EFFECTS OF DIRECT CURRENT FIELD ON POWDER-PACKED BORIDING PROCESS ON MARTENSITIC STAINLESS STEEL AISI 420

摘要

The effects of direct current field on a powder-packed bonding process on a martensitic stainless steel AISI 420 have been investigated at a temperature of 900 °C for about 2-6 hr. A powder-packed bonding process without direct current field (conventional powder-packed boriding process, PB) is a reference as compared to the powder-packed bonding process with applied current densities (PB-DC) of 60-170 mA/cm~2. The microstructure and the presence of boride layers of PB and PB-DC were characterized using optical microscope and X-ray diffraction (XRD). The hardness values of the boride layer were measured by Vickers microhardness tester. Experimental results show that the direct current filed can enhance the decomposition and chemical reaction in the boriding agent and also drive active free boron ions as well as atoms to diffuse toward the cathode. Therefore, a boron concentration around the specimen at the cathode of PB-DC is higher than that at the anode as well as PB (as a reference). As a consequence, higher boride layer thickness of PB-DC was detected. The double-phase boride layer (FeB and Fe_2B) on borided martensitic stainless steel AISI 420 was found both PB and PB-DC. The hardness of the boride layer of about 1800-2000 HV can be observed.