Treatment of cast iron is a promising application of surface strengthening by highly concentrated energy sources. As a structural material, cast iron in widely used in maoy branches of industry. The conventional methods of bulk heat treatment and surface strengthening (for example, by high-frequency currents) do not make it possible to realize completely the potentially high operating properties of cast iron. At present, considerable experience has been accumulated in plasma and laser strengthening of various grades of cast iron. However, the literature contains little data on the interrelation of the structure, phase composition, hardness, and wear resistance with the crack resistance of cast irons. At the same time, analysis of operational damage in cast iron parts shows that brittle fracture and breaking are an important cause of failure in such parts. The present work is devoted to investigation of the structure, the nature of disruption, and the criteria of short-term crack resistance of cast irons in surface strengthening by a highly concentrated plasma jet.The properties and structure of cast irons after plasma and laser treatments have been considered in many works [I -7].In the present work we investigated a high-strength cast iron (2.64% C, 1.41% Si, 0.36% Mn, 0.35% Cr, 0.88% Ni, 0.132% P, 0.009% S) with a perlite-cementite base and globular graphite. In the initial state the structure of the metal contains up to 10% free cementite and up to 8% graphite. Specimens l0 x l0 x 55 mm in size were subjected to plasma treatment normal to one of the side faces. The heating source was an indirect-action plasma generator with a sectioned insert between the electrodes [8]. The total thermal power of the plasma jet was 32 kW, the specific thermal power was 1.14x 105W/cm 2, the velocity of the plasma generator v = 25 and 40 m/h in treatment with fusion and without fusion of the surface, respectively. The plasma-forming gas was argon.We conducted a metallographic investigation of strengthened specimens and dynamic tests of them on an MK-30 impact machine with recording of disruption oscillograms in "force-time" coordinates. The choice of impact loading, as the most rigorous variant, for testing crack resistance was dePriazovsk State Engineering University; Chclyabinsk State Engineering University, Russia.termined by the fact that in operation of cast-iron parts dynamic overloads are especially dangerous.We studied several variants of strengthening, namely, plasma treatment of the specimens in the initial state with and without fusion of the surface and in combination with bulk heat treatment that consisted of quenching from 900°C in oil, tempering at 300°C for 2 h, and cooling with the furnace. The choice of these conditions of bulk hardening and tempering agrees with recommendations on heat treatment of cast iron after high-frequency [9] and laser [4] treatment.The dynamic crack resistance of the strengthened metal was evaluated in tests of two kinds of specimens, namely, smooth specimens for determining the fractu...
