Enhanced Spring Steel's Strength Using Strain Assisted Tempering.

Area of Science:

• Materials Science
• Metallurgy
• Mechanical Engineering

Background:

• Enhancing mechanical properties of spring steels can reduce vehicle mass, leading to decreased fuel or electric energy consumption.
• Conventional quenching and tempering (QT) is a standard heat treatment process for steels.
• Microstructure and mechanical properties can be significantly altered by incorporating strain during tempering.

Purpose of the Study:

• To investigate the effects of strain assisted tempering (SAT) on the microstructure and mechanical properties of spring steels.
• To compare the SAT process with conventional quenching and tempering (QT).

Main Methods:

• Application of strain assisted tempering (SAT) technology, involving alternating quenching, tempering, and strain operations.
• Controlled deformation using rotary swaging with 17% strain at a rate of approximately 120 s⁻¹ after the first tempering.
• Metallographic analysis and X-ray diffraction measurement to characterize microstructural differences.

Main Results:

• SAT processing resulted in considerably higher strength parameters compared to conventional QT.
• Enhanced notch toughness was observed with SAT, alongside decreased elongation and reduction of area.
• Microstructural analysis revealed carbideless islands with nanotwins in martensitic laths after SAT, unlike the tempered martensite with transition carbides seen after QT.

Conclusions:

• Strain assisted tempering is an effective technology for significantly enhancing the mechanical properties of spring steels.
• The unique carbideless, nanotwinned microstructure achieved through SAT contributes to improved strength and toughness.
• Optimizing the SAT process allows for achieving acceptable ductility parameters, making it a promising alternative to conventional heat treatments for automotive applications.