50B (930℃×1h oil quenching) metallographic diagram

The microhardness, composition and fraction and morphology of the as-quenched cobalt-containing iron-chromium-nickel alloys (930°C × 1h oil-quenched) were studied for the study of microstructure of the alloys. The cobalt-containing iron-chromium-nickel alloys were obtained from the vacuum arc melting (VAR) process.

The microhardness of the as-quenched cobalt-containing iron-chromium-nickel alloys was measured at room temperature. The results showed that the microhardness increased with increased time of oil quenching. The maximum microhardness of the as-quenched alloy was obtained after 2.5 h oil quenching. There was no significant difference in microhardness between the 1 h oil quenched and the 2.5 h oil quenched alloys.

The composition and fraction of the as-quenched cobalt-containing iron-chromium-nickel alloys were also studied. The results showed that the cobalt content decreased with increased time of oil quenching. The highest cobalt content was observed at 1 h oil quenching and then decreased progressively with increasing the oil quenching time beyond 1 h. The fraction of the alloy elements (iron, chromium, nickel, and cobalt) also decreased with increased oil quenching time, except for iron and cobalt.

The morphology of the as-quenched cobalt-containing iron-chromium-nickel alloys was also studied. The alloys were observed under an optical microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). The optical microscopy revealed that the as-quenched alloys had a granular microstructure. The SEM micrograph showed that the alloys had a dendritic microstructure. The TEM micrographs showed that the alloys had a very fine microstructure and small particles were also present in the microstructure.

The microstructure of the as-quenched cobalt-containing iron-chromium-nickel alloys was affected by the oil quenching temperature and treatment time. It was found that the microhardness of the as-quenched alloys was affected by the cobalt content, which decreased with increasing the oil quenching time beyond 1 h. The composition and fraction of the alloy elements also decreased with increasing the quenching time beyond 1 h. The optical, SEM and TEM micrographs showed that the alloys had a granular and dendritic microstructure. The alloys also had a very fine microstructure and small particles were present in the microstructure.

The metallographic image from a sample of 930℃×1h oil quenched 15CrMn50B steel is shown in the figure below.

From the microstructures observed, it can be seen that the sample is a quenched and tempered steel and the grains are approximately equiaxed. The microstructures consisted of martensite and/or bainite at the center, and pearlite/widmanstätten ferrite at the edge. The martensite/bainite exhibited a slightly lath-like structure, while the pearlite/widmanstätten ferrite was fibrous.

The microstructures of the sample indicate that the material has been effectively quenched and tempered. The martensite/bainite at the center provides satisfactory strength, while the pearlite/widmanstätten ferrite at the edge ensures sufficient toughness and ductility.

The element distribution of the sample also reveals that appropriate levels of carbon and manganese elements have been used, which provides the material with excellent wear resistance.

The combination of solid solution strengthening and precipitation hardening of the ferrite-martensite and ferrite-bainite structures result in the desired properties of 15CrMn50B steel. The metallographic image shows that the 930℃×1h oil quenched 15CrMn50B steel has excellent microstructures and is of satisfactory quality.