The key difference between hardenability and hardness is that hardenability is the ability of a material to be hardened, whereas hardness is the strength of a material and the ability to resist damage.
Hardenability and hardness are two terms that are often confused with each other because both these terms refer to the hard nature of an object.
CONTENTS
1. Overview and Key Difference
2. What is Hardenability
3. What is Hardness
4. Hardenability vs Hardness in Tabular Form
5. Summary – Hardenability vs Hardness
What is Hardenability?
The hardenability can be described as the ability of a material to be hardened when it is exposed to heat and then quenched or cooled rapidly. The depth to which a material is hardened after putting it through heat treatment is the hardenability of metal alloys. This term is closely related to hardness, but they are different from each other. Hardenability is an important property in the field of welding. This is because it is inversely proportional to weldability, which is the ease of welding a material.
Typically, if we quench a hot steel object, the area that is in contact with the water tends to immediately cool down, and the temperature also equilibrates with the quenching medium. However, the inner depth of this material does not cool down quickly. If the object is very large, then the cooling rate becomes slow enough to allow the austenite to transform completely into a structure that is different from martensite and bainite. This process can lead to the object not having the same crystal structure throughout its complete depth. This leaves a softer core and a harder shell. Generally, a softer core is made of ferrite and cementite, e.g. pearlite.
Figure 01: Jominy Test
Moreover, the liquid used in quenching the material can influence the cooling rate because of the varying thermal conductivities and specific heat. For example, substances including brine and water can cool down steel very quickly than oil or air. Further, the geometry of the object also can affect the cooling rate.
What is Hardness?
Hardness is the measure of the resistance of a material to indentation or scratching. In other words, it is the measure of the resistance to localized plastic deformation that is induced by either mechanical indentation or abrasion. Generally, materials are different from each other according to hardness, e.g. hard metals, including titanium and beryllium, can be observed as harder than soft metals, including sodium and metallic tin.
Figure 02: A Type of Hardness Tester
Furthermore, hardness depends on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity. The most common examples of hard materials are ceramics, concrete, some metal types, super-hard materials, etc.
Hardness can be measured in three major ways: scratch, indentation, and rebound. These three types have their own measurement scales. Practically, conversion tables are useful in converting between one scale and another.
What is the Difference Between Hardenability and Hardness?
Hardenability and hardness are closely related terms that are often confused with each other. However, these are two different terms. The key difference between hardenability and hardness is that hardenability refers to the ability of a material to be hardened, whereas hardness is the strength of a material and the ability to resist damage.
Below is a summary of the difference between hardenability and hardness in tabular form for side-by-side comparison.
Summary – Hardenability vs Hardness
Hardenability is the ability of a material to be hardened when it is exposed to heat and then quenched or cooled rapidly, while hardness is the measure of the resistance of a material to indentation or scratching. Therefore, the key difference between hardenability and hardness is that hardenability refers to the ability of a material to be hardened, whereas hardness refers to the strength of a material and its ability to resist damage.
Reference:
1. “Hardenability.” An Overview | ScienceDirect Topics.
Image Courtesy:
1. “Jominy-test” By Lead holder – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Vickers-tester” By http://en.wikipedia.org/wiki/User:Tariqabjotu – http://en.wikipedia.org/wiki/Image:Vickers-tester.png (Public Domain) via Commons Wikimedia