When classifying metals, focusing on a particular property is most often used as a way to divide them into two groups. Is this metal ductile or non-ductile? Is it magnetic or not?
When it comes to ferrous metals, one basic quality determines the groups: whether the metal contains iron. If iron makes up a large percentage of its composition, the metal is considered to be ferrous. If it contains no iron, or just trace amounts of it, it will be labeled a non-ferrous metal.
Beyond that, it becomes more difficult to apply general labels on the groups and the metals’ properties. While ferrous metals can range from iron itself to stainless steel, the alloying elements greatly affect the metal’s characteristics. For example, most ferrous metals are magnetic. But austenitic stainless steel is not, due to the high levels of nickel added to the steel for alloying. The nickel allows the steel to form in a crystal structure that is mostly austenite – and austenite is not magnetic.
So although it can be difficult to generalize about all ferrous metals as a group, there are some general characteristics that can be made about them. Ferrous metals are very hard and strong, especially in comparison to non-ferrous ones such as tin or copper. They’re vulnerable to rust due to their high percentage of iron, unless given corrosion resistance through alloying elements or protective coatings. And they’re usually (but not always) magnetic, which makes them very useful for motor and electrical applications.
The most common categories of ferrous metals include:
Carbon steel: there’s certainly no question of this being a ferrous metal, with over 90% of its composition being made up of iron. It is very hard and can keep a sharp edge, making it well-suited for mechanical uses such as drill bits and blades.
Cast iron: this metal is exceptionally hard due to its high levels of carbon, but the carbon also makes it quite brittle. For this reason, cast iron is now primarily used for smaller machine components or cookware.
Stainless steel: the most commonly used type of ferrous metals, especially for consumer goods. The addition of chromium is what makes a steel stainless, and gives it good corrosion resistance. And it’s magnetic, which is why you can stick magnetics on your refrigerator.
Alloy steel: the properties of this group of ferrous metals can vary much more widely than the others, since the alloy is specifically formulated for a particular purpose. So while alloy steels are ferrous, the added elements allows the metal to be tailored for more strength, ductility, hardness or other property.
When it comes to metal aging, the simplest way to understand the process is in terms of heat. In general, if a metal has the ability to withstand high temperatures during heat treatment, then it can be aged. For alloys containing aluminum, copper, magnesium or nickel, aging is the principal method of strengthening the finished product.
When metal is exposed to heat, any impurities (precipitates) contained within it begin to form on the surface. These precipitates help to prevent dislocations, which are defects in the metal’s crystal structure. Because dislocations are a primary cause of metal weakness, this means the precipitates are acting as reinforcements to strengthen the metal. Aging it has made the material stronger, more stable, and more resistant. So it’s clear why accelerating these changes through artificial aging is a popular choice!
The basic process of precipitation hardening, or age-hardening, consists of three steps:
Solution treatment: Also known as “solutionizing”, this involves heating a metal alloy to extremely high temperatures. This mix creates a solution, where the alloying material is suspended within the liquid base metal. More importantly, it dissolves the precipitates and helps disperse these particles evenly throughout the solution.
Quenching: Once an alloy solution has been created, the liquid metal is then cooled as quickly as possible. This quenching can be done using compressed air, oil, water, or brine. Whatever the method used, the aim is to “flash freeze” the metal so that the solid is as evenly-mixed as the solution. The faster it can be cooled, the less time the precipitates have to form on its surface.
Aging: The metal is heated again, although to a lower temperature to avoid any dissolving. Applying heat a second time ensures the precipitates within the metal are evenly dispersed. Afterwards the heated metal item is quenched a final time.
However, there are risks involved with heat treatment. Over-aging occurs when the metal is held too long at too high a temperature. This can result in uneven disbursement of precipitates in solution, which leads to cracking and distortion in the cooled product. When monitored carefully throughout the age-hardening process, metal alloys that have completed these steps will be a harder, stronger material.
Extrusion is the process of shaping material during
manufacture. Generally, this is done by forcing a block of metal, called a
billet, through a shaped die. Think of it like a frosting tip: whatever is squeezed
out appears with the specific design you selected.
How is aluminum
For aluminum, the two main methods of extrusion are direct
Direct extrusion is the most commonly used method, using a
stationary die. The billet is heated to 800 – 925 degrees F, then laid on a
loader and pushed through the die using a hydraulic press. The steady pressure
squeezes the softened metal through the die opening. Using direct extrusion,
this process produces a wide variety of solid bars, rods, and hollow tubing.
With indirect extrusion, the process is reversed – the
billet remains stationary while the die is forced onto the metal itself. This
creates far less friction on the billet than using direct extrusion. The result
is a product with more consistent dimensions, grain structure, and mechanical
properties. However, the method also has its disadvantages, mainly related to
the lack of friction. Billets must be carefully cleaned, since little to no
friction means any substances on the metal will affect the extrusion’s surface.
Why use the extrusion
Extrusion is favored for many metals since it is easier to
manufacture, with aluminum being particularly suited for the process:
Quick fabrication and assembly: compared to
other tooling processes such as stamping, casting or injection molding,
extrusion has a shorter lead time and done at a lower cost. This means items
will be much more quick-to-market, from prototype development to product
Easy tailoring: there are already a number of standard
aluminum extrusion designs already available. This speeds production and
assembly, by improving performance and cutting down on secondary operations.
Strength: with the extrusion process, the
metal’s strength can be concentrated in specific areas by varying the wall
thickness and internal reinforcement of the design. This is even more of an
advantage with aluminum extrusions intended for use in cold environments.
Unlike other metals which can become brittle with cold, aluminum strengthens
with lower temperatures. The combination of the extra reinforcement through
extrusion, coupled with the property of the aluminum itself, makes for a
dependably strong metal.
Excellent thermal and electrical conductors:
aluminum is nearly twice as conductive as copper, and much less expensive a
material. It also conducts both heat and cold better than many other common
metals. Because of this, extruded aluminum products are an attractive choice
for home builders. Its lower price, heat dissipation properties, and resistance
to fire are all advantages for house framing.
Sustainability: aluminum can be recycled
infinite times, with no degradation of the metal’s properties. This means
extruded aluminum products often contain a high percentage of recycled content.
The addition of recycled material to the primary aluminum has no effect on the
finished product’s overall aesthetics or functionality.
At first glance, it might be difficult to distinguish annealing from tempering. Both are heat treatments designed to alter the physical and mechanical properties of a metal, and both involve heating that metal and gradually cooling it. So what makes the annealing steel different, and what are the advantages of this process?
When it comes to annealing, it’s important to remember how dependent the process is on precision and control. Like tempering, annealing involves reheating quenched steel and then allowing it to cool. However, at each stage of the annealing process, careful oversight is crucial to producing the most high-quality result possible.
Annealing involves three separate stages:
Recovery: simply put, this is applying heat to soften the metal. To ensure the most even heat distribution, air should be allowed to circulate freely around the items being annealed. For this reason, the heating is most often done in large ovens which can be tightly sealed, raised to the desired temperature, and closely monitored. Recovery then occurs when the heat breaks down dislocations and other irregularities within the metal’s structure.
Recrystallization: during this stage, the heat is raised to above the metal’s recrystallization temperature while still remaining just below its melting point. This means that new smaller grains are formed within the steel, replacing older grains with pre-existing stresses. So while the finished product will be less hard then it was before, the uniform structure of the new grains will give the steel more strength and resiliency.
Grain growth: this is the cooling stage of the annealing process. In contrast to tempering, which allows the steel to cool naturally at room temperature, the cooling of annealed metals must be highly controlled. To do this, cooling is often done by immersing the hot steel into a low-conductivity environment such as burying it in sand or ashes. It can also be done by switching off the oven and allowing the metal to slowly cool within the machinery’s fading heat. Whatever the method used, the aim is to have as slow and gradual a cooling process as possible. When fully cooled, the steel will now possess a more refined micro-structure. In real terms, this means it has more elasticity, so that it can take the stress of machining or grinding with far less risk of cracking.
While all heat treatments result in a strengthened alloy, annealing is crucial for items that have previously been cold worked. Cold working produces stresses within the metal, which annealing then helps to reverse by bringing it closer to the metal’s original properties. That means the benefits of annealing are twofold: eliminating as much residual stresses as possible while restoring its strength and ductility. So while tempering is used for products such as structural beams, the more ductile steel produced through annealing is found in items like mattress springs, wiring, and tools.
Steel is a term we consider synonymous with strength. Having a steely glare, being tough as steel: both expressions used to describe someone who is hard, strong, and determined.
So then, it may surprise you to learn that untempered steel can be nearly as fragile as glass! Without the tempering process, any steel produced will be extremely hard but also quite brittle. If it remains this way, it would be too prone to breakage to use in most applications.
Tempering is a method of heat treatment used to increase the resilience of iron-based alloys such as steel. After an initial heat treatment has been done to boost the steel’s hardness, tempering then reduces some of that hardness to help improve its strength. The end result is a steel which is less brittle, with increased ductility and abrasion resistance.
The tempering process begins after the steel has gone through an initial hardening treatment. With hardening, steel is brought to very high temperatures just short of melting, and quenched to cool it as quickly as possible. This quenching essentially locks the steel’s crystal structure and creates a very hard material. Tempering is then done immediately afterwards; if left to sit after quenching, the risk of cracking within the material will increase. To temper the steel, it involves reheating it once again to a high temperature and cooling, but in a less extreme or abrupt way than with hardening. Once exposed to the desired temperature, the steady heat application helps to relieve any internal stresses within the steel. Finally, the metal is removed and allowed to cool naturally in still air. So perhaps the best way to imagine tempering is as though you were baking a cake: you’ll have the best result if you are careful to set the right temperature, length of time, and gradual cooling.
Adjusting the peak temperature for tempering allows you the opportunity to create a product for a specific need. There are 3 temperature range categories when tempering steel:
Low temperature: this tempering will somewhat reduce the metal’s brittleness, while retaining its hardness. Steel produced this way is often used for case hardening components and cold work tools.
Medium temperature: the heat used in this range will produce a more elastic product. This means it’s now a more machinable and formable metal, which can be shaped and worked without losing the original shape. This steel is often used to manufacture knives.
High temperature: the higher the temperature used during the tempering process, the greater toughness that is given to the steel. This combination of resiliency and toughness makes it a good choice when producing structural steel and machine components.
Overall, it’s a rule that any hardened steel must be tempered. And without tempering, your stainless steel and other alloys won’t have the high level of ductility and weldability that we’ve come to expect from high quality materials.
Aging [verb]: the process of growing older. While that definition does apply, in the metals industry “aging” is specific jargon referring to treatments which speed up that process. But why would you choose to age your new metal products? It helps if you remember not to view aging as a negative. In fact, much like wine, the properties of a metal alloy often improve with age.
As metal ages, its base material physically transforms. The interaction of the metal’s atoms with the oxygen in its environment – whether surrounded by air or water – will begin change its surface texture and color. This starts with a basic oxide layer being formed. The oxide then becomes a hydroxide, and the hydroxide layer continues to interact with the atmosphere.
So why is this exposure to the elements considered a desirable result, unlike rust? That’s because iron oxide, or rust, is much more fragile and ultimately destructive when compared to a hydroxide. Exposed iron develops rust which flakes off and forms again, and will continue this cycle until it deteriorates the metal below. Meanwhile, a hydroxide layer actually creates a more stable surface composition. This hydroxide effectively creates an outer shell, which shields the metal below from any further interaction to its environment. The aging process of the metal comes to a near halt, with the hydroxide layer giving it both greater strength and longevity.
In general, there are two types of metal aging:
Natural aging: just as the name suggests, this is letting the metal age with time, in its natural environment. The strengthening benefits of aging will be more gradual but still effective.
Artificial aging: this refers to any method used to artificially accelerate the aging process. This is usually done through heat treatment of the metal alloys.
Both types do carry a risk of over-aging. This happens when the aging process pushes the metal past the point of strengthening into stressing and deteriorating it. As you might expect, this is more likely to occur with artificial aging: either because the metal has already undergone the aging process, or the heat applied is too intense or prolonged. However, when properly carried out, metal aging is a great benefit to the finished product.
Like any other field of expertise, the steel industry has
its own jargon – one that may be confusing upon first encounter. Why are they
assigned four-digit codes? What’s the difference between Alloy 4130 and 4140?
Steel is sorted into four main categories as set by the AISI
(American Iron and Steel Institute):
Being steel, these contain the same two basic elements of
iron and carbon. Determining their category depends on the percentage of carbon
and other alloys added to the iron, which changes the properties of the
Within each category, steel can then be classified according
to type. This usually includes several of the descriptive factors below:
Composition: the main categories of carbon,
alloy, stainless, and tool steel.
Microstructure: these are the subcategories of
composition. For instance, stainless steel can be classed as ferritic,
austenitic, martensitic, and duplex steels.
Method of production: two methods account for
almost all modern steel production, known as EAF (electric air furnace), and
BOS (basic oxygen steelmaking).
Form/Shape: also known as primary forming, creating
shapes such as plate or bars.
Method of finish: this is referred to as
secondary forming, the techniques which give the final product its properties
and finish. This can include processes such as hot and cold rolling, tempering,
Physical strength: using ASTM (American Society
for Testing and Materials) standards, the designation typically includes a
letter prefix and assigned number.
There are two primary numbering systems used to classify
metals, so steel descriptions typically will include both. Along with AISI, the
numbering system set by SAE (Society of Automotive Engineers) is most used in
the metals industry. For the most part, SAE has adapted their system to align
with the classifications set by AISI, so that specifications are standardized for
So with this information, consumers have the ability to
recognize the category and classification of a steel item. In the four digit
code system, the first number will determine the type:
Starting with 1: Carbon steel
2: Nickel steel
3: Nickel-chromium steel
4: Molybdenum steel
5: Chromium steel
6: Chromium-vanadium steel
7: Tungsten-chromium steel
8: Nickel-chromium-molybdenum steel
9: Silicon-manganese steel and other SAE grades
The following numbers then give additional detail to the specific
type of steel. In most cases, the second digit indicates the percentage of
alloying element. The last two digits are the percentage of carbon
concentration within the steel.
So using the example of 4130 vs 4140 steel: both start with
a 4, so they are molybdenum steels – with the concentration of molybdenum being
1%. The difference between the two is that 4130 has a carbon percentage of
roughly 0.30%, while 4140 contains 0.40 percent carbon. Because of its lower
carbon percentage, 4130 would be more easily machined and weldable than 4140.
However, the higher degree of carbon in 4140 alloy gives it greater hardness
and strength than 4130. Armed with this knowledge, this may better help you
choose the right type of steel for your needs.
LOS ANGELES, Feb. 19, 2020 (GLOBE NEWSWIRE) — Reliance Steel & Aluminum Co. (NYSE: RS) today announced the launch of its new e-commerce business, FastMetals, Inc. (www.fastmetals.com), which offers a catalogue pricing model for a diverse selection of metal products including carbon, stainless, aluminum and specialty alloy steels. Located in Massillon, Ohio, FastMetals ships nationwide and has direct access to Reliance’s vast network of metals service center locations which carry over 100,000 products.
“FastMetals was created in response to the growing demand for digital purchasing solutions from metalworkers of all backgrounds,” commented Jim Hoffman, President and Chief Executive Officer of Reliance. “Consistent with Reliance’s core business strategy, FastMetals specializes in small orders with quick-turn around and best-in-class customer service. We are excited to launch this new, innovative venture that differs from our traditional sales model as simply another option for customers to purchase metal from us. Many of our existing service centers presently offer online capabilities and continue to receive inquiries via phone, email or other means based on the individual customer’s preference. FastMetals is yet another channel to experience Reliance’s unique, customer-focused service.”
FastMetals’ model is tailored to smaller, specialized end-users including artists, fabricators, machine shops, hobbyists, and do-it-yourself practitioners. Customers can choose from standard shapes and sizes or select specific dimensions to satisfy unique project requirements. FastMetals provides instant pricing, same-day shipping, no minimum order quantity and direct fulfillment to the individual customer.
About Reliance Steel & Aluminum Co. Reliance Steel & Aluminum Co. (NYSE:RS), headquartered in Los Angeles, California, is the largest metals service center company in North America. Through a network of more than 300 locations in 40 states and thirteen countries outside of the United States, Reliance provides value-added metals processing services and distributes a full line of over 100,000 metal products to more than 125,000 customers in a broad range of industries. Reliance focuses on small orders with quick turnaround and increasing levels of value-added processing. In 2018, Reliance’s average order size was $2,130, approximately 49% of orders included value-added processing and approximately 40% of orders were delivered within 24 hours. Reliance Steel & Aluminum Co.’s press releases and additional information are available on the Company’s website at www.rsac.com.
Corrosion is the deterioration of a metal due to an electrochemical
reaction between the atoms on the metal’s surface and its surrounding environment.
Most commonly, corrosion refers to oxidation: the process where a metal reacts
to the oxygen in air or water. The most familiar example of corrosion is iron
oxide (rust), but other metals can corrode in similar ways. Given sufficient
time and exposure, corrosion will have a significant negative impact on the
metal’s appearance, strength, and durability. If left unchecked, corrosion will
eventually lead to the weakening or total disintegration of the metal parts.
The World Corrosion Organization (WCO) estimates the annual cost of corrosion
to be up to $2.5 trillion dollars – and that up to 25% of that damage is
General Attack Corrosion, also known as Uniform Attack Corrosion, is characterized as the reaction occurring over the exposed surface area of a metal object or structure. This is the most common type of corrosion, leading to the greatest overall destruction of metal by tonnage. However, from a technical standpoint, it is also considered to be the ‘safest’ form of corrosion to encounter. The damage which occurs with general attack corrosion, being fairly uniform and predictable in its progress, means it is the easiest to diagnose and prevent.
How to Prevent Uniform Metal Corrosion
1. Selecting the Right Metal: The four basic types of metals
referred to as “corrosion-proof”
Stainless Steel: This alloy contains iron, which easily oxidizes to form rust, and chromium, an element even more reactive to corrosion than iron itself. However, when chromium is added to steel, the corrosion which results then forms a protective layer on the surface of the metal. In contrast, corrosion which occurs on uncoated carbon steel will repeat continuously as the rust forms, wears off, and forms again. Eventually the rusting will lead to the metal’s disintegration. Iron oxide layer on stainless steel will resist further corrosion. This means the layer actually prevents oxygen from reaching the steel underneath. Corrosion-resistant in stainless steel can be further boosted by the addition of other elements in the alloy such as nickel and molybdenum.
Since aluminum alloys contain almost no iron, they are free from rust. The
corrosion with this metal is similar to chromium in stainless steel; after the
initial corrosion occurs, it creates a surface layer that protects the metal
from any further damage. This film of aluminum oxide can be unsightly with dark
marks or streaking, but as long as it remains, it will shield the underlying metal.
Brass, Bronze, and Copper: Like aluminum alloy, these metals
contain little to no iron. They do react with oxygen – most noticeably with
copper, which oxidizes to a distinctive green patina. The oxidized layer helps
protect the copper from further corrosion. The other two metals combine copper
with other metals, which makes them naturally corrosion-proof: copper and zinc
to produce brass, and copper and tin for bronze.
Galvanized Steel: This is carbon steel that is galvanized, or coated, with a thin layer of zinc. Like chromium and copper, zinc is highly reactive to oxygen and will quickly begin to oxidize. This layer of zinc oxide prevents any further corrosion on the galvanized coating. Even more importantly, it acts as a barrier preventing oxygen from reaching the steel. Eventually, the zinc will wear off which will make the carbon steel vulnerable to rust, so this type of metal is not entirely corrosion-proof. However, it will take much longer to rust than untreated carbon steel.
2. Protective Coatings
In addition to galvanized steel, other coatings can be applied as a barrier between the environment and the metal. Painting is one of the most cost-effective ways of preventing corrosion. Powder-coating is another popular option. This involves applying a dry powder to the metal and then heating it to fuse it in an even, smooth film. Both methods work by creating a uniform physical barrier between oxygen and the metal.
3. Monitoring the Environment
Simply put, corrosion is the reaction of the metal with its
surrounding environment. So whether the environmental factor is air, water, stresses
placed upon the metal itself, or all of the above, regular maintenance and monitoring
goes a long way towards preventing or lessening the impact of corrosion.
Crevice corrosion, for example, is commonly found in areas where metals overlap
each other. This means the metal parts are exposed to varying oxygen
concentrations, leading to uneven wear and deterioration. Proper maintenance
such as eliminating crevices when found, or ensuring complete drainage in
vessels, can help to prevent this corrosion. In harsher environments, replacing
parts and fastenings with higher
alloys can help preserve the metal’s functionality.
All metals will corrode eventually, but the process does not necessarily need to be a destructive one. By anticipating how and where an item will be used, the choice of metal and its maintenance can prevent corrosion from becoming a serious problem. Corrosion prevention not only helps save equipment and money, but it will also help keep metals safer for the people who use them.
Property and home improvement shows are more popular than ever – and according to those experts, a kitchen remodel is one of the most effective ways to maximize your budget for home renovation. Stainless steel’s durability and stylishness make it a great construction material and design element in a kitchen. Whether used to equip a sleek industrial space, adding modern touches to classic or mid-century design, or used for cookware and utensils, consider the benefits of using stainless steel to update your surroundings.
5 Reasons to Use Stainless in Your Kitchen
Durability: Stainless steel is the standard in the restaurant industry for good reason; it’s strong, rust-free, and resists heat damage! Grade 304, the most commonly available type of stainless steel, will hold up to the daily wear of food preparation and cleaning because it is a non-reactive metal. This makes it incredibly versatile for everything from appliances and cutlery to pots and pans. Metals like copper or aluminum will react to acidic ingredients such as vinegar, discoloring its shiny finish and adding unpleasant flavors to your food. Countertops made of stainless steel can hold up to heat, liquids, and cleansers without negative effects – the same treatment which can crack or stain granite surface
Low Maintenance: The addition of chromium to produce stainless steel makes it very resistant to oxidation, which can rust and wear down other materials. Whether it’s exposed to water in a kitchen sink, high temperatures in a barbeque grill, or the cold of a freezer, stainless steel requires little maintenance to keep it looking its best. Stainless steel cabinets will not warp, making them ideal for high humidity or outdoor cooking areas.
Style and Versatility: Despite what you may think, stainless steel is not simply for those who like minimalist or industrial design! It coordinates well with any color or décor and makes for easy matching between your appliances, fixtures, and pots and pans. Cabinets or countertops with a high shine finish can help brighten a dim kitchen area. Appliances made of brushed-finish stainless steel give an elegant glow. Blended with natural materials such as wood and stone, stainless steel helps to give a timeless yet modern look to your kitchen.
Hygiene: Stainless steel is a non-porous material. This means its surface doesn’t allow air or liquid to pass through, which prevents the growth of bacteria within the steel. So kitchen surfaces and implements can be easily and thoroughly cleaned. Stainless steel makes an ideal choice for kitchen sinks and backsplashes since it can hold up remarkably well to regular use, water, and household cleansers.
Eco-Friendly Material: Nontoxic, long-lasting, and recyclable: stainless steel makes an environmentally-friendly choice of material for your kitchen and home. When treated with care, the durability of stainless steel means your appliances, décor, and cookware will last for many years, preventing excess waste and landfills. The easy cleanup for stainless steel – just soap and water – helps to cut down on the use of chemicals. As consumer demand increases for sustainable choices, consider the advantages of building and outfitting your kitchen with stainless steel. Its long life makes it a good choice for your finances, and for the good of our communities.