With the development of modern industry towards automation, high-speed and precision processing, it is required that steel have good cutting process performance, improve production efficiency, and adapt to large-scale production. Therefore, it is necessary to use more steel with improved cutting performance to facilitate automatic cutting machine tools.

1、 Definition of Free Cutting Steel

Free cutting steel refers to alloy steel in which a certain amount of one or more free cutting elements such as sulfur, phosphorus, lead, calcium, selenium, tellurium, etc. are added to the steel to improve its machinability. With the automation, high speed, and precision of cutting processing, it is very important for steel to have good machinability. This type of steel is mainly used for processing on automatic cutting machines and therefore also belongs to specialized steel.

2、 The China Development History of Free Cutting Steel

China has been producing sulfur free cutting steel since 1953. Due to the high quality requirements and difficulty in production, special steel mills are unwilling to produce and ordinary steel mills are unable to produce, resulting in a large amount of imported free cutting steel in China. According to relevant statistical data, in 2002, China imported a total of 163700 tons of free cutting steel, while China’s domestic annual production was only about 30000 tons. With the development of the mechanical processing industry, especially the automotive industry, the demand for free cutting steel in China will rapidly increase. According to the annual increase in China’s automobile production and estimated based on the proportion of demand for free cutting steel in Japan’s automobile industry, China’s automobile production was around 24 million units in 2015, and the annual demand for free cutting steel in China will reach 400000 to 500000 tons. This shows that there is still a lot of development space for free cutting steel in China.

3、 Main free cutting steels and their characteristics

According to the different composition elements of easy cutting, it can be divided into sulfur easy cutting steel, lead easy cutting steel, calcium easy cutting steel, and composite easy cutting steel. According to their different uses, free cutting steel is divided into automatic machine steel, structural free cutting steel, and special free cutting steel (heat-resistant steel, stainless steel, tool steel, etc.). According to the different machinability, it can be divided into general machinable steel, ultra machinable steel, etc. Below, the editor will take you to understand the types and characteristics of free cutting steel classified according to their constituent elements:

1. Sulfur free cutting steel

Sulfur forms sulfide manganese inclusions with manganese and iron in steel. These inclusions can break the continuity of the base metal, promote the formation of small and short curling radii during cutting, and are easy to eliminate, reducing tool wear, lowering machining surface roughness, and improving tool life. The machinability of steel usually increases with the increase of sulfur content in the steel. However, there is a significant difference in the longitudinal and transverse mechanical properties of steel, with poor transverse plasticity and toughness, as well as reduced fatigue and corrosion resistance. When the sulfur content in steel is too high, it can lead to thermal brittleness, making it difficult to heat process the steel and deteriorating its mechanical properties. The sulfur content is usually 0.08% to 0.30%, and some can be increased to 0.4%. The sulfur content in both easy cutting tool steel and stainless steel should be between 0.06% and 0.10%. Phosphorus is often added to steel in combination with sulfur, with a phosphorus content typically ranging from 0.04% to 0.12%. Phosphorus solid solution in ferrite can increase hardness and strength, reduce toughness, and make chips easier to break and eliminate, resulting in good machining surface roughness. However, excessive phosphorus content can significantly reduce plasticity, increase hardness, and have harmful effects on the cutting performance of steel.

2. Lead free cutting steel

Lead exists in the form of small metal particles in steel, uniformly distributed or attached around sulfides. Due to the low melting point of lead, melting and exudation during cutting provide lubrication, reduce friction, and improve cutting performance, but do not affect the mechanical properties at room temperature. The lead content in steel is generally between 0.10% and 0.35%. Due to the high specific gravity of lead, if the content is too high, it can easily cause severe segregation and form large particle inclusions, which in turn reduces the beneficial effect of lead on cutting processing. The addition of lead and sulfur composite to low-carbon structural steel significantly improves the cutting effect of the steel.

3. Calcium free cutting steel

Calcium in steel combines with aluminum and silicon to form low melting point composite oxides (mainly CaO, Al2O3, SiO2). During high-speed cutting, calcium based oxides adhere to the surface of the cutting tool to lubricate and reduce friction, thereby improving the tool’s service life. If sulfur, lead and other elements are present at the same time, their combined effect will improve the cutting effect.

4、Selenium, tellurium, bismuth free cutting steel

The content of tellurium and bismuth is about 0.03% to 0.10%, and the content of selenium can reach 0.15%. Selenium exists in steel in the form of selenides such as FeSe, MnSe, etc. Its function is similar to that of sulfur. For steel that requires both high machinability and good plasticity, adding selenium to steel is better than adding sulfur. Tellurium can be added separately or simultaneously with lead or sulfur to steel to form composite inclusions, which can reduce cutting resistance and cutting heat, make chips easier to remove, significantly improve the cutting performance of steel, and obtain good machining surface roughness. However, adding tellurium will slightly reduce the plasticity and toughness of steel. Selenium and tellurium are generally used in alloy steel. The role of bismuth in steel is similar to that of lead, appearing as small metal particle inclusions uniformly distributed or attached around sulfides.

Comparison Table of Free Cutting Steel Grades

Country China America Janpan Germany
GB ASTM JIS DIN、DINEN
Grade Y15 1215 SUM24 1.0715
Free cutting steel Y12 1211； G12110(UNS) SUM12； SUM21 10S20
Y12Pb 12L13 SUM22L 10SPb20
Y20 1117； G11170(UNS) SUM32C22
Y40Mn 1144； G11440(UNS) SUM43 44Mn28
Y45Ca 1145 C45 —
Y1Cr18Ni9 — SUS303 X8CrNiS18-9

Table 1: Free cutting steel grades in China

4、 Domestic market situation of free cutting steel

 

Since 2024, for the domestic free cutting steel market, the overall spot market prices have been weak, with steel mills mainly supplying directly to end-users and fewer market distributors. Among the large and medium-sized steel mills producing free cutting steel in China, the price fluctuation of Guiyang Special Steel is relatively small, while the prices of other steel mills are in a weak adjustment state, with an overall fluctuation range of 200-300 yuan/ton; Due to the low demand in the free cutting steel market, there are relatively few price adjustment policies introduced by steel mills. Most steel mills implement a single negotiation pricing policy based on the customer’s order quantity. In the market, due to downstream enterprises directly connecting with steel mills for ordering free cutting steel, the amount of spot stock available for traders is decreasing.

Due to the particularity of the free cutting steel process, most domestic steel mills do not have production capacity, so there are relatively few domestic steel mills producing free cutting steel. At present, there are about 8 large and medium-sized enterprises in my sample steel network that produce free cutting steel. 12L14 is mainly produced by Guiyang Special Steel in China due to its high pollution caused by lead content; Steel mills such as Jiyuan Iron and Steel, Hualing Xiangtan Iron and Steel, Shaoguan Iron and Steel Group, and Shanxi Antai Group mainly produce 1215.

According to Mysteel’s research and statistics on sample steel mill production data, the overall monthly production is approximately 56800. Most steel mills have relatively stable production, but some steel mills adopt a policy of production based on sales due to external factors such as geographical location, as well as the current poor performance of the automotive and home appliance industries, resulting in unstable production.

free cutting steel bar

5. Characteristics and Applications of Free Cutting Steel

The characteristics of easy cutting steel mainly include good machinability and cutting performance. Easy cutting steel improves its machinability by adding a certain amount of easy cutting elements such as sulfur, phosphorus, lead, calcium, selenium, tellurium, etc. to the steel. These elements form inclusions in steel, cutting off the continuity of the base metal, promoting the formation of small and short curling radii of chips, which are easy to eliminate, reduce tool wear, lower machining surface roughness, and improve tool life. In addition, free cutting steel also has good mechanical properties and corrosion resistance, making it suitable for various processing environments.

Free cutting steel has a wide range of applications, mainly used for instruments and meters with strict requirements for size and roughness, watch parts, automotive components, machine tools, and various other machines. Specific applications include:

Construction machinery: used for manufacturing components that require high precision and good surface quality.
Automotive industry: used for manufacturing key components such as automotive engines, transmission systems, chassis, etc., to improve production efficiency and processing quality.
Aerospace: Used for manufacturing aircraft specific components to ensure good processing performance even in high-altitude environments.
Home appliance industry: used for manufacturing precision components in household appliances to improve product durability and reliability.
Office supplies: used for manufacturing precision instruments and office equipment, ensuring the accuracy and stability of the equipment

 

6、 Development Strategy for Cooperation in the Free Cutting Steel Industry

Firstly, strengthen communication and mutual trust between the upstream and downstream of the free cutting steel industry. Strengthen communication and exchange with upstream and downstream partners in the supply chain, enhance understanding, mutual trust, and support, and jointly discuss solutions. Secondly, connect the value chain of the free cutting steel industry. Through the free cutting steel industry association, industry alliance and other carriers, timely understanding of the bottlenecks in the value chain, and jointly taking measures to solve problems such as raw material supply and logistics transportation. Finally, there are risks associated with diversifying the supply chain. Jointly explore the best path for diversified development of the supply chain, diversify the risks of force majeure, and balance the expectations and demands of all parties as much as possible; And create a complete supply chain circulation for the free cutting steel industry in the main regions, enhancing risk resistance capabilities.