Effect of V-Mn-Cr inoculant on microstructure and mechanical properties of grey cast iron

Abstract

In this study, the effects of different composition V-Mn-Cr inoculants on the microstructure and mechanical properties of GCI were investigated through Optical microscope (OM), Scanning electron microscope (SEM), Energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), etc. The results showed that the optimum quantity of inoculant was 7% V, 1% Mn and 6% Cr, and compared with the commercial inoculant samples, the tensile strength, Brinell hardness, and elastic modulus of the V-Mn-Cr inoculant samples increased by 16.7%, 14.2%, and 12.8%, respectively. V-Mn-Cr inoculants were found to refine austenite, graphite, pearlite and eutectic cells size, reduce pearlite lamellar spacing, and increase pearlite and eutectic cells number, thus improving mechanical properties. In addition, graphite nucleation substance may consist of oxides (SiO₂, FeO, Cr₂O₃), carbides (SiC, TiC), sulfides (MnS, FeS), and XO·SiO₂ silicates (X: Mn, Fe, Ca).

Introduction

As the most widely used cast iron material, grey cast iron (GCI) is broadly used in shipbuilding, automobile, machine tools, and other manufacturing industries due to its good casting performance, vibration resistance, wear resistance and cutting performance [1–3]. It is very important to improve the performance of GCI with the increasingly high requirements [4,5]. Among the variables that influence the mechanical properties of GCI are reasonable chemical composition, heat treatment, inoculation treatment, and more [6–10]. Inoculation treatment is a common method to obtain high-performance GCI, which is favourable for the nucleation of graphite and promotes the formation of lamellar pearlite [11].

Many investigators have researched the inoculation performance of inoculants, such as Fe-Si inoculants, rare-earth (RE) inoculants, Sr-Si inoculants, Ba-Si inoculants and so on [12–15]. For example, Riposan et al. [12] declared that Al-Zr-Fe-Si inoculant decreased the eutectic undercooling and recalescence, improved graphite characteristics, and avoided carbides, thus increasing the tensile properties of GCI. Li et al. [13] indicated that RE-containing inoculants could enhance the quality of castings, which was attributed to RE elements eliminating the hazards of trace elements, improving the morphology of graphite, and increasing the number of eutectic cells. He et al. [14,15] demonstrated that Sr-Si inoculants and Ba-Si inoculants could improve the morphology of graphite and increase the number of eutectic cells, resulting in an increase in the tensile strength and hardness of GCI.

Alloying elements usually need to be added to the inoculant to obtain excellent castings, such as carbide-forming elements V, Mn, and Cr that promote pearlite formation and refine pearlite, thus they have been investigated in GCI [16–18]. For instance, Wang et al. [16] revealed that the carbides generated by V could play a role in refining the grain and strengthening the matrix microstructure, significantly enhancing the tensile strength and wear resistance of GCI. Fu et al. [17] signified that the addition of Cr, Ba-Si, and Fe-Si composite inoculants improved microstructure uniformity and increased the tensile strength and hardness of GCI. Wang et al. [18] pointed out that adding a certain amount of Mn and CaSi inoculants could obviously increase the inoculation effect, refine pearlite, and improve the morphology of graphite, thereby enhancing the mechanical properties.

At present, the technology level of GCI has improved greatly with decades of development, but less research has been done on the effects of V, Mn, and Cr in the inoculants on the performance of GCI. Therefore, the purpose of this work was to investigate the influence of different compositions V-Mn-Cr inoculants on the microstructure and mechanical properties of GCI by orthogonal experiment. The corresponding mechanism for the improvement of the performances of GCI was also discussed, providing the theoretical basis for the development of GCI application.

Experimental procedure

Experimental details

The raw materials composition of GCI is shown in Table 1. These raw materials were melted in a 100 Kw medium frequency induction furnace at 1480–1500°C. Subsequently, the melt was inoculated to adopt the method of in-ladle inoculation. The added amount of inoculant (particle size of 0.5∼1.0 mm) was 0.4% of melt mass. The melt was poured into the resin sand molds with the geometry shown in Figure 1. The pouring temperature is 1360∼1370°C. Before pouring, a small amount of melt was poured into a metal mold to produce white cast iron specimens, which were used for chemical composition verification. The results of chemical analyses are shown in Table 2.

Figure 1.

Geometry of standard sand mold single cast test bar (mm).

Table 1.

Chemical composition of raw materials (wt-%).

Materials	C	Si	Mn	S	P	Cr	Al	Fe
Scrap steel	0.184	0.169	0.334	≤0.05	≤0.05	0.038		Bal.
Pig iron	4.43	0.69	0.231	0.024	0.059			Bal.
Ferromanganese	6.51	1.36	65.38	0.012	0.135			Bal.
Ferrosilicon	0.092	72		0.004	0.0036		1.75	Bal.
Ferrochromium	7.62	2.2		0.016	0.02	54.500		Bal.

Table 2.

Chemical composition of GCI samples (wt-%).

Elements	C	Si	Mn	P	S	Cr	V	Ti
Content	3.065	1.701	0.845	0.022	0.084	0.053	0.023	0.015

To determine the composition of inoculants corresponding to the best mechanical properties of GCI, the orthogonal experiment of three factors and three levels was designed, and the composition of commercial inoculant was also displayed, as shown in Table 3. The addition of V (Factor A) was 13%, 10% and 7% (wt-% of inoculant). The addition of Mn (Factor B) was 1%, 3% and 5% (wt-% of inoculant). The addition of Cr (Factor C) was 2%, 4% and 6% (wt-% of inoculant). According to Table 3, nine groups of inoculation treatment were carried out based on inoculants consisting of different components.

Table 3.

Orthogonal experimental design of inoculant composition (wt-%).

Experiment No.	Si	Ti	V	Mn	Cr	N	Fe
Commercial inoculant	35	1.8	13	–	–	2	Bal
1	34–36	1.7–1.9	13	1	2	2	Bal
2	34–36	1.7–1.9	13	3	4	2	Bal
3	34–36	1.7–1.9	13	5	6	2	Bal
4	34–36	1.7–1.9	10	1	4	2	Bal
5	34–36	1.7–1.9	10	3	6	2	Bal
6	34–36	1.7–1.9	10	5	2	2	Bal
7	34–36	1.7–1.9	7	1	6	2	Bal
8	34–36	1.7–1.9	7	3	2	2	Bal
9	34–36	1.7–1.9	7	5	4	2	Bal

Microstructure analysis

Metallographic samples (Φ20 mm × 10 mm) were obtained from the castings. Before testing, the specimens were polished with coarse-to-fine grit emery papers, washed with distilled water, and dried in air. After polished, the graphite microstructure was directly observed by an Optical microscope (OM), then the specimens were etched with 4% nitric acid alcohol solutions, and the matrix microstructure was observed under OM. Subsequently, after being re-polished, the specimens were etched with 4 g copper sulfate, 20 ml concentrated hydrochloric acid, and 20 ml distilled water, and the eutectic cell microstructure was also observed through OM. Finally, the sample was placed in a barrel resistance furnace, heated to 860 °C at a heating rate of 1000 °C/5 h, kept for 35 min, and then cooled to 600 °C with the furnace, and then the sample was taken out and cooled to room temperature. After the heat treatment, metallographic specimens were prepared, a 4% nitric acid alcohol solution was used for external corrosion, and the austenite dendrites morphology was observed by OM.

The morphology of matrix, graphite, and fracture was also characterised by a Scanning electron microscope (SEM), equipped with the Energy-dispersive spectroscopy (EDS) system for elemental analysis and quantitative mapping.

The phases of the microstructures in GCI were determined by X-ray diffraction (XRD). The specimens were placed in a continuous scanning X-ray diffractometer using a Cu target with a tube voltage of 40 kV and a tube current of 20 mA, the scanning speed was 4°/min, and the diffraction angle was 20° to 90°.

Performance testing

The tensile standard specimen of GCI is shown in Figure 2, which were got from the castings. Three tensile tests were performed for each group, and the average was valued as the final result. Furthermore, the elastic modulus of the samples was calculated according to the following formula:

$${\rm E}={\rm }\displaystyle{{{\rm \Delta F}} \over {{\rm S0}}}{\rm /}\displaystyle{{{\rm \Delta L}} \over {{\rm \; L0}}} = \displaystyle{{{\rm \Delta FL0}} \over {{\rm \; S0}\triangle {\rm L}}}$$

E = \frac{Δ F}{S 0} / \frac{Δ L}{L 0} = \frac{Δ FL 0}{S 0 △ L}

(1)

In the formula,

${\rm \Delta L}$

Δ L

is the displacement at two adjacent points,

${\rm \Delta F}$

Δ F

is the force increment at two adjacent points,

${\rm L0}$

L 0

is the electronic extender distance, and

${\rm S0}$

S 0

is the original cross-sectional area, respectively.

Figure 2.

Specimen of the tensile test (mm).

The hardness specimens (Φ20 mm × 20 mm) were obtained from the castings, and the specimens were measured by the 320HBS-3000 type digital display Brinell hardness tester. Using a hardened steel ball indenter (diameter of 10 mm), the loading time and dwell time were 10 and 12 s under constant force (3000 kg), respectively. Five points were tested randomly for each group of the sample, and the average value was calculated as the final result.

Results

Orthogonal experiment results

Tables 4 and 5 show the orthogonal experiment results and optimisation results, respectively. As shown in Table 5, the V (Factor A) was the most dominant parameter for tensile strength, Mn (Factor B) was the medium parameter for Brinell hardness and elastic modulus, and Cr (Factor C) was the most dominant parameter for Brinell hardness and elastic modulus. According to the results of Tables 4 and 5, the performance of the specimens for the optimised schemes is shown in Table 6. The results show that the A₃B₁C₃ scheme provided the best comprehensive performance of GCI. Compared with commercial inoculant, the samples inoculated with V 7%, Mn 1% and Cr 6% had increased tensile strength, Brinell hardness, and elastic modulus by 16.7%, 14.2%, and 12.8%.

Table 4.

Results of orthogonal experiment.

Experiment No.	Tensile strength (MPa)	Brinell hardness (HB)	Elastic modulus (GPa)
Commercial inoculant	305	204	132
1	316	216	138
2	331	224	136
3	335	225	152
4	330	224	140
5	337	219	149
6	332	213	139
7	356	233	149
8	350	216	135
9	335	217	138

Table 5.

Optimisation of orthogonal experiment results.

Properties	No.	Factor A (V)	Factor B (Mn)	Factor C (Cr)
Tensile strength	range	19.7	5.3	10.7
	sequence	A > C > B
	optimisation	A₃	B₂	C₃
Brinell hardness	range	3.3	6.0	10.7
	sequence	C > B > A
	optimisation	A₃	B₁	C₃
Elastic modulus	range	2	3	12.7
	sequence	C > B > A
	optimisation	A₂	B₃	C₃

Table 6.

Mechanical properties of optimal schemes.

Scheme	Tensile strength (MPa)	Brinell hardness (HB)	Elastic modulus (GPa)
A₃B₁C₃	356	233	149
A₃B₂C₃	300	208	147
A₂B₃C₃	320	207	158

Microstructure

The graphite (not etched) microstructure of GCI samples inoculated with different inoculants is shown in Figure 3. It is evident the 7%V-1%Mn-6%Cr inoculant has a positive effect on the bending and refinement of graphite. According to GB/T 7216-2009 [19], the graphite shape and length are evaluated mainly by graphite morphology and size, respectively. As shown in Figure 3(a), the graphite shape is A type and few of D type (about 10%), and the graphite length is 3∼4 level (12∼50 mm). As shown in Figure 3(b), the graphite shape is A type, and the graphite length is 4 level (12∼25 mm).

Figure 3.

Graphite morphology of the different inoculant GCI samples. (a) Commercial inoculant, (b) 7%V-1%Mn-6%Cr inoculant.

To study the composition of graphite, EDS point analysis was performed on the specimens inoculated with 7%V-1%Mn-6%Cr, and the results are presented in Figure 4. As shown in Figure 4(b), the elements in point A are C, Si, S, Ti, V, Cr, Mn, and Fe. As shown in Figure 4(d), the elements in point B are C, N, O, Si, Mn, and Fe. EDS analysis indicates that the graphite may be made up of MnS, FeS, TiC, SiC, Cr₂O₃, FeO, etc. Meanwhile, SiO₂ and XO·SiO₂ silicates (X: Mn, Fe, Ca) may exist.

Figure 4.

SEM morphology and EDS spectra of graphite in the 7%V-1%Mn-6%Cr inoculant samples. (a) The morphology, (b) The EDS analysis of point A. (c) The morphology, (d) The EDS analysis of point B.

Figure 5 shows the matrix (etched) microstructure of GCI samples inoculated with different inoculants. The microstructures both consist mainly of flake graphite, ferrite, and pearlite. The white area is the ferrite microstructure, and the grey area is the pearlite microstructure. It can be seen that the quantity of ferrite decreases slightly, and pearlite increases slightly in the 7%V-1%Mn-6%Cr inoculant samples, compared with the commercial inoculant samples.

Figure 5.

Matrix morphology of the different inoculant GCI samples. Commercial inoculant, (b) 7%V-1%Mn-6%Cr inoculant.

To observe the lamellar spacing of pearlite, SEM analysis (1000×) was performed on samples, and the results are presented in Figure 6. It is obvious that graphite end passivation, the lamellar spacing of pearlite decreases, and the density increases in the 7%V-1%Mn-6%Cr samples. The pearlite lamellar spacing is 0.45-0.6 µm in Figure 6(a) and 0.35-0.5 µm in Figure 6(b).

Figure 6.

SEM morphology of the different inoculant GCI samples. (a) Commercial inoculant, (b) 7%V-1%Mn-6%Cr inoculant.

To determine the phase components of the GCI sample, XRD analyses was conducted on the samples inoculated with 7%V-1%Mn-6%Cr, and the result is displayed in Figure 7. The microstructure may contain mainly α-Fe, TiC, SiC, VC, FeS, MnS, Fe₃O₄, Cr₂O₃, FeSiO₃, and MnSiO₃ phases.

Figure 7.

X-ray diffraction pattern of the 7%V-1%Mn-6%Cr inoculant specimen.

Figure 8 shows the primary austenite dendrites morphology of GCI samples inoculated with different inoculants. It can be seen that the amount of primary austenite dendrites is lower, and dendrites arm spacing is larger in the commercial inoculant samples, as shown in Figure 8(a). However, primary austenite dendrites amount increases significantly, dendrites arm spacing decreases significantly, and form a complex space structure in the 7%V-1%Mn-6%Cr inoculant samples, as shown in Figure 8(b).

Figure 8.

Primary austenite dendrites morphology of the different inoculant GCI samples. (a) Commercial inoculant, (b) 7%V-1%Mn-6%Cr inoculant.

The eutectic cells microstructure of GCI samples inoculated with different inoculants is shown in Figure 9. It is obvious that in the 7%V-1%Mn-6%Cr inoculant samples, the eutectic cells number increases and the size reduces. The average size of eutectic cells is 470 µm in Figure 9(a) and 370 µm in Figure 9(b).

Figure 9.

Eutectic cell morphology of the different inoculant GCI samples. (a) Commercial inoculant, (b) 7%V-1%Mn-6%Cr inoculant.

Discussions

Formation mechanism of graphite

Studies have shown that the formation of graphite crystals is mainly by heterogeneous nucleation [20–22]. According to heterogeneous nucleation theory [23], heterogeneous nucleation of graphite mainly includes carbides, sulfides, oxides, nitrides, silicates, and unmelted graphite. Thermodynamic calculations were performed to predict the primary reaction occurring after the inoculant was added. According to thermodynamic theory [24], the following reactions might take place.

$${\rm Si}+{\rm O2}={\rm SiO2\comma \; \;\Delta H}={\rm }-{\rm 904760\;\lpar J/mol\rpar \comma \; \;\Delta S}={\rm }- 173{\rm .38\;\lpar J/mol\rpar \comma \; \; T}\in {\rm \;\lpar 298\sim 1685K\rpar }$$

Si + O 2 = SiO 2, Δ H = - 904760 (J / mol), Δ S = - 173 .38 (J / mol), T \in (298 \sim 1685 K)

(2)

$${\rm Si}+{\rm C}={\rm SiC\comma \; \;\Delta H}={\rm }-{\rm 73050\;\lpar J/mol\rpar \comma \; \;\Delta S}={\rm }- 7{\rm .66\;\lpar J/mol\rpar \comma \; \; T}\in {\rm \;\lpar 298\sim 1685K\rpar }$$

Si + C = SiC, Δ H = - 73050 (J / mol), Δ S = - 7 .66 (J / mol), T \in (298 \sim 1685 K)

(3)

$${\rm Fe}+{\rm 1/2O2}={\rm FeO\comma \; \;\Delta H}={\rm }-{\rm 264000\;\lpar J/mol\rpar \comma \; \;\Delta S}={\rm }- 64{\rm .59\;\lpar J/mol\rpar \comma \; \; T}\in {\rm \;\lpar 298\sim 1650K\rpar }$$

Fe + 1 / 2 O 2 = FeO, Δ H = - 264000 (J / mol), Δ S = - 64 .59 (J / mol), T \in (298 \sim 1650 K)

(4)

$${\rm Fe}+{\rm 1/2S2}={\rm FeS\comma \; \;\Delta H}={\rm }-{\rm 164000\;\lpar J/mol\rpar \comma \; \;\Delta S}={\rm }- 61{\rm .09\;\lpar J/mol\rpar \comma \; \; T}\in {\rm \;\lpar 1261\sim 1468K\rpar }$$

Fe + 1 / 2 S 2 = FeS, Δ H = - 164000 (J / mol), Δ S = - 61 .09 (J / mol), T \in (1261 \sim 1468 K)

(5)

$${\rm Mn}+{\rm 1/2S}={\rm MnS\comma \; \;\Delta H}={\rm }-{\rm 296500\;\lpar J/mol\rpar \comma \; \;\Delta S}={\rm }- 76{\rm .74\;\lpar J/mol\rpar \comma \; \; T}\in {\rm \;\lpar 973\sim 1473K\rpar }$$

Mn + 1 / 2 S = MnS, Δ H = - 296500 (J / mol), Δ S = - 76 .74 (J / mol), T \in (973 \sim 1473 K)

(6)

$${\rm Ti}+{\rm C}={\rm TiC\comma \; \;\Delta H}={\rm }-{\rm 184800\;\lpar J/mol\rpar \comma \; \;\Delta S}={\rm }- 12{\rm .55\;\lpar J/mol\rpar \comma \; \; T}\in {\rm \;\lpar 298\sim 1943K\rpar }$$

Ti + C = TiC, Δ H = - 184800 (J / mol), Δ S = - 12 .55 (J / mol), T \in (298 \sim 1943 K)

(7)

$${\rm 2Cr}+{\rm 3/2O2}={\rm Cr2O3\comma \; \;\Delta H}={\rm }-{\rm 1110140\;\lpar J/mol\rpar \comma \; \;\Delta S}={\rm }- 247{\rm .32\;\lpar J/mol\rpar \comma \; \; T}\in {\rm \;\lpar 1173\sim 1923K\rpar }$$

2 Cr + 3 / 2 O 2 = Cr 2 O 3, Δ H = - 1110140 (J / mol), Δ S = - 247 .32 (J / mol), T \in (1173 \sim 1923 K)

(8)

The Gibbs free energy at constant temperature and constant pressure can be expressed:

$${\rm \Delta G}={\rm \Delta H}-{\rm T\Delta S\lpar J/mol\rpar \; }$$

Δ G = Δ H - T Δ S (J / mol)

(9)

where

${\rm \Delta H}$

Δ H

and

${\rm \Delta S}$

Δ S

are the enthalpy and entropy changes within the use temperature range, respectively. According to Eqs. (2–9), the Gibbs free energy of the above reactions can be calculated by thermodynamic parameters at the inoculation temperature of 1360 °C (1633 K). The results of Gibbs free energy (

${\rm \Delta G}$

Δ G

) and the mismatch (δ) between compounds and graphite are shown in Table 7.

According to the thermodynamic calculation results, SiO₂, SiC, FeO, FeS, MnS, TiC, Cr₂O₃ and XO·SiO₂ silicates (X: Mn, Fe, Ca) can be used as the substance of graphite nucleation (Figures 4 and 7), and the results have been verified in some studies [25–27].

Table 7.

Gibbs free energy (

${\rm \Delta G}$

Δ G

) and the mismatch (δ) between compounds and graphite [10].

Compounds	${\rm \Delta G}$ $Δ G$ ( ${\rm J/mol}$ $J / mol$ )	δ (%)
SiO₂	$-$ $-$ 621630.46	15.41
SiC	$-$ $-$ 60541.22	0.5
FeO	$-$ $-$ 158524.53	9.22
FeS	$-$ $-$ 74319.88	7.73
MnS	$-$ $-$ 183461.98	5.63
TiC	$-$ $-$ 164305.85	8.33
Cr₂O₃	$-$ $-$ 706266.44	4.54

According to heterogeneous nucleation theory, schematic representation of heterogeneous nucleation is shown in Figure 10, and the calculation of the work of heterogeneous nucleation (

$\Delta {\rm G}_{{\rm het}}^{\rm \ast }$

Δ G_{het}^{*}

) and wetting angle (θ) can be done through the formula below:

$$\Delta {\rm G}_{{\rm het}}^{\rm \ast } = \displaystyle{{{\rm \lpar 2}+{\rm cos\theta \rpar \lpar 1}\hbox{-}{\rm cos\theta }\rpar ^ 2} \over 4}\Delta {\rm G}_{{\rm hom}}^{\rm \ast } $$

Δ G_{het}^{*} = \frac{(2 + \cos θ) (1 - \cos θ)^{2}}{4} Δ G_{hom}^{*}

(10)

$${\rm cos\theta}={\rm }\displaystyle{{{\rm \sigma }_{{\rm LW}}-{\rm \sigma }_{{\rm \alpha W}}} \over {{\rm \sigma }_{{\rm \alpha L}}}}$$

\cos θ = \frac{σ_{LW} - σ_{α W}}{σ_{α L}}

(11)

In which

$\Delta {\rm G}_{{\rm hom}}^{\rm \ast }$

Δ G_{hom}^{*}

is the work of homogeneous nucleation,

$\Delta {\rm G}_{{\rm het}}^{\rm \ast }$

Δ G_{het}^{*}

is the work of heterogeneous nucleation, θ is the wetting angle,

${\rm \sigma }_{{\rm LW}}$

σ_{LW}

${\rm \sigma }_{{\rm \alpha W}}$

σ_{α W}

, and

${\rm \sigma }_{{\rm \alpha L}}$

σ_{α L}

are the interfacial tension of L-W, α-W, and α-L, respectively.

Figure 10.

Schematic diagram of heterogeneous nucleation [23].

It is easy to know the work of heterogeneous nucleation (

$\Delta {\rm G}_{{\rm het}}^{\rm \ast }$

Δ G_{het}^{*}

) is always less than the work of homogeneous nucleation (

$\Delta {\rm G}_{{\rm hom}}^{\rm \ast }$

Δ G_{hom}^{*}

) (

${\rm 0\;\lt \;\theta \;\lt \; 180^\circ }$

0 < θ < 180^{\circ}

). Generally, the substance can nucleate when the mismatch (δ) with graphite is less than 12%. Nevertheless, it was found that SiO₂ can be combined with SiC, Al₂O₃ and AlN to form the graphite nucleation substance [10].

According to the results of Table 7, SiO₂, SiC, FeO, FeS, MnS, TiC, Cr₂O₃ and XO·SiO₂ silicates (δ

${\rm \lt }$

<

8%, X: Mn, Fe, Ca) have a smaller δ compared with graphite; in other words, the interfacial tension (

${\rm \sigma }_{{\rm \alpha W}}$

σ_{α W}

) is lower, and the

$\Delta {\rm G}_{{\rm het}}^{\rm \ast }$

Δ G_{het}^{*}

is smaller. Consequently, these compounds can become the substance of graphite nucleation, such as SiO₂, SiC, FeO, FeS, MnS, TiC, Cr₂O₃ and XO·SiO₂ silicates (X: Mn, Fe, Ca).

Effect of V-Mn-Cr inoculant on microstructure and performances

The addition of V-Mn-Cr inoculant increases the carbon activity and provides the substances of graphite nucleation, which increase the graphite nucleation rate, thus improving the graphite microstructure (Figure 3). During austenite transformation, the carbide-forming elements V, Mn, and Cr in the inoculant can promote the nucleation of cementite, leading to an increase in the amount of pearlite (Figure 5). In addition, Mn can increase the eutectoid undercooling which accelerates the eutectoid reaction process, thus enhancing the tendency of austenite to pearlite transformation that reducing the lamellar spacing of pearlite (Figure 6), and Cr elements further improve the complexity of dendrites (Figure 8). Consequently, the eutectic graphite count raises with the addition of V-Mn-Cr inoculant, which increases eutectic cells number (Figure 9), resulting in an improvement of the mechanical properties of GCI.

Conclusions

The microstructure and mechanical properties of GCI with V-Mn-Cr inoculants were investigated through OM, SEM, EDS, etc. The following main conclusions could be drawn:

The optimal composition of the inoculant was determined by orthogonal experiment as 7% V, 1% Mn and 6% Cr (wt-% of inoculant), and the tensile strength, Brinell hardness, and elastic modulus of the V-Mn-Cr inoculant samples were 356 MPa, 233 HB, and 149 GPa, respectively. Compared with the commercial inoculant samples, the tensile strength, Brinell hardness, and elastic modulus of the V-Mn-Cr inoculant samples increased by 16.7%, 14.2%, and 12.8%, respectively.

V-Mn-Cr inoculant can refine the microstructure of GCI, improve graphite morphology, increase pearlite and eutectic cells number, and reduce pearlite lamellar spacing, resulting in an improvement of the mechanical properties.

V-Mn-Cr inoculant can provide the substance of graphite nucleation. The substrate of the graphite nucleation may consist of oxides (SiO₂, FeO, Cr₂O₃), carbides (SiC, TiC), sulfides (MnS, FeS), and XO·SiO₂ silicates (X: Mn, Fe, Ca).

Footnotes

Acknowledgements

The authors acknowledge and thank the Zhengzhou University Analytical and Testing support.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

Almanza

Pérez

Almanza

Microstructure and mechanical properties of gray iron cylinder blocks casting. Inter Metalcast. 2015;9:84–86. doi:10.1007/BF03355609

Wang

Chen

et al.Influence of V content on microstructure and mechanical properties of gray cast iron for super-large cylinder liner. Inter Metalcast. 2022;17:1806–1814.

Khuntrakool

Janudom

Muangjunburee

et al.Effects of chemical composition on microstructure and properties of high phosphorus grey cast iron brake shoe. Inter Metalcast. 2022;16:1221–1234. doi:10.1007/s40962-021-00671-y

Wang

Chen

YX.

Fuzzy neural network analysis on gray cast iron with high tensile strength and thermal conductivity. China Foundry. 2019;16:190–197. doi:10.1007/s41230-019-9012-y

Ding

Huang

Matthias

et al.Development of high performance cast iron with combination of improved mechanical and thermal properties through Mo addition. Metall Mater Trans, A. 2018;49:3173–3177. doi:10.1007/s11661-018-4699-8

Hassani

Habibollahzadeh

Sadeghinejad

Influence of vanadium and chromium additions on the wear resistance of a gray cast iron. Int J Miner Metall Mater. 2012;19:602–607. doi:10.1007/s12613-012-0601-7

Coy

Russell

Heidelberger

et al.Effect of scandium on cast iron microstructure. Inter Metalcast. 2020;14:275–277. doi:10.1007/s40962-019-00382-5

Thomser

Bodenburg

Sturm

JC.

Optimized durability prediction of cast iron based on local microstructure. Inter Metalcast. 2017;11:207–215. doi:10.1007/s40962-016-0091-x

Oloyede

Cochrane

Mullis

AM.

Effect of rapid solidification on the microstructure and microhardness of BS1452 grade 250 hypoeutectic grey cast iron. J Alloy Compd. 2017;707:347–350. doi:10.1016/j.jallcom.2016.08.214

10.

Xue

Pretreatments of gray cast iron with different inoculants. J Alloy Compd. 2016;689:408–415. doi:10.1016/j.jallcom.2016.07.052

11.

Kopyciński

Dorula

Effective inoculation of grey cast iron. Cham: Springer; 2016.

12.

Riposan

Chisamera

Stan

et al.Al, Zr–FeSi preconditioning of grey cast irons. Mater Sci Technol. 2008;24:579–584. doi:10.1179/174328408X298842

13.

Zheng

et al.Elimination of the harmful effects of trace elements on gray cast iron by rare earths and their composite inoculants. Modern Cast Iron. 1997;4:10–15.

14.

Zhao

Xin

et al.Effect of silicon-strontium complex breeding on the organization and properties of boron-containing gray cast iron. Casting. 2005;54:164–167.

15.

Zhao

Xin

et al.Effect of silica-barium composite inoculant on the organization and properties of boron-containing gray cast iron. J Northeastern Univ (Nat Sci Ed). 2005;26:359–362.

16.

Wang

Fan

Wang

et al.Effect of vanadium and titanium on microstructure and properties of gray cast iron brake drum. Hot Work Technol. 2015;44:50–52 + 56.

17.

Yang

et al.Research and application of cylinder block materials for cylinderless automotive diesel engines. Automot Eng. 2003;25:407–409.

18.

Wang

Yang

et al.Effect of different inoculants on microstructure and properties of high carbon equivalent high manganese gray cast iron. Hot Work Technol. 2004;11:56–57.

19.

GB/T 7216-2009 . Metallographic test for gray cast iron. Beijing: China Standard Press; 2009, 1–4.

20.

Riposan

Chisamera

Stan

et al.Three-stage model for nucleation of graphite in grey cast iron. Mater Sci Technol. 2010;26:1439–1447. doi:10.1179/026708309X12495548508626

21.

Alonso

Stefanescu

Larrañaga

et al.Graphite nucleation in compacted graphite cast iron. Inter Metalcast. 2020;14:1162–1171. doi:10.1007/s40962-020-00441-2

22.

Riposan

Chisamera

Stan

Analyses of possible nucleation sites in Ca/Sr overinoculated grey irons. AFS Trans. 2001;109:1151–1162.

23.

Mittemeijer

EJ.

Fundamentals of materials science. Berlin: Springer; 2010, 303–337.

24.

Huang

XH.

Principles of iron and steel metallurgy. Beijing: Metallurgical Industry Press; 2013, 630–635.

25.

Sommerfeld

Tonn

Theory of graphite nucleation in lamellar graphite cast iron. Inter Metalcast. 2009;3:39–47. doi:10.1007/BF03355457

26.

Stefan

Chisamera

Riposan

et al.Graphite nucleation sites in commercial grey cast irons. Mater Today Proc. 2021;45:4091–4095. doi:10.1016/j.matpr.2020.11.009

27.

Feng

Sun

et al.Effect of La-O-S complex inoculant on microstructure and mechanical characteristics of ductile iron. J Mater Sci. 2022;57:5288–5297. doi:10.1007/s10853-022-06976-5