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High‐strength cast iron is used for manufacturing the supporting elements of minerals and cement clinker grinding machines. The dross layer remains inside large dimension castings after manufacturing. It has worse mechanical properties and resistance to fatigue crack formation and propagation. In this paper, the results of an experimental investigation of cyclic bending strength of semi‐natural specimens from cast iron with a dross layer of 10–11 mm thickness are presented. The mechanical properties and structures of the base and dross layers differed considerably. Before testing the methods of defectoscopy were applied to detect technology defects. The stress ratio was r = ‐0,62 and the stress alternating range varied from 70 to 280 MPa. To 1*108cycles, crack growth was insignificant. Further crack propagation was controlled. The 1st specimen was broken after 3*108 and the 2nd one after 2*108 cycles. The dependencies of crack propagation on cycle number and stress intensity factor range were estimated. The dross layer stops crack propagation, when crack front passes from dross to base metal.

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The research presented here aims at evaluating the strength of the welded joints of spheroidal cast iron of large mineral crushers based on the limit states under very high-cycle loading. Several experiments were performed using semi-natural and standard specimens. This study derived the summary fracture process diagram, including the test results for compact tension specimens and semi-natural specimens, for all fracture process stages. A method for evaluating the strength of these welded joints based on safety factors, when the number of loading cycles exceeds 10 8 , is proposed.