Comparative Study of Microstructure and Mechanical Properties of

Hot Work Tool Steel SKD 6 with Different Manufacturing Process

Roni Kusnowo

, Hanif Azis Budiarto

, Cecep Ruskandi

and Gita Novian Hermana

Department of Foundry Engineering, Bandung Polytechnic for Manufacturing, Bandung 40135, West Java, Indonesia

Department of Design Engineering, Bandung Polytechnic for Manufacturing, Bandung 40135, West Java, Indonesia

Department of Advanced Materials Engineering, Bandung Polytechnic for Manufacturing, Bandung 40135, West Java,

Indonesia

Keywords: SKD 6 Tool Steel, Heat Treatment, Precipitation, Carbide, Tool Steel, Cast Steel.

Abstract: SKD 6 tool steel is a medium carbon-alloy steel known as a creep-resisting alloy used as lightweight

aluminium (Al) component die casting under high-temperature conditions. SKD 6 tool steel is an imported

steel material manufactured by rolling and forging processes. Some studies also developed advance

technology to fabricated SKD 6 by recrystallization and partial melting (RAP) process. However, due to the

complex geometry and cost efficiency, sand casting method is the most effective method to produce Al dies.

The SKD 6 cast alloy sample was heat treated at 850°C for 4 hours and cooled slowly inside the furnace by

opening the oven door to 45 degrees. The observation showed that the microstructure of cast SKD 6 is

identical to the as-cast product (imported) that has normalized. The microstructure showed that the normalized

cast alloy has a ferrite matrix with spherical secondary carbide grain on the grain boundary. However, the

hardness value of cast alloy Cr-M-V is slightly lower, 13.6 HRC, while the as-cast alloy is 18.1 HRC. The

low hardness value may cause by the lower content of secondary carbides in casting sample, and segregation

from secondary carbide. With these results, the imported substitute material is suitable for use.

1 INTRODUCTION

SKD 6 alloy is a medium carbon alloy steel known as

a creep-resisting alloy. It is the most common

material used in die casting to produce nonferrous

materials parts with complex shapes (Hong et al.,

2016; Xue et al., 2021). Recently, commercial SKD 6

steels have fabricated through different

manufacturing process such as rolling and forging.

Some studies also developed advance technology to

fabricated SKD 6 by recrystallization and partial

melting (RAP) process (Meng et al., 2012). However,

due to the complex geometry and cost efficiency,

sand casting method is the most effective method to

produce Al dies.

Commonly dies are made by machining process

from rolling steel Cr-Mo-V. Cr-Mo-V bar/ plate are

machining by CNC machine (fig. 1). Though, the

machining process increase machine time and the

https://orcid.org/0000-0002-7632-3434

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https://orcid.org/0000-0003-1860-1130

production of scrap, while sand casting process has

the advantage of near net shape product. Then, it is

carried out using CNC to achieve dimensional

accuracy (Adeleke et al., 2022; El-Hofy, 2013).

Figure 1: 3D model of dies.

Normalizing shall be given to the as-cast product

so that the product can be used under work

conditions. Hardness test and metallographic test are

746

Kusnowo, R., Budiarto, H., Ruskandi, C. and Hermana, G.

Comparative Study of Microstructure and Mechanical Properties of Hot Work Tool Steel SKD 6 with Different Manufacturing Process.

DOI: 10.5220/0011876100003575

In Proceedings of the 5th International Conference on Applied Science and Technology on Engineering Science (iCAST-ES 2022), pages 746-750

ISBN: 978-989-758-619-4; ISSN: 2975-8246

carried out both from imported and cast alloy Cr-Mo-

V steel to get mechanical properties so that meet the

specification of industries.

2 METHODS

2.1 Materials and Heat Treatment

In this study, the SKD 6 was produced by sand casting

method. Each alloy was melted by using an induction

furnace (Inductotherm) with a capacity 250 kg. The

casting of SKD 6 material uses metal casting rules,

starting from making Y-block patterns, making

moulds, and smelting. SKD 6 rolled steel was

imported from Buderus Edelstahl GmbH, Bulgaria as

a comparison.

Figure 2: Y-Block of Cr-Mo-V.

The compositions of SKD 6 alloy steel were

determined according to JIS Standard and being

tested by using an Optical Emission of Spectroscopy

(OES, ARL 234) before pouring into the sand mould

as shown in Table 1.

Table 1: JIS Cr-Mo-V (SKD 6) material standard

composition (% W) (International ASM, 2000).

3 Si Mn Cr V Mo

0.32-

0.42

0.8-

1,2

0,5

max

4,5-

5,5

0.3-

0,50

1,00-

1,5

<0,0

Normalizing was carried out to refine the grain,

improve machinability, eliminate residual stress and

improve the mechanical properties of construction

carbon steel and low alloy steel (Kristianto, 2018;

Roberts et al., 1998). The Y block SKD 6 steel was

separated into 2 specimens. the first sample were heat

treated at 850 °C for 4 hours and cooled slowly inside

the furnace by opening the oven door to 45 degrees

while the second were heat treated at 850 °C, held for

2 hours and cooled by air temperature. Last, the all of

sample were cut out with the dimension 20x20x10

mm (figure 3).

Figure 3: Sample As-recieved (left), As-Cast (middle),

Normalizing (right).

2.2 Microstructure Investigations

After the normalizing process, samples were ground

and polished with Al

paste for the hardness

measurements and microstructure analysis. Each

sample were polished and etched in 1 g picric acid, 4

mL HCl, 96 mL ethanol. A scanning electron

microscope (SEM; Hitachi SU 3500; Japan) was used

to examine the microstructure of the SKD 6 steels.

2.3 Hardness Measurement

The hardness measurements were made on a polished

surface of sample by using the Rockwell’s method.

Measurements were conducted on Future Tech

Rockwell Hardness Tester Machine with 1.498 N in

load and held for 10 seconds.

3 RESULTS AND DISCUSSIONS

3.1 Chemical Compositions

The chemical composition test showed that the

sample was confirmed as SKD 6 steels. As Shown in

Table 2, the chemical compositions of the specimen

are in the range recommended by standard JIS.

Table 2: The chemical composition of specimen Cr-Mo-V

cast alloy steel.

JIS Standard

C Si Mn Cr V Mo

0.32-

0.42

0.8-

1,2

0,5 max 4,5-

5,5

0.3-

0,50

1,00-

1,5

<0,02 <0,03

Cast Alloy Cr-Mo-V Steel Sample

C Si Mn Cr V Mo

0.41 0.9 0.21 4.5 0.3 1.02 0.01 0.01

Comparative Study of Microstructure and Mechanical Properties of Hot Work Tool Steel SKD 6 with Different Manufacturing Process

747

3.2 Microstructure Investigations

The Scanning Electron Microscope (SEM) images of

the SKD 6 steel showed in Figure 4. Picture of 4(a) is

as received sample (imported steel) which shows

some small spherical carbide known as Secondary

Carbides (SCs). The secondary carbides are

distributed evenly in the ferrite matrix with range of

size 500 nm to 1 µ in the ferrite matrix. Figure 4(b)

shows the microstructure of As-cast Cr-Mo-V steel.

It has observed that the lath martensite was fully

distributed in the alloy with the retained austenite

(Meng et al., 2012; Qamar, 2015). Further, figure 4(c)

is a cast alloy Cr-Mo-V steel after normalized. As can

be seen in that figure, the microstructure is identical

with the as-received sample. Nevertheless, the

secondary carbides in normalizing sample tend to

distributed in the grain boundary with the range of

size 500 nm to 1 µ. Both SCs on sample are indicated

as M

carbides (Michaud et al., 2007).

Moreover, The SEM-EDS data (Figure 5) showed

that there were Cr and Mo content in area 1 and area

3 that indicated M

carbides.

Precipitation carbides on the grain boundaries due

to high temperature known as sensitization. Heating

the sample at the sensitization temperature will cause

the C Atoms in the interstitial diffuse and tend toward

the grain boundaries. However, Cr atoms are

different. Cr atoms are hard to diffuse freely, even at

high temperatures. Therefore, the C atoms at the grain

boundaries will bind the atom Cr around it (Maulana

and Sulistijono, 2015).

(a) (b)

(c)

Figure 4: Microstructure of samples (a) As-received (b) As-cast (c) Normalized.

iCAST-ES 2022 - International Conference on Applied Science and Technology on Engineering Science

748

Figure 5: Graphics of Carbides SEM-EDS measurement (a) area 1 (b) area 2 (c) area 3 (d) area 4.

3.3 Hardness

Table 3 shows the hardness measurement by using

Rockwell hardness tester type C. The as-received Cr-

Mo-V alloy steel has higher hardness value 18.1 HRC

than normalizing sample 13.6 HRC. Although the two

samples had identical microstructures, the as-

received samples had a higher SCs content, and the

segregation was more even. This is what causes the

hardness value of As-received sample to be higher,

although not significant.

Table 3: Hardness test result.

Sample

Hardness (HRC) Average

1 2 3 4 5 (HRC)

As-received 18.3 18.1 17.7 17.9 18.3 18.1

Normalizing 13.4 13.7 13.3 13.8 13.7 13.6

4 CONCLUSIONS

The microstructural and hardness investigation on

Imported Cr-Mo-V Steel and Cast Alloy Cr-M0-V

Steel has been established. The observation showed

that the microstructure of cast alloy Cr-M-V is

identical to the as-cast product (imported) that has

normalized. The microstructure showed that the

normalized cast alloy has a ferrite matrix with

spherical secondary carbide grain on the grain

boundary. However, the hardness value of cast alloy

Cr-M-V is slightly lower, 13.6 HRC, while the as-cast

alloy is 18.1 HRC. The low hardness value may cause

by the lower content of SCs in the casting sample and

segregation from secondary carbide on the grain

boundaries. With these results, the imported

substitute material is suitable for use.

ACKNOWLEDGEMENTS

The authors acknowledge financial support from the

Ministry of Education, Culture, Research, and

Technology, Indonesia. The author is also thankful

for the help from Bandung Polytechnic for

Manufacturing and PT. Pako Akuina.

REFERENCES

Adeleke, A. A., Oki, M., Anyim, I. K., Ikubanni, P. P., and

Adediran, A. A. (2022): Recent Development in

Casting Technology : A Pragmatic Review Revue des

Composites et des Matériaux Avancés-Journal of

Composite and Advanced Materials Recent

Development in Casting Technology : A Pragmatic

Review, (May).

El-Hofy, H. A.-G. (2013): Machining by Thermal Erosion,

Fundamentals of Machining Processes, 429–468.

https://doi.org/10.1201/b15339-19

Hong, S. P., Kim, S. Il, Ahn, T. Y., Hong, S. T., and Kim,

Y. W. (2016): Effects of extended heat treatment on

carbide evolution in Cr-Mo steels, Materials

Characterization, 115, 8–13. https://doi.org/10.1016/

j.matchar.2016.03.013

Comparative Study of Microstructure and Mechanical Properties of Hot Work Tool Steel SKD 6 with Different Manufacturing Process

749

International ASM (2000): ASM handbook: Volume 8 (A.

International, Ed.). https://doi.org/https://doi.org/

10.31399/asm.hb.v08.9781627081764

Kristianto, R. (2018): Analisa Perlakuan Panas Pada Baja

Karbon Sedang Setelah Proses Pengelasan Dilihat Dari

Uji Kekerasan Dan Struktur Mikro, Jurnal Teknik

Mesin Ubl, 5(2), 14–18.

Maulana, F. H., and Sulistijono (2015): Pengaruh

Temperatur Sensitisasi dan Variasi Stress Terhadap

Laju Korosi SS 409 pada Lingkungan Salt Spray,

Jurnal Teknik ITS, 4(1).

Meng, Y., Sugiyama, S., and Yanagimoto, J. (2012):

Journal of Materials Processing Technology

Microstructural evolution during RAP process and

deformation behavior of semi-solid SKD61 tool steel,

Journal of Materials Processing Tech., 212(8), 1731–

1741. https://doi.org/10.1016/j.jmatprotec.2012.04.003

Michaud, P., Delagnes, D., Lamesle, P., Mathon, M. H., and

Levaillant, C. (2007): The effect of the addition of

alloying elements on carbide precipitation and

mechanical properties in 5% chromium martensitic

steels, Acta Materialia, 55(14), 4877–4889.

https://doi.org/10.1016/j.actamat.2007.05.004

Qamar, S. Z. (2015): Effect of heat treatment on mechanical

properties of H11 tool steel, Key Engineering

Materials, 656–657(2), 434–439. https://doi.org/

doi:10.4028/www.scientific.net/KEM.656-657.434

Roberts, G. ., Krauss, G., and Kennedy, R. (1998): Tool

Steels: 5th Edition, ASM International, 364.

https://doi.org/10.1361/t

Xue, S., Yang, T., Guo, R., Deng, A., Liu, X., and Zheng,

L. (2021): Crack analysis of Cr-Mo-V-Si medium-

carbon alloy steel in casting die, Engineering Failure

Analysis, 120(July 2020), 105083. https://doi.org/

10.1016/j.engfailanal.2020.105083

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