Mechanical, machinability, high temperature wear, corrosion and tribocorrosion behavior of alloyed EN-GJS-500-7 quality spheroidal graphite ductile iron

Currently, spheroidal graphite cast iron (KGDD) is widely used in industrial production because of its favourable mechanical properties and economic advantages over the steels, and manufacturers are exploring ways to develop components from KGDD with lower thicknesses to increase specific strength (strength/weight ratio). The requirements on high strength, machining, corrosion and wear resistance, high tribocorrosion performance of KGDD are increasing, and its producing technology has been an important field of research for several years. The mechanical, machining, corrosion, wear and tribocorrosion properties of KGDD are largely determined by its metallographic structure. An appropriate balance of ferrite and pearlite in the ductile iron matrix can produce satisfactory strength, machining, corrosion, wear and tribocorrosion performance. In KGDD production, the alloying elements (Si,Mn,Cu,Cr,Sn and Sb) are usually used to control the microstructure and to improve the mechanical properties of the material. Each alloying element doesn't work independently and exhibits some complex interaction between them. Hence, the appropriate balance of the amount of the alloying elements must be carefully considered in the KGDD production. The effect of alloying (Mn, Cu and Mn) on the mechanical, machinability, corrosion, tribocorrosion, and high temperature wear behavior of 15 mm diameter EN-GJS-500-7 quality pearlitic/ferritic KGDD supplied from Demisaş A.Ş. were investigated. When alloyed with both 0.8% Mn and 0.8% Cu by weight, the number of graphite nodules in KGDD decreased, while their sizes increased. Unalloyed KGDD contains a large amount of the ferrite phase, and the volume fraction of pearlite expands with alloying. With alloying, the amount of pearlite increases, while the amount of ferrite decreases. Alloying improves yield strength, tensile strength, and hardness values, while reducing impact toughness. The lowest cutting force value was recorded when turning the unalloyed KGDD. However, the unalloyed KGDD showed the highest surface roughness values. It was observed that alloying had a significant effect on surface roughness, with slightly lower effects on cutting forces (11%). A positive change of approximately 50 % for surface roughness values was detected. The minimum wear loss was obtained in the KGDD alloyed with 0.8% Mn by weight, but the highest mechanical properties were achieved in the KGDD alloyed with both 0.8% Mn and 0.8% Cu by weight. In the wear test conducted at room temperature for the Mn-alloyed KGDD, the wear rate increased at 200 °C, and the wear rate remained constant up to 600 °C. The most significant increase in wear rate with increasing temperature was observed in the unalloyed KGDD and in the KGDD alloyed with both Mn and Cu. The corrosion resistance of KGDD alloyed with 0.8% Mn by weight was found to be the highest in a 3.5% NaCl environment. However, alloying KGDD with both 0.8% Mn and 0.8% Cu by weight significantly reduces its corrosion resistance. KGDD alloyed with 0.8% Mn by weight exhibits lower coefficients of friction (COF) and lower wear rates in both dry and corrosive environments. The wear mechanism of KGDDs under both dry and corrosive conditions involves the plastic deformation and ploughing of the soft ferrite phase, along with the penetration of wear debris and corrosive solution due to structural defects. However, wear damage is reduced by the lubricating properties of graphite in the matrix, supported by the hard perlite phase.