Continuous casting nozzle and production method therefor

Abstract

Disclosed is a continuous casting nozzle, which comprises a layer formed to have high functions, such as high corrosion resistance and high anti-deposition capability, and disposed on the side of an inner bore thereof to serve as an inner bore-side layer, so as to enhance durability, wherein the continuous casting nozzle is capable of preventing expansion cracking of an outer periphery-side layer serving as a nozzle body thereof, due to a difference in thermal expansion between respective compositions of the inner bore-side layer and the outer periphery-side layer, while preventing peel-off of the inner bore-side layer during casting. The continuous casting nozzle has a structure in which respective opposed boundary surfaces between the inner bore-side layer 2 and an intermediate layer 4 and between the intermediate layer 4 and the outer periphery-side layer 3, are in direct contact with each other, wherein a bonding strength between the intermediate layer and each of the inner bore-side layer and the outer periphery-side layer adjacent to the intermediate layer is in the range of 0.01 to 1.5 MPa, as measured in a non-oxidation atmosphere at 1000° C., and a compressive rate (%) of the intermediate layer in a non-oxidation atmosphere at 1000° C. and under a pressure of 2.5 MPa is in the range of 10 to 80%.

1 . A continuous casting nozzle comprising a tubular refractory structure which has an inner bore formed along an axial direction thereof to allow molten metal to pass therethrough, and at least partly includes an inner bore-side layer disposed on the side of said inner bore, and an outer periphery-side layer disposed on a radially outward side relative to said inner bore-side layer, wherein said inner bore-side layer has the thermal expansion greater than that of said outer periphery-side layer, said continuous casting nozzle being characterized in that said tubular refractory structure includes an intermediate layer having compressability and lying between said inner bore-side layer and said outer periphery-side layer, wherein:
 said inner bore-side layer, said intermediate layer and said outer periphery-side layer are simultaneously integrated together during a forming process to form a multi-layer structure;   a bonding strength between said intermediate layer and each of said inner bore-side layer and said outer periphery-side layer adjacent to said intermediate layer is in the range of 0.01 to 1.5 MPa, as measured in a non-oxidation atmosphere at 1000° C.; and   said intermediate layer has a compressive rate K (%) satisfies the following Formula 1 as measured in a non-oxidation atmosphere at 1000° C. under a pressure of 2.5 MPa,
     K >[( Di×αi−Do×αo )/(2 ×Tm )]  Formula 1 
   wherein: Di is an outer diameter (mm) of said inner bore-side layer;
 Do is an inner diameter (mm) of said outer periphery-side layer; 
 Tm is an initial thickness (mm) of said intermediate layer at room temperature; 
 αi is a maximum thermal expansion coefficient (%) of the refractory composition of said inner bore-side layer in a temperature range of room temperature to 1500° C.; and 
 αo is a thermal expansion coefficient (%) of the refractory composition of said outer periphery-side layer at a temperature at start of discharge or pouring of molten metal through said continuous casting nozzle. 
   
   
   
       2 . The continuous casting nozzle as defined in  claim 1 , wherein said intermediate layer in a state after being subjected to a heat treatment in a non-oxidation atmosphere at 600° C. or more contains expanded expansive graphite particles (hereinafter referred to as “expanded graphite particles”). 
   
   
       3 . The continuous casting nozzle as defined in  claim 1  or  2 , wherein said intermediate layer in a state after being subjected to a heat treatment in a non-oxidation atmosphere at 1000° C. contains a carbon component (except any carbon compound with the remaining components) in a total amount of 16 mass % or more (including 100 mass %). 
   
   
       4 . The continuous casting nozzle as defined in  claim 1  or  2 , wherein said intermediate layer in a state after being subjected to a heat treatment in a non-oxidation atmosphere at 1000° C. contains a carbon component (except any carbon compound with the remaining components) in a total amount of 16 mass % or more, with the remainder other than said carbon component being a refractory material comprising one or more selected from the group consisting of oxide, carbide, nitride and metal. 
   
   
       5 . A method of producing a continuous casting nozzle comprising a tubular refractory structure which has an inner bore formed along an axial direction thereof to allow molten metal to pass therethrough, and at least partly includes an inner bore-side layer, an intermediate layer and an outer periphery-side layer which are arranged in this order in a radially outward direction with respect to said inner bore, said method comprising the steps of:
 preparing a mixture (ingredients) for said intermediate layer, which contains un-expanded expansive graphite particles in an amount ranging from 5 to 45 mass %, and burnable particles in an amount ranging from 55 to 95 mass %, and further contains an organic binder in a given mass %, with respect to a total mass % of said un-expanded expansive graphite particles and said burnable particles, and in addition to said total mass %, wherein said given mass % of said organic binder is set to allow a ratio of a carbon component only of said organic binder (except any carbon compound with the remaining components) to an entire refractory composition of said intermediate layer, in a state after the refractory composition of said intermediate layer is subjected to a heat treatment in a non-oxidation atmosphere at 1000° C., to fall within the range of 2.5 to 15 mass %;   subjecting said mixture (ingredients) for said intermediate layer to a pressure forming using a cold isostatic pressing (CIP) machine, simultaneously and integrally together with a mixture (ingredients) for said inner bore-side layer and a mixture (ingredients) for outer periphery-side layer, to obtain a single shaped body; and   subjecting said shaped body to a heat treatment at a temperature of 600 to 1300° C. to allow said burnable particles contained in said mixture (ingredients, i.e., green body after pressing) for said intermediate layer in said shaped body to be vanished so as to form voids, and then expand said un-expanded expansive graphite particles contained in said mixture (ingredients, i.e., green body after pressing) for said intermediate layer in said shaped body so as to allow said voids to be filled with said expanded graphite particles.   
   
   
       6 . A method of producing a continuous casting nozzle comprising a tubular refractory structure which has an inner bore formed along an axial direction thereof to allow molten metal to pass therethrough, and at least partly includes an inner bore-side layer, an intermediate layer and an outer periphery-side layer which are arranged in this order in a radially outward direction with respect to said inner bore, said method comprising the steps of:
 preparing a mixture (ingredients) for said intermediate layer, which contains un-expanded expansive graphite particles in an amount ranging from 5 to 45 mass %, burnable particles in an amount ranging from 55 to 95 mass %, and a refractory material which is one or more selected from the group consisting of oxide, carbide, nitride and metal, in a total amount of 40 mass % or less, and further contains an organic binder in a given mass %, with respect to a total mass % of said un-expanded expansive graphite particles, said burnable particles and said refractory material which is one or more selected from the group consisting of oxide, carbide, nitride and metal, and in addition to said total mass %, wherein said given mass % of said organic binder is set to allow a ratio of a carbon component only of said organic binder (except any carbon compound with the remaining components) to an entire refractory composition of said intermediate layer, in a state after the refractory composition of said intermediate layer is subjected to a heat treatment in a non-oxidation atmosphere at 1000° C., to fall within the range of 2.5 to 15 mass %;   subjecting said mixture (ingredients) for said intermediate layer to a pressure forming using a cold isostatic press (CIP) machine, simultaneously and integrally together with a mixture (ingredients) for said inner bore-side layer and a mixture (ingredients) for outer periphery-side layer, to obtain a single shaped body; and   subjecting said shaped body to a heat treatment at a temperature of 600 to 1300° C. to allow said burnable particles contained in said mixture (ingredients, i.e. green body after pressing) for said intermediate layer in said shaped body to be vanished so as to form voids, and then expand said un-expanded expansive graphite particles contained in said mixture (ingredients, i.e. green body after pressing) for said intermediate layer in said shaped body so as to allow said voids to be filled with said expanded graphite particles.