Residual stresses in the production of titanium and titanium alloys in brief

2025,05,12

A few days ago, when producing titanium chopping boards for a customer. When the laser cutting was finished, all the titanium chopping boards were bent after being placed for one night. When looking at these bent titanium plate, the first reaction was residual stress.

What is residual stress? The official definition of residual stress is the self-equilibrating internal stress that remains in an object after the removal of an external force or an uneven temperature field, for example. Residual stresses can be induced by machining and strengthening processes. Such as cold drawing, laser cutting, cutting, rolling, shot blasting, casting, forging, welding and metal heat treatment, etc., due to uneven plastic deformation or phase transformation may cause residual stress.

This definition is not very clear. Explain it in everyday layman's terms, not very precise, but very graphic. Just like we usually use rubber bands. Elongated rubber bands will be retracted when you let go, retracted back after the rubber band will be twisted. When a metal material is forced to deform in processing, a “force of resistance” is also generated internally. Even if the external force disappears, this “resistance force” remains inside the material, forming an invisible “stress field”.

Where do residual stresses come from? There are three main reasons for this:

1 The cause of machining: the turning tool cuts the metal, the part that is cut off releases the stress, while the part left behind is forced to “twist”.

2 machining process of hot and cold alternating “fire and ice”.

For example:Welding when the weld high temperature zone and low temperature zone. Like the sun-exposed pavement expansion, around the low-temperature zone but like the cold winter contraction of the water pipe, hot and cold fight to produce stress.

3 metal material phase change stress caused by “transformation aftermath”. Metals cooled when the organization shift, volume changes out of sync, resulting in deformation.

Residual stresses have three main destructive forces:

1 Causing changes in the size and shape of the object.

2 Shorten the service life of parts.

3 Reduce the corrosion resistance and fatigue strength of the metal.

How can residual stresses be removed? As the most commonly used methods are three:

1 Natural aging: the metal workpiece is placed in a natural environment, through temperature changes and climate effects to promote the natural release of internal stresses of the process, mainly used to improve the dimensional stability of the material.

2 Heat treatment: it is to eliminate or reduce the residual stress by utilizing the thermal relaxation effect of the residual stress, generally using annealing, tempering and other methods of treatment.

3 Vibration aging: refers to engineering materials commonly used to eliminate its internal residual internal stresses of a method, is through vibration, so that the workpiece internal residual internal stresses and additional vibration stresses of the vector and reached more than the yield strength of the material when the material undergoes a small amount of plastic deformation, so that the internal stresses within the material can be relaxed and reduced.

Author:

Mr. Shen

E-mail:

shenguanlun9696@gmail.com

Phone/WhatsApp:

+86 13709173123