JP2003253384A - Hot-forged product with no lead added - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot-forged product with no lead added, having equivalent characteristics to the hot-forged product containing lead. <P>SOLUTION: This hot-forged product with no lead added, comprises 0.08-0.61% C, 0.02-1.00% Si, 0.20-2.00% Mn, 0.08-0.35% S, and the balance Fe with unavoidable impurities. The product preferably includes one or more elements selected among 0.1-2% Cr, 0.05-1% Mo, 0.1-3.5% Ni, 0.01-0.5% V, 0.01-0.1% Nb, 0.01-0.1% Ti, 0.0005-0.01% B, 0.0005-0.02% Ca, 0.0003-0.02% Mg, 0.01-0.3% Bi, 0.003-0.01% Te, 0.003-0.01% Se, 0.0003-0.01% Zr, 0.001-0.1% Hf, and 0.001-0.1% REM. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hot die forging product which has characteristics comparable to those of conventional lead-containing hot die forging products and which is advantageous in environmental protection without adding lead.

[0002]

2. Description of the Related Art For example, crankshafts for automobiles are
After performing hot die forging, the burrs produced by the hot die forging are trimmed, and further finishing cutting is performed. For this reason, conventional hot die forgings such as crankshafts have used hot die forgings that use lead-containing steel having both hot forgeability and machinability.

[0003]

[Problems to be Solved] Meanwhile, with the increasing awareness of environmental protection in recent years, it is required to develop a steel product containing no lead, which is a harmful substance. The same applies to hot die forgings, and there has been a demand for the development of lead-free hot die forgings, which replaces the conventional lead-containing hot die forgings. However, at present, a lead-free hot die forging having the same hot forgeability and machinability as those of lead-containing ones has not yet been developed.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide a lead-free hot die forging having characteristics comparable to those of a lead-containing hot die forging. .

[0005]

According to the present invention, in% by weight, C:
0.08-0.61%, Si: 0.02-1.00%,
Mn: 0.20 to 2.00%, S: 0.08 to 0.35
%, And the balance is Fe and unavoidable impurities, which is a lead-free hot die forged product (claim 1).

First, regarding the reasons for limiting the above-mentioned constituents,
The preferred range will be described. C: 0.08 to 0.61%, C is an essential element for ensuring strength, and is 0.08
% Or more. However, if the amount is too large, the hardness increases and the toughness and machinability deteriorate, so the upper limit is made 0.61%. More preferably, it is 0.25 to 0.50%.

Si: 0.03 to 1.00%, Si is essential as a deoxidizer during steel making, so the lower limit is made 0.02%. However, if added excessively, not only the ductility is lowered, but also SiO ₂ which is a high hardness inclusion is generated in the steel to deteriorate the machinability, so the upper limit is made 1.00%. More preferably, it is 0.15 to 0.70%.

Mn: 0.20 to 2.00%, Mn is generally an important element for securing the strength, toughness, hot ductility and hardenability of steel, and in the present invention,
0.20 because it is an essential element for the formation of sulfide inclusions
% Or more. However, if the amount is too large, the hardness increases and the machinability deteriorates, so the upper limit is made 2.00%. It is more preferably 0.50 to 1.50%.

S: 0.08 to 0.35%, S is a forming element of sulfide inclusions for improving the machinability, and in order to obtain the machinability equal to or higher than that in the case of containing lead. It is necessary to add at least 0.08% or more, and as the amount of S increases, machinability improves. However, if too much, the hot die forgeability deteriorates, so the upper limit is made 0.35%. It is more preferably 0.12 to 0.25%.

As described above, the present invention does not add lead (Pb) at all, and instead uses steel in which the S content is increased to an extremely high level as compared with the conventional hot die forgings. . As a result, after performing hot die forging, machinability comparable to Pb free-cutting steel can be realized, and a lead-free hot die having the same workability as the lead-containing hot die forgings. You can get a forged product.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the hot die forged product of the present invention, Cr: 0.1-2.0%, Mo: 0.05-
1.00%, Ni: 0.1-3.5%, V: 0.01-
0.50%, Nb: 0.01 to 0.10%, Ti: 0.
01 to 0.10%, B: 0.0005 to 0.0100%
It is preferable to contain one kind or two or more kinds selected from (Claim 2).

Cr: 0.1 to 2.0%, Cr is added to improve the hardenability and toughness of steel. To obtain this effect, Cr needs to be 0.1% or more. On the other hand, when a large amount is added, the hardness of the work material increases, so Cr must be 2.0% or less to secure the machinability. More preferably 0.10 to 1.2
0% is good.

Mo: 0.05-1.00%, Ni: 0.
1 to 3.5%, Mo and Ni are elements that improve the hardenability and toughness of steel, and are added when necessary. In order to obtain the effect, it is preferable to add 0.05% or more of Mo and 0.1% or more of Ni. When added in a large amount, the hardness of the work material increases, so Mo is 1.00% to ensure machinability.
Hereinafter, Ni is preferably 3.5% or less. Further, Mo is more preferably 0.15 to 0.30%, and Ni is more preferably 0.15 to 0.50%.

V: 0.01 to 0.50%, V is an element having a strong precipitation strengthening action, so V is added when the quenching and tempering treatment is omitted. To obtain this effect, 0.
It is preferable to add 01% or more. On the other hand, 0.50%
If the content is exceeded, the effect will be saturated, so the upper limit is 0.5.
It is preferably 0%. More preferably 0.05-
0.20% is good.

Nb: 0.01 to 0.10%, Ti: 0.
01 to 0.10%, Nb, and Ti each generate a carbonitride and have the effect of refining the crystal grains by the pinning effect, and are added as necessary. To obtain this effect, the content is required to be 0.01% or more, but the effect is saturated even if the content exceeds 0.10%, so the upper limit is preferably made 0.10%. More preferably, 0.01% to 0.04% is preferable in each case.

B: 0.0005 to 0.0100% B contains a small amount to improve the hardenability and the mechanical properties of steel, and is added if necessary. To obtain this effect, 0.0005% or more is necessary, but
The effect is saturated even if the content exceeds 0100%, so the upper limit is preferably made 0.0100%. More preferably, it is 0.0005 to 0.0025%.

Further, the lead-free hot die forged product further contains Ca: 0.0005 to 0.020% and Mg: 0.0
003 to 0.020%, Bi: 0.01 to 0.30%,
Te: 0.0003 to 0.010%, Se: 0.003
~ 0.010%, Zr: 0.0003-0.010%,
Hf: 0.001 to 0.100%, REM: 0.001
It is preferable to contain one or more selected from 0.10% (claim 3).

Ca: 0.0005 to 0.020%, Ca is a sulfide-forming element together with Mn and Mg, and also forms a complex oxide with Al and Si. There is an effect of improving the anisotropy of mechanical properties by controlling the morphology. To achieve that effect, at least 0.0
It is preferable to contain 005% or more. Further, the Ca yield in the steelmaking stage is very poor, and the effect is saturated even if it is contained more than necessary, so the upper limit of Ca is preferably made 0.020%. More preferably 0.0005-
0.0025% is preferable.

Mg: 0.0003 to 0.020%, Mg exhibits the same effect as Ca, and when it is combined with Ca, a large machinability improving effect and anisotropy improving mechanical property are obtained. Is obtained. In order to obtain the effect, it is preferable to contain at least 0.0003% or more. On the other hand, even if it is contained more than necessary, the effect is saturated and wasteful, so the upper limit of Mg is preferably made 0.020%. More preferably 0.0005 to 0.00
25% is good.

Bi: 0.01 to 0.30%, Bi is effective in improving chip disposability and perforability without substantially deteriorating the anisotropy of mechanical properties. Is added when it is particularly necessary. 0.01% or more is necessary to obtain this effect, but 0.3
If the content exceeds 0%, the effect is saturated and the cost becomes high, so the upper limit is preferably made 0.30%.
More preferably, it is 0.05 to 0.15%.

Te: 0.0003 to 0.010%, S
e: 0.003 to 0.010%, Zr: 0.0003 to
0.010%, Hf: 0.001 to 0.100%. These components have the machinability improving effect and the mechanical property anisotropy improving effect, respectively. The lower limit values for obtaining that effect are 0.003% for Te, 0.003% for Se, 0.0003 for Zr, and 0.001 for Hf, respectively.
% Is preferable. On the other hand, even if it is contained more than necessary, the effect is saturated and wasteful, so the upper limits are 0.010% for Te and 0.010 for Se, respectively.
%, Zr is preferably 0.010%, and Hf is preferably 0.100%. More preferably, Te is 0.0005-
0.0050%, Se is 0.003 to 0.007%, Z
r is 0.0005 to 0.0025%, Hf is 0.005
~ 0.050% is good.

When the hot die forged product has an uneven shape in the cross section contour, burrs generated around the cross section contour after the hot die forging are formed. Trimming is performed using a trimming die having a blade along the line, and then cutting is performed, and
At least a part of the concave corner portion of the blade portion in the trimming die is provided with a protrusion projecting in the punching direction more than other general parts, and the protrusion is prior to other general parts during trimming. It is preferable that the burr positioned at the concave corner portion is first trimmed by bringing it into contact with the burr, and then the burr of the other part is trimmed (claim 4).

That is, when the hot die forging product has an uneven shape in its cross-sectional contour, the burr generated by the hot die forging is trimmed by using the trimming die having the above-mentioned special structure. Preferably. A point to be noted in the trimming die is that the concave corner portion of the blade portion is provided with a protrusion protruding in a mountain shape. Here, the concave corner portion of the trimming die is a portion of the trimming die corresponding to a burr around the convex portion of the cross-sectional contour of the hot die forged product. It should be noted that it is not necessary to provide the protrusions on all the concave corners in the trimming die, and the protrusions may be provided only on the portions where peeping defects easily occur in experience.

By performing the cutting process after trimming with such a special trimming die, it is possible to obtain a hot die forged product which is efficient, has a high yield, and is excellent in dimensional accuracy.

By using the special trimming type, the following excellent operational effects can be obtained. In the trimming die, the protruding portion is provided on the blade portion at the concave corner portion as described above. Therefore, when trimming is performed using this trimming die, the protruding portion first comes into contact with the burr of the hot die forged product before other portions. Since this protrusion projects in the shape of a mountain as described above, its apex abuts the burr, and immediately after that part is cut, it is cut sequentially from the apex to the mountain, and then the general part without a projection is formed. Is cut by. That is, in the concave corner portion provided with the above-mentioned protruding portion,
Smooth cutting is achieved as if by a cutting device having a shear angle. Therefore, even a hot die forged product having a shape that easily causes peeling defects can be trimmed without causing peeling defects.

Further, since the other general parts are cut after the trimming by the projecting portion is completed, the trimming load can be made smaller than in the case where the whole is trimmed at once. Therefore, it is possible to prevent the occurrence of deformation and the like due to the large trimming load.

As described above, in the obtained hot die forged product, it is possible to prevent the occurrence of peeling defects during deburring (at the time of trimming), so that the defect rate can be suppressed and products can be obtained efficiently. be able to.

A more preferable form of the trimming type will be described. It is preferable that the apex of the protrusion has an arcuate curved surface. The apex of the protrusion may be an obtuse angle or an acute angle. However,
As described above, the curved surface having an arc shape has the effect of improving the durability of the blade.

The radius of curvature of the apex of the chevron shape is
It is preferably 3 to 7 mm. The radius of curvature is 3m
If it is less than m, there is a problem that the durability of the protruding portion is lowered, while if it is more than 7 mm, the trimming property due to the protruding portion may be lowered.

Further, it is preferable that the height of the above-mentioned protrusion is within the range of 3 to 7 mm. If the height of the protrusion is less than 3 mm, the above-described excellent effect of providing the protrusion may not be sufficiently exhibited. On the other hand, 7 mm
If it exceeds, the rigidity of the protrusion may decrease.

The radius of curvature of the concave corner portion provided with the protrusion is preferably 10 mm or less. In other words, the occurrence of the plucking defect is caused especially when the radius of curvature is 10 m.
It tends to occur in a portion corresponding to a concave corner of m or less. Therefore, by selectively providing the protruding portion at the concave corner portion having a radius of curvature of 10 mm or less, it is possible to almost certainly prevent the peeling defect.

The hot forged product is preferably a crankshaft (claim 5). Crankshafts are generally hot-die forged and then finished by cutting, and lead-containing hot-die forged parts have been widely used. Instead, by applying the above-mentioned excellent lead-free hot die forgings to the crankshaft, it is possible to promote the lead-free use of crankshafts that are used in large quantities, which greatly contributes to environmental conservation. be able to.

[0033]

EXAMPLE In order to evaluate the characteristics of the lead-free hot die forged product of the present invention, five types of examples (E1 to E5) having the composition of components shown in Table 1 and three types of comparative examples (C1 to C1) were used. A crankshaft (hot forging product) as C3) was manufactured, and hot forgeability and machinability were evaluated.

[0034]

[Table 1]

First, in producing each hot die forged product, 2.3 ton steel ingots were produced by melting the above eight compositions. Then, a 130-square steel piece was formed by forging, and a material before hot die forging was produced.

Next, the above material was subjected to hot die forging in which it was constrained in a pair of upper and lower molds having burr grooves. As a result, a crankshaft with burrs around the cross-sectional contour was obtained. Next, as shown in FIGS. 1 and 2, trimming for removing burrs was performed using a trimming die 1 having a special structure.

More specifically, as shown in FIGS. 1 (a) and 1 (b), the trimming die 1 is provided at the center of the main body 10,
It has a space 11 provided so as to match the contour shape of the cross section of the forged crankshaft. The blade portion 2 is provided around the space portion 11 in a state of protruding further than the main body portion 10 by one step.

Then, as shown in FIG.
There are a large number of concave corners, of which the protruding portions 21 projecting in the above-mentioned chevron shape selectively at eight concave corners.
Was formed. The protruding portion 21 is, as shown in FIGS.
The apex 210 has a mountain shape having an arcuate curved surface. In this example, the radius of curvature R of the apex 210 is 5 mm.
Set up in. The height H of the protruding portion 21 was set to 5 mm. In addition, as shown in FIG.
The horizontal length L of the apex from 1 to the outside was set to about 5 mm or more, and the height of the apex was gradually reduced toward the outside, and finally the height was lowered to the same level as the general portion.
The radius of curvature of the concave corner portion provided with the protrusion 21 is 10 mm or less.

Next, when trimming the crankshaft 8 using the trimming device having the trimming die 1, the crankshaft 8 is held between the trimming upper die 7 and the trimming die 1 as shown in FIG. And move them relative to each other in the vertical direction. As a result, the burr 85 of the crankshaft 8 is trimmed. Then, the surface of the crankshaft 8 after deburring was cut to obtain a crankshaft having a final size.

In this example, evaluation of the hot forgeability of the obtained hot die forged product (crankshaft) was performed on the basis of Comparative Example C3 which is a lead-containing hot die forged product. The evaluation was performed by using the incidence of peeling defects and the like that occur when burrs around the hot die forging product are removed by trimming after hot die forging. In Table 2, when excellent hot forgeability comparable to that of Comparative Example C3 was obtained, it is indicated by ⊚, and Comparative Example C
Although it is slightly inferior to 3, the case where excellent hot forgeability capable of being sufficiently mass-produced was obtained is indicated by ◯. In addition, the case where hot forging is extremely difficult at the mass production level is shown by x.

Further, the machinability of the obtained hot die forged product was evaluated with reference to Comparative Example C3 which is a lead-containing hot die forged product. Specifically, in the journal part (columnar shape) of the hot die forged product, using a high speed drill SKH51, a cutting speed of 30 m / min and a feed rate of 0.1 mm / re
v, depth 20 mm, lubrication was dry type (air only), and a drill wear test was conducted under the drilling condition of drill diameter φ5 mm to evaluate. In Table 2, when excellent machinability comparable to that of Comparative Example C3 was obtained, it is indicated by ⊚, and although slightly inferior to Comparative Example C3, sufficient machinability capable of mass production was obtained. The case is indicated by a circle. In addition, when the machinability that can be mass-produced is obtained, the case is shown, and when the machinability is extremely difficult at the mass-production level, it is shown by x.

Further, in this example, the impact anisotropy of the obtained hot die forged product was evaluated with reference to the lead-containing hot die forged product of Comparative Example C3. Specifically, a T-direction Charpy impact test piece in the forging direction was sampled from the journal portion (cylindrical shape) of the hot die forged product, and an impact test was performed at room temperature for evaluation. And, in Table 2, the case where excellent impact anisotropy comparable to that of Comparative Example C3 was obtained is indicated by ◯, and a sufficiently superior impact anisotropy was obtained although it was slightly inferior to Comparative Example C3. The case where it was done is shown by Δ.

[0043]

[Table 2]

As is known from Table 2, Examples E1 to E5, which are the products of the present invention, have the same hot forgeability and machinability as Comparative Example C3, which is a conventional lead-containing hot die forging product. It was also found to have impact anisotropy. From this, it is understood that if the hot die forging of the present invention is used in place of the conventional lead-containing hot die forging, it can greatly contribute to environmental protection.

When trimming was performed using a conventional ordinary trimming die instead of the trimming method of this example, in all hot die forgings except Comparative Example C3,
Peeling defect occurred during trimming. From this,
Among the hot die forgings of the present invention, it is very effective to use the above special trimming die 1 in manufacturing a hot die forging having a concavo-convex cross-sectional contour such as a crankshaft. I understand.

Considering this further, the concave corners of the blade portion 2 of the trimming die 1 are provided with protrusions 21 that protrude more in the punching direction than the other general portions 29.
Therefore, at the time of trimming, the protruding portion 21 comes into contact with the burr 85 before the other general portion 29. Then, after trimming the burr 85 located at the concave corner first,
Trimming the burr 85 in the other part. Since such a trimming method can be performed, it is considered that the crankshaft 8 can be trimmed in this example without causing a peeling defect.

That is, when the trimming die 1 is used for trimming, as described above, the projecting portion 21 has the other portion 2
The burrs 85 of the crankshaft 8 come into contact with the burrs 85 before 9. Since the projecting portion 21 projects in a mountain shape,
Immediately after the vertex 210 abuts on the burr 85 and the portion is cut, the vertex 210 is sequentially cut to the mountain portion, and then the general portion 29 without the protrusion 21 is cut. As a result, in the concave corner portion having the above-mentioned protruding portion, a much smoother cutting than in the conventional case is performed. Therefore, the trimming can be performed without causing the peeling defect.

Further, since the cutting by the other general portion 29 is performed after the trimming by the protruding portion 21 is completed, the trimming load can be made smaller than in the case of trimming the whole at once. Therefore, it is possible to prevent the occurrence of deformation and the like due to the large trimming load.

Further, the forming position of the projecting portion 21 in the trimming die 1 can be changed depending on the material of the hot die forged product and a slight difference in shape. For example, as shown in FIG. 4, the protrusion 21 may be provided at a position different from that of the trimming die 1 of FIG.

[Brief description of drawings]

FIG. 1A is a plan view of a trimming die according to the first embodiment, and FIG.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a sectional view taken along the line BB of FIG.

FIG. 4 is a plan view showing another example of a trimming die in the first embodiment.

[Explanation of symbols]

1. ． ． Trimming type, 2. ． ． Blade, 21. ． ． Protrusion, 29. ． ． General department, 8. ． ． Crankshaft forgings, 85. ． ． Bari,

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) C22C 38/60 C22C 38/60

Claims (5)

[Claims] 1. C: 0.08 to 0.6 in weight%
1%, Si: 0.02-1.00%, Mn: 0.20-
A lead-free hot die forged product containing 2.00% and S: 0.08 to 0.35%, and the balance being Fe and inevitable impurities. 2. The method according to claim 1, further comprising Cr: 0.1.
.About.2.0%, Mo: 0.05 to 1.00%, Ni: 0.
1 to 3.5%, V: 0.01 to 0.50%, Nb: 0.
01 to 0.10%, Ti: 0.01 to 0.10%, B:
A lead-free hot forged product containing one or more selected from 0.0005 to 0.0100%. 3. The method according to claim 1 or 2, further comprising Ca:
0.0005 to 0.020%, Mg: 0.0003 to
0.020%, Bi: 0.01 to 0.30%, Te:
0.0003 to 0.010%, Se: 0.003 to 0.
010%, Zr: 0.0003 to 0.010%, Hf:
0.001 to 0.100%, REM: 0.001 to 0.
A lead-free hot die forged product containing one or more selected from 10%. 4. The method according to claim 1, wherein
The hot die forging product has an uneven shape in its cross-sectional contour, and after hot die forging, burrs generated around the cross-sectional contour are trimmed with a blade portion along the cross-sectional contour. A trimming die is used for trimming, followed by cutting work, and at least a part of the concave corners of the cutting edge of the trimming die has a protrusion protruding more in the punching direction than other general portions. When the trimming is performed, the protrusion is brought into contact with the burr before the other general parts to trim the burr positioned at the concave corner first, and then the burr of the other part is trimmed. A hot-die forging product containing no lead, which is characterized by being added. 5. The method according to any one of claims 1 to 4,
The hot forged product is a lead-free hot forged product, which is a crankshaft.