hardness of martensite is greater than bionite and fine pearlite.
Lath martensite and plate martensite are two morphologies of martensite formed during the rapid cooling of austenitic steel. Lath martensite appears as thin, elongated plates or laths and is typically found in low-carbon steels, resulting in a more ductile microstructure. In contrast, plate martensite consists of thicker, broader plates and is generally found in high-carbon steels, leading to higher hardness and brittleness. The differences in their formation and structure influence the mechanical properties of the steel they comprise.
Martensite transformation begins when austenite is cooled below a certain critical temperature, called the matrensite start temperature. As we go below the tmartensite start temperature, more and more martensite forms and complete transformation occurs only at a temperature called martensire finish temp. Formation of martensite require that the austenite phase must be cooled rapidly.
60*sqrt(C)+20 HRC
when austenite change into martensite, change in the temprature occurs(cooling). Due to this thermal stress devlop between the core and surface . Surface try to expand and core try to compress the size due to this a change in 'c' parameter take place. So a=b but not=c . this is called BCT stracture.
Martensite is considered a non-equilibrium phase because it forms rapidly during the quenching process, bypassing the slow diffusion-based transformations typical of equilibrium phases. Its formation involves a shear mechanism that occurs at low temperatures, resulting in a unique crystal structure that does not correspond to the equilibrium phase diagram. This rapid transformation does not allow for the atomic rearrangements required for equilibrium, leading to its metastable nature. Consequently, martensite possesses distinct mechanical properties compared to equilibrium phases like pearlite or bainite.
Martensite
For two reasons: 1. martensite is bct structure which prevent the movement of dislocations. 2. martensite has higher carbon concentraton.
Lath martensite and plate martensite are two morphologies of martensite formed during the rapid cooling of austenitic steel. Lath martensite appears as thin, elongated plates or laths and is typically found in low-carbon steels, resulting in a more ductile microstructure. In contrast, plate martensite consists of thicker, broader plates and is generally found in high-carbon steels, leading to higher hardness and brittleness. The differences in their formation and structure influence the mechanical properties of the steel they comprise.
Martensite transformation begins when austenite is cooled below a certain critical temperature, called the matrensite start temperature. As we go below the tmartensite start temperature, more and more martensite forms and complete transformation occurs only at a temperature called martensire finish temp. Formation of martensite require that the austenite phase must be cooled rapidly.
Because Martensite transformation is almost instantaneous, the Martensite has the identical composition of the parent phase. Formation of Martensite involves a transformation from a body-centered cubic structure to body-centered tetragonal structure. The large increase in volume that results creates a highly stressed structure.
Carbon Steel - Martensite
Martensite
M. P. Arbuzov has written: 'Condition of martensite electrolytically isolated from quenched steel' -- subject(s): Steel, Electrolysis, Martensite, Electrometallurgy
60*sqrt(C)+20 HRC
During quenching, austenite transforms into martensite through a rapid cooling process. This transformation involves the carbon atoms being trapped within the crystal lattice structure of the martensite, resulting in a hard and brittle microstructure.
To make 100% pearlite, the steel should be slowly cooled, while bainite and martensite are achieved through rapid cooling. Each microstructure has different heat treatment processes that must be followed to form. A combination of these processes can be used to achieve a mix of pearlite, bainite, and martensite in varying percentages based on the cooling rate and temperature control during heat treatment.
Martensite is a very hard and strong phase of steel, formed through the rapid cooling of austenite, which traps carbon in a supersaturated solution. However, it is not ductile; instead, it tends to be brittle due to its high hardness. This brittleness can limit its practical applications, often requiring subsequent heat treatments to improve its toughness. Thus, while martensite is characterized by its hardness and strength, it sacrifices ductility in the process.