Boronizing of ductile irons used in glass moulds

In this study, ferritic GGG40.3 ductile iron samples embedded in commercial Ekabor I powder were boronized with pack boronizing technique at 850, 900 and 950 ?C for 1, 2 and 4 hours and then same iron was also subjected to boronizing with commercial Ekabor II powder was used as the boronizing agent and boronizing treatment were carried out at 950 ?C for 4 hour. Generally, compound of Ekabor powder consists of B4C, SiC and KBF4. Finally, it was boronized by using %85B4C +%15 Na2CO3 powder mixture instead of Ekabor powder at 950°C for 4h, due to harmful effect of fluorine gas in KBF4. The presence of FeB and Fe2B phases on iron substrate was confirmed by optical microscopy and scanning electron microscopy (SEM) and it was observed tooth-shape morphology of boride layers. It was investigated X-ray diffraction, fracture toughness and microhardness and calculated growth rate constant. Wear tests were carried out using the ball on disc apparatus under 30 N load, 1000 m sliding distance and results were evaluated. Although commercial Ekabor I and Ekabor II powders have same composition, powder sizes of them are not the same. It was investigated the effect of powder size on boronizing. The smaller the particle size of the powder, the bigger the contact surface, and so the better the diffusion. The thickness of boride layers of samples boronized by using Ekabor I was thicker than the boride layers obtained by using Ekabor II. X-ray diffraction analysis of boride layers on the surface of the iron revealed the existence of FeB, Fe2B phases. After boronizing, thickness of the obtained boride layers was measured by using optical microscopy. While thickness values of boride layers of borided samples at 850 ?C for 1, 2 and 4 hours were between 38 and 60 µm, thickness values of boride layers of borided samples at 950 ?C ranged from 92 to 198 µm. It was found that hardness values were between 1170 and 1820 HV and fracture toughness were in the range of 2,79-3,78 MPa m1/2 . It was observed that prolonged boronizing time resulted in low fracture toughness values. After wear tests, It was observed that unboronized sample exhibited inferior wear resistance compared to boronized samples. It was determined that diffusion coefficient values were in the range of 1,078x10-8-1,537x10-7 cm2/sn.