Why is High-Performance Alloy Tool Steel Better?

Overcoming difficulties in the metallographic preparation of high alloy tool steels

Avoiding thermal damage
As heat treatability of high alloy tool steels is a quality criterion, thermal influence during cutting has to be avoided in order to ensure a true representation of the actual microstructure. When cutting larger sections, this preparation step has to be carried out with great care.

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Fig. 2: Thermal damage due to faulty cutting conditions 

Preserving carbides and inclusions
The main difficulty during grinding and polishing of high alloy tool steels is ensuring that carbides and non-metallic inclusions are retained. In cold working tool steels, the primary carbides are very large and fracture easily during grinding. In fully annealed conditions, secondary carbides are very fine and can easily be pulled out from the softer matrix.

Fig. 3: Fractured primary carbides (Mag: 200x) 

Large volume processing of high alloy tool steels
For quality control teams working within high alloy tool steel production, processing large sample volumes requires a very efficient organization of the workflow, automatic equipment and standard procedures.

Recommendations for the grinding and polishing of high alloy tool steel

When preparing high alloy tool steels for metallographic analysis, the form, size and amount of carbides must be accurately represented. In addition, non-metallic inclusions must be retained in an undeformed matrix.

• Large volumes are best processed on fully automatic grinding and polishing machines, which guarantee a fast and efficient workflow and reproducible results.
• Tool steels are hard. Therefore, fine grinding with diamond is more efficient and economical than grinding with silicon carbide foil.
• Sometimes a final oxide polish can be useful for contrasting and identifying carbides.

Table 1: Preparation method for high alloy tool steel on large automatic equipment.
DiaPro diamond suspensions can be substituted with DP-Diamond suspension P as follows: For FG with 9 μm, DP 2 with 1 μm used with DP-Blue/Green lubricant. 

Table 2: Preparation method for high alloy tool steel on table-top semi-automatic equipment.
DiaPro diamond suspensions can be substituted with DP-Diamond suspension P as follows: For FG with 9 μm, DP 1 with 3 μm, DP 2 with 1 μm used with DP-Blue/Green lubricant.

Find out more

• Get more knowledge, expertise and insight in our grinding and polishing section.
• See our range of grinding and polishing machines and equipment.
• Get consumables and accessories for metallographic grinding and polishing.

Recommendations for the etching of high alloy tool steel

High alloy tool steel samples are usually initially examined unetched to identify inclusions and carbide size and formation. To reveal the microstructure, various concentrations of nital or picral are used.

For example, to show the carbide distribution in cold work steel, a 10% nital ensures the matrix is dark and the white primary carbides stand out. For fine globular pearlite, a brief submersion into picric acid followed by 2% nital gives a good contrast and avoids staining.

Nital etching solution:
100 ml ethanol
2-10 ml nitric acid (Caution: Do not exceed 10% of the solution as it becomes explosive!)

Picral etching solution:
100 ml ethanol
1-5 ml hydrochloric acid
1-4 g picric acid


Fig 5: Cold work tool steel etched with 10% nital, primary carbides stand out white

Fig. 6: Hot work tool steel etched with picral and nital, globular pearlite (Mag: 500x)

Classification

Based on DIN EN -1, high-alloy steel is marked with an X to distinguish it from alloy steels. The X is followed by details of the chemical composition, such as the carbon content and other alloying elements that influence the properties of the steel. For example, the EN abbreviation for stainless steel 1. is “X5CrNi18-10”. This is a high-alloy steel with a chromium content of 18% and a nickel content of 10%.

Composition

Alloying Elements

The composition of high-alloy steel is characterized by a significant presence of alloying elements, each contributing to the steel’s unique properties:

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• Carbon (C): Though not a traditional alloying element, carbon plays a crucial role in steel. It enhances hardness and strength but can reduce ductility if present in higher quantities. In high-alloy steel, the carbon content varies based on the desired properties but is usually balanced to maintain a good mix of strength, hardness, and toughness.
• Chromium (Cr): Often above 10%, chromium enhances corrosion resistance and hardness. It is crucial in the formation of stainless steel, where its presence allows for the formation of a protective oxide layer.
• Nickel (Ni): Improves toughness, strength, and resistance to oxidation. Nickel alloys also offer enhanced ductility.
• Molybdenum (Mo): Increases strength and high-temperature stability. It also helps in preventing corrosion and maintaining strength at high temperatures.
• Others: Elements like vanadium, tungsten, and cobalt may also be present, each adding specific properties to the steel.

Significance of Alloying Elements

• Carbon: Provides the basic framework for steel’s mechanical properties. Its content is carefully controlled to provide a balance between hardness and ductility.
• Chromium: Forms a passivation layer of chromium oxide on the surface, which helps in preventing further corrosion.
• Nickel: Adds to the overall strength and maintains the material’s robustness under varying temperature conditions.
• Molybdenum: Its main role is to enhance the material’s strength, especially at higher temperatures, making it suitable for high-stress applications.

These elements, in combination, allow high-alloy steel to achieve a balance of strength, toughness, and corrosion resistance, making it a versatile material for various demanding applications.

Types of High-Alloy Steel

Common Varieties

High-alloy steel comes in various types, each suited for specific applications:

1. Stainless Steel: Known for its exceptional corrosion resistance, stainless steel contains a significant amount of chromium, often over 10%. It’s used in everything from kitchen utensils to medical equipment.
2. Tool Steel: Characterized by its hardness and durability, tool steel is ideal for cutting and drilling equipment. It often includes elements like tungsten and vanadium.
3. Others: This category includes specialized steels like maraging steel, known for its strength and toughness, and Hadfield’s manganese steel, recognized for its high impact strength.

Key Characteristics

Each type of high-alloy steel offers unique properties:

• Stainless Steel: Corrosion resistance, aesthetic appeal, and low maintenance.
• Tool Steel: Wear resistance, hardness, and ability to retain a sharp edge.
• Others: Specific characteristics like extreme toughness or high wear resistance.

Properties

High-alloy steel exhibits a range of properties that make it suitable for various applications:

1. Strength and HardnessThese steels are known for their high strength-to-weight ratio and superior hardness. This makes them ideal for applications requiring durability and resistance to deformation under stress.
2. Corrosion ResistanceThanks to elements like chromium, high-alloy steels offer excellent resistance to corrosion and oxidation, making them suitable for use in harsh environmental conditions.
3. Application-Specific PropertiesDepending on the alloying elements and heat treatment, these steels can also exhibit properties like high-temperature strength, wear resistance, and magnetic permeability, broadening their range of applications.

Applications

Common Uses

High-alloy steel finds extensive use in several sectors due to its superior properties:

1. Tools and Machinery: Includes cutting tools, drills, molds, and dies, leveraging its hardness and wear resistance.
2. Aerospace and Automotive: Used in components that require strength and durability under high stress and temperature conditions.
3. Construction and Infrastructure: Utilized in structures demanding longevity and resistance to environmental factors.
4. Medical Equipment: Surgical tools and implants benefit from the corrosion resistance and strength of certain high-alloy steels.

Specific Products

Notable products made from high-alloy steel include:

• Stainless steel kitchenware: Utensils, cookware, and appliances.
• Surgical instruments: Scalpels, forceps, and implants.
• Automotive parts: Engine components, exhaust systems, and gears.

Advantages and Limitations

Advantages

High-alloy steel offers several benefits:

• Enhanced Durability: Resists wear and deformation, extending the life of components.
• Corrosion Resistance: Ideal for applications exposed to corrosive environments.
• Versatility: Customizable properties through varied compositions and heat treatments.

Limitations

However, there are certain limitations:

• Cost: Generally more expensive than low-alloy or carbon steels due to the higher content of costly alloying elements.
• Machinability: Some types may be challenging to machine due to their hardness.
• Weight: Certain high-alloy steels can be heavier, impacting their suitability in weight-sensitive applications.

Enhance Your High-Alloy Steel with Specialized Treatments

Advancing the properties of high alloy steels through specialized treatments can lead to significant performance enhancements. Explore these cutting-edge services to understand how they can benefit your applications:

1. Boronizing (BOROCOAT®): A thermochemical process that diffuses boron into the material surface, creating hard, wear-resistant boride coatings. This treatment is known for its high layer hardness, significant improvement in adhesion, resistance to abrasive and adhesive wear, and high thermal resistance. Learn More about Boronizing. 
2. Hardening of Stainless Steel (BORINOX®): A patented low-temperature process for surface hardening of stainless steel and nickel-based alloys, enhancing hardness and wear properties without affecting corrosion resistance. Discover BORINOX® Hardening. 
3. Nickel Plating (NICKELCOAT®): An electroless nickel procedure that offers high corrosion and wear protection, applicable to a range of workpiece geometries. Explore NICKELCOAT® Nickel Plating. 
4. Nitriding / Nitrocarburizing: A heat treatment process that uses nitrogen to harden the surface of steel, enhancing wear resistance, fatigue strength, and corrosion resistance. Find Out More about Nitriding and Nitrocarburizing. 

Each of these treatments can significantly improve the properties of high-alloy steel, making them ideal for a wide range of industrial applications.

For more information, please visit Hiperco 50A alloy supplier.