KR20050008823A - Steel excellent in machinability - Google Patents

Abstract

The present invention provides a steel with excellent machinability, in mass%, C: 0.001 to 1.5%, Si: 3% or less, Mn: 0.01 to 3%, P: 0.001 to 0.2%, S: 0.0001 to 1.2% , Zn: 0.001 to 0.5%, N: 0.0001 to 0.02%, O: 0.0005 to 0.05%. If necessary, the machinable element Sn: 0.002 to 0.5% and / or B: 0.0005 to 0.05% may be contained.

Description

Machinable Steels {STEEL EXCELLENT IN MACHINABILITY}

General machines and automobiles are manufactured by combining a variety of parts, but the parts are manufactured through cutting processes in many cases from the viewpoint of required precision and manufacturing efficiency. At this time, cost reduction and improvement of production efficiency have been demanded, and improvement of machinability has also been demanded in steel.

SUM23 and SUM24L, which are called low-carbon high-speed cutting steels with an amount of C added less than 0.2%, have been developed with emphasis on machinability. Until now, it is known that adding machinability improving elements, such as S and Pb, in order to improve machinability. However, in recent years, Pb tends to avoid its use due to environmental load, and the amount of Pb is decreasing.

Until now, in the case where Pb is not added, a method of improving machinability by forming soft inclusions in a cutting environment such as MnS like S has been used. However, low carbon sulfur free cutting steel SUM23 and the same amount of S are added to the low carbon free cutting steel SUM24L. Therefore, in order to improve machinability, it is necessary to add the amount of S more than conventionally. However, when a large amount of S is added, not only MnS is coarsened, but the distribution of MnS is not effective for improving machinability. In addition, a large number of S causes a number of manufacturing problems, such as a starting point of fracture in rolling and forging. Frequently, in the sulfur free cutting steel based on SUM23, the component edges are easily attached, and unevenness occurs on the cutting surface due to the falling off of the component edges and the separation of cutting chips, resulting in deterioration of surface roughness. Therefore, also from a viewpoint of machinability, the fall of precision by surface roughness deterioration becomes a problem. Also in cutting crumbness, it is known that cutting crumbs are easily broken shortly. However, since ductility of the matrix is large by simple S addition alone, the crumbs are not sufficiently divided and cannot be greatly improved.

Although elements other than S, Te, Bi, P, etc. are also known as machinability improving elements, even if the machinability can be improved to some extent, cracks are likely to occur during rolling and hot forging, and very few are considered to be preferable.

In addition, steel containing 0.2% or more of C contains many alloying elements, such as C, Cr, and Mo, and has comparatively high strength. In the case of such structural steel, the surface roughness is relatively good because the problem of the formation of the constituent cutting edge and the unevenness (roughness) of the cutting surface caused by it is small and is originally a hard material. However, if S, which is a machinability improving element, is added because of its high basic strength, the resulting MnS is drawn by rolling or forging, so that anisotropy appears in the mechanical properties. In addition, S steel is not added to the high-strength steel to improve machinability, and the machinability is often sacrificed.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to steel that can be used for parts such as automobiles and general machinery, and more particularly, to steel having excellent machinability, such as tool life during cutting, cutting surface roughness, and processing of cutting chips after cutting.

Fig. 1 (a) is a diagram showing an outline of a flange cutting test, showing a flange cutting test method.

Fig. 1 (b) is a diagram showing the outline of the flange cutting test showing the movement of the tool.

Fig. 2 is a diagram showing a Ono rotary bending test piece having a notch.

Fig. 3 (a) is a schematic diagram showing carburizing conditions, which is a schematic diagram showing carburizing quenching.

Fig. 3 (b) is a schematic diagram showing carburizing conditions, which is a schematic diagram showing a roughing condition.

Best Mode for Carrying Out the Invention

The basic idea of the present invention is to improve the machinability without impairing mechanical properties by containing Zn in addition to S as an essential component of steel.

In other words, Zn is a particularly important element in the present invention. Zn has the effect of embrittling steel, has the effect of improving the machinability, and particularly has the effect of improving the cutting surface roughness. Moreover, since it exists in a matrix, without taking the form of a coarse inclusion like conventionally known MnS, deterioration of a mechanical property can be suppressed to the minimum. This effect is particularly recognized as anisotropic. On the contrary, even if it has the same degree of mechanical properties, good machinability can be obtained when Zn is added. This is considered to be because the embrittlement effect of Zn becomes remarkable when the temperature rises due to the cutting heat. In addition, it is thought that lubrication effect is performed at the tool / work material interface during cutting. The effect is small at less than Zn: O.OO1%. On the other hand, since Zn is very easy to vaporize during the solvent, it is necessary to add a large amount of Zn in order to retain Zn in molten steel and maintain the amount of Zn exceeding 0.5% even after solidification. 0.5% was made into an upper limit because it was not. Therefore, the component range of Zn in the steel of the present invention was limited to 0.001 to 0.5%.

In addition to Zn, machinability improving elements such as Sn, B, and Te may be contained, but Sn alone does not improve machinability and improves machinability by interaction with Zn.

Below, the reason which limited the steel component other than Zn is demonstrated.

C: 0.001 to 1.5%

Since C is related to the basic strength of steel and the amount of oxygen in the steel, it has a great influence on machinability. When a large amount of C was added to increase the strength, the machinability was lowered, so the upper limit thereof was 1.5%. On the other hand, it is necessary to control the amount of oxygen in an appropriate amount in order to suppress the generation of solid solution oxygen at high temperatures such as pinholes during the solidification process while preventing the formation of hard oxides that lower machinability. If the amount of C is reduced too much by simply blowing, not only the cost increases but also the amount of oxygen in the steel remains in a large amount, causing a defect such as a pinhole. Therefore, C amount 0.001% which can easily prevent defects, such as a pinhole, was made into the lower limit.

Si: 3% or less

Excessive addition of Si lowers the hot ductility, making rolling or the like difficult, but proper addition imparts mechanical properties or softens oxides to improve machinability. The upper limit is 3%, and above that, hot ductility falls, rolling becomes difficult, and industrial production becomes difficult. Moreover, the deterioration, such as generating hard oxides and reducing machinability, arises.

Mn: 0.01 to 3.0%

Mn is necessary to fix and disperse sulfur in steel as MnS as a deoxidation element. It is also necessary to soften oxides in the steel, making the oxides harmless. The effect also depends on the amount of S added, but if it is less than 0.01%, the added S cannot be sufficiently fixed as MnS, and S becomes FeS and becomes brittle. When the amount of Mn increased, the hardness of the base increased and the machinability and cold workability decreased, so 3.0% was taken as an upper limit.

P: 0.001 to 0.2%

Since P has a high hardness of the base in steel and not only cold workability but also hot workability and casting characteristics, the upper limit should be 0.2%. On the other hand, embrittlement made the cutting easy, and the lower limit was made into 0.001% as an element which is effective in improving machinability.

S: 0.0001 to 1.2%

S binds with Mn and exists as an MnS inclusion. Although MnS improves machinability, elongated MnS is one of the causes showing the anisotropy at the time of forging. Although large MnS should be avoided, a large amount of addition is preferable from the viewpoint of machinability improvement. Therefore, it is desirable to finely disperse MnS. The machinability improvement requires 0.0001% or more of addition, preferably 0001% or more. On the other hand, if it exceeds 1.2%, not only the formation of coarse MnS is unavoidable, but also cracking occurs during manufacture due to deterioration of casting characteristics and hot deformation characteristics due to FeS or the like, and this is the upper limit.

N: 0.0001 to 0.02%

N hardens steel in the case of solid solution N. In cutting, in particular, it hardens in the vicinity of the cutting edge by the dynamic strain aging, and reduces the life of the tool, but also improves the cutting surface roughness. It is also combined with B to produce BN to improve machinability. When the N content is less than 0.0001%, the surface roughness improvement effect by solid solution nitrogen and the machinability improvement effect by BN are not recognized. If the N content exceeds 0.02%, since the solid solution nitrogen is present in a large amount, the tool life is rather reduced. In addition, bubbles are generated during casting, which causes scratches and the like. Therefore, in this invention, the upper limit was 0.02% in which such a trouble becomes remarkable.

O: 0.0005 to 0.05%

If free is present, bubbles form during cooling and cause pinholes. In addition, control is required in order to soften the oxides and suppress hard oxides harmful to machinability. In addition, when finely dispersing MnS, an oxide is used as the precipitation nucleus. If the O content is less than 0.00O5%, the MnS cannot be finely dispersed sufficiently, and coarse MnS is generated, which adversely affects mechanical properties. Therefore, 0.0005% was made into a lower limit. If the O content is more than 0.05%, bubbles are formed during the casting and become pinholes, so the content is made 0.05% or less.

Sn: 0.002 to 0.5%

Sn is a soft metal, and is distributed in grain boundaries in steel to embrittle steel. This improves machinability. If it is 0.002% or less, the effect is not recognized, and when it exceeds 0.5%, steel will be embrittled and casting and rolling will become difficult. Therefore, the range was made into 0.002 to 0.5%.

B: 0.0005 to 0.05%

B is effective for improving machinability. This effect is not remarkable at less than 0.0005%, and the effect is saturated even if it is added in excess of 0.05%. If BN is precipitated too much due to thermal history, on the contrary, cracking occurs during manufacturing due to deterioration of casting characteristics and hot deformation characteristics. Let's do it. This ranges from 0.0005 to 0.05%.

Cr: 0.01% to 7%

Cr is an element which improves hardenability and gives softening resistance. Moreover, corrosion resistance can be obtained by adding in large quantities. Therefore, it is added to the steel which needs high strength. In that case, 0.01% or more of addition is required. However, when a large amount is added, Cr carbides are formed to embrittle, so 7% is the upper limit.

Mo: 0.01 to 3%

Mo is an element which gives a softening resistance and improves hardenability. If it is less than 0.01%, the effect is not recognized, and even if it adds more than 3%, since the effect is saturated, 0.01 to 3% was made into addition range.

V: 0.O1-3.0%

V forms carbonitride and can strengthen a steel by secondary precipitation hardening. If it is less than 0.01%, there is no effect on high strength, and when it exceeds 3%, many carbonitrides will precipitate and rather it will damage mechanical property, and it made it the upper limit.

Nb: 0.001 to 0.2%

Nb also forms carbonitrides and can strengthen the steel by secondary precipitation hardening. If it is less than 0.001%, there is no effect on high strength, and when it exceeds 0.2%, many carbonitrides will precipitate, and mechanical property will be impaired, Therefore, this was made into an upper limit.

Ti: 0.001 to 0.5%

Ti also forms carbonitrides and strengthens the steel. It is also a deoxidation element, and it is possible to improve machinability by forming a soft oxide. If it is less than 0.001%, the effect is not recognized, and even if it adds exceeding 0.5%, the effect will be saturated. In addition, Ti becomes a nitride even at high temperatures to suppress the growth of austenite particles. Thus, the upper limit was made 0.5%.

W: 0.01 to 3%

W forms carbonitride and can strengthen the steel by secondary precipitation hardening. If it is less than 0.01%, it is not effective in increasing the strength, and if it is added more than 3%, coarse carbonitride is precipitated, thereby damaging mechanical properties. This was made into an upper limit.

Ni: 0.05 to 7%

Ni is effective in strengthening ferrite, improving ductility, and improving quenching and corrosion resistance. If it is less than 0.05%, the effect is not recognized, and even if it adds exceeding 7%, since an effect is saturated in the point of mechanical property, this was made into an upper limit.

Cu: 0.02-3%

Cu is effective in reinforcing ferrite, improving ductility and improving quenching and corrosion resistance. If it is less than 0.02%, the effect is not recognized, and even if it adds exceeding 3%, since an effect is saturated in the point of mechanical property, it set it as an upper limit. In addition, when Cu is added alone, the hot ductility is extremely lowered, which causes a problem in casting and rolling such as cracks. When the addition amount exceeds 0.3%, it is preferable to add the addition amount of Ni so that Ni% ≥Cu% in order to avoid a manufacturing problem.

Al: 0.001 to 2%

Al is a deoxidation element and forms Al ₂ O ₃ or AlN in steel. This is effective in preventing coarsening of the austenite grain size during quenching and improving toughness. However, if it is less than 0.001%, the effect is not recognized. If it exceeds 2%, coarse inclusions are generated, and mechanical properties are lowered. In addition, since Al ₂ O ₃ is hard, it may cause damage to the tool at the time of cutting and may accelerate wear. At this time, the coarsening effect of austenite particles and the like was saturated, and the limit of 2% of the harmful effect of Al ₂ O ₃ was set as an upper limit. Especially if first the machinability is preferably not more than O.015% do not produce the Al ₂ O ₃ in a large amount, and also is preferably 0005% or below, if first to a softening of the oxide.

Ca: 0.0002 to 0.01%

Ca is a deoxidation element, and it produces | generates a soft oxide, improves machinability, and it has the activity which melt | dissolves in MnS, reduces its deformation | transformation capability, and suppresses the elongation of MnS shape even when rolling or hot forging. Therefore, it is an element effective for reducing anisotropy. If it is less than 0.0002%, the effect is not remarkable, and even if it exceeds 0.01%, yield will not only become extremely bad, but will produce hard CaO, CaS, etc. in large quantities, and will rather reduce machinability. Therefore, the component range was defined as 0.0002 to 0.01%.

Zr: 0.0003 to 0.5%

Zr is a deoxidation element and produces an oxide. The oxide becomes an precipitation nucleus of MnS and is effective in fine uniform dispersion of MnS. Moreover, there exists an activity which suppresses extending | stretching of MnS shape, even if it melt | dissolves in MnS and reduces its deformation | transformation capability, and rolling or hot forging. Therefore, it is an element effective for reducing anisotropy. Is less than 0.0003%, the effect is not remarkable, as well as also the yield is extremely deteriorated by the addition over 0.5%, to lower the bulk created by the light of the ZrO ₂ and ZrS and so on, and rather the machinability. Therefore, the component range was defined as 0.00O3 to 0.5%.

Mg: 0.0002 to 0.02%

Mg is a deoxidation element and produces an oxide. The oxide becomes an precipitation nucleus of MnS and is effective for fine uniform dispersion of MnS. Therefore, it is an element effective for reducing anisotropy. If it is less than 0.0002%, the effect is not remarkable, and even if it adds more than 0.02%, the yield will become extremely worse but the effect will be saturated. Therefore, the component range was defined as 0.0002 to 0.02%.

Te: 0.001 to 0.5%

Te is a machinability improving element. In addition, there is an activity of generating MnTe or coexisting with MnS to reduce the deformation ability of MnS and to suppress the stretching of the MnS shape. Therefore, it is an element effective for reducing anisotropy. This effect is not recognized below 0.001%, and when above 0.5%, the effect is saturated.

Pb, Bi: 0.01 to 0.7%

Pb and Bi are elements which are effective in improving machinability. The effect is not recognized at less than 0.01%, and addition of more than 0.7% not only saturates the machinability improving effect, but also decreases the hot forging characteristic, which is likely to cause scratches. Therefore, each content was made into 0.01 to 0.7%.

From the above circumstances, the present invention has excellent machinability which improves both tool life and surface roughness with respect to so-called low carbon steels, which have a C content of less than 0.15% while avoiding rolling, forging and product performance defects. The object of this invention is to provide steel, and in the case of structural steel and high-strength steel containing 0.15% or more of C, the object is to provide a steel having both mechanical properties (including anisotropy) and machinability.

Cutting is a breaking phenomenon that separates cutting debris, and promoting it becomes one point. However, there is a limit to simply increasing S as described above.

Therefore, the present inventors have conducted extensive experiments and have not only increased S, but also contained Zn as a basic component to embrittle the matrix, to facilitate breakage, to prolong tool life and to suppress unevenness of the cutting surface. I found out what I could do.

This invention is made | formed based on the above discovery, The summary is as follows.

(1) at mass%,

C: 0.001 to 1.5%,

Si: 3% or less,

Mn: 0.01 to 3%,

P: 0.001 to 0.2%,

S: 0.0001 to 1.2%,

Zn: 0.001 to 0.5%,

N: 0.000 l to 0.02%,

O: 0.0005 to 0.05%

Steel excellent in machinability, characterized by containing a.

(2) The steel having excellent machinability of the above (1) substrate, which further comprises Sn: 0.002 to 0.5% by mass.

(3) The steel having excellent machinability according to the above (1) or (2), wherein the mass% contains B: 0.0005 to 0.05%.

(4) Further, in mass%, Cr: 0.01 to 7%, Mo: 0.01 to 3%, V: 0.01 to 3.0%, Nb: 0.001 to 0.2%, Ti: 0.001 to 0.5%, W: 0.01 to 3 The steel excellent in the machinability in any one of said (1)-(3) characterized by containing any 1 type, or 2 or more types in%.

(5) In addition, when the mass% contains any one or two of Ni: 0.05 to 7% and Cu: 0.02 to 3%, and Cu contains 0.3% or more, Ni% ≥Cu% Steel excellent in the machinability in any one of said (1)-(4) characterized by the above-mentioned.

(6) In addition, the mass% contains any one or two or more of Al: 0.001 to 2%, Ca: 0.0002 to 0.01%, Zr: 0.0003 to 0.5%, and Mg: 0.0002 to 0.02%. Steel excellent in the machinability as described in any one of said (1)-(5).

(7) In addition, any one or two or more of Te: 0.001 to 0.5%, Pb: 0.01 to 0.7%, and Bi: 0.01 to 0.7% are contained in mass%. Steel excellent in machinability according to any one of 6).

The effect of this invention is demonstrated by an Example. Some of the test materials having the chemical components shown in Table 1 were dissolved in a 270 ton converter, and then decomposed and rolled into a bead, and then rolled into a steel bar of Φ 50 mm. Others were solvent and rolled in a 2t-vacuum melting furnace. The machinability evaluation of the material shown in Examples 1-40 of Table 2 shows a cutting condition in Table 3 by a drill drilling test. Machinability was evaluated at the highest cutting speed (so-called VLl000) capable of cutting up to a cumulative hole depth of 1000 mm.

Moreover, surface roughness was evaluated by what is called flange cutting which transfers a tool shape with the tool which cut out. The outline of the test method is shown in FIG. In other words, as shown in Fig. 1 (a), the test material 2 rotating in the cutting direction 1 is cut by the tool 3, and as shown in Fig. 1 (b), the tool 3 Move to form the surface roughness measurement surface 4. In addition, the cutting conditions are shown in Table 4. In the experiment, the surface roughness (10-point surface roughness Rz µm) in the case of 200 grooves was measured. In this case, the cutting debris becomes a curl shape in relation to the cutting debris treatment property shown in Table 2, but the cutting debris wound up to 5 times or less breaks and produces short cutting debris. The case where the long cutting debris which does not break even if it wound over the bun is produced is described with "x".

Cutting condition drill Other Cutting speed 10 to 200 m / min Feed 0.33 mm / rev Water insoluble coolant Φ 5mmNACHI Normal drill output 65mm Hole depth 15 mm Tool life to failure

Cutting condition drill Other Cutting speed 80 m / min Feed 0.05 mm / rev Water insoluble coolant SKH51 equivalent face angle 15 ° Free angle 6 ° 200 cycles of protrusion evaluation

All of the invention examples were excellent in the tool life of a drill compared with the comparative example, and the surface roughness in flange cutting was favorable. Even if the addition amount of C, S, etc. was different, the order did not change, and when elements, such as Zn, Sn, and B, were added, they were excellent in tool life and surface roughness compared with the comparative steel of the same C, S, etc. Although a large part of the amount of S tended to have good machinability, even when the amount of S was relatively small, it was found that the cutting chip treatment property was improved.

On the other hand, even in the case where Sn was added as in Comparative Examples 6 and 26 in the example, the machinability did not improve unless Zn was added.

In addition, even in the case of including conventionally known machinability enhancing elements such as Te, Pb, and Bi, addition of Zn showed better machinability.

Similarly, the chemical composition of the sample evaluating the machinability and mechanical properties of the structural carbon steel-based steel is shown in Table 5, and the evaluation results are shown in Table 6. Each of the specimens was partly solated in a 270t converter and then decomposed and rolled into a bead and further rolled into a bar of φ65 mm. Others were solvent-rolled and rolled in a 2t vacuum furnace.

Impact value (J / cm <^2> ) created and evaluated the U notch test piece of 2 mm depth based on JIS.

The machinability evaluation of Examples 41 to 43 containing about 0.1% of C shows the cutting conditions in Table 3 by the drill drilling test. Machinability was evaluated at the highest cutting speed (so-called VL1000) capable of cutting to a cumulative hole depth of 1000 mm.

In addition, surface roughness was evaluated by what is called flange cutting which transfers a tool shape with a stone cutting tool. In the experiment, the surface roughness at the time of 200 grooving was measured. Surface roughness was evaluated by flange cutting shown in Table 4.

With respect to Examples 44 to 46 containing about 0.3% of C and Examples 47 to 77 in excess of C, the impact value and its anisotropy were shown in order to emphasize the mechanical properties. Here, the (impact value of the cross-sectional direction sample) / (impact value of the longitudinal direction sample) is shown as anisotropy, as well as the ("C direction" column) indicating the impact value of the sample cut out in the cross-sectional direction of the steel bar (the "anisotropy" column). Larger value indicates less anisotropy.

In addition, the machinability evaluation of Examples 47-77 was performed with the drill drilling characteristic VL1000, and the cutting conditions shown in Table 7 were evaluated. In these cases, the cutting surface roughness is not evaluated.

Cutting condition drill Other Cutting speed 1 to 200 m / min Feed 0.25 mm / rev Water insoluble coolant Φ3mmNACHI Normal Drill Output 45mm Hole depth 9 mm Tool life to failure

In the comparison of Examples 41 to 43, the invention example was superior to the comparative example in the VL1000 and the surface roughness. In addition, with respect to Examples 44 to 77, the invention example shows the hardness HV, the impact value of the cross-sectional sample, and the (impact value of the cross-sectional sample) / (impact value of the longitudinal sample) for the comparative example containing almost equivalent C and other alloying elements. Although is almost equivalent, it can be seen that the invention example is excellent in machinability because VL100O is good.

In addition, when the machinability was improved by increasing S as in Comparative Example 53, the anisotropy of the impact value was lowered, and therefore, the performance as structural steel was considered to be inferior to Inventive Examples 47 and 48.

In Table 8, the Example based on the steel which added a large amount of alloying elements and improved hardenability is shown. Some of the test materials were dissolved in a 270t converter and then decomposed and rolled into a bead and further rolled to Φ50mm. The others were solvent and rolled in a 2t vacuum furnace.

Examples 78-82 were used for the cutting test after carrying out the roughing (920 degreeC * 1hr-> air cooling) about the steel based on SCr420. The machinability evaluation is a drill drilling test, the cutting conditions are shown in Table 5, and the evaluation item is the highest cutting speed (so-called VL1000) that can be cut up to a accumulated hole depth of 1000 mm. The unit of this VL10OO is m / min, and the larger it is, the more excellent the tool life is. In addition, the hardness was measured, and as shown in Fig. 2, a notched Ohno-type rotary bending test piece having a notch of R1.16 mm was formed on the test piece of 9 mm Φ, and carburized under the conditions shown in Figs. 3 (a) and (b). After that, the fatigue characteristics were evaluated.

As a result, the VL1000 was better in the development steel, although the hardness after the collimation shown in Fig. 3B was almost the same. The fatigue property after carburization is almost equivalent, and it turns out that the technique of this invention improves machinability, but does not reduce subsequent gear performance.

In Table 9, the Example based on the steel which added a large amount of alloying elements and improved hardenability is shown. Some of the test materials were dissolved in a 270 ton converter, and then cracked and rolled into a bead and then rolled to Φ 50 mm. The others were solvent and rolled in a 2t-vacuum melting furnace. Machinability evaluation is a drill drilling test, the cutting conditions are shown in Table 7, and the evaluation item is the maximum cutting speed (so-called VL1000) that can be cut up to a cumulative hole depth of 1000 mm.

In Examples 83 to 88, SCM440 was used as the base steel, the hardness was adjusted to about HV310 by the hardening treatment, and the machinability evaluation was VL1000. In addition, the impact value was evaluated as mechanical properties. The impact value was cut out from the longitudinal direction of the steel bar, and measured by JIS3 test piece (test piece cut out to 2 mm U). As a result, although the invention example had almost the same hardness and impact value (J / cm <^2> ) with respect to a comparative example, machinability VL100 was larger and superior than a comparative example.

In addition, Examples 89 to 94 were softened by a rounding annealing treatment 700 × 20 hr correction based on the bearing steel, and the machinability VL1000 was measured. As a result, although the invention example had a substantially equivalent hardness compared with the comparative example, machinability VL1000 was large and was superior to the comparative example.

According to the steel of the present invention, by promoting the breakage of the matrix in the steel, the tool life and the cutting surface roughness is improved in the so-called low carbon free cutting steel of less than 0.15% C, and even if it does not contain Pb, the tool life and the cutting surface roughness are good. In addition, in the structural steel containing 0.15% or more of C, the machinability can be improved, and the deterioration of mechanical properties, in particular, the anisotropy can be suppressed to the minimum. Alternatively, the steel of the present invention can obtain better machinability than steel having the same degree of mechanical properties.

Claims (7)

In mass%, C: 0.001 to 1.5%, Si: 3% or less, Mn: 0.01 to 3%, P: 0.001 to 0.2%, S: 0.0001 to 1.2%, Zn: 0.001 to 0.5%, N: 0.000 l to 0.02%, O: 0.0005 to 0.05% Steel excellent in machinability, characterized by containing a. The steel having excellent machinability according to claim 1, further comprising Sn: 0.002 to 0.5% by mass. The steel having excellent machinability according to claim 1 or 2, further comprising B: 0.0005 to 0.05% by mass. The method according to any one of claims 1 to 3, wherein, in mass%, Cr: 0.01 to 7%, Mo: 0.01 to 3%, V: 0.01 to 3.0%, Nb: 0.001 to 0.2%, Ti The steel excellent in the machinability characterized by containing any 1 type (s) or 2 or more types out of: 0.001-0.5% and W: 0.01-3%. The mass% further comprises any one or two of Ni: 0.05 to 7% and Cu: 0.02 to 3%, and Cu is 0.3% or more. In the case of containing a steel having excellent machinability, characterized in that it satisfies Ni% ≥Cu%. The mass% according to any one of claims 1 to 5, wherein Al: 0.001 to 2%, Ca: 0.0002 to 0.01%, Zr: 0.0003 to 0.5%, Mg: 0.0002 to 0.02% Steel excellent in machinability, characterized by containing two or more species. The mass% according to any one of claims 1 to 6 further contains any one or two or more of Te: 0.001 to 0.5%, Pb: 0.01 to 0.7%, and Bi: 0.01 to 0.7%. Steel excellent in machinability, characterized by the above-mentioned.