The steel GGD M2 is the most recommended and most used in the manufacture of tools for cutting, continuous or intermittent cutting conditions. Its chemical composition on the tungsten, molybdenum and vanadium assures a high level of hardness in tempering, about 64.5 HRC, and high hot hardness maintenance, ensures excellent retention of the cutting power in service.
Chemical Composition – C (0.90) • Mn (0.30) • Si (0.30) • Cr (4.20) • W (6.20) • Mo (5.00) • V (1.90 )
Supply conditions – Supplied in the annealed condition with an approximate hardness of 240 HB.
The GGD M2 is used in drills, taps, end mills and snail common type, knives, broaches, reamers, thread rolling combs, etc. It is also used in cutting and cold forming in dies and punches, in which tools can be used with lower hardness according to the particular application.
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 550 – 650 ° C for at least 2 hours and then cool slowly.
Temper: austenize at temperatures between 1190 and 1200 ° C. The cooling time is critical for this steel and should be considered in light of its cross section. It can be hardened salt baths or in vacuum furnaces. 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 should be around 550-560ºC. In cold working operations to lower hardness recommended for cutting by removal trough, 64-65 HRC should not be practiced increasing tempering temperature. Hardness minors must be achieved by modifying the austenitizing temperature, maintaining the tempering temperature.
Quenching from 1200 ° C. Double tempering of 2 hours each.
Nitriding: The steel can be nitrided to increase the wear resistance of the surface hardening. The maximum hardness after nitriding is the 1200HV order. The presence of white layer is highly fragilizante.
Finish: The fast steels are traditionally coated by PVD process (Physical Vapour Deposition). The ceramic coating produces films with high hardness, on average 2000 HV, low coefficient of friction, on average 0.3 with respect to steel. These films are important to elevate the resistance to abrasive and adhesive wear.