Analysis on temper brittleness of 30CrMnSi steel

30CrMnSi steel has good mechanical properties and good weldability because it does not contain the rare element nickel, and is widely used in steel parts for shipbuilding and aerospace. However, 30CrMnSi steel is prone to temper brittleness when tempered and heated at 450-550 °C, resulting in a decrease in impact toughness, and fatigue fracture accidents along grain boundaries occur during use. It is very important to analyze the reasons and take effective measures to avoid this phenomenon.

There are three main reasons for the temper brittleness of 30CrMnS steel: one is the influence of quenching heating temperature; the other is the influence of quenching cooling rate; the third is temper embrittlement phenomenon.

The measures to eliminate the temper brittleness of 30CrMnSi steel are as follows: 30CrMnSi steel is first subjected to 900-950 ℃ oil quenching high temperature solid solution pretreatment. Make M23C6, P compounds, δ ferrite and alloying elements in 30CrMnSi steel fully melt into austenite to alloy austenite. After quenching, 30CrMnSi steel is easy to obtain more quenched lath martensite, strong and tough. And promote more lath martensite formation in the subsequent sub-temperature quenching. 87°C sub-temperature quenching oil cooling is selected, and after 550°C, 4h oil cooling high temperature tempering, 30CrMnSi steel obtains excellent mechanical properties, especially makes 30CrMnSi steel have high strength and toughness, and eliminates temper brittleness near 550°C.