Different stainless steel pipe
cutting performance are very different. Generally speaking, the cutting performance of stainless steel pipe worse than other, is the austenitic stainless steel pipe
cutting performance is poor. This is due to severe hardening of austenitic stainless steel pipe, low thermal conductivity caused. To this end in the cutting process need to use water-based cutting coolant to reduce cutting thermal deformation. Especially when the welding heat treatment is not good, no matter how to improve the cutting accuracy, the deformation is inevitable. Other types of stainless steel such as martensitic stainless steel tube, ferritic stainless steel tube cutting performance as long as it is not quenched after cutting, then with carbon steel is not much different. But both are the higher the carbon content, the worse the cutting performance. Precipitation hardening stainless steel tube due to its different organization and processing methods and show different cutting performance, but in general its cutting performance in the annealed state with the same series and the same strength of martensitic stainless steel tube and austenitic stainless steel tube the same.
To improve the cutting performance of stainless steel pipe, and carbon steel can be added by adding sulfur, lead, bismuth, selenium and tellurium and other elements to achieve. Which add elements such as sulfur and selenium and tellurium can reduce tool wear, add lead and bismuth and other elements can improve the cutting state.
Although sulfur is added to improve the machinability of stainless steel pipes, corrosion resistance is significantly reduced since it is present in steel in the form of MnS compounds. To solve this problem, usually add a small amount of molybdenum or copper.
For martensitic chromium-nickel stainless steel pipe, generally require quenching - tempering heat treatment. In the process of different alloying elements and their amount of hardenability have different effects.
When the martensitic stainless steel tube is quenched from 925-1075 ℃ temperature quenching. Due to the low phase transition speed, sufficient hardening can be achieved both in oil cooling and in air cooling. Also in the tempering process must be carried out due to the different tempering conditions can be a wide range of different mechanical properties.
In the martensitic chromium stainless steel tube, due to the addition of chromium can improve the hardenability of iron-carbon alloy, and thus need to be hardened steel has been widely used. The main role of chromium is to reduce the critical cooling rate of quenching, the hardenability of steel has been significantly improved. From the C curve, due to the addition of chromium to slow down the transformation of austenite, C curve significantly shifted to the right.
In martensitic chromium-nickel stainless steel tubes, the addition of nickel increases the hardenability and hardenability of the steel. Chromium close to 20% of the steel if you do not add nickel quenching capacity. Add 2%-4% nickel to restore quenching ability. However, the content of nickel can not be too high, or excessive nickel content will not only expand the r-phase region, but also reduce the Ms temperature, so that the steel becomes single-phase austenite also lost the ability to quench the organization. Select the appropriate nickel content, can improve the martensite stainless steel tempering stability, and reduce the degree of tempering softening.
In addition, the addition of molybdenum in a martensitic chromium-nickel stainless steel tube increases the tempering stability of the steel.
Although the ferritic stainless steel tube can not be hardened by quenching because austenite is not generated at a high temperature, partial martensitic transformation occurs in the low-chromium steel.
Austenitic stainless steel tube belongs to the Fe-Cr-Ni system and Fe-Cr-Mn system, austenitic structure. Therefore, high strength and good ductility are exhibited over a wide range of temperatures from low temperature to high temperature. The entire non-magnetic austenite structure can be obtained by carrying out a rapid solid solution treatment starting from 1000 °C. or more to obtain good corrosion resistance and maximum elongation.