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DENKI-SEIKO (Electric Furnace Steel), vol. 76 (2005), No. 4, p. 279 – 286.
Paper

The Development of High Hardness and Toughness Matrix Type High
Speed Tool Steels: DRMTM
Shunsuke Nakahama, Yukinori Matsuda, Kunio Namiki and Kozo Ozaki*This English article is an abridged version of the original Japanese one.

Synopsis
The best way to attain high toughness in carbon-high hard tool steels is to refine carbides. Besides powder
metallurgy, carbides control by alloy designing and production process is the key technology. This time we havedeveloped three matrix type tool steels, DRM steels, and have clarified their superiority to conventional typesteels not only in fundamental study but in practical use.
This series are composed of three steels, DRM1 to 3 which are used with the maximum hardness of 58, 62
and 66 HRC, respectively. These steels are characterized by their more finely dispersed carbides free from coarse
primary ones, higher toughness and fatigue strength than conventional type steels. DRM1 is mainly used for
hot and warm forging tools with the hardness of 56 to 58 HRC. DRM2 is applied to warm and cold forging
tools with higher hardness of 58 to 62 HRC. DRM3, highest hardness one, is the best grade for cold toolings.
These DRM steels have shown longer life and contributed to total cost reduction mainly in forging tools of
automobile and machinery components. They are further expected to expand their application fields.

1. Preface
Plastic forming is one of the important elemental technologies and forging is one of them. Dies
play an important role in forging processes. In order to respond to the recent customers request forcost reduction or shorter lead-time, plastic forming technology has developed rapidly by applying
net-shape or near-net-shape. For that reason, warm or cold forging processes have been chosen more
widely. This progress made die use conditions harsher by complicating products dimensions ordecreasing forging temperature. Therefore dies have been required to be harder and tougher to be
more durable against higher contact pressure, sliding wear and impact load1), 2).
In order to meet these severe requests, we have developed matrix-type high speed steel, “DRM
(Dream)”, featuring high hardness and high toughness for wide variety of application. In this paper
development concept and features of DRM steel as well as actual application cases are introduced.

2. Background of development
Dies, especially heading tools forming automotive parts, require high hardness and high toughness.
However since hardness and toughness are conflicting with each other, tough hot work die steels do
not have enough strength resulting in deformation of dies, or high strengthened high speed toolsteels (hereinafter HSS) easily generate die cracks so that high-precision forging or prolonged die life
was very difficult. There is a material which can fill the gap between hot work die steels and HSS,
called matrix-type HSS. Matrix-type HSS is a material which improves HSS by suppressing primary© 2021 Daido Steel Co., Ltd.

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2 / 10coarse carbides generation and adjusting its basic composition as its matrix composition. This
reduction of carbides contributes to better toughness and fatigue strength while high hardness canalso be secured because their matrix composition is the same as HSS’s matrix one 3), 4). Various typesof matrix-type HSS have been developed so far 5), 6) and Daido Steel has developed our own matrixtype HSS, MH85 as cold or warm work die steel which require severe performance and has put theminto the market. However with the recent change in die use environment, die service life cannot meetcustomers’ requirements even by MH85. We investigated the cause of damages of those dies andfound out that they were impact fracture or fatigue failure by high load, and wear because of lack ofhardness as shown in Fig. 1. In order to solve these issues, die steels with higher toughness andhardness at the same time were needed to be developed. Powder HSS is one solution for this, but
their production cost is expensive, thus we aimed to develop matrix-type HSS. That steel is “DRM
(Daido’s Revolutionary Matrix Type High Speed Tool Steels)” steel.
DRM has higher hardness and toughness than conventional matrix-type HSS and has three grades
rather than two grades (MH85 and MH88) previously, so that user choice is more flexible dependingon their applications. Figure 2 shows positioning map of DRM steels.

Fig. 1. Examples of failed forging tools and countermeasure to enlarge forging tools life

Fig. 2. Positioning of DRM steels in Daido tool steels© 2021 Daido Steel Co., Ltd.

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3. Development of DRM
3.1 Development Concept
The causes of damages of recent dies were found to be mainly impact fractures or fatigue failuresby high load as described above. Therefore we observed fracture surfaces of impact test and fatigue
test pieces of conventional matrix-type HSS and examined the form of the fractures. As a result,coarse primary carbides were found as shown in Fig. 3.
In addition, observation of microstructure of conventional matrix-type HSS were taken place andthe existence of primary carbides, even though their amount is small, were confirmed as shown in
Fig. 4. These carbides bring about suppression of toughness as shown in Fig. 5.
Moreover, decreasing size of carbides have been reported to raise fatigue strengths7), 8). Therefore
development target was to decrease those coarse carbides to the most and suppress fatigue andimpact fractures. Two grades; MH85 and MH88 were available previously for hot, warm and cold
work, but this time by strengthening each application’s characteristic feature, deeper consideration
was made so that the new steel will endure more severe environment.

Fig. 3. SEM fractographs of conventional matrix-type HSS (MH85)a) Charpy impact test specimen, b) Fatigue test specimen,c) EDX-ray analysis of starting point in fractured surface of b)

Fig. 4. Microphotograph of conventional matrix-type HSS (MH85)a) Microphotograph, b) EDX-ray analysis result© 2021 Daido Steel Co., Ltd.

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Fig. 5. Effect of the amount of primary carbides on Charpy impact values
3. 2 Alloy Design and Production Process
Following items were considered to achieve the development concept:
a. Alloy design to make most use of carbides: type of carbides, appropriate quantity
b. Production technology to refine coarse carbides: Dispersion in ingot-making and controlling
solution or precipitation in forging or rollingc. Grade lineup with excellent property corresponding to each hot, warm or cold work application
Basic philosophy of DRM1 and DRM2 is to design alloy composition where carbides can be
dissolved easily during high temperature heating to reduce coarse carbides. Examination ofcomposition was done using equilibrium calculation software, “Themo-calc” under the condition
where single γ-phase at certain carbide amount was broad enough and those carbides are easily
dissolved. The result is shown in Fig. 6. In spite that there is no single γ-phase region with AISI M2,
the developed alloy has broad region of it.
In order to reduce original primary carbide size, re-melting is applied for the production of DRM
steels. Applying re-melting enables molten steel in the pool to be refined and solidified rapidly,
which results in clean and uniform steel with finely distributed carbides from the surface to the centerand from the top to the bottom as well. Moreover, finely solidified primary carbides are remained tobe fine by controlling the heating temperature prior to forging and re-heating temperature for final
forging or rolling.
By applying these technologies we have newly developed two steels: DRM1 and 2.
Furthermore, by adding high hardness type high carbon steel 9), DRM3 which contains a little coarse
primary carbides, we have completed DRM series：Daido’s Revolutionary Matrix type High Speed
Tool Steels and launched to the market. Principal chemistries of these steels are shown in Table 1.

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Fig. 6. Calculated phase diagramsa) AISI M2, b) New matrix-type HSS
Table 1. Principal chemistries of DRM steels
Grade

C

Cr

Weq.*

V

Co

DRM1

0.6

4.2

5.0

1.5

Added

DRM2

0.7

5.5

6.0

1.0

-

DRM3

0.8

5.5

10.0

1.0

-

*Weq. = 2Mo + W

4. Special features of DRM steels
4.1 Features of DRM steels
Special features of DRM steels are shown in Table 2. DRM1 is applied mainly to hot and warm
forging dies because of its high hot hardness. DRM2 is suitable for warm and cold forging dies. Dueto its high fatigue strength cold forging dies is the most appropriate applicable field. DRM3 is cold
forging die steel which can be applied where AISI D2 and M2 have problems in strength andtoughness.
The primary feature of DRM steels is fine microstructure as shown in Fig. 7. DRM1 and 2 scarcely
show the coarse carbides compared to conventional matrix-type HSS, MH85. DRM3 realizes
uniformly dispersed carbides and contains less coarse carbides than AISI M2.
Table 2. Special features of DRM steels
Grade

Hardness

Applications

(HRC)
DRM1

56 – 58

Hot and warm working tools: High hardness, hot forging tools

DRM2

58 – 62

Warm and cold working tools: High toughness, cold forging tools

DRM3

62 - 66

Cold working tools: When AISI D2 or M2 has problems with strength and toughness© 2021 Daido Steel Co., Ltd.

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Conventional matrix-type HSS (MH85)

Fig. 7. Microphotographs of DRM steels as annealed
Sample: Taken from the center of 100mm dia. bar, Etchant: 1%Cr2O3 electrolytic etching
4. 2 Properties of DRM steels
Toughness properties are investigated by Charpy impact tests. The results are shown in Fig. 8.
DRM1 and 2 exhibit higher values than those of cold work die steels such as AISI D2 and Daido’s
DC53 and conventional matrix-type HSS, MH85. Toughness of DRM3 is better than that of AISI M2.
Micro-fractographic photos taken from the Charpy impact specimens of DRM1 and MH85 areshown in Fig. 9. As we have intended, it is confirmed that coarse VC carbides were observed at thecrack origin in MH85, but none of those were found in DRM1.
Fatigue test results, the relation between the applied stress and the numbers of cycles to fracture,are shown in Fig. 10. Rotating bending fatigue tests were carried out by using smooth specimens.
DRM1 and 2 show higher fatigue strength than MH85. As confirmed in Charpy impact specimens,
micro-fractography also reveals that there is no coarse carbides at fatigue crack origin in DRM1 and2 as well.
Heat checking test and tempering softening resistance test were conducted to evaluate the thermal
fatigue properties. The results of heat checking test are shown in Fig. 11. The maximum crack lengthof DRM1 and DRM2 is shallower than that of MH85 and AISI H13, which means the superiority of
the new grades to conventional steels.
Tempering softening resistance is the other important property for forging die steels, and the test
results are shown in Fig. 12. DRM1 shows higher hardness than MH85 and AISI H13. DRM2 is almost
equivalent to MH85 but superior to AISI H13.

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Fig. 8. Charpy impact values of DRM steels
and conventional tool steels

Fig. 9. SEM images ofCharpy impact test specimens

Fig. 10. Fatigue strength of DRM1, DRM2 and conventional matrix-type HSS (MH85)a) SEM images of fatigue test specimens, b) EDX-ray analysis result© 2021 Daido Steel Co., Ltd.

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Fig. 11. Heat checking resistance of DRM1, DRM2 and conventional tool steels

Fig. 12. Temper softening resistance of DRM1, DRM2 and conventional tool steels

5. Application Study
5. 1 Application of DRM1
Examples of the application of DRM1 are shown in Table 3. DRM1 shows longer life than MH85
and AISI H13 especially for dies the failure mode of which is crack. Furthermore, DRM1 is effective
to prolong the life of the dies which have problems in the surface softening. The cause of the die life
improvement from H13 is the greater tempering softening resistance by increasing the initialhardness 10).

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Table 3. Applications of DRM1 steel
Application
Outer race

Size(mm)

HRC

Life

90 dia.

55±1

13,000S

Forming punch
Knockout pin

40 dia.

Conventional grade
3Cr-2Mo: 12,000S****

matrix-type HSS*: 12,700S**

15,000S

matrix-type HSS*: 15,000S(No stelite)(Stelite welding overlay)

57±1

Back die120 dia.

57±1

18,600S

matrix-type HSS*: 16,000S

Front die140 dia.

57±1

6,700SAISI M2: 2,400S

20,600S**
Pressing die

100 dia.

56±1

13,000SAISI H13: 8,000S

Connecting rod

45 X 130s

58±1

10,000SAISI H13: 8,000S

forming die*Conventional matrix-type high speed tool steel, **Salt nitriding
5. 2 Application of DRM2
Table 4 shows examples of the application of DRM2 indicating the longer life than conventional
matrix-type HSS. Factors to prolong die life are prevention of yielding and fatigue by increasing
the strength with remaining high toughness. DRM2 was applied to a mandrel used for cold forming
and originally made of powder metallurgy high speed steel. The failure mode was fatigue fracture.
Although the new grade shows almost the same life with fatigue fracture, it is superior to P/M steel
from the viewpoint of material cost 10).
Table 4. Applications of DRM2 steel
Applications
Cold

Warm

Size(mm)

HRC

Life

Conventional grade

Knockout sleeve

20 dia.

59≥ 18,000S

matrix-type HSS*: 14,000S

Mandrel

30 dia.

61±1

12,000S

P/M HSS: 12,000S

Punching die

15 dia.

60

Longer than M2AISI M2

Threading die

200 dia.

62

22,000S

matrix-type HSS*: 20,000S

Forming sleeve

50 dia.

58

60,000S

matrix-type HSS*: 50,000S

Forming die

100 dia.

58

60,000S

matrix-type HSS*: 50,000S

Warm punch

120 dia.

58≥ 15,000S

Hot work die steel: 10,000S

5.3 Application of DRM3
Examples of the application of DRM3 are shown in Table 5. Longer life has been attained especiallyfor the tools where AISI D2 and M2 fail with chipping. Since DRM3 has higher hardenability,
prolonged life has been realized for large size dies like rolling-mill rolls where toughness deficiency
may happen easily.

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Table 5. Applications of DRM3 steel
Application

Size(mm)

HRC

Warm rolling die

75 X 85s

65

CVJ

150 dia.

65

Cold forming die
Cold forging

70 dia.

65

punch
Cold work roll

Emboss roll

100 dia.

200 dia.

66

65

Life

Conventional grade

30,000SAISI M2, 60HRC

Chipping

10,000S, Chipping

35,000S

8Cr type die steel

Chipping

12,000S, Chipping

60,000SAISI M2, 61HRC

Chipping

10,000S, Chipping

Three times

AISI M2, 61HRC

Wear

Wear

Twice

AISI M2, 61HRC

Wear

Wear

6. Conclusion
We have developed new matrix-type high speed steels, DRM steels, aiming at high toughness andfatigue strength by decrease coarse primary carbides with maintaining the required amount ofcarbides 11). This concept has been realized by the combination of alloy designing and state-of-the-art
production technologies. These new grades, DRM steels, have shown their superiority toconventional steels in actual applications and are expected to expand their application fields by
replacing conventional steels for hot, warm and cold forging tools.
DRM and DC53 are trademarks or registered trademarks of Daido Steel Co., Ltd.

References
1) Y. Matsuda: Journal of the JSTP, vol.42 no.480, (2001), p. 3.
2) S. Nakahama, K. Ozaki and Y. Matsuda: Die & Mold Technology, vol. 19 no. 12, (2004), p. 56.
3) George A. Roberts and John C. Hamaker, Jr.: United States Patent Office, no.3, 117,863 (1964)
4) Alan M. Bayer: METAL PROGRESS, vol.97 no.4, (1970), p. 86.
5) Y. Tamura and T. Okuno: HITACHI METALS TECHNICAL REVIEW, vol. 6, (1990), p. 59.
6) N. Uchida: HITACHI METALS TECHNICAL REVIEW, vol. 13, (1997), p. 83.
7) K. Kiyonaga: Toward Improved Ductility and Toughness, (1971), p. 209.
8) K. Ozaki, Y. Matsuda and K. Sudoh: ‘‘Mechanical Properties of New Die Steels for Semi-Hot andCold Forging’’ reported by 26th ICFG Plenary Meeting Osaka, Program No.16, (1993), oral only.
9) Y. Matsuda and T. Yanagisawa: ELECTRIC FURNACE STEEL, vol.68 No.2, (1997), p. 123.
10) S. Nakahama, K. Ozaki and Y. Matsuda: Die & Mold Technology, vol. 20 no. 8, (2005), p. 126.
11) S. Nakahama, Y. Matsuda, K. Namiki and K. Ozaki: SEAISI 2005 Conference Exhibition, (2005),
p. 39© 2021 Daido Steel Co., Ltd.

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