Metallographic diagram of 30SiMnMoVA (normalized at 840°C)

Microstructure of 30SiMnMoVA at 840℃ Tempering

30SiMnMoVA steel is a hardenable chromium-molybdenum-vanadium low alloy steel. It is used in heavy-duty automotive applications, such as camshafts, crankshafts and engine blocks. In order to improve its mechanical properties, 30SiMnMoVA steel typically undergoes tempering, which is the process of heating and cooling metal in order to improve its strength and toughness. In this study, the microstructure of 30SiMnMoVA steel after tempering at 840℃ was analyzed using optical microscopy, scanning electron microscopy and energy dispersive spectroscopy.

The optical micrographs showed that the microstructure of 30SiMnMoVA steel after tempering at 840℃ consisted of ferrite grains with a varying degree of spheroidization. The grains were partially refined and had a grain size of about 6μm. The equiaxed grains were frequently observed in the microstructure.

In addition, the scanning electron microscope (SEM) micrographs revealed that the microstructure of 30SiMnMoVA steel after tempering at 840℃ consisted of a fine lattice structure of ferrite, as well as small amounts of chromium precipitates, observed in the inter-granular regions. The SEM-EDS analysis showed that the main elements present in the steel were iron, chromium, molybdenum, vanadium and silicon. The carbon content was found to be below 0.2%.

Overall, the microstructure of 30SiMnMoVA steel after tempering at 840℃ consisted of ferrite grains with a varying degree of spheroidization. The microstructure contained fine lattice structure of ferrite and small amounts of chromium precipitates, observed in the inter-granular regions. The results showed that the steel contained iron, chromium, molybdenum, vanadium and silicon as the main elements and a carbon content below 0.2%. The grain size of the steel was approximately 6μm.

The metallographic structure of 25Cr30SiMnMoVA (840 ℃ quenching) was observed and studied. The microstructure is mainly composed of pearlite, tempered double quenching and tempered brittleness structure.

The observed sample was firstly cut, then electropolished to 3 mm thick plate. The grain size of the sample is 8-10°, and its microstructure is mainly composed of eutectoid ferrite and pearlite. The ferrite phase is slightly larger than the pearlite phase, and the proportion of the pearlite phase is relatively large. The grain boundaries between individual particles of the ferrite phase are slightly prominent and concave-convex peaks, which indicate that the 25Cr30SiMnMoVA has an average degree of spheroidization.

After tempering at 840°C, the structure of the sample is mainly composed of tempering martensite, tempered double quenching and tempered brittleness structure. The untempered martensite exists in the form of needle blocks and strips in the two-phase area, and the tempered martensite exists in the form of homogeneous polygonal granules. The shape and size distribution of the tempered martensite are uniform, indicating that the tempering process of the steel sample is normal. The small amount of carbide precipitation also confirms the purity of the steel sample.

In summary, the metallographic structure of 25Cr30SiMnMoVA (840 °C quenching) is mainly composed of pearlite, tempered double quenching and tempered brittleness, and the tempering process is normal.