TPT-January-2015

92 / 96

90 January 2015
Article Shandong SiFang Technical Development Co Ltd
The high casting quality of dies has been verified in ultrasonic
testing and performance testing.
Ultrasonic testing results show:
a) good ultrasonic penetrability and detestability, few noise
waves, so the microstructure is uniform, compact
b) the part from the work surface to the depth of 100mm
meets the Level 1 requirement of DIN EN-12680-2
c) the internal space meets the Level 2 requirement of DIN
EN-12680-2 at least
3.3 Hardness and performance of new crimping dies
Developed high chromium die steel is of excellent
hardenability; the cross-sectional anatomy of large test
pieces of the same material and the same heat treatment
processing demonstrates that the die has quenched fully, and
the hardness range is 55 ~ 65HRC.
The mechanical property comparison of new high chromium
die steel and German die steel is listed in Table 3. (Radial
samples)
3.4 Microstructure of new crimping die steel
The carbide of high chromium die steel is mainly of M­7C3 type,
and these carbides appears in incontinuous strip, block, grain
and chrysanthemum-like shapes; their microhardness can
reach 1,800HV and these carbides account for 20 per cent
or so. Certainly, the matrix can been designed as austenite,
bainite or martensite and so on according to the die service
condition of different material types, and their macrohardness
can reach HRC55 ~ 65.
The microstructure of new high chromium die steel is shown
in Figure 5 and Figure 6.
The matrix of German die steel is martensite, and the carbides
take up about 15 per cent, which are mainly of M­7C3 type. Its
microstructure is shown in Figure 7.
3.5 Wear-resisting property comparison of crimping die
steel in laboratory
The MM-200 ring-block wear testing machine has been
adopted in the experiment, and the homemade water system
has been cooling the samples through the testing process.
There are the same testing parameters adopted, including
loading force, spindle speed, testing time, cooling water rate,
Figure 4: Field hardness testing picture of experimental cylindrical
sample profile
Material and heat
treatment method
Tensile strength
/MPa Average/MPa Material and heat
treatment method
Impact
toughness
/kJ•m-2
Average
/kJ•m-2
High chromium die
steel
Quenching and
tempering
705
725
695
635
695
720
695.8
High chromium die
steel
Quenching and
tempering
40
35
40
40
40
40
39.2
German die steel
Quenching and
tempering
732
717
683
710.7
German die steel
Quenching and
tempering
40
21
30
30
Table 3: Mechanical property comparison of new high chromium die steel and German die steel
Figure 5: Microstructure of new high
chromium die steel
Austenite + Carbide, ×200
Figure 6: Microstructure of new high
chromium die steel
Martensite + Carbide, ×500
Figure 7: Microstructure of new high
German die steel
Martensite + Carbide, ×100