DE-GP4M – A NEW GENERATION FOR TOOL
STEEL CASTING.

A. Oldewurtel and C. Escher

D¨orrenberg Edelstahl GmbH, Engelskirchen,

Germany

Abstract

DE-GP4M is a new cast tool steel that offers not only the benefits of low-alloy
materials but at the same time has all the favorable characteristics of the high-
alloy material grades. Due to its low carbon content the material has a very
high toughness. The secondary hardness behavior of the material is governed
by the adjustment of the alloying constituents. This enables the high working
hardness to be appropriately adjusted at high tempering temperatures so that
both a nitriding treatment and a hard material coating can be performed.

INTRODUCTION

A great variety of tool steel grades can be used for tool castings. The

materials listed in Table 1 will satisfy the needs of most applications. DE-

Table 1.

Standard materials for large tools castings

Material

Reference analysis

DE-

Brand

Grade name

W.-№

C

Si

Mn

Cr

Mo

V

Ni

GPCNP(S)

G-45CrNiMo4-2

1.2769

0.45

0.50

0.60

1.00

0.25

0.10

(0.50)

GMF

G-47CrMv6

1.7140

0.50

0.60

0.80

1.50

—

—

—

GP3M

G-60CrMoV10-7

1.2320

0.60

0.50

1.20

2.50

0.70

0.10

—

G-AMO

G-59CrMoV18-5

1.2333

0.60

0.40

0.80

4.50

0.50

0.20

—

GP5M

G-X100CrMoV5-1

1.2370

1.00

0.50

0.50

5.00

1.00

0.30

—

GCPPU

G-X155CrVMo12-1

1.2382

1.55

0.60

0.50

12.0

0.80

1.00

—

175

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GP4M is another favorable material by means of which greater sizes and
weights, improved workability and characteristics of use can be attained.

In the development of DE-GP4M emphasis was on the requirement to

achieve greater casting sizes and a tempering behavior resulting in secondary
hardness during heat treatment. Moreover, surface hardenability and a sat-
isfactory weldability were additional features to be attained.

REQUIRED PROPERTIES OF CAST MATERIALS

Tool and die making facilities make efforts to reasonably limit the number

of materials for clarity reasons. The materials to be processed shall feature
excellent workability and maximum service life, furthermore they shall be-
have in a non-distorting manner during heat treatment. Unfortunately, not
all of these needs can be satisfied so that related problem areas should be
discussed and suitable solutions achived before production starts.

The required material characteristics for large tools are:

high hardness

high compressive strength

high tensile strength

high toughness

high wear resistence

good hardenability

good dimensional stability

low distortion

The material characteristics are adjusted via the chemical composition and

heat treatment. To achieve a high toughness the carbon content is reduced
to the required amount. Moreover, the secondary hardness behavior can
be influenced by adding for example molybdenum and/or vanadium. Fig. 1
gives a general overview of the effects of the individual alloying constituents.

In material grade DE-GP4M the carbon content was limited to approx.

0.6% to achieve a primary carbide content as low as possible. This resulted

DE-GP4M – a New Generation for Tool Steel Casting.

177

Figure 1.

Material characteristics.

in a considerable increase in toughness in comparison with e.g. material
grades 1.2370 and 1.2382. Other than in material 1.2320 the alloying con-
tent was modified to the extent that at elevated tempering temperatures the
transformation of retained austenite as well as the precipitation of special
carbides appears. As is generally known, this is the prerequisite to obtain
the desired secondary hardness in the framework of a tempering treatment.

HEAT TREATMENT OF DE-GP4M

During materials development the hardness were determined as a function

of the austenitizing temperatures. Tentatively, austenitizing was carried out
in the range of 800–1100

◦

C with the results as shown in Fig. 2. It is evident

that up to approx. 1070

◦

C the hardness increases with increasing austen-

itizing temperature which is the result of greater carbide dissolution. The
restraint of martensite increases as more carbon is released causing higher
austenitizing temperatures.

Various tempering curves were prepared on the basis of different austen-

itizing temperatures. The aim was to achieve a secondary hardness in the
range of 60 HRc. In Fig. 3 typical tempering curves for materials 1.2320,
1.2382 and DE-GP4M are compared. It can be seen that due to its alloying
characteristics especially grade 1.2320 shows a reduced hardness at higher
tempering temperatures. Grades 1.2382 and DE-GP4M both show a pro-
nounced maximum secondary hardness.

Another point to be assessed was the changes in dimension resulting

from heat treatment. Tests were carried out using flat speciments size 180 ×

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6TH INTERNATIONAL TOOLING CONFERENCE

40 × 40 mm. Figure 4 shows changes in dimension in comparison to the
annealed state. In Fig. 5 an excerpt from the heat treatment tests is shown.
The figures indicate microstructural formations in hardened, hardened and
tempered (450

◦

C ) as well as hardened and tempered (525

◦

C ) state. It can be

seen that especially in tempered state (525

◦

C ) the extensive transformation

has already taken place so that subsequent ageing and changes in dimension
need no longer be expected.

Material DE-GP4M can be delivered both in annealed and hardened and

tempered conditions. A structural comparison between grades 1.2320 and
1.2382 and the new material is shown in Fig. 6. It is to be seen that the
new material only has individual small primary carbides which means it is
comparable to cast material 1.2320 in terms of toughness. On the other hand,
material grade 1.2382 shows a pronounced carbide network.

SURFACE HARDENABILITY

The material DE-GP4M was developed with a view to enabling a surface

hardening to be carried out as well. In the context of surface hardening it is to
be noted that an as high as possible supporting effect should be aimed at. It is
therefore recommendable that the base material should not be of annealed but

Figure 2.

Hardness projection of DE-GP4M.

DE-GP4M – a New Generation for Tool Steel Casting.

179

Figure 3.

Tempering behaviour of cast materials GP3M, GP4M and GCPPU.

of hardened and tempered if a surface hardening process is applied. Due to
the alloying characteristic and attained structure all three surface hardening
processes (flame, induction, laser beam) can be applied. In this case the
austenitizing temperatures are in the range of 980–1050

◦

C . In connection

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6TH INTERNATIONAL TOOLING CONFERENCE

Figure 4.

Changes in dimension of DE-GP4M.

with self-quenching in air hardness values between 58–62 HRc are achieved.
In Fig. 7 details of induction hardening are shown as an example.

WELDING OF DE-GP4M

A desirable main criterion of tool castings is that the material can be

welded, particularly to realize geometric modifications. Although official

Figure 5.

Gef¨ugeausbildung GP4M.

DE-GP4M – a New Generation for Tool Steel Casting.

181

Figure 6.

Structure comparation GP4M.

Figure 7.

Induction hardening of DE-GP4M.

practices prescribe that large tools and dies shall not be subjected to welding,
it is well known that in actual practice welding work is carried out on nearly
all tools. In such cases the relevant welding recommendations should be
followed to ensure that to the extent possible no cracks occur in welding
and adjacent areas. If cracks developed, a spalling off of the weld during
the initial work operations may lead to tool failure. Figure 8 shows an

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interesting aspect in that hardenability as well as weldability characteristics
are both perceivable. Due to its alloying characteristics the hardenability of

Figure 8.

Cast materials for large tools fabrication.

the new cast material DE-GP4M is superior to that of grades 1.2320, 1.2333
and 1.2370. On the other hand, its weldability is comparable to that of
material 1.2333 and thus considerably better than that of the grades 1.2370
and 1.2382.

NITRIDING

As can be concluded from what has been said earlier GP4M is a ma-

terial that can be employed both in hardened and tempered state (900–
1250 N/mm

2

) as well as heat treated in the range of the secondary hardness

of max. 62 HRc. If desired the material can also be subjected to a nitriding
treatment to enhance its wear resistance. If required and depending on the

DE-GP4M – a New Generation for Tool Steel Casting.

183

arising stresses various basic hardness levels can be set. This is of particular
importance since, on the one hand, a high compressive strength is needed
and, on the other, it should also be possible to manufacture larger sizes.

Furthermore, plasma nitriding tests were conducted, inter alia, with em-

phasis on the requirement that the wear resistance was to be purposefully
enhanced by the nitriding process. To this end the material was initially
quenched and tempered to attain a core hardness of approx. 580 HV follow-
ing which a nitriding treatment was performed. The results are shown in
Fig. 9. A depth of nitration Nht of approx. 0.21 mm was determined.

Figure 9.

Nitriding of DE-GP4M.

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SUMMARY

To summarize the above it can be concluded that the newly developed

cast material designated DE-GP4M fills a still existing gap. Not only is it
possible to cast tools of largewr size but what is more a secondary hardness
can be achieved that enables benefits to be derived from the subsequent treat-
ment processes. Moreover, the new DE-GP4M cast material offers clearly
improved weldability and toughness characteristics compared to material
1.2382. Advantages can be summarized as follows:

Secondary hardness (60–62 HRc)

Suitable for PVD/CVD-coating and nitriding

Dimensional adjustments possible

Surface layer hardenability with cooling in air (60–62 HRc)

Good edge retention properties

Greater sizes can be manufactured in comparison to grade 1.2382

Weldability is superior to that of grade 1.2382

Conditions of delivery:

– soft annealed, max. 250 HB

– hardened and tempered 900–1250 N/mm

2

The advantages over previous material grades and additional fields of use

are of course to be viewed as very positive. In particular, a typical use of
this material would be to replace grade 1.2382 for applications where higher
toughness properties are obligatory.