Stainless Steel Cutting Performance and Hardenability

First, cutting performance
Different stainless steel cutting performance is very different. Generally speaking, the cutting performance of stainless steel is worse than that of other steel, which means that the machinability of austenitic stainless steel is poor. This is due to austenitic stainless steel work hardening serious, low thermal conductivity caused. To this end in the cutting process need to use water-based cutting coolant to reduce the heat distortion. Especially when the heat treatment when welding is not good, no matter how to improve the cutting accuracy, the deformation is inevitable. Other types such as martensitic stainless steel, ferritic stainless steel and other stainless steel cutting performance as long as it is not quenched after cutting, then the carbon steel is not much different. But both are the higher the carbon content, the worse the cutting performance. Precipitation hardened stainless steels exhibit different cutting performance due to their different compositions and treatment methods, but in general their cutting performance is the same in the same state as the same series of martensitic stainless and austenitic stainless steels.

To improve the cutting performance of stainless steel, 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 selenium and tellurium can reduce the wear of the tool, add lead and bismuth and other elements can improve the cutting state.

Although the addition of sulfur can improve the cutting performance of stainless steel, it is in the form of MnS compounds in the steel, so that significantly reduced corrosion resistance. To solve this problem, usually add a small amount of molybdenum or copper.

Second, hardenability
For martensitic chromium-nickel stainless steel, generally need to be quenched – tempering heat treatment. Different alloying elements and their additions in this process have different effects on hardenability.

The quenching of martensitic stainless steel is quenched from the temperature of 925-1075 ?. As the phase transition rate is low, so whether it is oil cold or empty green can be fully hardened. Also in the process of tempering must be carried out due to the different tempering conditions can be a wide range of different mechanical properties.

In martensitic chrome stainless steel, the addition of chromium can improve the hardenability of iron-carbon alloy, which in the need for quenching steel has been widely used. The main role of chromium is to reduce the critical cooling rate of quenching, so that the hardenability of steel has been significantly improved. From the C curve, due to the addition of chromium to austenite transformation slowed down, C curve was significantly shifted.

In martensitic chromium-nickel stainless steel, the addition of nickel can improve the hardenability and hardenability of steel. Chromium containing less than 20% of the steel without adding nickel without quenching capacity. Add 2% -4% nickel to restore the quenching capacity. But the nickel content can not be too high, otherwise the high nickel content will not only expand the r-zone, but also reduce the Ms temperature, so that the steel into a single-phase austenite tissue also lost the quenching capacity. Select the appropriate nickel content, can improve the tempering stability of martensitic stainless steel, and reduce the degree of softening softening.

In addition, the addition of molybdenum to the martensitic chromium-nickel stainless steel increases the tempering stability of the steel.

Although the ferritic stainless steel does not produce austenite at high temperatures, it can not be hardened by quenching, but some martensitic transformation occurs in the low-chrome steel.

Austenitic stainless steel belongs to Fe-Cr-Ni system and Fe-Cr-Mn system, which is austenite structure. So that a high range of strength and good elongation are exhibited in a large range from low temperature to high temperature. It is possible to obtain a non-magnetic all-austenite structure by performing a quenching solution from 1000 ° C or higher to obtain good corrosion resistance and maximum elongation.