High-nitrogen austenitic stainless steel

Abstract

This invention provides a high-nitrogen austenitic stainless steel superior to the conventional one both in the corrosion resistance and strength, despite a low Ni content, characterized in having a Fe content of 50% by mass or more; containing Cr: 15.0% by mass to 35.0% by mass, Mo: 0.05% by mass to 8.0% by mass %, Mn: 0.2% by mass to 10.0% by mass, Cu: 0.01% by mass to 4.0% by mass and N: 0.8% by mass to 1.5% by mass, both ends inclusive, having a C content of 0.20% by mass or less, a Si content of 2.0% by mass or less, a P content of 0.03% by mass or less, a S content of 0.05% by mass or less, a Ni content of 0.5% by mass or less, an Al content of 0.03% by mass or less, and an 0 content of 0.020% by mass or less; wherein the contents of Cr, Mo, N and Mn are adjusted so that a compositional parameter η expressed by the equation: η≡(W Cr +3.3W Mo +16W N )/W Mn where W Cr is Cr content (% by mass), W Mo is Mo content (% by mass) W N is N content (% by mass) and W Mn is Mn content (% by mass) has a value of 5 or above. and optionally further containing either one of, or both of: W: 0.01% by mass to 1.0% by mass; and Co: 0.01% by mass to 5.0% by mass, both ends inclusive; and optionally further containing at least one of: Ti: 0.01% by mass to 0.5% by mass; Nb: 0.01% by mass to 0.5% by mass; V: 0.01% by mass to 1.0% by mass; and Ta: 0.01% by mass to 0.5% by mass, both ends inclusive; and optionally further containing at least one of: B: 0.001% by mass to 0.01% by mass; Zr: 0.01% by mass to 0.50% by mass; Ca: 0.001% by mass to 0.01% by mass; and Mg: 0.001% by mass to 0.01% by mass, both ends inclusive; and optionally further containing either one of, or both of: Te: 0.005% by mass to 0.05% by mass; and Se: 0.01% by mass to 0.20% by mass, both ends inclusive.

1 . A high-nitrogen austenitic stainless steel having a Fe content of 50% by mass or more, and containing: 
 Cr: 15.0% by mass to 35.0% by mass;    Mo: 0.05% by mass to 8.0% by mass;    Mn: 0.2% by mass to 10.0% by mass;    Cu: 0.01% by mass to 4.0% by mass; and    N: 0.8% by mass to 1.5% by mass,    both ends inclusive,    having a C content of 0.20% by mass or less, a Si content of 2.0% by mass or less, a P content of 0.03% by mass or less, a S content of 0.05% by mass or less, a Ni content of 0.5% by mass or less, an Al content of 0.03% by mass or less, and an 0 content of 0.020% by mass or less;    wherein the contents of Cr, Mo, N and Mn are adjusted so that a compositional parameter □ expressed by the equation:      □≡(W Cr +3.3W Mo +16W N )/W Mn      where W Cr  is Cr content (% by mass), W Mo  is Mo content (% by mass), W N  is N content (% by mass) and W Mn  is Mn content (% by mass) has a value of 5 or above;    and optionally further containing either one of, or both of:    W: 0.01% by mass to 1.0% by mass; and    Co: 0.01% by mass to 5.0% by mass,    both ends inclusive;    and optionally further containing at least one of:    Ti: 0.01% by mass to 0.5% by mass;    Nb: 0.01% by mass to 0.5% by mass;    V: 0.01% by mass to 1.0% by mass; and    Ta: 0.01% by mass to 0.5% by mass,    both ends inclusive;    and optionally further containing at least one of:    B: 0.001% by mass to 0.01% by mass;    Zr: 0.01% by mass to 0.50% by mass;    Ca: 0.001% by mass to 0.01% by mass; and    Mg: 0.001% by mass to 0.01% by mass,    both ends inclusive;    and optionally further containing either one of, or both of:    Te: 0.005% by mass to 0.05% by mass; and    Se: 0.01% by mass to 0.20% by mass,    both ends inclusive.    
   
   
       2 . The high-nitrogen austenitic stainless steel as claimed in claims  1 , having no Cr-base nitride having a diameter of 2 □m or larger observed in the sectional structure thereof after being subjected to solution heat treatment at 1,100° C. to 1,250° C., both ends inclusive.  
   
   
       3 . The high-nitrogen austenitic stainless steel as claimed in  claim 2 , having a tensile strength of 1,000 MPa or more after being subjected to the solution heat treatment.  
   
   
       4 . The high-nitrogen austenitic stainless steel as claimed in any one of  claims 1  to  2 , being cold-worked in a form of wire product, having no Cr-base nitride having a diameter of 2 □m or larger observed in the structure thereof which appears in a section normal to the axis of the wire product, and having a mean grain size of the austenitic matrix phase of 100 □m or smaller.  
   
   
       5 . The high-nitrogen austenitic stainless steel as claimed in any one of  claims 1  to  2 , being cold-worked in a form of sheet product, having no Cr-base nitride having a diameter of 2 □m or larger observed in the structure thereof which appears in a section normal to the drawing direction of the sheet product, and having a mean grain size of the austenitic matrix phase of 100 □m or smaller.  
   
   
       6 . The high-nitrogen austenitic stainless steel as claimed in  claim 4 , having a tensile strength of 1,500 MPa or more.  
   
   
       7 . The high-nitrogen austenitic stainless steel as claimed in  claim 5 , having a tensile strength of 1,500 MPa or more.