Ferritic free-cutting stainless steel material

Abstract

The present invention relates to a ferritic free-cutting stainless steel material having a component composition contains: in terms of mass %, 10.0%≤Cr≤25.0%, 0.2%≤Mn≤2.0%, 0.30%≤Al≤2.50%, 0.02%≤Si≤0.60%, and 0.10%≤S≤0.45%, and further two or more selected from the group consisting of: 0.03%≤Pb≤0.40%, 0.03%≤Bi≤0.40%, and 0.01%≤Te≤0.10%, with a balance being Fe and unavoidable impurities. The component composition satisfies: 900([C]+[N])+170[Si]+12[Cr]+30[Mo]+10[Al]≤300, and ([Cr]+[Mo]+1.5[Si]+4[Al])/([Ni]+0.5[Mn]+30[C]+30[N])≥7. The ferritic free-cutting stainless steel material contains sulfides having a circle equivalent diameter of 1.5 μm or more, and the sulfides have an average circle equivalent diameter of 3.0 to 15.0 μm, an average aspect ratio of 2.5 or less, and an area ratio of 0.5 to 2.0%, and the maximum value of Vickers hardness of 170 HV or less.

1 . A ferritic free-cutting stainless steel material,
 having a component composition consisting of: in terms of mass %,
 10.0%≤Cr≤25.0%, 
 0.2%≤Mn≤2.0%, 
 0.30%≤Al≤2.50%, 
 0.02%≤Si≤0.60%, and 
 0.10%≤S≤0.45%, and 
 further 
 two or more selected from the group consisting of:
 0.03%≤Pb≤0.40%, 
 0.03%≤Bi≤0.40%, and 
 0.01%≤Te≤0.10%, and 
 
 optionally 
 C≤0.015%, 
 P≤0.050%, 
 Cu≤1.5%, 
 Ni≤1.5%, 
 Mo≤2.0%, 
 B≤0.0080%, 
 Mg≤0.0100%, and 
 Ca≤0.0100%, 
 with a balance being Fe and unavoidable impurities, 
   wherein, when [M] represents a mass % of an element M, the component composition satisfies the following formulae (1) and (2):
   900([C]+[N])+170[Si]+12[Cr]+30[Mo]+10[Al]≤300, and  formula (1):
 
   ([Cr]+[Mo]+1.5[Si]+4[Al])/([Ni]+0.5[Mn]+30[C]+30[N])≥7, and  formula (2):
 
 wherein the ferritic free-cutting stainless steel material contains sulfides having a circle equivalent diameter of 1.5 μm or more, and the sulfides have an average circle equivalent diameter of 3.0 μm to 15.0 μm, an average aspect ratio of 2.5 or less, and an area ratio of 0.5% to 2.0%, and 
 the ferritic free-cutting stainless steel material has a maximum value of Vickers hardness of 170 HV or less. 
   
     
     
         2 . The ferritic free-cutting stainless steel material according to  claim 1 , wherein the component composition further satisfies one or two or more selected from the group consisting of:
 0.0001≤B≤0.0080%,   0.0005≤Mg≤0.0100%, and   0.0005≤Ca≤0.0100%.   
     
     
         3 . The ferritic free-cutting stainless steel material according to  claim 1 , wherein the component composition further satisfies, as the unavoidable impurities:
 O≤0.0100% and   N≤0.035%.   
     
     
         4 . The ferritic free-cutting stainless steel material according to  claim 1 , being free of an unrecrystallized structure. 
     
     
         5 . The ferritic free-cutting stainless steel material according to  claim 1 , having a form of a bar steel or a wire material. 
     
     
         6 . The ferritic free-cutting stainless steel material according to  claim 1 , having a corrosion resistance such that rust does not occur after being left for 24 hours in a wet atmosphere having a temperature of 50° C. and a relative humidity of 98%.