Inclusions within 42CrMo4 steel forgings are a common cause of microcracks and other defects during hot forming, especially in large-size components. To better understand the damage and failure mechanisms associated with different types of inclusions during hot deformation, a systematic study was conducted on as-cast 42CrMo4 steel.
Samples were taken from the as-cast steel, polished, and etched for microstructural analysis. Scanning Electron Microscopy (SEM) was used to observe the morphology of inclusions, while Energy Dispersive Spectroscopy (EDS) was employed to determine their chemical composition. Nanoindentation tests were also carried out on inclusions that caused significant matrix damage, in order to obtain accurate mechanical property parameters.
The results showed that the room-temperature microstructure of the as-cast 42CrMo4 steel consists of a mixture of ferrite and pearlite. The primary types of inclusions identified were aluminum oxide (Al₂O₃), titanium nitride (TiN), silicates, and small amounts of calcium sulfide (CaS). Under the same loading conditions, nanoindentation results indicated that TiN exhibited the smallest residual indentation depth, reflecting its lowest plastic deformation and highest elastic recovery. Al₂O₃ followed, while the steel matrix showed the largest plastic deformation and the poorest elastic properties.
Microscopic pores were observed around some inclusions, suggesting that their higher hardness can disrupt the continuity of the steel matrix during forming, potentially leading to crack initiation and propagation, which in turn degrades product quality.
Further analysis revealed that large-sized inclusions were mostly Al₂O₃. These inclusions tend to destabilize the matrix during hot deformation and reduce the steel’s performance. TiN inclusions, which are harder and typically have sharp-edged square or angular shapes, were found to be especially detrimental. Their sharp corners act as stress concentration points, significantly increasing the risk of crack formation and severely affecting the mechanical integrity of the steel.
In conclusion, the type and size of inclusions have a pronounced effect on the hot-forming behavior of 42CrMo4 steel. In particular, large Al₂O₃ inclusions and high-hardness TiN inclusions are the main contributors to microcrack formation and performance degradation.
Post time: May-09-2025
