Does the eutectic exist in this system? If so, determine the following: i. Compo

Question

Does the eutectic exist in this system? If so, determine the following: i. Composition of eutectic ii. Eutectic temperature iii. Eutectic reaction (i) Heat Treatment of steels is based on controlling the solid state transformation, i.e. (a) Eutectic reaction (b) Eutectoid reaction (c) age hardening (d) precipitation reaction explain/Justify your answer (ii) Write down what you know about the crystal structure of each of the 4 solid phases Alpha-Ferrite, Gamr Austenite, Delta Ferrite and Cementite phases

Explanation / Answer

b. A eutectic system from the Greek eu = easy and teksis = melting describes a homogeneous solid mix of atomic and/or chemical species, forming a joint super-lattice, by striking a unique atomic percentage ratio between the components — as each pure component has its own distinct bulk lattice arrangement. Yes it does exist in this system. It is only in this atomic/molecular ratio that the eutectic system melts as a whole, at a specific temperature (the eutectic temperature) the super-lattice releasing at once all its components into a liquid mixture. The eutectic temperature is the lowest possible melting temperature over all of the mixing ratios for the involved component species.

i) A eutectic mixture is defined as a mixture of two or more components which usually do not interact to form a new chemical compound but, which at certain ratios, inhibit the crystallization process of one another resulting in a system having a lower melting point than either of the components.

ii) The temperature at which a eutectic mixture becomes fluid (melts).The eutectic temperature is the lowest possible melting temperature over all of the mixing ratios for the involved component species.

iii) A eutectic reaction is a three-phase reaction, by which, on cooling, a liquid transforms into two solid phases at the same time. It is a phase reaction, but a special one. For example: liquid alloy becomes a solid mixture of alpha and beta at a specific temperature (rather than over a temperature range).

i) Heat treatment is based on controlling the solid state transformation, i.e,

d) Age hardening

Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering, normalizing and quenching. It is noteworthy that while the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.

Precipitation hardening, also called age hardening or particle hardening, is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys of aluminium, magnesium, nickel, titanium, and some steels and stainless steels.

ii) Ferrite is a body-centered cubic (BCC, alpha iron) form of iron. It is this crystalline structure which gives steel and cast iron their magnetic properties, and is the classic example of a ferromagnetic material. The term is beta ferrite or beta iron (-Fe).

Below 910 °C (1,670 °F) the body-center-cubic allotrope of pure iron is stable. Above this temperature the face-centred cubic allotrope of iron, austenite (gamma-iron) is stable. Above 1,390 °C (2,530 °F), up to the melting point at 1,539 °C (2,802 °F), the body-centred cubic crystal structure is again the more stable form, as delta-ferrite (-Fe). Ferrite above the critical temperature A2 (Curie temperature) of 771 °C (1,044 K; 1,420 °F), where it is paramagnetic rather than ferromagnetic. The term is beta ferrite or beta iron (-Fe). The term beta iron is not any longer used because it is crystallographically identical to, and its phase field contiguous with, -Iron.Because of its significance for planetary cores, the physical properties of iron at high pressures and temperatures have also been studied extensively. -ferrite, which is the form of iron that is stable under standard conditions, can be subjected to pressures up to ca. 15 GPa before transforming into a high-pressure form termed -iron, which crystallizes in a hexagonal close-packed (hcp) structure.

Austenite, also known as gamma-phase iron (-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron, with an alloying element.[1] In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K (727°C); other alloys of steel have different eutectoid temperatures. The austenite allotrope exists at room temperature in stainless steel. It is named after Sir William Chandler Roberts-Austen.Austenitization means to heat the iron, iron-based metal, or steel to a temperature at which it changes crystal structure from ferrite to austenite. The more open structure of the austenite is then able to absorb carbon from the iron-carbides in carbon steel. An incomplete initial austenitization can leave undissolved carbides in the matrix.For some irons, iron-based metals, and steels, the presence of carbides may occur during the austenitization step. The term commonly used for this is two-phase austenitization.

Cementite,also known as iron carbide, is an intermetallic compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe3C. By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure. It is a hard, brittle material, normally classified as a ceramic in its pure form, and is a frequently found and important constituent in ferrous metallurgy. While iron carbide is present in most steels and cast irons, it is produced as a raw material in the Iron Carbide process, which belongs to the family of alternative ironmaking technologies.While cementite is thermodynamically unstable, eventually being converted to ferrite and graphite at higher temperatures, it does not decompose on heating at temperatures below the eutectoid temperature (723 °C) on the metastable Iron-Carbon phase diagram.

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