Patent ID: 8783063

Claim:
A method of manufacturing a glass substrate for a magnetic disk, wherein the glass contains in expression of percent by mass: SiO 2 57 to 75%; Al 2 O 3 5 to 20%; (where the total amount of SiO 2 +Al 2 O 3 is 74% or more) the total of ZrO 2 , HfO 2 , Nb 2 O 5 , Ta 2 O 5 , La 2 O 3 , Y 2 O 3 , and TiO 2 exceeding 0% to 6% or less; Li 2 O exceeding 1% to 9% or less; Na 2 O 5 to 18%; (where the mass ratio Li 2 O/Na 2 O is 0.5 or less) K 2 O 0 to 6%; MgO 0 to 4%; CaO exceeding 0% to 5% or less; (where the total amount of MgO and CaO is 5% or less, and the content of CaO is higher than the content of MgO) and SrO+BaO 0 to 3%, the method comprising the step of applying chemical reinforcement treatment to the glass substrate, wherein a glass composition of the glass substrate and conditions of the chemical reinforcement treatment are selected to perform the chemical reinforcement treatment on the selected conditions so that when the glass substrate for a magnetic disk is made by the chemical reinforcement treatment, a penetration length in an uppermost-portion stress layer on a main surface of the glass substrate for a magnetic disk is 49.1 μm or less, and that assuming that an angle between the main surface and compressive stress in a stress profile by a Babinet compensator method is θ, the penetration length in the uppermost-portion stress layer is a value y of {12·t·ln(tan θ)+(49.1/t)} or less, the penetration length in the uppermost-portion stress layer is a length of the longer diagonal in an indentation when a diamond quadrangular pyramid indenter of rhombic transverse section with vertex angles of 172° 30′ and 130° is pressed against the main surface with a pressing force of 100 g, the tan θ is a value {(L 1 +L 2 )/(P 1 +P 2 )} calculated from stress values and stress depths obtained by the Babinet compensator method, the t is a thickness of the substrate, P 1 is a compressive stress value, P 2 is a tensile stress value, L 1 is a compressive stress depth, and L 2 is a tensile stress depth.