JPH10121187A - Free cutting ferrous member and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferrous casting having free cutting property. SOLUTION: This ferrous casting has a heat treated structure having a matrix V and many massive fine α-grain groups VI dispersed in the matrix V, and further, graphite IX and graphite X in respectively great numbers are dispersed in the matrix V and the fine α-grain groups VI, respectively. When A represents the area ratio of the graphite IX and graphite X in the whole heat treated structure and B represents the area ratio of the graphite X in all the fine α-grain groups VI, the ratio between both area ratios A, B is set at a value satisfying B/A>=0.138. By this method, the difference between the machinability of the matrix V and that of respective fine α-grain groups VI can be reduced and the machinability of the ferrous casting can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a free-cutting Fe-based member and a method for producing the same.

[0002]

2. Description of the Related Art Heretofore, as a free-cutting Fe-based member, a member made of flaky graphite cast iron has been known.

[0003]

However, flaky graphite cast iron has a drawback that its mechanical properties are lower than that of steel. Therefore, in order to obtain mechanical properties equivalent to steel, means for spheroidizing graphite and increasing the hardness of the matrix have been adopted. However, if such means are employed, the machinability of the Fe-based member is reduced. It will be greatly damaged.

[0004] This is because graphite precipitated in crystal grains by the spheroidizing treatment aggregates at the crystal grain boundaries, and therefore, no or very little graphite is present in the crystal grains. This is because the machinability of the matrix surrounding the grains is good, while the machinability of the crystal grains is poor, resulting in a large difference in machinability between the matrix and the crystal grains.

[0005]

SUMMARY OF THE INVENTION The present invention provides a method for dispersing a specific amount of graphite in a cluster of fine α grains corresponding to crystal grains, that is, a clump formed by a collection of fine α grains. It is an object of the present invention to provide a free-cutting Fe-based member having improved machinability.

[0006] In order to achieve the above object, according to the present invention,
A matrix and a group of fine α particles forming a large number of agglomerates dispersed in the matrix, and the matrix and each fine α particle group each include a heat treatment structure in which a large number of graphites are dispersed, and the entire heat treatment structure Is A, the area ratio of graphite in all the fine α-particle groups is B, and the ratio B / A of both area ratios A and B is B.
A free-cutting Fe-based member having /A≧0.138 is provided.

The mass of fine α-particles is formed by the transformation of primary γ-particles at the eutectoid temperature Te, and the graphite in the fine α-particles precipitates from the primary γ-particles. It was done. Further, the group of fine α grains contains cementite. By specifying the amount of graphite in all of the massive fine α-particle groups as described above, it is possible to improve the machinability of those fine α-particle groups and reduce the difference in machinability between them and the matrix. It is. However, B / A <0.1
At 38, the machinability of the Fe-based member deteriorates.

[0008] Both area ratios A and B of graphite can be determined by polishing the test piece and etching without using an image diffraction apparatus (I).
P-1000PC, manufactured by Asahi Kasei Corporation).

Here, the area of the matrix is defined as C.
Further, the area of each group of fine α grains is d ₁ , d ₂ , d ₃ ... D
_Assuming that _n , the sum D of the areas of all the fine α-particle groups is D = d ₁
+ A _{d 2 + d 3 ...... + d} n. Further, _assuming that the area of each graphite in the matrix is e ₁ , e ₂ , e ₃ ... En, the sum E of the area of all the graphite in the matrix is E
Becomes _{E = e 1 + e 2 +} e 3 ...... + e n. Further, the area of all graphite in each group of fine α grains is represented by f ₁ , f
_2, when f ₃ ...... f _n, the sum F of the area of the graphite in the entire fine α grain group becomes _{F = f 1 + f 2 +} f 3 ...... + f n.

Therefore, the area ratio A of graphite in the entire heat-treated structure is A = {(E + F) / (C + D)} × 10
It is expressed as 0 (%). In addition, the area ratio B of graphite in the whole group of fine α grains is expressed as B = (F / D) × 100 (%).

It is another object of the present invention to provide the above-mentioned manufacturing method capable of easily mass-producing the Fe-based member.

According to the present invention, in order to achieve the above object,
When the eutectoid temperature of the Fe-based material after the quenching process is Te, the heat treatment temperature T is set to Te ≦ T ≦ Te +
A method for producing a free-cutting Fe-based member is provided, in which heat treatment is performed at 170 ° C. and the heat treatment time t is set to 20 minutes ≦ t ≦ 90 minutes.

[0013] The Fe-based material has a solidified structure by rapid cooling. When such an Fe-based material is subjected to a heat treatment under the above conditions, a free-cutting Fe-based member having the above-described configuration can be obtained.

[0014] At least one of network cementite and dendritic cementite is liable to precipitate in the solidified structure, which causes a reduction in mechanical properties, particularly toughness, of the Fe-based member. Therefore, conventionally, such a Fe-based material is subjected to a heat treatment to completely decompose the reticulated cementite and the like to graphitize. However, when the graphitization of network cementite or the like is completely performed, there is a problem that the Young's modulus of the Fe-based member is reduced, and the heat treatment temperature is high, so that it is not possible to meet the demand for energy saving.

When the Fe-based material is subjected to a heat treatment under the above conditions, it is possible to cut and refine the network cementite or the like. An Fe-based member having the above-mentioned heat-treated structure and having achieved a finely divided fracture of network cementite or the like has a Young's modulus and a fatigue strength substantially equal to those of carbon steel for machine structures, even if it is a cast product.

However, when the heat treatment temperature T is T <Te, the above-mentioned heat-treated structure cannot be obtained, and it is not possible to carry out the fragmentation and refining of network cementite or the like. On the other hand, T> T
At e + 170 ° C., agglomeration of graphite from within the group of fine α grains to the boundary easily occurs, and graphitization of network cementite or the like proceeds. The heat treatment temperature T is preferably T> Te +
The temperature is 100 ° C., whereby a decrease in the Young's modulus of the Fe-based member can be suppressed. When the heat treatment time t is t <20 minutes, such a metal structure cannot be obtained. On the other hand, when the heat treatment time t is t> 90 minutes, the aggregation and the graphitization proceed.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A pressure casting apparatus 1 shown in FIG.
It is used to obtain an Fe-based casting (as-cast product) as an Fe-based material under application of a thixocasting method using an e-based casting material. The pressure casting apparatus 1 includes a fixed mold 2 and a movable mold 3 having vertical mating surfaces 2a and 3a, and a casting molding cavity 4 is formed between the two mating surfaces 2a and 3a. A chamber 6 in which the semi-molten Fe-based casting material 5 is placed in the fixed mold 2 is formed, and the chamber 6 communicates with the cavity 4 via a gate 7. Also fixed mold 2
In addition, a sleeve 8 communicating with the chamber 6 is horizontally attached, and a pressure plunger 9 inserted into and removed from the chamber 6 is slidably fitted to the sleeve 8. The sleeve 8 has a material insertion port 10 in the upper part of the peripheral wall.

Table 1 shows the composition of the Fe-based casting material. This composition belongs to the Fe-C-Si hypoeutectic alloy. P and S in Table 1 are unavoidable impurities.

[0019]

[Table 1]

FIG. 2 shows a phase diagram of an Fe-C-2% by weight Si alloy. The eutectoid temperature Te of this alloy is Te で 770 ° C.

In casting an Fe-based casting, the Fe-based casting material was induction-heated to 1200 ° C. to prepare a semi-solid Fe-based casting material in which a solid phase and a liquid phase coexist. The solid fraction R of this material was R = 70%.

Next, in the pressure casting apparatus 1 shown in FIG.
Controlling the temperature of the fixed and movable molds 2 and 3 and installing the semi-solid Fe-based casting material 5 in the chamber 6 thereof;
The pressurizing plunger 9 was operated to fill the cavity 4 with the Fe-based casting material 5. In this case, the filling pressure of the semi-solid Fe-based casting material 5 was 36 MPa. By holding the pressurizing plunger 9 at the end of the stroke, a pressing force is applied to the semi-molten Fe-based casting material 5 filled in the cavity 4, and the semi-molten Fe-based casting material 5 is pressed under the pressure.
Was solidified to obtain an Fe-based casting (as-cast product).

FIG. 3 is a photomicrograph showing the metal structure (solidification structure) of the as-cast Fe-based product, and FIG. As is clear from FIGS. 3 and 4, according to the thixocasting method, it is possible to obtain an as-cast product having a dense metal structure without pores on the order of microns. In FIGS. 3 and 4, the quenching from the semi-molten state by the mold causes the reticulated cementite II to reach the boundary between the primary crystal γ grains, in this case, the mass I formed of the martensitic α needles and the residual γ. Is present, and a layered structure of dendritic cementite III and a part IV composed of an α phase and a residual γ phase is observed in a eutectic part existing outside the massive part I.

Next, the as-cast Fe-based product is
Heat treatment was performed under the conditions of heat treatment temperature T = 770 ° C. (eutectoid temperature Te), heat treatment time t = 60 minutes, and air cooling to obtain Example 1 of an Fe-based casting as an Fe-based member. Further, the as-cast Fe-based products were subjected to a heat treatment at different heat treatment temperatures T and / or heat treatment times t to obtain Examples 2 to 15 of Fe-based castings. Table 2 shows the heat treatment conditions of Examples 1 to 15.

[0025]

[Table 2]

FIG. 5 is a photomicrograph showing the metal structure (heat treated structure) of Example 1, and FIG. In FIGS. 5 and 6, a matrix V and a large number (four in the illustrated example, four distinct ones are selected) dispersed in the matrix V are recognized as a group of fine α particles VI. Matrix V is composed of α-phase VII and a large number of cementites VIII obtained by fragmentation and refining of network cementite II and the like. ing. In addition, each fine α group
Many cementite XI are dispersed in VI.

Next, for Examples 1 to 15, both area ratios A,
Determine the specific B / A of B, also perform cutting tests using bytes to determine the maximum flank wear width V _B. The cutting test conditions are as follows. Blade: T for carbide tip
With iN coating; speed: 200 m / min
Feed: 0.15 to 0.3 mm / rev .; cut: 1 mm;
Cutting oil: water-soluble cutting oil. Table 3 shows both the area ratio A, the ratio of B B / A and the maximum flank wear width V _B regarding Examples 1 to 15.

[0028]

[Table 3]

FIG. 7 is a graph of the relationship between the two area ratio A, the ratio of B B / A and the maximum flank wear width V _B based on Table 3. As is clear from FIG. 7, as in Examples 1 to 9, the ratio B / A of the two area ratios A and B is set to B / A ≧ 0.138.
The maximum flank wear width V of the tool
_B can be significantly reduced and therefore Examples 1-9
It can be seen that has easy cutting properties. Incidentally, the maximum flank wear width V _B is the ratio B / A is substantially constant at a B / A ≧ 0.2 The upper limit of the ratio B / A is set to B / A ≒ 0.2.

FIG. 8 shows Examples 1 to 5, 10, and 15 in Tables 2 and 3 in which the heat treatment time t was set to t = 60 minutes.
6 is a graph showing a relationship between a heat treatment temperature T and a ratio B / A of both area ratios A and B. As is apparent from FIG.
5, the heat treatment temperature T is set to 770 ° C. (Te) ≦ T ≦ 940 ° C. (Te + 1) during the heat treatment time t = 60 minutes.
70 ° C.), the ratio B / A of both area ratios A and B is set to B
/ A can be ≧ 0.138.

FIG. 9 shows examples 2, 6, 9, 11, 12 in which the heat treatment temperature T was set to T = 780 ° C. and examples 3, 7, 8, 13, 13 in which T = 800 ° C. in Tables 2 and 3. 14 is a graph showing the relationship between the heat treatment time t and the ratio B / A of the two area ratios A and B. As is clear from FIG. 9, at the heat treatment temperature T = 780 ° C. as in Examples 2, 6, and 9, or at the heat treatment temperature T = 800 ° C. as in Examples 3, 7, and 8, each of the heat treatment times t is 20 minutes ≦ t ≦ If it is set to 90 minutes, the ratio B / A of both area ratios A and B is B / A ≧
It can be 0.138.

Next, Young's modulus, fatigue strength and hardness of Examples 1, 3, 4, 5, and 15 were measured. Table 4 shows the measurement results. Table 4 also shows the area ratio A of graphite in the entire heat-treated structure of Example 1 and the like, and the Young's modulus of a steel forged product as a comparative example.

[0033]

[Table 4]

As apparent from Table 4, Examples 1, 3, 4,
5 has a Young's modulus close to that of a steel forged product, has a fatigue strength higher than that of a steel forged product, and is equivalent to that of a steel forged product.
Or it is understood that it has hardness of more than that.

FIG. 10 shows examples 1, 3 based on Tables 2 and 4.
7 is a graph showing the relationship between the heat treatment temperature T for 4, 5, and 15, the Young's modulus, and the area ratio A of graphite in the entire heat treated structure. From FIG. 10, it can be seen that the area ratio A of graphite increases as the heat treatment temperature T increases, and the Young's modulus decreases.

In the Fe—C—Si—Mn hypoeutectic alloy, C and Si are related to the eutectic amount.
% Or less, the C content is 1.8% by weight ≦ C ≦
2.5% by weight, and the Si content is 1.4% by weight ≦ Si
≦ 3.0% by weight. However, when the C content is C <1.8% by weight, the casting temperature (the temperature of the semi-solid Fe-based casting material,
The same shall apply hereinafter), so that the advantage of thixocasting is diminished. On the other hand, when C> 2.5% by weight, the amount of graphite increases, so that the heat treatment effect of the Fe-based casting is small, and therefore its mechanical properties are improved. I can't let it. When the Si content is Si <1.4% by weight, C <1.
As in the case of 8% by weight, the casting temperature rises. On the other hand, when Si> 3.0% by weight, silicoferrite is generated, so that the mechanical properties of the Fe-based casting cannot be improved.

Mn functions as a deoxidizing agent and is necessary for producing cementite, and its content is set to 0.3% by weight ≦ Mn ≦ 1.3% by weight. Where Mn
When the content is Mn <0.3% by weight, the deoxidizing effect is reduced, so that defects caused by entrapment of oxides and bubbles due to oxidation of the molten metal are liable to occur. On the other hand, when Mn> 1.3% by weight, cementite is used. Since the crystallization amount of [(FeMn) ₃ C] increases, it becomes difficult to reduce the large amount of cementite by heat treatment, and the machinability of the Fe-based casting decreases.

The solidified structure as shown in FIG. 3 is obtained not only by thixocasting but also by subjecting an Fe-based sintered body to a heating and quenching treatment. Therefore, the present invention is not limited to Fe-based castings.

[0039]

According to the first aspect of the present invention, it is possible to provide a free-cutting Fe-based member having the above-described structure and having greatly improved machinability.

According to the third aspect of the present invention, it is possible to easily obtain an Fe-based member having free cutting properties and excellent mechanical properties.

[Brief description of the drawings]

FIG. 1 is a sectional view of a pressure casting apparatus.

FIG. 2 shows a phase diagram of an Fe—C-2 wt% Si alloy.

FIG. 3 is a micrograph showing a metal structure (solidification structure) of an as-cast product.

FIG. 4 is an essential part schematic diagram of FIG. 3;

FIG. 5 is a micrograph showing the metal structure (heat-treated structure) of Example 1 of an Fe-based casting.

FIG. 6 is an essential part schematic diagram of FIG. 5;

7 is a graph showing the relationship between the two area ratio A, the ratio of B B / A and the maximum flank wear width V _B.

FIG. 8 is a graph showing a relationship between a heat treatment temperature T and a ratio B / A of both area ratios A and B.

FIG. 9 is a graph showing a relationship between a heat treatment time t and a ratio B / A of both area ratios A and B.

FIG. 10 is a graph showing a relationship between a heat treatment temperature T, a Young's modulus, and an area ratio A of graphite in the entire heat treated structure.

[Explanation of symbols]

 V matrix VI Fine α particles IX, X graphite

Claims (3)

[Claims] 1. A matrix (V) and a large number of massive α-particles dispersed in the matrix (V) (VI)
And the matrix (V) and each of the fine α-particle groups (VI) each include a heat-treated structure in which a large number of graphites (IX, X) are dispersed, and the graphite (IX, X) in the entire heat-treated structure is provided. ) Is A, and the group of fine α grains (V
I) When the area ratio of graphite (X) in the whole is B,
A free-cutting Fe-based member, wherein the ratio B / A of the two area ratios A and B is B / A ≧ 0.138. 2. 1.8% by weight ≦ C ≦ 2.5% by weight,
4% by weight ≦ Si ≦ 3.0% by weight, 0.3% by weight ≦ Mn ≦
2. The free-cutting Fe-based member according to claim 1, comprising 1.3 wt% and the balance Fe containing unavoidable impurities. 3. An Fe-based material having undergone a quenching process,
When the eutectoid temperature of the system member is Te, the heat treatment temperature T is set to T
A method for producing a free-cutting Fe-based member, characterized in that heat treatment is performed at e ≦ T ≦ Te + 170 ° C. and a heat treatment time t is set at 20 minutes ≦ t ≦ 90 minutes.