Free-cutting steel – properties, types and applications

Free-cutting steels - an introduction

Free-cutting steels belong to a group of unalloyed steels that facilitate machining due to the addition of suitable chemical elements. Unlike standard structural steels, free-cutting steels are not suitable for welding and for parts subjected to dynamic loads, but they are ideal for the production of precision parts in large series. After machining, some free-cutting steels are used for machine components without additional heat treatment, and some are subjected to tempering or carburizing.

What is a free-cutting steel?

Free-cutting steel belongs to the group of unalloyed quality steels and is classified according to its chemical composition. Its greatest advantage is its very good machinability. It is designed for machining carried out on high-speed machine tools and automatic lathes. The appropriate content of sulfur and phosphorus, ensures the formation of short and brittle chips during machining. In addition, the lead content reduces tool wear. It is a steel grade used mainly in batch production, where fast and precise production of parts with precise dimensions and a good surface finish of the workpiece is required.

Thanks to the addition of sulfur, phosphorus and lead, auto steels are characterized by:

• easy chip removal - reducing machining time,
• low cutting tool wear - reducing production costs,
• high surface quality - eliminating the need for additional finishing.

The most commonly used automatic steels are:
🔹 11SMn30 (1.0715) - standard automatic steel without lead addition.
🔹 11SMnPb30 (1.0737) - a variety with lead (Pb) addition for even better machinability.
🔹 11SMn37 (1.0736) - a version with higher manganese content, increasing hardness and wear resistance.
🔹 46S20 (1.0726) - automatic tempering steel with improved mechanical strength.

Chemical composition of free-cutting steel

Free-cutting steels differ from other steels in their sulfur (S) and phosphorus (P) content, which improve chip brittleness and facilitate chip removal during machining. Some grades also contain lead (Pb), which further improves lubrication of cutting tool surfaces.

Element Influence on steel properties
Carbon (C) Provides basic hardness and strength
Manganese (Mn) Improves strength
Sulfur (S) Facilitates cutting, reduces chip toughness
Phosphorus (P) Increases strength and improves machinability
Lead (Pb) Improves surface quality and tool lubrication

The high sulfur and phosphorus content makes auto-steels unsuitable for welding, forging and forming, as their structure is more brittle and prone to cracking.

Mechanical properties of free-cutting steel

Free-cutting steels are characterized by high hardness and good wear resistance, but have limited tensile strength and low resistance to dynamic loads.

These steels are intended for the production of components with low mechanical loads, but requiring high precision workmanship.

Machining and weldability

Machining:
✔ Automated steels are excellent for turning, drilling and milling.
✔ They form short, brittle chips that do not clog cutting tools.
✔ They do not cause excessive tool wear, which reduces production time.

Molding:
✔ Due to their high sulfur and phosphorus content, auto steels are brittle and not suitable for bending, forging or stamping.

Weldability:
🚫 Automat steels are not suitable for welding - high sulfur and phosphorus content causes cracking and porosity of welds.

Application of free-cutting steel

Free-cutting steels are widely used in the automotive, electronics, engineering and precision industries, especially in mass production. Typical applications include:

• Precision components:

🔹 Bolts, nuts, screws, pins and bushings.
🔹 Threaded parts and small mechanical components.

• Automotive industry:

🔹 Steering components, bushings, pins.
🔹 Brake and suspension components.

• Electronics industry:

🔹 Steel components for electrical connectors and contacts.
🔹 Parts requiring high precision manufacturing.

• Machinery industry:

🔹 Precision shafts, drive components and gears.
🔹 Hydraulic and pneumatic components.

Advantages of free-cutting steel

✅ Excellent machinability - facilitates production of precision components.
✅ Low abrasiveness of cutting tools - increases machining efficiency.
✅ Speed of production - ideal for mass production of small parts.
✅ Good surface quality - often requires no additional finishing.
✅ Economical solution - reduces machining time and tooling costs.

🚫 Limitations:
❌ Not suitable for welding - steel may crack in weld areas.
❌ Low resistance to dynamic loads - not suitable for loaded structures.
❌ Limited forming and bending capabilities - high sulfur content makes the material brittle.

Summary

Free-cutting steel is an important material in various industries for fast and efficient production of complex parts on CNC machines and automatic lathes. Thanks to its excellent machinability and low production costs, it is widely used in automotive, electronics, precision mechanics and hydraulics.

🔩 If you are looking for the right grade of free-cutting steel for your project - contact us and we will help you choose the best solution! ⚙️