Metal strength is one of the most essential mechanical properties in determining a metal's suitability for given applications. It signifies how well a metal can resist external loads or force without deforming or breaking. Metals with high strength are invaluable in construction, machinery, and aerospace, where they support structures and withstand extreme conditions.
In this guide, we will distinguish the types of strength, discuss the factors that influence metal strength and how they can be manipulated to enhance a metal's performance. Additionally, we will provide a metal strength chart to help you choose the metal material you want more intuitively.
Types of Metal Strengths
Materials exhibit different types of strength depending on how a load is applied. Here are the fundamental types of loading conditions for a rod:
Tensile Loading: Forces that pull or stretch the material.
Compressive Loading: Forces that push or compress the material.
Shear Loading: Forces that act parallel to the surface of a material, causing the material to experience layers or planes sliding past each other.
Bending (Flexural) Loading: Forces that cause the material to bend.
Torsional Loading: Forces that twist the material.
Impact Loading: Sudden, forceful impact or shock loads.
Next, we will discuss in detail several of the most common types of strength.
1. Tensile Strength
Tensile strength refers to the maximum amount of tensile (pulling or stretching) stress that a material can withstand before breaking. It measures how much load a material can handle before failure.
Stress: Represents magnitude of an external force acting over the cross-sectional area of a body. Strain: Describes the amount of deformation experienced by the body in the direction of that force.
This stress-strain curve depicts a typical tensile performance. Points A, B, and C represent three key nodes of tensile strength, which serve as reference points indicating significant transformations in the product's properties under tension. Let’s check these three points one by one.
Yield strength (Point A): It signifies the maximum stress a material can withstand before experiencing permanent plastic deformation. Beyond this point, the material will not return to its original shape when the stress is removed.
Manufacturers use the yield point to set safe operational limits to maintain the structural integrity and functionality of materials. It is also used as a criterion to define failure in many engineering codes.
Ultimate strength (Point B): When discussing tensile strength generally, it usually refers to Ultimate Tensile Strength (UTS). It represents the maximum load a material can carry before it starts to neck. After this point, the cross-sectional area reduces, leading to a decrease in the stress the material can withstand until it breaks.
You can evaluate a metal’s tensile strength using a tensile testing machine (also known as a Universal Testing Machine or UTM). It has two grips that hold the specimen at both ends. During testing, the machine applies a controlled tensile force to the piece until it breaks. The applied tensile force (or stress) and elongation are measured throughout the test to determine the metal’s yield and ultimate tensile strengths.
Breakable strength (Point C): The stress at which the material ultimately fails and breaks apart. It is used to design components that can withstand extreme conditions, ensuring safety by preventing catastrophic failure.
2. Compressive Strength
This type of strength measures the ability of a material to resist forces that compress or shorten it. It is the maximum compressive load a material can bear without failure.
You may evaluate compressive strength using a compression testing machine. It typically uses plates that apply pressure to the piece from both ends, applying a controlled compressive force until the metal deforms or breaks. The point where deformation begins to occur indicates the compressive strength of that metal.
3. Impact Strength
Impact strength measures a material's ability to resist fracture or deformation when subjected to sudden, rapid impacts or shocks. It represents the material's capacity to absorb and withstand kinetic energy from impacting objects.
It is typically measured using an Impact Testing Machine, such as Charpy or Izod testers. These machines strike a notched specimen with a pendulum hammer and record the energy absorbed by the specimen during fracture.
Why do We Need to Learn About Metal Strength?
Understanding metal strength is a crucial aspect of comprehending material performance. This allows us to make informed decisions about selecting the right materials for various applications.
Safety and Durability
The strength of metals holds a paramount significance in guaranteeing the safety and durability of structures and components, especially in crucial applications encompassing machinery, bridges, and buildings. Acquiring knowledge about this helps prevent failures that may lead to accidents, injuries, or fatalities, and ensures a prolonged service life of products, ultimately reducing the frequency of repairs and replacements.
Improving Performance
Learning about metal strength allows for the optimization of performance in various applications. For instance, in the automotive and aerospace industries, using metals with the appropriate strength can enhance fuel efficiency, reduce weight, and improve overall performance.
Cost Efficiency
By understanding the strength of different metals, manufacturers can make cost-effective decisions. Choosing the right metal for the right application can minimize material waste, reduce production costs, and extend the lifespan of products, leading to long-term savings.
Innovative Design
Learning about metal strength opens up possibilities for innovative design and engineering solutions. It enables the creation of lighter, stronger, and more efficient structures and products, pushing the boundaries of what is technically possible.
Strongest Metals Used in Metal Fabrication
Tungsten
Next, we will introduce some metals that are widely used in practice due to their high strength.
Titanium
Titanium is a naturally occurring metal, renowned for its high strength-to-weight ratio. Besides its lightweight nature and exceptional tensile strength, titanium is also highly resistant to corrosion, making it an excellent choice for aerospace, medical implants, and high-performance automotive parts.
It is often used in alloy form to enhance its properties further. A common example is the titanium alloy Ti-6Al-4V, which includes aluminum and vanadium and is widely used in the aerospace industry.
Tungsten
Among naturally occurring metals, tungsten is regarded as the strongest due to its highest tensile strength, reaching up to 1,725 MPa. Coupled with its highest melting point, tungsten is incredibly valuable in applications that demand extreme durability and heat resistance. However, it is often brittle. To compensate for this property, tungsten is commonly alloyed with other elements such as carbon. Tungsten carbide is widely used in cutting tools, mining equipment, and wear-resistant surfaces due to its exceptional hardness and durability.
Chromium
With a hardness of 8.5 on the Mohs scale, chromium is considered one of the hardest metals on Earth and is included in the list of the strongest metals. However, chromium is not commonly used in its pure form due to its brittleness. It is often used in chromium plating to provide a hard, corrosion-resistant surface on metals and plastics. Additionally, chromium is also used in high-performance alloys to improve strength, wear resistance, and corrosion resistance. Stainless steel is a typical example of such an alloy, and it is one of the most widely used materials across various industries.
Steel
Steel, made by alloying iron with carbon and some other elements, is the most important engineering and construction material. The strength of steel varies depending on its alloying components. Here are some common types of the strongest steel:
Stainless steel is an alloy of iron, chromium, and often manganese. It's known for its excellent corrosion resistance, with a yield strength of around 1560 MPa and an ultimate tensile strength of up to 1600 MPa. This makes it ideal for kitchen utensils, medical instruments, and construction materials because it's durable and resists rust.
High-Strength Low-Alloy Steel (HSLA) is another type. It’s an alloy of iron with small amounts of copper, nickel, vanadium, titanium, and niobium. HSLA is lightweight but very strong and tough, thanks to microalloying and heat treatment techniques. It’s widely used in automotive manufacturing, structural construction, bridge building, and pipelines where high strength and low weight are crucial.
Maraging steel is an alloy of iron with nickel, cobalt, molybdenum, and titanium, and it has very low carbon content. This steel is known for its ultra-high strength and toughness, achieved through aging heat treatment. It's used in high-performance applications like aerospace, tooling, aircraft landing gear, rocket motor casings, and high-performance gears.
Tool steel is made with elements like tungsten, molybdenum, chromium, and vanadium. It’s incredibly hard and abrasion-resistant, and it can keep a sharp edge at high temperatures. Tool steel is essential for making cutting tools, dies, and molds, especially where high wear resistance and toughness are needed.
Inconel is a family of nickel-chromium-based superalloys known for its high strength and excellent resistance to oxidation and corrosion, even at high temperatures. Inconel is particularly useful in aerospace, marine, and chemical processing industries, where materials must endure severe mechanical and thermal stress without degrading.
How to Improve the Strength of Metal?
After understanding the strongest metals commonly used in metal fabrication, we can appreciate that alloying (specifically adding new elements) is a key method to enhance strength. Beyond alloying, other practical methods are often employed to further improve the strength of metals to meet the ever-increasing demands of modern applications.
Solution Hardening Strengthening
While this is technically a form of alloying, it focuses on how the added elements are integrated into the metal's crystal structure to enhance its strength. This process involves adding atoms of an alloying element to the crystal lattice of the base metal to form a solid solution. The incorporated atoms create lattice distortions that impede dislocation movement, thereby increasing the metal's strength.
Heat Treatment
Heat treatment is a controlled process used to improve a metal's performance by modifying its structure. Here are some common heat treatment methods to enhance the strength of metal:
Quenching & Tempering
Quenching involves heating the metal to a high temperature and then rapidly cooling it in a medium such as water, oil, or air. This rapid cooling traps carbon atoms within the crystal structure, forming a hard martensitic phase. This increase in hardness is usually accompanied by an increase in tensile strength. But this extreme cooling can also introduce internal stresses and brittleness.
Tempering is often applied after quenching to relieve these stresses and restore some of the ductility lost during quenching. While it slightly lowers hardness, it improves toughness and creates a more stable microstructure, thereby enhancing the metal's ability to withstand impacts and stresses.
Normalizing
Normalizing involves heating the metal above its critical temperature and then air-cooling it. This process produces a more uniform and fine-grained structure, enhancing the metal's strength.
Precipitation Hardening (Aging)
It involves heating the metal to a moderate temperature and maintaining that temperature for an extended period to allow fine precipitates to form within the metal's crystal structure. These precipitates increase the material's yield strength and hardness by impeding dislocation movement.
Cold Working
Cold working, also known as strain hardening, involves plastically deforming the metal at room temperature through processes such as rolling, drawing, or extrusion. This deformation increases the density of dislocations within the crystal structure, hindering their movement and thereby strengthening the material.
Metal Strength Chart
The metal strength chart provides a reliable criterion for choosing well-suited materials for specific applications. It provides a comprehensive evaluation of a metal's performance under various loading conditions. You can use it to compare the properties of different metals quickly.
Types of Metals
Tensile Strength (PSI)
Yield Strength (PSI)
Hardness Rockwell (B-Scale)
Density (Kg/m³)
Stainless steel 304
90,000
40,000
88
8000
Aluminum 6061-T6
45,000
40,000
60
2720
Aluminum 5052-H32
33,000
28,000
-
2680
Aluminum 3003
22,000
21,000
20 to 25
2730
Steel A36
58-80,000
36,000
-
7800
Steel Grade 50
65,000
50,000
-
7800
Yellow Brass
-
40,000
55
8470
Red Brass
-
49,000
65
8746
Copper
-
28,000
10
8940
Phosphor Bronze
-
55,000
78
8900
Aluminum Bronze
-
27,000
77
7700-8700
Titanium
63,000
37,000
80
4500
Metal Strength Chart
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Strength vs Ductility vs Toughness
Strength, ductility, toughness and resilience represented on a stress-strain curve
At last, let's take a quick view of some important but easily confusing material properties through the stress-strain curve shown below.
Ultimate Strength: The maximum stress reached during the tensile test.
Yield Strength: The stress at which a material begins to deform plastically.
Ductility: A measure of the ability of a material to deform plastically (strain) before fracturing.
Toughness: A measure of the ability of a material to absorb energy up until fracture. It can be thought of as the area under the stress-strain curve. For a material to have high toughness, it should have a good balance of both high strength and high ductility. Low strength and brittle materials tend to have low toughness.
Resilience: A measure of the ability of a material to absorb energy while deforming elastically.
Hardness: The ability of a material to resistance to deformation, particularly permanent deformation, indentation, or scratching. Generally, materials with high hardness tend to also have high strength, especially in terms of compressive and tensile strength. However, this correlation is not absolute.
