How is martensite structure formed in steel?
Martensite is formed in carbon steels by the rapid cooling (quenching) of the austenite form of iron at such a high rate that carbon atoms do not have time to diffuse out of the crystal structure in large enough quantities to form cementite (Fe3C).
Is martensite a phase or microstructure?
Although martensite is described as phase containing a small amount of carbon, in databases it is not listed as a specific phase. Like bainite it is described as microstructure and not as phase. Both are usually defined as ferrite.
What kind of transformation occurs during tempering of martensite steel?
What kind of transformation occurs during tempering of martensite steel? Explanation: Tempering is a process of heating martensite steel below the eutectoid transformation temperature. This heat treatment process transforms martensite (BCT, single phase) into tempered martensite (α+Fe3C) by the diffusional process. 5.
At what temperature does martensite form?
about 200°C.
Why is martensite so brittle?
Because the cooling rate is so sudden, carbon does not have enough time for diffusion. Therefore, the martensite phase consists of a metastable iron phase oversaturated in carbon. Since the more carbon a steel has, the harder and more brittle it is, a martensitic steel is very hard and brittle.
Is high carbon steel FCC or BCC?
Carbon is added (about 1% by weight) to iron to make “carbon steel”, which is a very hard material. Carbon is rather soluble in the FCC phase of iron, but not in the BCC phase.
What is the crystal structure of pure iron?
Pure iron can have two different crystal structures as its temperature is increased from room temperature to its melting point. At room temperature it is body-centered cubic, between 912 and 1394 C if is face- centered cubic, and between 1394 and its melting point at 1538 C it returns to body-centered cubic.
What is iron carbide phase diagram?
The iron-carbon phase diagram is widely used to understand the different phases of steel and cast iron. Both steel and cast iron are a mix of iron and carbon. This iron carbon phase diagram is plotted with the carbon concentrations by weight on the X-axis and the temperature scale on the Y-axis.
What is meant by phase diagram?
Phase diagram is a graphical representation of the physical states of a substance under different conditions of temperature and pressure. A typical phase diagram has pressure on the y-axis and temperature on the x-axis. As we cross the lines or curves on the phase diagram, a phase change occurs.
What is the use of phase diagram?
phases present in any given alloy at a specific temperature. one of the primary functions of an equilibrium phase diagram is to graphically show the extent and boundaries of composition-temperature regions within which an alloy exists as a single phase or as two phases.
What is the importance of phase diagram?
Phase diagrams are useful because they allow us to understand in what state matter exists under certain conditions.
What are the types of phase diagram?
There are three main types of binary phase diagrams : Complete solid and liquid solution diagram, Eutectic diagram (including Eutectic diagram with partial solubility of the components in solid state and Eutectic diagram with intermetallic compound) Peritectic diagram.
What are the type of phases?
The three fundamental phases of matter are solid, liquid, and gas (vapour), but others are considered to exist, including crystalline, colloid, glassy, amorphous, and plasma phases. When a phase in one form is altered to another form, a phase change is said to have occurred.
What is peritectic phase diagram?
Peritectic point – The point on a phase diagram where a reaction takes place between a previously precipitated phase and the liquid to produce a new solid phase. When this point is reached, the temperature must remain constant until the reaction has run to completion. A peritectic is also an invariant point.
What is isomorphous phase diagram?
Isomorphous 1 Phase diagrams represent the relationship between temperature and the composition of phases present at equilibrium. An isomorphous system is one in which the solid has the same structure for all compositions. The phase diagram shown is the diagram for Cu-Ni, which is an isomorphous alloy system.
What do you mean by Gibbs phase rule?
Gibbs phase rule states that if the equilibrium in a heterogeneous system is not affected by gravity or by electrical and magnetic forces, the number of degree of freedom is given by the equation. F=C-P+2.
What is lever rule in phase diagram?
The lever rule is a rule used to determine the mole fraction (xi) or the mass fraction (wi) of each phase of a binary equilibrium phase diagram. It can be used to determine the fraction of liquid and solid phases for a given binary composition and temperature that is between the liquidus and solidus line.
What is solvus line?
In a physical or geochemical system, a solvus is a line (binary system) or surface (ternary system) on a phase diagram which separates a homogeneous solid solution from a field of several phases which may form by exsolution or incongruent melting. It defines the limit of solid solubility in an equilibrium diagram.
What is meant by phase rule?
The phase rule is a general principle governing “pVT systems” in thermodynamic equilibrium, whose states are completely described by the variables pressure (p), volume (V) and temperature (T). If F is the number of degrees of freedom, C is the number of components and P is the number of phases, then.
What is phase rule equation?
The phase rule states that F = C – P + 2. Thus, for a one-component system with one phase, the number of degrees of freedom is two, and any temperature and pressure, within limits, can be attained.
What are the limits of phase rule?
Limitations of Phase Rule • Phase rule is applicable only for those systems which are in equilibrium. It is not much use for those systems which attain the equilibrium state very slowly. Only three degrees of freedom viz, temperature, pressure and components are allowed to influence the equilibrium systems.
What is the use of phase rule?
Gibbs’ Phase Rule provides the theoretical foundation, based in thermodynamics, for characterizing the chemical state of a (geologic) system, and predicting the equilibrium relations of the phases (minerals, melts, liquids, vapors) present as a function of physical conditions such as pressure and temperature.
What does phase mean?
1 : a particular appearance or state in a regularly recurring cycle of changes phases of the moon. 2a : a distinguishable part in a course, development, or cycle the early phases of her career. b : an aspect or part (as of a problem) under consideration.