Iron- nickel alloy with low coefficient of thermal expansion for making shade masks

Abstract

The invention concerns an alloy whereof the chemical composition comprises, by weight: 35%=Ni=37%. 0.001% %=C=0.05, % Mn=0.10%, Si=0.15%, Co=0.5%, S<0.002%, P=0.006%, B=0.0005%, Al+Mo+Cu+Cr=0.15% 0.015%=2(V+Ti)+Nb+Zr+Ta+III=0.2%, 0.0025%=N+O=0.015% optionally calcium and/or magnesium with total content ranging beween 0.001 and 0.005%, the rest consisting of iron and unavoidable impurities resulting from preparation, and a method for making a strip of said alloy.

1 . An alloy, the chemical composition of which comprises, by weight:  
       35%≦Ni≦37%  0.001%≦C≦0.05%  Mn≦0.10%  Si≦0.15%  Co≦0.5%  S<0.002%  P<0.006%  B≦0.0005%  Al+Mo+Cu+Cr≦0.15%  0.015%≦2(V+Ti)+Nb+Zr+Ta+Hf≦0.2%  0.0025%≦N+O≦0.015%  
     possibly calcium and/or magnesium in a total content of between 0.0001 and 0.005%, 
 the remainder consisting of iron and inevitable impurities resulting from the production process.  
 
   
   
       2 . The alloy as claimed in  claim 1 , which furthermore has a niobium content of below 0.1%.  
   
   
       3 . The alloy as claimed in  claim 1  or  2 , which furthermore has a carbon content of above 0.0035%.  
   
   
       4 . The alloy as claimed in any one of  claims 1  to  3 , and the grain size of which is below 10 (in accordance with G ASTM E112).  
   
   
       5 . The alloy as claimed in any one of  claims 1  to  4 , and which exhibits a coefficient of thermal expansion between 20° C. and 100° C. of below 0.7×10 −6 /K.  
   
   
       6 . The alloy as claimed in any one of  claims 1  to  5 , and of which the conventional elastic limit at 0.2% OYS in the annealed state is above 280 MPa.  
   
   
       7 . The alloy as claimed in  claim 6 , and of which the conventional elastic limit at 0.2% OYS in the annealed state is furthermore above 300 MPa.  
   
   
       8 . The alloy as claimed in any one of  claims 1  to  7 , wherein the niobium and carbon contents are furthermore such that:  
       Nb×C≦0.01.  
   
   
       9 . The alloy as claimed in any one of  claims 1  to  8 , wherein the titanium, niobium and nitrogen contents of the alloy composition are furthermore such that:  
       Ti×N≦0.00006  Nb×N≦0.001.  
   
   
       10 . The alloy as claimed in any one of  claims 1  to  9 , and which contains precipitates based on titanium and/or on niobium and/or on vanadium and/or on tantalum and/or on zirconium and/or on hafnium, the mean size of which is equal to 100 nm or smaller.  
   
   
       11 . A method of manufacturing a strip of alloy as claimed in any one of  claims 1  to  10 , comprising the steps whereby: 
 a semi-finished version of said alloy is hot-rolled after reheating to a temperature of above 850° C. and below 1350° C. so that the rolling temperature is above the solutionizing temperature of the titanium- and/or niobium- and/or vanadium- and/or zirconium- and/or tantalum- and/or hafnium-based precipitates and so that the temperature at the end of rolling is below the temperature at which said precipitates begin to precipitate, so as to obtain a hot-rolled strip,    the hot-rolled strip is cold-rolled in one or more passes to obtain a cold-rolled strip, possibly with one or more intermediate annealing operations between two passes.    
   
   
       12 . The method as claimed in  claim 11 , wherein the temperature of the intermediate annealing operation or operations performed during the cold-rolling is below the solutionizing temperature of said precipitates.  
   
   
       13 . The method as claimed in  claim 11 , wherein the temperature of the intermediate annealing operation or operations performed during the cold-rolling is above the solutionizing temperature of said precipitates.  
   
   
       14 . The method as claimed in  claim 11  or  12 , wherein the temperature at the end of hot-rolling is equal to 850° C. or lower.  
   
   
       15 . The use of an alloy as claimed in any one of  claims 1  to  10  for the manufacture of shadow masks for color display cathode ray tubes.  
   
   
       16 . The use of an alloy as claimed in any one of  claims 1  to  10  for the manufacture of cryogenic storage containers.  
   
   
       17 . The use of an alloy as claimed in any one of  claims 1  to  10  for the manufacture of electron gun grids.  
   
   
       18 . The use of an alloy as claimed in any one of  claims 1  to  10  for the manufacture of shadow masks held in the vertical or horizontal direction for flat screen monitors.  
   
   
       19 . The use of an alloy as claimed in any one of  claims 1  to  10  for the manufacture of shadow mask support frames.