JPH10158777A - Production of high strength cast iron, and high strength cast iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high strength and superior machinability without causing precipitation of chilled crystal at the time of casting, by adding specific amounts of manganese and rare earth element or misch metal to a sulfur-containing cast iron. SOLUTION: At the time of producing a cast-iron casting, a cast iron containing 0.02-0.2wt.% S is melted and Mn is added to the resultant molten metal by 1.0-3.0wt.%, and further, rare earth element or misch metal is added to the molten metal by the amount twice the amount of S in the molten metal, that is, 0.04-0.4wt.%, followed by casting. There are no particular limitations on the kind of cast iron as raw material that can be used as long as it has sulfur content 0.02-0.2wt.%) higher than that of ordinary cast iron, and it can contain inevitable impurities in the amounts within the ranges where no adverse effects are exerted on the characteristics of the high strength cast iron. Moreover, because of the formation of a compound sulfide, leading to crystallization of graphite, and the improvement of a graphite matrix structure, a casting of this molten metal has characteristics of high tensile strength (about 260 to 300MPa) and low Brinell hardness (about 100 to 210).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high-strength cast iron and a product thereof, and more particularly to a method for producing high-strength cast iron having improved strength characteristics while ensuring machinability, and a product thereof. is there.

[0002]

2. Description of the Related Art As a cast iron material for an engine casing,
For example, flaky graphite cast iron or the like is used. However, in order to cope with the recent increase in engine output, weight reduction, and energy saving, a tough cast iron material is required.

From the viewpoint of increasing the output of an engine, it is effective to increase the strength of a cast iron material by adding an alloy element or the like. By using this high-strength cast iron, it is possible to reduce the thickness and weight of an engine casing. Thus, it is possible to reduce the weight and energy consumption of the engine.

[0004]

However, although the strength of the cast iron material can be increased by the addition of an alloying element or the like, there is a problem of the accompanying increase in hardness. Further, due to the thinning of the engine casing, the molten cast iron is rapidly cooled, so that a cold-hardened structure (chill structure) is precipitated and the product is significantly embrittled.

[0005] That is, when high output, light weight, and energy saving of the engine are achieved by using high-strength cast iron, there is a problem that the machinability is reduced. A decrease in machinability deteriorates the workability of the product, which contributes to an increase in cost.

Accordingly, an object of the present invention is to provide a method for manufacturing a high-strength cast iron having high strength and good machinability, and a high-strength cast iron that solves the above-mentioned problems.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, the invention of claim 1 melts cast iron containing 0.02 to 0.2 wt% of S to form a molten metal, and contains Mn in the molten metal. In addition to adding 1.0 to 3.0 wt%, a rare earth element or a misch metal is added in an amount of 0.04 to 0.4 wt%, which is twice the amount of S in the molten metal.

According to a second aspect of the present invention, S is set to 0.02 to 0.2.
In a molten metal obtained by melting a cast iron containing wt%, Mn is 1.0 to 3.0 wt%, and a rare earth element or a misch metal is 0.04 to twice as large as the S amount in the molten metal.
0.4 wt% is contained.

The reasons for limiting the above numerical values will be described below.

The reason why the addition amount of S is limited to 0.02 to 0.2 wt% is that if the addition amount is less than 0.02 wt%,
This is because the effect of adding Mn and rare earth elements or misch metal is reduced, and if the added amount is more than 0.2 wt%, the material becomes brittle.

The reason why the amount of Mn added is limited to 1.0 to 3.0 wt% is that if the amount is less than 1.0 wt%, the effect of improving the tensile strength is small, so that the amount of Mn is 3.0 wt%. 0
If the content is more than wt%, the precipitation of the chill structure extends to the deep portion of the material (the chill depth increases), and the material hardness increases.

The amount of the rare earth element or misch metal added is twice the amount of S in the molten metal to 0.04 to 0.4 wt%.
This is because when the amount of addition is twice the amount of S in the molten metal, both the chill depth and the tensile strength are good.

According to the above configuration, S is set to 0.02 to 0.
Molten cast iron containing 2 wt% is melted, Mn is added in an amount of 1.0 to 3.0 wt%, and a rare earth element or a misch metal is doubled in amount of the S in the melt. Since 0.04 to 0.4 wt% of the above is added, a high-strength cast iron having high strength and excellent machinability can be obtained.

[0014]

Embodiments of the present invention will be described below.

A method for producing a high-strength cast iron according to the present invention will be described.

First, a raw cast iron containing 0.02 to 0.2 wt% of S is melted in, for example, a high frequency electric furnace to obtain a molten cast iron. In the molten cast iron, Mn is set to 1.0 to 3.0 w.
Add within the range of t%.

Next, a rare earth element or a misch metal (hereinafter referred to as RE) is added to the cast iron molten metal in an amount of 0.04 to 0.4 wt%, which is twice the amount of S in the molten metal. The molten cast iron is poured into a mold and cooled to produce a high-strength cast iron.

The raw material cast iron is not particularly limited as long as it has a higher S content (0.02 to 0.2 wt%) than ordinary cast iron. Inevitable impurities.

The method of melting the raw cast iron is not limited to the high-frequency electric furnace, but may be appropriately changed according to the purpose and application.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a flowchart of a method for manufacturing a high-strength cast iron according to the present invention.

As shown in FIG. 1, high purity pig iron, electrolytic iron,
Fe-Si, Fe-P, Fe-S and Fe-Mn
The amount of each dissolution was 3 kg, and the mixture was melted in a 3 kHz, 12 kW high frequency electric furnace. The chemical composition was C: 3.3 wt%, S
i: 2.1 wt%, S: 0.08 wt%, P: 0.06
wt%, balance: A cast iron melt made of iron is prepared.

At this time, the Mn content in the molten cast iron is set to 0 to
By changing the content within the range of 5.0 wt%, molten cast irons having different Mn contents are produced. The maximum melting temperature at this time is set to 1,753K.

Next, RE-Si (RE: 3) is used as RE.
2.5 wt%, Si: 34.4 wt%)
In each cast iron melt at 23K, RE is converted to RE.
Add 2 wt%.

Thereafter, each cast iron melt to which RE has been added is
At a temperature of 1,673K, each of the test pieces (high-strength cast iron) was poured into various molds (C3 plate chill test shell mold, φ30 mm × 200 mm CO ₂ mold, emission spectroscopic analysis mold) and cooled. Is prepared.

A test piece was taken out from the C3 plate chill test shell mold, and the chill depth was measured using this plate chill test piece.

Further, a test piece is taken out from a CO ₂ mold of φ30 mm × 200 mm and processed to obtain a JIS8C
To prepare a tensile test piece. A tensile test was performed on the test piece, and the structure was observed and the Brinell hardness was measured near the fractured surface.

(Tensile Strength and Chill Depth with Mn Added Amount) FIG. 2 shows the relationship between the Mn added amount and the tensile strength, and FIG. 3 shows the relationship between the Mn added amount and the clear chill depth. 2 and 3
The solid line connecting the black circles indicates cast iron with 0.2% by weight of RE added, and the two-dot chain line connecting squares indicates cast iron with no RE added.

As shown in FIG. 2, the amount of Mn added was about 0.9.
In the case of less than wt%, the cast iron without RE
Although the tensile strength is higher than that of the cast iron containing 0.2 wt%, when the amount of added Mn is increased to about 0.9 wt% or more, the RE 0.2 w
The t% -added cast iron has a higher tensile strength than the RE-free cast iron. In particular, the improvement in tensile strength is remarkable when the Mn content of the cast iron containing 0.2% by weight of RE is 1.0 to 2.0% by weight.

As shown in FIG. 3, the clear chill depth of RE-free cast iron is generally deeper than that of RE 0.2 wt% -added cast iron. In particular, when the Mn addition amount of the cast iron containing 0.2% by weight of RE is 1.0 to 2.0% by weight, the clear chill depth is significantly reduced.

(Changes in Metallographic Structure with Addition of Mn) Optical micrographs of the metallographic structure in each cast iron are shown in FIGS. 4, 5 and 6. FIG. 4A shows the Mn addition amount of 0.05 wt.
4 (b) shows the Mn addition amount of 0.3 wt%.
5 (a) shows a cast iron with an Mn addition of 0.6 wt%, FIG. 5 (b) shows a cast iron with an Mn addition of 1.5 wt%, and FIG. 6 (a) shows a Mn addition FIG. 6B shows cast iron of 3.0 wt%, and FIG. 6B shows cast iron of Mn added amount of 3.0 wt%.

As shown in FIG. 4 (a), cast iron containing 0.05 wt% of Mn has fine graphite flakes and has not grown into a good shape. Further, the ratio of graphite is small. For this reason, as shown in FIG. 2, a relatively high tensile strength (about 270
MPa), but the hardness is also high. FIG.
As shown in FIG. 5 (b) and FIG. 5 (a), in the cast iron containing 0.3 wt% and 0.6 wt% of Mn, the graphite flakes are elongated, the shape is planar and sharp, and ferrite precipitates on the matrix. Therefore, as shown in FIG.
Tensile strength (about 240MP) compared to 05wt% cast iron
a) It is decreasing.

On the other hand, as shown in FIG.
The high-strength cast iron of the present invention containing 1.5 wt% of Mn has a short graphite flake and a "worm-like" shape, so that the tensile strength is also improved as shown in FIG. 2 (about 300 MPa). doing.

FIGS. 7 and 8 show SEM photographs of the pearlite structure in each cast iron. FIG. 7A shows the Mn added amount 0.0
FIG. 7 (b) shows a 5 wt% cast iron, and FIG.
Fig. 8 (a) shows the amount of Mn added 1.5w
FIG. 8 (b) shows the amount of Mn added 3.0 wt%.
% Of cast iron is shown.

As shown in FIGS. 7 and 8, the lamella interval becomes narrower with an increase in the amount of Mn added.

As shown in FIG. 6 (a), the cast iron containing 3.0% by weight of Mn has a change in base pearlite as shown in FIG. 7 and FIG. However, the tensile strength is further improved (about 350 mm) as shown in FIG.
MPa). This is because ferrite in which Mn is dissolved is precipitated, and tensile strength and hardness are increased by solid solution strengthening of the ferrite. Further, as shown in FIG. 6 (b), the cast iron containing 5.0 wt% of Mn has a chill structure throughout.

As described above, the high-strength cast iron of the present invention achieves high strength by a synergistic effect of the graphite being slightly "worm-like" and the pearlite lamella spacing being small. .

The results of EPMA analysis showed that MnS and RE ₂
The complex sulfide of S ₃ becomes an effective underlayer for graphite crystallization and significantly promotes graphitization.

(Tensile Strength and Brinell Hardness with Mn Addition) FIG. 9 shows the relationship between the amount of Mn added, tensile strength and Brinell hardness. FIG. 10 shows the relationship between tensile strength and Brinell hardness when the amount of Mn added was changed from 0 to 3.0 wt%. The solid line connecting the black circles in FIG. 9 indicates the tensile strength, the dotted line connecting the black squares indicates the Brinell hardness, and the straight line in FIG. 10 indicates RH = 1 in the JTMackenzie relation.

As shown in FIG. 9, the amount of Mn added was 0.05
The wt% cast iron has a tensile strength of about 270 MPa, a Brinell hardness of about 255 HB, and an Mn content of 0.3%.
The wt% cast iron has a tensile strength of about 235 MPa and a Brinell hardness of about 205 HB, both of which are located above the straight line shown in FIG. 10, and the hardness is too high with respect to the tensile strength.

On the other hand, when the added amount of Mn is 0.6 wt.
%, 1.2 wt%, 1.5 wt%, 2.0 wt%, 3.
0 wt% cast iron has a tensile strength and a Brinell hardness of about 240 MPa and about 195 HB, about 275 MPa and about 195 HB, about 295 MPa and about 195 HB, and about 30 MPa, respectively.
5MPa and about 205HB, about 350MPa and about 230H
B, which is located below the straight line in the figure, indicates that the hardness is not too high for the tensile strength and the material is good.

Particularly, when the added amount of Mn is 1.2 wt%,
The high-strength cast iron of the present invention having a wt% of 2.0 wt% has a high tensile strength of about 260 to 300 (MPa) and a low Brinell hardness of about 190 to 210 (HB). The characteristic is shown. That is, 1.0 to 2.0 w
By adding t% of Mn, a composite sulfide as a base for graphite crystallization is generated and a graphite matrix structure is improved, so that a high-strength cast iron having high tensile strength and low Brinell hardness can be obtained. it can.

(Chill Depth and Tensile Strength with Ce (RE)) FIG. 11 shows the relationship between the amount of added Ce and the clear chill depth.
FIG. 12 shows the relationship between the amount of added Ce and the tensile strength. FIG.
In FIG. 12, the solid line connecting the black circles is S0.003 wt.
% Indicates cast iron, and the solid line connecting the black triangles is S0.05w
t% -containing cast iron, and the solid line connecting the black squares is S0.1w
Shows cast iron containing t%.

As shown in FIG. 11, the cast iron containing 0.003 wt% of S having a low S content has a minimum clear chill depth of about 8 mm, and the effect of improving the structure by adding Ce (RE) is low.

On the other hand, S0.0
The cast iron containing 5 wt% and the cast iron containing 0.1 wt% have a minimum clear chill depth of about 0 to 1.5 mm, and have a Ce
The effect of improving the structure by the addition of (RE) is high.
When the added amount of e (RE) is twice the S content, the effect is remarkable.

As shown in FIG. 12, cast iron containing 0.003 wt% of S with a low S content has a maximum tensile strength of about 27.0 kgf / mm ² (about 265 MPa), and Ce (RE) The effect of improving the strength by the addition of is low.

On the other hand, S0.0
The cast iron containing 5 wt% and the cast iron containing S0.1 wt% have a maximum tensile strength of 30 to 31.5 kgf / mm ² (about 29%).
5 to 310 MPa), and the effect of improving strength by the addition of Ce (RE) is high. In particular, when the amount of Ce (RE) added is twice the S content, the effect is remarkable.

(Machinability) The machinability of each cast iron was evaluated. FIG. 13 shows a diagram of a cutting apparatus for evaluating this cutting property. FIG. 13A shows a perspective view of a cutting device, and FIG.
13B is an enlarged view of a main part of FIG.
(C) shows a method of measuring the flank wear width.

As shown in FIG. 13A, cutting is performed using each cast iron as the workpiece 3.

As shown in FIGS. 13 (b) and 13 (c), the workpiece 3 is rotated and the tool 1 is placed on the surface of the workpiece 3.
Flank wear A occurs at the tip of the tool 1 during the cutting process.

The flank wear width T was measured by measuring the flank wear width at the tip of the tool 1 immediately after the start of the cutting process, while the flank wear width T was equal to T = 0. The surface wear width is T = L.

FIG. 14 shows the relationship between the cutting length and the flank wear width. In FIG. 14, dotted lines connecting black circles indicate Mn as 2.
0 wt%, S is added 0.08 wt%, and RE-Si (R
E32.5 wt%, Si34.4 wt%) shows the high-strength cast iron of the present invention, the dotted line connecting the black diamonds added Mn 2.0 wt%, S added 0.02 wt%, RE-Si
Is shown, and the solid line connecting the white triangles is Ca-S
i, FC300 inoculated with white squares, FC300 inoculated with Fe-Si, solid lines connected with black triangles, FC350 inoculated with Ca-Si, solid lines connected with black squares, Shows FC350 inoculated with -Si.

Here, the high-strength cast iron of the present invention, Mn 2.0
wt%, S 0.02 wt% addition, RE-Si inoculated cast iron (hereinafter referred to as comparative cast iron), Ca-Si inoculated FC30
0, Fe-Si inoculated FC300, Ca-Si inoculated FC3
50, and the tensile strength of Fe-Si inoculated FC350 is
341.5 MPa, 340.5 MPa, 30 respectively
4.7MPa, 270.1MPa, 338MPa, 28
It is 1.4 MPa.

As shown in FIG. 14, the high-strength cast iron, Ca-Si-inoculated FC300, and Fe-Si-inoculated FC300 of the present invention have a flank wear width of about 200 μm even when the cutting length exceeds 1000 mm. , Showing good abrasion resistance.

FC350 has a larger flank wear width (amount of wear) by the higher tensile strength than FC300.
Since the comparative cast iron has a low effect of inoculation of RE-Si due to a small S content, the chill depth is large and the flank wear width (amount of wear) is large as shown in FIG.

FIG. 15 shows the relationship between the tensile strength and the flank wear width. In FIG. 15, black circles indicate the high-strength cast iron of the present invention, black diamonds indicate the comparative cast irons, and open triangles indicate Ca-Si inoculated F.
C300 is shown, a white square shows Fe-Si inoculated FC300, a black triangle shows Ca-Si inoculated FC350, and a black square shows Ca-Si inoculated FC350.

As shown in FIG. 15, the high strength cast iron of the present invention has a large tensile strength of about 335 MPa,
The flank wear width is as small as less than 150 μm.

On the other hand, Ca—S having good wear resistance
i-inoculated FC300 and Fe-Si-inoculated FC300
Compared with the high-strength cast iron of the present invention, the tensile strength is about 305M
Pa, as small as about 270 MPa. In addition, comparative cast iron, Ca
FC-350 inoculated with Si and FC35 inoculated with Fe-Si
0 indicates that the flank wear width exceeds 200 μm in all cases, and the wear resistance is poor.

That is, the high-strength cast iron of the present invention contains S sufficiently (0.05 to 0.2 wt%), and Mn and R
E in a specified range (Mn: 1.0 to 2.0 wt%, RE: S
Doubling (0.1-0.4 wt%), the flank wear width is small even if cutting is performed for a long time,
And the tensile strength is high.

[0059]

In summary, according to the present invention, S is set to 0.
0.5-0.2 wt%, Mn 1.0-2.0 wt%, R
Since E is contained in an amount of 0.1 to 0.4 wt%, which is twice the amount of S, it is possible to obtain a high-strength cast iron that is not too high in hardness for high tensile strength and hard to wear. Demonstrates excellent effects.

[Brief description of the drawings]

FIG. 1 is a flowchart of a method for manufacturing a high-strength cast iron according to the present invention.

FIG. 2 is a diagram showing the relationship between the amount of added Mn and tensile strength.

FIG. 3 is a diagram showing the relationship between the added amount of Mn and the clear chill depth.

FIG. 4 is an optical microscope photograph of a graphite shape in cast iron with an Mn addition amount of 0.05 wt% and an Mn addition amount of 0.3 wt%.

FIG. 5: Mn added amount 0.6 wt% and Mn added amount 1.
It is an optical microscope photograph of graphite shape in 5 wt% cast iron.

FIG. 6 shows a Mn added amount of 3.0 wt% and a Mn added amount of 3.
It is an optical microscope photograph of graphite shape in 0 wt% cast iron.

FIG. 7 is an SEM photograph of a pearlite structure in cast iron with an Mn addition amount of 0.05 wt% and an Mn addition amount of 0.6 wt%.

FIG. 8: 1.5 wt% of Mn addition amount and 3 Mn addition amount.
It is a SEM photograph of a pearlite structure in 0 wt% cast iron.

FIG. 9 is a graph showing the relationship between the amount of added Mn, tensile strength, and Brinell hardness.

FIG. 10 is a graph showing the relationship between tensile strength and Brinell hardness when the amount of Mn added is changed from 0 to 3.0 wt%.

FIG. 11 is a diagram showing the relationship between the amount of added Ce and the clear chill depth.

FIG. 12 is a graph showing the relationship between the amount of added Ce and the tensile strength.

FIG. 13 is a diagram of a cutting device for evaluating cutability.

FIG. 14 is a diagram showing a relationship between a cutting length and a flank wear width.

FIG. 15 is a diagram showing the relationship between tensile strength and flank wear width.

Claims (2)

[Claims] 1. A cast iron containing 0.02 to 0.2 wt% of S is melted to form a molten metal, and Mn is contained in the molten metal in an amount of 1.0 to 0.2 wt%.
In addition to adding 3.0 wt%, rare earth elements or misch metals are added in an amount of 0.0 times the amount of S in the molten metal.
A method for producing high-strength cast iron, characterized by adding 4 to 0.4 wt%. 2. In a molten metal obtained by melting a cast iron containing 0.02 to 0.2 wt% of S, Mn is 1.0 to 3.0 wt.
%, A rare earth element or a misch metal is contained in an amount of 0.04 to 0.4 wt% twice the amount of S in the molten metal.