Lecture

Martensitic Transformation: Characteristics and Influences

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Description

This lecture discusses the martensitic transformation in metals, focusing on the differences between diffusional and martensitic phase transformations. It outlines the characteristics of martensitic transformations, including the movement of atoms and the conditions under which these transformations occur. The instructor explains the significance of temperature and time in determining the extent of transformation, emphasizing that martensitic transformations can happen at very low temperatures. The lecture also covers the role of carbon atoms during the transformation, highlighting how they affect the structure and hardness of martensite. Additionally, the influence of alloying elements on the stability of different phases is examined, detailing how certain elements can promote or hinder the formation of martensite. The discussion includes diagrams and examples to illustrate the concepts, making it clear how the martensitic transformation is crucial in materials science and engineering applications.

Official source

Ontological neighbourhood

Chemical engineering

Materials science: Alloys

Related concepts (32)

Diffusionless transformation

Diffusionless transformations, also referred to as displacive transformations, are solid-state changes in the crystal structure that do not rely on the diffusion of atoms over long distances. Instead, they occur due to coordinated shifts in atomic positions, where atoms move by a distance less than the span between neighboring atoms while maintaining their relative arrangement. An illustrative instance of this is the martensitic transformation observed in steel.

Martensite

Martensite is a very hard form of steel crystalline structure. It is named after German Adolf Martens. By analogy the term can also refer to any crystal structure that is formed by diffusionless transformation. 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). Austenite is gamma-phase iron (γ-Fe), a solid solution of iron and alloying elements.

Steel

Steel is an alloy of iron and carbon with improved strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels, which are resistant to corrosion and oxidation, typically need an additional 11% chromium. Because of its high tensile strength and low cost, steel is used in buildings, infrastructure, tools, ships, trains, cars, bicycles, machines, electrical appliances, furniture, and weapons. Iron is the base metal of steel.

Thermodynamics

Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of thermodynamics which convey a quantitative description using measurable macroscopic physical quantities, but may be explained in terms of microscopic constituents by statistical mechanics.

Austenite

Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. 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 is named after Sir William Chandler Roberts-Austen (1843–1902); it exists at room temperature in some stainless steels due to the presence of nickel stabilizing the austenite at lower temperatures.

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