Effect of Silicon Content on Intergranular Embrittlement of Ferritic Spheroidal Graphite Cast Iron Suffered from Cyclic Heating

Abstract

The effect of silicon content on intergranular embrittlement of ferritic spheroidal graphite cast irons after suffer a certain number of thermal cycles is investigated. The tensile elongation tends to increase with the number of thermal cycles, and increased silicon content leads to eventual embrittlement. The fracture surface of a 2.9Si specimen changes from dimple pattern feature to intergranular fracture, whereas the fracture surfaces of both 4.0Si and 4.3Si specimens change from the brittle cleavage to intergranular fracture that following with increasing the number of thermal cycles. The intergranular cracking path will initiate and propagate through the eutectic cell boundaries due to the presence of microsegregated inclusions that clustered in the eutectic cell boundary region. These inclusions are oxides that mainly contain magnesium, phosphorus and cerium. Experimental analysis detected that the magnesium elements not only segregated in the vicinity of eutectic cell boundaries, but also the annealed ferritic grain boundaries. However the embrittlement resulted from cyclic heating is strongly dependent on the morphology of clustered inclusions and is pertaining to the variation of silicon content. The observed magnesium-containing inclusions located in the central region of the matrix may profoundly affect the overall tensile fracture behavior of heat resistant used SG cast irons.

Effect of Si Content on the Deterioration of Vibration Fracture Resistance of Ferritic SG Cast Iron under an Aqueous Environment

“…Moreover, from our previous results, the cracks tended to nucleate from and propagate toward the prior-eutectic cell-wall regions where a fair amount of MgO inclusions embedded inbetween the nodular graphite. 5,9) Figure 1, also reveals that the silicon content will affect the microstructural feature, and although the MgO inclusion clustered 10,11) region is an inevitable route for vibration crack propagation, little influence can be recognized in this study. However, more detailed investigation is needed.…”

Towards a temperature dependent and probabilistic lifetime concept for nodular ductile cast iron materials undergoing isothermal and thermo-mechanical fatigue

“…The IE damage mechanism was studied by several authors [2][3][4][5][6]. Nevertheless there is no clear explanation for this phenomenon.…”

“…It is known to be dependent on microstructural features, such as the graphite size and the eutectic cell wall size, where greater sizes should promote intergranular fracture [2]. Based on tensile testing, it was also studied in [3] how increasing the percentage of silicon, changes the fracture mechanism from a mix of dimpled and intergranular fracture to cleavage and intergranular fracture. This change of fracture mechanism is thought to be related with the presence of MgO particles in the eutectic cell wall region serving as crack initiation sites [4].…”

“…Based on tensile testing, it was also studied in [3] how increasing the percentage of silicon, changes the fracture mechanism from a mix of dimpled and intergranular fracture to cleavage and intergranular fracture. This change of fracture mechanism is thought to be related with the presence of MgO particles in the eutectic cell wall region serving as crack initiation sites [4]. Another investigation [5] concludes that MgO inclusions serve as crack initiation sites and the amount of phosphorus segregation on the grain boundaries dictates the fracture mode within the IE temperature of ferritic DCIs.…”

Effect of Maximum Temperature on the Cyclic-Heating-Induced Embrittlement of High-Silicon Ferritic Spheroidal-Graphite Cast Iron

“…[1][2][3][4][5][6] High-silicon spheroidal graphite cast iron is considered to be one of the most promising candidate alloys for these components due to its castability, low oxidation, and good wear resistance. 7,8) In these cases, SG cast iron components periodically operate at elevated temperatures of up to 1123 K and, in particular, are subjected to cyclic thermal shocks from heating/cooling.…”