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DHA is a trademark or registered trademark of Daido Steel Co., Ltd.
Background of development of DHA-WORLDDie casting parts needs are increasing not only for engine blocks and transmission cases but also chassis
and body parts for lightweight demand with aiming higher fuel efficiency. It requires prolonged die casting
mold life.
Typical factors to affect service life of die casting molds can be categorized into 2 groups. One isrepairable damage such as heat checking, erosion or corner crack, and the other is unrepairable major
failure such as gross cracking at an early stage.
Repairable damage can be observed gradually, thus it is easier to make maintenance schedule.
Furthermore, the gross cracking should also be definitely avoided because it is difficult to predict and repair.
Higher hardness can restrain heat checking which is the main failure mode of die casting molds (Photo.1).
However, since higher hardness gives rise to lower toughness, caution against cracking becomes crucial(Fig.1). In general, molds broken by gross cracking an at early stage trend to have lower impact value.
Especially, large size molds have lower impact values metallurgically, so raising hardness is challenging
so far.

Photo. 1. Effect of hardness on heat checking© 2020 Daido Steel Co., Ltd.

Fig. 1. Relationship between hardness and toughness

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Daido Steel have developed and now provides steel “DHA-WORLD” which has stable structure andtoughness throughout mold from surface to center so that it can both prevent large size molds from grosscracking and raise large size molds’ hardness to have a better heat checking resistance compared withconventional standard grade steel.
Feature of DHA-WORLD
DHA-WORLD, high reliable hot working die steel alternative to AISI H13 (DIN 1.2344), can be used forlarge size die casting molds with confidence.
-High hardenability: Improved hardenability by optimization of alloy design makes it possible to obtainhigher toughness even in the center of large size die casting mold by simple heattreatment.
-Air melted grade: Stable quality similar to double melted grade can be achieved by our integrated
manufacturing process which Daido Steel have developed based on ouraccumulated technology. It contributes to reducing cost of mold material.
Chemical composition
Table 1. Typical chemical composition of DHA-WORLD.
Steel gradeCSiMnCrMoV

Note

DHA-WORLD

0.35

0.5

0.7

5.5

1.2

0.6Example

H110.33-0.43

0.80-1.25

0.20-0.60

4.75-5.50

1.10-1.60

0.30-0.60

From

H13 (1.2344)

0.32-0.45

0.80-1.25

0.20-0.60

4.75-5.50

1.10-1.75

0.80-1.20

standard

Main application
DHA-WORLD having uniform microstructure and secured high toughness due to higher hardenability isapplicable to large size die casting molds as well as to hot working die steel application widely.
Table 2. Main application of DHA-WORLD

Applications
Al, Zn, Mg die casting molds
Die casting mold parts(Plunger sleeve, Plunger chip etc.)

Hardness (HRC)
41 ~ 4845~ 50Hot extrusion dies

43 ~ 50

Hot shear blade

35 ~ 45

Hot forging dies

42 ~ 50

Property of DHA-WORLD(1) More stable and higher quality than H13 (1.2344)
Photograph 2 shows the microstructure of cutting section from the material center assuming applicationof large size mold. DHA-WORLD microstructure on Photo. 2(a) did not show white needle-like shape© 2020 Daido Steel Co., Ltd.

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microstructure called bainite that were observed at H13 (1.2344) on Photo. 2(b).

Photo. 2. Microstructure of center of heat-treated specimen simulating large molds
Specimen dimension: 200mm H x 600mm W x 300mm L (Center)
Quenching: 1030℃, 6 bar gas
Figure 2 shows the relationship between the cooling rate in the range from 400 to 200 degrees C wherebainitic transformation occurs and Charpy impact values under the same hardness condition (48 HRC).
For DHA-WORLD decrease in impact values along with decrease in cooling rates tends to smaller
compared with H13 (1.2344).

Fig. 2. Cooling rate dependency on impact

Fig.3. CCT diagrams of DHA-WORLDvalues
Figure 3 shows CCT diagram of DHA-WORLD and H13 (1.2344). DHA-WORLD’s bainite transformation
start temperature shifts to rightward (longer time) compared with H13 (1.2344). This means it is easier for
DHA-WORLD to obtain refined martensitic microstructure even if cooling rates are slow enough for H13(1.2344) to bring about bainitic transformation and thus, deterioration of impact values can be suppressed.
Therefore, DHA-WORLD has an advantage in application of large size molds where the cooling rate ought
to be slow.

© 2020 Daido Steel Co., Ltd.

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4/7(2) The result of die casting mold evaluation test
Photograph 3 indicates the difference of the heat checking status in molds made from DHA-WORLD andH13 (1.2344) with the same design and hardness. Even though these molds have the same hardness,
DHA-WORLD mold restrains heat checking compared with H13 (1.2344) mold.
It has not been completely explained yet, but the difference in heat checking resistance that Photo. 3
indicate was considered to be caused by a higher thermal conductivity of DHA-WORLD compared withH13 (1.2344), as shown in Fig. 4. Improved thermal conductivity should reduce thermal stress at thesurface. Consequently, heat checking have restrained.

Photo. 3. Heat checking status by die castingFig. 4. Thermal conductivity

trial(3) Heat treatment conditions
Table 3 indicates general heat treatment conditions. The quenching and tempering temperature same asH13 (1.2344) are applicable.
Figure 5 indicates hardness according to tempering temperatures. DHA-WORLD obtains slightly lower
hardness after quenching and tempering than H13 (1.2344). Therefore, adjusting hardness by referringFig.5 is strongly recommended.
Figure 6 indicates dimensional change according to tempering temperatures. DHA-WORLD shows
isotropic behavior regarding the dimensional change by heat treatment and the ratio of dimensional change
is smaller than H13 (1.2344). Reference of Fig. 6 is recommended to determine the machining allowancefor finishing.

© 2020 Daido Steel Co., Ltd.

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Table 3. Heat treatment condition of DHA-WORLD
Forging
temperature(℃)

900~1200

Heat treatment (℃）

Transformation Temp. (℃)

Hardness
Quenched

Annealing

QuenchingTempering Annealed&Ac

Ms

Tempered820~870

1000~1050

550~650

Slow cooling

Air cooling

Air cooling

300≦229HB 35~53 HRC 815~875(Austenitizedat 1030℃)(4) Surface treatment conditions
Figure 7 shows the hardness distributions of DHA-WORLD and H13 (1.2344) by applying the samenitriding condition. DHA-WORLD will show nitriding property as same as H13 (1.2344). Accordingly, thesame nitriding conditions as H13 (1.2344) can be applied to DHA-WORLD.

Fig. 5. Tempering temperature and hardness

Fig. 6. Tempering temperature and dimensionalchangeFig. 7. Hardness distribution after nitriding© 2020 Daido Steel Co., Ltd.

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6/7(5) Machinability of DHA-WORLD
Figure 8 and Figure 9 indicate the machinability of milling and drilling to DHA-WORLD as annealed status.
DHA-WORLD has almost the same machinability as H13 (1.2344).

Fig. 8. Machinability of DHA-WORLD (Milling)

Fig. 9. Drilling Machinability(6) Basic properties
DHA-WORLD basic properties are shown below.
Mechanical properties
Below results has been tested with the same hardness condition between DHA-WORLD and H13(1.2344).

Fig. 10. Tensile property (Tensile strength)

Fig. 11. Tensile property (Elongation andReduction of area)© 2020 Daido Steel Co., Ltd.

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Fig.12. Charpy impact value at high temperature

Fig.13. High temperature hardness

Physical properties
Table 4. Average coefficient of thermal expansion from room temperature
Temp.

20～100℃ 20～200℃ 20～300℃ 20～400℃ 20～500℃ 20～600℃ 20～700℃-6×10 /K

11.3

11.7

12.1

12.5

12.8

13.1

13.2

Table 5. Thermal conductivity at each temperature
Temp.

100℃

200℃

300℃

400℃

500℃

600℃

W/ m・K

28.4

29.1

30.0

30.3

30.1

29.5

Table 6. Specific heat at each temperature
Temp.

100℃

200℃

300℃

400℃

500℃

600℃

700℃

J/kg･K

473

509

558

604

667

760

934

[cal/ g･℃]

[0.113][0.122][0.133][0.144][0.159][0.182][0.023]

Measuring method: Laser flash method, Heat treatment of specimen: 1030 ℃ quenching, 610 ℃tempering■Important Note
The product characteristics included in this brochure are the representative values based on the result ofour measurements, and do not guarantee the performance in use of the products.
Please inquire the latest information to our department in charge as the information of this brochure is
subject to further updates without any notice.

© 2020 Daido Steel Co., Ltd.

No. SD2002 (2020.08)