The steel GGD 420 is a martensitic stainless steel having excellent response to heat treatment of quenching and tempering, can be hardened to maximum hardness between 48 and 52 HRC. When intended for segment molds for plastic injection processing search excellent polishability properties, corrosion resistance in different environments and to near oxidation temperatures of 500 ° C, and wear resistance.
Chemical Compositions – C (0,40) • Mn (0.50) • Si (0.40) • Cr (13,50) • V (0.25)
Supply conditions – Supplied in the annealed condition with a maximum hardness of 230 HB
The combination of its properties makes it suitable for applications where corrosive materials of molds, for example, the 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, thermosets (Bakelite) with load and other reinforcement. It is also suitable for molds in glass and optics industry. It can also be used in: cutlery, surgical instrumentation, valve components and pumps, shafts and other structural components.
Stress relief: In tools of complex shapes, heterogeneous material removal in roughing, sudden changes in sections, etc., should be carried out treating strain relief to minimize dimensional variations and form during the quenching and tempering. The treatment should be between 600 – 650 ° C for at least 2 hours. Cool slowly in the oven to 300 ° C and then in still air.
Temper: austenize in temperature of 1025ºC. Heat for 1 hour for each 25 mm thick and add 1 additional hour for each 25 mm. Cool air, warm oil, salt bath or nitrogen pressure in a vacuum oven. During the heating to the austenitizing should be performed 2 pre-heating to ensure temperature uniformity and minimize distortions.
Tempering: It must be done immediately after hardening when the temperature reaches about 70 ° C. The tempering temperature must be selected according to the desired hardness. This steel can be tempered in the range from 520ºC to 200ºC or a hardness level around 48-52 HRC. Keeping the tempering temperature for at least 1 hour for each 25 mm thick, for at least 2 hours using double tempering. To optimize the fracture strength conduct a third temper. The variation in hardness at tempering is shown below curve.
Quenching from 1025ºC. Double tempering of 2 hours each.
When the tool is undergoing surface treatment, nitriding or coating, you should opt for tempering high temperature. The Figure shows that both the low tempering temperature as high corrosion resistance is still maintained at higher levels in the steel annealing condition.