The GGD APT steel, known as “silver steel”, is a steel for high-carbon cold-working with excellent value for money in the making of tools and simpler components, but require high hardness. It has a simple heat treatment cycle being hardenable in water or in oil. Of hardenable steels in water is one that has less deformation.
Chemical Composition – C (1.20) • Si (0.25) • Mn (0.30) • Cr (0.20) • W (1.00) • V (0.10)
Supply conditions – Provided rectified in the annealed condition with a maximum hardness of 230 HB.
Mainly applied in spear points (to dig), woodworking tools, guide pins, pin pullers, reamers, punches, guide pins and measuring instruments. In cutting tools such as saws, drills, taps, tape recorders, etc.
Stress relief: In tools of complex shapes, with heterogeneous material removal in roughing, sudden change of sections, etc., before hardening in tempering should be performed the treatment of stress relief to minimize dimensional variations. Treatment should be done at a temperature of 660ºC for at least 1 hour for each 25 mm and then cool in the oven to at least 200 ° C and then in 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 780 – 820ºC. Heat for 1 hour for each 25 mm thick and add 1 additional hour for each 25 mm. For larger sections in cool water or cool sections of thinner oil. You can reach maximum hardness in tempering de67 HRC.
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. As this steel does not have secondary hardening, tempering must be around 200 ° C, but never below 180 ° C. For this use as a guide the tempering curve below. Keeping the tempering temperature for at least 1 hour for each 25 mm of thickness. Using a minimum of 2 hours. The double tempering is recommended for greater dimensional stability.
Quenching from 820ºC. Double tempering of 2 hours each.
Nitriding: The steel can be nitrided to increase the wear resistance of the surface hardening. However, the nitriding process should be controlled so as not to significantly decrease the hardness of the tool body. The nitriding steel this may or may not lead to the formation of White Layer. The maximum hardness after nitriding is in the range of 900 – 1000HV.