How to Buy Exotic & Refractory Metals Part 2: Conditions and Properties of Metal

properties of metal and surface conditions

Helping Specialty Metals Buyers with the Purchasing Process

The complexity of exotic and refractory metals and the applications that depend on them mean the purchasing process can be complex. We want to make it easier for you! That’s why last week, we introduced a three-part series on how to buy exotic and refractory metals. This is part two, focused on the conditions and properties of metal.

As a reminder, the series will culminate in a handy downloadable guide that aims to simplify, streamline, and optimize your specification and purchase journey by covering:

Let’s dig into the properties of metal, conditions and surface conditions, and how they relate to the purchasing process.

Essential Properties of Metal Explained

The properties of metal encompass specific characteristics that define how metals behave under various conditions. These characteristics are categorized as physical, chemical, mechanical, electrical, and thermal properties. Here’s a brief overview of what falls under each category of metal properties:

Physical Properties: The important characteristics of density (mass per unit volume), melting point (the temperature where it changes from solid to liquid), and color (visual appearance) fall into the category of physical properties. Our customers don’t worry too much about color, but density and melting point are mission-critical in their specifications.

Chemical Properties: Chemical properties include the very important characteristics of corrosion resistance (ability to resist oxidation and degradation) and reactivity (how easily it reacts with other substances).

Mechanical Properties: This category covers a lot. It includes hardness (resistance to scratching, cutting, or deformation), tensile strength (maximum stress before breaking), ductility (ability to be drawn into wires), malleability (ability to be hammered or rolled), and toughness (ability to absorb energy and deform without fracturing).

Electrical Properties: This category is all about electrical conductivity, or the ability of a metal to conduct electric current. Sometimes that’s important to have, other times it’s important to avoid, depending on your application of course!

Thermal Properties: Thermal properties of metal include thermal conductivity (ability to conduct heat) and thermal expansion (the extent to which it expands upon heating). These properties tend to be ones you need to account for in your application.

Magnetic Properties: Finally, as touched on above, magnetic properties of metal (ability to be magnetized or attract a magnet) can be a very important factor in specifications both in the machining process and for the end-use application.

These properties define how metals behave in different environments and applications, allowing metallurgists to select the appropriate metal for specific purposes. That selection process does not stop with the properties listed above. It also considers elements like conditions, surface conditions, and tolerances.

Metal Conditions Defined

Although properties of metal are inherent, they are not fixed. The metal undergoes several treatments to achieve certain states or conditions that influence the properties. Understanding the interplay between the properties and the conditions listed below allows engineers and metallurgists to design metals that meet specific performance requirements, enhancing the functionality and longevity of metal components in your applications. Below are the key conditions that are important in the specification process.

Annealed: Heated to a specific temperature and then cooled slowly to soften the metal, improve ductility, and relieve internal stresses.

Centerless Ground: Ground without a center, resulting in a very smooth and precise surface finish, often used for rods and shafts.

Cold-Rolled: Rolled at room temperature, resulting in a smoother surface finish and increased strength through strain hardening.

Drawn: Pulled through a die to reduce diameter and increase length, improving surface finish and mechanical properties. Often used for wire.

Forged: Shaped by compressive forces, typically using a hammer or press, resulting in improved mechanical properties and structural integrity. Typically performed at elevated temperatures.

Heat-Treated: Subjected to a specific heat treatment process, such as quenching, tempering, or aging, to alter its mechanical properties like hardness, strength, and ductility.

Hot-Rolled: Rolled at high temperatures, typically above the recrystallization temperature, which makes the metal easier to shape and form.

Normalized: Heated to a high temperature and then air-cooled to refine the grain structure and improve toughness.

Quenched: Rapidly cooled from a high temperature to harden the metal by locking in a specific microstructure.

Stress-Relieved: Heated to a temperature below the recrystallization point and then cooled to reduce residual stresses from prior processing without significantly altering the metal’s structure.

Tempered: Heated to a temperature below the critical point after quenching to reduce brittleness while retaining hardness. Tempers range from fully hard to fully annealed.

Surface Conditions

Surface conditions can also vary and must be included in the specification. Here are the most important surface conditions to know:
Anodized: Electrochemically treated to form a thick, protective oxide layer, often used for aluminum to enhance corrosion resistance and dye retention.

As-Cast: Resulting directly from the casting process, often characterized by a rough texture and potential surface impurities.

As-Forged: Resulting from the forging process, typically exhibiting scale and roughness due to high-temperature deformation.
As-Rolled: Resulting directly from the rolling process, typically characterized by a relatively smooth finish but with visible scale and minor surface irregularities from the rolling mill.

Blasted: Treated by abrasive blasting (e.g., sandblasting, bead blasting) to remove scale, rust, and surface contaminants, providing a clean, roughened surface ideal for further coating or finishing.

Brushed: Finished with a brushed appearance, characterized by fine parallel lines created by brushing with an abrasive.

Coated: Covered with a protective or decorative layer, which can include paints, polymers, or other metal coatings to improve resistance to environmental factors or wear.

Electropolished: Smoothed and brightened through an electrochemical process that removes a thin layer of material to enhance corrosion resistance and cleanliness.

Etched: Chemically or electrochemically treated to create patterns or textures, often used for decorative or functional purposes.

Extruded: Resulting from the extrusion process, where the metal is forced through a die to create long shapes with a consistent cross-section, typically exhibiting a smooth finish with directional lines along the length of the extrusion.

Ground: Finished using abrasive techniques to achieve a fine surface finish, improving dimensional accuracy and surface texture.

Machined: Finished through mechanical cutting processes, providing a smooth and precise texture with visible tool marks.

Passivated: Treated to remove surface contamination and enhance the formation of a protective oxide layer, improving corrosion resistance. Primarily used on stainless steels.

Plated: Coated with a thin layer of another metal (such as chromium or nickel) through electroplating or other deposition methods to enhance properties like corrosion resistance or appearance.

Polished: Treated to achieve a high level of smoothness and shine, often used for aesthetic purposes or to reduce friction.

Sanded: Smoothed using abrasive materials such as sandpaper, resulting in a fine, uniform texture free from significant surface imperfections.

Exotic and Refractory Metal Tolerances

Understanding tolerances is another crucial component when buying exotic and refractory metals. Here are definitions for key tolerances:

Concentricity: Specifies the allowable deviation of the center of a cylindrical feature from a common axis, ensuring uniform wall thickness and balance.

Diameter: The permissible variation in cylindrical components’ diameter ensures that the parts fit correctly within their intended applications.

Flatness: The maximum allowable deviation from a perfectly flat surface is critical for components requiring tight contact with other surfaces.

Roundness: The allowable variation in the roundness of a cylindrical component, which affects the part’s ability to rotate smoothly and fit properly.

Surface Finish: The acceptable roughness or smoothness of a surface, which affects the material’s performance, aesthetics, and wear characteristics.

Thickness: The allowable variation in the material’s thickness from its specified dimension, ensuring uniformity and consistency across the entire surface.

These tolerances are essential in ensuring the precise manufacturing and performance of exotic and refractory metal components, particularly in high-precision applications like aerospace, medical devices, and high-temperature industrial processes. Understanding and adhering to these tolerances helps achieve metal parts’ desired fit, function, and longevity.

The Easiest Thing is to Talk to Our Pros About How to Buy

One quick way to cut to the chase on the standards is to visit our materials pages. There, you will find the applicable standards for the properties of the metal. We also recommend reviewing our Compliance & Quality page for valuable links and information.

Contact us to discuss how to buy specialty, refractory, and exotic metals or request a quote to cut right to the chase. Sign up to receive our monthly newsletter, and join the conversation on LinkedIn.

We compiled this information and developed this article meticulously under the watchful eye of our Chief Metallurgist, Bob Desberg. Except for our Chief Morale Officer Bonzo, who had no paw in this article, we are human. If you see anything missing or incorrect, please advise us and we’ll be sure to update or correct it!