Hard Metals vs. Hardened Steel: Properties, Heat Treatment & Machining

Most people get confused when choosing between hard metals and hardened steels because they need to balance hardness, strength, toughness, and cost all at once. Hard metals are wear-resistant yet brittle, while hardened steels are customizable yet require precise treatment. In this guide, we’ll walk you through the information you need to make the right choice.

What Are Hard Metals & Hardened Steel?

Hard metals are materials that are made up of fine hard particles, which are joined together by a soft binder metal. Hardened steel are alloys that gain hardness after going through a series of heat treatment. They are both used across various industries that require strength, durability, and resistance.

Defining Hard Metals (The Composites)

Hard metals are also known as cemented carbides. They are hard materials that are made by combining fine powders under heat and pressure. Examples of hard metals are tungsten carbide (WC) and titanium carbide (TiC).

The process works like this: powders of the hard materials are mixed with a softer metal, usually cobalt, which acts as a binder. This mixture is then pressed into a shape using a mould.

Finally, the shaped piece is heated at very high temperatures. Instead of melting, the binder metal spreads and fuses the hard particles, creating a solid and very durable material.

 Defining Hardened Steel (The Heat-Treatable Alloys)

Steel is hardened through the heat treatment process. Steels such as tool, alloy, and carbon can be hardened, while steels like stainless can be hardened depending on their type.

The process starts by heating the steel until its internal structure changes. It is then quickly cooled in oil or water to lock in a very hard structure called martensite. Since martensite is very brittle, the steel is reheated at a lower temperature and then cooled again.

This second step reduces brittleness and makes the steel tougher and more flexible while keeping it hard. Common alloying elements used in steel include chromium, manganese, and molybdenum.

Main Classifications of Hard Metals & Hardened Steel

Hard metals are classified by the type of carbide they contain and the binder that holds them together. Hardened steels are classified according to the heat treatment process they undergo. The main classifications of hard metals and Hardened steels are as follows.

Main Types of Hard Metals

The main types of hard metals discussed below

• Tungsten Carbide and Cobalt: This hard metal is also called cemented carbide. It contains tungsten carbide (WC) of  70% – 97% with the rest being cobalt. Cobalt (Co) acts as the binder joining the carbide particles together. The material balances hardness with the toughness needed for heavy use. Uses include cutting tools, drilling tools, and aerospace and defense components.

• Titanium Carbide (TiC): This is a hard, black substance that is similar to tungsten carbide. It has high melting points (3160°C), wear resistance, and can conduct electricity. It is a material used in producing abrasives and slicing tools. Applications include cermets, electrocatalysts, and coating parts.

• Wear Alloys Based on Cobalt: These are metals made for wear applications at high temperatures. They are high in strength, corrosion-resistant, and can maintain their hardness at extreme temperatures. These types of alloys contain chromium, tungsten, and molybdenum, which form hard metal carbides. Examples include medical implants, valve elements, and gas turbine parts.

Main Types of Hardened Steel

The main types of hardened steels are discussed below

• Steels with Low Carbon Content: Otherwise known as mild steel, is composed of carbon less than 0.30%. These steels are easy to form because they are soft as opposed to other steels. After heat treatment, their hardness usually falls between 25 and 30 HRC, which is moderate when compared to steels with higher carbon content.

• Steels with Medium Carbon Content: These steels offer more strength and wear resistance than low carbon steels and contain 0.30% to 0.60% carbon. Medium content steels possess good workability and ductility, and they can be heat-treated (between 40 and 50 HRC) to improve their hardness.

• Steels with High Carbon Content: High-carbon content steels are significantly harder and stronger because they generally contain 0.6 to 1.0 carbon. They can achieve hardness situations of 55 – 65 HRC with the right heat treatment, which increases their resistance to bruising and wear.

• Steel Alloys: Nickel, vanadium, or chromium (alloying content) is added to these metals to enhance them. The metals are hard, won’t rust, and alloying makes them better. Low alloy steels (below 8% alloying content) and high alloy steels (above 8% alloying content) are alloying classes.

How to Harden Steel: The Heat Treatment Process

For steels to harden, controlled heat treatment is required. Composition alone cannot alter the steel’s internal structure to get the right balance of hardness and toughness. The heat treatment processes for steel hardening are as follows:

The Fundamentals of Heat Treatment (Annealing, Quenching, Tempering)

The fundamentals of heat treatment are made up of three cycles, which are discussed below

• Annealing: This is the process of making steel softer by cooling it after it has been heated above its temperature. It helps to reduce internal stress, increase ductility, all while balancing hardness and toughness. If this step is skipped, the steel could become hard and brittle, which could make it less reliable and lead to poor workability.

• Quenching: This is the process of speedily cooling hot steel in either water, oil, or air, transforming the steel structure into hard martensite. This method increases hardness (up to 65 HRC) and strength, but reduces the toughness of this steel. Missing this process could lead to a weak and soft steel, brittleness, and cracking.

• Tempering: This is the process of reheating steel below its temperature and cooling it again after quenching. It reduces brittleness and transforms its martensitic structure into a stable form. Proper tempering makes the steel suitable for applications that require resilience, and leaving out tempering can result in cracks under pressure.

Understanding and Achieving Target HRC Levels

HRC, also known as Hardness Rockwell C, is the measurement of how steels are resistant to deformity and penetration from other materials. The hardness of a steel is measured using a Rockwell C scale. The higher the number on the scale, the harder the steal; the lower the number on the scale, the less hard it is. Some HRC ranges for different steels are as follows:

• Knives and Cutting Tools: To keep their edges sharp after much use, they are hardened to about 60 – 67 HRC.
• General Cutting Tools and Molds: These require hardness and resistance, so they sit around 55 – 56 HRC.
• Gears: Treated to 48 – 52 HRC. This hardness range ensures they remain durable while handling heavy stress.
• Springs: This is around 40 – 45 HRC. It is done so they can bend and rebound countless times without losing shape.
• Automotive Parts: Things like shafts and bearings don’t need to be so hard. At 22 – 25 HRC, they’re tough enough to take on stress while staying resistant to brittleness.

Machining and Processing Challenges

Machining and processing require extra care due to tool wear, heat, and precision issues. To get good results, it is important to understand these challenges.

Understanding the Machinability of Both Material Groups

Machining hard metals is not that simple. Their high strength and heat buildup during cutting slow things down, wear out tools faster, and can cause chip welding. Softer, annealed steels are much easier to handle, but once they’re hardened, they become a challenge. At that stage, you usually need advanced methods like laser machining or EDM to get a clean finish.

CNC Machining Tips for Hard Metals

• Use an intensive coolant for heat and chip discarding. 
• Maintain a cutting velocity between 50 and 100 m/min to reduce tool wear. 
• Use PCD or CBN inserts since they are resistant to severe abrasion. 
• Make sure your machine is set up rigidly because vibration can harm the workpiece and the tool.

CNC Machining Tips for Hardened Steel (Pre-Hardened vs. Annealed State)

• To minimize tool stress, always machine steel in the annealed state (~200 HB).
• Use moderate speeds and coated carbide tools for pre-hardened steel.
• To avoid distortion, make stress-relieving passes before final quenching.
• To attain exact tolerances, save EDM or finish-grinding for the hardened state.

How to Choose: Hard Metals vs. Hardened Steel

The decision between hard metals and hardened steels is based on application, cost, and performance requirements; each has unique advantages and disadvantages.

When to Choose Hard Metals?

Hard metals are better used in situations where abrasion resistance and tool life matter. They are more expensive and carry a higher risk of brittle fracture, but also hold up well in worn environments where other materials would fail. Applications include:

• Drills, milling inserts, and cutting tools that face continuous friction.
• Parts that are exposed to abrasives in processes like metal forming, drilling, or mining.
• Operations where downtime costs more than the material itself.

When to Choose Hardened Steel?

Hardened steel is a good choice when you need durability but only moderate wear resistance. It’s flexible and affordable; you can balance strength and rigidity, heat-treat it for hardness, and machine it more easily while it’s still annealed. Examples include:

• Structural parts that need impact resistance, such as shafts, gears, and machine components.
• General engineering uses where keeping costs low is important.
• Situations that require both machinability and consistent performance.

FAQs

What are the top 10 hardest metals?

Ans: The top 10 hardest metals are:

1. Tungsten
2. Steel
3. Chromium
4. Titanium
5. Iron
6. Vanadium
7. Lutetium
8. Zirconium
9. Osmium
10. Tantalum

Is titanium harder than steel?

Ans: No, steel is harder than titanium as it has a high HRC (45 – 65 HRC). Titanium has high corrosion resistance and a strength-to-weight ratio.

Is iron harder than steel?

Ans: No, steel is harder than iron as it has low carbon content that reduces its strength. Steel is hard because of the carbon content added to it.

Is iron a hard metal?

Ans: No, Iron is not regarded as a hard metal. Iron is soft, and this means that it can easily be scratched. This makes it unsuitable for applications that require hardness or wear resistance

Is copper a hard metal?

Ans: No. Copper is not a hard metal. Copper has a malleable nature. Its nature makes it easy to shape without breaking. Mild-tempered copper is used for ornamental work, while cold-rolled copper is used for construction.

Is gold a hard metal?

Ans: No. Gold is a soft metal. It is the most malleable of all metals and can deform without breaking. Gold is used in making jewelry and can be used for a long time.

Conclusion

The decision on hard metals and hardened steels really depends on whether you need more durability or a more budget-friendly option. If you want parts that last longer and perform better, we’ve got you covered. At HRC Metals, we use advanced CNC machining and smart tooling to deliver components that hold up, cut downtime, and save you money. Let’s build something that works harder for you.