JPS60190549A - Spheroidal graphite cast iron and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture spheroidal graphite case iron having high strength and toughness by austenitizing molten spheroidal graphite case iron by holding at a specified temp. and by stably providing a matrix structure consisting of bainite and retained austenite by heat treatment including rapid cooling. CONSTITUTION:Molten spheroidal graphite case iron contg. grahite spheroidized with Mg, etc. and having a composition contg. 3.0-4.0% C, 1.5-3.0% Si, 0.30- 0.45% Mn, <0.06% P, <0.02% S, 0.3-1.5% Cu, 0.7-3.5% Ni, <0.10% Cr and 0.02-0.06% Mg is austenitized by holding at 850-950 deg.C for 0.5-4hr. The molten metal is austempered by rapid cooling to 250-450 deg.C at such a high cooling rate that pearlite transformation is not caused and by holding at the temp. for 1- 4hr. The molten metal is then cooled to ordinary temp. to manufacture spheroidal graphite case iron having a structure consisting of bainite and retained austenite.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing spheroidal graphite cast iron that can stably form the matrix Il#a into a structure of bainite and retained austenite.

In recent years, spheroidal graphite cast iron and its manufacturing method have made great progress.
Many technologies have been developed. Especially tensile strength 100 kg
Spheroidal graphite cast iron with high strength and high toughness, with an elongation of 10% or more, has appeared, and progress has been made in heat treatment technology. The matrix structure of cast iron is a mixed structure of bainite and austenite, and such spheroidal graphite cast iron and heat treatment methods are described in Japanese Patent Publication No. 55-3422, Japanese Patent Application Laid-open No. 53-48014, Japanese Patent Application Laid-open No. 53-48015, etc. It is described in.

However, these techniques do not allow pearlite to remain in all of the spherical ironworks, especially in cases where the wall thickness exceeds 50+nn+.
It is extremely difficult to form a structure of bainite and retained austenite. Therefore, as a countermeasure to this problem, a technique of adding Mo was developed and filed as Japanese Patent Application No. 58-214761. Although a stable structure can be obtained by adding Mo, the first
As shown in the figure, there is a tendency for the elongation to be low and the retractability to be high, which may limit the properties or shape of the cast product. Note that the tjSi diagram shows the relationship between Mo and Ni weight % and elongation, and φ5oIIl! l Maru Azusa Gara J
An IS4 tensile test piece was cut out and the elongation was measured.

An object of the present invention is to provide a spheroidal graphite cast iron that stably forms the base structure of a cast product into bainite and retained austenite mm, has high elongation and impact values, and has low tensile properties, and a method for producing the same. .

The reason why C is limited to 03.0 to 4.0% in the present invention is that
．． If it is less than 0%, not only will defects in the cast product, especially shrinkage cavities, increase, but also cementite will remain, which is undesirable. If it exceeds 4.0%, Kischeg graphite will precipitate and the strength will drop significantly.

If Si is less than 1.5%, cementite will precipitate and if Si is less than 1.5%, cementite will precipitate.
If it exceeds %, it may cause the promotion of quiche graphite or decrease the toughness.

If Mn is less than 0.3%, it is difficult to achieve complete bainite and retained austenite, 11m, without increasing the amount of Ni added, but this Ni is expensive, causing an economic disadvantage. When Mn exceeds 0.5%, the tendency of carbide growth increases, and segregation in the structure increases, resulting in elongation and a decrease in i-impact value.

1) If it exceeds 0.06%, the amount of Stegate crystallized increases and the impact value decreases.

When S exceeds 0.02%, spheroidization of graphite is inhibited.

If Cu is less than 0.3%, the hardenability is poor, and if it exceeds 1.5%, the effect remains the same, so from an economic standpoint, it is preferable to set the upper limit to 1.5%.

N1 is added as necessary, but if it is less than 0.7%, the wall thickness will exceed φ501Il111, or even if it is less than that, it will be a stable mixture of bainite and retained austenite in the case of castings with complex shapes. Unable to obtain tissue;
become economically disadvantageous.

When Cr exceeds 0.10%, cementite tends to precipitate.

Furthermore, if Mg is less than 0.02%, it is difficult to achieve spheroidization of graphite, and if it exceeds 0.06%, cementite tends to precipitate.

For the above reasons, the range of components of various elements is limited.

Next, the heat treatment conditions will be described.

First, when austenitizing, the temperature is lower than 850℃,
Alternatively, since elongation decreases at temperatures higher than 950°C, the temperature is limited to 850 to 950°C.

If the holding time for austenitization is less than 0.5 hours, it is difficult to completely austenitize, and if it exceeds 4.0 hours, the austenite crystals become coarse and the tensile strength decreases, which is economically disadvantageous. .

Furthermore, even if the holding temperature during quenching is lower than 250°C, it will elongate and the impact value will drop sharply. It stretches even at temperatures higher than 450°C, and the impact value also decreases.

Furthermore, if the holding time of the austempering treatment is less than 1.0 hours, the bainite transformation will not be completed completely, and if it exceeds 4.0 hours, the bainite transformation will be retained even after the completion of the bainite transformation, and no effect can be expected. It is economically disadvantageous.

Example (1) The influence of Ni content and wall thickness on the matrix structure of a cast product
It is shown in the fSi table. The detailed dimensions of the test piece are tIS.
Shown in Figure 2.

Table 1 Note: X... Perlite remaining O...Bainite + retained austenite example (2) The relationship between austenitization temperature and elongation is shown in the m3 diagram.

In the figure, the case of Ni 2.0% is shown by a solid line, and the case of Mo 0.3% is shown by a broken line.

Example (3) The relationship between holding temperature and elongation during rapid cooling is shown in FIG. In the figure, the case of Mo2.0% is shown by a solid line, and the case of Mo0.3% is shown by a broken line.

Example (4) 1. Chemical components The chemical components of Samples 1 and 2 are shown in Table 2.

fjS2 table 2. Heat treatment The heat treatment shown in Figure 155 was performed.

3. Mechanical properties As shown in Table 3.

Microscopic micrographs (X400) of Tissue Sample 1.2 in Table 3 are shown in FIGS. 6 and 7.

As is clear from the above explanation, the present invention can stably obtain a matrix structure in which bainite and retained austenite are mixed regardless of the wall thickness of the cast product, and has a higher elongation than the Mo-added same-mix paper n product. , a spheroidal graphite cast iron with low impact value and low tensile properties, and a method for producing the same, which has extremely excellent industrial effects.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between Mo and Ni weight % and elongation, m
Figure 2 is a plan view of the test piece, Figure 3 is a diagram showing the relationship between austenitizing temperature and elongation, Figure 4 is a diagram showing the relationship between holding temperature during cooling and elongation, and Figure 5 is a heat treatment diagram.
6.7 Figures are micrographs showing the metal structure.6 Agent Patent Attorney Takashi Honma/~/. Next! Fox No. 2 Fig. 3 Fig. 4 260 Next ~ Fig. 5 Fig. 1 + “4 $I17θ) Fig. 7 (X wa W)

Claims (1)

[Claims] 1. 3.0-4.0% C by weight, 1. 5-3.0% S
i, 0.30-0.45% Mn, 0.06% or less P, 0
．． 0.2% or less S, 0.3-1.5% Cu. 0.7-3.5% Ni, 0.10% or less Cr, 0°02
Spheroidal graphite cast iron consisting of ~0.06% Mg, residual iron, graphite, bainite, and retained austenite. 2, weight% t' 3, 0-4, 0% C, 1, 5-
3.0%Si, 0.30-0.45%Mn, 0.06%
P below 0.02% S, 0.3-1.5% Cu. 0.7-3.5% Ni, 0.10% or less Cr, 0°02
Cast iron consisting of ~0.06% Mg, residual iron, 850-9
At 50°C t'0.5-4.0, it is kept in the dark to austenite, and then rapidly cooled from the above temperature at a cooling rate that does not cause pearlite transformation to an appropriate temperature of 250 to 450°C,
°1 at the appropriate temperature. A method for producing spheroidal graphite cast iron, which comprises holding it for 4.0 hours and then cooling it to form a structure of graphite, bainite, and retained austenite.