JP6846925B2 - Free-cutting electrical steel with excellent manufacturability - Google Patents

Description

This application is lead-free, has a low environmental load, has excellent corrosion resistance and machinability, and can be used as a member of various electromagnetic actuators such as solenoids and solenoid valves, and electromagnetic sensors. Regarding electrical steel cutting.

Electrical steel is also required to have good manufacturability from the viewpoints of excellent magnetic properties, machinability, corrosion resistance, and low cost and stable supply of materials. Pb-added electrical steels with good manufacturability and excellent machinability without impairing magnetic properties and corrosion resistance are already on the market. However, in recent years, the manufacturing industry has avoided the use of Pb in consideration of the toxicity of Pb. There is an example in which S is added as an alternative free-cutting element for Pb and sulfide is dispersed in steel as a machinability improving substance. However, this product deteriorates various required characteristics such as good manufacturability in addition to the above-mentioned magnetic characteristics, machinability, and corrosion resistance. Therefore, there is a demand for a material that is non-Pb and has excellent manufacturability such as excellent magnetic properties, machinability, corrosion resistance, and hot workability.

As a prior art, for example, _{a material to which free-cutting property is imparted by Ti 4} C ₂ S ₂ without impairing magnetic properties and corrosion resistance has been proposed and patented (see, for example, Patent Document 1). However, the patent of this proposal has not been examined in detail regarding manufacturability from the viewpoint of low cost and stable supply. In addition, this proposal has a problem in that it also allows the addition of Pb of 0.15% by mass or less.

This electrical steel has been proposed and patented as a material imparted with free-cutting property without impairing magnetic properties and corrosion resistance by adding (Cr, Mn) S and Te without using Pb (for example, patent). See Reference 2.). However, the patent of this proposal has a problem that the amount of S added, which is responsible for machinability, is as small as 0.040% by mass or less, and therefore the improvement in machinability is not always sufficient.

This electrical steel is a material that imparts free-cutting property without impairing magnetic properties and corrosion resistance by adding (Cr, Mn) S and Te without using Pb, and the amount of S added that is responsible for machinability is also Most of the applications are proposals having machinability equal to or higher than that of Pb-added steel (see, for example, Patent Document 3). Although the application for this proposal considers hot workability among the manufacturability, it is simply at the level of being manufacturable, and further improvement in manufacturability is necessary from the viewpoint of inexpensive and stable supply. Is.

Japanese Patent No. 4544977 Japanese Patent No. 5730153 Japanese Unexamined Patent Publication No. 2016-1136667

The problem to be solved by the invention of the present application is that various electromagnetic actuators such as solenoids and solenoid valves, electromagnetic sensor members, and the like are first required to have excellent soft magnetic properties. Furthermore, in addition, sufficient corrosion resistance for the usage environment and machinability that can be used for precision processing and mass production processing are also required. In order to meet such demands, the addition of Pb has been used for a long time in steel materials because the machinability is significantly improved without impairing the corrosion resistance. However, considering the reduction to the environmental load, it is necessary to avoid the use of Pb. Therefore, a method of adding S as a free-cutting element instead of Pb is used. However, the addition of S deteriorates the magnetic properties and corrosion resistance, which are essential properties, and further promotes the formation of low melting point compounds, which significantly impairs the manufacturability of the material, which is problematic in terms of stable supply and manufacturing cost. Occurs. In order to solve such a problem, it is an object of the present invention to provide a free-cutting electrical steel having sufficient corrosion resistance and machinability without adding Pb and having excellent manufacturability that can be stably supplied.

First, the means of the present invention for solving the above problems has a small environmental load, sufficient corrosion resistance and magnetic properties, and further, steel ingot crack resistance and hotness, which are material manufacturability. In order to obtain free-cutting electromagnetic steel with excellent workability, the following five measures will be taken.
1. 1. Non-Pb steel is used to reduce the environmental load.
2. A sulfide or a composite compound composed of a sulfide and a Te compound is dispersed in the steel to have a machinability equal to or higher than that of Pb steel.
3. 3. Deterioration of magnetic properties due to S addition is avoided by adjusting the Si addition amount and Cr addition amount.
4. It is good by controlling the composition of Cr, Mn, S and the value of Mn / S of the formula (1), fixing S as a sulfide to ensure hot workability, and making it Cr-rich. Obtain corrosion resistance.
5. The composition of one or more of Al, Ti, Nb, and V, and the formula (2) below enhances ferrite stability, resulting in excellent magnetic properties and manufacturability. Ensure workability.

Secondly, the following 6. We will take one of the measures.
6. By the composition of Te and the limitation by the formulas (3) and (4), the machinability and the magnetic properties are improved, and the deterioration of the hot workability due to the addition of Te is suppressed.
That is, it is an invention of the following first means and second means.

In the first means, in terms of mass%, C: 0.030% or less, Si: 0.5 to 3.5%, Mn: 0.05 to 0.50%, P: 0.030% or less, S: It contains 0.050 to 0.200%, Cr: 6.0 to 10.0%, N: 0.030% or less, and one or more of Al, Ti, V and Nb in total. in containing 0.005 to 0.800 percent, a steel balance consisting of Fe and unavoidable impurities, into steel, as machinability improving compound major diameter 400μm following (Cr, Mn) sulfide 10 ⁶ [mu] m ² 40 or more are dispersed in the range of, the size of the formula (1) is 1.2 to 5.0, and the size of the formula (2) is 30 or more. It is a free-cutting electromagnetic steel with excellent manufacturability of lump cracking and hot workability.
However,
Equation (1): Mn / S
Equation (2): 8Si + 8Al + Cr + 4Ti + 4V + 2Nb + 2 (Mn / S) -16 (C + N)

The second means has the chemical component of claim 1 and, in addition to the sizes of formulas (1) and (2), contains Te: 0.030% or less in mass%, and the balance. It is a steel composed of Fe and unavoidable impurities, and the free-cutting property-imparting compound is a composite inclusion having a major axis of 300 μm or less composed of (Cr, Mn) sulfide and a Te compound existing so as to surround the sulfide. There exists dispersed 30 or more in the range of 10 ⁶ [mu] m ^2, and the formula (3) is 0.15 or more, the formula (4) is耐鋼mass cracking, characterized in that 0.95 or less It is a free-cutting electromagnetic steel with excellent manufacturability and hot workability.
However, equation (3): Te / S
Equation (4): 55Te- {2Al + 2Ti + 4V + 4Nb + (Mn / 20S)

Since the invention of the above means is a non-Pb steel having no Pb, the environmental load is reduced and it is small, and it is composed of a sulfide composed of (Mn, Cr) S or a Te compound surrounding the sulfide. By dispersing the composite compound in the steel, it has machinability equal to or higher than that of Pb steel, has low coercive force, and has excellent corrosion resistance. Cr, Mn, S composition and Mn / S of formula (1) are controlled, S is fixed as sulfide and hot workability is processed, while Cr is avoided. By making it rich, good corrosion resistance can be obtained, and by increasing the ferrite stability according to the composition of Al, Ti, Nb, V and the formula (2), the steel ingot cracking resistance, which is excellent magnetic properties and manufacturability, is obtained. And hot workability is ensured, and while improving machinability and magnetic properties by limiting the composition of Te and formulas (3) and (4), deterioration of hot workability due to the addition of Te is suppressed. Has the effect of

Prior to the embodiment for carrying out the invention, the chemical composition and each condition in the present invention will be described. The chemical composition is shown in% by mass.

C: 0.030% or less C is an unavoidable impurity, and if it is more than 0.030%, the magnetic properties, corrosion resistance and free-cutting property of the obtained electromagnetic steel are deteriorated. Therefore, C is set to 0.030% or less.

Si: 0.5-3.5%
Si is an element that helps improve the intrinsic resistance and magnetic properties. Therefore, Si is set to 0.5% or more. However, if Si is more than 3.5%, the magnetic properties deteriorate due to excessive addition, and the toughness and workability of the material deteriorate. Therefore, Si is set to 0.5 to 3.5%.

Mn: 0.05 to 0.50%
Mn is an element that combines with S to form sulfide and improves machinability. Therefore, Mn is set to 0.05% or more. However, if Mn is more than 0.50%, the magnetic characteristics deteriorate. Therefore, Mn is set to 0.05 to 0.50%.

P: 0.030% or less P is an unavoidable impurity, and if it is more than 0.030%, the hot workability and magnetic properties of the obtained electromagnetic steel deteriorate. Therefore, P is set to 0.030% or less.

S: 0.050 to 0.200%
S is an element that combines with Mn to form a sulfide and improves machinability. For that purpose, S needs to be 0.050% or more. However, if S is more than 0.200%, the magnetic properties and corrosion resistance deteriorate. Therefore, S is set to 0.050 to 0.200%.

Cr: 6.0-10.0%
Cr is an element essential for improving corrosion resistance, and is an element that reduces coercive force and improves soft magnetic properties. For that purpose, Cr is set to 6.0% or more. However, when Cr is more than 10.0%, the effect of Cr is saturated, and the coercive force is increased and deteriorated due to excessive addition. Therefore, Cr is set to 6.0 to 10.0%.

N: 0.030% or less N is an unavoidable impurity, and if it is more than 0.030%, the magnetic properties of the obtained electromagnetic steel deteriorate and the machinability due to nitride formation deteriorates. Therefore, N is set to 0.030% or less.

Contains at least one or more of Al, Ti, V, Nb, the total of which is: 0.005 to 0.800%
Al, Ti, V, and Nb are all selective elements, and are elements involved in ingot cracking, hot workability, corrosion resistance, machinability, and magnetic properties. By the way, when the total of one or more of these elements is 0.005% or more, due to the stabilization of the ferrite phase, these ingot cracks, hot workability, corrosion resistance, machinability and magnetic properties Deterioration can be avoided. On the other hand, when the total of one or more of these elements is more than 0.800%, the above effect is saturated, and due to the formation of carbonitride, hot workability, corrosion resistance, machinability, and magnetic properties Deteriorates. Therefore, at least one or more of Al, Ti, V, and Nb are included, and the total thereof is 0.005 to 0.800%.

1.2 ≤: Equation (1): ≤ 5.0, where equation (1) = Mn / S
Formula (1) is a value related to hot workability and corrosion resistance. If the value of the formula (1) is smaller than 1.2, the hot workability deteriorates. On the other hand, if the value of the formula (1) is larger than 5.0, the corrosion resistance deteriorates. Therefore, 1.2 ≦ equation (1) ≦ 5.0 is set.

Equation (2): ≧ 30, where equation (2) = 8Si + 8Al + Cr + 4Ti + 4V + 2Nb + 2 (Mn / S) -16 (C + N)
Equation (2) is a value related to hot workability. If the value of the formula (2) is smaller than 30, the hot workability deteriorates. Therefore, the equation (2) ≥ 30 is set.

Te: ≤0.030%
Te is an element involved in machinability, magnetic properties and hot workability in the formation of Te compounds and the morphological control of Te sulfides. When Te is 0.030% or less, machinability and magnetic properties are improved by forming a Te compound and controlling the morphology of Te sulfide. On the other hand, if Te exceeds 0.030%, the hot workability deteriorates. Therefore, Te is set to 0.030% or less.

Equation (3): ≧ 0.15, where equation (3) = Te / S
The value of the formula (3) is related to the hot workability associated with the low melting point of the Te compound. Therefore, by setting the value of the formula (3) to 0.15 or more, it is possible to suppress the lowering of the melting point of the Te compound and secure the hot workability. Therefore, the value of the formula (3) is set to 0.15 or more.

Equation (4): ≤0.95, where equation (4) = 55Te- {2Al + 2Ti + 4V + 4Nb + (Mn / 20S)}
Equation (4) is a value related to ingot cracking, machinability and magnetic properties. That is, if the value of the formula (4) is larger than 0.95 , ingot cracking occurs and the machinability and magnetic properties deteriorate. Therefore, the value of the equation (4) is set to 0.95 or less.

Here, embodiments of the invention will be described below. No. 1 is an example composed of the chemical components shown in Table 1 and satisfying the formulas (1) to (4). No. 1 is a comparative example of the free-cutting electrical steel of the invention examples 1 to 14 and the invention example shown in Table 2. Ingots of 15 to 36 electromagnetic steels were melted by 100 kg VIM (vacuum induction melting method), and the obtained ingots were formed into rods having a diameter of 20 mm.

Formed from these ingots using EDX (Energy Dispersion X-ray Spectroscopy) to confirm the composition of inclusions contained in the ingots of the invention examples and the ingots of the comparative examples obtained above. The sulfide and Te compound of the free-cutting compound observed on the L cross section of the rod having a diameter of 20 mm were observed and analyzed, and examples of these inventions are shown in Table 3 and Comparative Examples are shown in Table 4, respectively. That is, in the column of the observed inclusions in Table 3 and Table 4, for the material consisting of steel without the addition of Te, diameter 400μm following (Cr, Mn) S is dispersed in a range of 10 ⁶ [mu] m ² If the number is 40 or more, the evaluation is evaluated as ◯, and if the number is less than 40, the evaluation is evaluated as x. For Te additive, 10 of ⁶ [mu] m ² range 30 or more (Cr, Mn) if S with the presence compound inclusions following major diameter 300μm consisting of Te compounds to surround its exists, The evaluation was evaluated as ◯, and when there was a composite inclusion having a major axis of 300 μm or less composed of less than 30 (Cr, Mn) S and a Te compound existing so as to surround the S, the evaluation was indicated as ×.

In the evaluation of steel ingot crack resistance in Table 3 of Invention Example and Table 4 of Comparative Example, 100 kg of steel is melted by VIM, cast into a columnar ingot, sliced at a position of about 250 mm from the upper end of the ingot, and cut. The end face was detected for cracks by a color check by penetrant inspection, and the area of the range where cracks were confirmed in the center of the steel ingot was measured by this color check. It was quantified and displayed by the calculation of steel ingot crack rate = crack occurrence area / test area of color check. If the steel ingot crack rate is less than 10%, the evaluation is good, and the evaluation is ◯. If the steel ingot crack rate is 10% or more, the evaluation is x, and they are shown in Tables 3 and 4, respectively.

In the evaluation of hot workability, after the evaluation of steel ingot cracking resistance, among the ingots cut 250 mm from the upper end, the upper end side was used to collect 15 mm square lumber with a length of 110 mm, and these were collected at 1150 ° C. After homogenizing heat treatment with, it was processed into a gleeble test piece having a length of 100 mm with a rod having a diameter of 8 mm, and an evaluation test of hot workability was carried out. These gleeble test pieces were heated to each temperature of 1000 ° C., 1050 ° C., and 1100 ° C. using a gleeble tester, and then a tensile test was performed at a tensile speed of 50 mm per second to measure the drawing value. The aperture value is measured at each of the above heating temperatures, and all the aperture values are evaluated as ○, and other than that, even if the aperture value of one processing temperature is 70% or more, the other two. If even one of the drawing values of the processing temperature is less than 70% of the drawing value, the evaluation of the drawing value is set to x, and they are shown in Tables 3 and 4, respectively.

For evaluation test pieces other than the above, after evaluation of steel ingot cracking resistance, cut at 250 mm from the upper end of the ingots and use the lower end side of the ingots to have a diameter of 60 mm and a diameter of 20 mm. It was forged into a bar and then annealed at 750 to 850 ° C. as a heat treatment to prepare the following samples having magnetic properties, machinability and corrosion resistance, excluding the gleeble test piece.

To evaluate the magnetic characteristics, a bar with a diameter of 20 mm is machined into a magnetic ring consisting of an outer diameter of 13 mm, an inner diameter of 9 mm, and a thickness of 5 mm, and further subjected to vacuum magnetic annealing at 750 to 900 ° C. The coercive force was measured at. The evaluation of the coercive force of less than 130 A / m was evaluated as ◯, and the evaluation of the coercive force of 130 A / m or more was evaluated as x.

The machinability was evaluated by smoothing the cross section of a bar having a diameter of 60 mm with a lathe. The evaluation method is a drill drilling test, which measures the time required to drill a depth of 10 mm, and evaluates those with a required time of less than 10.5 seconds as ○, and those with a depth of 10.5 seconds or more as ×. And said.

The detailed test conditions for the above drill drilling test are as follows.
Drill: SKH51, diameter 5 mm
Cutting oil: None Thrust: 414N
Rotation speed: 1190 rpm

For the evaluation of corrosion resistance, a sample for a corrosion test having a diameter of 12 mm and a length of 21 mm was prepared from a rod having a diameter of 20 mm. A salt spray test was conducted in which 50 ppm of dilute salt water was sprayed on this test piece at 35 ° C. for 16 hours, the surface of the test piece was observed, and those with a major axis of 3 mm or more and 20 or less punctate rusts were evaluated as ◯. The evaluation of the number of punctate rusts having a major axis of 3 mm or more and 21 or more was evaluated as x.

No. 1 of the invention example of the first means of the present application (that is, claim 1). No. 1 to 5 and the invention example of the second means (that is, claim 2). In Nos. 6 to 14, as shown in Table 1, the value of the formula (1) is in the range of 1.2 to 5.0, the value of the formula (2) is 30 or more, and the second means (that is, the claim). Item No. 2) of the invention example. In 6 to 14, the value of the formula (3) is 0.15 or more, and the value of the formula (4) is 0.95 or less. Furthermore, No. 1 of the invention example of the first means (that is, claim 1) of the present application. No. 1 to 5 and the invention example of the second means (that is, claim 2). 6-14, as shown in Table 3, 10 ⁶ [mu] m observed inclusions in ² (Cr, Mn) the number of S, the No. of the invention of the first means In each of 1 to 5, the number of sulfides having a major axis of 400 μm or less is 40 or more, and No. 1 of the invention example of the second means. Each of 6 to 14 has 30 or more sulfides having a major axis of 300 μm or less, and all of these invention examples of the present application are evaluated with a steel ingot cracking resistance of 10% or less. Is ○, the hot workability at 1000 ° C, 1050 ° C, and 1100 ° C is 70% or more, and the evaluation is ○, the coercive force of the magnetic characteristics is smaller than 130 A / m, and the evaluation is ○, and the machinability. The evaluation is ◯ when the drilling time is shorter than 10.5 sec, and the evaluation is ◯ when the number of corrosion-resistant punctate rusts is 20 or less.

On the other hand, No. 1 of the comparative example of the first means of the present application (that is, claim 1). No. 15-26 and Comparative Examples of the Second Means (ie, claim 2). Consider 27-36. In addition, No. of the comparative example. Reference numeral 37 denotes lead-added steel, which is a reference example.

Comparative example No. As shown in Table 2, in No. 15, the mass of C is 0.033%, which is larger than the upper limit of 0.030% of the mass of C in the present invention. Therefore, as shown in Table 4, the corrosion resistance deteriorates. The number of rusts is more than 20, and the evaluation is x.

Comparative example No. As shown in Table 2, in No. 16, the mass of Si is 3.7%, which is larger than the upper limit of 0.50% of the mass of Si of the present invention. Therefore, as shown in Table 4, the magnetic characteristics deteriorate. The coercive force is 141 A / m, which is more than the 130 A / m of the present invention and is evaluated as x.

Comparative example No. As shown in Table 2, in No. 17, the mass of Mn is 0.61%, which is larger than the upper limit of 0.50% of the mass of Mn of the present invention. Therefore, as shown in Table 4, the magnetic characteristics deteriorate. The coercive force is 138 A / m, which is more than the 130 A / m of the present invention and is evaluated as x.

Comparative example No. As shown in Table 2, No. 18 has a mass of P of 0.048%, which is larger than the upper limit of the mass of P of the present invention of 0.030%. It deteriorated, and the aperture values at 1000 ° C. and 1050 ° C. were 64% and 68%, which were less than the lower limit of 70% of the present invention, and the evaluation was x.

Comparative example No. As shown in Table 2, the mass of S in No. 19 is 0.247%, which is larger than the upper limit of 0.200% of the mass of S of the present invention, and as shown in Table 4, the hot workability is deteriorated. However, the aperture values at 1000 ° C., 1050 ° C., and 1100 ° C. were 65%, 59%, and 68%, which were less than the lower limit of 70% of the present invention, and the evaluation was x. Therefore, the evaluation of the coercive force of the magnetic characteristics was not performed.

Comparative example No. As shown in Table 2, No. 20 has a mass of S of 0.037%, which is less than the lower limit of the mass of S of the present invention of 0.050%. Therefore, as shown in Table 4, the number of inclusions is 20. However, the number of inclusions is not satisfied with 34 or more of the present invention, so the evaluation of inclusions is x, the perforation time of machinability is poor, and the evaluation is x more than the upper limit of 10.5 sec of the present invention.

Comparative example No. As shown in Table 2, in No. 21, the mass of Cr is 11.1%, which is larger than the upper limit of the mass of Cr of the present invention of 10.0%. Therefore, as shown in Table 4, the magnetic properties of 21 are maintained. The magnetic force is poor, and the evaluation is x, which is more than the upper limit of 130 A / m of the present invention.

Comparative example No. In Table 2, as shown in Table 2, the combined mass of Al, Ti, V, and Nb is 0.819%, which is larger than the upper limit of 0.800% of these combined masses of the present invention. As shown in 4, the coercive force of the magnetic property is 150 A / m, which exceeds the upper limit of 130 A / m of the present invention, and the evaluation is x.

Comparative example No. As shown in Table 2, No. 23 has a mass of N of 0.045%, which is larger than 0.030% of the present invention. Therefore, as shown in Table 4, the coercive force of the magnetic property is 150 A / m. , The upper limit of 130 A / m of the present invention is exceeded, and the evaluation is x.

Comparative example No. In No. 24, as shown in Table 2, the value of the formula (1) is 0.7, which is smaller than the lower limit of 1.0 of the present invention. Therefore, as shown in Table 4, the hot workability of 1000 ° C. Since the drawing values at 1050 ° C. and 1050 ° C. are 65% and 69%, which are less than 70% of the upper limit of the drawing value of the present invention, the evaluation of hot workability is x.

Comparative example No. In No. 25, as shown in Table 2, the value of the formula (1) is 5.5, which is larger than the upper limit of 5.0 of the present invention. Therefore, as shown in Table 4, the number of corrosion-resistant punctate rusts is large. Since it is larger than 27, which is the upper limit of the number of punctate rusts of the present invention, which is 20, the evaluation of the corrosion resistance is ×.

Comparative example No. In No. 26, as shown in Table 2, the value of the formula (2) is 27, which is smaller than the lower limit value of 30 of the present invention. Since it is 13%, which is larger than 10% of the upper limit of the ingot cracking rate of the present invention, the evaluation of the ingot cracking resistance is x.

Comparative example No. From 27, it is a comparative example of Invention Example 2. Comparative example No. In 27, as shown in Table 2, the mass of Te, which is a chemical component, is 0.045%, which is larger than 0.030% of the mass of the upper limit of Invention Example 2, and therefore, as shown in Table 4, it is hot. The workability drawing values of 1000 ° C., 1050 ° C., and 1100 ° C. are 57%, 62%, and 64%, all of which are smaller than 70% of the hot workability drawing values of the present invention. The evaluation of workability is ×.

Comparative example No. In No. 28, as shown in Table 2, the value of the formula (3) is 0.12, which is smaller than the lower limit of 0.15 of the present invention. The values of 1000 ° C. and 1100 ° C. are 64% and 69%, both of which are smaller than 70% of the drawing value of each temperature of the hot workability of the present invention, so that the evaluation of hot workability is x.

Comparative example No. As shown in Table 2, 29 has a value of the formula (4) of 1.02, which is larger than the upper limit of 0.95 of the present invention. Since the value at 1000 ° C. is 66%, which is smaller than 70% of the drawing value of each temperature of the hot workability of the present invention, the evaluation of hot workability is x.

Comparative example No. As shown in Table 2, No. 30 has a Mn mass of 0.58%, which is larger than 0.50% of the upper limit of the Mn mass of the present invention. Is 133 A / m, which is larger than the coercive force of 130 A / m of the magnetic characteristics of the present invention, so the evaluation of the magnetic characteristics is x.

Comparative example No. As shown in Table 2, No. 31 has a mass of C of 3.8%, which is larger than 3.5% of the upper limit of the mass of C of the present invention. Is 142 A / m, which is larger than the coercive force of 130 A / m of the magnetic characteristics of the present invention, so the evaluation of the magnetic characteristics is x.

Comparative example No. As shown in Table 2, in No. 32, the mass of Cr is 10.4%, which is larger than 10.0% of the upper limit of the mass of Cr of the present invention. Therefore, as shown in Table 4, the coercive force of the magnetic property is Is 149 A / m, which is larger than the coercive force of 130 A / m of the magnetic characteristics of the present invention, so the evaluation of the magnetic characteristics is x.

Comparative example No. As shown in Table 2, No. 33 has a mass of N of 0.036%, which is larger than 0.030% of the upper limit of the mass of N of the present invention. Is 149 A / m, which is larger than the coercive force of 130 A / m of the magnetic characteristics of the present invention, so the evaluation of the magnetic characteristics is x.

Comparative example No. As shown in Table 2, 34 has a value of the formula (1) of 5.3 and the formula (1) of the present invention.
) Is larger than the upper limit of 5.0, and as shown in Table 4, the number of corrosion-resistant punctate rusts is 24, which is larger than the upper limit of the number of corrosion-resistant punctate rusts of the present invention, which is 20. The evaluation of corrosion resistance is ×.

Comparative example No. As shown in Table 2, No. 35 has a value of the formula (2) of 28, which is smaller than the lower limit of 30 of the value of the formula (2) of the present invention. Since the ingot cracking rate of No. 16 is larger than the upper limit of 10 of the ingot cracking resistance of the present invention, the evaluation of the ingot cracking resistance is x.

Comparative example No. As shown in Table 2, No. 36 has a mass of S of 0.023%, which is less than the lower limit of the mass of S of the present invention, which is 0.050%. The number of inclusions is 25, which does not satisfy 30 or more of the present invention, so the evaluation of inclusions is x, the perforation time of machinability is poor, and the evaluation is x more than the upper limit of 10.5 sec of the present invention.

Comparative example No. 37 is a reference example, a lead-containing steel, as shown in Table 2, but containing 0.12% by weight of Pb, as shown in Table 4, observed during 10 ⁶ [mu] m ² The number of Pb inclusions with a length of 300 μm ² or less was not observed and the evaluation was ×. The evaluations of steel ingot cracking resistance, hot workability, magnetic properties, machinability and corrosion resistance are all ◯.

Claims (2)

By mass%, C: 0.030% or less, Si: 0.5 to 3.5%, Mn: 0.05 to 0.50%, P: 0.030% or less, S: 0.050 to 0. It contains 200%, Cr: 6.0 to 10.0%, N: 0.030% or less, and one or more of Al, Ti, V and Nb in total 0.005 to 0. containing .800%, a steel balance consisting of Fe and unavoidable impurities, into steel, as machinability improving compound major diameter 400μm following (Cr, Mn) sulfide 40 or more in the range of 10 ⁶ [mu] m ² Steel ingot crack resistance and hotness characterized by being dispersed, having a size of formula (1) of 1.2 to 5.0, and having a size of formula (2) of 30 or more. Free-cutting electromagnetic steel with excellent workability.
However,
Equation (1): Mn / S
Equation (2): 8Si + 8Al + Cr + 4Ti + 4V + 2Nb + 2 (Mn / S) -16 (C + N) It has the chemical composition of claim 1, and in addition to the sizes of the formulas (1) and (2), contains Te: 0.030% or less in mass%, and is composed of the balance Fe and unavoidable impurities. It is a steel, and the free-cutting property-imparting compound is a composite inclusion having a major axis of 300 μm or less composed of (Cr, Mn) sulfide and a Te compound existing so as to surround the sulfide in the steel, and is 10 ⁶ μm ² 30 or more are dispersed in the range of, the formula (3) is 0.15 or more, and the formula (4) is 0.95 or less. Free-cutting electromagnetic steel with excellent manufacturability.
However, equation (3): Te / S
Equation (4): 55Te- {2Al + 2Ti + 4V + 4Nb + (Mn / 20S)