Steels type GGD P20 and 2738 are the most used for making general plastic injection molds. Provided the beneficiary state (quenched and tempered) has excellent mechanical properties. Especially important for this segment has good polishability and response to texturing. The manufacture of large moldings can be performed easily due to its high machinability and hardness uniformity over large cross sections. For thicknesses above 400mm, use is indicated W. Nr. 1.2738, mainly for steel GGD GGD P20SM 2738.O steel is available from a variation GGD developed especially for small molds, particularly with a maximum thickness of 200mm.
Chemical Composition – C (0.36) • Si (0.50) • Mn (0.80) • Cr (1.70) • Mo (0.40) • Ni (-)
Supply conditions – with an approximate hardness of 250 HB. Provided in the temperate state and tempered with hardness between 28-34 HRC.
It is used in plastic injection molds of all kinds, but low to medium abrasiveness. Pads for forming blow. Never use in chlorinated plastic molds. In certain circumstances, it may be used for casting non-ferrous alloys.
Stress relief: In tools of complex shapes, with heterogeneous material removal in roughing, sudden change of sections, etc., treatment of stress relief should be carried out to minimize dimensional variations. Treatment should be done at 550 ° C temperature for at least 1 hour for each 25 mm and then cool the still air.
Tempering: When heating for austenitization to be performed pre-heating to ensure temperature uniformity and minimize distortion. Preheat at temperature of 550 ° C. Austenize in temperature between 815 – 870ºC. Heat for 1 hour for each 25 mm thick and add 1 additional hour for each 25 mm. Cool preferably in a preheated oil around 70 ° C under stirring.
Tempering: It must be done immediately after hardening when the temperature reaches about 70 ° C. The tempering temperature should be selected according to the specified hardness. For this steel tempering preferably in close to 600 ° C temperatures to achieve the desired level of hardness, usually between 28-33 HRC. For this use the tempering curve below. Keeping the tempering temperature for at least 1 hour for each 25 mm thick and used at least double tempering. Using a minimum time of 2 hours and held at the minimum of two tempering.
Quenching from 850 ° C. Double tempering of 2 hours each.
Nitriding: The steel can be nitrided to increase the wear resistance of the surface hardening. The nitriding can take or not the formation of the white layer, however the presence of the white layer will impart improved wear resistance.
The maximum hardness after nitriding is in the range of 900 – 1000HV, depending on the initial hardness after processing.
GGD P20SM = maximum thickness 200 mm.
GGD P20 = maximum specified thickness 420 mm.
GGD 2738 = over 400 mm thickness.