2.2. Microstructure examination
Microstructures of all specimens were analyzed by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EDS). For metallographic observations, all specimens were polished by SiC abrasive paper and polishing cloth, then etched with 4% nital. Microstructures of Fe–3.0 wt% B cast alloys were observed by a LEICA DMI 5000M optical microscopy and a VEGAIIXMUINCA-type scanning electron microscopy. To analyze the phase composition, X-ray diffraction (XRD) was carried out on a Rigaku D/Max-2400X diffractometer with copper Kα radiation at 40 kV and 200 mA as an X-ray source. And the specimens were scanned in the 2θ range of 15–90° in a step-scan mode (0.02° per step).
The volume fractions of borides in Fe–3.0 wt% B cast alloys with different Cr addition were detected by a DT2000 digital image analyzer. Ten random detecting points on the metallographic surface were selected for each specimen and the mean value was regarded as volume fraction of boride