AISI 1025 Carbon Steel Properties and Applications

AISI 1025 carbon steel is a frequently specified plain carbon steel utilized across various industrial sectors. It is classified as low-carbon steel, though depending on the specific context, it is sometimes referenced within medium-carbon listings. Its characteristics make it a versatile material for numerous applications.

1. 1025 Carbon Steel Chemical Composition (ASTM Standards)

The chemical makeup of 1025 steel is governed by established industry standards, ensuring consistency. Key specifications include:

• Standards:ASTM A29/A29M, ASTM A108, ASTM A576-90b (2000)
• Carbon (C): 0.22% – 0.28%
• Manganese (Mn): 0.30% – 0.60%
• Phosphorus (P): 0.040% maximum
• Sulfur (S): 0.050% maximum
• UNS Designation: G10250

These composition ranges define the grade’s fundamental properties.

2. 1025 Carbon Steel Mechanical Properties

The mechanical properties of 1025 steel, such as tensile strength and yield strength, are influenced by its condition (e.g., hot-rolled, cold-finished) and any subsequent heat treatment.

• Hot-Rolled: Typical values for hot-rolled bars (e.g., 16mm diameter) show moderate strength levels suitable for many general-purpose applications. Specific strength figures can vary. [Original document source 11 provides figures like 125-175 ksi TS / 80 ksi YS, while other sources suggest lower values typical for low-carbon steel. It’s best to consult specific mill certifications for guaranteed minimums].
• General Characteristics: Compared to higher carbon or alloy steels, 1025 offers lower tensile strength but generally good ductility and toughness.

1025 steel possesses good machinability, a key advantage, particularly when supplied in a cold-finished (CF) condition. Its lower carbon content contributes to easier machining compared to harder steels.

3. 1025 Carbon Steel Applications

• Shafting: Good machinability makes it a popular choice for industrial shafting.
• Structural Components: These are used in structural applications and are often supplied as hot-rolled products conforming to standards like EN 10025 or as sheet/strip under ASTM A1011/A1011M, where formability can be important.

4. Heat Treatment Guide for 1025 Steel

1025 steel is a versatile low-carbon steel. Its mechanical properties can be significantly altered through various heat treatment processes. Understanding these treatments is key to optimizing 1025 steel for specific industrial applications. This guide outlines the common heat treatments applicable to 1025 steel and their effects.

4.1 Annealing

Purpose: Annealing is primarily used to soften 1025 steel, making it more ductile and easier to form. It also relieves internal stresses and refines the grain structure.

Process:

1. Heat the steel uniformly to a temperature within the annealing range, typically 880-930°C for low-carbon grades like 1025.
2. Hold at this temperature long enough for complete austenitization (transforming the steel’s structure to austenite).
3. Cool the steel slowly, usually within the furnace.

Result: Slow cooling promotes the formation of a soft microstructure, mainly consisting of ferrite and pearlite. This enhances ductility and formability, preparing the steel for subsequent manufacturing steps.

4.2 Normalizing

Purpose: Normalizing refines the grain size and improves microstructural uniformity. It results in slightly higher strength and hardness than annealed 1025 steel while maintaining good ductility.

Process:

1. Heat the steel to the austenitizing temperature range (similar to annealing, around 880-930°C).
2. Hold at temperature for uniform heating.
3. Cool the steel in still air outside the furnace.

Result: The faster cooling rate (compared to annealing) produces a finer, more uniform grain structure. Normalizing is often applied to as-rolled or forged steel to prepare it for machining or further heat treatment.

4.3 Hardening (Quenching)

Purpose: To increase the hardness and strength of the steel. Note that due to its low carbon content, 1025 steel has limited hardenability compared to medium or high-carbon steels.

Process:

1. Heat the steel to its specific austenitizing temperature (around 770-800°C for low-carbon steel).
2. Rapidly cool (quench) the steel in a suitable medium, such as water, brine, or oil.

Result: Rapid cooling transforms the austenite phase into martensite, a hard microstructure. However, the martensite formed in 1025 steel is relatively low in hardness. Quenching introduces significant internal stresses and carries a risk of distortion. Achieving a fully martensitic structure can be challenging due to low hardenability; other microstructures like ferrite or pearlite might form even with aggressive quenching.

4.4 Tempering

Purpose: Tempering is performed after hardening (quenching) to reduce the brittleness inherent in martensite and increase toughness.

Process:

1. Reheat the previously quenched steel to a specific temperature below the lower critical point (Ac1, approximately 727°C).
2. Hold at the tempering temperature for a predetermined time.
3. Cool the steel, typically in air.

Result: Tempering modifies the martensitic structure, achieving a desired balance between hardness, strength, and toughness. The final properties depend directly on the chosen tempering temperature and duration – higher temperatures generally yield lower hardness and higher toughness.

4.5 Carburizing

Purpose: Carburizing is a surface-hardening treatment. It creates a hard, wear-resistant outer layer (case) on the steel while maintaining a softer, tougher interior (core).

Process:

1. Heat the 1025 steel component in a carbon-rich atmosphere (gas, liquid, or solid pack) at temperatures typically between 880-930°C. Carbon diffuses into the steel’s surface.
2. Control the process time and temperature to achieve the desired case depth and carbon concentration.
3. Follow carburizing with quenching to harden the high-carbon case.
4. Temper the component to refine the properties of the case and the core.

Result: Ideal for components requiring high surface wear resistance combined with core ductility and toughness.

4.6 Carbonitriding

Purpose: Like carburizing, carbonitriding is a surface-hardening process that introduces carbon and nitrogen into the steel’s surface layer.

Process:

1. Heat the steel in an atmosphere containing carbon and nitrogen sources, typically at slightly lower temperatures than carburizing (around 900°C).
2. Both elements diffuse into the surface. The addition of nitrogen increases the hardenability of the case.
3. Quench the component. Thanks to the increased hardenability, a less severe quench (e.g., oil) can often be used compared to carburizing.
4. Temper as required.

Result: Produces a hard, wear-resistant case. The enhanced hardenability allows for effective hardening with potentially less distortion, making it suitable for components requiring good dimensional control.

4.7 Stress Relieving

Purpose: To reduce internal stresses locked into the steel from prior manufacturing processes like heavy machining, cold forming, or welding.

Process:

1. Heat the steel component uniformly to a temperature below the lower critical point (Ac1), typically around 600°C.
2. Hold at temperature for a sufficient duration (e.g., 1 hour per inch of thickness, minimum).
3. Cool slowly to minimize the reintroduction of thermal stresses.

Result: Improves dimensional stability during subsequent machining or use, and reduces the risk of distortion or cracking caused by residual stress.

4.8 Selecting the Appropriate Treatment

The optimal heat treatment for 1025 steel depends entirely on the final requirements of the component:

• For maximum formability and softness: Choose Annealing.
• For a refined structure with balanced strength and ductility: Consider Normalizing.
• For increased hardness (within limits) followed by improved toughness: Use Quenching and Tempering.
• For high surface hardness and wear resistance with a tough core: Employ Carburizing or Carbonitriding.
• To minimize internal stresses from fabrication: Apply Stress Relieving.

Choosing the correct process ensures that the 1025 steel performs reliably in its intended application. If you require further assistance in selecting the best heat treatment for your specific needs, please consult with our technical team.