Stainless steels can
be machined using conventional equipment and techniques. Because
of their toughness, stainless steels generally require more
power to machine than carbon steels. They also are readily
work-hardened, so excess deformation should be avoided; for
example, positive feeds must be maintained, tools should be
sharp and fixtures should be rigid. Optimal cutting speeds
are usually lower than those for carbon steel. Good lubrication
and cooling are essential.
The various families of stainless show marked differences
in their machining character.
Turning: Single-point tools for turning the austenitic chromium-nickel
grades must have adequate clearance to avoid work hardening
of freshly cut surfaces. The back rake angle should be as
large as permissible, to aid in breaking of chips. Chip breakers
are helpful, but their design must be such that the cutting
edges will not be weakened. Improperly designed chip curlers
can cause chip crowding and tool damage.
The use of a cutting fluid is more desirable for machining
stainless
steels than for machining carbon or alloy steels for two reasons:
a) stainless steels are generally less machinable than carbon
or
alloy steels.
b) the lower heat conductivity of stainless steels increases
the need
for cooling.
Speeds and Feeds:
High speed steel & carbide tools:
Nominal Turning Speeds for Stainless Steels: Single-Point
and Box Tools
Drilling:
Because stainless steel is more easily work hardened than
carbon or alloy steel, more attention needs to be paid to
starting the drill. Should a spot become severely work hardened,
it will cause the drill to wander or overheat, thus dulling
the drill in a few revolutions.
When starting or re-entering the hole, the drill should be
at full speed with positive feed. Dwell periods should not
be permitted. Speeds and Feeds:
Nominal Speeds & Feeds for High Speed Steel Drills
Ann = Annealed, Q&T = Quenched and Tempered, CD = Cold
Drawn
S30400, S31600 and the free machining grades are austenitic.
S41000 and S43100 are martensitic.
Tapping:
Nominal Speeds for Tapping Stainless Steels
Ann = Annealed, Q&T = Quenched and Tempered, CD = Cold
Drawn
For tapping steels under 375 Bhn, M10, M7 and M1 high speed
steel taps. For steels over 375 Bhn, M3 and M40 taps.
Milling:
Nominal Speeds & Feeds for Face Milling with High Speed
Steel Cutters
