UNE C35k Alloy Steel Bar C35k Round Bars C35k Rods

Product Description

UNE C35k (1.1181) Steel Overview

UNE C35k is a high-quality medium-carbon steel grade defined under the Spanish national standards (Asociación Española de Normalización). The "k" suffix in the UNE system signifies a "special" or "quality" steel, characterized by low levels of impurities (sulfur and phosphorus) and a more controlled chemical composition.

In modern European standards, this grade is effectively replaced by C35E (Material Number 1.1181). It is a versatile engineering steel used when a balance of strength, toughness, and machinability is required.

Chemical Composition (%)

The "special" designation ensures that the phosphorus and sulfur levels are kept low to prevent brittleness and improve the steel's response to heat treatment.

Mechanical Properties (Normalized)

Typical values for UNE C35k round bars in the normalized condition:

• Tensile Strength ($R_m$): 520 – 660 MPa

• Yield Strength ($R_e$): $\ge$ 300 MPa

• Elongation ($A_5$): $\ge$ 19%

• Impact Energy (KV): $\ge$ 35 J (at 20°C)

• Hardness (Brinell): 150 – 195 HB

International Equivalents

UNE C35k is the Spanish equivalent to several other major global standards for 0.35% carbon steel:

Key Characteristics

1. Heat Treatment Response: C35k is a "through-hardening" steel for smaller cross-sections. For larger parts, it is frequently used for surface hardening (induction or flame hardening) to achieve a wear-resistant skin while maintaining a tough core.

2. Machinability: It offers excellent machinability in the normalized or annealed state, making it a preferred choice for high-volume turning and milling operations.

3. Weldability: Moderate. Due to the carbon content, pre-heating to 150°C–200°C is recommended to avoid the formation of martensite in the heat-affected zone, which can lead to cracking.

4. Toughness: Superior to higher carbon steels like C45 or C60, making it better suited for parts subjected to moderate shock or vibration.

Common Available Formats

• Round Bars: Available in hot-rolled (black) or bright-drawn (cold-finished) conditions. These are the primary stock for shafts and axles.

• Rods: Often used for manufacturing high-strength fasteners, studs, and forged links.

• Forgings: Popular as a starting material for drop-forged components in the automotive and agricultural sectors.

Common Applications

• Mechanical Engineering: Medium-load shafts, spindles, gears, and pinions.

• Automotive: Steering arms, connecting rods, and levers.

• Fasteners: High-tensile bolts (typically Class 8.8 when quenched and tempered) and studs.

• General Industry: Hand tools, brackets, and structural pins.

Processing Temperatures

• Hot Forming/Forging: 850°C – 1100°C.

• Normalizing: 860°C – 890°C.

• Annealing (Soft): 650°C – 700°C.

• Hardening: 840°C – 880°C (Quench in Water or Oil).

• Tempering: 550°C – 660°C.