Semi-toughened or heat-strengthened glass did have a thermal treatment similar to the thermal curing, but where the obtained voltage is lower than the one of toughened glass, because the cooling was slower.
Semi-toughened or heat-strengthened glass doesn't have the same characteristics compared to the commodities which it was made of:
Heat strengthened or semi-toughened glass can not be cut, sawn, drilled or modified after the thermal treatment, Any cutting or drilling of holes must happen before the treatment.
The load impact is 2 to 3 times bigger compared with standard (float) glass.
The flexural strength is 2 to 3 times bigger compared with standard (float) glass.
Heat strengthened or semi-toughened glass has a better resistance to thermal shocks than annealed glass: it resists temperature differences of circa 100°C, while annealed glass breakage can occur with a temperature difference of circa 30°C. However, this value is highly variable and depends on the quality of the edge of the glass.
Heat strengthened or semi-toughened glass has the same fragmentation as a standard (float) glass. Because this glass has a big risk of injury, heat-strengthened glass is not a safety glass
Heat strengthened or semi-toughened glass has a better optical quality than toughened or tempered glass by reduction of the optical distortions which are inherent to the temperature and duration of the curing process.
In case of glass breakage the shards (similar to those of annealed glass) can cause injury. That's why it is not considered a safety glass. The fracture image of semi-toughened glass can easily be recognized because of the star shape.
The Heat Soak Test, which is applied to reduce the risk of spontaneous breakage due to nickel sulphide inclusions, is not necessary for heat strengthened or semi-toughened glass.
Heat-strengthened or semi-toughened glass is particularly used to prevent a fracture as a result of large temperature differences in the glass element due to for exemple drop shadows.
Heat-strengthened or semi-toughened glass is used in glass façades.