Have you ever wondered why some bolts（Such as din 933 bolt） can firmly fix bridges, cars, and even aircraft engines, while others break after a few twists? The answer lies in heat treatment!
Through a series of “high-temperature training + cooling recovery”, heat treatment makes it stronger, more durable, and able to cope with various extreme working conditions. So what exactly is going on? Let’s find out!
- The first step of heat treatment: increase strength!
Bolts have to withstand huge pressure, so the strength and hardness must be online. Quenching + tempering (like “high-intensity training + stretching”) can make the metal structure of the bolt more compact, improve the tensile strength and hardness, and make it as stable as Mount Tai when facing heavy loads. - Advantages of heat treatment: not afraid of fatigue, longer life!
Bolts work “overloaded” every day in the fields of automobiles, construction, aerospace, etc., and withstand countless pressure cycles. If its “endurance” is not good, it will soon fatigue and break. Heat treatment can improve the microstructure of the metal, greatly improve its fatigue resistance, and ensure that it will not “fall down” due to long-term use. - Balance between hardness and toughness
Imagine that glass is very hard, but it will break if it falls. Similarly, if the bolt is too hard, it may become brittle and easy to break. Therefore, heat treatment must find a balance point, making it hard enough and retaining a certain toughness, so that it can withstand impact without being brittle. - Stress relief
Bolts may accumulate a lot of internal stress during the manufacturing process (similar to the pressure accumulated by people over a long period of time). If not released, these stresses will cause the bolts to deform, crack, or even break suddenly. Through annealing or stress relief annealing, the bolts are like experiencing a deep relaxation and can work more stably. - Rust prevention and increased service life
Certain heat treatment methods (such as austenitization + quenching + tempering) can make the microstructure of the bolts denser and improve corrosion resistance. If combined with surface treatments such as galvanizing, it is like putting on a layer of “bulletproof raincoat” for the bolts, which can greatly increase the practical life in harsh environments. - Adapt to different fields of use
Each bolt can be used in different fields, some require ultra-high strength (such as bolts for buildings and bridges), and some require high wear resistance (such as engine bolts). Heat treatment can be “customized” according to different needs, so that the bolts can play the greatest role in their positions. - Make the thread more compatible
The combination of bolts and nuts is like a handshake, which must be tight and reliable. Take spring nut and bolt as an example. If the thread quality is not up to standard, the connection may loosen or even fail. Heat treatment can enhance the strength and durability of the thread, making it less likely to slip or damage under high load. - Different heat treatment methods are suitable for different bolts!
There is more than one heat treatment method, and each method has its role:
Annealing: Let the bolt “relax”, soften, and reduce internal stress.
Quenching: Like a cold water bath, it makes the bolt harden quickly.
Tempering: Secondary heating, reduce the brittleness caused by quenching, and make it tougher.
Normalizing: Make the grain structure of the bolt finer and improve the overall performance.
Surface hardening: Make the bolt surface harder and the core tougher, suitable for high-strength applications.
Simply put, heat treatment upgrades the performance of bolts, making them more durable, more fatigue-resistant, less prone to rust, and able to function stably in various harsh environments. Although heat treatment will increase production costs, compared with the cost of later replacement and maintenance, this investment is very worthwhile!
