Metallographic diagram of Cr12MoV (quenched at 980°C and tempered at 200°C)

Cr12MoV is a very popular tool steel used in many industries, including automotive, aerospace and metal fabrication. This steel is commonly heat treated for strength and ductility. The most common heat-treat cycle for Cr12MoV involves a quench to 980℃ and then tempering to 200℃.

Lets take a closer look at the microstructural features of Cr12MoV that result from this heat-treat cycle. First, well examine the ferrite microstructure present after quenching. Following quenching, Cr12MoV is in an as-quenched martensitic state of structural transformation. This means that the crystal lattice has been changed from a more random form to one that consists of hard, needle-shaped martensite crystals. The martensitic structure provides the steel with the increased strength necessary for tooling applications.

Following quenching, Cr12MoV is tempered to 200℃. This tempering process permits the re-arrangement of the needle-shaped martensite crystals into a more regular ferrite structure. This process leaves the steel in an annealed state, with a ferrite microstructure. This ferrite microstructure is much more ductile than the martensitic structure, allowing the steel to be used in applications where maximum ductility is essential.

Now, lets examine the microstructural features of Cr12MoV in a metallograph prepared after heat-treat. A series of crossed polarized light images were taken using a light microscope. Under this type of light, the microstructure of Cr12MoV appeared as a complex mixture of ferrite and carbides, with the ferrite being the dominating structural component.

The ferrite is seen as small, needle-shaped grains that are distributed in a regular, lightly cuboid type pattern. These grains typically range in size from 400 to 1000 nm. These grains grown after tempering were relatively soft and brittle, as opposed to the hard and strong needle-shaped martensite crystals that form after quenching.

Also observed in the metallograph were small pockets of cementite that precipitated out of the structure during the tempering process. The cementite present in the form of small, lamellar particles distributed throughout the ferrite grains. Typically, the cementite particles are 1-2 nm in size and are not considered to be very influential in terms of improving the strength or ductility of the steel.

In summary, the microstructure of heat-treated (quench to 980℃ and then tempering to 200℃) Cr12MoV is a complex mixture of ferrite grains and very small cementite particles that are distributed throughout the ferrite microstructure. The ferrite grains, which constitute the majority of the microstructure, are small and needle-shaped after quenching, but become more regular and softer after tempering, resulting in increased ductility and forming capabilities for the steel. The very small cementite particles that are distributed throughout the ferrite do not influence the strength or ductility of the steel, but appear to act as nucleation sites for grain growth.

Cr12MoV(980℃ Quenching and 200℃ Tempering) Microstructure

Cr12MoV is a kind of martensitic-type high-intensity steel with excellent wear resistance and heat-resistant. It is widely used in mechanical parts with special service conditions, such as shale cutters of coal-mining machinery, pump centrifugal blades, blade shafts, hammers, and high-temperature heaters and heat exchange evaporators.

Under the condition of 980℃ quenching and 200℃ tempering, the microstructure of Cr12MoV can be observed through optical microscopy or scanning electron microscope. Under the microscope, the microstructure of Cr12MoV consists of white matrix, black alloy carbide, red alloy carbide and some small particles. The white matrix of Cr12MoV is a body-centered cubic lattice (BCC) composed of austenite, and the black and red alloy carbide particles are uniformly distributed in the matrix.

The mechanical properties of Cr12MoV under the condition of 980℃ quenching and 200℃ tempering are determined by the microstructure components and the matrix structure in the steel. The white matrix is BCC austenite, which improves the overall plasticity of the steel, while the chemically inert alloy carbides at the grain boundaries increase the hardness and reduce the cutting performance of the steel. In addition, the homogeneous distribution of white matrix and alloy carbides can improve the uniformity of the structure and improve its comprehensive mechanical properties.

In summary, Cr12MoV in the condition of 980℃ quenching plus 200℃ tempering, the microstructure of Cr12MoV consists of white matrix and alloy carbides, the white matrix is BCC austenite, and the homogeneous distribution of the matrix and carbides can improve the structural uniformity and comprehensive mechanical properties of Cr12MoV.