To improve the corrosion resistance, seize resistance, wear resistance, and heat resistance of the coiler roll for hot rolling, a new high Cr cast steel has been developed by using optimum alloy design, heat treatment technology, and the continuous pouring process for cladding (CPC). Comparison tests of fundamental physical properties and mechanical properties corresponding to the environment of use of the equipment were conducted for conventional and developed materials. In addition, on-line application tests were carried using mills with different load conditions. The results showed that the corrosion resistance and wear resistance of the newly developed materials were respectively greater by more than four or five times than those of the conventional ones. Moreover, the seize resistance and high temperature oxidation resistance of the new rolls were significantly improved. By applying the developed materials to the coiler roll, the life span also increased by more than three times.
To examine the effects of nickel addition on not only static tensile properties and impact properties but also fracture toughness, castings of two sizes, namely heavy-section (600mm thickness) and Y-block (75mm thickness) spheroidal graphite cast irons, with the same chemical composition were prepared, and attempts were made to clarify and evaluate the fracture toughness. CT specimens of 25 mm in thickness were then obtained from the two materials by machining, according to ASTM regulations for heavy sectional castings, and fatigue pre-cracks were formed on the specimens by applying some 20 kilo-cycles of repeated axial loads using a hydraulic servo fatigue tester at room temperature. Next, 60 degree-V shaped side-grooves were formed on the CT specimens after inducing an approximately 2 mm large fatigue pre-crack at the machined crack tip, and CT testing was then performed on the specimens using an Instron type material tester at 296K (R. T.) and 233K. The applied load (L) and load-line-displacement (LLD) of the CT specimens were recorded on computer by the unloading elastic compliance method based on the JSME method. The results showed that two kinds of almost fully ferritic spheroidal graphite cast irons were obtained from heavy sectional sands molds. The microstructures and mechanical properties of these materials were that of typically normal spheroidal graphite cast irons ones. (ie : UTS > 300 MPa, Elongation > 20%, HV > 130)
The obtained fracture toughness (JIc) of these specimens was 26-33 and 10-23 kN/m at R. T. and 223K, respectively. The converted fracture toughness (KIc) values from estimate equation showed > 45 MPa at 233K of heavy-section specimens added with 0.6% Ni. The calculated fracture toughness (converted KIc)) and Charpy impact characteristics of these materials showed good correlation with parameters when impact yield stress was applied in impact testing.