Main damages on upper die in industrial hot forging Glavne ... - RMZ
Main damages on upper die in industrial hot forging Glavne ... - RMZ
Main damages on upper die in industrial hot forging Glavne ... - RMZ
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<str<strong>on</strong>g>Ma<strong>in</strong></str<strong>on</strong>g> <str<strong>on</strong>g>damages</str<strong>on</strong>g> <strong>on</strong> <strong>upper</strong> <strong>die</strong> <strong>in</strong> <strong>in</strong>dustrial <strong>hot</strong> forg<strong>in</strong>g457Table 1. Chemical compositi<strong>on</strong> of applied <strong>die</strong> steel (Dievar) <strong>in</strong> mass fracti<strong>on</strong>s, w/%C Si Mn Cr Mo V0.37 0.26 0.5 5.0 2.36 0.55Figure 3. Microstructures and microhardness profile <strong>on</strong> cross-secti<strong>on</strong> of the <strong>die</strong>edge: nitrided diffusi<strong>on</strong> layer with compound layer (a-b), microhardness profile (c)Results and discussi<strong>on</strong>Initial nitrided microstructuresDiffusi<strong>on</strong> layer can be well seen <strong>on</strong>cross-secti<strong>on</strong>s of the surface edge (Figure3a). The depth of diffusi<strong>on</strong> layer isnot homogenous and it is thick from73 μm to 122 μm (see Figure 3a). Thisn<strong>on</strong>homogeneity could be atributed tounappropriate preparati<strong>on</strong> of <strong>die</strong> surfacebefore the nitrid<strong>in</strong>g process thatresulted <strong>in</strong> different adsorpti<strong>on</strong> abilitiesof nitrogen <strong>in</strong>to the <strong>die</strong> surface layer.Thickness of compound layer was <strong>in</strong>the range of about 0–3.5 μm (Figure3b). Further, presence of nitrides wasvisible <strong>on</strong> gra<strong>in</strong> boundaries. It wasalso remarked that microstructure wasslightly overnitrided (nitrides <strong>on</strong> gra<strong>in</strong>boundaries were <strong>in</strong> that area pependicularto diffusi<strong>on</strong> fr<strong>on</strong>t and parallel to<strong>die</strong> surface) that could result <strong>in</strong> prematurespall<strong>in</strong>g of <strong>die</strong> material from the<strong>die</strong> surface layer. Figure 3c gives microhardnessprofile; max. values wereabove HV = 1200.<strong>RMZ</strong>-M&G 2010, 57
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