| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a steel wire for a high strength spring which can combinedly have high strength and satisfactory cold spring formability. SOLUTION: The high strength spring has a composition containing, by mass, 0.55 to 0.65% C, 1.2 to 2.5% Si, 0.3 to 0.6% Mn, and 0.4 to 2.0% Cr, and in which the content of P is limited to <=0.015%, and S to <=0.015%, and if required, containing one or two metals selected from 0.05 to 2.0% Mo and 0.05 to 0.3% V (wherein, the total content of Mn and V is <=0.6%), and the balance iron with inevitable impurities. The dimensions of nonmetallic inclusions are <=15μm, and its tensile strength is >=1,960 MPa, and its yield ratio (σ0.2/σB) is 0.8 to 0.9, or its yield ratio is >0.9, and also, the content of retained austenite is <=6%. Further, old austenite grain size number is >=11, its surface roughness Rmax is <=11, and the compressive residual stress of the surface part is >=600 MPa. Further, the steel has a durability of 1×10<7> times when mean stressτm=600 MPa, and amplitude stressτa=514 MPa.</p> |
