Revista de Metalurgia

Vol. 53, Issue 1, January–March 2017, e086

ISSN-L: 0034-8570
http://dx.doi.org/10.3989/revmetalm.086

The possibilities for reuse of steel scrap in order to obtain

blades for knives

Nada Štrbaca, Ivana Markovića,*, Aleksandra Mitovskia, Ljubiša Balanovića,

Dragana Živkovića, †, Vesna Grekulovića
a
University of Belgrade, Technical Faculty in Bor, VJ 12, 19210 Bor, Serbia
*Corresponding author: imarkovic@tfbor.bg.ac.rs
(†Deceased 26th November 2016)

Submitted: 4 February 2016; Accepted: 22 February 2017; Available On-line: 23 March 2017

ABSTRACT: The paper presents the characterization results of various types of steel component at the end
of product life with the unknown chemical composition, mechanical properties and previously implemented
thermo–mechanical treatment. This study was done aiming to examine the possibilities for reuse of some end–
of–life agricultural and industrial steel products in order to obtain blades for knives in non–industrial conditions
with appropriate and acceptable properties. Demanded shapes of the blades were obtained by applying vari-
ous types of thermo–mechanical treatment. Chemical analysis of the investigated steel components was done
using the energy–dispersive spectrometer. The microstructure was analyzed using optical and scanning electron
microscopy. Hardness of analyzed steel scrap and obtained blades was measured using Rockwell C scale. The
hardness values of the obtained blades (with optional quenching or not) indicate to a good selection of the steel
end–of–life products for this purpose.
KEYWORDS: Blade for knife; Hardness; Microstructure; Steel scrap

Citation / Citar como: Štrbac, N.; Marković, I.; Mitovski, A.; Balanović, L.; Živković, D.; Grekulović, V. (2017)
“The possibilities for reuse of steel scrap in order to obtain blades for knives”. Rev. Metal. 53(1): e086. http://dx.doi.
org/10.3989/revmetalm.086

RESUMEN: Posibilidades de reutilización de la chatarra de acero para la obtención de cuchillas para cortar. El
trabajo presenta los resultados de la caracterización de diversos tipos de aceros que han llegado al final de su
ciclo de vida útil, y de los que se desconocía su composición química, propiedades mecánicas y tratamiento
termomecánico aplicado previamente. El estudio se realizó con el objetivo de analizar las posibilidades de reuti-
lización de algunos de estos materiales en aplicaciones agrícolas e industriales, obteniendo hojas de corte. Las
formas exigidas a las hojas de corte se consiguieron aplicando diversos tipos de tratamientos termomecánicos.
El análisis químico de la chatarra de acero de acero se realizó utilizando Energías Dispersivas de Rayos X. La
microestructura se estudió utilizando Microscopía Óptica y Microscopía Electrónica de Barrido. La dureza de
la chatarra de acero y de las cuchillas obtenidas se midió utilizando la escala Rockwell C. Los valores de dureza
de las cuchillas obtenidas indican una buena selección de los productos finales de acero.
PALABRAS CLAVE: Chatarra de acero; Cuchilla; Dureza; Microestructura

ORCID ID: Nada Štrbac (http://orcid.org/0000-0003-4836-1350); Ivana Marković (http://orcid.org/0000-0003-

4431-9921); Aleksandra Mitovski (http://orcid.org/0000-0002-9130-2076); Ljubiša Balanović (http://orcid.org/0000-
0002-3551-6731); Dragana Živković (http://orcid.org/0000-0002-2745-5676); Vesna Grekulović (http://orcid.
org/0000-0001-6871-4016)

Copyright: © 2017 CSIC. This is an open-access article distributed under the terms of the Creative Commons
Attribution License (CC BY) Spain 3.0.
2 • Nada Štrbac et al.

1. INTRODUCTION possibilities for reuse of some end–of–life agricul-

tural and industrial steel products in order to obtain
Steels refer to alloys of iron with up to approxi- blades for knives (hereinafter termed as blades) in
mately 2 wt. % of carbon, very complex by structure, non–industrial conditions with appropriate qual-
and widely used as engineering materials because of ity. The article presents the characterization results
high iron content in the Earth’s crust, very good fea- of four different steel scrap materials with various
tures and low price (Zeng et al., 2009; Kumar and structural, chemical, mechanical properties and
Bhushan, 2015). They are characterized by a wide previously implemented thermo–mechanical treat-
range of mechanical properties, due to correspond- ment in order to study the possibility for blades
ing microstructures, generated during phase trans- production.
formations. The special significance of these alloys
represents a possibility for a very precise properties 2. EXPERIMENTAL
modification during thermal treatment under con-
trolled conditions (Goune et al., 2015). For the experimental research, four differ-
Any steel product has its own life cycle consisting ent steel components were selected, which repre-
of ore extraction, production, processing and fin- sent consumable parts (at the end of their life) of
ishing, product use, recycling or withdrawal at the the agricultural and industrial machineries with
end of its life cycle (Morfeldt et al., 2015). All steel the unknown chemical composition, previously
products have limited usable life cycle after which implemented thermo–mechanical treatment and
they lose their properties and become scrap that can mechanical properties. The labels of the steel scrap
be returned to the reproductive cycle (Bramfitt and (SS1, SS2, SS3 and SS4) and a pre–given purpose
Brenscoter, 2002). of these components at the end of their life are
Steel production can be divided into two tech- listed in Table 1.
niques: primary and secondary production tech- Figure 1 shows the macrophotographs of the
niques which use iron ore or steel scrap, respectively, investigated steel components at end of products
as a ferrous resource. Steel primary production life. Experimental procedure included production
requires high process energy and large amounts of of blades from the steel scrap by applying different
coal, resulting in high CO2 emissions (steel produc- thermo–mechanical treatment. End–of–life prod-
tion is the major source of carbon dioxide emis- ucts marked with SS1 and SS4 were mechanically
sions). Secondary production technique has a lower treated by cutting, grinding, and polishing in order
energy requirement (about one–third of the energy to obtain the desired shape of the blades. The steel
for primary production) and CO2 emissions (less scrap marked as SS2 was heated in a forge fire at
than one–quarter of the emissions during the pri- temperature 800 – 850 °C for scrap straightening
mary production) (Oda et al., 2013; Morfeldt et al., and reshaping it to the straight product. Further
2015). Recycling and reuse of steel component shaping to the final blade was done in the same
influence to the decrease in CO2 emissions, decrease route as in samples SS1 and SS4. The steel scrap
in use of iron ore as ferrous resource, reduction of sample marked as SS3 was heated to 400 °C and
waste and used energy. Steel recycling includes melt- further mechanically treated in the same way as
ing of steel components, their recasting and reshap- samples SS1 and SS4. After processing and obtain-
ing into new products. Recycling is always more ing the desired blade shapes, the blades made from
acceptable option wherever the primary produc- SS2 and SS3 were further annealed in a forge fire to
tion can be avoided. Steel reuse is a nondestructive red–heat and quenched in oil. Figure 2 shows the
method of reshaping steel components at the end obtained knives as the final products made from the
of product life without melting. It can be very effec- initial steel scrap defined by Table 1.
tive due to the avoiding of the high costs of energy The samples of the initial steel scrap, obtained
required for recycling and conserving the micro- blades and blades made of SS2 and SS3 after oil
structure and properties of the initial components quenching were subjected to hardness measurement
(Cooper and Allwood, 2012). using the WPM Leipzig Rockwell C hardness tester.
During the exploitation and maintenance of agri-
cultural and industrial machineries, certain amount
of steel scrap is being produced. The maintenance Table 1.  Labels and pre–given purpose of the investigated
of these machineries, among other things, includes steel scrap
consumable machinery components replacement at
Label Pre–given purpose of steel scrap
the end of their useful life. Therefore, agricultural
and industrial steel scrap is of a great environmental SS1 Hacksaw
and economic potential (Pacelli et al., 2015). Reuse SS2 Steam turbine moving blade
of steel components at the end of product life offer SS3 Sword of a chainsaw
even greater advantages for the environment than SS4 Rototiller hoe
recycling. Because of that, this article studies the

Revista de Metalurgia 53(1), January–March 2017, e086. ISSN-L: 0034-8570 doi: http://dx.doi.org/10.3989/revmetalm.086
 The possibilities for reuse of steel scrap in order to obtain blades for knives • 3

Figure 1.  Macrophotographs of the investigated steel scrap.

(a)

(b)

(c)

(d)

Figure 2.  Knives as the final products made from different steel scrap: (a) SS1 – hacksaw; (b) SS2 – steam turbine moving blade;
(c) SS3 – sword of a chainsaw; and (d) SS4 – rototiller hoe.

The hardness of the blades was measured at five etched using a solution prepared by mixing 15 ml
points, depending on the distance from the cutting HCl, 5 ml HNO3, and 80 ml H2O. Microstructure
edge. The average value was taken for further analy- was analyzed using Carl Zeiss Jena Epityp 2 optical
sis. The microstructure of the initial steel scrap was microscope (OM) and Tescan Vega 3LMU scanning
analyzed after standard procedure for microstruc- electron microscope (SEM). Oxford Instruments
tural preparation (grinding, polishing and etching X – Act energy–dispersive spectrometer (EDS) was
with 2% solution of nital). Only the sample SS2 was used to determine the chemical composition of the

Revista de Metalurgia 53(1), January–March 2017, e086. ISSN-L: 0034-8570 doi: http://dx.doi.org/10.3989/revmetalm.086
4 • Nada Štrbac et al.

initial steel scrap samples and the element distribu- Figure 4 shows the results of SEM – EDS analy-
tion maps of the sample SS4. sis for the steel scrap SS2. Chemical analysis of the
area in Fig. 4a is given by EDS spectrum in Fig. 4b.
3. RESULTS AND DISCUSSION It shows that the investigated material is a chrome–
alloyed steel with medium carbon content with
In Fig. 3, the results of SEM – EDS analysis for grade X20Cr13, according to EN 10250 standard
the steel scrap SS1 are given. Chemical analysis of (EN 10250–2, 2000). This was expected, because the
the area in the Fig. 3a was given by EDS spectrum steel scrap SS2 was the end–of–life steam turbine
in Fig. 3b. It can be observed that the investigated moving blade. Due to its high chrome content, this
material is a tool steel with tungsten, molybdenum, steel has got good corrosion resistance, plasticity
chromium and vanadium, corresponding to the and high shock resistance (Xi et al., 2008).
high speed tool steel with grade HS 6–5–2 according SEM microstructure of the steel scrap SS3 is
to EN ISO 4957 (1999). The numerical designation shown in Fig. 5a. Fig. 5b shows the EDS spectrum
in the steel grade refers to the content of W, Mo and of the area in the microphotograph in Fig. 5a. The
V in wt.%, respectively. This steel has got improved EDS analysis shows that the investigated end–of–
cutting performance due to a high content of tung- life product SS3 is a spring steel of grade 38Si7,
sten, and it is often used in the manufacturing of according to EN 10089 standard (EN 10089, 2002).
a numerous cutting tools (Da Silva Rocha et al., Its chemical composition contains 0.4 – 0.45 wt.%
1999), hacksaws among others. Results of EDS C, 1.8 – 1.9 wt.% Si, 0.8 – 1 wt.% Mn.
analysis of white phase (carbides) at points 1, 2 and Figure 6a represents the SEM microstructure of
3 in Fig. 3c were given in Fig. 3d. It is shown that the steel scrap SS4. In Fig. 6b, the EDS spectrum of
this phase was the complex carbide phase with W, the area in the microphotograph in Fig. 6a is shown.
Mo, Fe, V and Cr. Having into account the chemical composition,

(a) (b)

14000 Spectrum 1
12000 Fe

10000

8000

6000 Fe
4000 Mn
Cr
2000 V W Mo Cr Fe
V Mn W W
C W W
0
0 2 4 6 8 10 12 14 16 18
Full Scale 14430 cts Cursor: 19.794 (3 cts) keV

(c)
(d)

Point Elements’ content, at . %

C Ti V Cr Fe Mo W

1 34.27 12.10 6.40 15.67 19.76 11.81

2 26.93 9.86 4.81 30.00 16.86 11.54

3 42.77 1.53 16.31 3.00 28.72 4.29 3.38

Figure 3.  SEM – EDS results of the steel scrap SS1: (a) SEM microphotograph; (b) EDS spectrum of the area in the
microphotograph in Fig. 3a; (c) SEM microphotograph with higher concentration of the white phase; and (d) Results of EDS
analysis of white phase (carbides) at points 1, 2 and 3 in Fig. 3c.

Revista de Metalurgia 53(1), January–March 2017, e086. ISSN-L: 0034-8570 doi: http://dx.doi.org/10.3989/revmetalm.086
 The possibilities for reuse of steel scrap in order to obtain blades for knives • 5

(a) (b)

15000 Spectrum 1
Fe
Mn

10000

5000 Fe
Mn Cr
Cr Cr Fe
C Si Mn
0
0 2 4 6 8 10 12 14 16 18 20
Full Scale 15362 cts Cursor: 20.248 (4 cts) keV

Figure 4.  SEM – EDS results of the steel scrap SS2: (a) SEM microphotograph; and (b) EDS spectrum of the area in the
microphotograph in Fig. 4a.

(a) (b)

35000 Spectrum 1
Fe
30000
25000

20000
15000 Fe
10000 Mn

5000 Fe
C Si Mn
0
0 2 4 6 8 10 12 14 16 18 20
Full Scale 35944 cts Cursor: 20.118 (7 cts) keV

Figure 5.  SEM – EDS results of the steel scrap SS3: (a) SEM microphotograph; and (b) EDS spectrum of the area in the
microphotograph in Fig. 5a.

it is concluded that the material used in the produc- of production and thermo–mechanical treatment
tion of this component is a low–alloy steel of grade in order to product a hacksaw. A 2% nital solution
59Si7 according to ISO 683 – 14 standard (ISO 683– was used for etching steel scrap SS1 because it is the
14, 2004). Its chemical composition contains 0.58 – most commonly used etchant for tool steels. It is a
0.61 wt.% C, 1.8 – 2 wt.% Si, 0.8 – 0.9 wt.% Mn, 0.2 suitable etchant for showing structure of carbides
– 0.37 wt.% Cr. The distribution maps of elements (Small et al., 2008). The microstructure is consisted
Fe, Cr, Mn, Si and C in the scanning region in Fig. of tempered martensitic structure and un–dissolved
6a are shown in Fig. 7. From the distribution maps, eutectic carbide particles (Leskovsek and Ule,
the even distribution of all elements on the investi- 1998). In this kind of steel, directed carbide par-
gated region can be observed. ticles of the following types can occur: M6C, MC,
The optical microphotographs of the initial steel M2C and M7C3, indicating previous deformation
scrap are given in Fig. 8. SEM and optical micro- (Dziedzic, 2007). The chemical composition of the
photographs of the steel scrap SS1, given in Figs. 3a carbides done by EDS (Figs. 3c and 3d) shows that
and  8a, respectively, show a fine–grained structure the carbides are mainly of the type M2C or M7C3.
with directed distribution of complex carbides, Additionally, some primary carbides of the type
which has been achieved by the specific methods MC are visible.

Revista de Metalurgia 53(1), January–March 2017, e086. ISSN-L: 0034-8570 doi: http://dx.doi.org/10.3989/revmetalm.086
6 • Nada Štrbac et al.

(a) (b)

30000 Spectrum 1

Fe
25000

20000

15000

10000

Fe
5000 Fe
Cr
C Si Mn
0
2 4 6 8 10 12 14 16 18 20
Full Scale 30810 cts Cursor: 20.474 (0 cts) keV

Figure 6.  SEM – EDS results of the steel scrap SS4: (a) SEM microphotograph; and (b) EDS spectrum of the area in the
microphotograph in Fig. 6a.

(a) (b) (c)

60 µm 60 µm 60 µm
(d) (e)

60 µm 60 µm

Figure 7.  Distribution map of elements in the scanning region in Fig. 6a: (a) Fe; (b) Cr; (c) Mn; (d) Si; and (e) C.

Revista de Metalurgia 53(1), January–March 2017, e086. ISSN-L: 0034-8570 doi: http://dx.doi.org/10.3989/revmetalm.086
 The possibilities for reuse of steel scrap in order to obtain blades for knives • 7

(a) (b)

(c) (d)

Figure 8.  Optical microphotographs of the starting steel scrap: (a) SS1; (b) SS2; (c) SS3; and (d) SS4.

The microstructure of the steel scrap SS2 is It is known that in the steel which contains 2% sili-
shown in Figs. 4a and 8b. For steel of this composi- con, a large amount of austenite is retained during
tion, homogene martensitic structure is expected to cooling to room temperature. With increasing the
be formed after air cooling from austenitiziting tem- amount of retained austenite, both ductility and
perature (Mann, 2013; Gupta, 2015). Depending strength increase. Silicon is an inhibitor of carbide
on a heat treatment conditions, various phases can precipitation and ferrite stabilizer (Matsumura
occur in the microstructure. The most appropriate et al., 1987; Chen et al., 1989). The microstructure
procedure for heat treatment of this steel involves of steel with silicon may contain retained austenite,
quenching from the temperature of about 1000 °C ferrite and martensite or bainite, depending on heat
in oil or in the air, following tempering at 700 °C. treatment (Chen et al., 1989). Microstructural con-
The resulting microstructure which consists of uni- stituents vary with annealing temperature and time.
formly distributed globular carbides in the ferrite For a shorter annealing time during tempering, a
matrix can be expected in the structure (Masters, martensite–ferrite structure is a predominant, with
1989), which corresponds to the microstructures a small fraction of bainite and retained austenite,
shown in Figs. 4a and 8b. Gooch (Gooch, 1982) similar to the microstructures shown in the Figs. 6a
identified these precipitates as M23C6 carbides. and 8d. Longer holding time at annealing tempera-
SEM and optical microphotographs of the steel ture results in removal of retained austenite and
scrap SS3 are shown in Figs. 5a and 8c. The micro- formation of ferrite–bainite structure (Matsumura
structure of the steel scrap SS4 is shown in Figs. et al., 1987).
6a and 8d. According to their composition, both Figure 9 shows the hardness values of the initial
steel scrap, SS3 and SS4, belong to spring steel scrap (first column), obtained blades (second col-
of type Si2Mn, which have a good combination umn) and hardness values of the blades made of
of high strength, good ductility and high shock–­ end–of–life products SS2 and SS3 after oil quench-
resistance in the quenched condition as well as in ing (third column).
the tempered condition. These types of steel belong The hardness value of the scrap SS1 is 63 HRC,
to the hypo–eutectoid class (Qinghua et al., 2003). while the blade made of this steel scrap only by

Revista de Metalurgia 53(1), January–March 2017, e086. ISSN-L: 0034-8570 doi: http://dx.doi.org/10.3989/revmetalm.086
8 • Nada Štrbac et al.

70 Steel scrap the starting steel scrap. The same hardness value
Blades was obtained on the blade made of steel scrap SS3
60 Blades after oil quenching after thermo–mechanical treatment followed by
quenching. The hardness values of blades made of
50
steel scrap SS2 and SS4 were lower, 34 HRC and
43 HRC, respectively. By reusing steel scrap for dif-
Hardness, HRC

40
ferent purposes various benefits can be achieved
30
(reduction costs, saving energy, less raw material
usage and  decrease in waste disposal costs), which
20 is in accordance to the basic requirements of the
European Union waste management strategy
10 (Vehlow et al., 2007).
0 ACKNOWLEDGMENT
SS1 SS2 SS3 SS4
Samples
The research results were developed under the
Figure 9.  Hardness values (HRC) of steel scrap SS1, SS2, projects TR34023, TR34003 and OI172037 for
SS3, and SS4; blades made of SS1, SS2, SS3, and SS4; and
blades made of SS3 and SS4 after oil quenching. which the funds were provided by the Ministry of
Education, Science and Technological Development
of the Republic of Serbia. The authors would like
using mechanical treatment (cutting, grinding and to thank Prof. Dr. Svetlana Nestorović (deceased in
polishing) shows the same hardness value. 2015) and Igor Kalinović for their help.
The steel scrap SS2 has a significantly lower
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Revista de Metalurgia 53(1), January–March 2017, e086. ISSN-L: 0034-8570 doi: http://dx.doi.org/10.3989/revmetalm.086