JP2003201536A - Non-heat-treated steel for hot working having excellent wear resistance and hot worked product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the wear resistance of a non-heat-treated steel subjected to no high frequency quenching after hot working while securing its machinability on a prescribed level even without controlling the area ratio of ferrite to 0%. <P>SOLUTION: The non-heat-treated steel for hot working contains, by mass, 0.32 to 0.6% C, 0.05 to 1.5% Si, 0.30 to 2.0% Mn, ≤0.01% Al, ≤1.5% Cr, and 0.01 to 0.5% V, and has a ferrite-pearlite structure in which the area ratio of ferrite is >0 to 35% after hot working. The hardness of the above ferrite part is 170 to 270 HV. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel used for the purpose of omitting induction hardening for improving wear resistance.
The present invention relates to a non-heat treated steel capable of ensuring wear resistance even if the induction hardening treatment is omitted, and a hot-worked product having excellent wear resistance even if the induction hardening treatment is omitted.

[0002]

2. Description of the Related Art Mechanical structural parts such as automobile parts are sometimes required to have wear resistance. In particular, in response to high output of automobiles in recent years, improvement in wear resistance of parts used for engine sliding parts such as crankshafts and camshafts has been strongly demanded. In order to improve the wear resistance of mechanical structural parts, in many cases, the surface of the sliding portion is hardened, for example, induction hardening, nitriding, carburizing or the like. In addition, in order to increase the strength of the core portion, a strengthening element such as V is added. The core strength of this V-added steel is enhanced by hot forging and then cooling according to a controlled cooling process.

In recent years, there has been a demand for improvement in cost due to lead time at the time of surface hardening treatment and electric fuel cost, and for the purpose of energy saving and cost reduction, surface hardening treatment (induction hardening treatment etc.) may be omitted. Is being considered. If the induction hardening process can be omitted, there is an advantage that a large amount of energy can be saved. In order to improve the wear resistance on a par with induction-hardened steel even if the induction hardening treatment is omitted, it is conceivable to add C in an increased amount. But in that case,
There is a concern that machinability will decrease, making it difficult to manufacture parts.

As a steel for enhancing wear resistance while omitting the surface hardening treatment, for example, in JP-A-2000-265242, C: 0.40 to 0.70%, Si: 0.50.
% Or less, Mn: 0.90 to 1.80%, Cr: 0.05
.About.1.00%, s-Al: 0.01 to 0.045%, and N: 0.005 to 0.025%, with the balance being F.
e and impurities, the structure after hot forging is ferrite + pearlite, and the area ratio of proeutectoid ferrite is 10%.
The following non-heat treated steels for hot forging containing no V are disclosed. In the invention disclosed in this publication, the wear resistance is enhanced by suppressing the pro-eutectoid ferrite area ratio to 10% or less. More specifically, seven examples of steel are used in the Examples section, and six of them have a ferrite area ratio of 0%.
To increase the wear resistance, and in one example, the ferrite area ratio is set to 6.9% to improve the wear resistance. However, it is difficult to ensure the ferrite area ratio to 0%.
On the other hand, in the case where the ferrite area ratio is 6.9%, which is not 0%, the wear resistance is still insufficient. In addition, in this publication, "the conditions for keeping the pro-eutectoid ferrite area ratio at 10% or less can be determined by combining the actual addition amounts of the alloy components within the above-mentioned alloy composition and experimentally obtaining an appropriate combination. ", But does not describe at all what is to be done.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its purpose is to provide a non-heat treated steel that does not undergo induction hardening after hot working. It is an object of the present invention to provide a non-heat treated steel and a hot-worked product having excellent wear resistance while ensuring a predetermined level of machinability even if the ferrite area ratio is not 0%.

[0006]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present inventors investigated the cause of wear damage. Then, a bearing-shaped test member was manufactured using non-heat treated steel, and 4M
When a rotational wear test was performed 18,000 times while applying a load of Pa and the damage state of the sliding portion was observed with a micrograph, it was found that a small crack was formed by breaking the ferrite portion. Therefore, in order to improve wear resistance, it was found that not only the reduction of the ferrite area ratio as disclosed in JP-A-2000-265242 but also the hardening of the ferrite portion is important.

In order to harden the ferrite portion, it seems effective to add Si or V. On the other hand, since it is not known how to reduce the ferrite area ratio, further investigations have revealed that the ferrite area ratio becomes smaller as the amount of C or Mn increases. .

Therefore, in order to enhance the wear resistance, Si and V are added to harden the ferrite portion, and C and Mn are added.
Although it has been considered that the ferrite area ratio is reduced by increasing the amount, the machinability deteriorates and it becomes difficult to secure a predetermined level of machinability.

As a result of further studies, it was discovered that the ferrite area ratio becomes small even when the Al content is suppressed. Even if the ferrite portion is hardened by adding Si or V, if the ferrite area ratio is reduced by suppressing the amount of Al, the machinability is higher than that in the case where the ferrite area ratio is reduced by increasing C or Mn. The present invention has been completed by finding that the machinability of a predetermined level can be secured without deterioration.

That is, the non-heat treated steel excellent in wear resistance according to the present invention has C: 0.32 to 0.6 mass% and Si: 0.0
5 to 1.5% by mass, Mn: 0.30 to 2.0% by mass, A
1: 0.01 mass% or less, Cr: 1.5 mass% or less,
V: 0.01 to 0.5 mass% is contained, the structure after hot working is a ferrite-perlite structure having a ferrite area ratio of more than 0% and 35% or less, and the hardness of the ferrite part is 1
The gist is that it is 70 to 270 HV.
The non-heat treated steel further contains, as other elements, S: 0.1% by mass or less (0% is not included), Pb: 0.3% by mass or less (0% is not included), Bi: 0.3. It may contain mass% or less (0% is not included), Ca: 0.01 mass% or less (0% is not included), Mg: 0.01 mass% or less (0% is not included), and the like. .

In the present invention, C: 0.32 to 0.6% by mass,
Si: 0.05 to 1.5 mass%, Mn: 0.30 to 2.
0% by mass, Al: 0.01% by mass or less, Cr: 1.5% by mass or less, V: 0.01 to 0.5% by mass, ferrite area ratio of more than 0%, 35% or less of ferrite- It has a pearlite structure and the hardness of the ferrite part is 170 to 2
It also includes a hot-worked product having excellent wear resistance, which is characterized by 70 HV.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, after hot working of steel, a ferrite-perlite structure having a ferrite area ratio of more than 0% and 35% or less is obtained, and the hardness of the ferrite portion (Vickers hardness) is 170 to. It is set to 270 HV. If the ferrite area ratio is small and the hardness of the ferrite portion is increased, the wear resistance can be further increased.

The hardness of the ferrite part is 170 HV or more,
Preferably 175 HV or higher, more preferably 180 HV
It is V or more. The harder the ferrite part is, the more reliably the wear resistance can be improved. However, if the ferrite part is too hard, the machinability may decrease. Therefore, the ferrite hardness is 270 HV or less, preferably 260 HV or less, and more preferably 250 HV or less.

The ferrite area ratio is preferably more than 5%,
More preferably, it is more than 10%. On the other hand, if the ferrite area ratio is too large, the wear resistance cannot be sufficiently enhanced even if the ferrite hardness is increased. Therefore, the ferrite area ratio is 35% or less, preferably 30% or less, and more preferably 25% or less.

The ferrite area ratio means the area-based ratio of the ferrite structure to the total of the ferrite structure and the pearlite structure.

Although the structure after the hot working is substantially a ferrite-pearlite structure, it does not completely deny the existence of some other structure, and the total of the ferrite structure and the pearlite structure is It is, for example, 95 area% or more, preferably 99 area% or more, and more preferably about 100 area% with respect to the entire tissue.

When controlling the hardness of the ferrite portion within the above-mentioned predetermined range, it is effective to adjust the amount of Si or V. S
Although appropriate amounts of i and V vary depending on C and other elements, they can be selected from the range shown below in consideration of the property that the ferrite portion becomes harder as Si and V increase.

Si: 0.05 to 1.5% by Mass If the amount of Si is too small, the ferrite hardness may be insufficient even if V is added. Therefore, the amount of Si is set to 0.05 mass% or more, preferably 0.10 mass% or more, and more preferably 0.15 mass% or more. On the other hand, if Si is excessive, machinability may be insufficient. There is also a problem that decarburization during hot working of non-heat treated steel increases. Therefore, in the present invention, the Si content is 1.5% by mass or less, preferably 1.2% by mass or less, more preferably 1.0% by mass or less.

V: 0.01 to 0.5% by mass V is an element effective for increasing the hardness of ferrite as described above. The content of V is 0.01 mass% or more, preferably 0.05 mass% or more, and more preferably 0.08 mass% or more. On the other hand, if V is excessive,
The ferrite hardness may become too hard. Therefore,
The V content is 0.5 mass% or less, preferably 0.3 mass% or less, and more preferably 0.25 mass% or less.

On the other hand, when reducing the ferrite area ratio,
It is effective to increase the content of C or Mn or decrease the content of Al. However, in the present invention, as described above, Si or V is added in a predetermined amount or more in order to harden the ferrite hardness, and further increase of C or Mn is
Deteriorate machinability. Therefore, in the present invention, by suppressing the Al content (total-Al amount) within the range shown below, the ferrite area ratio is reduced while maintaining a predetermined level of machinability.

Al: 0.01% by mass or less The preferable range of Al is, for example, 0.009% by mass or less, and particularly 0.008% by mass or less.

The non-heat treated steel contains C, Mn and Cr in the following range.

C: 0.32 to 0.6% by mass When the content of C is increased, the ferrite area ratio can be decreased, but the toughness and ductility are decreased and the tensile strength is increased and the machinability of steel is decreased. Therefore, in the present invention, the ferrite area ratio is reduced by suppressing Al as described above, and the amount of C is not increased. The content of C is 0.6 mass% or less, preferably 0.55 mass%
Hereafter, it is more preferably 0.5% by mass or less. On the other hand, if the C content is too small, the ferrite area ratio may not be sufficiently reduced even if the Al amount is suppressed, and the strength and wear resistance of the steel may be insufficient. Therefore, the content of C is 0.32% by mass or more, preferably 0.35% by mass or more, and more preferably 0.4% by mass or more.

Mn: 0.30 to 2.0 mass% Although the ferrite area ratio can be reduced even if the content of Mn is increased, bainite is generated and machinability deteriorates. Therefore, in the present invention, the ferrite area ratio is reduced by suppressing Al as described above, and the amount of Mn is not increased. The Mn content is 2.0 mass% or less, preferably 1.7 mass% or less, and more preferably 1.5 mass% or less. On the other hand, if the Mn content is too low, not only the strength and toughness of the steel may be insufficient, but also the ferrite area ratio may not be sufficiently reduced even if the Al amount is suppressed. Therefore, the Mn content is 0.
30 mass% or more, preferably 0.35 mass% or more, and more preferably 0.4 mass% or more.

Cr: 1.5% by mass or less Cr is useful for reducing the pearlite lamellar spacing to improve ductility or proof stress, and to improve fatigue strength. The content of Cr is, for example, 0.10 mass% or more, preferably 0.15 mass% or more, and more preferably 0.20 mass% or more. On the other hand, if Cr is excessive, bainite is generated, so machinability may be insufficient. The Cr content is 1.5% by mass or less, preferably 1.3% by mass or less, and more preferably 1.0% by mass or less.

The balance of the non-heat treated steel may be Fe and unavoidable impurities, and may contain other elements as required.

For example, the non-heat treated steel may contain free-cutting elements (S, Pb, Bi, Ca, Mg, etc.). The addition amount of these free-cutting elements is as follows, for example.

S: 0.1% by mass or less (not including 0%) S is useful for increasing the machinability of steel by forming MnS by combining with Mn. The content of S is, for example, 0.03
It is at least mass%, preferably at least 0.04 mass%, more preferably at least 0.05 mass%. However, if S is excessive, cracks are likely to occur during hot working, so S
The content of is 0.1 mass% or less, preferably 0.08 mass% or less.

Pb: 0.3% by mass or less (0% is not included
B) Pb is an element effective in improving machinability. The content of Pb is, for example, 0.03 mass% or more, preferably 0.04 mass% or more, and more preferably 0.05 mass%.
That is all. However, even if Pb is added excessively, the effect is saturated, so the Pb content is preferably 0.3 mass% or less, and more preferably 0.2 mass% or less.

Bi: 0.3% by mass or less (0% is not included
B) Bi is also an element effective in improving machinability. The content of Bi is, for example, 0.02 mass% or more, preferably 0.03 mass% or more, and more preferably 0.04 mass%.
That is all. However, the effect is saturated even if Bi is added in excess, so the Bi content is preferably 0.3 mass% or less, and more preferably 0.2 mass% or less.

Ca: 0.01% by mass or less (0% is not included
B) Ca is also an element effective in improving machinability. The content of Ca is, for example, 0.0015 mass% or more, preferably 0.0020 mass% or more, and more preferably 0.00.
It is 30% by mass or more. However, even if Ca is added excessively, the effect is saturated, so the content of Ca is preferably 0.01% by mass or less, and more preferably 0.008% by mass or less.

Mg: 0.01% by mass or less (0% is not included
B) Mg is an element effective for improving machinability and improving anisotropy due to MnS. The content of Mg is, for example,
The content is 0.0010 mass% or more, preferably 0.0015 mass% or more, and more preferably 0.0020 mass% or more. However, even if Mg is added excessively, the effect is saturated, so the content of Mg is preferably 0.01% by mass or less, and more preferably 0.005% by mass or less.

The free-cutting elements may be added alone or in combination of two or more.

The non-heat treated steel is extremely useful for applications where hot working (for example, hot forging, etc.) is not followed by surface effect treatment such as induction hardening. In other words, because it has excellent wear resistance after hot working, it is possible to obtain products with excellent wear resistance (engine parts such as crankshafts and camshafts) even if induction hardening is omitted. it can. Also, machinability after hot working is secured,
The product can be easily manufactured.

[0035]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples, and may be appropriately applied within the scope of the above and the following points. It is of course possible to make changes and implement them, and all of them are included in the technical scope of the present invention.

Experimental Examples 1 to 19 Steels having the chemical compositions shown in Table 1 (the balance being Fe and unavoidable impurities) were melted in a vacuum furnace, and then the temperature was 1250.
It was heated to ℃, forged into a round bar having a diameter of 60 mm by hot forging, and allowed to cool. Ferrite area ratio of the obtained round bar steel,
While measuring the ferrite hardness, the wear resistance and machinability were evaluated by the following tests.

[Abrasion resistance] Disc-shaped test pieces were cut out from the round bar steel. This test piece and pin (JISSUJ2
Steel) and peripheral speed: 0.05 m / s, surface pressure: 0.0
A pin-on-disk wear test was conducted under the condition of 5 GPa to measure the wear loss of the test piece.

[Machinability] Drill with a diameter of 10 cm (JIS
SKH9 steel), cutting speed 30m / min,
The round steel bar was cut under the conditions of 0.21 mm / rev feed and no lubrication. The total length that could be cut before the drill was melted was measured and defined as the L30 drill life.

The results are shown in Table 1 and FIGS.

[0040]

[Table 1]

As is apparent from FIGS. 1 and 2, the ferrite portion is set to 170 HV or more and the ferrite area ratio is set to 3
Wear resistance can be improved by setting it to 5% or less.

As is clear from Table 1, Experimental Example 1
In Nos. 1 and 13, since the amount of Si and V is relatively small and the ferrite hardness is softened due to the influence of other elements such as C, wear resistance is insufficient even if the ferrite area ratio is small. is there. On the other hand, in Experimental Example 18, Si and V
Is appropriate and the ferrite hardness is sufficient,
Since the amount of Al is large, the area ratio of ferrite is too large, and the wear resistance is insufficient.

On the other hand, in Experimental Examples 1 to 10, S
The amount of i or V is appropriate, the ferrite portion is hard, and the amount of Al is suppressed, so that the area ratio of ferrite is small, so that it has high wear resistance. Moreover, the ferrite area ratio is reduced by suppressing Al, not by increasing the amount of C or the amount of Mn, and thus has a sufficient level of machinability.

In Experimental Example 12, since C is too small,
In Experimental Example 15, since Mn was too small, the ferrite area ratio could not be sufficiently reduced even if Al was suppressed,
Wear resistance becomes insufficient. In Experimental Example 14, too much Si, in Experimental Example 16 too much Mn, and in Experimental Example 17, C
Since r is too large, machinability deteriorates. In Experimental Example 19, in relation to C and other elements, since the amount of Si and V is too large, the ferrite hardness is too hard and the machinability is poor.

[0045]

According to the present invention, since the hardness of ferrite is made hard by Si and V and the area ratio of ferrite is made small, wear resistance can be enhanced. Moreover, since the ferrite area ratio is reduced by suppressing Al, the machinability can be maintained at a good level as compared with the case where C and Mn are increased. Therefore, in a non-heat treated steel that is not subjected to induction hardening after hot working, wear resistance can be increased while ensuring a predetermined level of machinability without setting the ferrite area ratio to 0%.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a ferrite area ratio and a wear amount based on data of an experimental example.

FIG. 2 is a graph showing the relationship between ferrite hardness and wear amount based on the data of experimental examples.

Claims (3)

[Claims] 1. C: 0.32-0.6% by mass, Si:
0.05-1.5 mass%, Mn: 0.30-2.0 mass%, Al: 0.01 mass% or less, Cr: 1.5 mass% or less, V: 0.01-0.5 mass% %, The structure after hot working is a ferrite-perlite structure having a ferrite area ratio of more than 0% and 35% or less, and the hardness of the ferrite portion is 170 to 270 HV. Excellent non-heat treated steel for hot working. 2. As other elements, S: 0.1% by mass or less (not including 0%), Pb: 0.3% by mass or less (not including 0%), Bi: 0.3% by mass Contains at least one selected from the following (not including 0%), Ca: 0.01% by mass or less (not including 0%), and Mg: 0.01% by mass or less (not including 0%). The non-heat treated steel for hot working according to claim 1 or 2. 3. C: 0.32-0.6% by mass, Si:
0.05-1.5 mass%, Mn: 0.30-2.0 mass%, Al: 0.01 mass% or less, Cr: 1.5 mass% or less, V: 0.01-0.5 mass% %, A ferrite area ratio of more than 0% and 35% or less of ferrite-pearlite structure, and the hardness of the ferrite part is 170 to 270H.
V is a hot-worked product with excellent wear resistance.