SK85:an always good performance carbon tool steel

SK85 is a high-carbon tool steel belonging to the carbon tool steel series of the Japanese Industrial Standard (JIS). It is characterized by high hardness, high wear resistance, and good toughness. The heat treatment process of SK85 can be adjusted; performance and machinability vary depending on the hardness. SK85 is widely used in the manufacture of a variety of tools, molds, automobiles, and spring manufacturing.

In China’s manufacturing industry, due to the similarity of SK85 and SK5 properties, users sometimes use SK85 instead of SK5. In this blog, we will introduce SK85 and analyze the differences between the two.

What is SK85 steel?

SK85 Reference to the corresponding grades: China GB standard grade T8 (A) / T9 (A) steel; U.S. ASTM standard grade W1 – 7 1/2 and W1 – 8 1/2, UNS standard grade T72301; Germany DIN standard grade C80W1; British BS standard grade 060A78/060A81; France NF standard grade C80E2U; International Organization for Standardization (ISO) standard grade TC80/TC90.

Chemical Composition

According to the Japanese standard JIS G4401_2009, the chemical composition (mass fraction) of the steel is as follows: C 0.80%–0.90%, Si ≤ 0.35%, Mn ≤ 0.50%, P ≤ 0.03%, S ≤ 0.03%, Cr ≤ 0.20%, Ni ≤ 0.25%, Cu ≤ 0.30%.

Physical properties

Hardness:

Hardness ≤ 192 HBW in supply condition; hardness after quenching can reach 50 – 60 HRC; after appropriate heat treatment, hardness is usually between 58 – 62 HRC.

Density

Similar to ordinary carbon steel, with a density of about 7.85 g/cm³.

Coefficient of Thermal Expansion: Similar to ordinary carbon steel, the coefficient of thermal expansion is about 1.2×10⁻⁵/℃.

Mechanical properties

SK85 steel has a high tensile strength and yield strength, with a tensile strength of about 2150 MPa and a yield strength of about 1850 MPa. At the same time, the steel also has good impact toughness and can withstand a certain degree of impact without easy fracture.

Machinability

The machinability of SK85 depends on its hardness and heat treatment condition:

Unheat-treated condition: Due to its low hardness, it is easy to machine and is suitable for cutting, drilling, and other operations.

High hardness state: machining difficulty increases, usually requiring the use of carbide tools and the use of appropriate cooling and lubrication measures to improve machining efficiency and quality.

Heat treatment

Annealing

Full annealing: SK85 steel is heated to 750 – 770°C, held for an appropriate period of time, and then slowly cooled in the furnace. The purpose is to eliminate residual stresses within the steel, reduce hardness, increase plasticity, improve cutting performance, and prepare for subsequent processing and heat treatment.

Spheroidal annealing: heated to 740 – 760°C, insulation, and then cooled at a slower rate so that the carbide in the steel is distributed in the form of spheres. This improves the toughness and cutting performance of the steel and also facilitates subsequent quenching, reducing quenching distortion and cracking tendency.

Normalizing

Heat SK85 steel to 800 – 830°C, hold for some time, and then cool in air. Normalizing can refine the grain, improve the strength and hardness of steel, and improve cutting performance, commonly used in the elimination of forging or rolling after the organizational defects.

Quenching

Quenching temperature is generally in 760 – 780°C. After insulation, it can be water-cooled, water-oil dual-liquid cooling, or alkali bath cooling and other ways. Water-cooled cooling speed can obtain high hardness martensite organization, but the internal stress is large, making it easy to produce deformation and cracking; water and oil cooling or alkali bath cooling can reduce the internal stress and deformation to a certain extent. The hardness of steel after quenching can reach 59 HRC or so.

Tempering

Tempering is the key process immediately after quenching; the quenched workpiece is reheated to a range of temperatures below the critical temperature, heat preserved, and then cooled. SK85 steel is usually low-temperature tempered, tempering temperature (180 ± 10) °C. Low-temperature tempering can eliminate some of the quenching of internal stresses to maintain a high level of hardness so that the steel has a high degree of hardness and abrasion resistance at the same time to avoid brittle cracking.

It should be noted that the actual heat treatment process parameters may need to be adjusted appropriately according to the specific shape, size, use, and production equipment of the workpiece. Heat treatment operations should be carried out in strict accordance with the process requirements to ensure that good performance and quality are obtained.

Application of SK85 steel

Mold Manufacturing

Stamping mold

After quenching and tempering, the SK85 steel surface becomes harder and more wear-resistant. It can withstand a large number of stamping times to maintain the accuracy of the shape of the mold. In the stamping of high-strength plates, made of mold cavities and cores, can effectively resist wear and deformation to ensure that the stamping out of the parts of the precise size, high surface quality, significantly improve the service life of the mold, and reduce production costs.

Injection mold

SK85 steel has good processing performance so that it can be machined, EDM, and other means, made of a complex mold structure, to meet the needs of diversified mold design. In addition, it can also be used in the manufacture of sliding friction due to the need for high hardness and wear-resistant mold parts, such as guide pins, bushings, and ejector pins.

Tool making

Cutting tools

SK85 steel is often used in the manufacture of knives, scrapers, files, and other cutting tools. These tools in the cutting process can remain sharp; their high hardness and wear resistance make them suitable for processing a variety of materials, including some hardness of the metal, such as steel, stainless steel, alloys, etc. They can improve the processing efficiency and precision.

Woodworking tools

SK85 can be used to manufacture cutting tools for processing wood, such as planer knives, saw blades, milling cutters, etc. It can withstand the friction and impact of the wood processing process, maintain good cutting performance, and extend the service life of the tools.

Hardware tools

Daily use of hammers, wrenches, screwdrivers, and other hardware tools is often manufactured with SK85 steel. For example, the head of the hammer after heat treatment is not only hard and wear-resistant but also not easy to brittle; wrenches are not easy to deform and can effectively transfer torque; the screwdriver head with high hardness and abrasion resistance can be adapted to the screws of different materials.

Mechanical parts manufacturing

Spring

SK85 steel has excellent elasticity and high strength, suitable for the manufacture of spring sheets, spring wires, and other kinds of springs; it can maintain good elasticity when subjected to large external forces and is widely used in the need for elastic components of the equipment and machinery.

Gear and shaft parts

In mechanical manufacturing, SK85 steel can be used to manufacture gears, shafts, bolts, and other high-strength parts. Its high hardness and wear resistance can ensure that gears in the transmission process are not easy to wear, shaft parts can withstand large loads and torque, and it can ensure the stability and reliability of mechanical transmission.

Other fields

Medical devices

In the manufacture of medical devices, some surgical instruments, precision shaft parts, joint parts, etc., will use SK85 steel. After fine processing and heat treatment, it has high dimensional accuracy, good surface finish, good strength and toughness, and the instruments are not easy to deform and fracture in the process of use, ensuring the accuracy and safety of surgical operations. After special surface treatment, SK85 steel can also meet the biocompatibility requirements of medical devices.

Architectural decoration

SK85 steel’s high strength can be used to manufacture load-bearing structural components in architectural decoration, such as large commercial buildings in the unique shape of the metal decorative frame. After surface treatment, it can show a variety of appearance effects, such as polished to show a bright metallic luster or brushed to show a unique texture, while its good processing performance makes it possible to be processed into a variety of complex shapes of decorative components to meet the creative needs of architects.

SK85 VS SK5

There are a lot of user compare SK85 and SK5.SK85 and SK5 are both Japanese carbon tool steels with similarities in composition, properties, processing and applications, but with some differences.

Chemical composition

Carbon content: carbon is the key element affecting the performance of carbon tool steel, SK5 steel carbon content of 0.80 – 0.90%; SK85 steel carbon content is relatively higher, in the 0.85 – 0.95% between.

Other elements: the two in silicon, manganese, phosphorus, sulfur and other elements of the content of the provisions of the same, but due to the carbon content of the difference, but also on the overall chemical

properties will have a certain impact.

Performance Differences

Hardness: In general, the hardness of steel is positively correlated with the carbon content. Since SK85 has a slightly higher carbon content than SK5, under the same heat treatment conditions, SK85 will usually be slightly harder after hardening than SK5, giving better wear resistance.

SK85 supply state hardness ≤ 192HBW, quenched hardness 50 – 60HRC. SK5 annealed state hardness ≤ 187HB, quenched hardness ≥ 62HRC.

Wear resistance: both have high hardness and good wear resistance, can resist wear to a certain extent, but SK85 wear resistance is relatively better.

Toughness: The toughness of steel decreases as the carbon content increases. Therefore, SK5 has better toughness than SK85 and is less likely to fracture when subjected to impact loads.

Hardenability: The higher the carbon content, the better the hardenability, SK85 has better hardenability than SK5, which means that during the quenching process, SK85 is able to obtain the required hardness and organizational properties in the deeper surface layer.

Heat treatment process

SK85: Starting temperature 1000 – 1050°C, ending temperature 850°C. Quenching temperature 760 – 780°C, water cooling, water-oil dual-liquid cooling, or alkali bath cooling, tempering temperature (180±10)°C.

SK5: Starting temperature 1000 – 1050°C, ending temperature 850°C. Quenching temperature 730 – 760°C, water-cooled, water-oil cooled or alkaline bath cooled, tempering temperature 160 – 180°C.

Application Differences

Application of SK5: Because of its better toughness, it is commonly used in the manufacture of tools and parts that require a certain degree of toughness and wear resistance, such as punches, shear blades, woodworking knives, saw blades and so on. These tools need to withstand a certain degree of impact and bending force in the process of use, the performance of SK5 can meet its working requirements.

Application of SK85: Due to its higher hardness and wear resistance, SK85 is more suitable for the manufacture of tools that require higher hardness and wear resistance, such as carving knives, scrapers, needles, razors, etc. The hardness and wear resistance of SK85 is also higher than that of SK5. These tools are mainly used for fine machining or cutting of materials and require sharp edges and good wear resistance.

Overall, SK85 is suitable for professional applications requiring high strength and superior cutting performance, while SK5 is suitable for consumer-grade toolmaking where cost and resistance to daily wear are important.

Conclusion

SK85 is characterized by high hardness and high wear resistance.It is widely used in the manufacture of a variety of tools, molds, automobiles and spring manufacturing.SK85 is usually available in the following shapes: round bar, square bar, flat bar, plate, coil and forgings. It can meet the requirements of different finished products.This steel has been widely used in China with more than enough experience in its using. If there are other questions, please feel free to contact us.