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Why 904L austenitic stainless steel is difficult to be processed

The grade of 904L stainless steel is 00Cr20Ni25M04.5Cu, which belongs to a high austenitic stainless steel with high carbon content and low carbon content. It has strong corrosion resistance in the dilute sulfuric acid environment, because the addition of copper makes it have strong acid resistance. It is designed for the harsh environment of corrosion. Therefore, this austenitic stainless steel is mainly used for the manufacture of corrosion resistant pressure vessels.
The composition of 904L is mainly composed of chromium and nickel. It is difficult to machine and has poor machinability. The main reasons are as follows.
First of all, 904L stainless steel is more powerful than other kinds of stainless steel. Because the hardness of 904L stainless steel is not high (70-90HRB), the plasticity is better, the elongation is more than 40%, the shrinkage of the section is more than 50%. The tensile strength is B more than 490MPa, and the yield strength is 0.2 or more 216MPa. Therefore, the plastic deformation is larger in the cutting process, and the cutting force is increased.
The second is the low thermal conductivity. The thermal conductivity of 904L stainless steel (20 C) is 12.9W / (mmK), and its thermal conductivity is low, only about 1 / 4 of the 45 steel. The thermal conductivity of the 45 steel is 47.5W / (mmK). Thermal conductivity is one of the main factors that affect the heat conduction of cutting. The lower the thermal conductivity of the processed material, the less the heat taken by the chip and the workpiece, and the more heat accumulated on the cutting tool, making the tool very easy to wear.
Third, it is easy to form the chip tumor. Because of the high toughness of 904L stainless steel, it has strong affinity with the tool material during the cutting process. The cutting tool face is strongly rubbed with the chip bottom metal during cutting. It will produce adhesion phenomenon under the action of high temperature and high pressure. It is not easy to get the surface with high surface roughness.
Fourth, the chip is not easy to bend and break. The elongation of 904L stainless steel is high, so the chip is not easy to bend and break in the cutting process. Failure to take proper measures will affect the normal operation of the cutting process, and scratch the machined surface easily, and even cause the tool to collapse and damage.
Because of the above features of 904L stainless steel, the cutting tool is very easy to wear and the machining efficiency is low, and the workpiece is difficult to achieve the surface roughness and machining precision required by the drawings.
Source: China Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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