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Alloy Steel Overview
Alloy steel is a steel type containing more than one alloying element. Whenever you add each element often introduces new characteristics or improves certain material properties. Generally, all basic steel has iron content and a small percentage of carbon. Chromium is a common alloying element that manufacturers add to other elements to enhance corrosion-resistance properties.
Other common elements suitable with alloy steel are vanadium, nickel, manganese, molybdenum, titanium, and tungsten. The specific elements added to the alloy steel often determine its properties. For instance, manganese improves ductility, wear resistance, and alloy steel’s hardenability. On the other hand, chromium enhances alloy steel’s toughness, hardness, and resistance to wear.
Types of Alloy Steel
Here are the categories under which alloy steel types are classified:
- High-Alloy Steels
These alloy steels usually contain a high amount (more than 5% of the total composition) of one or more alloying elements for excellent toughness, hardness, and strength. Common alloying elements for this alloy steel category include manganese, chromium, vanadium, nickel, and molybdenum. Stainless steel is a perfect example of high-alloy steel, containing a minimum of 12% chromium, depending on its grade.
- Low-Alloy Steels
Low-alloy steels contain a lower portion of one or more alloying elements (maximum of 5% of the total composition), offering improved toughness, strength, hardness, or other qualities. Typical examples of alloying elements in this category include tungsten, molybdenum, copper, chromium, manganese, boron, and nickel. Further, typical applications for low-alloy steels include mining and construction equipment due to their high requirement for good strength-to-weight ratios properties.
- Maraging Steels
These steels are famous for their superior toughness and strength. Manufacturers find a use for these steels in applications that require high-strength properties, including military and aerospace applications.
- Tool Steels
Tool steels are commonly known as highly alloyed steel suitable for tool and die applications in particular. Tool steels can resist wear and hardness even when exposed to high temperatures.
Advantages of Alloy Steel over Stainless Steel
Alloy steels offer certain benefits over stainless steel, making it a material worth considering for various applications. Here are some of these advantages:
- It offers an excellent strength-to-weight ratio.
- Alloy steel exhibit resistance to higher temperature.
- Alloy steels allow higher machinability, allowing their high versatility.
- It is a cost-effective option.
Stainless Steel Overview
Stainless steel is an alloyed steel with a minimum of 10.5% chromium. The chromium element offers stainless steel greater corrosion resistance, making it compatible with extensive applications ranging from medical equipment to cookware. In addition, it is a common choice for consumers and businesses due to its unique features. However, it would help to note that stainless steel has different grades with varying sets of qualities.
Common Types of Stainless Steel
Although there are thousands of stainless steel grades, they can be successfully grouped into the following categories:
- Austenitic Stainless Steels
The austenitic steels usually contain 8-20% nickel and 17-25% chromium at minimal (the basic stainless 304 contains 18% chromium and 8% nickel). These steel grades are usually non-magnetic, and manufacturers use them in food processing equipment and chemical plants due to their high resistance to rust, stain, and corrosion after exposure to water.
Austenitic grades offer excellent corrosion resistance, toughness, ductility, weldability, and high formability. This group’s good examples of stainless steel include 253, 304/304L, and 316/316L.
- Martensitic Stainless Steels
This category of stainless steel contains between 14 -18% chromium and balanced levels of carbon within the 0.2 and 2% range. You can temper and harden martensitic stainless steel like carbon steel. Likewise, they offer reduced ductility and low weldability. Typical examples are 431, 420C, and 431 stainless steel grades.
- Ferritic Stainless Steels
The ferritic group contains a portion of chromium, typically between 11- 27% and less or no nickel. This group’s steel is less corrosion-resistant than austenitic stainless steel due to its high amount of chromium. They share certain qualities with iron and show improved mechanical properties at high temperatures, and you can strengthen these steels through annealing.
However, ferritic stainless steels lack toughness which reduces their structural applications. They are only available in coil and sheet. Stainless steel 430 and 409 are apt examples.
- Duplex Stainless Steels
Duplex stainless steels have chromium between 18 and 28% and nickel alloying elements between 3.5 and 5.5%. Stainless steel in this grade possesses equal parts of ferrite and austenite and greatly resists pitting and chloride stress. They are weldable, easy to fabricate, magnetic, and offer better corrosion resistance than the austenitic grades. Examples are S32750 and 2205 stainless steel grades.
- Precipitation-hardening Stainless Steel Grades
They contain about 12-16% chromium, 3-8% nickel, and a small proportion of other alloying elements such as copper, aluminum, and titanium capable of forming a precipitate. They are usually very strong, ductile, and heat-treatable. They are machined in the annealed condition and then heat treated.
Advantages of Stainless Steel Over Alloy Steel
Stainless steel is one of the prominent materials with high use. It offers extensive advantages over alloy steel, such as:
- Recyclability
- It requires low maintenance
- It offers higher corrosion resistance
- Stainless steel provides better aesthetic appeal
Common Alloying Elements and Their Effects
Manufacturers across industries improve carbon steel’s mechanical properties with the help of more than 20 alloying elements. Each of these alloying elements offers distinct properties. Here are the top five (5) common alloying elements:
- Chromium: the effect of chromium as an alloying element is often determined by its percentage. For instance, it can enhance a material’s hardness when used at a smaller portion, such as 0.2 – 2%. At the same time, it improves a material’s resistance to corrosion when used at a higher percentage, such as 4 – 18%.
- Manganese: Using manganese with a low amount of sulfur and phosphorus ensures your formed steel is more malleable and less brittle.
- Tungsten: This alloying element enhances the structural composition of the formed steel alloy. Moreover, it improves the heat resistance resulting in a higher melting point.
- Nickel: Nickel affects a steel’s mechanical properties based on the percentage used. It increases the strength of the formed steel alloy when you use about 5%. Also, using a higher percentage above 12% enhances the corrosion resistance of the formed alloy.
- Vanadium: Vanadium can enhance carbon steel’s heat resistance, strength, and entire grain structure when used at 0.15%. However, it offers improved hardness without compromised formability when used with chromium.
Differences Between Alloy Steel vs. Stainless Steels
This section compares the different aspects of alloy steel and stainless steel:
Physical Properties
Alloy steel is famous for its high strength-to-weight ratio, strength, and durability. Also, it maintains hardness at high temperatures and offers good wear and corrosion resistance. On the other hand, stainless steel is easy to clean and highly resistant to corrosion and stain. It is non-magnetic, durable, electrically conductive, and highly resistant to higher temperatures.
Chemical Composition
The alloying elements of alloy steel include a high amount of chromium, molybdenum, and other alloying elements. Using higher alloying elements helps heat-treat alloys to a wide range of hardness levels.
In contrast, stainless steel is highly resistant to acid, bases, and other organic solutions. Its primary constituents include chromium, carbon, and iron. However, certain varieties often contain nickel, manganese, silicon, and other elements.
Applications
Manufacturers often use alloy steels in the construction, automotive, oil and gas, aerospace, and manufacturing fields. On the other hand, typical applications for stainless steel include Kitchenware, medical equipment, the chemical and petrochemical industry, and the food and beverage industry.
Tensile Strength
Tensile strength describes a material’s ability to withstand tensile strength before it breaks. However, the alloy and the employed heat treatment often determine this property. Alloy steel is very durable, and its tensile strength is about 960 Mpa, while stainless steel is less durable and with a tensile strength of 621 Mpa.
Fatigue Strength
Fatigue stress defines a material’s ability to withstand stress for a particular number of cycles. A material’s fatigue stress is the maximum stress it can withstand. For instance, 146.45 Mpa is the fatigue stress of the stainless 316L.
Generally, stainless steels have lower fatigue strength than alloy steel—nonetheless, stainless steel grades like duplex stainless steel exhibit high fatigue strength due to their microstructure.
Other Comparisons for Alloy Steel Besides Stainless Steel
Besides stainless steel, other alternatives to using alloy steel include:
- Chromium-vanadium
Combining vanadium atoms with chromium forms lattice structures with excellent strength-to-weight ratios. This makes chromium-vanadium ideal for various applications that need a strong and lightweight material. However, due to its strength, most manufacturers use chromium-vanadium to create cutting tools.
- Aluminum
Aluminum is a typical material widely utilized in the automobile manufacturing industry. Aluminum products resist corrosion when exposed to water like iron-based metals do. Also, aluminum is perfect for making body panels and other structural components of vehicles because it is very strong and lightweight.
Other Comparisons for Stainless Steel Besides Alloy Steel
Here are other similar materials that stainless steel is compared against besides alloy steel:
- Carbon Steel
Carbon Steel is one of the famous steel types. It is commonly used because of the durability and high strength it offers. Manufacturers generally use carbon steel for several applications because it costs less than stainless steel. High carbon steel provides excellent strength and resistance to wear, which many cutting tools need. Meanwhile, low-alloy steel offers versatility and malleability for machinery parts, cookware, and pipes.
- Tool Steel
This is a carbon steel type commonly used for making tools. It exhibits remarkable hardness and wear resistance. As a result, manufacturers utilize these features in manufacturing products such as drill bits, knives, and saws.
Helpful Tips to Consider When Determining the Ideal Steel for Your Machining Project
Considering the tips below, you should be able to determine the right steel for your application.
Functional Requirement
The functional requirement of a product will always determine the steel type suited for such application. For instance, if a part is required to function in a marine environment, its corrosion resistance property is a primary factor. Hence, a stainless steel grade material is a perfect choice. Also, alloy steel would be ideal for structural applications such as construction.
Maintenance and Lifespan
Stainless steel is better than alloy steel when considering maintenance and lifespan. Stainless steel grades need little to no maintenance and exhibit longer lifespans because of their self-repairing properties. More importantly, stainless steel is recyclable.
Aesthetic Preferences
Stainless steel is quite famous for its aesthetic appeal. Hence, product designers and manufacturers in the architecture and interior designing sectors commonly use stainless steel for most parts. Its highly reflective surface makes it shiny and modern. Additionally, it is available in various shapes offering manufacturers extensive products.
Budget Constraint
The limitations of your budget determine the ideal steel type for your project. As far as cost goes, alloy steel is less expensive than stainless steel. However, it is advisable not to compromise quality for cost.
Conclusion
This article has detailed an explanation of alloy steel vs. stainless steel, discussing their distinct properties. Although both materials offer impressive mechanical properties and are critical to modern manufacturing, it would be best to determine the one that fits your machining project best, considering all variables.
However, if you need the help of professionals determining the suitable material between alloy steel and stainless steel, contact AT-Machining. We provide extensive manufacturing capabilities and value-added services for your prototyping and manufacturing needs. Our team of expert engineers has in-depth knowledge and experience in CNC machining, sheet metal fabrication, and other manufacturing solutions you seek. Contact us today; let’s discuss the details of your next project.
