Martensitic stainless steel tube and manufacturing method thereof

Abstract

In a martensitic stainless steel tube according to the present invention, the content is determined by each of elements C, Si, Mn and Cr, and the bubble content ratio is further prescribed in accordance with the scale thickness on the outer surface of the steel tube, so that defects can be detected with high precision in the non-destructive inspection, such as ultrasonic test or the like. This allows the non-destructive inspection to be carried out with high efficiency. Moreover, there is another advantage that the weather resistance can be enhanced. The steel tube according to the present invention and the manufacturing method thereof can be suitably used in all of the technical fields in which a martensitic stainless steel tube having equal chemical composition is treated.

1 - 9 . (canceled) 
   
   
       10 . A system for manufacturing a martensitic stainless steel tube including C: 0.15-0.22%, Si: 0.1-1.0%, Mn: 0.30-1.00% and Cr: 12.00-16.00% in mass % or a martensitic stainless steel tube further including one group or more of Al: 0.1% or less, Ni: 1.0% or less and Cu: 0.25% or less in mass % in addition to said components, said system comprising:
 a quenching furnace; a high-pressure water descaler disposed on the exit side of said quenching furnace; an air-cooling apparatus disposed on the exit side of said high-pressure water descaler; a water-cooling apparatus disposed on the exit side of said air-cooling apparatus; and a tempering furnace.   
   
   
       11 . A system for manufacturing a martensitic stainless steel tube according to  claim 10 , wherein thermometers are disposed in at least one position among those such as; on the entrance side and exit side of said air-cooling apparatus; on the entrance side and exit side of the water-cooling apparatus; and on the entrance side of said tempering furnace. 
   
   
       12 . A system for manufacturing a martensitic stainless steel tube according to  claim 10 , wherein a brush or shot apparatus is disposed on the exit side of said tempering furnace. 
   
   
       13 . A system for manufacturing a martensitic stainless steel tube according to  claim 10 , wherein a high-pressure water spray apparatus for spraying a high-pressure water onto the outer surface of said steel tube is disposed on the exit side of said tempering furnace. 
   
   
       14 . A system for manufacturing a martensitic stainless steel tube according to  claim 10 , wherein a brush or shot apparatus is disposed on the exit side of said tempering furnace, and a high-pressure water spray apparatus is further disposed on the downstream side thereof. 
   
   
       15 - 18 . (canceled) 
   
   
       19 . A system for manufacturing a martensitic stainless steel tube according to  claim 11 , wherein a brush or shot apparatus is disposed on the exit side of said tempering furnace, and a high-pressure water spray apparatus is further disposed on the downstream side thereof. 
   
   
       20 . A system for manufacturing a martensitic stainless steel tube according to  claim 12 , wherein a brush or shot apparatus is disposed on the exit side of said tempering furnace, and a high-pressure water spray apparatus is further disposed on the downstream side thereof. 
   
   
       21 . A system for manufacturing a martensitic stainless steel tube according to  claim 13 , wherein a brush or shot apparatus is disposed on the exit side of said tempering furnace, and a high-pressure water spray apparatus is further disposed on the downstream side thereof.