The AISI 8620 is a low-alloy steel found in a wide variety of engineering applications. It is most commonly used for components and structures where strength is of a critical factor. It has a relatively high yield strength and is suitable for carburising and hardening processes. This material is comprised of a combination of iron and approximately 1%–2% chromium, 0.2%–0.4% manganese, 0.4%–0.65% molybdenum, 0.2%–0.35% Nickel, 0.15%–0.5% Carbon and 0.08%–0.3% Silicon. AISI 8620 usually comes in three different grades that can be differentiated by their hardness: AISI 8620, AISI 8620C and AISI 8620H.
The metallurgical properties of the AISI 8620 steel were investigated by performing a series of microstructural analysis. Through a Rockwell C test and hardness test, it was found that the material has a low ductility and that it demonstrates very high Brinnell hardness values. The Rockwell C test revealed that the material had a hardness of 50–53 HRC (Rockwell C scale) while hardness tests detected values in the vicinity of 205–223 HB (Brinnell scale).
Furthermore, the microstructure of AISI 8620 was probed through scanning electron microscopy. SEM analysis revealed the microstructure of the material to be composed of a ferrite-pearlite matrix, with a few tiny carbide regions scattered throughout. Extensive examination of the material under the scanning electron microscope revealed no visible signs of microstructural phase transformation.
In order to understand the effect of heat treatment on the material’s mechanical properties, a series of tensile tests were conducted on as-received and heat-treated specimens. The heat treatment process consisted of austenitizing, tempering and quenching. The tensile tests were carried out in accordance with ASTM A370-05A and ASTM E8/E8M-14a standards. Results from the tensile tests revealed that the as-received specimens had an average specimen strength of 834 MPa, a yield strength of 756 MPa and an elongation at break of 8.68%. Marked improvements in the material’s mechanical properties were observed after heat treatment; with the treated specimens exhibiting an average specimen strength of 926 MPa, a yield strength of 855 MPa, and an elongation at break of 12.15%.
Finally, a Rockwell C test and a hardness test were conducted on samples of AISI 8620 that had been subjected to heat treatment. The Rockwell C test showed that the heat-treated samples had a hardness of 55–59 HRC while the hardness tests detected values of 225–247 HB.
In conclusion, the AISI 8620 is a low-alloy steel suitable for a wide variety of engineering applications. It has a ferrite-pearlite matrix microstructure and demonstrates high Brinnell hardness values. Through various tests, it has been shown to exhibit considerable strength, especially when subjected to a heat treatment process.
