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Pearlite is a two-phased, lamellar (or layered) structure composed of alternating layers of ferrite (87.5 wt%) and cementite (12.5 wt%) that occurs in some steels and cast irons. During slow cooling of an iron-carbon alloy, pearlite forms by a eutectoid reaction as austenite cools below 723 °C (1,333 °F) (the eutectoid temperature).
[2] [3] Acicular ferrite is a fine Widmanstätten constituent, which is nucleated by an optimum intragranular dispersion of oxide/sulfide/silicate particles. The interlocking nature of acicular ferrite, together with its fine grain size (0.5 to 5 μm with aspect ratio from 3:1 to 10:1), provides maximum resistance to crack propagation by cleavage.
Under a light microscope, the microstructure of bainite appears darker than untempered martensite because the bainite has more substructure. [9] The hardness of bainite can be between that of pearlite and untempered martensite in the same steel hardness. The fact that it can be produced during both isothermal or continuous cooling is a big ...
This increases the brittleness of the steel in a way that can only be relieved by recrystallizing. Widmanstätten structures made from ferrite sometimes occur in carbon steel, if the carbon content is below but near the eutectoid composition (~ 0.8% carbon). This occurs as long needles of ferrite within the pearlite. [16]
Molar volume vs. pressure for α-Fe at room temperature. The primary phase of low-carbon or mild steel and most cast irons at room temperature is ferromagnetic α-Fe. [8] [9] It has a hardness of approximately 80 Brinell. [10] [11] The maximum solubility of carbon is about 0.02 wt% at 727 °C (1,341 °F) and 0.001% at 0 °C (32 °F). [12]
This is a photograph of a gemstone taken under a microscope. If you're thinking, "I could look at these breath taking images forever," you're not the only one.
They are often observed in cases where a phase transition front moves quickly, leaving behind two solid products, as in rapid cooling of eutectic (such as solder) or eutectoid (such as pearlite) systems. Such conditions force phases of different composition to form but allow little time for diffusion to produce those phases' equilibrium ...
President-elect Donald Trump distanced himself from Project 2025 on the campaign trail but has since nominated several authors or contributors from the controversial conservative presidential ...