Machining Stainless Steel? 

Directions for Stainless Steels Machining

Stainless Steels are well known thanks to it”s superior corrosion-resistance.

Superior corrosion-resistance of stainless steels results from higher Cr content as an alloy-element.
Cr content is more than 4% in general, mostly more than 10%.

Classifications of Stainless Steel

1) Austenite series : It is a most general kind of stainless steels and has the best corrosion-resistance due to
high Cr content and Ni. On the other hand, High Ni content makes machining difficult. It is used for can of
foods, chemical products and construction purposes. (AISI303, 304, 316, STS303, 304, 316)
2) Ferrite series : It has similar Cr content with Austenite series, but none of Ni content results in easy
machining. (AISI410, 430, 434, STS410, 430, 434)
3) Martensite series : It is the only stainless steels able to be heat treated. It has high carbon content and corrosion
resistance is not so good, so it is used for a parts that need higher hardness.
(AISI410, 420, 432, STS410, 420, 432)
4) Precipitate hardened series : As a Cr-Ni alloy, it has improved hardness through low temperature heattreatment
and has superior corrosion-resistance and toughness at the same time. (AISI 17, 15)
5) Austenite-Ferrite series : Though it has similar properties with Austenite and Ferrite, it has much superior
heat-resistance (approx. 2 times better). It can be used at the place where require thermal-corrosion
stability such as condenser (AISI S2304, 2507)

Hard to cut factors of Stainless Steel

1) Work-hardening – Cause premature wear of tool and makes it hard to chip control.
2) Low thermal conductivity – Cause plastic deformation of cutting edge and fast wear of tool.
3) Build-up-edge – Easy to make micro-chipping on cutting edge and cause bad surface-finish.
4) Chemical affinity between tool and work-piece caused by work-hardening and low thermal-conductivity of
work-piece, generates easily not only normal-wear but also chipping and abnormal fracture.

Tips for machining Stainless Steel

1) Using a tool has higher thermal-conductivity: Low thermal-conductivity of Stainless steels accelerates wear resulted from decline of hardness of cutting
edge due to heat pile up.
2) Sharper cutting edge-line: It is necessary to make rake-angle bigger and chip-breaker land wider to reduce cutting-load and prevent
build-up-edge so that chip is treated well.
3) Optimal cutting condition: Inappropriate machining conditions like extremly low or high-speed, too low feed rate, can cause poor tool
life due to work-hardening of work piece.
4) Tools: Tools for Stainless steels should have good toughness and strength on edge-line & film adhesion has to be
higher.