Austenitic cast iron and manufacturing process for the same, austenitic-cast-iron cast product and component part for exhaust system

Abstract

An austenitic cast iron according to the present invention has Ni: from 7 to 15% by mass, and is characterized in that it comprises a base structure in which an austenite phase makes a major phase even in ordinary-temperature region by adjusting the respective compositions of Cr, Ni and Cu, excepting C and Si, so as to fall within predetermined ranges. In accordance with the present invention, it is possible to obtain an austenitic cast iron, which is excellent in terms of oxidation resistance and the like, inexpensively, while reducing the content of expensive Ni.

1 . An austenitic cast iron, being characterized in that:
 it comprises:   basic elements comprising carbon (C), silicon (Si), chromium (Cr), nickel (Ni), manganese (Mn) and copper (Cu); and   the balance comprising iron (Fe), inevitable impurities and/or a trace-amount modifier element, which is effective in improving characteristic, in a trace amount;   it is an austenitic cast iron being a cast iron that is structured by a base comprising an Fe alloy in which an austenite phase makes a major phase in ordinary-temperature region;   wherein said basic elements fall within compositional ranges that satisfy the following conditions when the entirety of said cast iron is taken as 100% by mass (hereinafter being simply expressed as “%”) :   C : from 1 to 5%;   Si: from 2 to 6%;   Ni: from 7 to 15% ;   Mn: from 0.1 to 8%;   Cu: 2.5% or less;   Cr: 6% or less; and   Cu+Cr: 0.5% or more.   
     
     
         2 . The austenitic cast iron as set forth in  claim 1 , wherein said Ni is from 8 to 12%. 
     
     
         3 . The austenitic cast iron as set forth in  claim 1 , wherein said Si is from 3 to 5%. 
     
     
         4 . The austenitic cast iron as set forth in  claim 1 , wherein said Mn is from 5 to 8%. 
     
     
         5 . The austenitic cast iron as set forth in  claim 1 , wherein said Cr is from 0.5 to 4%. 
     
     
         6 . The austenitic cast iron as set forth in  claim 5 , wherein said Cr is from 1 to 2% . 
     
     
         7 . The austenitic cast iron as set forth in  claim 1 , wherein said Cu is 0.1% or more. 
     
     
         8 . The austenitic cast iron as set forth in  claim 7 , wherein said Cu is 0.5% or more. 
     
     
         9 . The austenitic cast iron as set forth in  claim 8 , wherein said Cu is from 1 to 2%. 
     
     
         10 . The austenitic cast iron as set forth in  claim 1 , wherein:
 said Cr is 0.1% or more; and   said Cu is 0.1% or more.   
     
     
         11 . The austenitic cast iron as set forth in  claim 10 , wherein:
 said Cr is 0.5% or more; and   said Cu is 0.5% or more.   
     
     
         12 . The austenitic cast iron as set forth in  claim 1 , wherein:
 a value, Creq (i. e., Creq=Cr+1.5Si), is further from 5 to 8%; and   another value, Ni eq  (i.e., Ni eq =Ni+30″ C s +0.5″ Mn+Cu where C s : solute carbon content) is further 18% or more.   
     
     
         13 . The austenitic cast iron as set forth in  claim 1 , wherein:
 a Cr eq  value is from 7 to 9%; and   a Ni eq  value is 13% or more.   
     
     
         14 . The austenitic cast iron as set forth in  claim 1 , wherein said basic elements further fall within compositional ranges that satisfy the following conditions:
 C: from 2.5 to 3.5% ;   Si: from 3.5 to 5.5% ;   Ni: from 9 to 14% ;   Mn: from 1 to 6% ;   Cr: from 1 to 2% ; and   Cu: from 1 to 2% .   
     
     
         15 . The austenitic cast iron as set forth in  claim 1 , wherein said basic elements further fall within compositional ranges that satisfy the following conditions:
 C: from 2.5 to 3.5% ;   Si: from 3.5 to 4.5%;   Ni: from 12 to 14% ;   Mn: from 5 to 6% ;   Cr: from 1 to 2% ; and   Cu: from 1 to 2%.   
     
     
         16 . The austenitic cast iron as set forth in  claim 1 , wherein a spheroidized proportion of said graphite that is crystallized or precipitated in said base is 70% or more. 
     
     
         17 . The austenitic cast iron as set forth  claim 1 , wherein said graphite that is crystallized or precipitated has particles in a quantity of 100 pieces/mm 2  or more, particles whose particle diameter is 5 μm or more and which are present in a section of cast product whose wall thickness is 5 mm or less. 
     
     
         18 . The austenitic cast iron as set forth in  claim 1 , wherein said base comprises an austenite single phase. 
     
     
         19 . A manufacturing process for austenitic cast product, the manufacturing process being characterized in that it comprises:
 a molten-metal preparation step of preparing a molten metal with the compositional range as set forth in  claim 1 ;   a pouring step of pouring the molten metal into a casting die; and   a solidification step of cooling the molten metal that has been poured into the casting die, and then solidifying the mol ten metal;   wherein a cast product comprising an the austenitic cast iron is obtainable, the austenitic cast iron being made of a cast iron that is structured by a base comprising an Fe alloy in which an austenite phase makes a major phase in oridinary-temperature region.   
     
     
         20 . A manufacturing process for austenitic cast product, the manufacturing process being characterized in that it comprises:
 a modifier-free-molten-metal preparation step of preparing a modifier-free molten metal comprising a molten metal with the compositional range as set forth in  claim 1 ;   an auxiliary-agent addition step of adding an auxiliary agent, which includes at least one member being selected from the group consisting of inoculant agents that make cores of graphite to be crystallized or precipitated, and spheroidizing agents that facilitates spheroidizing of the graphite, to the modifier-free molten metal directly or indirectly;   a pouring step of pouring a molten metal into a casting die, the mol ten metal being after the auxiliary-agent addition step or during the auxiliary-agent addition step; and   a solidification step of cooling the mol ten metal that has been poured into the casting die, and then solidifying the molten metal;   wherein a cast product comprising an austenitic cast iron is obtainable, the austenitic cast iron being made of a cast iron that is structured by a base comprising an Fe alloy in which an austenite phase makes a major phase in ordinary-temperature region, and the in which substantially spheroidal graphite is crystallized or precipitated within the base.   
     
     
         21 . An austenitic cast product being characterized in that the austenitic cast product is obtainable by means of the manufacturing process as set forth in  claim 19 . 
     
     
         22 . A component part for exhaust system being characterized in that the exhaust-system component part is obtainable by means of the manufacturing process as set forth in  claim 19 . 
     
     
         23 . An austenitic cast product being characterized in that the austenitic cast product is obtainable by means of the manufacturing process as set forth in  claim 20 . 
     
     
         24 . A component part for exhaust system being characterized in that the exhaust-system component part is obtainable by means of the manufacturing process as set forth in  claim 20 .