JPS6026609A - Production of cv graphite cast iron - Google Patents

Abstract

PURPOSE:To control the amt. of Mg and to obtain easily a CV graphite cast iron having a good characteristic by selecting the amt. of the alloys to be added and the elapsed time in the stage of adding an Fe-Si-Mg alloy to a molten base metal having a prescribed compsn. then adding Fe-Si thereto. CONSTITUTION:Silicon steel plate scrap, low-S carburized material and Fe-Si are melted in the remaining molten metal corresponding to FC15 and the molten metal is then desulfurized by using a low frequency induction furnace by which the molten base metal for a spheroidal graphite cast iron consisting of 3.6- 3.9wt% T.C, 1.4-1.6% Si, 0.3-0.4% Mn, 0.044-0.057% P, 0.02-0.03% S and the balance Fe is produced. An Fe-Si-Mg alloy is added at 0.4-0.75% to such molten base metal, then Fe-Si is brought into contact therewith. The lapsed time after the inoculation is selected from the region II of the figure showing the relation between the amt. of the alloy to be added and the elapsed time. The amt. of the remaining Mg and S after the alloy treatment is selected in the range II between the straight lines A and B of the figure showing the relation between the amt. of the remaining Mg and the amt. of the remaining S. The control range of the remaining Mg is thus widened and the appearance of CV graphite is quantitatively known.

Description

[Detailed Description of the Invention] The present invention relates to a method for producing compacted vermicular graphite 1J iron (hereinafter referred to as C-■ graphite cast iron), in particular, the composition, temperature, and treatment of devalued molten metal in low-frequency induction furnace melting. Using Japanese molten metal for spheroidal graphite cast iron with small fluctuations,
The present invention relates to a method for easily producing C■ graphite cast iron by processing the 'e-8i-Mg alloy.

Generally, 0.04% residual Mg is sufficient for molten cast iron with few impurities to spheroidize graphite, but 0.06% residual Mg is required in molten cast iron with many impurities.

If the molten metal subjected to spheroidization treatment with Mg is held without being poured into a mold, Mg escapes from the molten metal over time, causing a so-called fading phenomenon, and the residual Mgt rapidly decreases. The longer the molten metal is held, the less the graphite becomes spheroidized. However, due to the influence of a small amount of Mg, graphite with a rounded tip appears. This cast iron is compacted vermicular graphite cast iron (C.

■・Graphite cast iron). This C1■ graphite cast iron is
Although it is inferior to spheroidal graphite cast iron in terms of tensile strength and elongation, it is much better than flake graphite cast iron.It is inferior to flake graphite cast iron in terms of vibration damping ability and thermal conductivity, but is superior to spheroidal graphite cast iron. It is something.

Conventionally, when the above-mentioned CV graphite cast iron is produced on-site by a treatment method with the addition of a small amount of Fe-8t-Mg alloy, other alloys such as Fe-Si-Mg-Ti or R
When using EM-Mg alloys as molten metal processing agents, it is said that the tolerance range for residual Mgt relative to Si present in the source metal must be controlled narrowly, and this range is usually The residual Mg weight % (hereinafter, all % indicates weight %) is 0.005%.

However, in actual operation, the temperature of the molten metal during treatment, the amount of molten metal processed, and the oxygen and sulfur content vary, so if the residual Mg amount is controlled within the narrow range described above, if the S content is slightly high, it will not be possible to convert the molten metal into spheroidal graphite cast iron. On the other hand, when the S content is high, flake graphite cast iron becomes extremely brittle, and therefore, although this treatment method is simple and economical, it has not been put into practical use.

Furthermore, even if Cv graphite cast iron is obtained by pouring the molten metal immediately after the treatment by adding an amount of Fe-81-Mg alloy corresponding to the S content of the molten metal, the fading phenomenon caused by the change in the amount of residual Mg over time will cause However, the actual situation is that there is no quantitative understanding of how long it takes for the cast molten metal to turn into CV graphite cast iron over time after treatment. The purpose of the present invention is to provide a method for efficiently manufacturing CV graphite cast iron that has excellent mechanical properties by solving the problems of the conventional manufacturing method described above. It is.

The gist of the present invention is to use a low frequency induction furnace to
5 equivalent residual, silicon steel plate layer, low S recarburizer, Fe-
8t was charged and melted, a desulfurizing agent was added to the obtained molten metal, and T
, C: 3.6-6.9% by weight, Si: 1,4-1.6% by weight, Mn: 0°3-0.4% by weight, p: o, 044-
0.051%, S: 0.02 to 0.05% by weight, balance F (11). 0.4
~0.75 wt% added and then contacted with Fe-8i,
The elapsed time after the inoculation is shown in the relationship diagram between alloy addition amount and elapsed time in the addition range of the Fe-81-Mg alloy (
Figure 3) is a relationship diagram between the residual average amount selected from the [[
The range between the A line and the B line (I
f) A method for producing CV graphite cast iron.

The details of the present invention will be described below based on the findings of Examples.

The present invention is characterized by using a low-frequency induction furnace, and silicon steel plate scraps and Fe-8i are suitably mixed and melted in the remaining hot metal equivalent to FC-15 in the furnace, and the melt is poured into a ladle at a temperature of 1520±. 10℃
Desulfurization treatment is performed to remove the low S molten metal. Desulfurization cannot be performed in molten metal containing Si, so soda ash, lime, or
Desulfurize using calcium carbide, etc. Calcium carbide CaC is preferable from the viewpoint of desulfurization efficiency, and its addition amount is 0.5% based on the molten metal.The higher the treatment temperature, the faster the desulfurization reaction proceeds, so the above range of tapping temperature is preferable.

Thus T-03, 6-6.9% Si: 1.4
~1.6%, Mn: 0.3~0.4%P: 0.
044~0.057%, st:o, oz~0.06%
A source hot water having a composition range in which the remainder is Fe is melted. In this case, the silicon steel plate layer plays an important role.

The present inventor added 4.5% Fe to this source water with a Mg-containing lid.
-81-Mg alloy is used as a molten metal processing agent and the amount added is varied, and FeSi (S1: 50%) is used to adjust the number of graphite grains, prevent chilling, and change pearlite to ferrite. Residual Mg after 5g addition glazing and inoculation
As a result of examining the relationship between the amount and the S content, the attached Figure 1 was obtained. The amount of FeFe-8t-alloy added was 0.8.

The area narrowed between straight line A, which has a slope of approximately 45'', and straight line B, which has a slope of 2 degrees above straight line A, indicates the amount of residual Mg and the amount of S to realize CV graphite cast iron.

In addition, even when alloy addition i is 0.54 to 0.67%, it is 0.6
% addition was obtained. In FIG.

b1 point is Mg0.03 and 0y for 30.03%
015% a2 b2 point is Mg0 for SO, 02%
．． 02 and 0.01%, 0 point indicates 0 for both S and Mg.

In this case, within the range of S content t0.02-0.06%, the allowable range of residual M・g amount is 0.01-0.06%. p1 Residual Mg due to molten metal temperature, processing amount, processing method, etc.
Even with variations in the amount, the average allowable range is 0.015% for an S content of 0.02%, which is three times the residual Mg content compared to conventional methods.
Amount tolerances were obtained.

Also, from Figure 1, if the S content is 0.06% or more, F
If the addition amount of e-81-Mg alloy is 0.8 or more, CV
It is assumed that graphite cast iron can be obtained, and that the allowable range of residual Mg content will also expand, but normally the S content of the source water for producing Cvv lead cast iron should be 0.03% or less. Even if Cvv lead cast iron could be obtained at a certain experimentally known and reasonable S content, increasing the amount of alloying added thereto would not be an economical method. The numerical values (in the figure) are tensile strength values, which are appropriate in the range of 64 to 41 figf/rrrIR for Cvv lead cast iron.

Next, the same lli' e-8i-Mg alloy treatment as described above was performed, and the relationship between the elapsed time after 5% inoculation of pe-8iO and the physical properties of the obtained cast iron was determined by varying the amount of alloy added. As a result of the test, the results shown in Figure 2 were obtained.

Figure 2 (a), (b), and (c) show the elapsed time, pouring temperature (°C), tensile strength, millet gf/rpm, respectively. ), Hardness HB
) and elongation (%). △ in the diagram
, ○, marks indicate the FeFe-8t- addition amount of 0 and 7.0, respectively.
, 6 and 0.5 inch, the X mark indicates alloy addition t0.6
%, which indicates the value at the time of Y block casting.

In Figure 2, when 0.7% of alloy is added, C starts to increase after 15 minutes.
−■・, and before that it was spheroidal graphite cast iron,
When 0.6% and 0.5% were added, Cv conversion occurred immediately after treatment, and in the case of 0.6% addition, a good Cv conversion waiting time range was within 20 minutes, and eutectic graphite appeared after 60 minutes. . 0.
In the case of addition of 50% of cementite, a good range was within 15 minutes, and free cementite appeared after 60 minutes.

Therefore, in view of the 7 aiding phenomenon caused by changes in the amount of residual Mg over time, addition of 0.4 to 0.75%, preferably 0.6%, can be said to be the most suitable addition amount for producing Cvv lead cast iron. Still, Figure 2 (b) shows that the addition amount of 0.6 g is an appropriate value for YV graphite cast iron.

Furthermore, more detailed experiments were conducted, and the relationship between the amount of alloy added and the elapsed time was obtained as shown in Figure 6.

Points a to h in the figure indicate the Fe-81-Mg alloy addition amount and good C.
The table below shows the limit of the elapsed time to form V-graphite cast iron, and the relationship between the amount added and the elapsed time.

a bed e fgh Addition amount (%) 0.750.70.60.50.450
．． 40.60.7 Elapsed time (minutes) 302520151
0 0 0 In Figure 15, (1) shows the spheroidal graphite cast iron area, and the shaded area (If) is the Cv graphite cast iron area, and its mechanical properties include tensile strength of 30 to 4549 f 71 m2 elongation 5
-7chi, hardness Hm': 160-180. (IID is flake graphite cast iron. In other words, within the range of the above-mentioned alloy addition fi0.4 to 0.75%, this sixth
Good Cv can be obtained by selecting the elapsed time from the addition amount and elapsed time Φ that are within the range marked in the figure, and manufacturing by alloying.
v-lead cast iron will be obtained.

A typical cast iron structure photograph (200x magnification) of Cvv lead cast iron obtained by adding 0.6% of Fe-81-Mg alloy is shown as reference photograph A1. This photo clearly shows that CV graphite is crystallized in a mixed base of ferrite and pearlite.

In summary, the method for producing CV graphite cast iron according to the present invention expands the control range of the amount of residual Mg compared to the conventional method, and quantitatively understands the appearance of CV graphite, making it an extremely useful invention. It is. Examples will be described below.

Example 1 Using a 3-ton capacity low-frequency induction furnace, residual metal equivalent to FC15, silicon steel plate layer, waste pig iron, low S recarburization material of electrode graphite layer, Fe
-8t (Si: 50%) alloy is appropriately blended to create CaC0,
A base metal for spheroidal graphite cast iron which is desulfurized by adding 5% of spheroidal graphite is prepared. In this case, the composition of the source water is controlled to be within the following range. In this case, the silicon steel plate layer plays an important role.

T, C,: 3.6-3.9%, Si: 1.4-
1.6%, Mn: 0.3-0.4%, P: 0.044
~0.057%, Si: 0.02~0.06% balance F
e 0.5, 0.6, 0.8% by weight of Fe-81-Mg alloy containing 4.5% Mg was added to the above source water,
Inoculated with 0.5% Fe-8i (Si: 50%) alloy and approx.
If sampled after 1 minute, residual Mgt and S after treatment
Figure 1 was obtained as a relationship with the content.

In other words, when the addition amount is 0.8% (・mark), it becomes spheroidal graphite cast iron, when it is 0.5% (mm), it becomes flaky graphite cast iron, and when 0.6 inch (○ mark) is added, it becomes CV graphite cast iron (hatched graphite cast iron). part) was obtained stably.

Example 2 A source hot water was obtained in the same manner as in Example 1, and Mg4.
．． 5% FeFe-8t-alloy at 0.5.0.
6.0.7tft&% added and further Fe-8i0.5
As a result of examining the relationship between the elapsed time after % inoculation and the physical properties of the cast iron obtained, the results shown in FIG. 2 were obtained.

Example 6 Furthermore, Fe-81 at a pouring temperature of 1380 to 1480°C
-The relationship between the amount of Mg alloy added and the elapsed time was investigated to find a range that satisfies the mechanical properties of CV graphite cast iron, and the results are shown in FIG.

In Figure 6, the Sochi region surrounded by curves A' and B' is the CV graphite cast iron region (n), and its mechanical properties are 60 to 45 f/wn2 in tensile strength and elongation. was 5-7%, and hardness HB was 160-180. Note that (I) is a spheroidal graphite cast iron region (2) is a flaky graphite cast iron region.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the amount of residual Mg and the S content after treatment for each addition amount of FeFe-8t-alloy of the present invention.
The figure shows Fe-8 with the addition of the Fe-81-Mg alloy of the present invention.
Figure 6 is a graph showing the relationship between the elapsed time immediately after inoculation of Cv graphite cast iron and the physical properties of the obtained cast iron. It is a graph showing the relationship with elapsed time. Agent Patent Attorney Sanro Kimura

Claims (2)

[Claims] (1) Using a low-frequency induction furnace, charge and melt a silicon steel sheet layer, low S recarburizer, and Fe-8i into the remaining molten metal equivalent to FC15 in the furnace, and add a desulfurization agent to the obtained molten metal. Add, T, C: 3.
6-3.9% by weight, Si: 1.4-1.6% by weight
, Mn: 0.3-0.4 Weight L P: 0.04
4 to 0.057 s, S: 0.02 to 0.03 Amount of molten metal for spheroidal graphite cast iron consisting of balance Fe, and 0.4 to 0.4 to 0.4 of Mg-containing FeFe-3t-alloy 0.
75% of the Fe-31-Mg alloy, then inoculated with Fe-8i, and the elapsed time after the inoculation is shown in (Figure 6) of the relationship between alloy addition amount and elapsed time within the addition range of the Fe-31-Mg alloy. It), and the residual Mg amount and S amount after alloying treatment are 1. The range (II
) A method for producing C0■ graphite cast iron. (2) Before melting the base metal of the molten metal for the spheroidal graphite cast iron, charge the waste pig iron and an electrode graphite layer as a low S recarburizing material, and tap the hot metal into a ladle at a tapping temperature of 1520 ± 10°C, 0.5% of CaC was added as a desulfurizing agent to this, and a base metal with the above composition was melted, and Fe-31-M with a Mg content of 4.5
Fe-8t (
0.5% by weight of St: 50% by weight) was inoculated into the base water, and the pouring temperature was increased to 1680-1 within 20 minutes after adding the alloy.
Claim 1, characterized in that the casting is performed at 480°C.
C and V described in Section. Method of manufacturing graphite cast iron.