Influence of Mo and W on High Temperature Hardness of M₇C₃ Carbide in High Chromium White Cast Iron

Abstract

The influence of Mo and W addition on the high temperature hardness of M 7 C 3 carbide was investigated using unidirectionally solidified hypereutectic cast iron with 25 mass%Cr. Concentrations of alloying elements in primary M 7 C 3 carbide were measured by EDS. As Mo or W content of the cast iron increases, the concentration of Mo and W in the carbide increased and that of Fe decreased. However, the Cr content was almost the same as about 60 mass% in spite of increasing the Mo and W contents. It was found from the XRD results that the lattice constant of M 7 C 3 carbide changed and its attendant volume of a unit cell increased as the Mo or W content was increased. From this point of view, it can be considered that Fe atoms in the M 7 C 3 carbide were substituted by Mo or W which has larger atomic radius than Fe. In all the specimens, the hardness of M 7 C 3 carbides are about 1600HV0.3 at the room temperature, and it decreases gradually with a rise of the test temperature. The decreasing ratio of carbide hardness becomes smaller at high temperature as the Mo or W concentration in M 7 C 3 carbide increases. Thus, the dissolution of Mo or W atom into M 7 C 3 carbide is very effective to maintaining the high temperature hardness of carbide. However, the increment of the hardness became smaller at higher Mo and W contents, so that an excess addition of both elements gave less effect than expected. The fracture toughness of M 7 C 3 carbide at the room temperature was measured using an indentation fracture method, and the values were very similar among the carbides regardless of Mo and W concentration in the M 7 C 3 carbide.

Influence of Vanadium and Boron Additions on the Microstructure, Fracture Toughness, and Abrasion Resistance of Martensite-Carbide Composite Cast Steel

“…Therefore and from fracture mechanics point of view, the most straightforward parameter to characterize fracture toughness is the critical stress intensity factor ( ) or dynamic fracture parameter ( id ). Fracture toughness (Pa⋅√m) measurements were made on primary carbide matrix at room temperature by the indentation factor method [12] which can be calculated from the width of crack induced on applying the Vickers Pyramid hardness test as follows ( Figure 12):…”

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“…Therefore from fracture mechanics point of view the most straight forward parameter to characterize fracture toughness is the critical stress intensity factor (K) or dynamic fracture parameter (K id ). A fracture toughness Kc (Pa. measurement was made at room temperature by the indentation factor method [15] which can be calculated from the width of crack induced on applying the Vickers Pyramid hardness test as shown in Fig. 7.…”

Microstructure and properties of modified as‐cast hypereutectic high chromium cast iron

“…When the addition amount of rare earth cerium is 0.5 %, the impact toughness is increased from 2.6 J cm À 2 to 3.9 J cm À 2 . Thermodynamic calculations show that cerium sesquisulphide has been formed in the molten iron at 1500 °C and can exist stably, and it can be used as a heterogeneous nucleation point to refine primary carbides [12,13].…”