Steel Choice Matters for Corrosion Resistance
Tool steel resists condensation, and waterline corrosion, which is especially important as the use of corrosive materials like fire-retardant additives, PVC and aminoplast increases. However, with every positive there is typically a negative. For example, corrosion-resistant plastic injection mold steels require additional machining time that increases wear, and more complex mold bases cause 60 percent of the steel to become chips.
To address these challenges, steel suppliers continue to develop specialty steels to combat the extremely corrosive injection molding environment while improving steel’s machinability and stability. For example, a free-machining stainless steel that offers a balance between machinability and corrosion resistance by combining a special chemical composition with a special heat-treatment process.
Low-carbon content and alloying elements such as chromium, manganese, and other additions play an important role in this free-machining stainless steel. The alloying elements are added during production and combine to yield optimal hardness, machinability and corrosion resistance (see Table 1).
Table 2. Machining values for free-machining stainless steel (hardness 290 - 332 HB)
Mold material choice is one of the key variables influencing plastic part production profitability, so it may be time to consider the machinability, dimensional stability and weldability benefits of a free-machining stainless steel, which can also enhance mold performance with its toughness, minimal residual stresses, and good corrosion resistance.