PSI - Issue 19

Keiji Yanase et al. / Procedia Structural Integrity 19 (2019) 504–512 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Materials and experimental method

2.1. Materials

The examined materials were high speed steel composed of high alloy and high carbon content, and indefinite chilled iron with alloy. The former material is called Material A and the latter is called Material B hereafter. The materials were melted in a high-frequency furnace, cast, and heat treated, as shown in Fig. 4. From an ingot of 8 kgf, several specimens were prepared. The intended chemical composition of Material A was 2%C-5%Cr-5%Mo-5%V-5%W in mass %. The Rockwell hardness was 64HRC (equivalent to the Vickers hardness of 780HV). Fig. 5 shows the etched images of Ma terial A. Overall carbide area fraction was 17%. Material B is an enhanced ICDP (Indefinite Chill Double Poured cast iron) and it contains cementite, graphite, and some hard carbide. The chemical composition in this study was 3.3%C 1.2%Si-0.9%Mn-4%Ni-1.6%Cr-0.5%Mo-1.5%V-0.7%Nb in mass %. It is a representative material of enhanced ICDP. The Rockwell hardness was 58HRC (equivalent to the Vickers hardness of 650HV). Fig. 6 show the etched and non etched images of Material B. Before the fatigue tests, the surface of specimens (Fig. 4) was finished with electro-polishing, paper-polishing (#2000) and buff-polishing interchangeably to minimize the residual stress at the specimen surface. In practice, more than 60 μ m in diameter was removed by this series of polishing. It is noted that a prolonged electro-polishing of these materials can introduce the surface roughness, and thus paper-polishing and buff-polishing after electro-polishing were required.

50µm

200µm

(a) Magnification = 50x

(b) Magnification = 200x Fig. 5. Etched images of Material A (with ammonium persulfate). (Matrix is colored in black and carbides are colored in white)

200µm

200µm

(a) Image after etching with ammonium persulfate

(b) Image after polishing with alumina paste (Graphite is colored in black, MC-carbides are colored in gray and matrix+M3C-carbides are colored in white)

(Matrix is colored in black and carbides are colored in white)

Fig. 6. Etched and non-etched images of Material B.