Caracterização microestrutural e análise de descarbonetação da rosca do grampo de mola do aço 4140M

Abstract

The present work aims analyze the decarburization and the microstrucutre obtained in thread of the clamps for leaf spring suspension. The clamp is considered a safety item and as such needs special procedures to guarantee the design mechanical properties. Since it must be heat treated in a continuous production furnace with out controlled atmosphere the temperatures for quench and temper and the austenitization time must optimized to achieve the allowed amount of decarburization and the proper mechanical properties in accordance with the ISO 898-1 2013 standard. This research used 5 sets composed of three clamps each of 4140M steel (similar to SAE 4140). Each set was austenitized at 880˚C for different times and quenched in a water-polymer solution with 48.84% of polymer. The tempering treatment afterwards was carried out at 490˚C for 54 minutes. The best result were for the set that was austenitized for 2min and produced a hardness of 33 to 38 HRC for measurements made at the surface and the center of the cross section of the part. The tensile strength was between 1257 and 1307, the elongation and area reduction were between 13–16% and 48,6–55,5% respectively. The decarburization depth at the thread was 0.103 mm. All values were within the allowed range as specified in the ISO 898-1/2013 standard. The microstructure was composed of ferrite, pearlite, martensite and bainite.