PSI - Issue 17

Berta Igor et al. / Procedia Structural Integrity 17 (2019) 509–513 Berta, I., Pokusová, M./ Structural Integrity Procedia 00 (2019) 000 – 000

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steel (13% Mn , 1.3% C ) to abrasion applying at low pressures is due to the fact that the martensite is formed only in deformed regions. The generally known shortcoming is the brittleness and low resistance to fracture under abrasive loading with impacts.

3. Realization

Due to the chosen orientation of the Fe-C-Cr system and regarding to the required good foundry properties (given by the minimum wall thickness of 3 mm), the selection was narrowed to sub-eutectic up to eutectic chromium cast iron with a content wt. % of C from 2.2 to 3.3 and Cr from 17 to 24. Such cast iron containing only basic components C and Cr have, at real cooling rates of castings a structure composed of coarse carbides C (FeCr) 3 C, C1 (FeCr) 23 C 6 and C2 (FeCr) 7 C 3 in a martensitic-pearlite matrix practically free of austenite, i.e. consistent with the stable phase diagrams of the Fe-C-Cr system according to Giršovič (1978) and Laird et all (2000) which are shown in Fig. 2. The casting alloyed only Cr in a C content range from 2.5 to 3.3 wt. % is extremely fragile and therefore the work was aimed at increasing its toughness by forming a sufficiently high proportion of austenite in the matrix and refining the carbide phases by micro-alloying.

Fig. 2. Section in ternary stable diagram Fe-C-Cr : a) 17 wt% of Cr ; b) 24 wt % of Cr .

Toughness depends crucially on the amount of austenite. Its representation in the matrix can be supported either by alloying with  -region expanding elements, or by those that shift the temperature of the martensitic transformation to low temperatures, so that metastable non-transformed austenite remains in the matrix. According to Giršovič (1978) and Walton (1981), elements Ni , Mn and Mo have come into consideration in terms of the technological properties and economics. The experimental casts were performed in a folding laboratory arc furnace with a crucible of 5 kg. The chemical composition of the melt of the realized casts was chosen to provide a review of the properties of the basic Fe-C-Cr system and together with the influence of selected types of alloying elements. From the specifically prepared melt by the furnace tilting was cast directly into the body the groups of specimens for abrasion resistance tests, metallographic tests, wedge specimens for leak in tests and small prismatic bar