Hardness of 9H (9H hardness 9 = corundum (sapphire) grinding hardness 1000 according to Rosiwal only the diamond is harder = 10H) This quenching causes the surface to solidify and the external dimensions of the component now change only comparatively little. However, the warmer core continues to contract even more strongly because the thermal expansion above the transformation point is significantly higher than below it. This frozen prestress allows the tempered glass to compensate for significantly higher tensile loads than untreated glass. Since the compressive strength of glass significantly exceeds the tensile strength, this represents an overall improvement. However, a workpiece treated in this way can no longer be cut in a non-destructive manner, as is possible with untreated gla.
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