30Cr (slow cooling after carburizing) metallographic diagram

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According to the microstructural observations of the 30Cr (carbonized and tempered) forged steel, ferrite was found to be the dominant phase and at the same time, some eutectoid ferrite/carbide interlaced microstructures were also found. Moreover, there were ferrite/carbide layered structures including lamellar structure, blocky structure and embedded structure.

At the grains boundaries, a few chromium-rich carbides were observed and the eutectoid ferrite/carbide interlaced microstructure were finer at the boundaries. The optical micrograph clearly revealed that it was a tempered martensite. In addition, there were also some circular-shaped inclusions, which could be identified as MnS.

In the ferrite-carbide interface, high-Angle-Boundary (HABS), low-Angle-Boundary (LABS) and Widmanstatten ferrite were observed. For the Widmanstatten ferrite structure, carbonized steel exhibited a weaker texture at the ferrite-carbide interface than tempered martensite and blocky martensite which indicates that it is relatively difficult for carbonized steel to form Widmanstatten ferrite.

EDS showed that the inclusions mainly consisted of MnS and MnSi and that the modes of occurrence at the ferrite-carbide interface were found to be HABS, low alternating boundary block and lamellar.

The crystallographic analysis revealed that the structure in the carbide mainly showed a face-centered-cubic structure with a {100}〈110〉 texture and that its orientation at the ferrite-carbide interface was mainly {110}〈111〉. The orientation in the ferrite was mainly <111>.

Wo-analysis showed that the grain size of the carbonized and tempered steel was more uniform than the tempered martensite and blocky martensite and that the size of ferrite grains increased with tempering. This indicated the grain growth was an important factor in the microstructure evolution of the 30Cr steel.

The energy dispersive spectroscopy (EDS) of the carbonized and tempered steel revealed the presence of many elements including Cr, C, Mn and Si. In addition, Fe was still the main constituent element.

It is concluded that the microstructure of the 30Cr (carbonized and tempered) forged steel is composed of ferrite as the dominant phase with some Widmanstatten ferrite/carbide interlaced microstructure at the ferrite-carbide interface. This microstructure is related to the high orientation of {120} carbides. Additionally, some MnS and MnSi were observed and the grains of the carbonized and tempered steel were more uniform than the tempered martensite and blocky martensite. Finally, EDS analysis suggested that the elements Fe, Cr, C, Mn and Si were present in this structure.

Case Hardening Steel 30Cr

Case hardening steel 30Cr is a type of steel designed to be strengthened which by a process known as ‘case hardening’. The process is used to improve the wear and tear resistance of the material and to add strength to the steel. The process is done through introducing carbon into the outer layers of the material at high temperatures and then cooling rapidly, specifically through the use of nitrate salts.

The steel’s composition is typically 0.25% Carbon, 1.17% Manganese, 0.75% Silicon, 0.6% Chromium, and 0.6% Molybdenum. Typically, the steel is heated and quenched to achieve the desired structure and carbon content. After the quenching process and upon cooling, the steel will become quite strong, with a hardness of around 40-45HRC on the Rockwell C scale, which is the industry standard.

The microstructure achieved in 30Cr steel consists of a tempered martensite and carbide network which provide the steel with an excellent combination of strength and toughness. The microstructure also increases stability under heat treatment as well as improving resistance to wear and tear.

The typical application of this material is in the production of high-performance components for the automotive industry such as piston pins and valves, or for components used in heavy-duty mining and agricultural machinery, where a combination of tensile strength and wear resistance is required.

Overall, case hardened steel 30Cr is an excellent material for use in a variety of applications due to its combination of strength, toughness, wear resistance, and stability under heat treatment. It is one of the most popular materials used in the production of high-performance automotive and mining components, and its popularity continues to increase.