How to Choose What Is Mild Steel?

By: Hobart Brothers

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Mild steels offer numerous benefits — from easy weldability to the ability to bend and mold the material — making them well-suited for a wide range of welding applications. With many mild steel options available, how can an operation determine which filler metal is the right choice for a specific application?  

Learn more about the solid, metal-cored and flux-cored filler metals available for these materials and how to choose the right option for the job. 

What is mild steel? 
Base materials that are considered mild steel typically have little to no alloying elements. Mild steels have a carbon limit of .25 percent and are also referred to as low carbon steels. Two common mild steels used in many fabrication and manufacturing applications are ASTM A36 and AISI 1018. 

The characteristics of mild steel differ by material type, but generally, mild steels have lower tensile and yield strengths than low-alloy steels. Tensile strengths are typically 70 ksi or lower, while yield strengths can be as low as 30 ksi. 

Lower tensile and yield strengths mean the material isn’t as hard, so it can be bent or rolled into different shapes. In applications where higher yield and tensile strengths are required, the material can be made into thicker, heavier sections to offset the lower strengths. 

In general, mild steels offer very good weldability, and the lack of additional alloying elements in mild steels also makes them a cost-effective option for many welding applications. 

Filler metal options
Mild steel filler metals are typically designed to outperform the base materials, with higher tensile and yield strengths. 

Standard mild steel filler metals are known to offer good weldability. Mild steel filler metals for wire welding applications are available in solid, metal-cored and flux-cored wire options for manufacturing and fabrication. 

Solid wires
Solid wires are versatile for many applications because they can be used at very low or very high amperages. When welding thicker materials with solid wire, it’s recommended to use a spray transfer process; for thinner materials, a short-circuit transfer process works best. 

Solid wires offer good travel speeds and bead appearance, along with the ability for deep penetration when welding tighter joints or corners due to a narrower penetration profile. Common mild steel solid wire filler metals include American Welding Society (AWS) classifications such as ER70S-3 and ER70S-6.

Solid wires are commonly used in automotive and robotic welding applications. Because solid wires have high column strength and are often copper coated, they are a bit stiffer than other wires and provide good feedability. However, keep in mind that solid wires can have higher heat inputs than metal-cored wires, so the deep, driving arc of solid wires can result in overpenetration or burn-through at times. 

Also, be aware that solid wires don’t wet out as well on surfaces with mill scale. Because solid wire has fewer deoxidizers added, it doesn’t handle surface impurities as well as other filler metals can, requiring welders to use slower travel speeds on materials with mill scale or rust. 

Metal-cored wires
Nearly any mild steel welding application that uses solid wire can use a metal-cored wire. Where solid wires have a narrower, finger-like penetration profile, metal-cored wires have a broader, wider penetration profile that isn’t as deep. As a result, metal-cored wires wet out and tie into sidewalls better and typically can be used at lower heat inputs while producing the same bead appearance. The wider penetration profile and additional wetting also can make wire placement more forgiving.

Since metal-cored wires have a powdered core they can be formulated with more deoxidizers than solid wires. Because of this, they can handle mill scale and dirty base materials better and with higher travel speeds. Their greater deposition rates result in higher productivity. While metal-cored wires tend to be more expensive than solid wires, the productivity gains can deliver a fast return on investment. Because of these factors, metal-cored wires are often recommended when completing welds 6 inches or longer and for operations that are trying to increase travel speeds. One of the most common metal-cored options for mild steel applications is E70C-6M. 

Mild steels can be welded with solid, metal-cored or 
flux-cored wires in wire welding applications. Choosing 
the right filler metal for the application requires 
consideration of the material properties, surface 
material condition and desired productivity. 

Gas-shielded flux-cored wires
When welding mild steels, two common gas-shielded flux-cored wire options are E70T-1 for flat and horizontal welds and E71T-1 for all-position welds. 

Offering similar or higher deposition rates than metal-cored wires, E70T-1 filler metals are well-suited for thick, heavy weldments requiring a lot of weld metal. These wires are also good options for materials with heavy mill scale or rust, and can provide good bead appearance and higher travel speeds even on those materials. 

Because it can be harder to make large welds that don’t sag with metal-cored and solid wires, the flat and horizontal flux-cored wires are good for these applications because the slag helps hold the weld bead in place as it cools. However, the slag does require more time in post-weld cleanup. 

When the application doesn’t allow the weld to be made in a flat or horizontal position, E71T-1 flux-cored wires offer an all-position option. Well-suited for vertical up or overhead welding, these wires deliver higher travel speeds and a much flatter bead profile. Like the E70T-1 filler metals, the all-position wires do generate slag that must be cleaned up after welding. It’s recommended to use a drag technique with wires that generate a slag, and a push technique for wires that don’t generate slag. 

Tips for selecting mild steel filler metals  
When choosing the right filler metal for mild steel welding applications, there are some additional factors to keep in mind.

The condition of the base material is an important factor when selecting a filler metal. Some A36 and 1018 mild steels come in a hot-rolled or cold-rolled condition. A hot-rolled mild steel can result in mill scale on the material surface, which is more difficult to properly weld. Mild steels that have been cold-rolled have a clean finish but sometimes have a light oil on the surface. When the base material has a light mill scale or rust, it’s recommended to remove it. If that’s not possible, select a metal- or flux-cored wire, which generally provide better results in these situations. For parts that are cold-rolled or have a light oil on the surface, solid wire filler metals such as ER70S-6 are acceptable. 

Also, take into account the joint design to be welded. A narrow v-groove weld joint may require deeper penetration into a tighter spot, and would be best-suited to a solid wire. All-position flux-cored wires don’t provide the deep, finger-like penetration that solid wires offer and would be better-suited for welding the shallower joint designs.

Understanding mild steel 
Mild steel materials provide benefits for easy weldability and flexibility in many welding applications. Understanding the characteristics of the type of mild steel base material, the goals of the welding application and weld joint design — and matching it with an appropriate mild steel filler metal — helps improve productivity, throughput, and weld quality.

Choosing the correct steel grade is essential for the success of your project. A bad grade can result in poor performance, reduced durability, or even catastrophic failure.

When selecting a steel grade, factors such as strength, rust resistance, heat resistance, and weldability must be considered. Additionally, the intended use and environmental conditions should be taken into account.

With the right steel grade, you can ensure that your project will meet its intended purpose and provide long-lasting performance. Make sure to consult with a steel expert before starting a project.

Factors to Consider When Choosing Steel Grades

Project Requirements

• Strength and Durability

Strength and durability are the most critical factors when selecting the steel type for your project area. Your project requirements will dictate the level of strength and durability that your steel must possess to withstand the intended conditions of use.

To determine the appropriate level of grading systems, several factors must be considered: the expected load-bearing capacity of the steel, the environmental conditions the steel will be exposed to, and the lifespan of the finished product.

For example, If your project involves constructing a bridge carrying heavy traffic, you’ll need high-strength steel to handle the weight without buckling or bending. If you’re building a fence or a railing, you may only need lower-strength steel that can provide sufficient durability and resistance to weathering.

Other considerations that may impact your choice of steel grade include the required level of rust resistance, the ease of fabrication, and the cost-effectiveness of the steel.

Ultimately, selecting the correct steel grade for your project requires careful analysis and consideration of all the relevant factors. Ensure that it is strong and performs reliably over time.

• Corrosion Resistance

You must consider the level of anti-corrosive property, especially if it will be exposed to harsh environmental conditions. Corrosion can cause structural damage, reduce the product’s lifespan, and increase maintenance costs. The level of rust-proof quality required will be determined by factors like moisture, salt water, and chemicals.

Galvanized steel is another option for corrosion resistance. It is coated with a layer of zinc that acts as a barrier against rust and corrosion. However, galvanized steel may not be suitable for products exposed to extremely corrosive environments.

Other common grades with high corrosion resistance include weathering steel, which forms a protective layer of rust over time, and aluminum, naturally corrosion resistant.

Consideration of the environmental conditions to which the metal will be exposed and selection of the one with the appropriate level of corrosion resistance is essential to ensuring the longevity and durability of the finished product.

• Temperature and Pressure

Consider the ability to withstand the temperature and pressure requirements of the application. Different steel grades have varying melting points and yield strengths, which can affect their performance in high-temperature or high-pressure environments.

For example, if you’re working on a project involving boilers, pressure vessels, or piping systems, you must choose a steel grade with high-temperature and high-pressure capabilities. Alloy and stainless steels are often used in these applications due to their excellent strength and durability at elevated temperatures.

Similarly, if your project involves cryogenic applications, you need a steel grade to maintain strength and flexibility at shallow temperatures. Low-temperature steels, such as those with nickel or manganese content, are often used in these applications.
In addition to the temperature and pressure requirements, consider factors like corrosion resistance, ease of fabrication, and cost-effectiveness when selecting a steel grade for your project.

 

Cost Considerations

• Raw Material Costs

When choosing the suitable steel grade for your project, raw material costs are a factor. Different steel grades have varying raw material costs based on their composition and availability.

High-strength steel grades with alloying elements such as chromium, nickel, or molybdenum tend to be more expensive due to the cost of these materials. On the other hand, lower-strength steel grades with lower alloying elements tend to be more cost-effective.

Another factor that can impact raw material costs is the demand and availability of the steel grade. If a particular steel grade is in high demand, its raw material costs may be higher due to supply and demand.

When choosing the correct steel grade, it’s important to balance cost considerations with other factors, such as the project’s requirements, performance, and safety. While cost may be a critical consideration, choosing a steel grade based on price alone can result in a suboptimal product.

• Fabrication Costs

Fabrication costs are another consideration when choosing the right steel grade for your project. Different steel grades require varying levels of fabrication processes, which can significantly impact the project’s overall cost.

For example, high-strength steel grades may require more specialized equipment and processes, which can increase fabrication costs. Conversely, lower-strength steel grades may be easier to work with, resulting in lower fabrication costs.

Other factors that can impact fabrication costs. Projects with complex designs or tight tolerances may require more skilled labor and specialized equipment, resulting in higher fabrication costs.

When choosing the correct steel grade, it’s a good idea to balance fabrication costs with other factors, such as the project’s requirements, performance, and safety. While cost may be critical, choosing a steel grade based solely on fabrication costs can result in a suboptimal product.

Availability

• Local Availability

Local availability can help you choose the correct steel grade for your project. Depending on your location, some steel grades may be more readily available than others.

Working with steel grades that are locally available can save time and reduce transportation costs. However, it is essential to ensure that the chosen steel grade meets the project’s requirements and specifications.

Local availability may not be an issue, particularly for large-scale projects. However, for smaller projects or those with unique specifications, it’s essential to consider the availability of the chosen steel grade.

• Lead Time

Lead time is also something you should be aware of. Some steel grades may have longer lead times than others, impacting project timelines and deadlines.

Factors such as availability, production capacity, and transportation can all impact lead times for different steel grades. It’s crucial to consider lead times when planning your project and selecting the correct steel grade.

Working with steel suppliers with a track record of meeting deadlines can help ensure timely project completion. It’s also essential to communicate project timelines and deadlines with your supplier to ensure they can meet your needs.

You must also manage lead time. Any project manager will tell you of past disasters. When a deadline is delayed, it causes a ripple effect, like falling dominoes, as each deadline behind it is pushed further and further away.

• Supply Chain Considerations

When choosing the steel for your project, you must consider the supply chain. Understanding the supply chain of your steel grade selected can help you avoid potential disruptions and delays.

Production location, transportation routes, and inventory levels can all impact the supply chain of different steel grades. It’s better to work with suppliers with a reliable supply chain to ensure timely delivery and avoid potential issues.

Consider any potential risks to the supply chain, such as natural disasters or geopolitical events. By understanding potential threats and developing contingency plans, you can address any disruptions to the supply chain.

Common Steel Grades and Their Applications

Carbon Steel

Low Carbon Steel

Low-carbon steel is commonly used with less than 0.25%. This steel grade has excellent weldability and formability, making it the choice for construction, auto, and machinery.

Due to its lower carbon content, low-carbon steel is also more ductile and has better machinability than higher-carbon steel. It’s also more economical, making it ideal for projects with tight budgets.

However, low-carbon steel has lower strength and hardness than higher-carbon steel, making it less suitable for applications that require high strength and durability. So consider the specific requirements of your project and choose the steel grade accordingly.
Low-carbon steel is a versatile and cost-effective steel grade used in various applications.

Medium Carbon Steel

Medium carbon steel is a steel grade with a carbon content ranging from 0.3% to 0.6%. This steel grade balances strength and toughness, making it suitable for gears, axles, and crankshaft applications.

Medium carbon steel has higher strength and hardness than low carbon steel but is less ductile and more difficult to weld.

One advantage of medium carbon steel is its excellent machinability, which makes it easier to cut, drill, and machine. This steel grade can also be heat-treated to improve strength and hardness.

High Carbon Steel

High carbon tool steel is a steel grade with an amount of carbon ranging from 0.6% to 1.4%. This steel grade offers high strength and hardness, making it suitable for cutting tools, knives, and springs.

Due to its content, high-carbon steel is brittle and less ductile than lower-carbon steel. It’s also more difficult to weld and form. However, it can be heat treated to improve its strength and hardness.

High-carbon steel is often used in applications that require high wear resistance and durability.  High carbon steel is a specialized steel grade that can perform excellently in specific applications.

Applications of Carbon Steel

Carbon steel is a widely used steel grade due to its versatility and affordability. It is used in various industries, including construction, and some of its standard applications include structural components, fasteners, pipelines, and machinery parts.

Carbon steel’s strength and durability make it an excellent choice for structural applications, such as building frames and bridges. Its high tensile strength and low cost make it a popular choice for manufacturing applications.

Carbon steel is often used in the car industry for body panels, suspension components, and exhaust systems. It’s also used in hand tools, knives, and blades due to its hardness and wear resistance.

Alloy Steel

Types of Alloy Steel

Alloy steel contains elements other than iron and carbon, such as manganese, silicon, nickel, copper, and chromium. These added elements enhance the properties of the steel, making it more robust, durable, and corrosion-resistant.

There are several types of steel and alloy, each with its unique properties and applications. Here are a few examples:

1. Low alloy steel: This type contains less than 5% of other elements, making it less expensive and more readily available. It is used in bridges and buildings.

2. High-strength low alloy steel

   
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    (HSLA): HSLA steel contains small amounts of alloying elements, making it strong and lightweight. It is in the auto and aerospace industries, as well as in construction.

3. Chromium-molybdenum steel: This type of alloy steel contains chromium and molybdenum, which enhance its strength and corrosion resistance. It is commonly used in pressure vessels, such as boilers and storage tanks.

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4. Nickel-chromium-molybdenum steel: This type of alloy steel contains nickel, chromium, and molybdenum, making it highly resistant to corrosion and oxidation at high temperatures. It is commonly used in chemical processing and power generation.

5. When choosing the correct steel grade for your project, consider the specific application and the required properties of the steel. Alloy steel is an excellent choice for projects that require strength, durability, and corrosion resistance. However, you should still consult a professional to determine the best alloy steel type for your project.

Applications of Alloy Steel

Alloy steel contains a higher percentage of elements other than iron and carbon. These additional elements are typically chosen to impart specific characteristics such as increased strength, corrosion resistance, or improved weldability.

One common application of alloy steel is in constructing pipelines and pressure vessels. Adding elements such as chromium, molybdenum, and nickel makes these materials more resistant to corrosion and high-pressure environments.

Alloy steel is also used in the production of aircraft and aerospace components. The high strength-to-weight ratio of some alloys makes them ideal for structural components, while others are chosen for their resistance to high temperatures and wear.

Gears, axles, and drive shafts are among the applications of this kind of steel. Elements such as vanadium and tungsten can improve the strength and durability of these components. Meanwhile, other alloys are chosen for their ability to withstand high temperatures and extreme environments.

Stainless Steel

Types of Stainless Steel

Stainless steel is a choice for industrial and commercial applications. There are types of stainless steel grades, each with its unique properties and characteristics.

Austenitic stainless steel is a different type of steel. This type of steel is non-magnetic and has excellent weldability, making it ideal for use in the construction of tanks, steel pipes, and pressure vessels.

Another popular type is ferritic stainless steel, known for its high resistance to corrosion and oxidation. This steel is used in exhaust systems of vehicles, heat exchangers, and other high-temperature applications.

Martensitic stainless steel is a high-strength steel often used in applications where wear resistance and hardness are important factors. This type of steel is found in producing cutlery, surgical instruments, and industrial equipment.

Duplex stainless steel combines the benefits of austenitic and ferritic stainless steel. Its high strength and resistance to corrosion make it commonly used in producing chemical processing equipment, oil and gas pipelines, and other high-pressure applications.

Applications of Stainless Steel

Stainless steel is a versatile material used in various industrial and commercial applications. Its resistance to corrosion, durability, and aesthetic appeal make it a popular choice for many projects.

One common application of stainless steel is in producing kitchen appliances and utensils. Its hygienic properties and resistance to corrosion make it ideal for food preparation and storage.

Another common use of stainless steel is in constructing architectural features such as building facades, handrails, and elevator interiors. Its aesthetic appeal and durability make it a popular choice for these projects.

Stainless steel is also commonly used in the production of medical equipment and devices due to its high level of cleanliness and resistance to corrosion. It is often used to produce surgical instruments, dental equipment, and implants.

In the automotive industry, stainless steel products include exhaust systems, mufflers, and other components due to their resistance to heat and corrosion.

Understanding Steel Grade Designations

American Iron and Steel Institute (AISI) Designations

Examples of AISI Designations

The American Iron and Steel Institute (AISI) is a widely recognized organization that establishes standards for the steel industry. AISI designations are commonly used to classify steel based on its chemical composition and mechanical properties.

One example of an AISI designation is 4140, a chromium-molybdenum alloy steel. This steel type is commonly used to produce shafts, gears, and other machine parts that require high strength and wear resistance.

Another AISI designation is 304 stainless steel, a commonly used austenitic stainless steel known for its corrosion resistance. This steel is often used to produce kitchen appliances, piping, and architectural features.

AISI designations are also used to classify carbon steels, such as AISI 1018 and AISI 1045. These steels are commonly used to produce machine parts and structural components.

It’s important to note that AISI designations are just one way to classify different grades of steel, and other organizations may use different designations or classification systems.

Society of Automotive Engineers (SAE) Designations

Examples of SAE Designations

The Society of Automotive Engineers (SAE) is a professional organization that develops standards for the automotive industry. SAE designations are commonly used to classify based on their chemical composition and mechanical properties.

One example of an SAE designation is 1010, which is low-carbon steel.  Another example of an SAE designation is 4130, a chromium-molybdenum alloy steel.

Stainless steels are also classified using SAE designations, with examples such as SAE 304 and SAE 316. The production of automotive exhaust systems and other high-temperature applications commonly uses these steel types.

Unified Numbering System (UNS) Designations

Examples of UNS Designations

ASTM International and SAE International developed the Unified Numbering System (UNS) to assign a unique identification number to different metals and alloys. Industry professionals commonly use UNS designations to classify different steel grades based on their chemical composition and properties.

One example of a UNS designation is S31600, a type of austenitic stainless steel. Manufacturers commonly use this to produce chemical processing equipment, medical devices, and other applications.

Another example of a UNS designation is G10450, commonly used to produce machine parts and tools.

Manufacturers use UNS designations to classify specialty steels, which include N07718 (a nickel-chromium alloy) and K02600 (a low-carbon steel).

Other Designations

Apart from the American Iron and Steel Institute (AISI), Society of Automotive Engineers (SAE), and Unified Numbering System (UNS) designations, various other systems exist to classify steel grades. Some examples include the Japanese Industrial Standards (JIS), the European Standard (EN), and the International Organization for Standardization (ISO).

In Japan, industries commonly use JIS designations, similar to the AISI and SAE designations used in the United States. In Europe, industries use EN designations to identify different steel types, providing a standardized system for classification. Globally, industries use ISO designations to identify different types of metals and alloys, providing a standardized system for classification.

Final Thoughts

Selecting the right steel grade for your project requires consideration of several factors, including the application, required strength and toughness, and corrosion resistance. Finally, understanding the classification systems and designations, such as AISI, SAE, UNS, JIS, EN, and ISO, can help identify the right steel grade.

Frequently Asked Questions

Why Does Steel Grade Matter?

Selecting the appropriate steel grade impacts the performance, durability, and cost of your project. For instance, a high-strength steel may be needed for a bridge, while a more corrosion-resistant grade may be suitable for use in a chemical plant.

How Do I Determine the Right Steel Grade for My Project?

Start by identifying the requirements of your project, such as load-bearing capacity, corrosion resistance, and welding capabilities. Once you have these details, consult various standards like ASTM, AISI, or EN to find a matching steel grade. It’s also a good idea to consult experts in the field for additional insights.

Can I Use Multiple Steel Grades in One Project?

Yes, using multiple steel grades is not uncommon, especially for complex structures. Different sections may have varying requirements, making it advisable to use the most suitable steel grade for each specific purpose.

 Are There Any Downsides to Picking a Higher-Grade Steel?

Higher-grade steels generally come at a higher cost and may require specialized handling or fabrication techniques. For instance, some high-grade steels are not as easily weldable as lower grades. So, using a higher-grade steel when unnecessary can lead to unnecessary expenses and complications.

 Is Recycled Steel of Lesser Quality?

Not necessarily. Recycled steel often undergoes rigorous processing to restore its properties, making it comparable to virgin steel in many applications. It’s also a more environmentally friendly option.

References

1. American Iron and Steel Institute. (n.d.). Steel Industry Glossary.

   https://www.steel.org/steel-industry/glossary.aspx

2. Engineering Toolbox. (2021). Steel Grades – Properties and Global Standards.

   https://www.engineeringtoolbox.com/steel-grades-d_1566.html

3. Metal Supermarkets. (2021). How to Choose the Right Steel Grade.

   https://www.metalsupermarkets.com/how-to-choose-the-right-steel-grade/

4. Society of Automotive Engineers. (n.d.). SAE Steel Grades.

   https://www.sae.org/standards/content/j403_201406/

5. Unified Numbering System. (n.d.). UNS Numbering System. https://www.unsnumber.com/

 

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