Steel material for vacuum tube and method of manufacturing same

Abstract

A steel material for a vacuum tube according to an aspect of the present disclosure may include C: 0.1˜0.2%, Si: 0.05∞0.5%, Mn: 1.0∞1.6%, Ni: 0.5∞1.0%, Cr: 1.5∞4.0%, and the balance of Fe and unavoidable impurities in percentage by weight, and may have a complex structure of ferrite and pearlite as a microstructure.

1 . A steel material for a vacuum tube, the steel material comprising
 C: 0.1˜0.2%, Si: 0.05˜0.5%, Mn: 1.0˜1.6%, Ni: 0.5˜1.0%, Cr: 1.5˜4.0%, and the balance of Fe and unavoidable impurities in percentage by weight,   wherein the steel material has a complex structure of ferrite and pearlite as a microstructure, and   an outgassing rate of the steel material is 1.0*10 −10  mbar·l·s −1 ·cm −2  or less.   
     
     
         2 . The steel material of  claim 1 , wherein a total content of Ti, Nb, and V of the impurities included in the steel material is less than 0.01% (including 0%). 
     
     
         3 . The steel material of  claim 1 , wherein a fraction of the ferrite is 60˜90 percent by area, and
 a fraction of the pearlite is 10˜40 percent by area. 
 
     
     
         4 . The steel material of  claim 1 , wherein a fraction of martensite or bainite included in the steel material is less than 1 percent by area (including 0%). 
     
     
         5 . The steel material of  claim 1 , wherein the steel material has yield strength (YS) of 400˜600 MPa, a yield ratio (YR) of 0.8 or less, and elongation (El) of 19˜30%. 
     
     
         6 . The steel material of  claim 1 , wherein the steel material has Charpy impact energy of 30˜50 J at −20° C. 
     
     
         7 . The steel material of  claim 1 , wherein a thickness of the steel material is 5˜30 mm. 
     
     
         8 . A method of manufacturing a steel material for a vacuum tube, the method comprising:
 providing a steel material by reheating a slab including C: 0.1˜0.2%, Si: 0.05˜0.5%, Mn: 1.0˜1.6%, Ni: 0.5˜1.0%, Cr: 1.5˜4.0%, and the balance of Fe and unavoidable impurities in percentage by weight, and then by hot-rolling the slab at a finishing rolling temperature of 900˜1000° C.;   primarily cooling the hot-rolled steel material up to a temperature range of 550˜650° C. at a primary cooling speed of 5˜50° C./s;   coiling the steel material into a coil at a primary cooling end temperature after the primary cooling; and   secondary cooling the coil to room temperature at a secondary cooling speed of 0.005˜0.05° C./s.   
     
     
         9 . The method of  claim 8 , wherein a total content of Ti, Nb, and V of the impurities included in the slab is less than 0.01% (including 0%). 
     
     
         10 . The method of  claim 8 , wherein a thickness of the hot-rolled steel material is 5˜30 mm. 
     
     
         11 . The method of  claim 8 , wherein a cooling type of the primary cooling is water cooling, and
 a cooling type of the secondary cooling is discharge of cold.