Special features of microcomposite structurization of ferrite in iron with elevated silicon content

Influence of Strain Rate, Temperature and Chemical Composition on High Silicon Ductile Iron

“…The solid solution hardening of Si is limited to around 4.3% [42][43][44]. Around and above this level, the elongation falls sharply.…”

“…Maximum tensile strength occurred at 4.2% Si where the elongation exceeded 10%; then, the microstructure contained 25% silicumferrite (α 1 ) [43]. Thereafter, the tensile properties and the elongations declined, leading to 500 MPa UTS For different Si concentrations, the spinodal decomposition occurs at different temperatures [44]. To describe this further, phase diagrams, as seen in Figure 4 [44], are helpful.…”

“…Here, it is logical to assume that this spinodal decomposition is masked by the shakeout process for as-cast industrially produced GJS-450-18 HSI. However, if these are annealed at around 300-350 • C, then spinodal layering can be detected [44].…”

“…For 3.5% to 4.2% silicon, hypereutectoid decomposition of the elevated temperature ferrite (α 2 -phase even called B2 phase [57]) occurs at 400-500 • C prior to spinodal decomposition of the ferrite with slow cooling. This leads to a microcomposite structure of the ferrite, where the harder Si-rich silicumferrite (α 1 ) rods are around 200-400 nm thick and about 4-5 µm long is enveloping the softer and tougher ferrite (α) [44].…”

“…For over 4.2% silicon and slow cooling, the ordered arrangement of phases is violated, and a brittle structure resembling over-aged microstructures results in spherical inclusion clusters that are also twinned [44].…”