SAE 1118 is a low-carbon, resulfurized, and rephosphorized free-machining steel grade that occupies a unique position in the world of CNC machining and precision manufacturing. Often specified when engineers need a balance between machinability and mechanical performance, SAE 1118 is part of the 11xx series of steels, which are designed specifically for high-speed machining operations. This guide provides a comprehensive technical overview of SAE 1118, covering its chemical composition, mechanical and physical properties, typical applications, machining considerations, and how it compares to other related steel grades. Whether you are a product designer selecting a material for a high-volume component or a procurement specialist evaluating supplier capabilities, understanding the nuances of SAE 1118 is essential for making informed decisions.
Chemical Composition of SAE 1118
The chemical composition of SAE 1118 is carefully controlled to deliver its characteristic free-machining properties. The addition of sulfur and phosphorus is the defining feature of this steel grade, distinguishing it from plain low-carbon steels like SAE 1018 or SAE 1020. These elements act as chip breakers and lubricants during machining, reducing cutting forces and improving surface finish.
The typical chemical composition of SAE 1118 is presented in the table below. It is important to note that these values represent typical ranges and that specific heats may vary slightly depending on the manufacturer and the applicable specification (e.g., ASTM A29, SAE J403).
| 要素 | 組成範囲（%） | 合金における役割 |
|---|---|---|
| 炭素（C） | 0.14 – 0.20 | Provides core strength and hardness; low content ensures good weldability and formability. |
| マンガン（Mn） | 1.00 – 1.30 | Improves hardenability, tensile strength, and acts as a deoxidizer; also combines with sulfur to form manganese sulfide inclusions. |
| リン（P） | 0.040 – 0.090 | Enhances machinability and strength, but must be controlled to avoid excessive brittleness. |
| 硫黄（S） | 0.08 – 0.13 | The primary free-machining additive; forms manganese sulfide inclusions that act as chip breakers. |
| シリコン（Si） | 0.10 – 0.30 | Used as a deoxidizer during steelmaking; contributes marginally to strength. |
| 鉄（Fe） | バランス | Base element. |
Typical values based on SAE J403 and ASTM A29 standards.
How Sulfur and Phosphorus Enhance Machinability
The deliberate addition of sulfur in SAE 1118 results in the formation of manganese sulfide (MnS) inclusions during solidification. These inclusions are soft and act as internal stress concentrators, causing the chip to break more readily during machining. This leads to shorter, more manageable chips that are less likely to tangle around the tool or workpiece. Phosphorus, on the other hand, increases the hardness and brittleness of the ferrite phase, which also contributes to chip breakage and improves the surface finish of the machined part.
Comparison of SAE 1118 with Other 11xx Grades
SAE 1118 is often compared with SAE 1117 and SAE 1215. While SAE 1117 has a slightly lower carbon content (0.14–0.20% compared to 0.14–0.20% for 1118, though the lower end is more common for 1117), SAE 1215 has a much higher sulfur content (0.26–0.35%) and virtually no manganese. The higher manganese content in SAE 1118 (1.00–1.30%) provides better strength and hardenability than SAE 1215, making it a better choice for parts that require a degree of case hardening after machining.
Mechanical Properties of SAE 1118
The mechanical properties of SAE 1118 are typical of a low-carbon, resulfurized steel. It is not designed for high-strength applications in the as-rolled or normalized condition, but it responds well to case hardening (carburizing) and can develop a hard, wear-resistant surface while retaining a tough, ductile core. The following table outlines the typical mechanical properties for SAE 1118 in the cold-drawn and normalized conditions.
| 特性 | Cold-Drawn Condition | Normalized Condition |
|---|---|---|
| 引張強度（MPa） | 540 – 620 | 450 – 520 |
| 降伏強度（MPa） | 440 – 510 | 340 – 380 |
| 50 mm における伸び率（%） | 15 – 20 | 25 – 30 |
| 断面収縮率（%） | 40 – 50 | 55 – 60 |
| 硬度（ブリネル） | 150 – 180 HB | 130 – 150 HB |
| 弾性係数（GPa） | 200 | 200 |
Typical values. Actual properties depend on section size, heat treatment, and processing history.
Case Hardening Response
One of the most important attributes of SAE 1118 is its excellent response to case hardening. The low carbon content of the core ensures it remains tough and ductile, while the surface can be carburized to a depth of 0.5 to 1.5 mm, achieving surface hardness values of 58-62 HRC. This combination of a hard, wear-resistant surface and a tough core makes SAE 1118 ideal for applications such as gears, camshafts, and other components that experience both wear and impact loading.
Machinability Rating
SAE 1118 has a machinability rating of approximately 80-85% relative to AISI B1112, which is the benchmark for free-machining steels (rated at 100%). While not as free-machining as SAE 1215 (which has a rating of 136%), SAE 1118 offers a better balance of machinability and mechanical properties. This makes it a popular choice for high-volume production where tool life and cycle times are critical factors.
Physical Properties of SAE 1118
The physical properties of SAE 1118 are largely similar to other low-carbon steels, as the alloying additions do not significantly alter these fundamental characteristics. However, these properties are important for design calculations, particularly when considering thermal expansion or electrical conductivity in specific applications.
| 特性 | 値 |
|---|---|
| 密度（g/cm³） | 7.87 |
| 融点（°C） | Approx. 1510 |
| 熱伝導率（W/m·K） | 51.9 (at 100°C) |
| 比熱容量（J/kg·K） | 486 (at 50°C) |
| Electrical Resistivity (µΩ·m) | 0.15 (at 20°C) |
| Thermal Expansion Coefficient (µm/m·°C) | 11.9 (at 20-100°C) |
Typical values for low-carbon steel.
磁気特性
SAE 1118 is ferromagnetic, meaning it can be magnetized. This property is often relevant in applications where the component may be subject to magnetic fields or where magnetic particle inspection is used for quality control. The magnetic properties are not significantly affected by the sulfur and phosphorus additions.
主要な特性と利点
Understanding the key characteristics of SAE 1118 is crucial for engineers deciding whether this material is suitable for their specific application. Its unique combination of properties makes it a versatile choice, but it also has limitations that must be considered.
Advantages of SAE 1118
The primary advantage of SAE 1118 is its excellent machinability. The presence of manganese sulfide inclusions reduces cutting forces, extends tool life, and allows for higher cutting speeds and feed rates. This translates directly into lower production costs, especially for high-volume parts. Furthermore, its case-hardening capability allows for the production of components with a hard, wear-resistant surface and a tough core, making it suitable for demanding mechanical applications.
限界と考慮事項
The main limitation of SAE 1118 is its reduced ductility and impact toughness compared to non-resulfurized steels like SAE 1018. The manganese sulfide inclusions, while beneficial for machining, act as stress concentrators and can reduce the fatigue strength of the material. Therefore, SAE 1118 is not recommended for applications involving high impact loads or severe cyclic stresses. Additionally, the higher sulfur content can lead to porosity issues during welding, so welding is generally discouraged unless special precautions are taken.
Typical Applications of SAE 1118
SAE 1118 is used in a wide range of industries where machinability and case-hardening capabilities are paramount. Its applications span from automotive components to general industrial machinery. The material’s ability to be machined into complex shapes with tight tolerances makes it a favorite among CNC machining service providers.
Automotive and Transportation Components
In the automotive sector, SAE 1118 is commonly used for manufacturing gears, pinions, shafts, and other powertrain components that require a hard, wear-resistant surface. The case-hardened surface provides the necessary durability for meshing gears, while the tough core absorbs shock loads. It is also used for producing precision shift knobs and other interior or mechanical components where a combination of machinability and strength is required. Many CNC machined shift knobs are produced from SAE 1118 for this reason, as detailed in our guide on CNC加工によるシフトノブ.
General Industrial and Machinery Parts
Beyond automotive, SAE 1118 is used for a variety of industrial components, including fasteners, fittings, and small machine parts. Its machinability makes it ideal for producing threaded components, as the clean cuts result in well-defined threads with minimal burr formation. It is also used for manufacturing mounting blocks and other support structures where strength and machinability are required. For a deeper understanding of how such components are designed and machined, you can refer to our article on 取付ブロックの理解.
Machining and Fabrication Considerations for SAE 1118
Machining SAE 1118 is generally straightforward, but adhering to best practices ensures optimal results in terms of tool life, surface finish, and dimensional accuracy. The following sections provide practical guidance for CNC machining this material.
推奨切削条件
SAE 1118 is designed for high-speed machining. When turning with carbide tooling, cutting speeds of 150-250 m/min are typical. For milling, speeds of 100-200 m/min are common, depending on the operation and tool geometry. High-speed steel (HSS) tools can also be used but at lower speeds (30-60 m/min). Feeds should be moderate to high, as the material’s chip-breaking characteristics allow for aggressive material removal rates without the risk of long, stringy chips.
| 作業工程 | 工具材料 | 切削速度（m/min） | 送り速度（mm/回転） |
|---|---|---|---|
| Turning (Roughing) | 超硬合金 | 200-250 | 0.3-0.5 |
| Turning (Finishing) | 超硬合金 | 180-220 | 0.1-0.2 |
| Milling (Face) | 超硬合金 | 150-200 | 0.1-0.2 (per tooth) |
| 穴あけ加工 | HSS | 30-40 | 0.1-0.15 |
| ねじ切り | 超硬合金 | 80-120 | — |
Recommended starting parameters. Actual values depend on machine rigidity, tool geometry, and desired surface finish.
Tooling and Chip Control
The manganese sulfide inclusions in SAE 1118 act as a built-in chip breaker, which means that standard tool geometries are generally sufficient. However, using inserts with a positive rake angle and a chip breaker design can further improve chip control and surface finish. For drilling operations, it is crucial to use a high-quality coolant to flush chips out of the hole and prevent them from packing. When tapping, a good quality tapping fluid or water-soluble coolant is recommended to prevent tool breakage.
熱処理と表面仕上げ
After machining, components made from SAE 1118 can be case hardened via carburizing. The process involves heating the part in a carbon-rich atmosphere, followed by quenching and tempering. This produces a hard, wear-resistant case (typically 0.5-1.5 mm deep) with a hardness of 58-62 HRC. For surface finishing, SAE 1118 can be plated, painted, or powder coated. It is also suitable for black oxide coating, which provides a mild corrosion resistance and an attractive appearance. For more information on such finishes, you might consider our article on 黒色継手 CNC加工.
関連鋼種との比較
Selecting the right steel grade for a project requires a clear understanding of how different materials compare. SAE 1118 is often evaluated against SAE 1018, SAE 1117, and SAE 1215. The table below summarizes the key differences.
| 特性 | SAE 1118 | SAE 1018 | SAE 1215 |
|---|---|---|---|
| Carbon (%) | 0.14-0.20 | 0.15-0.20 | 0.09 max |
| Manganese (%) | 1.00-1.30 | 0.60-0.90 | 0.75-1.05 |
| Sulfur (%) | 0.08-0.13 | 最大0.05 | 0.26-0.35 |
| Phosphorus (%) | 0.040-0.090 | 0.04 max | 0.07-0.12 |
| Machinability Rating | 80-85% | 70% | 136% |
| Case Hardening | 優れている | 良好 | 劣る |
| 溶接性 | 良好 | 優れている | 劣る |
| 典型的な用途 | Gears, shafts | General parts | High-volume screws |
Comparison of typical properties and characteristics.
SAE 1118 vs. SAE 1018
SAE 1018 is a plain low-carbon steel that is widely used for general fabrication. It has excellent weldability and formability but is more difficult to machine than SAE 1118. For parts that require extensive machining, SAE 1118 offers a significant advantage in terms of tool life and cycle time. However, if the part will be welded, SAE 1018 is the safer choice due to its lower sulfur content.
SAE 1118 vs. SAE 1215
SAE 1215 is the ultimate free-machining steel, with a machinability rating of 136%. However, it has very poor case-hardening response due to its low carbon and manganese content. SAE 1118, with its higher manganese content, provides a much better balance. If a component requires both high-volume machining and a hardened surface, SAE 1118 is the superior choice. For simple, non-hardened parts where maximum machining speed is the only priority, SAE 1215 may be considered.
Tuofa CNC: Precision Machining of SAE 1118 Components
At Tuofa CNC, we specialize in the precision CNC machining of a wide range of materials, including SAE 1118. Our state-of-the-art facilities and experienced engineering team are well-equipped to handle projects that demand tight tolerances, excellent surface finishes, and high-volume production efficiency. We understand the unique characteristics of free-machining steels and have optimized our processes to leverage their benefits while mitigating any potential drawbacks.
Our Capabilities with SAE 1118
Tuofa CNC offers comprehensive CNC turning, milling, and drilling services for SAE 1118. Our machinery is capable of achieving tolerances as tight as ±0.005 mm, ensuring that your components meet the most demanding specifications. We also offer in-house case hardening services, allowing us to deliver fully finished, hardened components that are ready for assembly. Our team can provide guidance on material selection, design for manufacturability, and optimal machining parameters to ensure the most cost-effective production of your parts.
Quality Assurance and Sourcing
We maintain strict quality control procedures to ensure that every component we produce meets or exceeds your expectations. Our sourcing team works with reputable steel suppliers to ensure that the SAE 1118 we use is of consistent quality and meets all relevant standards. When you partner with Tuofa CNC, you gain a manufacturing partner dedicated to your success. For projects requiring a robust supply chain, we also offer guidance on sourcing manufacturers in Mexico and other regions, helping you balance cost, quality, and lead time.
結論
SAE 1118 is a versatile and highly machinable low-carbon steel that offers an excellent balance of manufacturing efficiency and mechanical performance. Its unique composition, featuring elevated sulfur and phosphorus, makes it a top choice for high-volume CNC machining applications where tool life and cycle times are critical. The material’s excellent response to case hardening further extends its utility, allowing for the production of durable, wear-resistant components with a tough core. While it may not be suitable for applications requiring high impact toughness or extensive welding, its advantages in machinability and surface hardening make it an invaluable material in the engineer’s toolkit. By understanding its properties, applications, and machining considerations, you can make informed decisions that optimize both performance and cost. For expert assistance with your next SAE 1118 project, consider partnering with Tuofa CNC for precision, quality, and reliability.