Heat treatment is the key technology to control fastener performance, ensure long life and safety and reliability, and is the core element of the competitiveness of advanced materials and high-end mechanical equipment.
International fastener manufacturers that produce brand-name products have always attached great importance to the research and development of heat treatment technology. Through extensive investment, long-term accumulation and continuous improvement, we have mastered the unique heat treatment technology and kept it secret, and others can create geometric elements and precision. The same imitation, however, the service life and reliability are hard to come by. The development of modern heat treatment technology has two characteristics: First, based on the basic research of material organization transformation and its impact on performance, the new heat treatment theory and process are continuously formed; second, the results of other disciplines (such as electromagnetic induction, laser, ion) are absorbed. Beams, chemical thermodynamics and kinetics, combustion techniques, heat transfer, etc.) have developed new heat treatment technologies. China has become a big manufacturing country. Although the scale of heat treatment has grown rapidly in the past 20 years, there are still decades of gaps in technology heat treatment technology with the world's advanced level, which has led to the emergence of bottlenecks in domestic high-end fasteners behind the mainframe.
Advanced fasteners are the basis of high-end machinery manufacturing, and their functions can be called "four or two." The value of fasteners on the surface only accounts for a few percent of the machinery industry. In essence, the added value it brings to key components and equipment is much higher. For example, automotive fasteners are fasteners with high economic value. Due to the high requirements for quality and reliability, China's production cannot fully achieve localization; the engine is used for key parts of engine connecting rod bolts and flywheel bolts. Wheel bolts, suspension bolts, etc., are important fasteners that are related to life and property safety. At present, 40% to 60% rely on imports. Although their manufacturing techniques have some similarities with general fasteners, their manufacturing and testing techniques, equipment, materials, management controls, etc. are very different, and they are the highest and most concentrated embodiment of fastener technology. .
1 “Do a good job in heat treatment partsâ€, the potential for energy saving and consumption reduction is huge;
2 Improve the reliability of the use of products and ensure the safety of people's lives and property; Â
3 Relying on advanced heat treatment technology to produce fasteners with small size, light weight, long life and high reliability, greatly increasing the added value of the whole machine;
4 Research results in the field of heat treatment are catalysts for new materials, new products, and new equipment.
Heat treatment application examples: such as 10.9 high-strength bolts, quenching and tempering can greatly improve the tensile strength of the material, specify the non-proportional extension stress, increase the yield ratio and impact toughness, so that the material has a good fit of strength and plastic toughness. Due to the improvement of fatigue strength and impact toughness, a smaller material section can be used in the design of high-strength bolts, thereby reducing the overall weight of the whole machine and saving component space and energy consumption.
Commonly used low and medium carbon structural steels, low alloy structural steels, 20, 35, 45, 20MnTiB, 35CrMoA in GB/T699-1999 "Quality Carbon Structural Steel" and GB/T3077-1999 "Alloy Structural Steel" 40Cr, 42CrMoA, 40CrNiMoA, 30CrMnSiA and other steels can only fully exert the role of alloying elements through quenching and tempering treatment. No quenching is equivalent to wasting precious alloys.
GB/T3098.1-2010 "Fastener mechanical properties bolts, screws and studs" new standard release, stressing that the material requirements for grade 8.8 and above should have sufficient hardenability to ensure fastener thread cross section The core obtained about 90% of the martensite structure in the hardened state and before tempering. In fact, for fasteners with a diameter of 8.8 thread over 20 mm to ensure good hardenability, it is necessary to quench and temper the alloy steel material specified in the standard. For this reason, the metallographic examination has been rapidly developed in the fastener industry. The metallographic examination is not only to study the internal structure of the metal material by means of a metallographic microscope, but also to perform macroscopic inspection under the naked eye or a low magnification magnifying glass.
The main failure mode of high-strength bolts is fatigue, which is characterized by sudden failure without significant deformation. The key to solving the fatigue failure problem is heat treatment technology. Heat treatment not only gives the material ultimate performance and endurance performance of high-strength bolts, but also guarantees the service of high-strength bolts. Therefore, heat treatment of fasteners is very important. When some companies have problems with product quality in heat treatment, they think of the importance of heat treatment and the improvement of technology. It is not too late to make up for it. Time is not waiting for me, technological innovation is rare.