For any precision sheet metal fabrication shop, the choice of die material directly determines part quality, production efficiency, and die service life. Among the various types of die steel, high-speed steel (HSS) remains the benchmark for high-temperature and continuous wear-resistant applications.
Unlike traditional cold-work steels, high-speed steel retains its hardness at temperatures as high as 600°C—a property known as “red hardness”—making it indispensable for stamping, blanking, and forming operations. When manufacturing high-speed steel sheet metal parts, the choice of steel grade determines the cutting edge’s retention capability and the stability of machining cycles.
For example, M42 high-speed steel offers exceptional thermal hardness (HRC 67–70), making it suitable for machining stainless steel and high-strength alloys; whereas M2 high-speed steel combines toughness and wear resistance, making it ideal for general-purpose stamping dies.
Supro’s production experience shows that selecting the correct high-speed steel grade matched to the workpiece material can reduce downtime by 30–50% compared to standard tool steels. The following sections provide detailed information on the material’s composition, AISI grades, and practical selection criteria to help buyers make data-driven tooling decisions.
Metallurgical Composition of High-Speed Steel (HSS)
The metallurgical composition of high-speed steel directly determines its red hardness and wear resistance in stamping and forming applications. Precise alloy composition—including tungsten, molybdenum, chromium, vanadium, and cobalt—determines the tool’s service life.Both M42 and M2 high-speed steel rely on a unique carbide structure that enables them to withstand high cutting temperatures without causing cutting edge degradation.
Major Alloying Elements in High-Speed Steel (HSS)
The performance of high-speed steel in sheet metal dies depends on precise alloy ratios. Tungsten (W) and molybdenum (Mo) form stable carbides that impart “red hardness” to the material—that is, the ability to maintain cutting edge integrity at 600°C during high-speed stamping operations.
Chromium (Cr) improves hardenability and enhances corrosion resistance when the die comes into contact with coolant. Vanadium (V) forms extremely hard vanadium carbides (HV ~2800), which refine the grain structure while enhancing wear resistance. Cobalt (Co) further improves high-temperature hardness.
In the field of stamping dies, M2 high-speed steel achieves universal toughness by balancing the content of tungsten and molybdenum; whereas M42 high-speed steel utilizes higher cobalt and molybdenum content to achieve a hardness of HRC 67–69, making it highly suitable for long-term blanking of high-strength alloys. A reasonable carbide distribution directly extends the die’s service life between regrinds.
Classification by Alloy System
High-speed steel (HSS) can be classified into four alloy systems based on the primary carbide-forming elements. Tungsten-based HSS (e.g., T1) contains 12%–18% tungsten, offering excellent red hardness but lower toughness, making it suitable for finishing tools.
Molybdenum-based HSS (e.g., M1, M2) contains 5%–10% molybdenum, offering better impact resistance at a lower cost. M2 high-speed steel remains the industry standard for sheet metal punches and dies due to its balanced performance in wear resistance and machinability.
Tungsten-molybdenum HSS combines these two elements, thereby improving thermal plasticity. Cobalt-alloyed HSS (such as M35 and M42 high-speed steel) adds 5–8% cobalt to enhance thermal hardness, enabling continuous, heavy-duty punching of quenched steel sheets.
In sheet metal processing, selecting the correct alloy system can reduce downtime. M42 performs exceptionally well in high-temperature, high-wear applications such as punching advanced high-strength steel (AHSS), while M2 is sufficient for machining low-carbon steel and aluminum.
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Classification of High-Speed Steel by AISI Grades
The American Iron and Steel Institute (AISI) classifies high-speed steel (HSS) based on composition and performance characteristics to match HSS properties with specific stamping and punching requirements. When manufacturing high-speed steel sheet metal parts, selecting the correct steel grade—such as M2 for general-purpose dies or M42 for high-temperature, abrasive applications—directly impacts tool life and part tolerances.
M2 high-speed steel
M2 high-speed steel (AISI / 1.3343) is the most commonly used steel grade in general-purpose sheet metal dies. It has a balanced chemical composition—containing 0.85–0.95% carbon, 5.50–6.75% tungsten, 4.50–5.50% molybdenum, 1.75–2.20% vanadium, and 3.75–4.50% chromium—which, after proper heat treatment, achieves a hardness range of HRC 63–66.
M2 punches and dies offer an optimal combination of wear resistance, toughness, and machinability. The molybdenum-tungsten matrix provides sufficient red hardness to allow continuous punching of low-carbon steel and aluminum at temperatures up to 500°C without edge rounding.
In high-volume blanking operations, M2 dies typically extend production run times between regrinds by 30–50% compared to traditional D2 or O1 tool steels. However, for abrasive materials such as galvanized steel or stainless steel, M2 may experience increased flank wear, in which case steel grades with higher cobalt content are more suitable. Overall, in medium-volume OEM sheet metal processing, M2 high-speed steel remains the benchmark for cost-effectiveness in stamping dies, forming tools, and trimming blades.
M35 Cobalt-Alloyed High-Speed Steel
M35 is a cobalt-alloyed variant of M2, containing 4.50–5.00% cobalt in addition to significant proportions of tungsten, molybdenum, vanadium, and chromium. The addition of cobalt significantly improves red hardness and thermal stability, enabling the tool to maintain cutting efficiency at temperatures exceeding 550°C. In demanding stamping applications—such as punching through advanced high-strength steel (AHSS) or intermittent cutting of laminated sheets—M2 high-speed steel may experience premature softening, whereas M35 maintains a hardness of HRC 64–66 even under sustained thermal loads.
Compared to grades with higher cobalt content, M35 also offers superior impact toughness, thereby reducing the risk of chipping in close-clearance progressive dies.
From a production standpoint, when machining 304 stainless steel or carbon steel with a yield strength of 50 ksi, M35 tools offer a 20–25% longer regrinding interval than standard M2. When a balance between cost and high-temperature performance is desired, but high-end grades are not preferred, M35 high-speed steel provides a practical upgrade option for medium- to high-volume sheet metal production lines.
M42 High-Cobalt High-Speed Steel
M42 high-speed steel is a high-quality cobalt alloy steel with a composition of 7.75–8.75% Co, 1.05–1.15% C, and 9.00–10.0% Mo. When properly tempered, this composition achieves exceptional hardness of HRC 67–70, while also exhibiting excellent red hardness, maintaining a hardness of HRC 65 even at 625°C.
When machining difficult-to-cut materials—including precipitation-hardening stainless steels, titanium alloys, and wear-resistant (AR) steel plates—M42 punches and blanking dies offer the longest tool life under high-temperature, high-friction conditions. Its fine distribution of vanadium carbides provides exceptional wear resistance, effectively reducing microcracks on the cutting edge. However, M42 has lower impact toughness than M35 high-speed steel, making it less suitable for intermittent cutting or applications subject to heavy impact loads.
In practice, M42 tools are typically used for long-cycle, high-speed punching of advanced high-strength steel (AHSS, tensile strength >800 MPa), where downtime caused by tool changes is a major factor in production costs. With proper heat treatment, the tool life of M42 can be 2–3 times longer than that of conventional M2.
T Series Tungsten-Based Alloys
The T series of high-speed steel (HSS) grades, primarily T1 (AISI 1.3355) and T15, rely mainly on tungsten rather than molybdenum as the carbide-forming element. T1 contains 17.50–18.50% tungsten and 0.70–0.80% carbon, and 4.00% chromium. It offers excellent red hardness but has lower toughness and machinability compared to molybdenum-based grades. In sheet metal applications, T1 is rarely used in progressive dies due to its poor impact resistance, which can lead to edge chipping under cyclic stamping loads.
However, T15 contains high proportions of vanadium (4.75–5.25%) and cobalt (4.75–5.25%), as well as 12.00–13.00% tungsten, resulting in extremely high wear resistance—in the pin-on-disc test, its volumetric wear loss is only 0.3–0.35 mm³. T15 performs exceptionally well in the forming and punching of highly abrasive materials, such as silicon steel sheets for electric motors.
Although M42 high-speed steel is often used as a substitute for T15 due to its superior machinability and lower cost, T15 is still specified for specific high-volume, high-wear applications—those requiring strict dimensional tolerances to be maintained over millions of stamping cycles.
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Mechanical Properties and Heat Treatment Requirements of High-Speed Steel
For high-speed steel punches and dies used in precision sheet metal processing, the interaction between post-quenching hardness, tempering cycles, and retained austenite determines their actual service life. Post-quenching hardness alone does not guarantee wear resistance; during multiple tempering cycles (typically at 540°C–570°C), the precise precipitation of secondary carbides determines red hardness and impact toughness.
M2 high-speed steel is typically austenitized at 1180°C–1220°C and tempered three times, achieving a hardness of HRC 63–65 while maintaining sufficient toughness, making it suitable for blanking operations on ordinary low-carbon steel and aluminum.
Due to its higher cobalt and carbon content, M42 high-speed steel requires stricter austenitizing control (1170°C–1190°C); when properly treated, it can achieve a hardness of HRC 67–69 while maintaining thermal hardness at temperatures as high as 625°C.
Overheating of either grade can result in excessive retained austenite (over 15%) and grain coarsening, leading to premature chipping of the cutting edge. Insufficient heating, on the other hand, can cause carbides to remain undissolved, thereby reducing wear resistance.
For high-volume production of high-speed steel sheet metal parts, a three-cycle tempering process following vacuum heat treatment can reduce the residual austenite content to below 5%. Compared to traditional cold-work steels such as D2, this can extend tool regrinding intervals by 40–60%.
Applications of High-Speed Steel in Metalworking and Sheet Metal Fabrication
In the field of precision sheet metal fabrication, high-speed steel (HSS) plays a critical role in numerous production processes where the durability of cutting tools under thermal and mechanical stress is essential.
High-Speed Steel in Cutting Tool Manufacturing
In the sheet metal processing sector, HSS remains the preferred substrate for cutting tools that come into contact with the blank prior to stamping. Slitting saws, shearing blades, and trimming dies made from M2 high-speed steel combine balanced hardness (HRC 63–65) and toughness, enabling them to withstand continuous edge contact with hot-rolled or cold-rolled steel coils. The molybdenum-tungsten carbide matrix maintains sharpness under the moderate heat generated during high-speed slitting.
For cutting abrasive materials such as galvanized sheet or stainless steel coils, M42 high-speed steel blades are typically selected due to their excellent thermal hardness (HRC 67–69) and vanadium carbide wear resistance. However, due to M42’s lower impact toughness, the blade geometry must be carefully designed to prevent chipping.
Based on Supro’s production experience, M2 disc slitters achieve approximately 200–300 hours of service life before sharpening when cutting low-carbon steel; for M42, this duration extends to 400–500 hours when cutting advanced high-strength steel (AHSS) coils. Proper tool grinding and edge finishing are just as important as the high-speed steel grade itself.
High-Speed Steel for Die and Tool Applications
Die components—including forming punches, draw rings, and trimming blades—require high-speed steel (HSS) grades capable of resisting adhesive wear and galling. For progressive dies that use HSS dies to produce sheet metal parts from high-strength materials, M2 high-speed steel is widely used for non-impact forming blades due to its excellent grindability and resistance to edge deformation under compressive loads.
When forming abrasive steel grades such as DP800 or martensitic stainless steel, M42 high-speed steel blades reduce surface scratches on the drawn surface because fine vanadium carbides act as a microscopic wear-resistant barrier. However, the higher hardness of M42 (HRC 67–69) makes it more susceptible to cracking during welding or electrical discharge machining (EDM), so stress concentration points must be avoided in the design.
For high-volume production of automotive structural components, cobalt alloy high-speed steel die inserts often double tool life compared to traditional A2 or D2.
High-Speed Steel for Punching and Die Cutting
In sheet metal fabrication, punching and blanking represent the most demanding applications for high-speed steel (HSS). Punches are subjected to cyclic compressive stress, edge heating, and abrasive wear caused by sheared edges.
M2 high-speed steel punches are standard punches used for low-carbon steel with a thickness of up to 6 mm and hole diameters ranging from 2 mm to 50 mm. Depending on clearance and lubrication conditions, they can complete 50,000 to 100,000 punches before the edge becomes rounded.
When punching high-strength steel (e.g., with a tensile strength of 980 MPa) or high-silicon electrical steel, M42 high-speed steel punches maintain edge sharpness three to five times longer than M2 punches, as the addition of cobalt (8%) allows them to retain their thermal hardness even at temperatures above 600°C. However, M42 punches are more demanding in terms of alignment accuracy and punch-die clearance; poor alignment typically leads to chipping rather than progressive wear.
In high-speed presses (400+ SPM), high-speed steel tools must be used in conjunction with an internal coolant or mist lubrication system to dissipate heat. Vacuum heat treatment combined with low-temperature tempering can further optimize carbide distribution and reduce microcracks at the cutting edge.
Cold Heading and Thread Rolling
Cold heading and thread rolling dies are subjected to extreme compressive stresses and sliding friction. When producing fasteners and threaded inserts from wire rod, high-speed steel punches and thread rolling dies outperform cemented carbide in applications requiring moderate wear resistance but greater toughness to prevent cracking.
M2 high-speed steel punches are commonly used to manufacture low-carbon steel and low-alloy fasteners, capable of producing 200,000 to 300,000 parts before deformation occurs on the punch face. For stainless steel (304, 316) or high-strength alloy steel fasteners, M42 high-speed steel thread rolling dies exhibit excellent resistance to galling and pitch circle diameter wear, as their fine, hard carbides effectively prevent adhesive transfer. However, M42 has lower impact toughness, so tool geometry design requires extra caution—sharp corners must be rounded.
In cold heading processes for Inconel or titanium, powder metallurgy high-speed steel (HSS) grades sometimes replace traditional M42; however, for most OEM fastener applications, properly heat-treated M2 and M42 still offer the best cost-performance ratio.
Material Selection Criteria
Selecting the appropriate HSS grade for sheet metal dies requires a comprehensive evaluation of the workpiece material, production volume, and press characteristics. M2 high-speed steel is the preferred choice for machining low-carbon steel (tensile strength <250 MPa), aluminum, copper, and small-batch production (fewer than 100,000 stamping cycles), where die cost and regrindability are primary considerations.
When stamping abrasive or high-strength materials (such as advanced high-strength steel, stainless steel, and titanium) with a production volume exceeding 500,000 cycles, M42 high-speed steel is a reasonable choice, as its longer die life offsets the higher upfront material and heat treatment costs.
For mixed-material production, intermediate-grade materials such as M35 high-speed steel offer a compromise. Other selection factors include cutting edge geometry—due to its lower toughness, M42 is not suitable for handling sharp-angle shears—and stamping speed. For high-speed presses (over 300 SPM), cobalt-alloyed HSS must be used to resist tempering caused by frictional heat. Finally, it is essential to verify heat treatment data (austenitizing temperature, tempering cycle, and percentage of retained austenite) to ensure consistent die performance.
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Summary
High-speed steel (HSS) remains a fundamental tool material in the field of precision metalworking, characterized by its unique combination of hardness, red hardness, toughness, and wear resistance. The material classification system established under the ASTM A600 standard provides manufacturers with a structured framework for selecting the appropriate grade based on specific application requirements.
A thorough understanding of the composition, grades, and heat treatment parameters of high-speed steel facilitates optimal tool selection for processes such as stamping, punching, and machining, thereby reducing production downtime and improving part quality.
As metalworking technology continues to advance toward higher cutting speeds and more demanding workpiece materials, properly selected and heat-treated high-speed steel cutting tools remain indispensable.
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