Steel is the most widely used core raw material in the CNC machining industry. With its highly adaptable mechanical properties, excellent machinability, cost-effectiveness, and long service life, steel perfectly meets the demands of high-precision, high-efficiency, and multi-scenario CNC manufacturing. It has become the preferred base material for a wide range of industrial components.
The comprehensive advantages of steel can be summarized into four key dimensions:
The steel materials commonly used in CNC machining can be categorized into six major groups: carbon steel, free-cutting steel, alloy steel, cold work tool steel, hot work tool steel, and plastic mold steel. Each material type has significant differences in carbon content, mechanical properties, machinability, and application scenarios. The following table provides a comprehensive comparison of their characteristics.
| Material Category | Common Grades | Carbon Content Range | Key Advantages | Typical Applications |
|---|---|---|---|---|
| Low Carbon Steel | 1018, Q235, 20# Steel | ≤0.25% | Excellent machinability, low cost, good weldability and forming performance | Brackets, fixtures, housings, non-load-bearing sheet metal components |
| Medium Carbon Steel | 1045, 40# Steel | 0.25%–0.6% | Balanced strength, hardness, and toughness; significantly improved performance after heat treatment | Drive shafts, gears, bolts, mold bases, load-bearing structural parts |
| High Carbon Steel | 65Mn, 1095, T8, T10 | ≥0.6% | High hardness, excellent wear resistance, and good elasticity after hardening | Punches, springs, measuring tools, small cutting tools |
| Free-Cutting Steel | 12L14, 1215, Y15, Y40Mn | Approx. 0.15% | Excellent chip breaking, superior surface finish, reduced tool wear | Precision pins, miniature shafts, electronic instrument components |
| Alloy Steel | 40Cr (4140), 20CrMnTi, 35CrMo | Approx. 0.40% | Higher fatigue strength and wear resistance than carbon steel; excellent heat treatment stability | Spline shafts, high-strength bolts, hydraulic components, precision gears |
| Cold Work Tool Steel | Cr12, Cr12MoV, D2, SKD11 | Approx. 1.5% | Ultra-high hardness (HRC58–64), excellent compressive strength and wear resistance | Stamping dies, cutting dies, forming dies, wear plates |
| Hot Work Tool Steel | H13, SKD61, 4Cr5MoSiV1 | Approx. 0.4% | High-temperature resistance, thermal fatigue resistance, excellent thermal conductivity | Die casting molds, hot forging dies, extrusion dies, mold cavities |
| Plastic Mold Steel | S136, NAK80, P20 | 0.3%–0.4% | Mirror polishing capability, pre-hardened condition, corrosion resistance | High-gloss injection molds, corrosion-resistant plastic molds, general-purpose molds |
Carbon steel is primarily composed of iron and carbon, with no significant amount of alloying elements. It offers the lowest machining cost among steel materials and is generally classified into three categories based on carbon content: low carbon steel, medium carbon steel, and high carbon steel.
Grade: AISI 1018, Q235, 20# Steel
Properties: Low hardness (HB120–160), excellent plasticity, easy cutting, good cold forming and welding performance; moderate strength with poor corrosion resistance.
Machining: High-speed cutting capability with low tool wear; suitable for rough machining with large feed rates and cutting depths. Rust prevention treatment is required after machining.
Applications: Brackets, fixtures, housings, non-load-bearing structural components, and sheet metal parts.
Grade: AISI 1045, 40# Steel
Properties: Balanced strength, hardness, and toughness. Overall performance can be significantly improved through quenching and tempering treatment.
Machining: Suitable for direct machining or finishing after heat treatment. Compatible with turning, milling, drilling, and grinding processes.
Applications: Shafts, gears, bolts, connecting rods, mold bases, and load-bearing structural components.
Grades: 65Mn, AISI 1095, T8, T10
Properties: High hardness, excellent wear resistance, good elasticity, high strength but poor toughness and machinability.
Machining: Usually requires rough machining in annealed condition. After hardening, only grinding processes are recommended. Requires low cutting speed and small cutting depth.
Applications: Cutting tools, punches, springs, wear blocks, and measuring tools.
Grade: 12L14, 1215, Y15, Y40Mn
Properties: Easy chip breakage during cutting, high surface finish, long tool life, high machining efficiency; strength and toughness are slightly lower than ordinary carbon steel.
Machining: Suitable for high-speed, high-feed machining; suitable for automatic lathes and CNC batch production of small precision parts.
Applications: Precision shafts, pins, nuts, electronic components, instrument parts.
Grade: 40Cr (AISI 4140), 20CrMnTi, 35CrMo
Properties: Strength, fatigue strength, and wear resistance are far superior to carbon steel; good hardenability and minimal deformation after heat treatment; good machinability.
Machining: Excellent machinability after quenching and tempering; suitable for heavy-duty, high-precision parts; requires matching cutting tools and parameters.
Applications: Gears, splined shafts, high-strength bolts, mold inserts, hydraulic components.
Grade: Cr12、Cr12MoV、D2、SKD11
Properties: High hardness (HRC 58–64), high wear resistance, high compressive strength; moderate toughness.
Applications: Cold stamping dies, shearing dies, drawing dies, forming dies, wear blocks.
Grade: H13、SKD61、4Cr5MoSiV1
Properties: High-temperature strength, resistance to thermal fatigue, good thermal conductivity; excellent toughness.
Applications: Die casting molds, hot forging molds, extrusion molds, injection mold cores/cavities.
Grades: S136、NAK80、P20
Properties: S136 is corrosion-resistant and can be mirror-polished; NAK80 is pre-hardened and requires no heat treatment; P20 is highly versatile.
Applications: High mirror finish molds, corrosion-resistant molds, and ordinary injection molds.
Regardless of steel grade, CNC machining operations must follow five fundamental principles: proper tool selection, optimized cutting parameters, effective cooling and lubrication, rigid workholding, and process sequencing. These standards ensure machining accuracy, surface quality, and extended tool life.
For common low carbon steel and medium carbon steel:
TiAlN-coated carbide cutting tools are recommended due to their excellent wear resistance, high-temperature stability, and suitability for high-volume carbon steel CNC machining applications.
For high-carbon steel and heat-treated mold steels with high hardness:
CBN (Cubic Boron Nitride) tools or ceramic cutting tools combined with TiCN coatings are preferred. These tool materials help prevent edge chipping, reduce rapid tool wear, and maintain stable cutting performance under high-hardness machining conditions.
Soft steel materials (low carbon steel and free-cutting steel):
High-hardness steel materials (hardened mold steel and high-carbon steel):
For standard carbon steel and free-cutting steel:
Use conventional water-based emulsion coolant systems. The coolant should be directed toward the cutting zone to effectively remove heat and improve tool performance.
For high-alloy steel and high-hardness mold steel:
Use extreme-pressure cutting fluids containing sulfur and chlorine additives. These lubricants help reduce tool adhesion, minimize high-temperature wear, and improve machining stability.
Workholding rigidity is a critical factor affecting dimensional accuracy.
The CNC machining process should separate roughing and finishing operations:
Rough Machining:
Rapidly removes excess material while releasing internal stresses within the raw material. After rough machining, stress relief time may be required before final machining.
Finish Machining:
Prefer climb milling operations to achieve stable dimensional control and improved surface quality. Proper finishing strategies help maintain tight tolerances and prevent deformation caused by residual machining stress.
Steel CNC machining is widely used across industrial manufacturing due to its excellent strength, machinability, and reliability. By selecting the appropriate steel grade and applying suitable heat treatment processes, manufacturers can achieve optimized performance for different application requirements.
Material: 1045 Medium Carbon Steel
Process: CNC turning + quenching and tempering treatment
1045 steel provides an excellent balance of strength, toughness, and machinability. After heat treatment, the material achieves improved mechanical performance, making it ideal for precision fluid pipeline connectors, adapters, and mechanical transmission components requiring stable dimensional accuracy.
Material: 40Cr Alloy Steel
40Cr alloy steel delivers high strength, excellent fatigue resistance, and superior wear performance. It is commonly used for engineering machinery hydraulic components, including precision piston parts that require long service life and reliable operation under high-pressure working conditions.
Materials: 20CrMnTi Alloy Steel + Free-Cutting Steel Combination
For new energy vehicle applications, different steel materials can be combined according to functional requirements. 20CrMnTi alloy steel provides high strength and excellent fatigue resistance, while free-cutting steel improves machining efficiency for high-volume precision manufacturing.
This material combination is widely applied in lightweight automotive structural components and precision metal parts requiring both performance reliability and production efficiency.
View Steel CNC Machining Capability.
A: For standard low carbon steel and medium carbon steel (the primary materials used in carbon steel CNC machining), TiAlN-coated carbide cutting tools are the preferred choice due to their excellent wear resistance and thermal stability.
For hardened high-carbon steel and cold/hot work tool steels, CBN (Cubic Boron Nitride) or ceramic cutting tools combined with TiCN coatings are recommended. These solutions effectively reduce tool edge chipping, premature wear, and machining instability under high-hardness conditions.
A: Tool breakage in steel CNC machining is mainly caused by three factors:
Mismatch between tool coating, cutting tool material, and workpiece hardness — an unsuitable tool selection can accelerate edge damage and reduce tool life.
Excessive cutting forces caused by improper parameters — machining hardened steel with overly high spindle speed, cutting depth, or feed rate can overload the cutting edge.
Insufficient fixture rigidity — unstable workholding can generate machining vibration and impact forces, causing tool chipping or breakage.
A: Rough machining removes large amounts of excess material, which generates significant cutting heat and releases internal stresses within the workpiece. These factors may cause slight deformation.
Separating roughing and finishing operations allows the material to release stress before final machining. During the finishing stage, dimensional accuracy and surface quality can be precisely controlled, reducing the risk of tolerance failure caused by deformation.
A: Generally, no additional cooling system is required.
Free-cutting steel contains elements such as sulfur and lead, which improve chip breaking, reduce tool adhesion, and enhance machining stability. Standard emulsion coolant is usually sufficient.
The key focus is maintaining smooth chip evacuation. Properly increasing spindle speed and feed rate can further improve production efficiency in high-volume CNC machining.
A: High-hardness mold steel requires dedicated fixtures to ensure sufficient clamping rigidity.
Important considerations include:
Control tool overhang ratio at L/D ≤ 3 to minimize vibration.
Apply appropriate clamping force to prevent workpiece deformation.
Maintain stable positioning throughout machining to ensure final dimensional accuracy.
The selection of cutting fluid should follow a material-matching principle:
Standard carbon steel: Use general-purpose water-based emulsion coolant for effective heat removal and lubrication.
High-alloy steel and mold steel: Select cutting fluids containing extreme-pressure additives to reduce high-temperature cutting wear, improve machining stability, and extend tool service life.
Fiona Huang is a Sales Engineer with 16+ years of experience in the mechanical and precision manufacturing industry. She specializes in CNC machining components, custom fasteners, and engineering-driven manufacturing solutions. With strong expertise in international trade and technical project support, she focuses on transforming complex engineering requirements into high-precision, production-ready solutions for global clients.
