Carbon Tool Steel Round Bar

Carbon tool steel round bar is a solid, circular, long steel product made from high-quality, high-carbon non-alloy steel. Its key characteristics include low cost and good machinability; after heat treatment, it achieves high hardness and excellent wear resistance, making it a fundamental material for manufacturing various cutting tools, molds, and measuring tools.

Carbon tool steel typically has a carbon content ranging from 0.65% to 1.35% and is classified as a special-quality non-alloy steel.
Based on application, it can be categorized as follows:
1. Carbon cutting tool steel: Used for making cutting tools such as lathe tools, drill bits, and taps.
2. Carbon mold steel: Used for making cold-working and hot-working molds.
3. Carbon measuring tool steel: Used for making measuring instruments.

Common grades begin with the letter "T," followed by a number indicating the average carbon content in thousandths (e.g., T7, T8, T10, T12). An "A" suffix (e.g., T8A, T10A) denotes high-quality steel with stricter controls on impurities like sulfur and phosphorus and superior toughness, making it suitable for tools with complex shapes and high precision requirements.

Heat Treatment of Carbon Tool Steel Round Bar

The production of carbon tool steel round bar relies on forging and heat treatment to refine its internal microstructure and achieve desired properties.
Taking the T10 heat treatment process as an example: T10 is a common carbon tool steel offering moderate toughness and low production costs. After heat treatment, it can achieve a hardness exceeding 60 HRC. However, it has low hardenability and poor heat resistance (up to 250°C), so it is primarily used for simple tools such as hand-held cutters.

Equipment: Thermoelectric thermometer, medium-temperature box-type resistance furnace.
Annealing: Heating temperature 760–780°C; furnace cooling. Annealing significantly reduces the steel's hardness.
Normalizing: Heating temperature 820–840°C; air cooling.
Tempering: Heating temperature 650–700°C. Quenching: Quenching medium: oil; heating temperature: 790°C; quenching method: for small, straight-bar blade blanks, the part is generally lowered vertically and slowly.
Tempering: At 150°C, hardness reaches 62 HRC but is prone to edge chipping; tempering is typically performed at 200–250°C, resulting in a hardness of 55–60 HRC.
The above outlines the standard heat treatment process for T10 steel in industrial settings.

Properties of Carbon Tool Steel Round Bars

1. High hardness and wear resistance: After heat treatment, hardness typically ranges from 60 to 64 HRC (reaching up to 66–67 HRC), providing excellent wear resistance.
2. Good machinability and low cost: Easy to forge and machine; raw materials are abundant and inexpensive, making it one of the most widely used tool steels.

Main Limitations:
1. Low hardenability: This is its most significant drawback. The through-hardening diameter is only about 15 mm in water and 5 mm in oil; consequently, it is unsuitable for large tools and is prone to deformation and cracking during quenching.
2. Poor hot hardness: Hardness and wear resistance drop sharply when operating temperatures exceed 250°C; therefore, it cannot be used for high-speed cutting or high-temperature applications.

Applications of Carbon Tool Steel Round Bars

Carbon tool steel round bars have a wide range of applications. They are suitable for manufacturing tools that require sharp cutting edges and a certain level of toughness—but are not subjected to sudden, severe impact or vibration—under conditions involving difficult cutting and high wear resistance requirements. Examples include lathe tools, planer blades, drill bits, taps, reamers, threading dies, milling cutters, and hacksaw blades. They are also used for cold heading dies, blanking dies, wire drawing dies, cold extrusion female dies for aluminum alloys, paper blanking dies, plastic molding dies, small cold trimming and punching dies, and low-precision, simple-shaped measuring tools (such as limit gauges), as well as wear-resistant parts not subject to heavy impact. 

Carbon tool steel round bars offer a combination of good hardness, wear resistance, and machinability, while also being cost-effective and practical. As an indispensable material in industrial production, they hold a significant position and offer broad application prospects.

Carbon structural steel round bars have different standards implemented in each country, the following are some common implementation standards

Chinese standard:
GB/T 14981-2009 "Dimension shape mass and tolerance for hot-rolled round wire rod"
This standard specifies the requirements for the size, shape, weight and allowable deviation of hot-rolled round wire rods. If the product standard specifies otherwise, it shall comply with the requirements of the corresponding product standard.

The production and inspection of carbon tool steel round bars primarily comply with the national standard GB/T 1298-2008, "Carbon Tool Steels."

British Standard:
The BS EN 10025 series of standards is part of European Standards (EN) which contain specifications for different types of hot-rolled non-alloy structural steels, including carbon structural steels.

American standard:
ASTM A36 is a standard issued by the American Society for Testing and Materials, which regulates the chemical composition, mechanical properties, and dimensional tolerances of carbon structural steel (including steel plates, billets, steel bars, etc.).

Japanese standard
JIS G3101 is the Japanese Industrial Standard specification for rolled steel for general structural use, including carbon structural steel.

The production process of carbon tool steel is not complicated and therefore very easy to obtain. The carbon tool steel standard formulated by the state has made clear regulations on all aspects.

T10 is a general-purpose, low-hardenability cold-work die steel. As a high-carbon tool steel, it exhibits low hardenability, relatively poor wear resistance, and significant deformation during quenching.

Chemical Composition:
(Mass fraction, %) C 0.95–1.04; Si ≤ 0.35; Mn ≤ 0.40; P ≤ 0.035; S ≤ 0.030.
It is suitable for small-to-medium batch production applications, including integral cold-heading dies and punching/shearing tools that operate with a hardened surface layer (case-hardened state).

Mechanical Properties:
Indentation diameter ≥ 4.30 mm;
Quenched hardness ≥ 62 HRC;
Heat treatment specification: Quench specimen at 760–780°C, water-cooled;
Delivery condition: Steel is delivered in the annealed state. Delivery in the unannealed state is also possible upon mutual agreement.

T10 carbon tool steel offers higher strength and wear resistance than T8 and T9 grades; however, it has low hot hardness and hardenability, and is prone to deformation during quenching. It possesses a fine grain structure that resists coarsening during quenching heat treatment, maintaining a fine-grained microstructure. After quenching, the steel retains undissolved excess carbides, resulting in high wear resistance; it is used to manufacture tools requiring sharp cutting edges and a degree of toughness. It is suitable for tools that operate under poor cutting conditions and require high wear resistance and sharp edges—without being subjected to sudden, severe impact or vibration—while still needing some toughness. It can also be used for wear-resistant parts not subjected to heavy impact.

Outer diameter: 2mm-500mm
Grade: 201,202,301.304.321.316.31