Tool Steels

Rapid solidification of the atomized powders used in the production of wrought P/M tool steels eliminates the segregation present in conventional tool steels and produces a very fine microstructure with a very uniform distribution of small carbides and nonmetallic inclusions. As a result, wrought P/M high-speed tool steels exhibit better machinability, dimensional control, and safety in heat treatment, grindability, and edge toughness during cutting than conventional high-speed tool steels of the same composition. A variety of Anti-segregation process (ASP) and P/M tool steels are available.

As with conventional tool steels, P/M tool steels are generally machined in two stages: rough machining of the workpiece with the steel in the annealed condition, followed by finish machining (typically grinding) after heat treatment when the steel is in the hardened-and-tempered condition. Table 4 lists the typical cutting conditions for P/M and conventional AISI highspeed steels of similar composition.

Table 4 Typical machining conditions for P/M and conventional grades of AISI high-speed tool steels

Operation

Tool width or

High-speed tooling

Carbide

tooling

depth of cut

Speed

Feed

Speed

Feed

mm

in.

m/min

sfm

mm/rev

in./rev

m/min

sfm

mm/rev

in./rev

Single-point turning

3.8

0.150

18

60

0.38

0.015

91

300

0.38

0.015

0.64

0.025

23

75

0.18

0.007

111

365

0.18

0.007

Drilling

6.4

4

12

40

0.08

0.003

13

2

12

40

0.13

0.005

25

1

12

40

0.23

0.009

50

2

12

40

0.33

0.013

Broaching

3

10

0.05

0.002

Face milling

3.2

0.125

20

65

0.20

0.008

78

255

0.30

0.012

0.64

0.025

26

85

0.15

0.006

101

330

0.25

0.010

Cutoff

1.6

0.062

14

45

0.03

0.001

53

175

0.05

0.002

3.2

0.125

14

45

0.03

0.001

53

175

0.08

0.003

6.4

0.250

14

45

0.04

0.0015

53

175

0.11

0.0045

An important advantage of the P/M process relates to the fact that the machinability and grindability of P/M tool steels can be improved by increasing their sulfur content to much higher than conventional levels without sacrificing toughness or cutting performance (see the article "Particle Metallurgy Tool Steels" in this Volume).

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