Microstructure and erosion wear properties of high chromium cast iron added nitrogen by high pressure in alkaline sand slurry

Abstract Erosion wear is a common and serious problem in slurry transportation field. In order to improve the erosion wear performance of high chromium cast iron (HCCI), a new type of high chromium cast iron with 0.38% nitrogen (HCCI–N) was fabricated by vacuum induction positive pressure melting furnace under 0.4 MPa nitrogen partial pressure on the basis of the established pseudo-binary phase diagram of (Fe–27Cr-2.2C)–N alloy system. The microstructure and erosion wear behavior of HCCI–N were researched in alkaline sand slurry. Results show that the microstructure of HCCI–N has the characteristics of multi-scale and multi-type carbides, including eutectic M7C3 (~20 μm), secondary M23C6 (~2 μm) and Cr2C (~1 μm), distributed in matrix composed of martensite and austenite. A sandwich structure of M7C3-ferrite-martensite was formed at the interface of eutectic M7C3. The nitrogen element is mainly distributed in matrix. The Cr2C (−1011) is coherent with Martensite (110). The erosion wear is caused by the synergy of corrosion and wear. The pure wear rate (Ve) of HCCI–N accounts for 71%–93% of total erosion wear rate (Vt) under different test conditions, indicating that wear loss mainly results from the mechanical action under alkaline sand slurry. Nevertheless, the synergism rate of corrosion and wear (Vs) is also significant to Vt, which accounts for 7%–29% of Vt for HCCI–N relative to 13%–31% of HCCI. The HCCI–N has more excellent erosion wear resistance compared with that of HCCI under all the test conditions, and the optimal wear resistance of HCCI–N is 1.34 times that of HCCI. The nitrogen and chromium dissolved in matrix improves corrosion resistance, and reduces the synergistic rate of corrosion and wear. Multi-scale carbide strengthens the matrix and resists mechanical wear. The combined action of the two factors makes the HCCI–N have excellent erosion wear resistance.