Hardness was one of a important target for steel tube to fight a hard object on its surface.The higher the hardness, the better the abrasive resistance was.There are three commonly used hardness index for steel pipe:Brinell hardness ,Rockwell hardness and Vickers hardness .Because of its low force, high speed, and nondestructive nature, Rockwell hardness testing commonly is used on all sizes of tubing.Then how to improve the hardness of steel pipe?
1)The best way to increase the hardness without affecting the chemical composition is heat treatment.Heat treatment is a process designed to alter the properties of the metal to better suit its intended use. Heating the metal will displace atoms from their position and the displaced atoms form a new structure. This process is known as allotropic phase transformation. When iron is heated past 1,674 degrees Fahrenheit it is able to absorb more carbon, which is an ingredient that will increase the hardness of any steel pipe
In addition,Cryogenic treatment is also an option. Better results can be obtained by combination of several treatment methods.
2)Add some other metal which compliments parent metal’s strength. The different alloying elements have specific effects on the properties of steel pipe.Carbon element is a strong austenite former that also significantly increases mechanical strength. In ferritic grades carbon strongly reduces both toughness and corrosion resistance. In martensitic grades carbon increases hardness and strength, but decrease toughness.
3)Laser peening is probably the most powerful method for work-hardening metals and improving fatigue strength.
Laser peening uses a high-energy pulsed laser to generate a plasma burst on the metal surface. The rapidly expanding plasma imparts a high-amplitude stress wave that plastically deforms the material and produces compressive residual stresses.
It’s a similar principle to shot peening, a method that has been used for decades to harden metal components for improved fatigue strength and damage tolerance, however laser peening imparts residual stresses much deeper and can improve metal fatigue strength by ten times or more.
