Chemically strengthened glass

A chemically strengthened glass comprising a compressive stress layer that is formed in a surface layer of the glass by an ion exchange method, wherein:

• the glass has a surface roughness (Ra) of 0.50 nm or more;
• the glass has a depth of the compressive stress layer of 55 μm or more;
• the glass has a composition comprising, in mole percentage on an oxide basis, 55.5 to 76.5% of SiO2, 5 to 20% of Al2O3, 8 to 25% of Na2O and 0.1% or more of P2O5;
• a hydrogen concentration Y1 in a region of a depth X from an outermost surface of the chemically strengthened glass satisfies Expression (I) below at X1=0.10 to 0.25 (μm);
• a hydrogen concentration Y2 in a region of the depth X from the outermost surface of the chemically strengthened glass satisfies Expression (II) below at X2=0.25 to 0.4 (μm);
• and
• a surface strength F (N) measured on the conditions below by a ball-on-ring test satisfies a relation of F≥1200×t2 with respect to a sheet thickness t (mm) of a sheet of the glass:
• Y1=a1X1+b1 (I),
• wherein:
• Y1 is the hydrogen concentration (mol/L, measured as H2O);
• X1 is the depth from the outermost surface of the glass (μm);
• a1 is −1.700 to −0.500;
• and
• b1 is 0.100 to 0.460,
• Y2=a2X2+b2 (II),
• wherein:
• Y2 is the hydrogen concentration (mol/L, measured as H2O);
• X2 is the depth from the outermost surface of the glass (μm);
• a2 is −0.200 to −0.010;
• and
• b2 is 0.050 to 0.150,
• ball-on-ring test conditions:
• A glass sheet having a sheet thickness t (mm) is disposed on a stainless steel ring having a diameter of 30 mm and including a contact portion rounded with a curvature radius of 2.5 mm, and a steel ball having a diameter of 10 mm is brought into contact with the glass sheet;
• In this state, the ball is loaded at a center of the ring under a static load conditions;
• A breaking load (in units of N) at which the glass is broken is regarded as a BOR strength, and an average value of 20 times measurements of the BOR strength is regarded as the surface strength F;
• Here, the case where a breaking start point of the glass is 2 mm or more away from a loading point of the ball is excluded from data for calculating the average value.