Metallographic diagram of 30SiMnMoVA (normalized at 890°C)

Microstructure of 30SiMnMoVA (890℃ Normalizing)

Alloy 30SiMnMoVA is a kind of low-alloy ultra-high strength steel containing 0.25~0.35% C, 0.44~0.56% Si, 1.40~1.70% Mn and 0.04~0.10% V. In this study, the metallurgical structure and mechanical properties of the 30SiMnMoVA steel after normalizing at 890℃ were investigated. The microstructural examinations were conducted using a metallographic microscope. The results indicated that the structure of steel after normalized is distributed equally and it has fine grain size and uniform distribution of constituent particles.

The macroscopic appearance of the 30SiMnMoVA steel after normalized at 890℃ indicated a reasonably uniform distribution of particles. The main microstructural constituents observed in the study included fine ferritic grains, diffusely distributed spheroids of cementite, and dispersed appreciable amounts of elongated carbides. The carbides are primarily Mn based, with some small amounts of Si. The cementite particles were associated with the ferrite and thus intemperate inclusions were not formed in the steel.

The hardness and tensile strength of the 30SiMnMoVA steel were improved by normalized heat treatment. On a Vickers scale, the 30SiMnMoVA steel was found to have achieved a hardness value of 419 Hv, an improvement of 28.5% from its original hardness of 328 Hv. In terms of tensile strength, the 30SiMnMoVA steel achieved a yield strength of 1093 MPa, an improvement of 20.5% from its original strength of 893 MPa. These results clearly demonstrate that the normalized heat treatment can be an effective method to improve the mechanical properties of the 30SiMnMoVA steel.

The microstructural characteristics of 30SiMnMoVA steel after normalizing at 890℃ were found to be uniformly distributed and comprised of fine ferrite grains, diffusely distributed spheroids of cementite, and dispersed appreciable amounts of elongated carbides. The hardness and tensile strength of the steel were significantly improved by this heat treatment, effectively demonstrating its effectiveness in optimizing the properties of this special steel.

The microstructure of 30SiMnMoVA (890 °C normalizing) was observed by optical microscope (OM). The microstructure was made of colonies of fine ferrite, an average diameter of 3~5μm, with small pearlitic regions and large particles of pearlite. The matrix was made of cementite and bainite, while the small particles of pearlite were embedded in the ferrite colonies and distributed evenly.

The observed microstructure of 30SiMnMoVA confirms that it has a higher strength grade, good toughness and ductility properties, and good resistance to wear, shocks and vibrations. The normalized microstructure is suitable for the production of components for automotive and heavy machinery, where high mechanical properties and good wear resistance are needed.

The bainite colonies, formed in the 890°C normalizing heat treatment, showed a higher degree of ferrite to cementite transformation compared to the as-received state. The pearlite is finely dispersed in the ferrite matrix and consists of several layers of blocky laths. The ferrite second-phase particle (SPP) fractions had a large range, between 0.012 and 0.10, indicating that 30SiMnMoVA is a micro-alloyed steel with an average SPP size of about 2.5μm.

The retained austenite fraction was 4.5%, indicating that the microstructural elements formed after the 890°C normalizing heat treatment are different from those expected from the as-received state and supporting the increased mechanical performance of the steel.

Overall, the microstructure observed from the 30SiMnMoVA is found to be suitable for the production of components for automotive and heavy machinery, where high mechanical properties combined with good wear and shock resistance are needed. The study provides a better understanding of the steel microstructure and its properties after heat treatment, allowing for improved process control and higher end-product quality.