In manufacturing and design, choosing the right material is essential—it directly affects a product’s performance and durability. Metal materials, in particular, offer a wide range of characteristics and are used in everything from industrial products and buildings to mechanical components.

This article provides a clear overview of what metal materials are, the types of ferrous and non-ferrous metals, their key properties (strength, hardness, toughness, specific gravity), as well as basic processing methods and points to consider in material selection. It is designed for engineers and designers who want a solid, structured understanding of metal materials.

What Are Metal Materials?

Metal materials are materials whose main components are metallic elements. They are broadly divided into ferrous and non-ferrous metals and are widely used in everyday products and industrial equipment. Metals are known for their luster, high electrical and thermal conductivity, and excellent workability such as ductility and malleability. When alloyed with other elements, their properties can be further enhanced and diversified.

Ferrous Metals

Ferrous metals are alloys based on iron (Fe) with controlled carbon content. Their hardness and strength vary with carbon levels. Major categories include:

• Carbon steels (SS, SC grades) used in structures and automotive parts
• Stainless steels (SUS grades) known for high corrosion resistance
• Alloy steels (SKH, SKD grades) used for cutting tools and dies
• Cast iron, valued for its excellent castability

Ferrous metals offer a balanced combination of strength and workability, making them widely applicable across industries.

Non-Ferrous Metals

Non-ferrous metals are metals and alloys that do not contain iron as their main component. Although generally more expensive, many offer advantages such as low weight, excellent conductivity, corrosion resistance, and non-magnetic properties.
Common examples include:

• Aluminum – lightweight, used in aircraft and automobiles
• Copper – highly conductive
• Titanium – strong and corrosion-resistant
• Gold and silver – widely used in electronics and decorative items
• Brass and bronze – popular alloy materials

These materials play important roles in specialized applications.

Key Properties of Metal Materials

The properties of metal materials determine how they perform in mechanical design and processing, influencing suitability for different applications. Each metal has its own characteristics, and improving one property often leads to trade-offs in others. Understanding these relationships is essential for selecting the right material.

The four major properties commonly used to describe metal behavior are strength, hardness, toughness, and specific gravity.

Strength

Strength is a material’s ability to withstand external forces. It is often described as “durability” and is typically evaluated by tensile strength, the maximum load a material can withstand without breaking.

Although materials experience various kinds of forces—compression, shear, bending—these can be traced to tensile forces at a microscopic level. For this reason, tensile strength is considered a key indicator of a material’s overall “strength.”

High-strength materials should be selected for components that experience significant loads.

Hardness

Hardness describes a material’s resistance to local deformation or surface damage, such as scratching or indentation. While strength allows a material to endure deformation, hardness reflects its ability to resist deformation altogether.

Hardness is closely related to wear resistance, and can be improved through heat treatments such as quenching. However, higher hardness often means more difficult machining. For parts exposed to repeated friction—such as gears and bearings—high-hardness materials are recommended.

Toughness

Toughness refers to a material’s ability to absorb energy and resist fracture—its “resilience.” Unlike brittle materials such as ceramics, tough metals deform rather than break suddenly when subjected to force.

Toughness measures how much energy a material can absorb beyond its maximum load before complete fracture occurs. Materials with high toughness are ideal for environments involving impact or fluctuating loads.

Specific Gravity

Specific gravity is the ratio of a material’s density to that of water and serves as an intuitive measure of weight. Materials with high specific gravity are heavier; those with low specific gravity are lighter.

Although density is the formal term used in standards such as JIS, specific gravity is often preferred in design and engineering settings due to its ease of understanding when estimating material weight.

How Metal Properties Relate to One Another

Metal properties show several general tendencies:

• Higher strength often comes with higher weight.
  Truly strong and lightweight metals are relatively rare.
• Greater hardness usually reduces toughness.
  For example, ceramics resist indentation but break easily under impact.
• Higher hardness generally increases strength.
• Materials become harder to process as strength or hardness increases.
  Just as frozen meat is harder to cut than a banana, strong and hard materials are more difficult to machine or form.

Because improving one property often affects others, selecting materials requires balancing these characteristics according to design requirements.