MECHANICAL DAMPING CHARACTERISTICS OF DUCTILE AND GREY IRONS MICRO-ALLOYED WITH COMBINATIONS OF Mo, Ni, Cu AND Cr

Damping behaviour of micro alloyed ductile and gray cast irons were investigated in this study. This was aimed at establishing the effect of composition and microstructural parameters on the damping properties of the micro alloyed cast irons, which have shown promise for utilization in automobile and machine building where enhanced damping performance are vital. Gray cast iron containing manganese as base metal was micro alloyed randomly with molybdenum, nickel, chromium and copper at an amount not more than 0.2 % each; magnesium was added to the melt prior to casting. The microstructures show that both ductile and gray irons were developed, ductile irons consisted of pearlite and ferrite phases with their nodular graphite surrounded by the ferrite phase. The micro-alloyed ductile irons generally had higher storage (78906.39 – 120868.51 MPa) and loss modulus (78906.39 - 120868.51MPa) than the micro-alloyed gray cast irons and the ductile iron composition without alloying elements. Although the damping capacity of the composition without micro alloying elements was highest for all the cast irons (~ 0.085), but it failed at approximately 110 ᵒC, while most of the micro-alloyed ductile irons exhibited satisfactory capacity for vibration energy dissipation up to 190 ᵒC than the micro-alloyed gray irons.

Lanthanum Role in the Graphite Formation in Gray Cast Irons

The present paper reviews original data obtained by the authors from recent separate publications with additional unpublished data, specifically concerning the Lanthanum (La)’s role in the solidification pattern and graphite formation in gray cast irons. Iron melting at 0.018–0.056%S, a 3.7–4.1% carbon equivalent (CE) and less than 0.005%Alresidual are inoculated with La-bearing FeSi alloys at different associations with other inoculating elements. Complex Al-La small inclusions as possible better nucleation sites for (Mn,X)S compounds and La-Ca presence in the body of these sulfides, which possibly provide better nucleation sites for flake graphite, are identified in 0.026%S cast iron. At a lower sulfur content (0.018%S), La,Ca,Al-FeSi alloy still has a high efficiency, but more complex La-bearing alloys are recommended for a higher dendritic austenite amount (LaBaZrTi–FeSi) or for lower eutectic recalescence (LaBaZr–FeSi). La has limited but specific benefits at 0.05–0.06%S irons, including favorable graphitizing factors (a higher amount of graphite precipitated at the end of solidification), lower eutectic recalescence, and a lower value of the first derivative at the end of solidification. When La,Ca,Ba,Al,Zr,S-FeSi treatment (0.035%S base iron) is used, Scanning Electron Microscopy (SEM) analysis finds that the first formed micro-compound is a complex Al-silicate (Zr,La,Ca,Ba presence), which supports the nucleation of the second compound (Mn,Ca,La)S type. At the sulfide-graphite interface, there is a visible thin (nano size) Al-silicate layer (O-Al-Si-Ca-La system), which is more favorable for graphite nucleation (it has better crystallographic compatibility). La is identified in all three important areas of nucleants (the first is formed oxidic nucleus, the second is nucleated Mn-sulfide and the third is a sulfide-graphite interface), thereby increasing the efficiency of graphite nucleation sites.

Effect of Hard Coatings on Surface Gray Iron on Fracture Toughness

The characterization and fracture toughness with hard coatings formed at the surface of gray cast irons class 30 is evaluated in the present study. The formation of hard coatings was obtained out means of the pack boriding process; the treatment was carried out at temperatures of 1173 and 1223 K during 6 hours. The layers were evaluated by the techniques of X-ray diffraction (XRD), energy dispersive spectrometry (EDS) and microindentation across the thickness of the iron boride layer. Three-point bending tests are carried out to examine the fracture toughness of gray cast irons boriding according to the ASTM 399 standard. Consequently, the stress intensity factor was evaluated by means of the finite element method (FEM) using the package ANSYS 11. 0 creating a two-dimensional model with elements of singularity around the tip crack. The results were compared with the experiments and have been found to be in good correlation.