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CPM M4 Tool Steel: Properties, Process, Uses
- John
CPM M4 Tool Steel is a standout in the world of high-performance materials, offering exceptional wear resistance and toughness. In this article, SteelPro Group will explore its key properties and applications. We also provide CPM M4 steel products, tailored to meet the needs of industries requiring precision and durability.
What Is CPM M4 Tool Steel?
CPM M4 is a high-vanadium, powder metallurgy (PM) high-speed steel known for its excellent wear resistance, impact toughness, and bending strength. These characteristics make it perfect for use in cutting tools, molds for cold work. Compared to conventional high-speed steels like M2, CPM M4 offers extended tool life and superior toughness. Its hardness and durability, however, pose challenges when machining in the hardened condition.
What Is CPM M4 Steel Equivalent To?
There are the equivalent grades of CPM M4 tool steel:
- S690
- DIN 1.3343
- JIS SKH51
- ISO HS 6-5-3
- BS 4659-3
- GB T9
Chemical Composition of CPM M4 Tool Steel
The chemical composition of CPM M4 tool steel is rich in chromium, molybdenum, tungsten, and vanadium. The high carbon content ensures robust hardness while vanadium and tungsten improve toughness and thermal stability. The table below outlines the chemical composition of CPM M4 tool steel.
| Element | Content (wt%) |
| Carbon (C) | ≤ 1.35 |
| Sulfur (S) | ≤ 0.06 |
| Chromium (Cr) | ≤ 4.25 |
| Molybdenum (Mo) | ≤ 4.5 |
| Tungsten (W) | ≤ 5.75 |
| Vanadium (V) | ≤ 4 |
Physical Properties of CPM M4 Tool Steel
CPM M4 tool steel is known for its high density and strong thermal conductivity, making it stable and reliable in heat-intensive environments. Its low thermal expansion coefficient ensures that it experiences minimal changes in size when exposed to temperature variations. The following table outlines the key physical properties of CPM M4 steel.
| Property | Metric | Imperial |
| Density | 7.80 g/cm³ | 0.282 lb/in³ |
| Thermal Conductivity | 25.9 W/m·K | 18.0 BTU·in/hr·ft²·°F |
| Specific Heat Capacity | 0.46 J/g·K | 0.11 BTU/lb·°F |
| Coefficient of Thermal Expansion | 5.1 µm/m·K | 2.83 x 10⁻⁶ in/in·°F |
Mechanical Properties of CPM M4 Tool Steel
CPM M4 tool steel offers exceptional hardness and tensile strength, making it highly resistant to wear and deformation under heavy loads. The table below outlines the mechanical properties of CPM M4 tool steel.
| Property | Metric | Imperial |
| Hardness (Rockwell C) | 64-66 HRC | 64-66 HRC |
| Tensile Strength | 2,400 MPa | 348,000 psi |
| Yield Strength | 2,050 MPa | 297,500 psi |
| Elongation at Break | 6-7% | 6-7% |
| Modulus of Rupture (Transverse) | 3,000 MPa | 435,000 psi |
| Impact Toughness (Charpy) | 10 J | 7.4 ft-lb |
| Shear Strength | 1,650 MPa | 239,000 psi |
Heat Treatment of CPM M4 Tool Steel
At SteelPro Group, we prioritize precise heat treatment to optimize the performance of CPM M4 tool steel. Our expertise ensures consistent hardness, toughness, and stability, meeting the high standards of demanding applications. Below is the detailed heat treatment process for CPM M4 tool steel.
Annealing
Heat the steel to 857-885°C (1575-1625°F) at a rate not exceeding 222°C (400°F) per hour. Hold the temperature for 1 hour for every 25.44 mm (1 inch) of thickness, with a minimum hold time of 2 hours.
Slowly cool the steel in the furnace at a rate not exceeding 28°C (50°F) per hour until reaching 538°C (1000°F). Continue cooling in air or in the furnace to room temperature. After annealing, the maximum hardness achievable is typically around 229 HB (Rockwell B 95).
Hardening
Preheating
To avoid distortion during the heating process, preheat the steel at a rate not exceeding 222°C per hour (400°F per hour) to a uniform temperature range of 816-871°C (1500-1600°F).
Austenitizing
The austenitizing temperature for CPM M4 tool steel depends on the intended application, ensuring optimal hardness and toughness for specific tools.
For cutting tools
- Furnace heating: Heat to 1177-1191°C (2150-2175°F), soaking for 10 to 20 minutes depending on the tool’s thickness.
- Salt bath heating: Heat to 1163-1191°C (2125-2175°F), soaking for 10 to 20 minutes.
For cold work tools
- Furnace heating: Heat to 1023-1163°C (1875-2135°F), soaking for 15 to 30 minutes depending on thickness.
- Salt bath heating: Heat to 1010-1149°C (1850-2100°F), soaking for 15 to 30 minutes.
Quenching
Pressurized gas
Achieves the desired hardness and minimizes distortion with a quenching rate of 222°C per minute (400°F per minute) to below 538°C (1000°F), ensuring uniform cooling and stability.
Oil
Heat to 800-850°C (1475-1560°F) and quench in oil. The slower cooling rate reduces cracking risks and preserves toughness while achieving the required hardness.
Salt
Quench in molten salt at 550-600°C (1020-1110°F). Salt quenching provides even cooling and minimizes thermal shock, maintaining consistent hardness while avoiding cracking.
Tempering
After quenching, CPM M4 typically reaches a hardness range of 58-65 HRC (Rockwell C).
Tempering should be done immediately at 538-593°C (1000-1100°F) for 2 hours, then air cool. Tempering below 538°C (1000°F) is not recommended.
Double tempering is required to optimize both toughness and hardness. If austenitizing is done at ≥ 1149°C (2100°F), triple tempering is needed to reduce stresses and enhance toughness.
CPM M4 Steel Product Forms
At SteelPro Group, we provide CPM M4 tool steel in bars, billets, and flat stock, tailored to meet the demands of precision industries. Our products are offered in a range of sizes, ensuring optimal performance for various applications.
| Form | Size Range | Size Range |
| Bars/Rods | Diameter: 6 mm to 150 mm | Diameter: 0.25 in to 6 in |
| Length: 1000 mm to 3000 mm | Length: 40 in to 120 in | |
| Billets | Square/Rectangular: 50 mm x 50 mm to 150 mm x 150 mm | Square/Rectangular: 2 in x 2 in to 6 in x 6 in |
| Length: 1000 mm to 3000 mm | Length: 40 in to 120 in | |
| Flat Stock | Thickness: 3 mm to 75 mm | Thickness: 0.125 in to 3 in |
| Width: 50 mm to 300 mm | Width: 2 in to 12 in | |
| Length: 1000 mm to 3000 mm | Length: 40 in to 120 in |
CPM M4 Steel Applications
- Broaches – For shaping or enlarging holes.
- Gear Hobs – For cutting teeth in gears.
- Thread Rolls – For forming threads on fasteners.
- Milling Cutters – For high-precision milling operations.
- Shaper Cutters – For cutting intricate profiles in shaping machines.
- Shaving Cutters – For gear finishing in high-precision tooth cutting.
- Drills – For drilling through tough materials.
- End Mills – For high-speed machining and intricate milling tasks.
- Forming Tools – Such as punches, dies, and stamping tools.
High-Performance CPM M4 Tool Steel in Every Form You Need
At SteelPro Group, we offer CPM M4 tool steel in bars, billets, and flat stock, with custom sizes to meet your exact needs. Our precision processing and advanced heat treatment ensure optimal hardness, toughness, and wear resistance for longer tool life. We also provide other tool steel products like T1 tool steel sheets, bars, and rounds.
Partner with us for reliable solutions to your toughest challenges. Contact us today to get started!
