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What are the limitation of iron iron-carbide diagram?
1) The nonequilibrium martensite does not appear on the diagram; and 2) The diagram provides no indication as to the time-temperature relationships for the formation of pearlite, bainite, and spheroidite, all of which are composed of the equilibrium ferrite and cementite phases.
Why martensite is so hard and brittle?
For two reasons: 1. martensite is bct structure which prevent the movement of dislocations. 2. martensite has higher carbon concentraton.
What structure forms in hypoeutectoid steel after full hardening?
Martensite
What is trip steel?
TRIP steel is Transformation Induced Plasticity steel. It is a composite steel that consists of ferrite, bainite, martensite precipitants and restrained austenite. The austenite will transform into martensite when strained, thus increasing the strength of the steel. To stabilize the austenite you need to introduce alloy elements, usually Manganese.
Is steel a composite material?
Steel is not usually considered a composite, as it is macroscopically homogeneous.However, some steel types, including "classical" iron-carbon steel, can be considered as metal-matrix composites, as they contain a second phase... sometimes.For simple iron-carbon steel, cooling after high-temperature forging or heat treatment will precipitate out iron carbide (cementite, Fe3C) particles and leave a carbon-depleted iron matrix. If cooling is slow, coarse bands of iron / cementite will form, a microstructure called pearlite, which is not very hard.If the cooling speed is increased, the pearlite will become finer (finer bands), until another composite microstructure, with more acicular patterns forms, called bainite. This is also heterogeneous, i.e. a composite of carbon-poor iron and cementite.Going to very fast cooling (quenching) will result in a single-phase (not composite) material called martensite. Here the carbon doesn't have time to "exit the iron", and this martensite phase is very hard, but also normally too brittle. Hence, it is normally re-heated to 200-400°C, a process called "tempering", where again some cementite precipitates out: it becomes a composite again, yielding a somewhat softer, but much tougher material.Alloyed steels (i.e. with other elements than just iron and carbon) strongly vary in behaviour:Normal non-magnetic "austenitic" stainless steels are single-phase, not composites.Tool steels (high carbon + carbide-forming alloying elements) are definitely composites. They form a lot of hard particles, such as chromium carbides, that impart good resistance against wear.Magnetic Fe-Cr stainless steels may be essentially single-phase (very low carbon, better corrosion resistance) or also contain carbides (higher carbon, better strength)So-called "maraging" (martensite aging) steels may achieve both high strength and good corrosion resistance. Here, strength is imparted by an "aging" treatment around 500°C, to precipitate out so-called "intermetallic" particles, making it again a "composite material".These considerations also apply to many other metallic alloys, based on metals such as aluminium, titanium or nickel. In most cases, the strongest variants are engineered to be "microcomposites" or "nanocomposites", i.e. they precipitate out intermetallic particles during heat treatment.The reason behind such engineering is that the particles block dislocations, which are responsible for plastic deformation of metals. For each alloy, there is an optimum heat treatment to achieve the best "blocking ability" for dislocations, and thus the highest strength.
Why cementite is harder than austenite?
Cementite is harder than austenite because it is a compound of iron and carbon with a well-ordered crystal structure, whereas austenite is a solid solution of iron and carbon with a disordered structure. The ordered structure of cementite provides greater resistance to deformation and makes it harder.
Why pearlite makes steel harder?
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.
What are the limitation of iron iron-carbide diagram?
1) The nonequilibrium martensite does not appear on the diagram; and 2) The diagram provides no indication as to the time-temperature relationships for the formation of pearlite, bainite, and spheroidite, all of which are composed of the equilibrium ferrite and cementite phases.
What is the difference between pearlite and ferrite?
Pearlite is a layered structure of ferrite and cementite formed by the eutectoid reaction in steel, while ferrite is a pure form of iron in its BCC crystal structure. Ferrite is soft and ductile, while pearlite is harder due to the presence of cementite.
What are some uses for martensite?
hardness of martensite is greater than bionite and fine pearlite.
What is the difference between pearlite and cementite?
Pearlite is a layered structure of alternating layers of ferrite and cementite, while cementite is a specific iron carbide phase with a chemical formula of Fe3C. Pearlite forms when austenite transforms into a mixture of ferrite and cementite during the cooling of steel.
Why martensite is so hard and brittle?
For two reasons: 1. martensite is bct structure which prevent the movement of dislocations. 2. martensite has higher carbon concentraton.
What are the examples of cementite?
Cementite is a compound of iron and carbon with a fixed composition of around 6.7% carbon. It is commonly found in steels and cast irons, where it provides hardness and strength to the material. Examples include pearlite, which is a mixture of ferrite and cementite, and spheroidite, which is a microstructure that forms when cementite particles are spheroidized.
What is austenite-cementite?
ledeburite
What is the percentage of carbon in cementite?
Cementite has a chemical formula Fe3C, which means it contains 25.9% carbon by weight.
Is martensite formed when a steel is quenched?
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.
What is cementite?
Cementite is a compound in steel consisting of iron and carbon, with the chemical formula Fe3C. It is a hard and brittle phase that forms during the cooling and solidification of steel. Cementite can affect the properties of steel, such as hardness and strength.
