The material used for stabilizer forgings possesses excellent comprehensive mechanical properties, ensuring a good combination of high strength and toughness. Firstly, it requires sufficient hardenability so that, after quenching, the cross-section of the forging achieves a martensitic layer as thick as possible. Additionally, by controlling the size and dispersion of carbides during tempering, the desired performance requirements can be met. The main strengthening element at play here is carbon, which governs the steel’s strength in the form of dispersed carbides. Alloying elements such as chromium (Cr) and molybdenum (Mo) primarily ensure sufficient hardenability, enabling a suitable microstructure to form in the cross-section of the forging to maximize the effect of carbon. Another critical role of these alloying elements is to improve the toughness of tempered sorbite. This steel belongs to the category of medium-carbon low-alloy steels with excellent hardenability. Thus, based on the tempering and quenching processes of similar steels in the past, the preliminary process involves water quenching followed by oil cooling.
Before loading the furnace, the surface quality of the workpiece must be inspected to avoid defects such as cracks and shrinkage cavities that may compromise the quality of tempering. During loading, the workpiece must be hung vertically to prevent bending during heating and quenching. The water-cooling time must be strictly controlled according to the process. During heating and tempering, attention should be paid to maintaining uniform furnace temperature to prevent excessive thermal stress and structural stress during quenching, which could lead to cracking of the forgings. Additionally, uniform furnace temperature ensures consistent performance and hardness during tempering, avoiding quality issues caused by uneven temperatures.
If the hardness is found to be lower than required, and investigations confirm that no temperature deviations or furnace temperature inconsistencies occurred during the actual operation, and that all processes were executed as specified, the most probable cause is an excessively high tempering temperature.
Hardenability is of great importance to structural steels used in mechanical manufacturing. Hardenable steel can achieve high strength and a high yield-to-tensile ratio. Moreover, hardened steel can attain the highest fracture toughness (KIC), the highest fatigue strength and impact toughness, as well as the lowest ductile-brittle transition temperature (FATT50 in °C). During tempering, the hardness and strength of steel generally exhibit a similar trend, both decreasing with increasing tempering temperature. The preliminary quenching process in this production achieved maximum hardenability, meeting the required tensile and yield strengths. However, the excessively high tempering temperature resulted in non-compliant hardness. Through continuous improvements to the tempering process, the final tempering temperature was determined, ensuring compliance with the hardness requirements.
Post time: Feb-05-2025
