THE EFFECT OF PROCESSING ROUTE, COMPOSITION AND HARDNESS ON THE WEAR RESPONSE OF CHROMIUM BEARING STEELS IN A ROLLING-SLIDING CONFIGURATION

The commercial attractiveness of rolls with greater resistance to wear and fatigue damage is substantial, providing reduced rolling mill dow n times, increased roll life, reduced product surface defects and impr oved stock gauge tolerances. Relatively little is known about the wear mechanisms of these materials which limit the useful life of cold rol ling mill work rolls. Two steels of composition 0.8%C/3%Cr and 0.8%C/5 %Cr, which are representative of industry standard materials, have bee n tested in a rolling-sliding configuration (slippage, 8%) against a h igh speed steel (M2) counterface. A comparison has been made between s amples manufactured by conventional processing (casting and forging) a nd by spray forming. Spray forming provided a microstructure similar t o that of the heavily forged material but with a finer average carbide size (134 nm in the spray formed and 317 nm in the forged, both for t he 3%Cr steels) and the spray formed material did not contain the occa sional coarse carbides (similar to 2 mu m) found in the forged materia l. The increase in Cr content from 3% to 5% changed the carbide from ( Fe,Cr)(3)C (3%Cr steel) to (Fe,Cr)(7)C-3 (5%Cr steel) in both spray fo rmed and forged materials. However, both the carbide size and carbide type had little effect on wear rate when tested in the quenched and te mpered condition. Tempering of the quenched steel was undertaken in th e temperature range 200-500 degrees C, which yielded hardness in the r ange 540-890 H-v for the 3% Cr steel and 470-880 H-v for the 5% Cr ste el. The wear coefficient decreased significantly for an increase in ha rdness from to 470 H-v (k approximate to 1.72 x 10(-5) mm(3) N-1 m(-1) ) to 750 H-v (k approximate to 1.35 x 10(-6) mm(3) N-1 m(-1)) but only fell slightly for hardness values above 750 H-v. The friction coeffic ient was 0.49-0.63 irrespective of load or material temper. Characteri sation of worn surfaces indicated that surface strain was limited to a depth of similar to 5-15 mu m In the hardest conditions, the wear deb ris was predominantly oxide, while the soft tempers produced metallic delamination sheets as well asoxide. The wear behaviour of the four ma terials is discussed in relation to the microstructure. (C) 1997 Elsev ier Science S.A.