M390 Steel (Bohler PM Stainless): Properties and Key Applications
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Table Of Content
M390 steel, also known as Bohler PM Stainless, is a high-performance stainless steel that falls under the category of martensitic stainless steels. It is classified as a powder metallurgy steel, which allows for a fine microstructure and enhanced properties. The primary alloying elements in M390 include chromium (Cr), molybdenum (Mo), vanadium (V), and carbon (C), each contributing significantly to its overall characteristics.
Comprehensive Overview
M390 steel is renowned for its exceptional wear resistance, corrosion resistance, and edge retention, making it a popular choice in high-end knife manufacturing and tooling applications. The high chromium content (around 20%) provides excellent corrosion resistance, while the addition of molybdenum and vanadium enhances its hardness and wear resistance. The fine microstructure achieved through powder metallurgy results in a uniform distribution of carbides, which contributes to its superior mechanical properties.
Advantages of M390 Steel:
- Exceptional Edge Retention: M390 maintains its sharpness longer than many other steels, making it ideal for cutting tools and knives.
- High Corrosion Resistance: The high chromium content provides excellent resistance to rust and corrosion, suitable for use in humid or wet environments.
- Good Toughness: Despite its hardness, M390 exhibits good toughness, reducing the risk of chipping or breaking during use.
Limitations of M390 Steel:
- Difficult to Sharpen: The hardness of M390 can make it challenging to sharpen compared to softer steels.
- Higher Cost: As a premium steel, M390 tends to be more expensive than standard stainless steels.
- Limited Availability: While gaining popularity, M390 may not be as widely available as other more common grades.
Historically, M390 has found its niche in the high-performance market, particularly in custom knives and high-end industrial applications, where its unique properties can be fully utilized.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | S39000 | USA | Closest equivalent to Bohler M390 |
| AISI/SAE | - | USA | Not directly classified under AISI/SAE |
| ASTM | A240 | USA | Standard specification for stainless steel plates |
| EN | 1.4116 | Europe | Similar properties, but may differ in composition |
| JIS | - | Japan | No direct equivalent, but similar grades exist |
M390's closest equivalents, such as 1.4116, may have minor compositional differences that can affect performance, particularly in edge retention and corrosion resistance. It is essential to consider these differences when selecting materials for specific applications.
Key Properties
Chemical Composition
| Element (Symbol and Name) | Percentage Range (%) |
|---|---|
| C (Carbon) | 1.90 - 2.10 |
| Cr (Chromium) | 19.00 - 20.00 |
| Mo (Molybdenum) | 0.80 - 1.20 |
| V (Vanadium) | 0.10 - 0.50 |
| Mn (Manganese) | 0.30 - 0.50 |
| Si (Silicon) | 0.20 - 0.50 |
| P (Phosphorus) | ≤ 0.03 |
| S (Sulfur) | ≤ 0.03 |
The primary alloying elements in M390 steel play crucial roles in defining its properties:
- Chromium (Cr): Provides corrosion resistance and contributes to the formation of a hard, wear-resistant surface.
- Molybdenum (Mo): Enhances hardness and improves resistance to pitting and crevice corrosion.
- Vanadium (V): Increases wear resistance and helps refine the grain structure, contributing to overall toughness.
Mechanical Properties
| Property | Condition/Temper | Typical Value/Range (Metric - SI Units) | Typical Value/Range (Imperial Units) | Reference Standard for Test Method |
|---|---|---|---|---|
| Tensile Strength | Quenched & Tempered | 2000 - 2200 MPa | 290 - 320 ksi | ASTM E8 |
| Yield Strength (0.2% offset) | Quenched & Tempered | 1800 - 2000 MPa | 261 - 290 ksi | ASTM E8 |
| Elongation | Quenched & Tempered | 6 - 8% | 6 - 8% | ASTM E8 |
| Hardness | Quenched & Tempered | 58 - 62 HRC | 58 - 62 HRC | ASTM E18 |
| Impact Strength | Quenched & Tempered | 30 - 40 J at -20°C | 22 - 30 ft-lbf at -4°F | ASTM E23 |
The combination of high tensile and yield strength, along with excellent hardness, makes M390 steel suitable for applications requiring high mechanical loading and structural integrity. Its toughness ensures that it can withstand impact without fracturing, making it ideal for demanding environments.
Physical Properties
| Property | Condition/Temperature | Value (Metric - SI Units) | Value (Imperial Units) |
|---|---|---|---|
| Density | Room Temperature | 7.8 g/cm³ | 0.282 lb/in³ |
| Melting Point | - | 1400 - 1450 °C | 2552 - 2642 °F |
| Thermal Conductivity | Room Temperature | 25 W/m·K | 17.3 BTU·in/(hr·ft²·°F) |
| Specific Heat Capacity | Room Temperature | 500 J/kg·K | 0.119 BTU/lb·°F |
| Electrical Resistivity | Room Temperature | 0.7 µΩ·m | 0.7 µΩ·in |
| Coefficient of Thermal Expansion | Room Temperature | 10.5 x 10⁻⁶ /K | 5.8 x 10⁻⁶ /°F |
Key physical properties such as density and thermal conductivity are significant for applications in high-performance environments. The high melting point indicates that M390 can withstand elevated temperatures without losing structural integrity, making it suitable for applications in heat-intensive processes.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C/°F) | Resistance Rating | Notes |
|---|---|---|---|---|
| Chlorides | 3-10% | 20-60°C (68-140°F) | Good | Risk of pitting corrosion |
| Acids | 10-30% | 20-80°C (68-176°F) | Fair | Susceptible to stress corrosion cracking |
| Alkaline Solutions | 5-20% | 20-60°C (68-140°F) | Good | Generally resistant |
| Atmospheric | - | - | Excellent | Performs well in humid environments |
M390 steel exhibits excellent resistance to atmospheric corrosion and is particularly effective in humid environments. However, it is susceptible to pitting corrosion in chloride-rich environments, which is a critical consideration for applications in marine or coastal areas. Compared to other stainless steels like 440C and S30V, M390 offers superior wear resistance and edge retention, although it may not perform as well in highly acidic environments.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 350 °C | 662 °F | Suitable for prolonged exposure |
| Max Intermittent Service Temp | 400 °C | 752 °F | Short-term exposure without significant degradation |
| Scaling Temperature | 600 °C | 1112 °F | Risk of oxidation at elevated temperatures |
M390 steel maintains its mechanical properties at elevated temperatures, making it suitable for applications that involve heat exposure. However, prolonged exposure to temperatures above 350 °C may lead to oxidation and scaling, which can compromise its performance.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| TIG | ER308L | Argon | Preheat recommended |
| MIG | ER308L | Argon/CO2 | Requires careful control |
| Stick | E308L | - | Not recommended for thick sections |
M390 steel can be welded, but care must be taken to avoid cracking. Preheating is often recommended to reduce the risk of thermal shock. Post-weld heat treatment may also be necessary to relieve stresses and restore toughness.
Machinability
| Machining Parameter | M390 Steel | AISI 1212 | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 50% | 100% | M390 is more challenging to machine |
| Typical Cutting Speed | 20-30 m/min | 50-70 m/min | Use carbide tools for best results |
M390 steel is more challenging to machine than lower alloy steels due to its hardness. Utilizing carbide tooling and appropriate cutting speeds can improve machinability.
Formability
M390 steel exhibits limited formability due to its high hardness. Cold forming is generally not recommended, while hot forming can be performed with care. The work hardening effect can make bending and shaping difficult, requiring specialized techniques.
Heat Treatment
| Treatment Process | Temperature Range (°C/°F) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
|---|---|---|---|---|
| Annealing | 800 - 900 °C (1472 - 1652 °F) | 1-2 hours | Air or Oil | Reduce hardness, improve toughness |
| Hardening | 1000 - 1100 °C (1832 - 2012 °F) | 30-60 minutes | Oil or Air | Increase hardness and strength |
| Tempering | 200 - 600 °C (392 - 1112 °F) | 1 hour | Air | Reduce brittleness, enhance toughness |
The heat treatment processes for M390 steel involve austenitizing followed by quenching and tempering. These processes result in a fine microstructure that enhances hardness and wear resistance while maintaining toughness.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection (Brief) |
|---|---|---|---|
| Knife Manufacturing | High-end kitchen knives | Excellent edge retention, corrosion resistance | Ideal for culinary applications |
| Tooling | Precision cutting tools | High hardness, wear resistance | Suitable for demanding machining |
| Medical Devices | Surgical instruments | Corrosion resistance, biocompatibility | Essential for hygiene and durability |
| Automotive | High-performance components | Toughness, fatigue resistance | Critical for safety and reliability |
M390 steel is chosen for applications requiring high performance and durability. Its exceptional edge retention makes it a favorite among knife makers, while its corrosion resistance is vital in medical and automotive applications.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | M390 Steel | 440C Steel | S30V Steel | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High hardness | Moderate hardness | High toughness | M390 offers superior wear resistance |
| Key Corrosion Aspect | Excellent | Good | Good | M390 excels in humid environments |
| Weldability | Moderate | Good | Moderate | M390 requires careful welding techniques |
| Machinability | Challenging | Good | Moderate | M390 is harder to machine than 440C |
| Formability | Limited | Good | Moderate | M390 is less formable due to hardness |
| Approx. Relative Cost | High | Moderate | Moderate | M390 is a premium steel with a higher cost |
| Typical Availability | Moderate | High | High | M390 may not be as readily available |
When selecting M390 steel for a specific application, it is essential to consider its mechanical properties, corrosion resistance, and fabrication challenges. While it offers superior performance in many areas, its higher cost and limited availability may influence the decision-making process. Understanding the trade-offs between M390 and alternative grades like 440C and S30V can help in making informed choices tailored to specific engineering needs.