Key technology for fastener manufacturing: heat treatment
Heat treatment is a critical technology for controlling the performance of fasteners, ensuring long service life, and guaranteeing safety and reliability. It is also a core factor in the competitiveness of advanced materials and high-end mechanical equipment. International manufacturers of branded fasteners have always placed great emphasis on the research and development of heat treatment technologies. Through substantial investment, long-term accumulation, and continuous improvement, they have developed unique and closely guarded heat treatment techniques. While others may be able to replicate the geometric design and precision, achieving comparable service life and reliability remains a challenge.
Modern heat treatment technology has two main characteristics: first, it is based on fundamental research into material microstructure transformation and its impact on performance, leading to the continuous development of new theories and processes. Second, it integrates results from other fields such as electromagnetic induction, laser technology, ion beams, chemical thermodynamics, combustion, and heat transfer, creating innovative heat treatment methods. Although China has become a major manufacturing country and the scale of heat treatment has grown rapidly over the past 20 years, there are still significant technological gaps compared to global leaders. This has led to bottlenecks in the production of high-end fasteners that support key machinery.
Advanced fasteners form the foundation of high-end mechanical manufacturing and are often referred to as the "four or two" components—meaning they are crucial yet often overlooked. The surface value of fasteners accounts for only a small percentage of the machinery industry, but their true value lies in the added value they bring to critical components and systems. For example, automotive fasteners, especially those used in engines like connecting rod bolts, flywheel bolts, wheel bolts, and suspension bolts, are vital for safety and performance. Currently, 40% to 60% of these high-performance fasteners are still imported due to stringent quality and reliability requirements. Their manufacturing techniques differ significantly from general fasteners, involving specialized equipment, materials, testing methods, and strict process controls.
Improving heat treatment technology offers tremendous potential for energy savings and efficiency improvements. It enhances product reliability, ensures safety, and increases the overall value of machines by enabling smaller, lighter, and more durable fasteners. Moreover, advancements in heat treatment play a key role in the development of new materials, products, and equipment.
**Examples of Heat Treatment Applications:**
For instance, 10.9 high-strength bolts benefit greatly from quenching and tempering, which significantly improves tensile strength, yield ratio, and impact toughness. This allows for better balance between strength and ductility, enhancing fatigue resistance and reducing the need for larger cross-sections, thus saving weight and space. Commonly used steels like 20, 35, 45, 20MnTiB, 35CrMoA, 40Cr, 42CrMoA, 40CrNiMoA, and 30CrMnSiA can only fully utilize their alloying elements through proper quenching and tempering. Without this process, the alloying elements are essentially wasted.
The latest version of GB/T3098.1-2010 emphasizes that materials for bolts rated at 8.8 and above must have sufficient hardenability to ensure that the core of the thread section achieves about 90% martensite structure before tempering. For fasteners with threads larger than 20 mm in diameter, quenching and tempering of the specified alloy steel is essential. As a result, metallographic examination has become an important part of the fastener industry. This involves not only microscopic analysis using a metallographic microscope but also macroscopic inspection under magnification or even the naked eye.
Fatigue failure is the primary cause of high-strength bolt failure, characterized by sudden fracture without noticeable deformation. Solving this issue relies heavily on advanced heat treatment technology. Heat treatment not only enhances the ultimate and endurance properties of the material but also ensures safe and reliable operation. Therefore, the importance of heat treatment cannot be overstated. When companies face quality issues during the heat treatment process, it’s never too late to improve and invest in better technology. Time waits for no one, and innovation is rare.
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