JPS60110841A - High si spheroidal graphite bainite cast iron - Google Patents

Abstract

PURPOSE:To obtain the titled cast iron having superior mechanical properties and corrosion resistance by austempering high Si spheroidal graphite cast iron having a specified composition contg. C, Si, Mn and Mg to form a bainite structure contg. a large amount of a retained austenite structure. CONSTITUTION:High Si spheroidal graphite cast iron consisting of, by weight, 3.0-4.5% C, 3.0-5.5% Si, 0.2-1.0% Mn, 0.02-0.10% Mg and the balance essentially Fe is austempered to adjust the amount of a retained austenite structure in the matrix to 30-80vol% and the amount of a bainite structure 70- 20vol%. High Si spheroidal graphite bainite cast iron having superior mechanical properties such as hardness, tensile strength, yield strength and elongation and superior corrosion resistance is obtd.

Description

Detailed Description of the Invention A. Field of Industrial Application The present invention relates to high-Si bainitic spheroidal graphite cast iron. Specifically, by increasing the Si content of the spheroidal graphite cast iron and austempering treatment, a large amount of austenite 1- This results in a high-Si bainite spheroidal graphite cast iron that retains both excellent mechanical properties and eating properties.

In conventional cast iron, it is necessary to maintain high strength and toughness so that it can meet the recent demands for weight reduction of parts and can be used as a substitute material for steel while maintaining the low cost of the material. , conventional spheroidal graphite cast iron is insufficient.

Therefore, it is already known that strength and toughness can be improved by austempering cast iron and forming the base into a bainite structure, and these properties are particularly improved in spheroidal graphite cast iron.

According to the inventors' research, the reason why austempering has a large mechanical property improvement effect in spheroidal graphite cast iron is that the matrix can be made into a mixed structure of retained austenite and bainite. It was found that the higher the amount, the better the mechanical properties.

Now, normally, spheroidal graphite cast iron becomes brittle as the Si content increases, but this drawback can be solved by austempering treatment.

In addition, according to the inventors' research, spheroidal graphite cast iron with a high 3i content has the property of leaving austenite in polyacid even under the same austempering conditions, and expensive alloying elements such as Mo and Ni are used. It has become clear that it is possible to maintain excellent mechanical properties at low cost even without this.

In addition, the inventors' research revealed that corrosion resistance is significantly improved compared to conventional cast iron due to the presence of a large amount of retained austenite and high Si content.

C1 Purpose of the Invention The present invention austempers spheroidal graphite cast iron with a high Si content to form a base into a haynite structure containing a large amount of residual ausnanite, thereby achieving high mechanical properties and corrosion resistance. The purpose is to provide Si-haynite spheroidal graphite cast iron.

21 Constitution of the Invention According to the present invention, in weight ratio, C;
3. O~4.5%, Si; 3.0~5.5%, Mn
; 0.2-1.0%, Mg; 0.02-0. l
High Si heinite spheroidal graphite cast iron with 0% Fe and the remainder substantially Fe. Through austempering treatment, the retained austenite structure in the matrix is reduced to 30 to 80% by volume, and the remaining bainite structure is reduced to 30 to 80% by volume. 70-20%, this is achieved by high-Si heinite spheroidal graphite cast iron, which is characterized by both excellent mechanical properties and corrosion resistance.

E1 Effects of the Invention As mentioned above, the material of the present invention has a high Si content and has a bainite structure containing a large amount of retained austenite as a base, thereby producing a spheroidal graphite material with excellent mechanical properties and corrosion resistance. Although it can be made of cast iron, the reason why the amount of retained austenite is set to 30 to 80% in terms of volume ratio is that if it exceeds 80%, an improvement effect commensurate with the increase cannot be obtained, This is because, if it is less than 20%, the effect of improving mechanical properties will not be significant.

Finally, the reason for limiting the ingredients will be explained.

As the Si content increases, the amount of retained austenite increases, but if it exceeds 5.5%, carbon floats up during casting, resulting in so-called carbon flotation, which impairs the effectiveness of adding C to cast iron. , the upper limit was set at 5.5%.

Furthermore, if the Si content is less than 3.0%, it falls within the range of normal spheroidal graphite cast iron, and is less effective in increasing the amount of retained austenite and improving corrosion resistance, so the lower limit was set at 3.0%.

Note that the other C, Mn, and Mg contents are in the same range as in commonly used spheroidal graphite cast iron, and the reason for limiting the range is also based on a well-known reason, so the explanation will be omitted.

EXAMPLES Hereinafter, the present invention will be described in detail based on the tables and accompanying drawings.

Example 1 Spheroidal graphite cast iron with the same Si content (4.7%) was subjected to austempering treatment and normalizing treatment to produce JIS standard F CD 7 (1 material) as the present invention material and comparative material. Then, a tensile test was conducted.

The test results are shown in the table below.

As is clear from the table, the elongation shows a low value due to the high Si content, but in Invention 4A, there is a large amount of retained austenite, which undergoes martenzite transformation due to the processing associated with the tensile test. As a result, the elongation is approximately three times larger than that of the JIS standard F CD 70 for comparison.

In addition, the tensile strength and yield strength of the comparative material are JIS standard F C1.
)70 showed higher results.

Example 2 A corrosion test piece having the shape shown in Fig. 1 was exposed to salty seashore salt air, but after being left in the atmosphere for 6 months in an environment where it would not get wet with rainwater, The amount of corrosion expressed by the following formula was compared.

c=w, -wo/wo -1/A (g/cJ) where, C; corrosion amount (g/cJ), (su0; weight before test (g) 1s; weight after test (g) A : Test piece surface area (o+l) The test pieces used for the test had three types of abrasive qualities: those listed in the table above and bainitic cast iron with 2.5% Si.

Further, the surface roughness of the test piece was 1.8 μRz.

As the test results are shown in Figure 2, even with the same -St content,
The amount of corrosion of the austempered material of the present invention is significantly reduced compared to conventional spheroidal graphite cast iron JIS standard FCD70.

In addition, 2.5% by weight Heinai cast iron is more S than that.
The amount of corrosion was lower than that of the comparison material JIS standard FCp70, which has a high i content, but the amount of corrosion was greater than that of the present invention material.

The above results are all considered to be due to the influence of the amount of retained austenite.

(1) Effects of the Invention As is clear from the above, according to the high-Si heinite spheroidal graphite cast iron of the present invention, spheroidal graphite cast iron with a high Si content is austempered, and the matrix is formed by a process that contains a large amount of residual austenite. The haynite structure has the advantage of having excellent mechanical properties and corrosion resistance.

Because of these advantages, the present invention material is suitable for parts that require strength and corrosion resistance, such as automobile suspension parts, such as steering knuckles, brake calipers, differential cases, differential carriers, and ball joint sockets. It is applicable.

[Brief explanation of drawings]

Figure 1 is a perspective view showing the shape of a corrosion test piece, Figure 2 is a
It is a graph showing corrosion test results. Figure 1 Figure 2 Dear Commissioner of the Patent Office 1. Display of the case 1982 Patent Application No. 218507 2, Name of the invention High Si Haynite Spheroidal Graphite Cast Iron 3, Person making the amendment Relationship to the case Patent Applicant Address 1 Toyota-cho, Toyota City, Aichi Prefecture 471 1980
February 28, 2015 5. Specification subject to amendment

Claims (1)

[Claims] Ci 3.1 in a weight ratio of 11. O~4.5%, Ss
; 3゜0-5.5%, Mn; 0.2-1.0%, Mg
; 0.02~(1,l 0%, the balance is substantially Fe, high S1 heinite spheroidal graphite cast iron, the residual austenite structure in the matrix is reduced to 30~80% by volume by austempering treatment) A high 81 bainite spheroidal graphite cast iron characterized by having the remainder of the bainite structure at a volume ratio of 70 to 20% and having both excellent mechanical properties and corrosion resistance.