GENERAL
Gnee 420 steel is a martensitic stainless steel that has an excellent response to a heat treatment of quenching and tempering, it can be hardened to the maximum hardness between 48 and 52 HRC. When used in plastic segment molds, the injection process seeks excellent polishing properties, resistance to corrosion in different environments and for oxidation temperatures close to 500 ° C, and resistance to wear.
Chemical compositions - C (0.40) • Mn (0.50) • Si (0.40) • Cr (13.50) • V (0.25)
Supply conditions - Supplied annealed with a maximum hardness of 230 HB
APPLICATIONS
The combination of its properties makes it suitable for applications where corrosive mold materials, for example, injection of chlorinated polymers, such as PVC and acetate. In hot runner molds, subject to intense atmospheric humidity and injection of abrasive polymers such as, for example, filled thermoset plastics (Bakelite) and other reinforcement. It is also suitable for molds in the glass and optics industry. It can also be used in: cutlery, surgical instrumentation, valve and pump components, shafts and other structural components.
HEAT TREATMENT
Stress relief: In complex shaped tools, removal of heterogeneous material in roughing, sudden changes in sections, etc., stress relief treatment should be carried out to minimize dimensional and shape variations during quenching and tempering . The treatment should be between 600 to 650 ° C for at least 2 hours. Cool slowly in the oven to 300 ° C and then calm air.
Temper : austenize from the temperature of 1025ºC. Heat for 1 hour for every 25mm of thickness and add an additional 1 hour for every 25mm. Cold air, hot oil, salt bath or nitrogen pressure in a vacuum furnace. During heating to austenitization, 2 preheating should be carried out to ensure temperature uniformity and minimize distortions.
Tempering: It should be done immediately after hardening when the temperature reaches approximately 70ºC. The tempering temperature must be selected according to the desired hardness. This steel can be tempered in the range of 520 ° C to 200 ° C or a hardness level of around 48 to 52 HRC. Maintain the tempering temperature for at least 1 hour for every 25 mm of thickness, for at least 2 hours using double tempering. To optimize resistance to fracture, perform a third temper. The variation in hardness on temper is shown below the curve.
The cooling of 1025ºC. double temper for 2 hours each.
When the tool is subjected to surface treatment, nitriding or coating, high temperature tempering should be chosen. The figure shows that both the low tempering temperature and corrosion resistance still hold at higher levels in the annealed condition of steel.
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