The Ultimate Guide to AISI 1018 Steel: Properties, Machining, Heat Treatment, and Applications

When it comes to versatility in manufacturing, AISI 1018 steel (also known as Grade 1018 Mild Steel) is the undisputed workhorse of the industry. Known for its excellent balance of strength, ductility, and affordability, this low-carbon steel is a staple in CNC machining, prototyping, and sheet metal fabrication.

 

 

In this guide, we will dive deep into what makes 1018 steel unique, properties and composition, material selection about 1018 steel with other alloys, its machining and surface protection,  heat treatment and hardening by carburizing.

 

 

 

 

What is AISI 1018 Steel?

 

 

 

AISI 1018 (commonly called 1018 steel, Grade 1018, or AISI/SAE 1018) is a versatile low-carbon mild steel with an average carbon content around 0.18%. It’s widely used across machining, fabrication, and general-purpose engineering because it balances cost, manufacturability, and mechanical performance. This steel is popular due to it has characteristics of:

 

• Cost-effective: As a low-carbon commodity steel, 1018 is inexpensive and widely available in bar, plate, and sheet forms, making it a practical choice for high-volume and prototype work.
  
• Excellent machinability: Its soft ferritic/pearlitic microstructure and predictable behavior in cutting lead to good surface finishes, lower tool wear, and faster cycle times—especially in cold-rolled (CRS) variants that provide tighter tolerances and smoother surfaces.
  
• Good formability and weldability: Low carbon content yields excellent weldability and shape ability, simplifying fabrication for stamped, bent, or welded components without stringent pre/post-weld procedures.
  
• Adaptable through surface hardening: While 1018 has modest bulk strength, it responds well to surface carburizing or case‑hardening, enabling a hard, wear-resistant outer layer over a tough, ductile core—ideal for pins, shafts, and mating parts.
  

 

 

 

Global Equivalents of 1018 Steel

 

 

Depending on where you are sourcing your materials, 1018 steel may go by different names:

 

 

Table 1: Equivalents of 1018 Steel in Different Regions

 

 

    

    

 

 

Chemical Composition and Microstructure of Grade 1018 Steel

 

 

The "18" in 1018 represents its carbon content—approximately 0.18%. Other simple composition include 98.81% - 99.26% lron (Fe) as the base metal;0.60% - 0.90% Manganese  (Mn) added to increase the material's strength; Phosphorus(P) ≤ 0.04% and Sulfur (S)≤ 0.05% as the trace elements.

 

 

At a microscopic level, 1018 steel is a mix of Ferrite (the softer, highly ductile part) and Pearlite (the harder, stronger part). This combination allows the metal to be easily formed while maintaining enough strength for structural use.

 

 

 

 

Key Properties of AISI 1018 Steel

 

 

You can find mechanical, physical and thermal properties in below table 2:

 

 

Table 2: Key Properties of AISI 1018 Steel

 

 

 

 

 

 

 

Heat Treatment: Turning a Soft Core into a Hard Surface

 

 

One of the biggest limitations of 1018 steel is that it cannot be deep-hardened (also the through-hardened, a heat treatment that makes a steel part uniformly hard, strong, and wear-resistant throughout its entire cross-section) because there isn't enough carbon to transform the entire core into martensite.

 

However, it is the best steel for carburizing (case hardening). By diffusing carbon into the surface layer at high temperatures, you can create a part with a glass-hard exterior and a tough, ductile core. And carburizing is a critical part of the overall heat treatment process. 

 

 

Common Heat Treatment Processes of 1018 Steel

 

• Carburizing: Adding carbon to the surface for hardness.
  
• Case Hardening: Creating a thin, hard outer "case."
  
• Annealing (850°C - 950°C): Softening the metal for better cold working.
  
• Normalizing (890°C - 940°C): Refining the grain structure after forging.
  
• Stress Relieving: Removing internal pressures caused by heavy machining.

 

 

Comparison: Surface Hardness Before & After Heat Treatment

 

 

You can find surface hardness of 1018 mild steel in its different stages in below table:

 

 

Surface Hardness of 1018 Mild Steel in Different Stages

 

 

 

            

 

            

What are Functions of Carburized AISI 1018 Steel

 

 

AISI 1018 is widely used for many machined and heat‑treated parts because of its favorable balance of machinability, formability, and response to surface hardening. The Carburized AISI 1018 Steel's processing logic can be separated into two practical stages:

 

 

Before carburizing — excellent machinability and formability

 

• Machinability: In the as‑rolled or cold‑drawn condition, 1018’s low carbon content gives moderate hardness and predictable cutting behavior. Drilling, turning, milling, and tapping are efficient with reduced tool wear and good surface finish.
  
• Formability: The steel’s ductility and elongation make it well suited for stamping, cold forming, flanging, edge rolling, and bulging operations. The low risk of cracking during severe deformation simplifies forming processes and reduces scrap.

 

After carburizing — “hard exterior, tough core”

 

• Hard surface (case): Carburizing raises the carbon content in the surface layer; after quenching this layer transforms to a hard martensitic case. The hardened case provides excellent wear resistance for sliding, rolling, and contact applications—ideal for components such as worms, ratchets, pins, and small gears.
  
• Tough core (core): The core retains the original low‑carbon, ductile microstructure, preserving impact resistance and overall toughness. This combination of a hard outer shell and a ductile core prevents brittle failure under shock or heavy loading and avoids cracking during severe bending or deformation.

 

Typical parts that exploit the “hard case / tough core” of carburized 1018 include:

 

• Power transmission and locking components: worms, pawls, ratchets, gears and pinions (small).
  
• Fasteners and pins: dowel pins, chain pins, anchor pins, studs, and special bolts.
  
• Wear and support parts: bushings, liners, oil‑tool slips, tie rods, and many general machinery parts

 

 

 

CNC Machining with 1018 Steel

 

 

 

What is CNC Machining and Prototyping with 1018 Steel?

 

CNC Machining 1018 Steel is the process of using CNC machinery—such as mills and lathes—to automatically cut and shape 1018 low-carbon steel into finished parts. 1018 Steel Prototyping refers to the rapid production of initial functional models or test samples using this specific material and technology.

 

 

Why 1018 Steel is Ideal for CNC Machining and Prototyping?

 

The popularity of 1018 steel is primarily due to its exceptional machinability, tool-friendliness, and excellent surface finish.

 

• Exceptional Machinability: With a low carbon content (0.14% to 0.20%), 1018 steel is relatively soft with good ductility. It boasts a 70% machinability rating, making the cutting process highly efficient and predictable.
  
• Reduced Tool Wear: Because the material is soft, it causes minimal wear on cutting tools. This significantly extends tool life and lowers overall production costs.
  
• Superior Surface Finish: Especially in its cold-rolled state, 1018 steel achieves a clean, bright, and smooth finish. This reduces the time and cost required for secondary post-processing.
  
• Excellent Weldability: 1018 steel is easy to weld using standard methods, which is highly beneficial for prototypes or final products that require the assembly of multiple components.
  
• Cost-Effectiveness: As a common low-carbon steel, 1018 is inexpensive and widely available, making it a budget-friendly choice for both mass production and economical prototyping.
  

 

 

 

 

What is AISI 1018 Steel Used for？

 

 

 

 

1018 steel is widely used in the manufacturing of various non-critical structural components and mechanical parts:

 

• Mechanical Components: Frequently used for gears, pins, spindles, and bushings.
  
• Structural Supports: Used for various mounting plates and brackets.
  
• Fasteners: Such as screws and studs.
  
• Case-Hardened Parts: 1018 steel is ideal for carburizing (surface hardening) heat treatments, which improve surface wear resistance while maintaining a tough, ductile core.
  

 

 

 

Corrosion Resistance and Surface Protection of 1018 Steel

 

 

 

 

Does 1018 steel rust? Yes, easily. Like most carbon steels, it lacks the chromium content found in stainless steel. 

 

• Without Chromium (like 1018 steel): 1018 is a carbon steel primarily composed of iron. When exposed to oxygen and moisture, it forms Iron Oxide, commonly known as rust. This oxide layer is porous and flaky; it does not adhere tightly to the surface. As it peels off, it constantly exposes fresh metal to the environment, allowing corrosion to continue deep into the material.
  
• With Chromium (like stainless steel): Stainless steel contains at least 10.5% chromium. Chromium reacts with oxygen to create a microscopic, dense, and "self-healing" layer of Chromium Oxide. This passive film acts as a barrier that prevents oxygen and water from reaching the iron underneath, effectively stopping rust. 

 

To prevent oxidation of 1018 steel, various surface treatments are recommended:

 

 

Black Oxide: Provides a sleek black look and mild rust resistance. 

 

 

It is a chemical conversion coating. The steel is submerged in a hot, alkaline salt solution (caustic soda and nitrates) which triggers a chemical reaction that converts the surface iron into magnetite, a black iron oxide. It adds negligible thickness (1–2 microns), making it ideal for high-precision CNC parts where tight tolerances must be maintained. It provides a sleek, non-reflective matte finish and mild corrosion resistance when oiled.

 

 

Zinc Plating: A sacrificial layer that prevents corrosion.

 

 

It is an electroplating process. The 1018 steel part is placed in an electrolyte bath, and an electric current is used to deposit a thin layer of metallic zinc onto the surface. It offers sacrificial protection. Zinc is more chemically active than iron; therefore, the zinc layer will corrode (sacrifice itself) first to protect the underlying steel, even if the coating is scratched. This is the standard for nuts, bolts, and automotive fasteners.  

 

 

Powder Coating: Best for structural parts exposed to the elements.

 

 

It is an electrostatic spray deposition. A dry powder (typically a polymer resin) is electrostatically charged and sprayed onto the grounded 1018 steel part. It provides a thick, durable barrier that is much tougher than liquid paint. It is highly resistant to impact, UV rays, and harsh weather, making it the best choice for structural brackets and outdoor machinery.

 

 

Chrome Plating: For high-wear applications and aesthetic shine. 

 

 

It's a complex electroplating process where a layer of chromium is deposited over the steel. You can choose this surface treatment for high-wear applications or aesthetic shine. Hard chrome is perfect for high-wear moving parts like hydraulic rods or pistons while decorative chrome provides a mirror-like shine that does not tarnish, making it ideal for high-end aesthetic applications.

 

 

 

 

Material Selection of 1018 vs. Other Steel Grades

 

 

When choosing a steel grade, the right question is not “Which is best?” but “Which is best for my purpose?” Below are concise, purpose-driven comparisons that highlight where AISI 1018 shines and where higher-carbon or alloy steels are preferable.

 

 

Precision machining and prototyping — choose 1018 steel

 

• Why choose 1018: Low carbon (~0.18%) and clean, predictable microstructure give excellent machinability, good surface finish, long tool life, and consistent dimensional control after machining. Cold-rolled 1018 offers tighter tolerances and smoother surfaces for precision parts and prototypes.
  
• Typical uses: functional prototypes, fixtures, jigs, shafts, pins, decorative parts, and general-purpose turned or milled components.
  
• Trade-offs: Lower bulk hardness and ultimate strength than medium/high-carbon steels; for wear-critical parts, surface hardening (carburizing) is recommended.
  

 

 

High strength and load-bearing components — choose 1045 and 4140

 

• 1045 (medium carbon): With ~0.45% carbon, 1045 provides markedly higher tensile strength and hardness after quenching and tempering than 1018. It’s a good choice for moderately loaded shafts, axles, and parts needing higher core strength without expensive alloying.
  
• 4140 (alloy steel): Chromium–molybdenum alloying gives superior strength, toughness, fatigue resistance, and hardenability. 4140 is the go-to for heavily loaded, fatigue-prone parts (gears, high-stress shafts, coupling components) especially when through-hardening or deep-section strength is needed.
  
• Comparison of 1045 vs 4140 vs 1018: Both 1045 and 4140 outperform 1018 in strength, wear resistance, and fatigue life but are less weldable and harder to machine. Cost and heat-treatment complexity are higher.
  

 

 

General structural members — A36

 

A36 (structural carbon steel) is optimized for welded, bolted, and riveted building/structural applications. It is economical, readily available in plates and sections, and designed to meet structural yield and ductility requirements.

 

• Typical uses: beams, channels, general construction plates, and non-precision structural brackets.
  
• Comparison of A36 vs 1018: A36 has comparable or slightly higher yield for structural sections but is not produced with the same emphasis on dimensional tolerances or machining finish as cold-rolled 1018. For parts requiring precision machining and good surface quality, 1018 (particularly CRS) is the superior choice. For large welded structures and heavy plate applications, A36 is more cost-effective.

 

 

 

Conclusion

 

 

AISI 1018 steel is the perfect choice for projects where ease of fabrication and cost-efficiency are priorities. Whether you are building complex CNC-machined components or simple structural brackets, understanding its response to heat treatment and surface finishing will help you maximize the performance of this mild carbon steel material.

 

 

 

 

 

Case Study: High-Precision Hydraulic Manifold Machining

 

 

A manufacturer of hydraulic systems needed to produce a batch of 1018 steel hydraulic manifolds. Despite 1018 being classified as a "free-machining" steel, the customer encountered two critical bottlenecks in their previous cooperated CNC machining plant:

 

• Poor Surface Finish ("Gummy" Material): Due to its low carbon content, 1018 steel is "gummy," leading to Built-Up Edge (BUE) on cutting tools. The customer could only achieve a surface roughness of Ra 3.2, while the sealing surfaces required Ra 0.8 to prevent high-pressure leaks.
  
• Deep-Hole Chip Evacuation: The parts featured cross-drilled oil galleries with a depth-to-diameter ratio of 10:1. The long, stringy chips characteristic of 1018 steel frequently tangled around the drills, causing tool breakage and a 15% scrap rate, causing higher cost.
  

 

 

VMT CNC Machining Factory resolved these issues through the following methods:

 

 

 

 

1. Digitized Cutting Parameter Modeling:

 

• Speed Optimization: Instead of relying on manual estimates, VMT used simulation software to identify the critical cutting velocity. The cutting speed (VC) was increased from 120m/min to 180m/min to move beyond the BUE zone.
• Tooling Geometry: Custom PVD-coated (TiAlN) carbide tools with a high-rake angle chip breaker were selected to force the "gummy" 1018 chips to snap into small, manageable segments.
  

 

2. Real-Time In-Process Monitoring:

 

Automated Probing: CNC centers were equipped with automated tool-wear sensors. The system captured dimensional data every 20 cycles, automatically applying offsets to the CNC controller to compensate for the slight abrasive wear caused by the manganese content in 1018 steel.

 

 

The implementation of VMT’s optimized process yielded the following good results:

 

• Surface Quality Excellence: Surface roughness was improved from Ra 3.2 to a consistent Ra 0.6–0.8, eliminating the need for secondary polishing and ensuring a 100% seal rate.
  
• Productivity Surge: By increasing cutting speeds and eliminating downtime caused by chip tangling, the cycle time per part was reduced from 45 minutes to 28 minutes, representing a 37% increase in efficiency.
  
• Scrap Rate Reduction: Tool breakage in deep-hole drilling was virtually eliminated. The scrap rate plummeted from 15% to less than 0.3%.
  
• Tool Life Extension: The digitized high-pressure cooling reduced thermal stress on the inserts, extending tool life by 50% and lowering the overall cost per part.
  

 

 

 

FAQs

 

 

Q: Is material 1018 steel expensive?

 

A: No. It is one of the most economical steels available due to its simple composition and wide market availability.

 

 

Q: Why is stainless steel more corrosion-resistant than 1018 carbon steel ?

 

A: Stainless steel contains at least 10.5% Chromium, which forms an invisible, self-healing protective layer. 1018 has negligible chromium.

 

 

Q: What are the main advantages of material 1018 steel?

 

A: Exceptional weldability, high ductility, excellent machining properties, and perfect response to case hardening.

 

 

Q: What are the main disadvantages of material 1018 steel ?

 

A: Low corrosion resistance and the inability to be through-hardened for high-strength core requirements.

 

 

Q: What is the difference between Hot Rolled (HR) and Cold Finished (CF) 1018 steel?

 

A: Cold Finished 1018 has a smoother surface, tighter dimensional tolerances, and higher strength due to work hardening, whereas Hot Rolled is more cost-effective but has a rougher scale finish and less precise dimensions.

 

 

Q: Can 1018 steel be used for high-wear parts like heavy-duty gears?

 

A: Only if it is case-hardened (carburized). In its raw state, it is too soft for high-wear applications, but case hardening creates a very hard outer shell while maintaining a ductile, shock-resistant core.