Author: Brian Zuelch

What is the Difference between Annealing and Tempering?

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:

  1.  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.
  1. 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.
  1.  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.

What is the Tempering Process?

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:

  1. 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.
  1. 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.
  1. 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.

What is Metal Aging?

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.

Decoding Steel by its Numbers

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 finished metal.

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, or galvanizing.
  • 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 steel.

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.

Reliance Steel & Aluminum Co. Launches FastMetals E-Commerce Platform

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.


Brenda Miyamoto
Investor Relations
(213) 576-2428
investor@rsac.com

or Addo Investor Relations
(310) 829-5400