Maraging steel and maraging steel for metallic belt

Abstract

A maraging steel for metallic belts which has a composition capable of being reduced in the content of TiN serving as a starting point for fatigue fracture in a high-cycle-rate region. The composition facilitates nitriding to heighten the surface hardness. The steel has a nitrided surface layer having increased compressive residual stress and hence improved flexural fatigue strength. In the steel, former austenite crystal grains have been reduced in size in order to secure higher strength and higher ductility. The maraging steel consists of, by mass %, up to 0.01% C, up to 0.1% Si, up to 0.1% Mn, up to 0.01% P, up to 0.005% S, 17.0-22.0% Ni, 0.1-4.0% Cr, 3.0-7.0% Mo, from more than 7.0 to 20.0% Co, up to 0.1% Ti, up to 2.5% Al, up to 0.03% N, up to 0.005% 0, up to 0.01% B (exclusive zero), and the balance of Fe and unavoidable impurities, wherein Co/3+Mo+4Al is 8.0-15.0%.

1 . Maraging steel consisting essentially of, by mass percent, not more than 0.01% C, not more than 0.1% Si, not more than 0.1% Mn, not more than 0.01% P, not more than 0.005% S, 17.0 to 22.0% Ni, 0.1 to 4.0% Cr, 3.0 to 7.0% Mo, more than 7.0% and not more than 20.0% Co, not more than 0.1% Ti, not more than 2.5% Al, not more than 0.03% N, not more than 0.005% 0, and not more than 0.01% B (exclusive zero %), and the balance of Fe and unavoidable impurities, wherein the value of “Co/3+Mo+4Al” is 8.0 to 15.0% by mass percent. 
   
   
       2 . The maraging steel according to  claim 1 , wherein the Cr content is 0.1 to 3.0% by mass, and the Al content is more than 0.15% and not more than 2.5% by mass. 
   
   
       3 . The maraging steel according to  claim 1 , wherein the carbon content is not more than 0.008% by mass, the Ni content is more than 18.0% and not more than 22.0% by mass, the Mo content is more than 5.0% and not more than 7.0% by mass, and the Ti content is not more than 0.05% by mass, wherein Co/3+Mo+4Al is 10.0 to 15.0% by mass percent. 
   
   
       4 . The maraging steel according to  claim 1 , wherein the Co content is more than 12.0% and not more than 20.0% by mass. 
   
   
       5 . The maraging steel having high fatigue strength according to  claim 1 , wherein the Co content is more than 10.0% and not more than 20.0% by mass, the Ti content is not more than 0.05% by mass, and less than 0.1% Al by mass, wherein the value of “Al+Ti” is less than 0.1% by mass. 
   
   
       6 . The maraging steel according to  claim 1 , which contains, by mass percent, one or more of not more than 0.01% Ca and not more than 0.005% Mg. 
   
   
       7 . The maraging steel according to  claim 1 , which has a fine grain size of ASTM No. 10 or more. 
   
   
       8 . A maraging steel for a metallic belt, which is made of the maraging steel as defined in  claim 1 .