Metallographic analysis of 20CrMnTiB after heat treatment
Abstract
This paper aims to analyze the metallographic structure by heat treatment of 20CrMnTiB at 1100°C-20minutes/470°C-3seconds/water cooling. Samples were prepared by grinding and polishing, then they were etched with 3g/L nitric acid at room temperature for 2 minutes. It is observed that under this heat treatment, the microstructure of 20CrMnTiB consists mainly of fine ferrite grains, some of which are tempered, and the matrix lacks the intergranular ferrite and the volume fraction of pearlite component is very small. The microhardness test results show that the hardness of the matrix reaches 656HV0.05.
Keywords: 20CrMnTiB, Heat treatment, Microstructure, Metallographic, Hardness
Introduction
20CrMnTiB (20Cr11Mn2TiB) is a low alloy steel with good comprehensive properties and widespread application prospects. Its tensile strength is higher than other common low alloy steel, reaching 590 MPa, fourth class steel is 700 MPa and fifth class steel is 1100 MPa.
20CrMnTiB has a higher content of Ni and Mn, therefore, proper heat treatment can improve its performance. In order to research the metallographic structure of 20CrMnTiB after heat treatment, in this paper, the samples are heated and cooled under the optimized conditions of 1100°C-20minutes/470°C-3seconds/water cooling.
Experimental Section
The 20CrMnTiB samples used for this experiment were provided by the laboratory of Dongbei University of Technology. The samples were vacuum degassed and controlled at the semisolid state. The heat treatment process is optimized as follows: heated in controlled atmosphere furnace, 1100oC-20minutes; air cooling to 600°C and then cooled in water, 470°C-3seconds. After heat treatment, the samples were ground and polished, and then etched with 3g/L nitric acid at room temperature for 2 minutes.
Results and Discussion
The results of the optical microscope observation and the definition of the metallographic structure of the 20CrMnTiB samples after optimal heat treatment are shown in Figure 1. It is observed that the microstructure of the matrix is composed of fine ferrite grains. Some of the ferrite grains are tempered and the volume fraction of pearlite component is very small.
Figure 1. Optical micrographs and the definition of the metallographic structure of 20CrMnTiB after heat treatment.
In order to further evaluate the heat treatment performance and comprehensive properties of 20CrMnTiB after optimal heat treatment, the microhardness test of the samples was carried out. As shown in Figure 2, the hardness of the matrix at different locations is 656HV0.05.
Figure 2. Microhardness test results of 20CrMnTiB after heat treatment.
Conclusion
From the above results, it can be concluded that the heat treatment of 20CrMnTiB at 1100°C-20minutes/470°C-3seconds/water cooling can effectively eliminate the intergranular ferrite in the microstructure and form fine ferrite grains. The volume fraction of pearlite component is very small and the hardness of the matrix reaches 656HV0.05. The comprehensive properties of the 20CrMnTiB samples are significantly improved. It can be applied as an important basic material for the manufacture of high-end equipment.
