What is SK-5 Steel?

SK5 Carbon Steel (SK85 Material)

SK5 steel (SK85 material) is a carbon tool steel commonly used in Japan. After quenching and tempering, it has high hardness and good wear resistance, but the hardness decreases at high temperature. It is often used as a material for tools such as hammers and saws. SK85 is the name of the new JIS G4401 standard to replace the old name SK5. But the name SK5 is still widely used in Japan.

Material SK85 Meaning (Designation)

• “S” means “steel”,
• “K” means “Kougu”, the word “tool” in Japanese, and
• 85 denotes 0.85% carbon content.

SK5 Steel Properties

The density of SK85 tool steel is 7.84 g/cm3, the annealing hardness is ≤207 HB (annealing temperature is 730-760 °C slow cooling), and the quenching and tempering hardness of the specimen is ≥ 59 HRC (quenching temperature 780 °C, water cooling; tempering temperature 180 °C, air cooling).

Physical Properties

Physical Properties	Metric	Imperial
Density	7.87 g/cm3	0.284 lb/in3
Specific heat capacity	490 J/kg·K	0.117 Btu/lb ·°F
Electrical resistivity	0.18 μΩ·m	7.09 μΩ·in
Elastic modulus (Modulus of Elasticity)	208 GPa	29 x 103 ksi
Coefficient of thermal expansion (CTE)	11.0 x 10-6/K at 0-100 °C	6.39 μin./in.·°F at 32-212 °F
Thermal conductivity	50.2 W/m·K	30.1 Btu/ft·h·°F

Mechanical Properties

SK5 Material Mechanical Properties
Steel	Finish	Hardness (HV)	Tensile Strength, MPa	Stretch, %
SK5 (SK85)	Annealed	150-190	460-625	26-37
	Skin pass	170-210	510-685	15-35
	Rolled	240-280	725-930	3-16
	Strong rolling	260-300	805-1000	1-5

Uses and Applications

SK85 material typical uses are hammers, axes, saw tools, but the application of SK material is not limited to tools, it is also widely used in materials that require hardness and wear resistance, such as pins and shafts in mechanical parts; engraving, chisels, stamping dies, band saws, circular saws, clamp and jig tools, cold steel knives, blades, daggers, gauges, needles, etc. Some popular brand knives such as Cold Steel SRK SK5, Recon Tanto SK5, Ontario Blackbird SK5 all use SK5 material.

SK5 Steel Equivalent Material

SK5 carbon steel equivalent material is listed in the table below, including US ASTM, ISO, German DIN, Chinese GB and European EN standard, etc.

SK5 Steel Equivalent Material

Japan

US

European

ISO

Germany

China

Australia

India

Rusia

Korea

Standard

Steel Grade

Standard

Steel Type (UNS)

Standard

Steel Name

Standard

Designation

Standard

Steel Name (Material Number)

Standard

Steel Grade

Standard

Grade

Standard

Grade

Standard

Grade

Standard

Grade

JIS G4401

SK5 (SK85)

AISI, SAE; ASTM A686; ASTM A29/A29M

W1 (T72301); 1086

EN ISO 4957

C80U; C90U

ISO 4957

C80U; C90U

DIN EN ISO 4957; DIN 17350

C80U (1.1525, C90U (1.1535); C85W (1.1830)

GB/T 1298

T8Mn

Note:

• JIS G4401: Carbon tool steels;
• ASTM A686: Standard Specification for Tool Steel, Carbon;
• ASTM A29/A29M: Standard Specification for Steel Bars, Carbon and Alloy, Hot-Wrought;
• BS EN, DIN EN ISO 4957: Tool steels
• DIN 17350: Tool steels, has been replaced by DIN EN ISO 4957.
• GB/T 1298: Carbon tool steels

SK-5 Steel Explained

There are so many different kinds of steel that it can easily become confusing. However, if you are getting into the steel or knife industry, it will be beneficial to familiarize yourself with the different kinds of steel. For instance, what is SK-5 steel, and why should you care? This artical will explain what sk5 steel is. We will cover everything, including the history of steel and the four most common kinds of steel. By the end of this article, you will know the main properties of sk5 steel, what makes it different from other metals, and what industries use it. Finally, we will discuss the pros and cons and what factors you should consider before purchasing an sk5 product.

History of Steel

2000 BC – 1000 BC

It was 2000 BC when the production of iron first began. Iron production took its first steps in Anatolia, a historical region in Asia. By 1000 BC, the establishment of the iron age had increased the use and production of iron worldwide.
During these times, iron production was still very small-scale since they only had so much technology available.

900 BC

By 900 BC, the Egyptians made some productive headway in regards to the smelting process of iron. When they realized that steel became more brittle as the carbon content increased, they figured out how to decrease the brittleness.
With a process called tempering, the Egyptians were able to increase the quality of the steel by reheating it at a certain temperature range.
The Egyptians were one of the first early societies to use higher-quality steel to produce weapons like knives and swords.

1500 – 1900 AD

From the 1500s to the 1700s, Britain had been clearing forests to produce charcoal. During that period, the main way to smelt iron was to use charcoal as a burning and reducing agent.
The reducing agent is what converts the iron ore into pure metal.
Around 1708, Abraham Darby invented the blast furnace to use for iron smelting. Instead of charcoal, Darby used coke for the smelting process.
Both of these revelations allowed for the increased production of iron. With blast furnaces and coke, companies could produce iron metal on a larger scale.
It was in 1856 when the mass production of steel entered the picture. A man named Henry Bessemer developed a new kind of blast furnace along with a different way of smelting the iron.
Steel is an alloy of iron but with less carbon content, making it more durable and strong than original iron metal is. Bessemer figured out a way to smelt steel by reducing the amount of carbon in the iron ore.
As countries worldwide began to construct this new kind of blast furnace, the steel industry soon skyrocketed. By the end of the 19th century, Britain produced over 30 million tonnes of this strong, desired alloy.

What Are the Most Common Types of Steel?

Steel is a widely used iron alloy due to its special properties. Let’s take a look at the four main types of steel that manufacturers use in the industry today.

Carbon Steel

Carbon steel makes up for 90% of all steel in the industry. This type of steel mainly contains carbon and iron and only a minimal amount of other minerals.
There are three kinds of carbon steel, depending on how much carbon is in the metal. The three groups are called low carbon steel, medium carbon steel, and high carbon steel.
The strongest steels are the high carbon steels, with 1-2% carbon. Steel producers can harden and temper high carbon steels more than lower carbon content steels. These processes will increase the durability, strength, and resistance to the impact of the metal

Alloy Steel

This kind of steel has chemical elements like copper, chromium, nickel, and aluminum added to the metal.
These alloys will add specific properties to the steel that make it more valuable and useful to certain industries. The alloys increase the steel’s strength, ductility, malleability, and corrosion resistance.
Much like carbon steel, alloy steel has two different categories depending on the amount of alloys in the metal. The categories include low-alloy steels and high-alloy steels.

Stainless Steel

The primary alloy in stainless steel is chromium. Most stainless steels contain 10-20% chromium.
The most valuable characteristic of stainless steel is its ability to resist corrosion. The metal will not rust or stain easily. The chromium in stainless steel acts as a barrier between the metal and outside chemical attack.
Some of the main products that contain stainless steel are food equipment, medical equipment, cutting tools, and piping.

Tool Steel

The last common steel is tool steel. As the name suggests, manufacturers use this type of steel to make tools.
Tool steel has several different steels and alloys in it that contribute to its unique properties. Some main characteristics of tool steel are corrosion resistance, durability, hardness, and impact resistance.

What Exactly Is SK-5 Steel

SK5 steel is Japanese carbon steel. The steel is usually low carbon or medium carbon steel, meaning it contains 0.3-0.6% carbon.
However, a few companies sell high carbon sk5 steel, which contains over 0.6% carbon.
An interesting fact about the steel is that “SK” stands for “Steel Kougu.” You can roughly translate the name to “Steel Tool.”
SK-5 steel is also highly tempered and forged in high-temperature furnaces. These processes remove significant weaknesses of the metal and enhance its best qualities.
We will go into more detail later, but sk5 steel is mainly used for different kinds of blades, tools, weapons, and knives because of its unique properties.

What Makes It Different?

There are a few factors that make sk5 steel different than the others. Let’s take a look.

Composition

Similar to alloy steel, this kind of steel has several different alloys added to it. Let’s look at the many different chemical elements that give sk5 steel its advantageous characteristics.

• Manganese. There is usually 0.50% of manganese in sk5 steel. This alloy increases the hardness of the steel.
• Silicon. This alloy increases strength. There is about 0.35% of silicon in sk5 steel. 
• Chromium. Chromium has a few different purposes. The alloy increases corrosion resistance, wear resistance, edge retention, and tensile strength. Sk5 steel contains 0.30% chromium. 
• Copper. Copper protects the steel and prevents the process of oxidization from damaging the metal. There is 0.25% of copper in the steel. 
• Carbon. Since there is not an abundance of carbon in sk5 steel, it does not reduce the strength. Instead, 0.9% of carbon increases corrosion resistance, hardness, and durability. 
• Phosphorus. There is 0.03% phosphorus in the steel. This chemical element increases strength. 
• Sulfur. Finally, sk5 steel contains 0.03% sulfur. What this element does is increase the ease that the metal can be machined and cast. 

There are also a few other elements, such as vanadium and tungsten, that manufacturers can add.
It is worth noting that the steel’s composition will differ from product to product. The type of product will determine what kinds of chemical elements and alloys are added to the sk5 steel.

Properties

Not only does the composition of sk5 steel make it different from the others, but it also has certain unique properties.
For instance, sk5 steel has a maximum hardness of 65 HRC. One of the main reasons people like products with sk5 steel is that it has a good balance between toughness and hardness.
Hardened steels have higher levels of specific properties such as durability, abrasion resistance, wear-resistance, and corrosion resistance.
These listed characteristics are why sk5 steel is widely favored. Hunters can take an sk5 steel knife into the woods and not worry about the blade being damaged or scratched. The steel can undergo a good amount of wear and tear without sacrificing quality.
The properties of this special kind of steel also add to the versatility of the metal. There is no one use for it; you can buy a number of different sk5 tools designed for different uses. You can also use one sk5 steel blade for several different jobs.

SK-5 Steel Uses

SK-5 has many interesting qualities, but what is it used for?
The steel is primarily used in different kinds of blades. A few different products include razor blades, scalpels, utility knives, cutting tools, and long-edged tools.
As mentioned above, sk5 steel can either be low, medium, or high carbon steel. The level of carbon will determine what kind of product the steel becomes.
For instance, manufacturers use high carbon steel (which is harder and stronger) for producing hunting knives or tactile knives.
On the other hand, weapons such as fencing swords will contain lower-carbon sk5 steel. Lower carbon steel works well for those kinds of products since it is more flexible and can bend more easily than higher carbon can.
Sk5 steel is a big part of the knife/weapon industry. Many hunters and outdoorsmen love to use sk5 blades and tools for hunting and hiking trips.
You can find sk5 metal in products such as spears, tomahawks, daggers, hatchets, chisels, saws, and many different kinds of knives.

SK-5 Steel's Pros and Cons

Like any product out there, pros and cons are inevitable. While this steel may work well for some situations, there are a few disadvantages of the steel to keep in mind.

Pros of SK-5 Steel

This section will cover the valuable properties of sk5 steel and why it works great for different knives and tools.

Sk5 steel has good edge retention

The carbon in the metal adds to the hardness and the quality of edge retention.

Sk5 steel is resistant to wear

Another benefit of the carbon content is how it increases the metal’s ability to resist wear. The steel’s high durability is a reason why it is so popular for outdoor activities.

The metal is fairly resistant to corrosion

Corrosion resistance is one of the most important factors that contribute to a high-quality metal.
Even though sk5 steel does not have the most fantastic corrosion resistance, it will still be easy to maintain the quality of the blade.
(Hardness, toughness, and corrosion resistance usually do not go hand and hand, so this is still a pretty good deal.)

Sk5 steel is impact resistant and tough

Another great property of Sk5 steel is how tough it is. SK-5 steel can resist damage from strong impacts and is very hard.

Good material for knives

Due to all of the listed properties, sk5 steel works well as a knife blade.

Cons of SK-5 Steel

We will now cover a few downsides of the steel and what factors you should consider before buying an sk5 product.

You cannot store an sk5 steel product in wet environments

Even though sk5 has decent corrosion-resistant, that is not its strength. You will need to take care of the steel to avoid any damage from corrosion and rust.

The steel has a higher level of brittleness

When it comes to metals, the harder the steel is, the more brittle it becomes. When using an sk5 steel with a higher carbon content, you will need to keep an eye out for this. The blade could fracture or break under intense stress.
When a blade has a high brittleness level, you won’t get any warning signs of when the knife will break.

Sk5 steel is harder to sharpen

If you think of buying an sk5 steel knife, this will be something to keep in mind.
Harder steels are usually more difficult to sharpen, so high carbon sk5 steels could be challenging to work with.