1.  Field of the Invention
This invention relates to a high strength non-magnetic stainless steel excellent in the corrosion resistance and a method for producing the stainless steel of this kind. 
2.  Description of the Prior Art
For example, in a case of oil excavation using a drill, the position of the drilling bit at the bottom of the bore hole is detected from the ground surface through magnetic sensing and controlled. 
In the excavator of this kind, a component called as a drill collar is equipped in the vicinity of the drill, and the drill collar is required to be made from non-magnetic material in order to detect and control the drill position through the magnetic sensing. 
The drill collar is further required for corrosion resistance and high strength in addition to the non-magnetism. 
Heretofore, high manganese non-magnetic stainless steels, such as 13Cr--18Mn--0.5Mo--2Ni--0.3N, 13Cr--21Mn--0.3N, 16.5Cr--16Mn--1Mo--1.3Ni--0.5Cu--0.4N or so, have been used as a material for the components required for the non-magnetism, corrosion resistance and high strength such as the drill collar. 
In the non-magnetic stainless steels of this kind, it is recognized that it is effective to contain N abundantly in the steel for improving the corrosion resistance and the strength. 
In the non-magnetic stainless steels containing large amounts of Mn and Cr, Mn and Cr are possible to dissolve N abundantly into the molten steel, however behave to lower solid solubility of N in the steel at the solidification stage of the molten steel, accordingly there is a problem in that it is difficult to abundantly contain N into the steel, and nitrogen blow holes are easy to be generated in the solidification process so that it is not possible to obtain sound ingots in a case of containing a large quantity of N in the steel.