In the field of automotive parts, in order to improve the cutting efficiency, 1144 free-cutting steel containing of lead (0.04% to 0.30%) is often used. Japan’s annual output exceeds 500,000 tons. However, in recent years, the environmental protection wave in the world has put forward strong requirements for reducing the use of toxic heavy metal lead, so it is necessary to develop a lead-free cutting steel.
The 1144 free-cutting steel features a significant improvement in the cutting process (ie disconnection) and the life of tools such as tools and drills. Another type of sulfur-free cutting steel has the effect of improving the cutting performance, but the chip breaking performance is not good. Further additions (0.08-0.12%) will increase the anisotropy of mechanical properties.
In order to develop machinability and mechanical properties comparable to machinable cutting steels, lead-free cutting steels have similar properties and functions as lead. To this end, the following basic research was carried out: lubrication. When the temperature rise during the cutting reaches the melting point of lead, the melting of lead becomes a lubricant between the tool and the chip, reducing the frictional resistance. The brittleness of B molten metal is brittle, which reduces the shear strength of the steel and increases the breakage of the chip (that is, the tool is not entangled). When the stress concentration source is cut, the cutting area generates small internal cracks, which reduces the cutting resistance and increases the chip breaking.
Both types of steel have high and low strontium content. Other representative components were 0.30% C, 0.20% I, and 0.70% manganese, i.e., ruthenium was added to carbon steel containing 0.30% carbon. Through the development of quenching and tempering heat-treated steel, the controlled hardness is about 250 hv, the mechanical properties of the steel are measured; the cutting performance of the steel is evaluated according to the tool life (wear) and chip processing; in addition, by limiting the compression of the cold forged steel crack rate. The results show that the double amount of steel is only 1/2 of the original lead and lead, but the cutting performance of both is also good. This is because the melting point of the calendar and lead is very low (about 300 ce). Under the conditions of cutting heating and heating, it also has the comprehensive functions of lubrication, friction reduction, melt metal embrittlement and stress concentration, resulting in chip breaking. Therefore, the tool has a long life when cutting and adding bimetal. Cutting various cutting conditions, especially at high speed cutting, the chips do not distort the tool, which is important for ensuring the stability of the automatic cutting operation. Therefore, it can fully meet the performance requirements of automotive parts. The developed 1144 free-cutting steel has excellent comprehensive performance (equivalent to or even better than the original lead steel), completely eliminating the harm of heavy metal lead to the environment and the human body, and has a good application prospect.