Abstract
	Surface cracks are occasionally present on the  continually cast slabs of low carbon steels. Two basic mechanisms of their origination were found. The first one is an exceeding of relaxation ability of the material to eliminate thermal and technological stresses by plastic deformation. High plasticity of the material restricts formation of crack like defects which, during further treatment of slabs, could propagate and negatively influence surface quality of the products. The second types of defects selectively arise on primary grain boundaries which are weakened from various reasons. Relatively common is the strength degradation of these boundaries by small particles of exogenous as well as endogenous character. 
	High temperature properties of the material of slabs, as reduction of area and strength, were tested in a temperature interval from 850 °C up to the melting temperature on a measuring equipment provided with high frequency heating. Testing conditions were in all cases identical. 
	Typical courses of reduction of area and strength values on the temperature measured on material of slabs from 24 various low carbon steel types are described and characteristic fracture morphologies arising at high temperature tests are documented in the contribution.