Ductility is an important property in the world of lifting. Chains and lifting components, for example, consist of an alloy that not only makes the steel stronger but also gives it more ductility. Ductility is an important factor in the design and manufacture of lifting and hoisting materials. A higher degree of formability ensures greater safety. But what exactly is ductility and why does it improve safety?

First of all, we will explain tensile strength before we move on to ductility. Tensile strength is the maximum mechanical load of a material. When the maximum tensile strength of a material - in this case steel - is reached, it will start to contract and eventually break. The stronger the material, the more load it can withstand.

For example, Grade 8 steel is made from a Cr-Ni-Mo alloy that is hardened and stress relieved. The steel is stress relieved during tempering, but the hardness is also reduced in a controlled manner to increase formability and impact resistance. The risk of embrittlement such as stress corrosion cracking and hydrogen embrittlement is thus reduced. The term "Grade" indicates the nominal breaking load, expressed in Newtons per mm², for this material type. For Grade 8, this is 800N/mm².

Of course, one does not want a chain to break into two parts immediately after exceeding the maximum tensile strength. Ductility is the ability of a metal to deform under tensile stress. For example, ductile metals can easily be pulled into a wire under tension.

Ductile materials have high toughness. The opposite of ductile materials are brittle materials. These are materials that immediately break when they reach their maximum tensile strength. Brittle materials are referred to as non-ductile materials.

Pictured are materials that change from left to right from brittle to tough, from non ductile to ductile. Chain (a) breaks without any deformation. Chain (b) breaks with very little deformation. Both chains are essentially low deformability. Chain (c) on the other hand has high ductility and will deform before breaking.

The industry standard is that lifting components should have a minimum formability of 20%. This percentage ensures that the deformation can always be clearly seen and thus provides more safety. 

A "safe" lifting chain or hook will therefore first show a visual deformation before breaking. This ensures that timely action can be taken before tragic accidents happen. It is also important that a visual check is always carried out on lifting and hoisting equipment before it is put into use. Lifting and hoisting equipment which has been subjected to loads exceeding its maximum tensile strength will stretch and deform due to its ductile properties. However, the deformation that has occurred will not disappear when the tension is removed. Whenever deformation is noticed, the material must be taken out of service immediately.