S7 Tool Steel vs. 8620: What’s the Difference?
When it comes to selecting the right material for your tooling and manufacturing needs, understanding the differences between S7 tool…
When selecting the right tool steel for your manufacturing or engineering needs, understanding the differences between S7 and H13 tool steels is crucial. These two popular materials each offer unique properties that can significantly impact the performance and longevity of your tools. Are you seeking exceptional toughness for cold work applications, or perhaps superior thermal stability for hot work processes? This article dives deep into the mechanical and thermal properties, specific applications, and heat treatment processes of S7 and H13 tool steels. By the end, you’ll have a clear understanding of which tool steel best suits your specific requirements. Ready to make an informed decision? Let’s explore the key distinctions between S7 and H13 tool steels.
Tool steels are specialized high-quality steels ideal for making tools, dies, and molds due to their hardness, toughness, and wear resistance. Among them, SAE-AISI S7 and H13 stand out for their unique properties and applications.
SAE-AISI S7 tool steel is renowned for its exceptional impact toughness, making it ideal for applications involving high impact and shock loads.
H13 tool steel is a chromium hot work tool steel, designed to maintain its properties even at high temperatures, making it perfect for hot work applications.
Both S7 and H13 tool steels are used for manufacturing tools and dies. However, S7’s shock resistance makes it ideal for high-impact tools, while H13’s high-temperature strength and thermal fatigue resistance are perfect for hot work applications.
Understanding these fundamental differences helps in selecting the appropriate tool steel for specific applications, ensuring optimal performance and longevity of the tools.
S7 tool steel has a Rockwell hardness between 48-58 HRC, ideally 54-56 HRC. While softer than many other tool steels, it stands out for its toughness and impact resistance. H13 tool steel achieves a Rockwell hardness of 56-57 HRC when hardened and can range from 55-40 HRC after tempering, depending on the tempering temperature. H13’s higher yield strength and fracture toughness make it suitable for applications requiring higher durability under stress.
S7 is famous for its impact toughness, perfect for tools like chisels and punches. H13, though also tough, excels in retaining properties at high temperatures, ideal for hot work applications.
S7 has a thermal conductivity of 16.5 BTU/hr-ft-°F (28.5 W/m/K), while H13’s higher rate at 29 W/m-K helps maintain performance in high-temperature environments.
S7 tool steel exhibits a thermal expansion coefficient of 12 µm/m-K. H13, with a lower thermal expansion coefficient of 10 µm/m-K, maintains dimensional stability during thermal cycling, advantageous for applications with drastic temperature changes.
S7 tool steel includes 0.45-0.55% carbon, 3.00-3.50% chromium, 0.25% silicon, 0.75% manganese, and 1.40% molybdenum. This balanced composition makes it ideal for high-impact uses. H13 consists of 0.32-0.45% carbon, 4.8-5.5% chromium, 1.00% silicon, 0.40% manganese, 1.25% molybdenum, and 1.05% vanadium. The vanadium and higher chromium content enhance its ability to retain hardness at elevated temperatures and resist wear.
S7 is tougher to machine due to its hardness but resists distortion during heat treatment, maintaining tool geometry. H13, easier to machine and weld, is stable and crack-resistant under high pressure and temperature, making it ideal for demanding tasks.
H13 tool steel is renowned for its ability to withstand extreme pressures and temperatures, making it ideal for high-pressure die casting applications. This makes it perfect for manufacturing tools and dies used in producing complex, high-precision components such as automotive parts and industrial machinery components.
H13 is commonly used in medium to high-run hot work tools, like forging dies. Its high-temperature strength and thermal fatigue resistance ensure durability, even under severe thermal cycling.
Extrusion dies made from H13 tool steel benefit from excellent thermal stability and high wear resistance, ensuring dimensional accuracy and longer service life in high-temperature processes.
S7 tool steel is perfect for cold work applications involving high impact, such as punches and shear blades. Its toughness prevents cracking or chipping under repeated stress.
S7 is also used in blanking dies, where its high wear resistance and ability to maintain sharp edges are essential. This makes it an ideal choice for operations that require precise and clean cuts.
S7 tool steel is frequently used in the production of cutting tools, such as keyway cutting tools, slitting saws, and broaches. Its high hardness and toughness allow it to maintain cutting efficiency and durability, even under heavy use.
Both S7 and H13 are used in forming tools, depending on the specific requirements of the application. S7 is preferred for cold forming tools due to its high impact resistance, while H13 is chosen for hot forming tools because of its ability to maintain strength at elevated temperatures.
S7 tool steel is often used in the production of injection molds for plastic components. Its high toughness and wear resistance make it suitable for withstanding the repeated stresses of the injection molding process.
H13 is the material of choice for die-casting molds, particularly for aluminum and zinc die-casting. Its high-temperature strength and resistance to thermal fatigue ensure that the molds can endure the rigors of the die-casting process without significant wear or deformation.
In automotive and aerospace industries, S7 and H13 tool steels are essential. S7 is used for wheel hub tools and punching dies due to its impact resistance, while H13 is chosen for aerospace forging dies and turbine blade tools for its high-temperature strength.
S7 tool steel finds applications in the mining and construction sectors, where it is used to manufacture drill bits, mining chisels, and rock-crushing tools. Its toughness ensures that these tools can withstand the harsh conditions and high-impact forces typical of these industries.
Both S7 and H13 are used in general tooling applications. S7 is ideal for tools like chisels, punches, and swaging dies that require high impact and shock resistance. H13, on the other hand, is suitable for tools exposed to high temperatures and pressures, such as gripper dies and specialized hot work tools.
S7 tool steel, valued for its shock resistance, needs precise heat treatment for optimal performance.
To anneal S7 tool steel, heat it to 820-850°C (1508-1562°F), hold it at this temperature, then slowly cool it to 600°C (1112°F) in the furnace before allowing it to cool in air. This process minimizes internal stresses and makes the steel easier to machine.
Preheating S7 tool steel prevents cracking during hardening. This is typically done in two stages: first to approximately 500-600°C (932-1112°F), followed by heating to 800-850°C (1472-1562°F).
Heat S7 steel to 870-900°C (1598-1652°F) for 2 hours to austenitize, then rapidly quench in air or oil to achieve a hardness of 55-60 HRC. The rapid cooling enhances wear resistance but requires careful handling to avoid warping.
After quenching, temper the steel to relieve stresses and optimize mechanical properties. Sub-zero treatment can be applied by cooling the material to approximately -73°C (-100°F) before re-tempering to further enhance wear resistance and dimensional stability.
H13 tool steel, a hot work steel, has different heat treatment requirements compared to S7.
The annealing process for H13 involves heating the steel to a lower temperature range compared to S7. The exact temperatures are less frequently specified but typically involve slow cooling to reduce internal stresses.
Preheating H13 steel is necessary to avoid thermal shock. The process generally involves heating to a temperature below the austenitizing range, though specific temperatures are less often detailed.
H13 steel is austenitized by heating it to around 1000-1050°C (1832-1922°F) and holding it for 30-60 minutes to achieve a uniform austenitic structure.
H13 steel is quenched in air or oil to reach a hardness of about 52 HRC. This process is generally less complex than that for S7, involving fewer stages of heating and cooling.
After quenching, temper H13 steel to relieve stresses and achieve the desired mechanical properties. The tempering process is similar to that used for S7 but typically involves different temperature ranges.
For S7 steel, the forging or rolling process involves heating to 1000-1100°C (1832-2012°F) to ensure a fine, uniform grain structure and prevent cracking. Gradual cooling is essential to relieve internal stresses.
Both S7 and H13 steels require careful machining. For S7, stress relieving involves heating to 649-677°C (1200-1250°F) and cooling in still air. This step is critical, especially after rough machining, to relieve machining stresses and maintain dimensional stability.
S7 steel is ideal for shock-resisting applications like chisel bits, while H13 is used for hot work applications such as die casting and forging dies.
S7 requires more complex heat treatment, including multiple heating and cooling stages, whereas H13’s process is simpler.
S7 steel can achieve a higher hardness (55-60 HRC) compared to H13 steel (around 52 HRC). However, both steels are known for their toughness, with S7 being particularly resistant to shock and impact.
Both S7 and H13 tool steels offer distinct advantages depending on the specific requirements of the application. Understanding their unique properties and applications is crucial for selecting the right tool steel.
Choosing between S7 and H13 tool steels depends on your project’s specific needs. S7 is perfect for high-impact tools, while H13 excels in high-temperature environments. Understanding their distinct properties ensures your tools perform optimally and last longer.
Below are answers to some frequently asked questions:
The key differences between S7 and H13 tool steels lie in their composition, hardness, and application suitability. S7 tool steel has lower carbon and chromium content, offering excellent impact and shock resistance but less wear resistance, making it ideal for cold work tools and some hot work tools with lower temperature demands. In contrast, H13 tool steel, with higher carbon and chromium content, excels in high-temperature strength, thermal stability, and resistance to thermal fatigue, making it more suitable for demanding hot work applications such as molds and dies. Additionally, S7 has better polishability and machinability, while H13 offers superior wear resistance and minimal distortion during heat treatment.
For hot work applications, H13 tool steel is generally considered better due to its higher temperature stability, resistance to thermal fatigue cracking, and superior hardenability. H13 offers a balanced combination of toughness and wear resistance, which is essential for tools subjected to cyclic heating and cooling, such as in die casting, extrusion, and drop forging. While S7 tool steel is known for its excellent impact resistance, H13’s specific properties make it more suitable for the demanding conditions of hot work applications.
The mechanical properties of S7 and H13 tool steels differ significantly, with S7 known for its very high impact toughness, making it ideal for applications requiring resistance to high impact and shock loading, while H13 is renowned for its excellent high-temperature strength and resistance to thermal fatigue cracking. S7 achieves a working hardness range of 48-58 HRC and excels in cold work applications, whereas H13, with a hardness of up to 54 HRC, offers superior wear resistance and is better suited for hot work applications due to its ability to maintain strength and resist softening at high temperatures.
S7 tool steel is typically used for applications requiring high impact toughness, such as shear blades, swaging dies, gripper dies, chisels, and punches, and is also suitable for hot work tools where temperatures do not exceed 1000°F (538°C). It is also employed in plastic injection molds due to its polishability. H13 tool steel, on the other hand, is ideal for hot work tooling like forging tools, hot shear knives, and die casting tools because of its excellent thermal fatigue resistance. It is also used in cold work applications such as dies and stamping tools, making it versatile for both high and low-temperature environments.
S7 and H13 tool steels have distinct heat treatment processes due to their differing properties. S7 is hardened by heating to 1725-1850°F, air-quenched, and tempered at 400°F for cold work or 900-1000°F for hot work, focusing on its high toughness and shock resistance. H13, on the other hand, is preheated to 1400-1500°F, austenitized at 1800-1850°F, air-cooled or oil-quenched, and tempered at 900-1200°F, which enhances its heat resistance and hardenability. These tailored treatments make S7 suitable for high-impact applications and H13 ideal for high-temperature environments.
Specific examples and case studies demonstrate the distinct applications of S7 and H13 tool steels. S7, known for its high impact toughness, is used in injection molds, cold forming dies, and automotive tools like wheel hub manufacturing tools due to its stability and minimal shrinkage during heat treatment. Conversely, H13 excels in hot work environments, such as extrusion and forging dies, and high-performance broaches, due to its high-temperature resistance and durability. A notable case study shows H13 molds running over 250,000 shots with minimal issues, highlighting its suitability for high-temperature applications.
