August 2020 Volume 2

alloy carbides is a complicated process involving solubility and diffusional processes, and this poses challenges to a heat-treater for specifying times and temperatures that extract the most from the alloy content. While substantial improvements to die performance are available with higher alloy contents, transitioning into the use of these alloys may represent a significant metallurgical change that warrants discussion with your die steel supplier regarding heat treatment practices as well as die preheating and operating temperature considerations.

MATERIALS

moderating the use of this alloy. Nickel is an austenite stabilizer that lowers the service ceiling for die operating temperature. Exceeding this critical temperature transforms the steel to austenite, altering the microstructure to the depth affected and making the die especially prone to heat-checking. A 3% nickel grade of die steel, for example, may have a transformation temperature 200 to 300 °F lower than a low nickel (<1%) die steel. For most hammers and possibly some presses this may not be a problem, especially for non die components. For applications with longer workpiece residence times, extra attention must be given to die surface temperature and lubrication practices when using high nickel die steels. The principal benefits of alloy additions in die steels include increasing the hardening potential of the steel through larger section sizes and providing improved resistance to heat and impact related failures through microstructural optimization. The contribution to die strength from alloy carbides is a complicated process involving solubility and diffusional processes, and this poses challenges to a heat-treater for specifying times and temperatures that extract the most from the alloy content. While substantial improvements to die performance are available with higher alloy contents, transitioning into the use of these alloys may represent a significant metallurgical change that warrants discussion with your die steel supplier regarding heat treatment practices as well as die preheating and operating temperature considerations. ■

Figure 1. Relative potency of alloying elements to the hardenability of steel Figure 1. Relative potency of alloying elements to the hardenability of steel

Table 1. Examples of DI values for carbon and low alloy steel versus die steel Table 1. Examples of DI values for carbon and low alloy steel versus die steel Steel Grade C Mn Si Ni Cr Mo* V DI* SAE 1055 0.55 0.70 0.25 0.20 0.25 0.06 0.01 2.0 SAE 4140 0.40 0.85 0.25 0.20 1.00 0.20 0.01 5.5 Finkl FX-Xtra® 0.50 0.85 0.25 0.90 1.15 0.50 0.07 14.5 Finkl CX® 0.34 0.50 0.25 2.85 1.15 0.75 0.10 19.0 Finkl Durodi® 0.55 0.65 0.50 1.65 1.00 0.80 0.07 22.0 Finkl WF-Xtra® 0.37 0.65 0.45 0.80 2.50 1.00 0.10 33.5 *Molybdenum contentabove0.55% requiresextrapolationbeyond theASTMA255 range

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