JP3270035B2 - Lead-free mechanical structural steel with excellent machinability and low strength anisotropy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a material having a small mechanical property anisotropy,
The present invention relates to lead-free steel for machine structural use that is excellent in machinability in a wide range of cutting methods and cutting conditions and contains no lead.

[0002]

2. Description of the Related Art With the recent increase in speed and automation of cutting, the machinability of steel materials used for machine structural parts has become more important, and so-called steel with improved machinability has become more important. Demand for cutting steel is growing. Moreover, the required strength of steel materials is becoming stricter. When the strength of the steel material is increased, the machinability deteriorates. That is, in recent years, steel for machine structural use has been required to improve the contradictory properties of high strength and machinability.

At present, as a free cutting steel generally used, there is a steel material containing Pb, S, and Ca. Among these, Pb-containing Pb free-cutting steel has less deterioration in mechanical properties than the basic steel, shows improved chip control in general turning, and includes drilling, tapping, reaming, It has an excellent feature that the tool life such as boring can be extended. Further, Pb free-cutting steel facilitates chip discharge during drilling of a deep hole where (hole depth / drill diameter) ≧ 3, and is excellent in preventing breakage of a tool due to unexpected chip. Further, P, which has these excellent properties by adding other S, Ca, etc. in addition to Pb.
b Various composite free-cutting steels have also been developed.

[0004]

[Problems to be solved] However, the conventional P
There are the following problems with b-containing free-cutting steel. That is, Pb
Is very effective in improving machinability as described above,
Environmentally hazardous substance. For this reason, development of a steel material comparable to a Pb-containing free-cutting steel without containing Pb has been desired in view of increasing interest in environmental issues in recent years.

[0005] On the other hand, there are other free-cutting steels which do not contain Pb conventionally, but these have the following disadvantages, and in many cases they cannot be used as substitutes for Pb-containing free-cutting steels. For example, S free-cutting steel to which S is added exhibits an improvement effect of extending the tool life in a relatively wide range of cutting work, but has poorer chipping property than Pb free-cutting steel. In addition, when S is contained, MnS existing as inclusions is stretched during hot rolling or hot forging, so that mechanical properties such as impact strength decrease as approaching a direction perpendicular to the rolling direction.
There is a problem of strength anisotropy. Therefore, it is necessary to suppress the S content as much as possible in steels for components for which impact strength is important, and as a result, sufficient machinability may not be obtained.

[0006] In addition, Ca deoxidized free-cutting steel in which oxide inclusions in the steel are reduced in melting point by Ca deoxidation has almost no effect on the strength characteristics of the steel material, and the service life of the cemented carbide tool in the high-speed cutting region is reduced. Shows a remarkable prolongation effect. However, Ca-deoxidized free-cutting steel has little effect on improving machinability other than the life of carbide tools, and is generally used in combination with S or Pb to obtain all-round machinability. It is a target.

[0007] Unlike conventional Ca deoxidized free-cutting steel, the strength anisotropy, which is a disadvantage of S free-cutting steel, is improved by uniformly dispersing and distributing inclusions in the steel by adding Ca. As an example of improved machinability, there is a steel material described in Japanese Patent Publication No. 5-15777. In this case, there is no disadvantage such as Ca deoxidized free-cutting steel, but a large amount of S must be added to obtain sufficient machinability. In such a case, it is extremely difficult to produce Ca as a mass-produced steel because the Ca yield is low if Ca is contained in a steel material in a necessary and sufficient amount to control the sulfide form.

Further, as an example aiming at the same effect as that of the above Ca, there is a steel material described in Japanese Patent Publication No. 52-7405. These are one or two of the first group elements of Mg and Ba.
It is a free-cutting steel containing one or more of the second group elements consisting of S, Se, and Te. In this steel, O
Since it is positively added in the range of 0.012%, the fatigue strength may be poor. Further, it is expected that oxides in the steel increase due to the active addition of O, and that the machinability such as drill workability decreases.

The free-cutting steel disclosed in Japanese Patent Publication No. 51-4934 contains one or two of the first group elements of Mg and Ba and one or more of the second group elements of S, Se and Te. And a free-cutting steel containing Ca selectively. However, in this steel, O
It is positively added in the range of 0.01%. for that reason,
The fatigue strength may be poor. Further, it is expected that oxides in the steel increase due to the active addition of O, and that the machinability such as drill workability decreases.

Japanese Patent Laid-Open Publication No. Sho 51-63312 discloses that
A free-cutting steel containing S, Mg and one or more of the elements Ca, Ba, Sr, Se and Te is disclosed. However,
The publication does not specify the specific composition of steel,
Insufficient disclosure of technology. This steel is premised on Al deoxidation, the Al content exceeds 0.02%, and O
There is no limitation on the amount, and the fatigue strength may be poor. Further, it is expected that oxides in the steel increase due to the active addition of O, and that the machinability such as drill workability decreases.

The present invention has been made in view of the above-mentioned conventional problems, and has excellent machinability, strength, and strength not containing Pb and having properties equal to or higher than those of conventional Pb-containing free-cutting steel. An object of the present invention is to provide a lead-free mechanical structural steel having a small anisotropy.

[0012]

According to the first aspect of the present invention, C: 0.10 to 0.65% and Si: 0.03 to 1.
00%, Mn: 0.30 to 2.50%, S: 0.03 to
0.35%, Cr: 0.1 to 2.0%, Al: 0.00
Less than 5%, Ca: 0.0005-0.020%, Mg:
0.0003-0.020%, O: 20ppm
Less than, Ri Do the balance Fe and inevitable impurities, or
A lead-free mechanical structural steel with excellent machinability and low strength anisotropy, characterized by being manufactured by continuous casting .

The most remarkable point in the present invention is that A
l and O contents are reduced to the above specified range, and S
The point is that the content is made higher than a general level, and Mg and Ca are added in combination, and the addition of Pb is completely eliminated.

[0014] The steel for machine structural use is roughly classified into three types of steel, namely, a tempered tough steel, a non-heat treated steel, and a case hardened steel. Therefore, even in the lead-free mechanical structural steel of the present invention, the preferable range of the component range may be slightly different for each of these three types of steel. The reasons for limiting the above components will be described below in the above 3
The preferred range of the steel types will be described first.

C: 0.10 to 0.65%, C is an essential element for securing the strength as steel for machine structural use.
Add 0.10% or more. However, if the content is too large, the toughness and machinability deteriorate due to the increase in hardness.
%. In particular, in the case of tempered tough steel, the content is preferably 0.28 to 0.55%, more preferably 0.32%.
~ 0.48% is good. In the case of non-heat treated steel, it is preferably 0.10 to 0.55%, more preferably 0.35%.
~ 0.50% is good. In case of case hardening steel, it is preferably 0.10 to 0.30%, more preferably 0.12%.
~ 0.28% is good.

Si: 0.03 to 1.00%. Since Si is indispensable as a deoxidizing agent in steel making, the lower limit is 0.03%.
And However, if added excessively, the ductility is reduced, and SiO ₂ , which is a high hardness inclusion, is generated in the steel to deteriorate the machinability. Therefore, the upper limit is set to 1.00%. Si
Is preferably 0.10 to 0.50%, more preferably 0.15% in any of the above three steel types.
~ 0.35% is good.

Mn: 0.30 to 2.50%, Mn is generally an important element for securing the strength, toughness, hot ductility and hardenability of steel. Since it is an element indispensable for the generation of system inclusions, 0.30% or more is added. However, if the amount is too large, the machinability deteriorates due to the increase in hardness, so the upper limit is set to 2.50%. Mn is preferably 0.40 to 2.00 in any of the above three steel types.
%, More preferably 0.60 to 1.50%.

S: 0.03 to 0.35%, S is an element forming sulfide-based inclusions for improving machinability, and at least 0.03% or more for obtaining machinability improving effect. It needs to be added, and the machinability improves as the amount of S increases. However, if the amount is too large, it becomes difficult to control the sulfide form by Ca and Mg, and the impact anisotropy deteriorates.
35%. S is preferably 0.04 to 0.30%, and more preferably 0.08 to 0.20% in any of the above three steel types.

Cr: 0.1 to 2.0%, Cr is added to improve the hardenability and toughness of steel. To obtain the effect, Cr needs to be 0.1% or more. On the other hand, when added in large amounts, the hardness of the work material increases,
To ensure machinability, Cr needs to be 2.0% or less. Cr is preferably 0.10 to 1.50%, and more preferably 0.15 to 1.20%, in any of the above three types of steel.

Al: less than 0.005% . In this lead-free mechanical structural steel, Al
If it is less than 05%, there is a problem in actual manufacturing.
Continuous castability can be greatly improved. That is,
If the Al content is 0.005% or more,
A large amount of CaS is generated in steel, and CaS is used for continuous casting.
The problem is that it accumulates on the nozzle and makes it easier to block it.
is there. This problem is reduced to less than 0.005% of the Al content.
With such restrictions, it can be surely resolved.

Ca: 0.0005-0.020%, Ca
Is a sulfide-forming element together with Mn and Mg,
A composite oxide with Al and Si is also generated, which has an effect of improving machinability and an effect of improving anisotropy of mechanical properties by controlling sulfide morphology. At least 0.00 for that effect
More than 05% is required. Further, the Ca yield at the steel making stage is very poor, and the effect is saturated even if it is contained more than necessary, so the upper limit of Ca is made 0.020%. Ca is preferably 0.00 in any of the above three steel types.
0.05 to 0.0060%, more preferably 0.005%.
05-0.0040% is good.

Mg: 0.0003-0.020%, Mg
Has the same effect as Ca, and when it is present in a composite with Ca, a large effect of improving machinability and an effect of improving anisotropy of mechanical properties can be obtained. To obtain the effect, at least 0.0003% or more is required. On the other hand, the effect is saturated even if it is contained more than necessary, and it is useless, so the upper limit of Mg is set to 0.020%. Mg is preferably in the range of 0.0003 to 0.3 in any of the above three steel types.
0.0060%, more preferably 0.0005%
0.0040% is good.

O: less than 20 ppm O is desirably reduced as much as possible in order to suppress the generation of oxide-based hard inclusions harmful to machinability. O is 20
If it is not less than ppm, the amount of oxide-based hard inclusions increases and the machinability is impaired, and the fatigue strength is reduced. Therefore, it is necessary to make O less than 20 ppm. As for O, there is almost no difference in the preferable range among the above three steel types.

As described above, according to the present invention, the oxide form is restricted by limiting the contents of Al and O as described above, and the S content is made higher than the general level, so that the Ca content is increased.
And Mg in the steel at the same time, it is possible to minimize the impact characteristics, especially the impact anisotropy (strength anisotropy), and to improve the machinability to the same degree as the Pb-containing free-cutting steel. Can be improved. This strength anisotropy and machinability improvement effect is a greater improvement effect than when only one of Ca and Mg is present in the steel material. Furthermore, in the present invention, A
By limiting the contents of l and O as described above, it is possible to obtain not only the effect of improving machinability but also the effect of improving fatigue strength.

[0025]

[0026] It should be most noticeable in the present invention, above
As described above, the Al content is to be reduced to less than 0.005%. And, in this lead-free steel for machine structural use, by making Al less than 0.005%, continuous castability, which is a problem in actual production, can be greatly improved.

That is, when the content of Al becomes 0.005% or more, a large amount of CaS is promoted in the molten steel, and CaS is deposited on the nozzle for continuous casting, which is likely to be clogged. There is a problem. This problem can be surely solved by the limitation of less than 0.005% of the Al content.

Further, as described in the second aspect of the present invention, the lead-free steel for machine structural use further comprises Mo: 0.05 to 1.0.
0%, Ni: 0.1 to 3.5%, V: 0.01 to 0.5
0%, Nb: 0.01 to 0.10%, Ti: 0.01 to
0.10%, B: It is preferable to contain one or more kinds selected from 0.0005 to 0.0100%.
The reasons for limiting the component ranges of these preferred components are shown below.

Mo: 0.05-1.00%, Ni: 0.
Mo, Ni is an element that improves the hardenability and toughness of steel, and is added when necessary. To obtain the effect, it is preferable to add Mo at 0.05% or more and Ni at 0.1% or more. If a large amount is added, the hardness of the work material increases.
It is preferable that o is 1.00% or less and Ni is 3.5% or less. Mo is preferably 0.10 to 0.40%, and more preferably 0.15 to 0.30%, in any of the above three steel types. Ni is the above 3
For any steel type, preferably 0.40
3.00%, more preferably 0.40 to 2.00
% Is good.

V: 0.01 to 0.50%, V is an element having a strong precipitation strengthening effect, and is added when the quenching and tempering treatment is omitted. To obtain this effect, it is preferable to add 0.01% or more. On the other hand, if the content exceeds 0.50%, the effect is saturated, so the upper limit is preferably set to 0.50%. In the case of a non-heat treated steel, the content is more preferably 0.05 to 0.35%, and still more preferably 0.05 to 0.35%.
5 to 0.30% is good.

Nb: 0.01-0.10%, Ti: 0.
01 to 0.10%, Nb, and Ti each generate carbonitride and have an effect of refining crystal grains by a pinning effect, and are added as necessary. To achieve this effect, use 0.
The content is required to be not less than 01%, but the effect is saturated even if the content exceeds 0.10%, so the upper limit is preferably set to 0.10%. It is more preferably 0.01 to 0.08%, and still more preferably 0.01 to 0.06%.

B: 0.0005% to 0.0100%, B has an effect of improving hardenability and improving mechanical properties of steel with a small amount of B, and is added as necessary. To obtain this effect, 0.0005% or more is required.
The effect is saturated even if the content exceeds 0.00%, so the upper limit is preferably set to 0.0100%. It is more preferably 0.0005 to 0.0060%, and still more preferably 0.0005 to 0.0040%.

Further, as in the invention of claim 3 , the lead-free steel for machine structural use further has a Bi: 0.01-0.
30%, REM: preferably contains one or two selected from 0.001 to 0.10%. The reasons for limiting the component ranges of these preferred components are shown below.

Bi: 0.01 to 0.30%, Bi is effective for improving the chip controllability and the perforability without substantially deteriorating the mechanical anisotropy. Is added when particularly necessary. To obtain this effect, 0.01% or more is necessary. However, if the content exceeds 0.30%, the effect is saturated and the cost is increased. Therefore, it is preferable to set the upper limit to 0.30%. . It is more preferably 0.01 to 0.10%, and still more preferably 0.01 to 0.08%.

REM: 0.001 to 0.10%, REM
(Rare earth element) has a large morphological control effect of sulfide,
Used for promoting the effect of Mg and Ca. Note that R
EM is mainly composed of a mixed alloy of Ce, La, Nd, Pr, and Sm. To obtain this effect, REM of 0.001% or more is necessary. However, if the content exceeds 0.10%, the effect is saturated and the cost is increased. Therefore, the upper limit is set to 0.10%. Is preferred. More preferably, 0.
001 to 0.006%, more preferably 0.0
01-0.004% is good.

Further, as in the fourth aspect of the present invention, the lead-free steel for machine structural use contains (C) as a sulfide-based inclusion.
one or two of a, Mg) S and (Ca, Mg, Mn) S
Preferably, it contains a species. S and Ca, Mg, M
There are various sulfides with n.
a, Mg, S complex sulfide (Ca, Mg) S,
Alternatively, by including at least one of the complex sulfides (Ca, Mg, Mn) S of Ca, Mg, Mn, and S, the wear resistance of the carbide tool can be significantly improved.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION In order to evaluate the excellent properties of the lead-free steel for machine structural use of the present invention, various tests were carried out for each of three types of steels: tempered tough steel, non-heat treated steel and case hardened steel. Was done. The test results are shown below as exemplary embodiments.

Embodiment 1 In this embodiment, as shown in Tables 1 and 3, invention steel A and conventional steels B and C in a tempered and tough steel were prepared and compared. Conventional steel B is a Pb free-cutting steel containing 0.1% of Pb. Further, in the conventional steel B, the S content and the O content are out of the range of the present invention. Conventional steel C is
a and Mg were not added.

Each steel material was melted in a 100 kg vacuum melting furnace and forged at 1200 ° C. to φ60 mm, and a part was further forged to a 40 × 70 mm square bar. After that, all 88
After quenching at 0 ° C., a heat treatment of tempering was performed at 580 ° C. Then, a machinability test, a tensile test, and an impact test in the forging and stretching direction (hereinafter, referred to as L direction) were performed using a φ60 mm material. Further, an impact test was performed using a 40 × 70 mm square bar in a direction perpendicular to the forging direction (hereinafter, referred to as a T direction).

Table 2 shows the machinability test method and the cutting conditions.
The JIS No. 4 test piece was used as the tensile test piece, and the JIS No. 3 test piece was used as the impact test piece. In view of the object of the present invention is to develop a steel to replace Pb free-cutting steel, the evaluation items of the machinability test were evaluated focusing on the chip processing property and drill cutting property which are the advantages of Pb free-cutting steel.

As shown in FIG. 1, in the drill deep hole test, which is one of the machinability tests, the cutting resistance (torque) is measured from the start of drilling, and the torque T ₂ is the stable drilling torque T _1. The perforation time t until it becomes twice as large as “stable perforation time”
"Stable drilling time (sec)" x "feed amount (mm /
“sec)” and “stable drilling depth (mm)” was calculated and evaluated.

Table 3 shows the test results and the like. As can be seen from Table 3, the steel A of the present invention in the tempered toughness steel exhibited better characteristics than the conventional steels B and C in all evaluation items. In particular, with respect to the drill life, the performance was much better than the conventional Pb free-cutting steel.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

Embodiment 2 In this embodiment, as shown in Tables 1 and 3 above, inventive steel D and conventional steels E to G, which are non-heat treated steels, were prepared and compared. Conventional steel E is a Pb free-cutting steel containing 0.17% of Pb. Conventional steel F has a Pb of 0.18
% Pb and Ca containing 22 ppm of Ca
Is a free-cutting steel with a complex addition of Conventional steel G is C
a, Mg is not contained. Conventional steel E ~
In each case of G, Al exceeds 0.010%.

Each steel material was melted in a 30 kg vacuum melting furnace and forged at 1200 ° C. to φ40 mm, and a part was further forged to a 40 × 70 mm square bar. After that, in each case 12
After maintaining at a temperature of 00 ° C. for 30 minutes, an air-cooled heat treatment was performed. Then, a machinability test, a tensile test, and an impact test in the L direction were performed using a φ40 mm material. Also, 40 × 7
An impact test in the T direction was performed using a 0 mm square bar. The test method, cutting conditions, tensile test pieces and impact test pieces are the same as those in the first embodiment.

Table 3 shows the test results and the like. As is known from Table 3, the steel D of the present invention among the non-heat treated steels exhibited better characteristics than the conventional steels E to G in all evaluation items. In particular, regarding the wear amount of carbide tools and the life of drills,
It showed much better performance than conventional Pb free-cutting steel. Compared to conventional steel F, a lead composite free-cutting steel with excellent free-cutting properties, Pb
One of the advantages of free-cutting steel, the drill life has been significantly improved
This is exactly the result of the simultaneous addition of Mg and Ca, combined with the addition of Mg and Ca, after simultaneously reducing the amount of Al and O and controlling the amount of oxide and its morphology as compared to conventional steel. Things.

Embodiment 3 In this embodiment, as shown in Tables 1 and 3 above, invention steels H and I and conventional steels J and K in case hardening steels were prepared and compared. The invention steels H and I are the most different in that Bi was added to the invention steel H. Conventional steel J
It is a free-cutting steel to which a large amount of S and Pb are added. Further, the conventional steels J and K both have an Al content exceeding 0.010%.

Each steel material was melted in a 100 kg vacuum melting furnace and forged at 1200 ° C. to φ60 mm, and a portion was further forged to a 40 × 70 mm square bar. After that, 90
A normalizing heat treatment was performed at a temperature of 0 ° C. for 60 minutes.
Then, a machinability test was performed using a φ60 mm material.
In addition, after performing a tensile test and a L-direction impact test piece from a φ60 mm material, and a T direction impact test from a 40 × 70 mm square material, rough processing, quenching at 880 ° C, tempering at 180 ° C, and finishing After that, a mechanical test was performed.
The test method and the like are the same as those in the first embodiment.

Table 3 shows the test results and the like. As is known from Table 3, the steels H and I of the present invention in the case hardening steel exhibited characteristics superior to the conventional steels J and K at least in machinability. In terms of mechanical properties, excellent properties that were almost the same as those of conventional steel were maintained. In particular, the steel H of the present invention to which Bi is added has a drastically improved drill life. This is due to the fact that the deformation of the inclusions is increased by the low melting point behavior of Bi, and the effect of preventing the progress of tool wear by the composite sulfides.

Embodiment 4 In this embodiment, as shown in Table 4, a steel L of the present invention, conventional steels M and N, and a comparative steel O were prepared based on a non-heat treated steel, and the fatigue characteristics were compared. . Conventional steel M is a free-cutting steel containing Pb, and conventional steel N is a lead composite free-cutting steel added with Ca in addition to Pb. Comparative steel O is obtained by increasing O to exceed 20 ppm with respect to the steel of the present invention.

Each steel material was melted in a 30 kg vacuum melting furnace and forged at 1200 ° C. to φ60 mm. And 12
After maintaining at a temperature of 00 ° C. for 30 minutes, an air-cooled heat treatment was performed. Then, a test piece was cut out from φ60mm material,
Tensile tests and Ono-type rotary bending fatigue tests were performed.

Table 5 shows the test results. As can be seen from Table 5, the steel L of the present invention has almost no difference in tensile strength as compared with the conventional steel M (lead free-cutting steel) and the conventional steel N (lead composite free-cutting steel), and has a fatigue limit and durability. In comparison, it exhibited excellent characteristics that were equal to or better than those. Further, the comparative steel O having a higher oxygen content than the steel L of the present invention has poor fatigue characteristics. This is probably because the amount and size of oxide inclusions increased.

[0055]

[Table 4]

[0056]

[Table 5]

Embodiment 5 In this embodiment, the continuous castability of a tempered toughened steel and a non-tempered steel was evaluated. For this evaluation, as shown in Table 6, inventive steels P to S and comparative steels T to W were prepared. Comparative steel T ~
W is obtained by increasing the Al content to 0.05% or more of the invention steels P to S.

The continuous casting test was conducted using a 130 ton electric furnace.
After smelting by LF (Ladle Refining Furnace) -RH (Vacuum Degassing Device), it was performed using a bloom continuous caster of 370 mm × 530. Then, it was tested whether or not 130 ton of molten metal can be cast by the continuous casting machine.

Table 7 shows the test results. As can be seen from Table 7, all of the steels P to S of the present invention in which Al was suppressed to less than 0.005% could continuously cast all 130 tons without blocking the nozzle of the casting machine.
On the other hand, comparative steels T to W in which the Al content
In each case, nozzle clogging occurred, and continuous casting of all 130 tons could not be performed.

[0060]

[Table 6]

[0061]

[Table 7]

Embodiment 6 In this embodiment, a steel X of the present invention based on a non-heat treated steel shown in Table 8 was prepared, and inclusions in the steel X were observed. Invention Steel X was smelted in a 30 kg vacuum melting furnace and forged at 1200 ° C. to φ40 mm. Then, at a temperature of 1200 ° C.
After holding for 0 minutes, air-cooled heat treatment was performed.

FIG. 2 shows the results of observation of inclusions. FIG.
EM image and Mn, Si, Mg, S, A at the same position
It is a drawing substitute photograph which shows each image of 1, Fe, O, P, Ca element. As can be seen from FIG.
g, S and Ca are detected in the same inclusion, and M
nS, (Mg, Ca) S and (Mn, Mg, Ca) S
Was confirmed. The shape of inclusions is generally M
The sulfide represented by nS becomes rod-like after forging, but is spherical in the present invention steel. It is considered that this reduces the notch effect due to inclusions during the test of the mechanical properties and improves the impact anisotropy of the mechanical properties.

[0064]

[Table 8]

Embodiment 7 In this embodiment, as shown in Table 8, in addition to steel X of the present invention, conventional steels Y and Z were prepared, and the wear amount of carbide tools, the chip disposal index, and the drill deep hole property were determined. A test was conducted to determine the life of the drill. The test conditions and the like are the same as in the first embodiment. And
The distribution of alloying elements in the rake face wear part (crater wear part) of the tool was observed.

Conventional steel Y is a lead composite free-cutting steel containing Pb and Ca. The conventional steel Z does not contain Pb, but increases the amount of Al and stops adding both Ca and Mg. These manufacturing methods were the same as those of the steel X of the present invention. Table 9 shows the test results.

[0067]

[Table 9]

As can be seen from Table 9, the steel X of the present invention
All the evaluation items were superior to the conventional steels Y and Z. Next, the observation results of the alloy element distribution are shown in FIGS. These figures show SEM images of the tool rake face wear part surface after the wear test and Ca, S, Mn, M at the same position.
It is a drawing substitute photograph each showing the image of element g, W, Fe, Si, Al, and O.

As is known from FIG. 3, in the steel X of the present invention, Mn, S, Ca,
Mg had adhered. From this, MnS and (Ca,
It is considered that the lubricating effect due to the combined effect of Mg) S was exerted and the progress of tool wear was suppressed.

On the other hand, as can be seen from FIG.
In the above, Ca and S are adhered to the wear portion, and Pb is adhered to the wear end. From these results, it can be estimated that the progress of wear was suppressed by the lubricating action of CaS, but this was not as high as that of steel X of the present invention. Also, as known from FIG.
In the conventional steel Z, S is slightly distributed in the tool wear portion, but a large amount of Fe and O adhere. It is considered that the oxide of Fe has a function of promoting the wear of the tool by causing a substitution phenomenon with Co in the tool, whereby the wear was intense.

Embodiment 8 In this embodiment, a larger number of steels of the present invention and comparative steels were prepared, and their machinability and other properties were evaluated in the same manner as in Embodiment 1. First, as the present invention steel, as shown in Tables 10 to 12, 78 kinds of steels a1 to a78 having variously changed components within the component range of the present invention were prepared.

As shown in Table 13, eight kinds of steels b1 to b8 which were out of the range of the composition of the present invention were prepared as comparative steels. Comparative steel b1 has an S content below the lower limit, and comparative steel b2 has an S content exceeding the upper limit. Comparative steel b3
Is an Al content exceeding the upper limit. Comparative steel b4 is Ca
In the case where the amount falls below the lower limit, the comparative steel b5 has the amount of Ca exceeding the upper limit. Comparative steel b6 has a lower limit of Mg content,
The comparative steel b7 has a Mg content exceeding the upper limit. Comparative steel b8 has an O content exceeding the upper limit.

The production of each steel was performed in the same manner as in the first embodiment for the heat-treated steel, and in the same manner as in the second embodiment for the non-heat-treated steel. In Tables 14 to 17 described below,
Those with data in the item of quenching and tempering are tempered steels, and those with data in the item of air cooling (after heating at 1200 ° C) are non-heat treated steels. The mechanical test was performed on the tempered steel after quenching and tempering, and on the non-heat treated steel after heating at 1200 ° C. and air cooling. Others are the same as those of the first to third embodiments.

Tables 14 to 17 show the evaluation results. In order to make the results easy to understand, very good samples are indicated by ◎, good samples are indicated by ，, and bad samples are indicated by ×. Table 18 shows the criteria for ◎, ，, and × for each evaluation item.

As can be seen from Tables 14 to 16, all the steels of the present invention showed excellent results in all evaluation items. On the other hand, as known from Table 17,
None of the comparative steels satisfied all of the evaluation items.

Specifically, the comparative steel b1 in which the S content was less than the lower limit value was obtained from the carbide tool wear, the chip treatment index, the drill deep hole property,
Sufficient properties were not obtained in the drill life. Comparative steel b2 having an S content exceeding the upper limit was not excellent in impact anisotropy and durability ratio. The comparative steel b3 in which the amount of Al exceeded the upper limit did not have excellent carbide tool wear and durability ratio. In addition, comparative steel b
No. 3 is made of non-heat treated steel, so that compared with the non-heat treated steels (air-cooled steels) among the steels a1 to a78 of the present invention, almost all of the above steels of the present invention have a deep hole hole characteristic of Pb free-cutting steel. And the drill life is very good, while the comparative steel b
3 did not reach a very good level but remained at a good level.

The comparative steel b4 in which the amount of Ca was less than the lower limit was not excellent in carbide tool wear, drill life and impact anisotropy.
The comparative steel b5 in which the amount of Ca exceeded the upper limit did not have an excellent durability ratio. Comparative steel b6 in which the amount of Mg was below the lower limit was not excellent in carbide tool wear, drill life, and impact anisotropy. The comparative steel b7 in which the Mg content exceeded the upper limit did not have an excellent durability ratio.
The comparative steel b8 in which the O content exceeds the upper limit was not excellent in carbide tool wear, drill life, and durability ratio.

[0078]

[Table 10]

[0079]

[Table 11]

[0080]

[Table 12]

[0081]

[Table 13]

[0082]

[Table 14]

[0083]

[Table 15]

[0084]

[Table 16]

[0085]

[Table 17]

[0086]

[Table 18]

[0087]

As described above, according to the present invention, the present invention does not contain Pb and has properties equal to or higher than those of conventional Pb-containing free-cutting steel, has excellent machinability, and has low strength anisotropy. A lead-free mechanical structural steel can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a method for evaluating a drill deep hole property in a first embodiment.

FIG. 2 is a drawing substitute photograph showing an image of each element in steel X of the present invention in Embodiment 6;

FIG. 3 is a drawing substitute photograph showing an image of each element attached to a tool obtained by cutting steel X of the present invention in Embodiment 7;

FIG. 4 is a drawing substitute photograph showing an image of each element attached to a tool for cutting conventional steel Y in Embodiment 7;

FIG. 5 is a drawing substitute photograph showing an image of each element attached to a tool obtained by cutting conventional steel Z in Embodiment 7.

[Explanation of symbols]

T ₁ , T ₂ . . . Cutting force, t. . . Drilling time,

──────────────────────────────────────────────────続 き Continued on the front page (73) Patent owner 000003207 Toyota Motor Co., Ltd. 1 Toyota Town, Toyota City, Aichi Prefecture (72) Inventor Naoki Iwama 1 Wanowari Arao Town, Tokai City, Aichi Prefecture Aichi Steel Corporation (72 Inventor Susumu Owaki 1 Wanowari, Arao-cho, Tokai City, Aichi Prefecture Inside (72) Inventor Masao Uchiyama 1-Wanowari, Arao-cho, Tokai City, Aichi Prefecture 1st Inside Aichi Steel Corporation (72) Inventor Isao Fujii Aichi No. 1, Wanowari, Arao-cho, Tokai, Aichi Steel Co., Ltd. (72) Inventor Katsushi Nishimon No. 1, Wanowari, Arao-cho, Tokai, Aichi, Japan No. 72 (72) Inventor, Norimasa Join, Himago No. 3007, Nakajima character, Sanyo Special Steel Co., Ltd. (72) Inventor, Kazuhiro Kobayashi Banchi Sanyo Special Steel Co., Ltd. (72) Inventor Kazutaka Ogo 41, Chuchu-Yokomichi, Nagakute-cho, Aichi-gun, Aichi, Japan 1 Toyota Toyota Central R & D Laboratories Co., Ltd. 41 Chuo-ku Yokomichi 1 Toyota Central Research Laboratory Co., Ltd. (72) Inventor Motohide Mori 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (56) References JP-A-2000-282169 (JP, A) JP-A-2000-87179 (JP, A) JP-A-2001-152280 (JP, A) JP-A-60-59052 (JP, A) JP-B-51-4934 (JP, B1) Nobuaki Sugiyama, Recent progress, The 72nd and 73rd Nishiyama Memorial Technical Lecture, Japan, The Iron and Steel Institute of Japan, February 10, 1981, 3. Electric furnace steelmaking and vacuum degassing, P. 67-78 Kanehiro Ogawa, Recent Advances in High-Purity Steel Smelting Technology, The 143rd and 144th Nishiyama Memorial Technical Lectures, Japan, The Iron and Steel Institute of Japan, April 30, 1992, 6. Slag smelting technology for high-purity steel smelting. 137-171 (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (4)

(57) [Claims] C. 0.10 to 0.6 in weight%
5%, Si: 0.03 to 1.00%, Mn: 0.30
2.50%, S: 0.03 to 0.35%, Cr: 0.1
~ 2.0%, Al: less than 0.005%, Ca: 0.00
05-0.020%, Mg: 0.0003-0.020
% Containing, O: less than 20 ppm, Ri Do the balance Fe and unavoidable impurities, and produced by continuous casting
A lead-free mechanical structural steel with excellent machinability and low strength anisotropy. 2. The method according to claim 1, further comprising: Mo: 0.0.
5 to 1.00%, Ni: 0.1 to 3.5%, V: 0.0
1 to 0.50%, Nb: 0.01 to 0.10%, Ti:
0.01 to 0.10%, B: 0.0005 to 0.010
A lead-free mechanical structural steel having excellent machinability and low strength anisotropy, characterized by containing one or more selected from 0%. 3. The method according to claim 1, further comprising:
i: 0.01 to 0.30%, REM: 0.001 to 0.
Lead-free mechanical structural steel having excellent machinability and low strength anisotropy, characterized by containing one or two selected from 10%. 4. The method according to claim 1, wherein:
(Ca, Mg) S, (Ca, M) as sulfide-based inclusions
g, Mn) A lead-free mechanical structural steel having excellent machinability and low strength anisotropy, characterized by containing one or two of S, Mn) S.