When the flat glass is heated close to the softening point, its internal molecular structure changes dramatically. As a result, the surface layer has uniform compressive stress and the interior has uniform tensile stress, which multiplies the mechanical strength of the glass. This kind of glass is toughened glass.
Semi-toughened glass defines semi-toughened glass. The processing principle of semi-toughened glass is similar to that of tempered glass. The heating temperature is about 650 C, which is lower than that of tempered glass, and the cooling rate is also slower. But the strength is lower than that of toughened glass, which is twice as strong as that of ordinary glass.