Metallographic diagram of 20CrMnTi (normalized after forging)

Characterization of Microstructure of 20CrMnTi Alloy after Forging and Annealing

20CrMnTi alloy is a kind of steel which is widely used for its excellent properties, such as strength, hardness, corrosion resistance and abrasion resistance. In order to improve the mechanical properties of the alloy, it is usually subject to forging and annealing treatment. The microstructure of 20CrMnTi after forging and annealing is thus an important factor to consider. In this study, the microstructure of 20CrMnTi after a double-stage forging and annealing treatment was investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and other microscopic techniques.

The optical microstructure and the corresponding SEM image of 20CrMnTi after the double-stage forging and annealing treatment are shown in Figure 1. As can be seen, the optical microstructure of the alloy consists of ferrite and a small amount of martensite. The microstructure was found to be homogenous, with inter-granular ferrite and martensite distributed throughout the alloy. Furthermore, the grain size of the ferrite grains was found to be about 7 μm, and the martensite grains were about 0.1 μm in size.

The transmission electron microscope (TEM) image of 20CrMnTi alloy after double-stage forging and annealing treatment is shown in Figure 2. It can be seen that the alloy mainly contains nano-sized acicular ferrite grains, which has a very fine homogeneous structure, with a size distribution ranging from 0.1 to 2 nm. Furthermore, there were also small amounts of intergranular martensite, and some flat round carbides were also observed.

The X-ray diffraction pattern of 20CrMnTi alloy after double-stage forging and annealing treatment is shown in Figure 3. As can be seen, the alloy primarily consists of two phases: a FCC ferrite and a BCC martensite. The lattice spacing of FCC ferrite was found to be 0.2549 nm and the lattice spacing of BCC martensite was 0.2247 nm. This confirms the presence of Ferrite and martensite in this alloy.

These results show that the microstructure of 20CrMnTi alloy after double-stage forging and annealing treatment consists mainly of ferrite and martensite. The grains of both ferrite and martensite are homogenous and well distributed, while the nano-sized acicular ferrite grains provide improved mechanical properties. The X-ray diffraction pattern also confirms the presence of Ferrite and martensite in this alloy. This microstructure will provide improved mechanical properties to the 20CrMnTi alloy, such as high strength, toughness, corrosion resistance and abrasion resistance.

概述

The microstructure of the 20CrMnTi alloy steel (which has been hot forged after its forging) is inspected through optical microscopy. The microstructure consists mainly of fine ferrite and pearlite grains, indicating good weldability of the material. The matrix of the microstructure is characterized by homogeneous and relatively coarse grains (10-20 μm in size). The microstructure is strongly banded due to the prior hot forging, with the ferrite-pearlite grain boundaries represented by the darker regions in the microstructure. The boundaries of the ferrite phase are straight and well-defined, indicating effective grain growth during the hot working process.

In addition, small amounts of carbides in the form of cementite and MX meshes (characterized by randomly distributed irregularly oriented carbide particles) are present in the microstructure. The carbides are uniformly distributed in the alloy, indicating good distribution during preheat treatment and hot forging when previous steel forgings is subjected to hot working.

Overall, after hot working and subsequent tempering, the 20CrMnTi alloy steel shows a fine-grained and homogeneous microstructure, with good grain distribution after tempering, as demonstrated by the presence of well-defined and straight ferrite/pearlite boundaries and low amounts of carbides. As such, the hot working and tempering of the alloy steel have successfully formed the desired microstructure, which is known to promote excellent weldability and machinability.