This article references the Metal Materials Encyclopedia and the national standard GB/T 699-2015 to provide a detailed analysis of the performance characteristics and processing applications of 15F rimmed steel. As a commonly used low-carbon rimmed steel, 15F offers slightly higher strength than 08F and 10F while maintaining excellent cold formability and weldability. Its balanced properties make it a versatile choice for stamped and structural components that require moderate load-bearing capacity, and it is frequently specified in automotive and general machinery applications where cost-effectiveness and manufacturability are prioritized.
1. Basic Information of 15F
15F is a high-quality carbon structural steel conforming to the GB/T 699-2015 standard. The designation “15” indicates an average carbon content of approximately 0.15%, while “F” denotes rimmed steel (Rimmed Steel). This steel grade features a moderately low carbon content and very low silicon content (≤0.07%), providing good cold stamping formability combined with a certain level of strength. It is suitable for stamping parts and structural components that require a degree of load-bearing capacity. Due to the rimmed steel production method, internal segregation exists in the core; therefore, attention must be paid to sampling locations for critical load-bearing components. From a metallurgical standpoint, the low silicon content minimizes the formation of silicates, improving surface quality during stamping, while the controlled rimming action results in a cleaner outer shell but a higher impurity gradient toward the center.
2. Chemical Composition
| Element | Content (%) |
|---|---|
| Carbon (C) | 0.12-0.18 |
| Silicon (Si) | ≤0.07 |
| Manganese (Mn) | 0.25-0.50 |
| Phosphorus (P) | ≤0.035 |
| Sulfur (S) | ≤0.035 |
| Chromium (Cr) | ≤0.25 |
| Nickel (Ni) | ≤0.30 |
| Copper (Cu) | ≤0.25 |
The chemical composition of 15F is tightly controlled to balance formability and strength. The low silicon content, typical of rimmed steels, ensures a clean surface finish and reduced oxide inclusions, which is beneficial for subsequent coating or welding processes. The manganese range of 0.25-0.50% provides sufficient deoxidation and solid-solution strengthening without significantly impairing ductility. Residual elements such as chromium, nickel, and copper are kept low to avoid hardenability effects that could compromise cold forming behavior.
3. Mechanical Properties
| Property | Value | Condition |
|---|---|---|
| Tensile Strength | ≥375 MPa | Normalized |
| Yield Strength | ≥225 MPa | Normalized |
| Elongation | ≥27% | Normalized |
| Reduction of Area | ≥55% | Normalized |
| Hardness | ≤143 HB | Hot-rolled or Annealed |
The mechanical properties listed are minimum values obtained from normalized specimens, ensuring consistent performance in as-delivered conditions. The elongation of ≥27% reflects excellent ductility, enabling deep drawing and complex bending operations without cracking. The relatively low yield strength allows for easy plastic deformation, while the tensile strength of at least 375 MPa provides adequate structural integrity for light to moderate loads. In practice, these values may vary slightly depending on the thickness and processing history of the material.
4. Heat Treatment Characteristics
The heat treatment characteristics of 15F are as follows:
- Normalizing: 900-940°C, air cooling, refines the grain structure.
- Annealing: 680-740°C, furnace cooling or air cooling, relieves residual stresses.
- Carburizing: Surface carburizing is possible (900-930°C); after carburizing, quenching produces a hard surface layer.
- Quenching and Tempering: Can be performed under certain conditions (quenching 860-900°C + tempering 500-650°C), but the hardness increase is limited.
- Weldability: Good, suitable for gas welding and arc welding.
Given its low carbon content, 15F does not respond strongly to conventional hardening heat treatments; however, carburizing can achieve a wear-resistant surface while maintaining a tough core. Normalizing is often employed to homogenize the microstructure after hot working, improving machinability and uniformity. The wide annealing temperature range allows flexibility in stress relief without significant grain growth, making it suitable for components requiring dimensional stability prior to final machining.
5. Typical Applications
- Automotive parts (stamped structural components, brackets, chassis reinforcing plates)
- Machinery manufacturing (flanges, connectors, tube sheets)
- Vessel manufacturing (pressure vessel heads, shells)
- Construction hardware (connection plates, fastening brackets)
- Agricultural machinery parts (frames, guard plates, protective covers)
- CNC machined parts (precision hole machining of stamped blanks, profile milling)
These applications leverage the combination of moderate strength, excellent formability, and good weldability that 15F provides. In automotive chassis components, the steel’s ability to absorb energy during deformation contributes to crashworthiness, while in pressure vessel parts, its ductility ensures safe fabrication and operation. The material’s cost-effectiveness also makes it a preferred choice for high-volume production of non-critical structural elements across various industries.
6. CNC Machining Performance
CNC machining characteristics of 15F:
- Machinability: Low-carbon steel with a slightly lower tendency to sticking than 08F or 10F, but attention is still needed to control built-up edge formation.
- Cutting Speed: 150-250 m/min (with coated carbide tools).
- Tool Selection: Carbide tools with PVD coating, rake angle 10-15°.
- Cooling: Emulsion cutting fluid at a concentration of 5-8%, with ample supply.
- Accuracy: After stamping, CNC finishing can achieve tolerances of IT7-IT8 grade.
The machinability of 15F is generally satisfactory, though the presence of soft ferrite can lead to a sticky chip behavior. Using sharp tools with positive rake angles and adequate coolant flow helps maintain surface finish and dimensional control. For precision CNC operations on previously stamped blanks, the material’s consistent hardness and low springback facilitate tight tolerance maintenance, particularly when machining hole patterns or contoured edges.
7. Procurement Guide
Market Price Reference (2025 Market Conditions):
- Cold-rolled sheet (0.5-3mm): 5-8 RMB/kg
- Hot-rolled plate (3-12mm): 4-6.5 RMB/kg
- Round bar: 4.5-6.5 RMB/kg
- Strip steel: 5-7.5 RMB/kg
Prices are indicative and can vary based on quantity, supplier, and regional factors. Cold-rolled products command a premium due to tighter thickness tolerances and better surface finish, making them suitable for exposed automotive or appliance parts. Hot-rolled and round bar forms are more economical for structural applications where surface appearance is not critical. When procuring, it is advisable to specify the required condition (normalized, annealed, or as-rolled) to match the intended processing route.
8. Data Sources
- GB/T 699-2015 “Quality Carbon Structural Steels”
- Metal Materials Encyclopedia, 15F Special Entry
The information presented is derived from authoritative standards and reference works. For specific design or processing decisions, engineers should consult the latest revisions of GB/T 699-2015 or contact material suppliers for certified test reports. The Metal Materials Encyclopedia entry provides supplementary data on typical in-service behavior and comparative analysis with adjacent grades like 10F and 20F.
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