When comparing alloy steel and stainless steel, one common point of confusion arises: Although stainless steel is technically a type of alloy steel, it is often treated as a distinct category and compared separately against other steel options during material selection. Why is that, and which material should you choose for your project? To answer these questions, it helps to first understand what alloy steel is and explore the various types it includes.
Understanding Alloy Steel
Alloy steel is a type of steel that contains more than one alloying element, such as chromium, nickel, molybdenum, vanadium, and manganese, to the basic iron and carbon composition. Unlike carbon steel, which primarily consists of iron and carbon, these added elements are carefully selected and combined in varying amounts to deliver specific properties like increased strength, better toughness, enhanced wear resistance, or improved corrosion and heat resistance.
Most Common Alloying Elements and Their Effects
Chromium (Cr): Chromium's effects in alloy steel depend on its concentration. At low levels (0.5%~2%), it improves hardenability and strength by forming carbides and refining the grain structure. At higher levels (above 10%), chromium enables the formation of a dense and stable chromium oxide layer— primarily Cr₂O₃— on the steel surface, which effectively blocks oxygen, moisture, and other corrosive agents, thereby significantly enhancing corrosion resistance.
Nickel (Ni): Also has an effect depending on the percentage. At lower percentages (roughly 1~5%), nickel increases the toughness and ductility of the alloy steel, indirectly enhancing its strength and impact resistance. At higher percentages (typically around 8~12% or more), it helps achieve excellent corrosion resistance while also ensuring good low-temperature toughness and ductility.
Molybdenum (Mo): Valued for its ability to strengthen steel at high temperatures. It increases hardness and helps steel resist softening during prolonged exposure to heat. Moreover, molybdenum improves resistance to localized corrosion, such as pitting and crevice corrosion, especially when combined with chromium.
Manganese (Mn): Helps form martensite during heat treatment, which increases strength and wear resistance. It also improves toughness and ductility, reducing the risk of cracking. Additionally, it acts as a deoxidizer by removing impurities and controlling sulfur— forming manganese sulfide (MnS) that prevents the formation of brittle microstructures.
Vanadium (V): Refines the grain structure of steel, resulting in higher strength, increased toughness, and improved wear and heat resistance. When combined with chromium, the alloy tends to have enhanced hardness while still retaining adequate formability, provided that the overall composition and processing are carefully controlled.
Tungsten (W): Forms stable carbides that improve alloy steel's strength, hardness, and wear resistance at high temperatures. This makes it a popular choice for tool steels and high-speed cutting tools.
Types of Alloy Steel
Alloy steels come in a variety of broad categories. Here we break these down in the table below.
Type
Characteristics
Examples
High-Alloy Steels
▪ Contain >5% alloying elements, commonly including chromium, nickel, and molybdenum.
▪ Some have exceptional corrosion resistance, especially in harsh environments (e.g., marine, chemical processing).
▪ Excellent mechanical properties in demanding engineering scenarios.
▪ Some types offer superior performance under high temperatures and pressures, such as heat-resistant steels.
▪ Many high-alloy steels, such as stainless steels, have high oxidation resistance, resulting in longer service life and lower maintenance.
▪ Contain <5% alloying elements, typically including molybdenum, chromium, manganese, silicon, boron, nickel, and vanadium.
▪ High strength and toughness.
▪ Generally good weldability and machinability.
▪ Cost-effective alternative for structural applications.
▪ Often used in mining and construction equipment due to their good strength-to-weight ratios.
▪ HSLA Steels
▪ Quenched and Tempered Steels (4340, A514)
▪ Pipeline Steels (API 5L X65, X70)
Tool Steels
▪ A special type of alloy steel, used to make cutting tools, dies, molds, jigs and fixtures.
▪ Contain a relatively high carbon content (typically 0.5% to 1.5%), though some types, like hot work steels, may have lower carbon levels.
▪ Extremely hard and wear-resistant.
▪ Some types, such as high-speed and hot work steels, retain their properties at high temperatures.
▪ Long service life under high stress.
▪ High-Speed Steels (M2, M42)
▪ Cold Work Steels (D2)
▪ Hot Work Steels (H13)
Maraging Steels
▪ Ultra-high strength, low-carbon steel.
▪ Superior strength-to-weight ratio.
▪ Strengthened through precipitation hardening rather than carbon strengthening.
▪ Excellent toughness and ductility compared to conventional high-strength steels.
▪ Widely used in aerospace, high-performance machinery, and tooling applications.
▪ 18Ni (250, 300, 350)
▪ Co-based Maraging Steels
Understanding Stainless Steel
As shown in the chart above, stainless steel falls under the category of high-alloy steel. It has a high chromium content (≥10.5%), which gives it strong resistance to rust. Depending on what the application requires, manufacturers often add elements like nickel, molybdenum, titanium, and copper to further enhance its strength, corrosion resistance, or performance at high temperatures. In addition, it also has good formability, an attractive appearance, and excellent durability. This makes it widely used in industries such as healthcare, construction, and kitchenware.
Types of Stainless Steel
There are hundreds of stainless steel grades available, but they are generally classified into five main categories:
Type
Characteristics
Common Gradesand Applications
Austenitic Stainless Steel
▪ Contains ≥16% chromium and 8-12% nickel，with high-nickel variants (e.g., 310S, 904L) containing up to 20-25% nickel.
▪ Non-magnetic (may become slightly magnetic after cold working).
▪ Excellent corrosion resistance, particularly in humid, acidic, and chemical environments.
▪ Can be strengthened through cold working (work hardening).
▪ Good ductility and weldability.
304 (18-8 stainless steel)：The most widely used stainless steel, common in food processing, construction, and chemical industries.
316 ： Higher corrosion resistance than 304, especially in marine and chemical environments.
310S ：High-temperature resistant, used in furnaces and boilers.
Ferritic Stainless Steel
▪ Contains10-30% chromium, low carbon, and little or no nickel.
▪ Ferromagnetic.
▪ Moderate to good corrosion resistance, lower than austenitic stainless steel, but generally better than martensitic stainless steel.
▪ Cannot be hardened by heat treatment but can be strengthened through cold working.
▪ Have relatively low toughness, which limits their use in certain structural applications.
▪ Lower thermal expansion and good oxidation resistance.
430 ：Cost-effective with moderate corrosion resistance, used in kitchenware and automotive exhaust systems.
444 ：High-chromium variant, showing improved chloride resistance in water and plumbing systems.
446 ：High oxidation resistance, suitable for high-temperature environments.
Martensitic Stainless Steel
▪ Contains 11-18% chromium, with higher carbon content (0.1-1.2%).
▪ Fully Magnetic.
▪ Generally lower corrosion resistance compared to austenitic and ferritic stainless steels.
▪ Can be hardened by heat treatment (quenching & tempering).
▪ Offer reduced ductility and low weldability.
410: General-purpose martensitic stainless steel, used for wear-resistant and corrosion-resistant parts.
420: Used for surgical instruments, scissors, and bearings due to its high hardness.
440C: Higher carbon content, providing extreme hardness for high-end knives and bearings.
Duplex Stainless Steel
▪ Contains 18-28% chromium, 3.5 -5.5% nickel, and often includes molybdenum (Mo) and nitrogen (N) to enhance corrosion resistance and strength.
▪ A balanced duplex structure (-50% austenitic,- 50% ferritic).
▪ Higher strength than austenitic stainless steel (1.5 to 2 times).
▪ Excellent resistance to pitting and crevice corrosion.
▪ Better chloride stress corrosion cracking (SCC) resistance than pure austenitic stainless steels.
▪ Good fatigue resistance.
▪ Moderate ductility and weldability.
2205: The most common grade with high strength and corrosion resistance for marine and chemical industries.
2507 (Super Duplex Stainless Steel): Designed for extreme corrosion resistance in seawater processing equipment.
Precipitation-Hardening Stainless Steel
▪ Contains 12-16% chromium, 3-8% nickel, and small amounts of copper, aluminum, and titanium for precipitation hardening.
▪ Strengthened by precipitation hardening (aging treatment).
▪ Offers high strength and good corrosion resistance.
▪ Higher strength than austenitic stainless steels, close to martensitic stainless steels, but with better toughness.
▪ Good weldability
17-4PH (630): The most commonly used PH stainless steel, ideal for high-strength, corrosion-resistant applications.
15-5PH: Similar to 17-4PH but with improved toughness.
Differences Between Alloy Steel and Stainless Steel
Although stainless steel is considered a type of alloy steel and both share the basic properties of iron-based alloys, they can differ significantly in terms of composition and performance. Below is a general comparison of their key differences.
Composition
Alloy steel contains a mixture of iron and various alloying elements such as chromium, nickel, manganese, vanadium, molybdenum, and silicon. The amounts and types of these elements can vary depending on the grade of alloy steel. In contrast, stainless steel is primarily composed of iron, carbon, and at least 10.5% chromium (by weight). The high chromium content is what gives stainless steel its resistance to corrosion. Other elements, such as nickel, molybdenum, and manganese, may also be included to further enhance its properties, but chromium remains the key differentiator.
Tensile Strength
Tensile strength is the maximum stress a material can withstand when being stretched or pulled before breaking; and it depends on the alloy and the heat treatment process. Alloy steels typically have higher tensile strength (758 ~ 1882 MPa or even higher) than stainless steel (515 ~ 827 MPa), although some specialized stainless steels, such as martensitic stainless steels can go up to 1200 MPa or higher. As a result, alloy steels have more structural applications.
Fatigue Strength
Fatigue strength is the ability of a material to withstand repeated or cyclic loading without failing over time, and it’s usually lower than the material's maximum tensile strength. Alloy steels tend to have better fatigue strength than stainless steels because they can be heat-treated to optimize their internal structure. However, some stainless steels, like duplex stainless steels, also have strong fatigue resistance due to their microstructure.
Impact Resistance
Impact resistance measures a material’s ability to absorb energy before fracturing. Alloy steels are often made for high strength and toughness. They are typically better at absorbing energy under sudden loads. But some alloy steels can be brittle, especially those with high carbon or those hardened by quenching and tempering.
Stainless steel’s primary advantage is its corrosion resistance, but this can sometimes come at the cost of its impact resistance. While certain stainless steel grades (such as austenitic stainless steels) are quite tough and resistant to fracture under impact, they may not perform as well in high-impact or shock-loading conditions as some high-strength alloy steels.
Hardness
The hardness of alloy steel can vary significantly depending on the grade and heat treatment process. It can range from around 200 HB (Brinell hardness) to over 600 HB, or even higher for high-carbon or tool steels. In comparison, the hardness of stainless steel typically falls between 150 HB and 300 HB. While certain martensitic grades of stainless steel can be heat-treated for higher hardness, they still do not reach the levels of hardness seen in high-carbon alloy steels or tool steels.
Ductility
Ductility is a material’s ability to deform without breaking. The ductility of alloy steels varies widely, with lower-carbon alloys being more ductile, while high-strength alloys or tool steels tend to have lower ductility. The balance between ductility and strength is controlled by adjusting the alloy composition and heat treatment.
Stainless steel, especially austenitic grades, generally offers better ductility than alloy steels of similar strength due to its higher nickel content. However, martensitic and ferritic stainless steels have lower ductility and are more prone to cracking under deformation.
Corrosion Resistance
Stainless steel’s corrosion resistance mainly comes from its chromium content. When exposed to oxygen, chromium forms a thin, stable oxide layer that protects the metal from general corrosion. Unlike alloy steels, stainless steels do not need extra protective coatings. Nevertheless, different grades show varying corrosion resistance.
Localized forms of corrosion, such as pitting and crevice corrosion, are common in stainless steel. Pitting occurs when the protective chromium oxide layer is locally damaged by chlorides and similar agents. Crevice corrosion typically develops in narrow gaps—like those found around bolts or in joints—where chlorides and moisture can accumulate and accelerate corrosion. Overall, the presence of chromium in stainless steel reduces the chances of pitting and crevice corrosion compared to alloy steel.
Stainless steel also provides higher resistance to galvanic corrosion, which occurs when two different metals contact each other in an electrolyte, causing the more active metal to corrode. Alloy steels are more prone to this type of corrosion due to their lower electrochemical potential。
Similarly, when it comes to stress corrosion cracking (SCC)—the cracking of a material under tensile stress in a corrosive environment—stainless steel generally performs better. Its protective chromium oxide layer not only resists general corrosion but also helps prevent crack initiation. However, resistance to SCC can vary among different stainless steel grades and depends on the specific service environment. For example, austenitic stainless steels (like 304 and 316) often offer strong SCC resistance in many settings, although they can be vulnerable in chloride-rich environments.
Heat Treatment
Alloy steel can undergo heat treatment over a wide temperature range, with common methods including annealing, normalizing, quenching, and tempering. It offers greater flexibility in optimizing properties such as hardness, strength, and wear resistance. For example, high-speed steel (HSS) can be heat-treated to achieve extremely high hardness, making it highly effective for cutting tools.
Stainless steel is mainly heat-treated through annealing, solution treatment, quenching, and tempering. However, the heat treatment process varies significantly with different grades. Martensitic stainless steels can be heat-treated by quenching and tempering to achieve high hardness and strength. Austenitic stainless steels primarily rely on solution treatment followed by cold working to improve strength, rather than conventional quenching and tempering, since high temperatures can compromise their corrosion resistance. Ferritic stainless steels are usually heat-treated to improve workability or relieve internal stresses, but such treatment does not significantly alter their hardness and strength.
Weldability
Both alloy steels and stainless steels are weldable, but each has its own characteristics. Low-carbon alloy steels are easier to weld, while high-strength or high-carbon grades require preheating and post-weld heat treatment to prevent cracking. Among stainless steels, austenitic grades offer the best weldability, whereas martensitic and ferritic grades are more challenging and tend to be prone to brittleness or cracking.
Machinability
Machinability measures how easily a material can be cut, shaped, or drilled. Alloy steel generally has better machinability than stainless steel, especially free-machining grades. For example, austenitic stainless steel 304 has a 40% machinability rating compared to alloy steels such as 1018 with a 78% machinability. Martensitic and ferritic stainless steels have improved machinability but require specialized tooling to handle their hardness.
Formability
Formability is the ability of a material to be shaped without breaking. Low-carbon alloy steels have good formability, but high-strength alloy steels and tool steels are more difficult to shape due to their increased hardness. Stainless steel’s formability varies by grade. Austenitic stainless steels offer exceptional formability, making them well-suited for deep drawing, bending, and complex forming applications. In contrast, martensitic stainless steels have the lowest formability due to their higher hardness and brittleness.
Advantages of Alloy Steel Over Stainless Steel
Alloy steel is a broader and more versatile group of materials that offers several advantages over stainless steel:
It is cost-effective.
It has a high strength-to-weight ratio and can be made very hard, which suits demanding applications.
Certain alloy steels offer better high-temperature resistance.
Its heat treatment options allow manufacturers to fine-tune its properties, often resulting in better fatigue resistance .
It is highly versatile due to its excellent machinability.
Advantages of Stainless Steel Over Alloy Steel
Stainless steel is also a widely used material that has several advantages over alloy steel：
It offers superior corrosion resistance.
It requires lower maintenance.
Its cleaner, more hygienic surface makes it ideal for food, medical, and sanitary applications.
Austenitic stainless steel is more ductile and easier to shape than most alloy steels.
Stainless steel is eco-friendly and can be 100% recyclable.
Helpful Tips to Consider When Selecting the Right Steel for Your Project
Choosing the right steel is important for ensuring optimal performance, durability, and cost-effectiveness in any project. Here are key points to consider when deciding between alloy steel and stainless steel.
Functional Requirements
The intended application of the material largely determines the type of steel required. If the part is exposed to a marine environment or chemical exposure, stainless steel is a better choice due to its superior corrosion resistance. However, for structural applications like bridges, buildings, and heavy machinery, alloy steel is preferred for its higher strength and toughness.
Budget Constraints
Budget limitations can determine the steel type for your project. Alloy steel is generally more affordable than stainless steel due to its lower alloying element content. However, it is not advisable to compromise quality for cost, as selecting an unsuitable material may lead to higher maintenance and replacement costs in the long run.
Maintenance and Lifespan
If low maintenance and long lifespan are key priorities, stainless steel may be a better investment. Unlike alloy steel, which often requires protective coatings to prevent corrosion, stainless steel is naturally resistant to rust and can last for decades with minimal upkeep. More importantly, stainless steel is recyclable, making it a sustainable choice.
Aesthetic Appeal
For projects where appearance matters, stainless steel is often the preferred choice. Its polished, reflective, and shiny surface gives it a sleek, modern look that is highly desirable in architecture, interior design, and high-end consumer products. Furthermore, its resistance to tarnishing or discoloration over time enhances its appeal. Additionally, stainless steel is available in various finishes, giving designers more flexibility in creating visually appealing products.
Conclusion
To choose the right steel, you need to weigh factors like functional requirements, overall cost, maintenance demands, and environmental impact. If corrosion resistance, aesthetics, and long-term durability are priorities, stainless steel is the best choice. However, if high strength, ease of machining, and cost savings are your main concerns, alloy steel is a better fit.
Chiggo offers a wide range of manufacturing capabilities and extra services to support your prototyping and production needs. Our skilled team of engineers is experienced in CNC machining, sheet metal fabrication, die casting, and other manufacturing solutions you need. Contact us today to discuss the details of your next project.
