Patent ID: 7703303

Claim:
A magnetic disk glass substrate manufacturing method comprising: a step of polishing a surface of a glass substrate to a mirror surface; a step of chemically strengthening the glass substrate by causing a chemical strengthening salt and the glass substrate to contact each other in a heated atmosphere so as to chemically strengthen the glass substrate at a temperature T 1 ; a gas cooling process step of causing a gas coolant and the glass substrate to contact each other so as to cool the glass substrate to a temperature T 2 ; a liquid cooling process step of causing a liquid coolant and the glass substrate to contact each other so as to cool the glass substrate to a temperature T 3 ; the steps being included in this order, wherein in said gas cooling process step, the glass substrate is cooled from the temperature T 1 to a freezing temperature T F of the chemical strengthening salt within 10 minutes and a cooling speed from the temperature T 1 to the freezing temperature T F is set to 18° C. or more per minute, wherein in said gas cooling process step, the temperature T 2 is set to a temperature less than a boiling temperature T B of the liquid coolant used in the liquid cooling process, wherein in said gas cooling process step, the temperature T 2 is set to a temperature less than the freezing temperature T F of the chemical strengthening salt, and wherein in said gas cooling process step, the glass substrate is cooled from the freezing temperature T F to the temperature T 2 .