The Machinability of Stainless Steel
The machinability of stainless steel is much worse than that of carbon steel. Regards the machinability of the ordinary 45 steel as 100%, the relative machinability of the austenitic stainless steel 1Cr18Ni9Ti is 40%, the ferrite stainless steel 1Cr28 is 48% and the martensitic stainless steel 2Cr13 is 55%. Among them, the austenitic and austenitic+ ferritic stainless steel have the worst machinability. There are below characteristics in stainless steel machining process.
1. Work hardening serious
In stainless steel, austenitic and austenite+ ferritic stainless steel has the most seriously work hardening problems. Because of the high plasticity of stainless steel, a hardening layer is produced during machining. the work hardening caused by last feed or last process will seriously impact the subsequent process.
2. Large cutting force
There is large plastic deformation in stainless steel processing, especially for austenitic stainless steel, so that it increased cutting force. Meanwhile, stainless steel has serious working hardening and high thermal strength, which makes it further increased of cutting resistance and more difficulty for chip crimping break. So the cutting force of stainless steel machining is large.
3. High cutting temperature
Plastic deformation and friction with the tools during cutting are both very large, resulting in high cutting heat. And thermal conductivity of stainless steel is about 1/2 or 1/4 of 45 steel, so plenty of cutting heat are concentrated in the cutting area and the interface where knife and chip are contacted. So it has poor heat dissipation. Under the same conditions, the cutting temperature of stainless steel is about 200 ℃ higher than that of 45 steel.
4. Chip is not easy to break and is easy to bond
The plasticity and toughness of stainless steel are both large, and generate processing chip continuously durning stainless steel turning. It not only affects smooth operation, the processed surface is also easy to be crushed by chip. Under high temperature and pressure, stainless steel is easy to adhesion with other metals, and generate built-up edge. Thus will both exacerbate tool wear, and become teared witch will makes the processed surface worst.
5. Tools wear easily
Due to the affinity during stainless steel processing, bonding and diffusion will generate between knife and chip. So that the tool has a adhesive wear or diffusion wear, result in forming crescent depression on rake face and the cutting edge also creates tiny peeling and notches. Meanwhile carbide particles in stainless steel (such as TiC) has high rigidity, so directly contact and friction will result in scratching the tools when cutting. As well as serious work hardening, they all make the tools worn heavily.
6. High linear expansion coefficient
Stainless steel has about 1.5 times linear expansion coefficient of carbon steel. Under the affect of cutting temperature, the workpiece is prone to generate 2thermal deformation and dimensional accuracy is difficult to control.
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