Introduction to M42 High Speed Steel (HSS) 

When machining tough materials like titanium or high-strength superalloys, standard tool steels often fail. They overheat, lose their edge, or chip under pressure. This is where M42 high speed steel excels. 

M42 is a molybdenum-series high-speed steel with a significant addition of Cobalt (approximately 8%). It is engineered for superior hardness and hot hardness compared to conventional high-speed steels. It is often referred to as a "super high speed steel" because it maintains its cutting edge even at the elevated temperatures generated during heavy-duty machining. 

For industrial procurement engineers, M42 steel represents reliability. Whether you are manufacturing aerospace components or sourcing durable cutting tools for automotive production, M42 provides the balance of wear resistance and toughness needed to keep production lines moving without constant tool changes. 

What is M42 High Speed Steel? 

M42 High Speed Steel is a premium cobalt-molybdenum tool steel designed for high-performance machining. Characterized by its high hardness (achieving 68-70 HRC after heat treatment) and excellent red hardness, it is the material of choice for cutting tools that must withstand extreme heat and abrasion. It is widely used in drills, end mills, and saws for machining difficult-to-cut metals.  

Chemical Composition of M42 HSS 

The exceptional performance of M42 HSS composition comes directly from its specific alloying elements. The high Cobalt content is the differentiator here. It allows the steel to resist softening at high temperatures, a property known as "red hardness." 

Here is the typical chemical breakdown for M42 steel: 

Mechanical & Physical Properties 

Understanding M42 steel properties is essential for selecting the right material for your application. M42 is not just hard; it is tough enough to resist chipping, which is a common failure mode in lesser steels. 

Key Mechanical Properties Table 

Engineers choose M42 tool steel because it does not fail catastrophically. Even when machining pre-hardened steels, the edge wears predictably rather than fracturing, allowing for planned tool maintenance rather than emergency stops. 

Heat Treatment Process 

To achieve the target hardness of 68-70 HRC, M42 must undergo a precise heat treatment cycle. Improper treatment results in brittle tools or soft edges. 

1. Annealing 

Annealing is performed to soften the steel for machining before the final hardening. 

• Temperature: 800°C – 875°C. 
• Cooling: Slow furnace cooling at 4°C per hour until 540°C, then air cool. 

Result: Hardness max 269 HB. 

2. Hardening (Austenitizing) 

This step dissolves carbides into the matrix to prepare for martensite formation. 

• Preheat: Two steps: 450-500°C, then 850-900°C. 
• Austenitizing Temp: 1160°C – 1180°C. 
• Quench: Oil, salt bath (540-560°C), or vacuum. 

3. Tempering 

Tempering is critical to transform retained austenite and relieve internal stresses. 

• Process: Triple tempering is mandatory. 
• Temperature: 540°C – 560°C. 
• Duration: At least 2 hours per temper cycle. 
• Target Hardness: 66 – 69 HRC. 

Advantages of M42 vs. M2 / M35 / T1 Steels 

Comparing M42 to other HSS grades helps clarify why it commands a premium in the market. 

• Vs. M2 HSS: M2 is the "standard" industry HSS. It lacks cobalt. M42 has significantly higher hot hardness and wear resistance. If your tool burns out quickly with M2, M42 is the logical upgrade. 
• Vs. M35 HSS: M35 contains about 5% Cobalt. M42 contains 8% Cobalt. While M35 is good, M42 steel applications often involve harder workpieces where that extra 3% cobalt provides a crucial edge in thermal stability. 
• Vs. T1 (Tungsten HSS): T1 is an older tungsten-based grade. M42 (Molybdenum-based) generally offers better toughness and grindability than T-series steels while matching their hardness. 

Why Upgrade? 
If you are machining exotic alloys, stainless steels, or heat-treated metals, standard HSS cannot hold an edge. M42 provides the "red hardness" necessary to cut hot without losing temper. 

M42 Steel Applications 

Manufacturers utilize M42 wherever standard tooling fails. It is the backbone of the cutting tool industry. 

1. Cutting Tools 

• Twist Drills & Taps: For drilling high-tensile steels. 
• End Mills: Used extensively in CNC milling of aerospace components. 
• Broaches & Reamers: Precision finishing tools that require edge retention. 

2. Industrial Saws 

• Band Saw Blades: The teeth of bi-metal band saw blades are frequently made from M42 wire electron-beam welded to a flexible backing. This allows the saw to cut through solid steel bars. 
• 3. Forming Tools 
• Punches & Dies: For cold forming operations where high compressive strength is required. 

4. Aerospace & Power Generation 

Machining turbine blades, fasteners, and engine components made from Inconel, Waspaloy, and Titanium alloys. 

Looking to source premium M42 High Speed Steel for your cutting tools or industrial applications? Explore our M42 product page at Nifty Alloys LLC for detailed specifications and availability. if your project requires different specifications or base materials for these applications. 

Machinability & Workability 

While M42 is designed to cut other metals, it must also be machined itself during tool production. 

• Grinding: M42 is "grindable," but its high hardness requires specific grinding wheels (often CBN - Cubic Boron Nitride) to avoid burning the surface. 
• EDM (Electrical Discharge Machining): Can be cut via EDM, but the recast white layer must be removed to prevent surface cracking. 
• Forging: Must be forged between 1050°C and 1150°C. Never forge below 900°C to avoid cracking. Slow cooling after forging is essential. 

Why Manufacturers Choose M42 HSS 

The decision to buy M42 steel usually comes down to Cost Per Part (CPP). Although M42 is more expensive than M2 or M35 initially: 

• Reduced Downtime: Fewer tool changes mean machines run longer. 
• Higher Speeds: M42 handles higher cutting speeds, increasing production rates. 
• Consistency: It provides predictable wear patterns, essential for automated CNC manufacturing. 
• Versatility: One grade can often handle a wide range of materials, simplifying inventory. 
•  

Corrosion Resistance Characteristics 

It is important to note that M42 high speed steel is not a stainless steel. 

• Oxidation: It will rust if exposed to moisture without protection. 
• Protection: Tools made from M42 are often coated (TiN, TiAlN) not just for hardness, but to provide a barrier against oxidation. 
• Storage: Raw bars or finished tools should be stored in a dry environment, preferably with a light oil coating. 

If corrosion resistance is a primary requirement for your application (rather than cutting ability), you might consider exploring specific martensitic stainless steels instead. 

 Real-World Performance Insights 

In practical scenarios, M42 steel shines in "interrupted cuts." 

Imagine a milling operation on a gear. The tool enters and exits the material repeatedly. This creates thermal shock—rapid heating and cooling. Carbide tools often chip under these conditions because they are brittle. M42, having superior toughness compared to carbide, absorbs this shock without fracturing. 

For M42 high speed steel suppliers, the demand is highest from machine shops dealing with 304/316 stainless steel and pre-hardened 4140 steel. Operators report that M42 drills can drill 3x to 4x more holes in 304 stainless compared to standard black oxide HSS bits. 

Buying Guide: How to Choose M42 Tools or Bars 

When looking to buy M42 steel, procurement officers should verify the following: 

• Mill Test Reports (MTRs): Ensure the Cobalt content is actually ~8%. Cheaper "cobalt" drills sometimes only have 5% (M35) but are marketed vaguely. 
• Surface Condition: For round bars, specify if you need "peeled and polished" (free of decarburization) or "black bar" (requires machining). 
• Hardness State: Confirm if you are buying annealed (soft, machinable) or pre-hardened blanks (ready for grinding). 
• Standard Compliance: Look for compliance with ASTM A600 (standard specification for tool steel). 

At Nifty Alloys LLC, we ensure every batch meets strict metallurgical standards, providing the reliability your supply chain demands. 

Conclusion 

M42 high speed steel remains a critical material in modern manufacturing. Its unique blend of Cobalt, Molybdenum, and Tungsten creates a tool steel that bridges the gap between standard HSS and expensive Carbide tooling. For applications requiring high hot hardness, excellent wear resistance, and sufficient toughness to avoid chipping, M42 is the industry standard. 

Whether you are cutting superalloys or managing a high-volume production line, choosing the right M42 tool steel ensures efficiency and precision.