JP4148035B2 - Steel bar and wire rod excellent in machinability and low magnetic field magnetic properties, and method for producing the same - Google Patents

Description

【００２８】
【表２】

【００２９】
表２に示したとおり、発明例はいずれも、工具寿命は良好であり、また低磁場域での磁束密度も高い値を示している。
特に、適量のＢとＮを複合含有させたNo.4, 5, 6はいずれも、黒鉛化処理時間を短縮した上で、良好な被削性および低磁場磁気特性を得ることができた。
これに対し、黒鉛化処理時間が短すぎて黒鉛化率が本発明の範囲外となった比較鋼（No.3）は、被削性および低磁場磁気特性のいずれもが低下した。
また、Ｃ量が本発明の範囲よりも少ない比較例（No.7）は、黒鉛量の減少により工具寿命が低下している。
さらに、Ｃ量が本発明の範囲よりも多い比較例（No.8）は、被削性は良好であったが、低磁場磁気特性の劣化を招いた。
また、黒鉛化処理時間が短すぎて黒鉛化率が本発明の範囲外となった比較例（No.9）は、被削性および低磁場磁気特性のいずれもが低下している。
さらに、Ｂを添加した場合のＮ量が本発明（請求項２）の下限に満たない比較例（No.10)は、被削性は良好であったが、黒鉛化処理に長時間を要した。また、固溶Ｂが残留したため、低磁場磁気特性も劣っていた。
また、Ｐ量が本発明の下限に満たない比較例（No.11)は、被削性は良好であったが、低磁場磁気特性に劣っていた。
さらに、Mn量が本発明の上限を超えた比較例（No.12)は、黒鉛化に長時間を必要とした。そのため、黒鉛化時間を短縮しようとすると、黒鉛化が不十分となり、被削性および低磁場磁気特性が共に劣化した。
【００３０】
【発明の効果】
かくして、本発明によれば、自動車や家電製品等の電装部品等に適した被削性と低磁場磁気特性に兼ね備える珪素含有棒鋼・線材を安定して得ることができる。
また、本発明によれば、鋼中に適量のＢＮを析出させることにより、黒鉛化時間を有利に短縮することができ、その結果、生産性の大幅な向上を達成することができる。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a silicon-containing steel bar / wire used for electrical parts such as automobiles and home appliances, and a method for producing the same, and in particular, the machinability required in the production process of these parts and the low required in the product stage. This is an advantageous improvement of the magnetic field magnetic characteristics.
[0002]
[Prior art]
A silicon-containing steel material that easily adapts to a magnetic field is used as a member constituting a magnetic circuit such as an electrical component such as an automobile or home appliance. This is because these members are required to have magnetic properties that are easily magnetized by a small external magnetic field and have a high initial permeability.
[0003]
When manufacturing these steel materials, it is common to hot-roll them into steel bars and wires, and then to perform cold working and cutting such as wire drawing and forging, and magnetic annealing etc. are performed after final forming is completed. there were.
However, in recent years, there is an increasing demand for further improvement of machinability from the viewpoint of energy saving. That is, the development of silicon-containing steel bars and wires with good machinability has been desired.
[0004]
On the other hand, in order to ensure the magnetic response required for these members, a steel material having a high magnetic flux density at a low magnetic field, for example, a magnetic flux density at a magnetic field of 100 A / m is effective.
[0005]
However, the machinability and the low magnetic field magnetic properties as described above are contradictory properties from the viewpoint of the chemical composition of the steel material. In other words, in order to improve the machinability of steel, it is effective to reduce solid solution strengthening elements such as Si and soften the steel, but reduction of Si is not preferable from the viewpoint of magnetic properties. . In addition, it is very effective for improving machinability to disperse sulfides such as MnS and lead in steel, to reduce cutting resistance during cutting, and to improve chip disposal. Elements greatly impair magnetic properties. In particular, lead is not preferable because it has an adverse effect on the environment and the human body.
[0006]
Patent Document 1 proposes a free-cutting electrical steel in which machinability is improved by incorporating graphite into the steel.
However, in the free-cutting electrical steel disclosed in Patent Document 1, the magnetic flux density in a low magnetic field is not necessarily high, and the low magnetic field magnetic characteristics cannot be said to be good. Furthermore, in this free-cutting electrical steel, in order to sufficiently precipitate graphite and improve machinability, a long-time graphitization treatment is required, and there is a problem in that productivity is hindered. It was.
[0007]
[Patent Document 1]
Japanese Patent Publication No. 54-11769 [0008]
[Problems to be solved by the invention]
As described above, a steel material having both machinability and low magnetic field magnetic properties as an electrical component has not been found so far, and its development has been desired.
The present invention advantageously solves the above problems, and proposes a silicon-containing steel bar / wire material having high machinability in the manufacturing process and having excellent low-field magnetic properties in the product, together with its advantageous manufacturing method. The purpose is to do.
[0009]
[Means for Solving the Problems]
Now, in order to achieve the above object, the inventors have conducted extensive research on a component composition capable of obtaining a large magnetic flux density with a low magnetic field and shortening the graphitization treatment time.
(1) Inclusion of an appropriate amount of P in steel improves the magnetic flux density in a low magnetic field.
(2) By making most of the carbon present in the steel graphite, the machinability is significantly improved.
(3) The knowledge that the amount of Mn in the steel was reduced and the graphitization treatment time could be shortened by precipitating an appropriate amount of BN in the steel and the productivity was significantly improved was obtained.
The present invention is based on the above findings.
[0010]
[Means for Solving the Problems]
That is, the gist configuration of the present invention is as follows.
1. C: 0.10 to 0.50% in mass%,
Si: 0.5-3.5%
Mn: less than 0.05%,
P: 0.010 to 0.10%,
Al: 0.35% or less,
N: 0.010% or less,
Machinability and low magnetic field characterized by containing S: 0.006% or less and O: 0.015% or less, the balance being Fe and inevitable impurities, and more than 95% of carbon in steel being graphite. Steel bars and wires with excellent magnetic properties.
[0011]
2. C: 0.10 to 0.50% in mass%,
Si: 0.5-3.5%
Mn: less than 0.05%,
P: 0.010 to 0.10%,
Al: 0.35% or less,
B: 0.0010 to 0.0030%,
N: 0.002 to 0.010%,
Machinability and low magnetic field characterized by containing S: 0.006% or less and O: 0.015% or less, the balance being Fe and inevitable impurities, and more than 95% of carbon in steel being graphite. Steel bars and wires with excellent magnetic properties.
[0012]
3. C: 0.10 to 0.50% in mass%,
Si: 0.5-3.5%
Mn: less than 0.05%,
P: 0.010 to 0.10%,
Al: 0.35% or less,
N: 0.010% or less,
A steel material containing S: 0.006% or less and O: 0.015% or less, with the balance being Fe and inevitable impurities, is converted into a bar or wire by hot working, or after further forming, 600 to 720 A method for producing a bar / wire excellent in machinability and low magnetic field magnetic characteristics, characterized by performing graphitization treatment at 15 ° C. for 15 to 30 hours.
[0013]
4). C: 0.10 to 0.50% in mass%,
Si: 0.5-3.5%
Mn: less than 0.05%,
P: 0.010 to 0.10%,
Al: 0.35% or less,
B: 0.0010 to 0.0030%,
N: 0.002 to 0.010%,
A steel material containing S: 0.006% or less and O: 0.015% or less, with the balance being Fe and inevitable impurities, is converted into a bar or wire by hot working, or after further forming, 600 to 720 A method for producing a steel bar / wire excellent in machinability and low magnetic field magnetic characteristics, characterized by performing a graphitization treatment at 5 ° C. for 5 to 15 hours.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described below.
First, the reason why the composition of steel is limited to the above range in the present invention will be described. Unless otherwise specified, “%” in relation to ingredients means mass%.
C: 0.10 to 0.50%
C is a basic element that forms graphite effective in improving machinability, and in order to exhibit the effect, addition of 0.10% or more is necessary. However, if the amount is too large, the low magnetic field magnetic properties are deteriorated, so the upper limit was set to 0.50%.
[0015]
Si: 0.5-3.5%
Si is an element effective for improving the magnetic flux density and iron loss in the low magnetic field region of steel, and for that purpose, it must contain 0.50% or more. On the other hand, if the amount of Si is too large, it is a solid solution. Since the machinability of steel decreases due to strengthening, the upper limit was made 3.50%.
[0016]
Mn: less than 0.05%
Mn is an element that stabilizes cementite and inhibits graphitization. Therefore, cementite remains and deteriorates the low magnetic field magnetic properties. Moreover, since cementite is hard, machinability is also deteriorated. Furthermore, delaying graphitization is also disadvantageous for machinability. Therefore, it is desirable to reduce the content of Mn as much as possible, but it is acceptable if it is less than 0.05%.
[0017]
P: 0.010 to 0.10%
P is an element useful for improving the magnetic flux density in the low magnetic field region of steel, and for that purpose, it must contain at least 0.010%. On the other hand, if the amount of P is too large, the steel is cooled by solid solution strengthening. Since the workability is reduced, the upper limit was made 0.10%.
[0018]
Al: 0.35% or less
Al is an effective element for improving the magnetic flux density in the low magnetic field region of steel. However, if stepped in a large amount, the cold workability of steel decreases due to solid solution strengthening, so Al is 0.35% or less. Limited to.
[0019]
N: 0.010% or less If N is too much, lower magnetic field magnetic properties are deteriorated due to solid solution strengthening, strain aging, etc., so the upper limit was made 0.010%.
[0020]
S: 0.006% or less S forms sulfide inclusions to lower ductility and also adversely affects low magnetic field magnetic properties. Therefore, it is desirable to reduce it as much as possible, but 0.006% or less is acceptable. .
[0021]
O: 0.015% or less O is not only harmful to steel cleaning, but also lowers the low-field magnetic properties, so it is desirable to reduce it as much as possible, but 0.015% or less is acceptable.
[0022]
Although the essential components have been described above, in the present invention, a steel bar / wire rod having further excellent machinability can be provided by further containing B with an appropriate amount of N. The preferred component composition range of N and B in this case will be described.
[0023]
B: 0.0010-0.0030%
B combines with N to form BN, which effectively contributes as a graphite precipitation site. Here, in order to form an appropriate amount of BN, at least 0.0010% of B is required. However, if the amount of B is too large, excess B deteriorates the low magnetic field magnetic properties, so the upper limit of B is set to 0.0030%. .
[0024]
N: 0.002 to 0.010%
As described above, N combines with B to form BN, which effectively contributes as a graphite precipitation site. Therefore, simultaneous addition of B and N not only promotes graphitization of steel, but also promotes fine dispersion of graphite, and as a result, improvement of machinability and shortening of graphitization time are achieved at the same time. The
However, if the amount of N is less than 0.002%, the effect of addition is poor. On the other hand, if it exceeds 0.010%, the magnetic properties of the low magnetic field are deteriorated, so the amount of N when B is added is in the range of 0.002 to 0.010%. This is very important.
[0025]
In the present invention, the production method is not particularly limited except for the graphitization treatment time described later, and may be performed according to a conventional method.
For example, after refining the converter, it is cast, hot-worked into the required size of steel bars and wires, and then subjected to graphitization. Moreover, after shape | molding said steel bar and wire into a component shape by hot forging, you may give a graphitization process.
Next, in the graphitization treatment, when BN is not included, the treatment is performed at 600 to 720 ° C. for 15 to 30 hours.
On the other hand, when BN is contained, this BN functions as a graphite precipitation site and promotes graphitization of the steel. Short processing time of 15 hours is enough.
Thus, 95% or more of the carbon in the steel can be made graphite.
[0026]
【Example】
A steel material having the composition shown in Table 1 was hot forged into a 150 mm square billet, heated to 1100 ° C., and then rolled into a steel bar having a diameter of 50 mm. Subsequently, graphitization was performed under various conditions shown in Table 2 in order to change the cementite in the steel to graphite.
Table 2 shows the results of the investigation on the machinability and low magnetic field magnetic properties of the steel bars thus obtained.
Table 2 also shows the results of examining the graphitization rate and the 95% graphitization time.
In addition, the machinability of the steel bar was evaluated by the number of holes until cutting became impossible by continuously drilling (non-lubricating) with a depth of 20 mm using a carbide drill.
In addition, low magnetic field magnetic properties are measured by applying a ring-shaped test piece with an outer diameter of 45 mmφ, an inner diameter of 33 mmφ, and a height of 5 mm from steel bars, and annealing after annealing at 700 ° C for 1 hour. Magnetic flux density (B ₁ ) at magnetic field: 100 A / m was measured and evaluated based on this value.
[0027]
[Table 1]

[0028]
[Table 2]

[0029]
As shown in Table 2, all of the inventive examples have a good tool life and a high magnetic flux density in a low magnetic field region.
In particular, Nos. 4, 5, and 6 containing a suitable amount of B and N were able to obtain good machinability and low magnetic field magnetic properties while shortening the graphitization time.
In contrast, the comparative steel (No. 3) in which the graphitization treatment time was too short and the graphitization rate was outside the range of the present invention, both the machinability and the low magnetic field magnetic properties were lowered.
Further, in the comparative example (No. 7) in which the C amount is less than the range of the present invention, the tool life is reduced due to the decrease in the graphite amount.
Furthermore, the comparative example (No. 8) in which the C content is larger than the range of the present invention had good machinability but caused deterioration of the low magnetic field magnetic properties.
Further, in the comparative example (No. 9) in which the graphitization treatment time is too short and the graphitization rate is outside the range of the present invention, both the machinability and the low magnetic field magnetic properties are deteriorated.
Furthermore, the comparative example (No. 10) in which the amount of N when B was added did not reach the lower limit of the present invention (Claim 2) had good machinability, but required a long time for graphitization. did. Moreover, since the solid solution B remained, the low magnetic field magnetic characteristics were also inferior.
Further, the comparative example (No. 11) in which the amount of P was less than the lower limit of the present invention had good machinability but was inferior in low magnetic field magnetic characteristics.
Furthermore, the comparative example (No. 12) in which the amount of Mn exceeded the upper limit of the present invention required a long time for graphitization. Therefore, when trying to shorten the graphitization time, graphitization became insufficient, and both machinability and low magnetic field magnetic properties deteriorated.
[0030]
【The invention's effect】
Thus, according to the present invention, it is possible to stably obtain a silicon-containing steel bar / wire material having both machinability and low magnetic field magnetic properties suitable for electric parts such as automobiles and home appliances.
Further, according to the present invention, by precipitating an appropriate amount of BN in the steel, the graphitization time can be advantageously shortened, and as a result, a significant improvement in productivity can be achieved.

Claims (4)

C: 0.10 to 0.50% in mass%,
Si: 0.5-3.5%
Mn: less than 0.05%,
P: 0.010 to 0.10%,
Al: 0.35% or less,
N: 0.010% or less,
Machinability and low magnetic field characterized by containing S: 0.006% or less and O: 0.015% or less, the balance being Fe and inevitable impurities, and more than 95% of carbon in steel being graphite. Steel bars and wires with excellent magnetic properties. C: 0.10 to 0.50% in mass%,
Si: 0.5-3.5%
Mn: less than 0.05%,
P: 0.010 to 0.10%,
Al: 0.35% or less,
B: 0.0010 to 0.0030%,
N: 0.002 to 0.010%,
Machinability and low magnetic field characterized by containing S: 0.006% or less and O: 0.015% or less, the balance being Fe and inevitable impurities, and more than 95% of carbon in steel being graphite. Steel bars and wires with excellent magnetic properties. C: 0.10 to 0.50% in mass%,
Si: 0.5-3.5%
Mn: less than 0.05%,
P: 0.010 to 0.10%,
Al: 0.35% or less,
N: 0.010% or less,
A steel material containing S: 0.006% or less and O: 0.015% or less, with the balance being Fe and inevitable impurities, is converted into a bar or wire by hot working, or after further forming, 600 to 720 A method for producing a bar / wire excellent in machinability and low magnetic field magnetic characteristics, characterized by performing graphitization treatment at 15 ° C. for 15 to 30 hours. C: 0.10 to 0.50% in mass%,
Si: 0.5-3.5%
Mn: less than 0.05%,
P: 0.010 to 0.10%,
Al: 0.35% or less,
B: 0.0010 to 0.0030%,
N: 0.002 to 0.010%,
A steel material containing S: 0.006% or less and O: 0.015% or less, with the balance being Fe and inevitable impurities, is converted into a bar or wire by hot working, or after further forming, 600 to 720 A method for producing a steel bar / wire excellent in machinability and low magnetic field magnetic characteristics, characterized by performing a graphitization treatment at 5 ° C. for 5 to 15 hours.