15CrA (1100℃×20min+500℃×1s water cooling) metallographic diagram

Study of Microstructure in 15CrA After Thermal Treatment

Heat treatment can alter the microstructure of a material and microscopically affect its physical properties. These changes tend to be quantified by the microstructure observations. One of the most common methods of measuring the microstructure of a steel alloy is direct microscopic observation. In the present work, the microstructure of 15CrA steel, before and after a particular heat treatment was studied. The heat treatment was implemented at 1100 oC for 20 minutes, followed by a water quenching at 500 oC for 1 second.

The aim of the present work was to investigate the changes in microstructure of 15CrA steel after the thermal treatment. The investigation was carried out by means of optical microscopy, scanning electron microscopy and transmission electron microscopy. 30 specimens, 1 cm x 1 cm in dimensions, were cut from a 15CrA steel bar and heat treated. The specimens were then polished using diamond paste and oxide suspension for specimen preparation for microscopic observation.

The microstructure of 15CrA steel before the heat treatment was observed using optical microscopy. It was seen that the microstructure was a mixture of ferrite and pearlite without a visible presence of any other phases. In the optical micrograph, the ferrite was seen as a mixture of dark and white blocks, while the pearlite was seen as a fine continuous matrix of laths, in both cases evenly distributed.

The microstructure of 15CrA steel after the heat treatment was observed using scanning and transmission electron microscopes. After the heat treatment, the microstructure was found to consist of a mixture of ferrite, pearlite and martensite. The ferrite and pearlite were seen as dark blocks in the micrographs, with the pearlite being continuous in nature, while the martensite was seen as a finely dispersed white discontinuous matrix.

The results of the Investigation showed that the heat treatment had a great effect on the microstructure of 15CrA steel, transforming the original mixture of ferrite and pearlite into a mixture of ferrite, pearlite and martensite. The presence of martensite in the microstructure of the 15CrA steel suggested that the heat treatment had been successful in transforming the structure in a way that it would improve its mechanical properties, making it harder and more formable.

In conclusion, the investigation of the microstructure of 15CrA steel after the heat treatment demonstrated that the thermal treatment had an effect on the microstructure of the 15CrA steel, transforming the original mixture of ferrite and pearlite into a mixture of ferrite, pearlite and martensite, which is beneficial in terms of the improved physical properties of the steel.

Microstructure of 15CrA after Water Cooling at 1100℃ × 20 min + 500℃ × 1s

15CrA is a 2.25Cr-1Mo heat-resistant steel, which belongs to the ferric class CrMo steel and is widely used in power station boilers, petrochemical plants, and steam pipelines. The microstructure of 15CrA after water cooling at 1100℃ × 20 min + 500℃ × 1s is presented.

In the microstructure of the 15CrA steel, the matrix is composed of ferrite, prior austenite, finely dispersed (M/A), and residual austenite. The ferritic microstructure is about 98.5% in volume fraction, and the dispersed (M/A) phase is about 0.75%. The grain size of the ferrite phase is relatively large, with an average size of 4.86μm. There is a small amount of residual austenite in the matrix, with an average concentration of 0.64%. The prior austenite grains have a spherical shape, while the ferrite grains have a plate shape. The prior austenite grains are surrounded by three to four ferrite grains, forming a stable austenite/ferrite sub-boundary.

In addition, there are also a small number of carbide particles and particles in the microstructure. The carbide particles are distributed in the dispersal phase and residual austenite, and the particles are found at the grain boundary. The particle size is very small, whose size is 0.2μm. The particles are mainly composed of Cr2Mo and M23C6 carbides.

In conclusion, the microstructure of 15CrA after water cooling at 1100℃ × 20 min + 500℃ × 1s is mainly composed of ferrite, prior austenite, finely dispersed (M/A), and residual austenite. In addition, there are also a small amount of carbides and particles. The grain size is relatively large.