wherein, in the second process, Mg is added to the molten steel A such that an amount of Mg in the molten steel B is more than 0% but less than or equal to 0.02% by mass. 
     
     
         9 . The method of producing a mold steel according to  claim 8 , wherein the addition of Mg is performed by at least one of slag refining of the molten steel A with a slag comprising MgO or adding an Mg alloy to the molten steel A. 
     
     
         10 . A method of producing a pre-hardened mold material, the method comprising:
 producing a mold steel by the method according to  claim 1 ;   hot-working the mold steel that has been produced, to obtain a material;   annealing the material after the hot-working; and   quenching and tempering the material after the annealing.   
     
     
         11 . A method of producing a pre-hardened mold material, the method comprising:
 producing a mold steel by the method according to  claim 1 ;   hot-working the mold steel that has been produced, to obtain a material;   directly quenching the material during cooling after the hot-working; and   tempering the material after the direct quenching.   
     
     
         12 . A mold steel produced by the method according to  claim 1 ,
 the mold steel comprising from 0.005% to 0.1% by mass of C, more than 0% but less than or equal to 3.0% by mass of Si, more than 0% but less than or equal to 2.0% by mass of Mn, 0.05% by mass or less of S (including no addition of S), from 1.0% to 5.0% by mass of Ni, from 3.0% to 8.0% by mass of Cr, more than 0% but less than or equal to 2.0% by mass of Mo, more than 0% but less than or equal to 3.5% by mass of Cu, from 0.1% to 1.5% by mass of Al, and 1.0% by mass or less of Co (including no addition of Co),   wherein an amount of O and an amount of N are limited to 0.001% by mass or less and 0.01% by mass or less, respectively, and   a balance of the mold steel comprising Fe and inevitable impurities.   
     
     
         13 . A mold steel produced by the method according to  claim 8 ,
 the mold steel comprising from 0.005% to 0.1% by mass of C, more than 0% but less than or equal to 3.0% by mass of Si, more than 0% but less than or equal to 2.0% by mass of Mn, 0.05% by mass or less of S (including no addition of S), from 1.0% to 5.0% by mass of Ni, from 3.0% to 8.0% by mass of Cr, more than 0% but less than or equal to 2.0% by mass of Mo, more than 0% but less than or equal to 3.5% by mass of Cu, from 0.1% to 1.5% by mass of Al, 1.0% by mass or less of Co (including no addition of Co), and more than 0% but less than or equal to 0.02% by mass of Mg,   wherein an amount of O and an amount of N are limited to 0.001% by mass or less and 0.01% by mass or less, respectively, and   a balance of the mold steel comprising Fe and inevitable impurities.   
     
     
         14 . A pre-hardened mold material produced by the method according to  claim 10 ,
 the pre-hardened mold material comprising from 0.005% to 0.1% by mass of C, more than 0% but less than or equal to 3.0% by mass of Si, more than 0% but less than or equal to 2.0% by mass of Mn, 0.05% by mass or less of S (including no addition of S), from 1.0% to 5.0% by mass of Ni, from 3.0% to 8.0% by mass of Cr, more than 0% but less than or equal to 2.0% by mass of Mo, more than 0% but less than or equal to 3.5% by mass of Cu, from 0.1% to 1.5% by mass of Al, 1.0% by mass or less of Co (including no addition of Co), and 0.02% by mass or less of Mg (including no addition of Mg),   wherein an amount of O and an amount of N are limited to 0.001% by mass or less and 0.01% by mass or less, respectively, and   a balance of the pre-hardened mold material comprising Fe and inevitable impurities.   
     
     
         15 . A pre-hardened mold material produced by the method according to  claim 11 ,
 the pre-hardened mold material comprising from 0.005% to 0.1% by mass of C, more than 0% but less than or equal to 3.0% by mass of Si, more than 0% but less than or equal to 2.0% by mass of Mn, 0.05% by mass or less of S (including no addition of S), from 1.0% to 5.0% by mass of Ni, from 3.0% to 8.0% by mass of Cr, more than 0% but less than or equal to 2.0% by mass of Mo, more than 0% but less than or equal to 3.5% by mass of Cu, from 0.1% to 1.5% by mass of Al, 1.0% by mass or less of Co (including no addition of Co), and 0.02% by mass or less of Mg (including no addition of Mg),   wherein an amount of O and an amount of N are limited to 0.001% by mass or less and 0.01% by mass or less, respectively, and   a balance of the pre-hardened mold material comprising Fe and inevitable impurities.