What is the martensitic phase?

What is the martensitic phase?

The martensitic transformation is a displacive phase transition and it occurs by coordinated shifts of atoms but, there is no long range diffusion during the phase change. In nearly equiatomic TiNi shape memory alloy, three different phases have been reported as a function of temperature.

What is a martensite structure?

Martensite is a supersaturated solid solution of carbon in ferrite with a body-centered tetragonal (BCT) structure. Upon rapid cooling, carbon is trapped in the crystal structure.

Is martensite stronger than pearlite?

Pearlite is cooled more slowly than its martensite counterpart, making it softer and easier to bend. Pearlite is typically found in the blade’s hamon, where it joins with the tempered martensite.

Can martensite turn into pearlite?

The pearlite transformation involves the redistribution of carbon followed by a structure change, the martensite transformation involves the structure change alone, and, in contrast, the bainite transformation involves a structure change followed by the redistribution of carbon, which precipitates as a carbide.

What does martensite look like?

For steel with 0–0.6% carbon, the martensite has the appearance of lath and is called lath martensite. For steel with greater than 1% carbon, it will form a plate-like structure called plate martensite. Between those two percentages, the physical appearance of the grains is a mix of the two.

Why is martensite so hard?

Untempered martensite is a strong, hard, brittle material. The stronger and harder it is, the more brittle it is. The strength and hardness is a due to elastic strain within the martensite, which is a result of too many carbon atoms being in the spaces between the iron atoms in the martensite.

Is cementite FCC or BCC?

The alpha phase is called ferrite. Ferrite is a common constituent in steels and has a Body Centred Cubic (BCC) structure [which is less densely packed than FCC]. Fe3C is called cementite and lastly (for us), the “eutectic like” mixture of alpha+cementite is called pearlite.

Is steel a FCC or BCC?

A ferritic steel has what is called a body-centered cubic (BCC) structure, while an austenitic steel has a face-centered cubic (FCC) structure and a martensitic steel has a body-centered tetragonal (BCT) structure.

Is nickel FCC or BCC?

Table 1: Crystal Structure for some Metals (at room temperature)

Why tempering is done after quenching?

Tempering is usually performed after quenching, which is rapid cooling of the metal to put it in its hardest state. Higher tempering temperatures tend to produce a greater reduction in the hardness, sacrificing some yield strength and tensile strength for an increase in elasticity and plasticity.

What happens during tempering?

Tempering, in metallurgy, process of improving the characteristics of a metal, especially steel, by heating it to a high temperature, though below the melting point, then cooling it, usually in air. The process has the effect of toughening by lessening brittleness and reducing internal stresses.

Which is the type of transformation that produces martensite?

Martensitic materials result from a specific type of phase transformation that produces the structure known as martensite. Martensitic transformations were first observed and described in steels although they occur also in may other materials, such as e.g. in Titanium alloys.

What kind of structure is a plate martensite?

The microstructure of martensite in steels has different morphologies and may appear as either lath martensite or plate martensite. For steel 0–0.6% carbon the martensite has the appearance of lath, and is called lath martensite. For steel greater than 1% carbon it will form a plate like structure called plate martensite.

What causes the white layer in surface martensite?

White Layers in steel is a generic term referred to as untempered martensite (UTM) layer or cover zones produced by abusive operating conditions such as high surface temperatures and stresses. A “white layer” has been found to result from operations such as drilling, grinding, milling, electron-discharge machining and abrasive cutting.

What are the physical properties of lath martensite?

Properties. For steel 0-0.6% carbon the martensite has the appearance of lath, and is called lath martensite. For steel greater than 1% carbon it will form a plate like structure called plate martensite. Between those two percentages, the physical appearance of the grains is a mix of the two.