Effect of Microstructure on Abrasion Resistance of High-chromium Cast-iron Deposited Metal

Abstract

Three commercially available welding consumables were surface welded to mild steel plate. Typical microstructures of their deposited metals were, hypoeutectic (Consumable A), hypereutectic (Consumable B), and hypereutectic with MC type carbides (Consumable C), respectively. The welding parameters were chosen so that the chemical composition of the deposited metals were kept about the same. When the welding was carried out in longitudinal direction with a bead-pitch of 8 mm, the deposited metal cooled rapidly. In contrast, when the welding was carried out reciprocating welding bead in transverse direction with a small bead-pitch of 3 mm, thermal cycle became shorter and the temperature of the welding zone was raised by the effect of multiple thermal cycles, resulting in a slow cooling of the deposited metals. Besides the thermal cycles, the thickness of the base plate was changed from 25 to 12 mm to reduce the cooling rate of the deposited metal. Abrasion resistance of each deposited metal was evaluated by the rubber wheel test. Main results obtained were as follows;
(1) By the preheating effect of multiple thermal cycles, the cracking of the high Cr cast-iron deposited metals was reduced remarkably.
(2) In general, the wear loss of the deposited metal was decreased as the hardness increased.
(3) The wear loss of the consumable A deposited metal was decreased when cooled slowly and larger austenitic dendrite and inter-dendritic eutectic carbides were formed.
(4) The wear loss of the consumable B deposited metal was decreased when cooled rapidly and primary carbides were surrounded by austenitic eutectic matrixes.
(5) The consumable C deposited metals, in which MC type carbides and primary-like carbides were dispersed in austenitic matrixes, showed the best abrasion resistance among the consumables investigated.