Essential Metal Processing Terminology
If you take a look at the products available from our online store you’ll see many references to various types of steel, other metals such as zinc and nickel alongside metal processes such as hardening and tempering. This terminology can be bewildering so in this post we aim to provide clear and understandable descriptions and definitions that will help you understand the attributes of the high quality security products we provide to our clients.
Almost everything we use in our day to day lives has something to do with metals of one sort or another. A variety of metals are used in products ranging from jeans to ball-point pens. Even items that don’t contain metal will have relied on metal based production lines, metal ships to transport the products and metal vans to deliver them. When shopping for products such as padlocks, bolts, screws and hasps it’s useful to have a basic understanding of relevant metal-related terminology and what it means.
Types of Steel
Steel is basically an alloy of iron and a small amount of carbon. Pure iron is quite ductile (bendy) due to its crystalline structure which makes it soft and easily formed. Steel includes carbon and other elements mixed with iron which act as hardening agents to make steel far less ductile than pure iron.
Mild steel is also known as ‘low carbon steel’ because it typically has only around 0.05% to 0.25% of carbon. High carbon steels typically have between around 0.3% and 2% carbon. Higher carbon content would be classified as cast iron.
Mild steel is not a steel alloy, which means it doesn’t contain significant amounts of elements other than iron and carbon. Low carbon content means that mild steel is more malleable, ductile and weldable than high carbon steels. But the low carbon content also means that mild steel is more difficult to harden using heating and quenching techniques.
Stainless steel is used extensively in a variety of products sold by Insight Security. It’s an alloy of iron combined with a minimum of around 10.5% - 11% chromium which prevents the iron from rusting (making it stainless) and makes it more heat-resistant.
There are a number of stainless steel types that include varying quantities of carbon, silicon and manganese along with additional elements such as molybdenum and nickel. These are included to enhance various properties such as improved resistance to corrosion, tensile strength and and hardening capability.
Tool steel refers to various forms of high-hardness steel that is resistant to abrasion and highly suitable for tooling. The inclusion of various amounts of tungsten, molybdenum, cobalt and vanadium increases the heat resistance and durability of the metal making it ideal for cutting and drilling tool applications.
Engineering steels are formulated to provide specific levels of strength, toughness, elasticity, ductility and fatigue resistance. They may also be required to be resistant to high and low temperatures along with corrosive and aggressive environments. These properties are achieved through the inclusion of small amounts of one or more alloying elements such as silicon, nickel, titanium, copper, chromium, manganese and aluminum.
Alloy steel includes various other alloyed elements that have an impact on the material’s mechanical properties. For example, chromium supports hardness, toughness and wear resistance while vanadium increases strength, toughness and shock resistance while improving corrosion resistance. Quantities of these alloyed elements vary between 1% and 50% by weight.
What is Metal Hardening?
Metal hardening refers to various processes used to harden metals. Hardness refers to a material’s ability to withstand localised, permanent deformation, also called plastic deformation. Some metals, such as tungsten, are naturally very hard making them suitable for use as alloys in tool steels.
There are 3 basic types of hardness:
- Indentation hardness: This refers to a materials resistance to permanent deformation due to continuous loading.
- Scratch hardness: This refers to a materials resistance to surface scratching.
- Rebound or dynamic hardness: Rebound hardness relates more to a materials elastic hardness than to its plastic hardness. It’s a measure of a material’s ability to return to the shape it was before impact.
Metal Hardening Processes
All metal hardening processes involve 3 main stages:
During the heating phase, metals may be heated to extremely high temperatures which can change the internal chemical composition of the metal. For example, a blacksmith will heat a piece of metal to a temperature at which it becomes more malleable, allowing it to be hammered into specific shapes.
The second phase of soaking doesn’t mean placing the metal in a hot, soapy bath. It refers to the practice of allowing the metal to “soak” for a period of time at the temperature to which it has been heated. The specific time period required varies but generally this needs to be long enough to be certain that all areas of the metal have achieved the desired temperature.
The third and final stage of the metal hardening process is cooling it. Once a metal object has been heated to a required temperature and soaked long enough to be sure that the heat has penetrated to all areas it is then cooled. The cooling process and the rate at which a metal object is cooled influences the resulting hardness. The term ‘quenching’ is used to refer to the process of rapidly cooling a piece of metal in either water, oil or air to achieve specific changes in the material properties.
What is Case Hardening?
Case hardening or ‘surface hardening’ refers to the process of hardening the surface of a metal item to form what is effectively a hard case around the metal core. The thin, surface layer of hardened metal is far more resistant to abrasion and sawing thus providing a resilient, protective ‘case’ around the metal object.
Case hardening is generally carried out after metal items have been formed into their final shapes as, once hardened, it’s not easy to rework case hardened objects. An important application of case hardening is in situations where metal objects are subject to abrasion and possibly attack (such as security chains and padlock shackles) with abrasive tools (angle grinders). The case-hardened surface provides excellent attack resistance while the ductile metal core will absorb impact and tensile stress without fracturing.
Good examples of where case-hardening is effectively used are the high security chains sold from our store. Case hardened chain links provide protection against saw and grinder attacks.
What is Tempering?
Tempering metal will typically alter its ductility and hardness properties. Tempering is generally carried out after a hardening process to achieve a balance between hardness and strength. When steel is hardened it can become brittle but when its not hardened, steel may not be adequately resistant to abrasion or strong enough for its intended use. Tempering can achieve a balance between these properties, improve the materials ability to be machined and reformed and reduce the possibility of cracking or failure due to internal stresses.
An example of a tempered metal product is the professional socket set available from our store. Like a lot of high quality tools, this socket set is manufactured from strong chrome vanadium steel which has been hardened and tempered before being coated with a phosphate finish for added corrosion resistance.
What is Brittling or Embrittlement?
The term ‘embrittlement’ refers to a significant reduction in a metal’s ductility that can make it brittle. During various metal working processes such as heat treatments, electroplating and cleaning, hydrogen can be unintentionally diffused into the metal object making it brittle and embrittled metal objects are susceptible to cracking.
De-embrittlement refers to processes used to remove the brittleness that may have been introduced due to preceding metal processes. A technique that is typically used is to bake embrittled objects for prolonged periods at specific temperatures in order to remove absorbed hydrogen. An example of where this process is used is on screws, bolts and fastenings which have been chemically or electrochemically coated. The coating process will often mean that the metal of the fastener absorbs hydrogen, making it brittle and susceptible to failure. The de-embrittlement process results in far stronger fastenings which are less likely to fracture and fail.
Metal plating refers to the process of adding an outer metal coating to metal objects. Metal plating is typically used to provide a protective outer coat that inhibits corrosion but metal plating is also commonly used to enhance appearances, for example in gold-plated jewellery. Commonly used plating metals include: nickel, copper, zinc, chromium, gold and silver.
Electroplating is the process that’s typically used wherein an item to be plated is placed in a bath of acid that contains the plating metal in oxide form. The item being plated forms the cathode and the anode is often formed using a block of the metal that is being plated. Electrolysis causes the deposition of the plating metal on the surface of the item that’s being plated.
A good example of how metal plating is used is our Hexagon head anchor screw bolts which are zinc plated to provide corrosion resistance.
The process of galvanisation applies a protective zinc coating to iron or steel to protect it from corrosion. The most commonly used technique is called hot-dip galvanisation wherein the item to be galvanised is dipped into a bath of molten zinc.
Metal items are generally galvanised after having been formed into their final shape. Galvanised steel is extremely durable and versatile and our galvanised products will provide around 15 to 20 years of reliable service.
A good example of a galvanised metal product is our Galvanised steel mounting post for Vialux mirrors. Galvanisation provides protection from the rigours of our British weather enabling the post to provide many years of reliable service.
If you need help in finding the products and solutions you need, please give us a call on 01273 475500. We are always happy to help.
This message was added on Thursday 15th October 2020