MX, M3C carbides in 14CrMoV6-9 steel

Figure 1: 14CrMoV6-9 + 0.009% N, extraction replica. Scale bar: 5 µm.

Figure 2: 14CrMoV6-9 gas nitrided, diffusion layer at 0.39% N, extraction replica. Scale bar: 5 µm.

Figure 3: 14CrMoV6-9 gas nitrided, diffusion layer at 0.65% N, extraction replica. Scale bar: 5 µm.

Figure 4: 14CrMoV6-9 gas nitrided, diffusion layer ca. 0.6%N, thin foil. Scale bar: 0.1 µm.

Figure 5: Selected-area diffraction pattern of area shown in Fig. 4.

Carbide name: MX, M3C
Record No.: 1451
Carbide formula: MX, M3C carbides in 14CrMoV6-9 steel
Carbide type: MX, M3C
Carbide composition in weight %: No data
Image type: TEM
Steel name: 14CrMoV6-9
Mat.No. (Wr.Nr.) designation: 1.7735
DIN designation: 14CrMoV6-9
AISI/SAE/ASTM designation: No data
Other designation: No data
Steel group: Nitriding steels
Steel composition in weight %: 0.11-0.17% C, max. 0.25% Si, 0.80-1.00% Mn, max. 0.020% P, max. 0.015% S, 1.25-1.50% Cr, 0.80-1.00% Mo, 0.20-0.300% V
Heat treatment/condition: See the text
Note: Nitriding steels are pearlitic-martensitic steels which are particularly suitable for nitriding on account of the nitride-forming elements they contain. Nitriding leads to an increase of the surface hardness, the wear resistance, the creep strength and/or the corrosion resistance in the nitrogen-enriched layer.
As an example, results are given for the steels 14CrMoV6-9 (Material No. 1.7735), 31CrMo12 (Material No. 1.8515) and 34CrAlNi7 (Material No. 1.8550) after nitriding under normal production conditions in ammonia gas at 500C for 84 h.
In the case of the steel 14CrMoV6-9, the starting material contains coarse M3C and MX precipitates (Fig. 1). In the diffusion layer at about 0.35 % N, many additional precipitates of mixed nitrides of the form MN have formed (Fig. 2). In contrast to the carbides and carbonitrides of the base material, these mixed nitrides are so fine that they are visible only as a grey tone of differing intensity.
Between the dark-shaded regions there are bright zones which apparently contain no additional precipitates. They have the highest volume fraction directly under the binding layer to about 0.65 % N (Fig. 3). These appararently precipitate-free zones appear to have a surface relief in thin foils on account of diffraction contrast effects (Fig. 4). The corresponding electron diffraction pattern (Fig. 5) shows diffuse streaks in the <100> directions in addition to the matrix spots. They indicate distortion of the cube planes by coherent, plate-shaped precipitates.
Links: No data
Reference: Not shown in this demo version.

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