Cr7C3 and Cr3C2 carbides in the chromium carbide coated on AISI D2 steel

Cr7C3 and Cr3C2 carbides in the chromium carbide coated on AISI D2 steel

Figure 1: Optical and SEM-BEI micrograph of chromium carbide coated AISI D2 steel at 1000 C 3 h. Scale bars: 20, 10 µm.

Figure 2: X-ray diffraction of chromium carbide coated AISI D2 steel at 1000 C 3 h.

Table 1: Chemical compositions of AISI test materials.

Carbide name: Cr7C3, Cr3C2
Record No.: 737
Carbide formula: Cr7C3, Cr3C2
Carbide type: M7C3, M3C2
Carbide composition in weight %: No data
Image type: LM, SEM, XRD
Steel name: AISI D2
Mat.No. (Wr.Nr.) designation: 1.2379
DIN designation: X153CrMoV12
AISI/SAE/ASTM designation: D2
Other designation: No data
Steel group: Cold work tool steels
Steel composition in weight %: See the table 1.
Heat treatment/condition: In this study, AISI D2 steel was used as substrates, the compositions of which are given in Table 1. The samples to be coated were machined as coupons to diameter of 20 and 5 mm in thickness, and prepared metallographically by polishing with 1200 grid emery paper at the final stage. Chromium carbide coating was performed by pack method in the powder mixture consisting of ferro-chromium, ammonium chloride and alumina in an alumina crucible sealed with an alumina led and alumina based cement. The process was performed at 1000 C for 3 h in an electrical resistance furnace followed by quenching in air.
Note: In this work, the tribological behavior of hardened, tufftrited and chromium carbide coated AISI 52100 steel balls against hardened and chromium carbide coated AISI D2 steel discs have been studied under 1, 2 and 5 N loads. Chromium carbide coating was performed by pack method. In this method, AISI 52100 steel sample was coated in the powder mixture consisting of ferro-chromium, ammonium chloride and alumina. Tufftriting treatment was performed in the commercial salt bath. The wear test was carried out with ball-on-disc configuration system. Test conditions covered 0.125 m/s speed and 1, 2 and 5 N loads.

The chromium carbide coating of AISI D2 steel performed by pack method in the powder mixture consisting of ferro-chromium, ammonium chloride and alumina at 1000 C for 3 h. Optical micrograph and scanning electron microscopy-back scattered electron image (SEM-BEI) cross-sectional view show that chromium carbide layer formed on AISI D2 steel surfaces are of compact, smooth and porosity-free morphology and homogeneous the entire surface of steel sample. Fig. 1(a) and (b) show the optical microstructure and SEM-BEI micrograph of chromium carbide coated AISI D2 steel, respectively. In this figures, two regions are observed. These are: (a) chromium carbide layer which includes Cr7C3 and Cr3C2 phases confirmed by X-ray diffraction analysis as shown in Fig. 2, and (ii) steel matrix. Chromium carbide coating layer thickness was measured as 13 µm by an optical micrometer attached to the optical microscope. The hardness of chromium carbide layer was measured as 1850 HV(0.025). It was found to be much higher than that of the hardened AISI D2 steel (61 HRc). The main advantages of chromium carbide coated steels are that the former has a diffusion controlled chromium carbide layer, which has the higher adhesion than the mechanical bonded coatings.
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