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From knives to armor: How does cold work improve the performance of metals?
In the field of metal processing, cold work is an important technology that improves the properties of metal through physical means. One of the key processes is "polishing". Polishing refers to the use of various means, such as heavy hammers, impact, laser, spraying metal particles, etc., to treat the metal surface to improve the durability and strength of the metal. With the advancement of science and technology, this technology is not limited to knives, but has even spread to the manufacturing of military equipment such as armor, becoming one of the keys to metal processing.
Polishing not only improves the properties of the metal, it also promotes surface strain hardening, thereby increasing its durability and fatigue resistance.
During the polishing process, the metal surface will generate residual compressive stress due to plastic deformation. This is an internal tensile stress state that is beneficial to the metal, similar to strengthened glass. These surface compressive stresses can effectively delay the growth of cracks, thereby improving the fatigue and corrosion resistance of the metal. However, this benefit is also accompanied by increased tensile stresses at greater depths.
Strain hardening process
The cold working process not only improves the surface properties of the metal, but also causes the hardening of the material. When a metal undergoes strain hardening, it not only increases its yield strength but also reduces its ductility, which greatly reduces the possibility of cracks forming on the metal surface. When the lattice structure of a metal contains a large number of dislocations, the plastic deformation process is hindered, allowing the material to maintain better elasticity and stability when stretched.
Strain hardening enables materials to maintain good properties under higher elastic yield stress, which is critical for applications in high-stress scenarios.
Metal styling using polishing
Polishing technology is widely used in modern industry. For example, in the automobile repair industry, manual or mechanically assisted polishing technology can be used to stretch thin metals and create curved surfaces. Some mechanized methods, such as using a power hammer for polishing, can effectively stretch the metal surface to achieve effects that are invisible to the naked eye. In these applications, polishing operations often need to be performed carefully to prevent the sheet metal from being deformed by overstretching.
Polishing is a valuable technology in metal processing. It can not only improve surface properties, but also help metal achieve more complex shapes.
Polishing technology after welding
After welding, hand polishing is also used to help relieve the tensile stresses created during cooling of the welded metal. Although the reduction in tensile stress at the weld is not significant, polishing technology can better improve the hardness of the metal weld, a feature that is often not recommended in many standard specifications. Therefore, the effect of polishing must be carefully evaluated during qualification testing of welding procedures to ensure that the final weld will meet the required mechanical property standards.
Improved sharpness of knives
In addition, in the production of knives, many agricultural knives such as broadswords and sickles are traditionally polished to keep them sharp. Through polishing, the surface of the blade edge can be reshaped, repairing scratches and damage caused by use, and then filed, so that the new blade edge will be more conducive to cutting action.
The history of polishing can be traced back to ancient times, with people using this technique to strengthen warriors' metal armor as early as 2700 BC.
The history of polishing
In fact, polishing technology has been used for a long time. Humans have used this technology to improve the properties of metals since ancient times. Bronze armor from the ancient Greek period would be stronger after being polished, and medieval swords were similarly strengthened. These traditional techniques are still used and passed down in modern metalworking today.
The development of the entire polishing technology has also been driven by the advancement of science and technology. With the development of new technologies such as laser and ultrasonic waves, today's polishing technology has become more efficient and precise, and stronger metal materials will be used in future battlefields and play an important role in industry. With these new production processes, can we envision a new future for metal applications, allowing metal materials to show unlimited possibilities in more fields?
