KR20120133778A

KR20120133778A - High strength grey cast iron and method manufacturing thereof

Info

Publication number: KR20120133778A
Application number: KR1020110052612A
Authority: KR
Inventors: 남덕현; 김의준
Original assignee: 현대자동차주식회사
Priority date: 2011-06-01
Filing date: 2011-06-01
Publication date: 2012-12-11

Abstract

Main component is Fe, C: 3.4 to 4.0 wt%, Si: 1.8 to 2.2, Mn: 1.4 to 1.8 wt%, P: 0.1 wt% or less (0 is not included), S: 0.1 to 0.2 wt%, Cu: 0.3-0.6 wt%, Sn: 0.07 wt% or less (0 is not included), Cr: 0.5-0.8 wt%, Ni: 0.2 wt% or less (0 is not included), Mo: 0.1 wt% or less (0 is not included) and High-strength gray cast iron composed of components containing other unavoidable impurities and a method of manufacturing the same are introduced.

Description

High strength gray cast iron and its manufacturing method {HIGH STRENGTH GRAY CAST IRON AND METHOD MANUFACTURING THEREOF}

The present invention relates to a pearlite-based gray cast iron (flake graphite cast iron) with improved tensile strength and workability compared to the prior art, and more particularly, to a high-strength gray cast iron manufactured by using high manganese steel scrap and a manufacturing method thereof.

Gray cast iron is widely used for automotive internal combustion engine blocks and cylinder heads because of its relatively low cost and high performance. Since the physical properties such as tensile strength and fatigue strength of materials, productivity, and workability are mutually compromised in use, various element ratios are used in combination at an appropriate level. In recent years, the load on the block and the head is increased due to the increase in vehicle output and the tightening of environmental regulations. Accordingly, there is an increasing need for a new gray cast iron that can maintain productivity while improving physical properties.

The present invention relates to a gray cast iron excellent in tensile strength and workability, and to a method for producing the same, more specifically, based on iron, C: 3.4 to 4.0 wt%, Si: 1.8 to 2.2, Mn: 1.4 to 1.8 wt%, and P: 0.1 wt% or less, S: 0.1-0.2 wt%, Cu: 0.3-0.6 wt%, Sn: 0.07 wt% or less, Cr: 0.5-0.8 wt%, Ni: 0.2 wt% or less, Mo: 0.1 wt% or less It relates to the inclusion flake graphite cast iron.

Cast iron of the present invention is superior to conventional cast iron due to the increase in the content of manganese elements and optimization of other alloy components compared to the 250 MPa gray cast iron compared to the existing tensile strength, it can be used suitably for the cylinder block or cylinder head of a high-power engine .

In addition, by using galvanized high manganese steel sheet, it can be applied to various fields by reducing alloy element cost and securing productivity such as workability at the same level as existing materials. Most suitably used.

The matters described as the background art are only for the purpose of improving the understanding of the background of the present invention, and should not be taken as acknowledging that they correspond to the related art already known to those skilled in the art.

The present invention has been proposed to solve this problem, and to provide a new gray cast iron material having excellent properties by improving the tensile strength and workability, and at the same time present a suitable manufacturing process. More specifically, the object is to provide a gray cast iron having a pearlite matrix without defects such as pores.

High-strength gray cast iron according to the present invention for achieving the above object is based on Fe as a main component, C: 3.4 ~ 4.0 wt%, Si: 1.8 ~ 2.2, Mn: 1.4 ~ 1.8 wt%, P: 0.1 wt% or less ( 0 is not included), S: 0.1-0.2 wt%, Cu: 0.3-0.6 wt%, Sn: 0.07 wt% or less (0 is not included), Cr: 0.5-0.8 wt%, Ni: 0.2 wt% or less Free), Mo: up to 0.1 wt% (0 not included) and other unavoidable impurities.

In addition, the gray cast iron, when observing the microstructure may be characterized in that the MnS tissue contained 2 to 5% by volume fraction.

On the other hand, the manufacturing method of high-strength gray cast iron according to the present invention, by administering a high manganese steel sheet or scrap containing Mn 1.0 ~ 2.5 wt% in the dissolution process of the substrate so that the components of Mn of gray cast iron is contained 1.4 ~ 1.8 wt% You can also make adjustments.

According to the high-strength gray cast iron having a structure as described above and a manufacturing method thereof, the existing cast iron of the existing tensile strength 250 MPa grade is superior to the existing cast iron due to the increase in the manganese element content and optimization of other alloy components.

In addition, it can be suitably used for cylinder block or cylinder head of high power engine, and by using galvanized high manganese steel sheet, it can be applied to various fields by reducing alloy element cost and securing productivity such as workability to existing materials. It can be best used for the cylinder head of a commercial diesel engine.

1 is a view showing a manufacturing method of high strength gray cast iron according to an embodiment of the present invention.
Figure 2 is a view showing the microstructure of the high-strength gray cast iron prepared according to the manufacturing method of the high-strength gray cast iron shown in FIG.

Hereinafter, a high-strength gray cast iron according to a preferred embodiment of the present invention and a manufacturing method thereof with reference to the accompanying drawings.

1 is a view showing a manufacturing method of high-strength gray cast iron according to an embodiment of the present invention, Figure 2 is a view showing the microstructure of the high-strength gray cast iron manufactured according to the manufacturing method of the high strength gray cast iron shown in FIG.

High-strength gray cast iron according to a preferred embodiment of the present invention, Fe as the main component, C: 3.4 ~ 4.0 wt%, Si: 1.8 ~ 2.2, Mn: 1.4 ~ 1.8 wt%, P: 0.1 wt% or less (0 is not included ), S: 0.1-0.2 wt%, Cu: 0.3-0.6 wt%, Sn: 0.07 wt% or less (0 is not included), Cr: 0.5-0.8 wt%, Ni: 0.2 wt% or less (0 is not included), Mo: 0.1 wt% or less (without 0) and other unavoidable impurities.

Looking at the function and the reason for the content limitation of the components contained in the spheroidal graphite cast iron according to the present invention, carbon (C) is an essential element to increase the hardness and strength by depositing carbide, 3.4 ~ in consideration of fluidity decrease and primary graphite crystallization Limit to 4.0 wt%. The relatively high carbon content increases the amount of graphite crystallization, leading to an improvement in processability.

Silicon (Si) is included in 1.8 ~ 2.2 wt%. Silicon contributes to graphite crystallization, and forms an Fe ₂ SiO ₄ oxide film in an oxidizing environment to improve oxidation resistance. However, the silicon content is limited to 1.8 ~ 2.2 wt% in the present invention in consideration of the effect on the carbon equivalent.

Manganese (Mn) and sulfur (S) combine with each other to form MnS, which is distributed in the cast iron structure to act as a lubricating phase during processing to improve workability. In addition, manganese is a carbide stable element, which is finely distributed in the form of carbides in the matrix, thereby increasing the strength of the matrix. However, when excessively added, manganese interferes with graphitization, and sulfur may interfere with the crystallization of austenite, so in the present invention, 1.4-1.8 wt% Mn and 0.1-0.2 wt may be used to maintain an appropriate Mn-S ratio. It was supposed to add% S. The gray cast iron of the present invention by the inclusion of such manganese is characterized in that the MnS structure contained 2 to 5% by volume fraction. The generation fraction of such MnS tissue can be clearly seen in the microstructure of FIG.

Copper (Cu) was determined to be 0.3 ~ 0.6 wt% in the present invention because it has the effect of promoting and stabilizing pearlite formation.

Chromium (Cr) increases the strength of cast iron because it has the effect of miniaturizing the pearlite structure. However, in the present invention, when excessively added, chromium-based carbides are formed to deteriorate the processability of cast iron.

Other up to 0.1 wt% phosphorus (P), 0.07 wt% tin (Sn), 0.2 wt% nickel (Ni), and 0.1 wt% molybdenum (Mo) have the effect of forming fine carbides during casting In addition, there is an effect of miniaturizing pearlite and forming flake graphite, but when added in excess, coarse carbides may be formed so as to be controlled to an appropriate level.

In order to produce gray cast iron having a composition as described above, the casting method as shown in FIG. 1 may be understood as an optimal method.

Manufacturing method for obtaining high strength gray cast iron is characterized in that the Mn component of gray cast iron is adjusted to contain 1.4 ~ 1.8 wt% by administering a high manganese steel sheet or scrap containing 1.0 ~ 2.5 wt% Mn during the dissolution of the substrate It is done. Checking the gate of the melting furnace while continuously injecting high-manganese steel plate, through which the fine components are adjusted and moved to the ladle when the Mn component of the melting furnace contains 1.4 to 1.8 wt%.

High manganese scrap used during casting is commonly referred to as a high-tension steel sheet for automobiles containing 1.0 to 2.5 wt% of manganese, and by using such a high manganese scrap to increase the strength and cost reduction.

As an example for confirming the performance of the gray cast iron according to the present invention, it will be described in detail by the embodiment having the composition shown in Table 1 below. However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited to the following examples.

division

C
Si
Mn
P
S
Cu
Sn
Cr
Ni
Mo
Example 1
3.61
2.05
1.71
0.04
0.13
0.38
0.02
0.63
0.05
0.02
Example 2
3.73
1.93
1.62
0.02
0.12
0.45
0.03
0.72
0.03
0.05
Comparative Example
3.60
1.82
0.65
0.03
0.04
-
-
0.41
0.01
0.01

The composition of Examples 1 and 2 is a new gray cast iron proposed by the present invention, the composition of the comparative example corresponds to a tensile strength 250 MPa class gray cast iron used for an internal combustion engine engine cylinder head.

Tensile strength and cutting load of each cast iron are shown in Table 2 below. Tensile strength was averaged after 3 times with KS B0801 No. 10 test specimen, and the cutting load was measured by drilling and tapping load, and the relative cutting load of the cast iron of the example was measured when the cast iron of the comparative example was 100%. Indicated.

As a result, the tensile strength of the cast iron of the Example was found to be improved by about 30% compared to the comparative example. In addition, the cutting load at the time of processing was increased within about 10% compared to the comparative example, which was a good level compared to the effect of high strength.

division
Example 1
Example 2
Comparative example
The tensile strength
360 MPa
375 MPa
273 MPa
Drilling Load
104%
109%
100%
Tapping Load
106%
107%
100%

While the present invention has been particularly shown and described with reference to specific embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims It will be apparent to those of ordinary skill in the art.

Claims

Main component is Fe, C: 3.4 to 4.0 wt%, Si: 1.8 to 2.2, Mn: 1.4 to 1.8 wt%, P: 0.1 wt% or less (0 is not included), S: 0.1 to 0.2 wt%, Cu: 0.3-0.6 wt%, Sn: 0.07 wt% or less (0 is not included), Cr: 0.5-0.8 wt%, Ni: 0.2 wt% or less (0 is not included), Mo: 0.1 wt% or less (0 is not included) and High-strength gray cast iron composed of components containing other unavoidable impurities.

The method according to claim 1,
The gray cast iron is high-strength gray cast iron, characterized in that the MnS structure contained 2 to 5% by volume fraction.

As a manufacturing method for obtaining high strength gray cast iron,
A high-strength gray cast iron manufacturing method, characterized in that the Mn component of the gray cast iron is adjusted to include 1.4 ~ 1.8 wt% by administering a high manganese steel sheet or scrap containing 1.0 ~ 2.5 wt% Mn during the dissolution of the substrate.