JP2018104753A - Free-cutting electromagnetic steel excellent in manufacturability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a free-cutting electrical steel having sufficient corrosion resistance and machinability without adding Pb and having excellent manufacturability capable of being stably supplied. SOLUTION: In 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. It has 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 is 0 in total. A steel having .005 to 0.800% and composed of the balance Fe and unavoidable impurities, and 40 or more (Cr, Mn) S having a major axis of 400 μm or less as a free-cutting imparting compound are dispersed in the steel in the range of 106 μm 2. However, the size of the formula (1) is 1.2 to 5.0, and the size of the formula (2) is 30 or more. steel. However, formula (1): Mn / S, formula (2): 8Si + 8Al + Cr + 4Ti + 4V + 2Nb + 2 (Mn / S) -16 (C + N) [Selection diagram] None

Description

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

  Electrical steel is also required to have good manufacturability from the viewpoints of excellent magnetic properties, machinability, corrosion resistance, and stable supply of materials at low cost. Pb-added electrical steels having excellent machinability and excellent machinability without impairing magnetic properties and corrosion resistance have already been put on the market. However, in recent manufacturing industries, the use of Pb is avoided in consideration of the toxicity of Pb. There is an example in which S is added as a Pb alternative free-cutting element, 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-described magnetic characteristics, machinability and corrosion resistance. Therefore, there is a demand for a material that is non-Pb and has all of excellent manufacturability such as excellent magnetic properties, machinability, corrosion resistance, and hot workability.

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

  This electromagnetic steel has been proposed and patented with a material that has been given free-cutting properties without impairing magnetic properties and corrosion resistance by adding (Cr, Mn) S and Te without using Pb (for example, patents) Reference 2). However, this proposed patent has a problem that the machinability is not always improved sufficiently because the amount of S which is responsible for machinability is as small as 0.040 mass% or less.

  This electromagnetic steel is a material that imparts free-cutting properties without impairing magnetic properties and corrosion resistance by adding (Cr, Mn) S and Te without using Pb. Many of the proposed applications have 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 merely a level that can be produced, and further improvement in manufacturability is necessary from the viewpoint of stably supplying at a low cost. It is.

Japanese Patent No. 4544977 Japanese Patent No. 5730153 Japanese Patent Laid-Open No. 2006-113667

  The problem to be solved by the present invention is that various electromagnetic actuators such as solenoids and electromagnetic valves, electromagnetic sensor members, and the like are required to have excellent soft magnetic characteristics. In addition, sufficient corrosion resistance with respect to the use environment and machinability that can cope with precision machining and mass production machining are also required. In order to meet these demands, in steel materials, the machinability is greatly improved without impairing the corrosion resistance, so the addition of Pb has been used for a long time. However, the use of Pb must be avoided in view of the reduction in environmental load. 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 impedes the manufacturability of the material, and is problematic in terms of stable supply and manufacturing costs. Occurs. In order to solve these problems, it is an object of the present invention to provide a free-cutting electrical steel that has sufficient corrosion resistance and machinability without adding Pb and has excellent manufacturability that can be stably supplied.

The means of the present invention for solving the above-mentioned problems are as follows. First, the environmental load is small, the steel has sufficient corrosion resistance and magnetic properties, and the steel ingot cracking resistance and hotness which are the manufacturability of the material. In order to obtain a free-cutting electromagnetic steel excellent in workability and the like, the following five points are taken.
1. Non-Pb steel is used to reduce environmental impact.
2. It is assumed that sulfide or a composite compound of sulfide and Te compound is dispersed in steel and has machinability equal to or higher than that of Pb steel.
3. The deterioration of the magnetic characteristics due to the addition of S is avoided by adjusting the Si addition amount and the Cr addition amount.
4). Controlling the composition of Cr, Mn, S and the value of Mn / S in the formula (1), fixing S as a sulfide and ensuring hot workability, while making Cr rich, good Get corrosion resistance.
5. One or more of Al, Ti, Nb, and V, and the following formula (2) increase ferrite stability, excellent magnetic properties and manufacturability of steel ingot cracking and hot Ensure processability.

Second, the following 6. We will take the following means.
6). The composition of Te and the limitations by the formulas (3) and (4) suppress the deterioration of hot workability due to the addition of Te while improving machinability and magnetic properties.
That is, the invention of the following first means and second means is provided.

In the first means, 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 0.200%, 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 0.800% and the balance Fe and unavoidable impurities, and (Cr, Mn) sulfide having a major axis of 400 μm or less as a free-cutting property imparting compound is 10 ⁶ μm ^2. 40 or more dispersed in the range, 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 electrical steel with excellent lump cracking and hot workability manufacturability.
However,
Formula (1): Mn / S
Formula (2): 8Si + 8Al + Cr + 4Ti + 4V + 2Nb + 2 (Mn / S) -16 (C + N)

In the second means, the chemical component of claim 1 is included, and in addition to the size of the formula (1) and the formula (2), the content of Te is 0.030% or less, and the balance. It is a steel composed of Fe and inevitable impurities. In the steel, as a free-cutting property imparting compound, (Cr, Mn) is a composite inclusion having a major axis of 300 μm or less composed of a sulfide and a Te compound existing so as to surround it. Yes, 30 or more dispersed in the range of 10 ⁶ μm ² , the formula (3) is 0.15 or more, and the formula (4) is 0.95 or less. Is a free-cutting electrical steel excellent in workability and manufacturability of hot workability.
However, Formula (3): Te / S
Formula (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 the sulfide is made of (Mn, Cr) S sulfide or the sulfide and a Te compound surrounding the sulfide. Dispersing the composite compound in steel has machinability equivalent to or better than that of Pb steel, has low coercive force, excellent corrosion resistance, and decreases the magnetic properties due to the addition of S. The composition of Cr, Mn, and S, and Mn / S in the formula (1) are controlled, and the hot workability is processed by fixing S as a sulfide while adjusting Cr. By making it rich, good corrosion resistance is obtained, and steel ingot cracking resistance, which is excellent magnetic properties and manufacturability by increasing the ferrite stability by the composition of Al, Ti, Nb, V and formula (2) And secures hot workability, e composition and formula (3), while improving the machinability and magnetic properties by a formula in (4) by limiting, having an effect of suppressing the hot workability of deterioration due Te added.

  Prior to the embodiments for carrying out the invention, chemical components and conditions in the present invention will be described. In addition, a chemical component is shown by the mass%.

C: 0.030% or less C is an inevitable impurity, and if it exceeds 0.030%, the magnetic properties, corrosion resistance and free-cutting properties of the obtained electrical steel are deteriorated. Therefore, C is set to 0.030% or less.

Si: 0.5 to 3.5%
Si is an element useful for improving specific resistance and magnetic properties. Therefore, Si is made 0.5% or more. However, if the Si content exceeds 3.5%, the magnetic properties deteriorate due to excessive addition, and the toughness and workability of the material deteriorate. Therefore, Si is 0.5 to 3.5%.

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

P: 0.030% or less P is an inevitable impurity, and when it exceeds 0.030%, the hot workability and magnetic properties of the obtained electrical steel deteriorate. Therefore, P is set to 0.030% or less.

S: 0.050-0.200%
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 exceeds 0.200%, the magnetic properties and corrosion resistance deteriorate. Therefore, S is set to 0.050 to 0.200%.

Cr: 6.0 to 10.0%
Cr is an element essential for improving the corrosion resistance, and is an element for reducing the coercive force and improving the soft magnetic characteristics. For that purpose, Cr is made 6.0% or more. However, if Cr is more than 10.0%, the effect of Cr is saturated, and coercive force increases due to excessive addition and deteriorates. Therefore, Cr is set to 6.0 to 10.0%.

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

Including at least one or two or more of Al, Ti, V and Nb, the total is: 0.005 to 0.800%
Al, Ti, V, and Nb are all selective elements and are elements involved in steel ingot cracking, hot workability, corrosion resistance, machinability, and magnetic properties. By the way, if the total of one or more of these elements is 0.005% or more, these steel ingot cracks, hot workability, corrosion resistance, machinability, and magnetic properties are achieved by stabilizing the ferrite phase. Degradation 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 hot workability, corrosion resistance, machinability, magnetic properties are formed by the formation of carbonitride. Deteriorates. Therefore, at least one or more of Al, Ti, V, and Nb is included, and the total is made 0.005 to 0.800%.

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

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

Te: ≦ 0.030%
Te is an element involved in machinability, magnetic properties, and hot workability in the formation of Te compounds and the control of the morphology of Te sulfide. When Te is 0.030% or less, the machinability and magnetic properties are improved by the generation of Te compound and the morphology control of Te sulfide. On the other hand, when Te exceeds 0.030%, hot workability deteriorates. Therefore, Te is set to 0.030% or less.

Formula (3): ≧ 0.15, where Formula (3) = Te / S
The value of 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, the low melting point of the Te compound is suppressed and the hot workability is ensured. Therefore, the value of Equation (3) is set to 0.15 or more.

Formula (4): ≦ 0.95, where Formula (4) = 55Te− {2Al + 2Ti + 4V + 4Nb + (Mn / 20S)}
Equation (4) is a value related to steel ingot cracking, machinability and magnetic properties. That is, if the value of the formula (4) is larger than 0.90, the steel ingot is cracked and the machinability and the magnetic properties are deteriorated. Therefore, the value of Equation (4) is set to 0.90 or less.

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

In order to confirm the structure of inclusions contained in the steel ingots of the invention examples and comparative examples obtained above, they are formed from these steel ingots using EDX (energy dispersive X-ray spectroscopy). The sulfides and Te compounds of the free-cutting property imparting compound observed in the L cross section of the bar with a diameter of 20 mm were observed and analyzed. Table 3 shows the invention examples and Table 4 shows the comparative examples. That is, in the observed inclusion column of Tables 3 and 4, (Cr, Mn) S having a major axis of 400 μm or less is dispersed in a range of 10 ⁶ μm ² for the steel material to which Te is not added. If it is 40 or more, the evaluation is ○, and if it is less than 40, the evaluation is ×. As for the Te additive, if there is a composite inclusion having a major axis of 300 μm or less composed of 30 or more (Cr, Mn) S and a Te compound existing so as to surround it in the range of 10 ⁶ μm ² , The evaluation was shown as “Good”, and when there were composite inclusions having a major axis of 300 μm or less composed of less than 30 (Cr, Mn) S and a Te compound surrounding the periphery, the evaluation was shown as “X”.

  Evaluation of steel ingot cracking resistance in Table 3 of the invention example and Table 4 of the comparative example was made by melting 100 kg of steel with VIM, casting it into a cylindrical ingot, cutting it into a ring at a position of about 250 mm from the upper end of the ingot, and cutting it. Cracks were detected on the end face by color check using penetrant flaw detection, and the area in the range where cracks were confirmed at the center of the steel ingot by this color check was measured. The steel ingot cracking ratio = the crack occurrence area / the color check test area was quantified and displayed. Since the steel ingot cracking rate is less than 10%, the evaluation is good, and the evaluation is “good”, and the steel ingot cracking rate is 10% or more.

  The evaluation of hot workability was performed by using the upper end side of the ingot cut from 250 mm from the upper end after evaluating the steel ingot cracking resistance, collecting 15 mm square pieces with a length of 110 mm, and obtaining these at 1150 ° C. After the homogenization heat treatment at, the hot workability evaluation test was carried out by processing into a 100 mm-long greeble test piece with a 8 mm diameter rod. These greeble test pieces were heated to 1000 ° C., 1050 ° C., and 1100 ° C. using a greeble tester, and then subjected to a tensile test at a tensile speed of 50 mm per second to measure a drawing value. The aperture value is measured at each of the heating temperatures described above, and all the aperture values are 70% or more as a result of evaluation. Otherwise, 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%, the evaluation of the drawing value is x, and the results are shown in Table 3 and Table 4, respectively.

  For the test pieces for evaluation other than the above, after evaluating the steel ingot cracking resistance, the ingots were cut at 250 mm from the upper end and the lower end side of those ingots was used, and the diameters of 60 mm and 20 mm were used. The sample was forged into a bar and then annealed at 750 to 850 ° C. as a heat treatment to prepare the following samples of magnetic properties, machinability and corrosion resistance, excluding the greeble test piece.

  Evaluation of magnetic properties was carried out by machining a bar having a diameter of 20 mm into a magnetic ring having an outer diameter of 13 mm, an inner diameter of 9 mm, and a thickness of 5 mm, and after subjecting it to vacuum magnetic annealing at 750 to 900 ° C. The coercive force was measured at. Evaluation with a coercive force of less than 130 A / m was evaluated as ◯, and evaluation with a coercive force of 130 A / m or more was evaluated as x.

  The machinability was evaluated by smoothing the cross section of a bar with a diameter of 60 mm with a lathe and performing machinability. The evaluation method is a drill drilling test, which measures the time required for drilling at a depth of 10 mm, evaluates that the required time is less than 10.5 seconds as ○, and evaluates that is more than 10.5 seconds × It was.

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

  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 water spray test in which 50 ppm of diluted salt water is sprayed on this test piece at 35 ° C. for 16 hours, the surface of the test piece is observed, and the evaluation of those having 20 or less point rusts having a major axis of 3 mm or more is given as “Good”. The evaluation of those having 21 or more dotted rusts having a major axis of 3 mm or more was evaluated as x.

No. 1 of the invention example of the first means (that is, claim 1) of the present application. Nos. 1 to 5 and the second means (i.e., claim 2) of the invention examples. 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, claims) No. 2) of the invention example. As for 6-14, the value of a formula (3) is 0.15 or more, and the value of a formula (4) is 0.95 or less. Further, the invention No. 1 of the first means of the present application (namely, claim 1). Nos. 1 to 5 and the second means (i.e., claim 2) of the invention examples. 6 to 14, as shown in Table 3, the number of inclusions (Cr, Mn) S observed in 10 ⁶ μm ² is the No. of the first invention example. Nos. 1 to 5 have 40 or more sulfides having a major axis of 400 μm or less. Each of 6-14 has 30 or more sulfides having a major axis of 300 μm or less, and all of the invention examples of the present application are evaluated with a steel ingot cracking resistance of 10% or less. Is ◯, the hot workability is 1000 ° C., 1050 ° C., 1100 ° C. with a drawing value of 70% or more, the evaluation is ◯, the magnetic coercive force is less than 130 A / m, the evaluation is ◯, and machinability The evaluation is good when the perforation time is shorter than 10.5 sec, and the evaluation is good when the number of corrosion-resistant point-like rusts is 20 or less.

  On the other hand, the comparative example No. 1 of the first means of the present application (ie, claim 1). Nos. 15 to 26 and the comparative example No. 2 of the second means (namely, claim 2). Consider 27-36. The comparative example No. Reference numeral 37 is a lead-added steel, which is a reference example.

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

  Comparative Example No. No. 16 has a mass of Si of 3.7% as shown in Table 2, which is higher than the upper limit of 0.50% of the mass of Si of the present invention. The coercive force is 141 A / m, and the evaluation is x more than less than 130 A / m of the present invention.

  Comparative Example No. No. 17, as shown in Table 2, the mass of Mn is 0.61%, which is higher than the upper limit of 0.50% of the mass of Mn of the present invention. The coercive force is 138 A / m, and the evaluation is x more than less than 130 A / m of the present invention.

  Comparative Example No. No. 18 has a mass of P as 0.048% as shown in Table 2, which is larger than the upper limit of 0.030% of the mass of P of the present invention. Deteriorated, and the aperture values at 1000 ° C. and 1050 ° C. are 64% and 68%, respectively, and the evaluation is x less than 70% of the lower limit of the present invention.

  Comparative Example No. No. 19 has a mass of S of 0.247% as shown in Table 2, more than 0.200% of the upper limit of the mass of S of the present invention, and the hot workability is deteriorated as shown in Table 4. The aperture values at 1000 ° C., 1050 ° C., and 1100 ° C. were 65%, 59%, and 68%, and the evaluation was “poor”, which was less than 70% of the lower limit value of the present invention. Therefore, the evaluation below the coercivity of the magnetic characteristics was not performed.

  Comparative Example No. No. 20 has a mass of S of 0.037% as shown in Table 2, which is less than 0.050% of the lower limit of the mass of S of the present invention. Therefore, as shown in Table 4, the number of inclusions 34 and 40 or more of the present invention are not satisfied, the inclusion evaluation is x, the drilling time of machinability is bad, and the evaluation is x more than the upper limit of 10.5 sec of the present invention.

  Comparative Example No. No. 21 has a Cr mass of 11.1% as shown in Table 2, which is more than 10.0% of the upper limit of the Cr mass of the present invention. The magnetic force is poor and the evaluation is x more than the upper limit of 130 A / m of the present invention.

  Comparative Example No. No. 22, as shown in Table 2, the combined mass of Al, Ti, V, and Nb is 0.819%, which is more than 0.800% of the upper limit of the combined mass of the present invention. As shown in FIG. 4, the coercive force of the magnetic characteristics 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. 23, as shown in Table 2, the mass of N is 0.045%, which is larger than 0.030% of the present invention. Therefore, as shown in Table 4, the coercive force of the magnetic properties 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. 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, so as shown in Table 4, the hot workability of 1000 ° C. The squeezing value at 1050 ° C. is 65% and 69%, which is less than 70% of the upper limit value of the squeezing value of the present invention.

  Comparative Example 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. 27, which is larger than the upper limit 20 of the number of point-like rusts of corrosion resistance of the present invention, the evaluation of corrosion resistance is x.

  Comparative Example No. 26, as shown in Table 2, the value of the formula (2) is 27, which is smaller than the lower limit of 30 of the present invention. Therefore, as shown in Table 4, the steel ingot cracking resistance is high. Since it is 13% and is larger than 10% of the upper limit value of the steel ingot cracking ratio of the present invention, the evaluation of the steel ingot cracking resistance is x.

  Comparative Example No. 27 is a comparative example of Invention Example 2. Comparative Example No. 27, as shown in Table 2, since the mass of Te of the chemical component is 0.045%, which is more than 0.030% of the mass of the upper limit value of Invention Example 2, The workability drawing values of 1000 ° C., 1050 ° C., and 1100 ° C. are 57%, 62%, and 64%, which are smaller than 70% of the drawing values at each temperature of the hot workability of the present invention. Evaluation of inter-workability is x.

  Comparative Example No. 28, as shown in Table 2, the value of the expression (3) is 0.12, which is smaller than the lower limit of 0.15 of the present invention. Since the values at 1000 ° C. and 1100 ° C. are 64% and 69%, respectively, which are smaller than 70% of the drawing value at each temperature of the hot workability of the present invention, the evaluation of hot workability is x.

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

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

  Comparative Example No. No. 31 has a mass of C of 3.8% as shown in Table 2, 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 130 A / m of the coercive force of the magnetic characteristics of the present invention, and the evaluation of the magnetic characteristics is x.

  Comparative Example No. 32, as shown in Table 2, 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. Is 149 A / m, which is larger than the coercive force 130 A / m of the magnetic characteristics of the present invention, and the evaluation of the magnetic characteristics is x.

  Comparative Example No. 33, as shown in Table 2, the mass of N is 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 130 A / m of the magnetic characteristics of the present invention, and the evaluation of the magnetic characteristics is x.

  Comparative Example No. 34, as shown in Table 2, the value of the formula (1) is 5.3, which is larger than the upper limit of 5.0 of the value of the formula (1) of the present invention. The number of spot-like rusts is 24, which is larger than the upper limit value of the corrosion-resistant point-like rust number of 20 according to the present invention, so the evaluation of the magnetic properties is x.

  Comparative Example No. 35, as shown in Table 2, the value of the formula (2) is 28, which is smaller than the lower limit of 30 of the value of the formula (2) of the present invention. The steel ingot cracking rate is 16 and is larger than 10 of the upper limit value of the steel ingot cracking resistance of the present invention, so the evaluation of the steel ingot cracking resistance is x.

  Comparative Example No. 36, as shown in Table 2, because the mass of S is 0.023%, which is less than 0.050% of the lower limit of the mass of S of the present invention, as shown in Table 4, the number of inclusions However, the inclusion evaluation is x, the machinability drilling time 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, which is a lead-added steel containing 0.12% by mass of Pb as shown in Table ² , but observed in 10 ⁶ μm ^{2 as} shown in Table 4. The number of Pb inclusions having a length of 300 μm ² or less was not observed, and the evaluation was x. The evaluations of steel ingot cracking resistance, hot workability, magnetic properties, machinability and corrosion resistance are all good.

Claims (2)

In mass%, C: 0.030% or less, Si: 0.5-3.5%, Mn: 0.05-0.50%, P: 0.030% or less, S: 0.050-0. 200%, Cr: 6.0 to 10.0%, N: 0.030% or less, and further, one or more of Al, Ti, V and Nb in total 0.005 to 0 .800% steel, the balance being Fe and inevitable impurities, and 40 or more (Cr, Mn) sulfides having a major axis of 400 μm or less as a free-cutting property imparting compound in the range of 10 ⁶ μm ² Steel ingot cracking resistance and hot, characterized by being dispersed, the size of formula (1) being 1.2 to 5.0, and the size of formula (2) being 30 or more Free-cutting electrical steel with excellent processability and manufacturability.
However,
Formula (1): Mn / S
Formula (2): 8Si + 8Al + Cr + 4Ti + 4V + 2Nb + 2 (Mn / S) -16 (C + N) It has the chemical component of claim 1 and contains, in addition to the magnitudes of the formulas (1) and (2), by mass%, Te: 0.030% or less, and consists of the balance Fe and inevitable impurities. It is a steel, and in the steel, as a free-cutting property imparting compound, (Cr, Mn) is a composite inclusion having a major axis of 300 μm or less made of a sulfide and a Te compound existing so as to surround it. 10 ⁶ μm ² The steel ingot cracking resistance and hot workability are characterized in that 30 or more of them are dispersed in the range of formula (3), the formula (3) is 0.15 or more, and the formula (4) is 0.95 or less. Free cutting electrical steel with excellent manufacturability.
However, Formula (3): Te / S
Formula (4): 55Te- {2Al + 2Ti + 4V + 4Nb + (Mn / 20S)