Electromagnetic stainless steel bar-shaped steel materials and electromagnetic components for warm forging

Abstract

To provide an electromagnetic stainless bar-like steel material for hot forging excellent in soft magnetic property even if magnetic annealing is omitted and provide an electromagnetic component therewith.SOLUTION: An electromagnetic stainless bar-like steel material for hot forging has the following chemical composition, in mass%, C: 0.001 to 0.030%, Si: 0.01 to 4.00%, Mn: 0.01 to 2.00%, Ni: 0.01 to 4.00%, Cr: 8.0 to 35.0%, Mo: 0.01 to 5.00%, Cu: 0.01 to 2.00%, N: 0.001 to 0.030%, Ti: 0 to 2.00%, Nb: 0 to 2.00%, residual parts: Fe and impurities, and the chemical components contain more than one kind selected from, by mass%, Ti: 0.001 to 2.00% and Nb: 0.001 to 2.00%, and an average particle size of a nitride from an uppermost surface layer of steel material to a surface layer 200 μm is 0.1 to 30 μm inclusive, and a dissolved N amount in the steel is 0.020 mass% or smaller.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to electromagnetic stainless steel, particularly an electromagnetic stainless steel bar-shaped steel material for warm forging that exhibits excellent soft magnetic properties even without magnetic annealing, and electromagnetic components using the same.

Background Art

[0002] Conventionally, electromagnetic stainless steel products represented by injectors and solenoid valves are processed and formed using ferritic stainless steel wire rods and steel wires such as SUS430 and SUS410L as raw materials, and magnetic annealing is performed on the products to reduce strain during processing and forming, and to obtain excellent soft magnetic properties by recrystallization and grain growth (for example, Patent Documents 1 to 3). However, stainless steel products processed and magnetically annealed from the above-mentioned ferritic stainless steel wire rods are costly. In particular, magnetic annealing requires long hours of atmosphere control, resulting in high production costs and having the drawback of being subject to application limitations. Magnetic annealing has the effect of enhancing soft magnetic properties, and technologies for optimizing alloy elements have been studied for improving soft magnetic properties (for example, Patent Documents 1 to 3). However, there is no invention that focuses on improving soft magnetic properties even without magnetic annealing in ferritic stainless steel bars and wires that utilize microstructure control by combining components and processes.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] Based on the above, an object of the present invention is to solve the above problems and provide an electromagnetic stainless steel bar-shaped steel material for warm forging that has excellent soft magnetic properties even without magnetic annealing, and an electromagnetic component using the same. In the present invention, excellent soft magnetic properties mean a small coercive force.

Means for Solving the Problems

[0005] The present invention has been made to solve the above problems, and the gist thereof is the following electromagnetic stainless steel bar-shaped steel material for warm forging and electromagnetic component. [1] The chemical composition is in mass %, C: 0.001 to 0.030%, Si: 0.01 to 4.00%, Mn: 0.01 to 2.00%, Ni: 0.01 to 4.00%, Cr: 8.0 to 35.0%, Mo: 0.01 to 5.00%, Cu: 0.01 to 2.00%, N: 0.001 to 0.030%, Al: 7.000% or less, furthermore, Ti: 0 to 2.00%, Nb: 0 to 2.00%, containing one or more selected from Ti: 0.001% or more and Nb: 0.001% or more, B: 0 to 0.1%, Sn: 0 to 2.50%, V: 0 to 2.0%, W: 0 to 3.0%, Ga: 0 to 0.05%, Co: 0 to 2.50%, Sb: 0 to 2.5%, Ta: 0 to 2.5%, Ca: 0 to 0.05%, Mg: 0 to 0.012%, Zr: 0 to 0.012%, REM: 0 to 0.05%, Pb: 0 to 0.30%, Se: 0 to 0.80%, Te: 0 to 0.30%, Bi: 0 to 0.50%, S: 0 to 0.50%, P: 0 to 0.30%, the balance: Fe and impurities, An electromagnetic stainless steel bar-shaped steel material for warm forging, wherein the average particle size of nitrides in the outermost surface layer to the surface layer 200 μm of the steel material is 0.1 to 30 μm, and the amount of solid solution N in the steel is 0.020 mass % or less. [2] The chemical composition is further in mass %, The electromagnetic stainless steel bar for hot forging according to [1], containing one or more selected from B: 0.0001 to 0.1%, Sn: 0.0001 to 2.5%, V: 0.001 to 2.0%, W: 0.05 to 3.0%, Ga: 0.0004 to 0.05%, Co: 0.05 to 2.5%, Sb: 0.01 to 2.5%, and Ta: 0.01 to 2.5%. [3] The chemical composition further includes, in mass%, The electromagnetic stainless steel bar for hot forging according to [1] or [2], containing one or more selected from Ca: 0.0002 to 0.05%, Mg: 0.0002 to 0.012%, Zr: 0.0002 to 0.012%, and REM: 0.0002 to 0.05%. [4] The chemical composition further includes, in mass%, Pb: 0.0001 to 0.30%, Se: 0.0001 to 0.80%, Te: 0.0001 to 0.30%, Bi: 0.0001 to 0.50%, S: 0.0001 to 0.50%, P: 0.0001 to 0.30%, and the electromagnetic stainless steel bar for hot forging according to any one of [1] to [3], containing one or more selected from these. [5] An electromagnetic component using the electromagnetic stainless steel bar for hot forging according to any one of [1] to [4].

Effect of the Invention

[0006] According to the present invention, an electromagnetic stainless steel bar for hot forging and an electromagnetic component excellent in soft magnetic properties can be obtained even without magnetic annealing.

Mode for Carrying Out the Invention

[0007] The inventors of the present invention conducted various studies to obtain an electromagnetic stainless steel bar for hot forging and an electromagnetic component excellent in soft magnetic properties. As a result, the following findings (a) to (c) were obtained.

[0008] (a) By combining a ferrite stainless steel whose components are adjusted with Ti and Nb and a hot rolling process (slab heating temperature, rolling speed with inclination), the average particle diameter of nitrides can be increased and the amount of dissolved N in the steel can be reduced.

[0009] (b) As a result, a new method for improving soft magnetic properties has been found, in which the coercive force becomes 15 A / m or less after warm working even when magnetic annealing is omitted.

[0010] The present invention has been made based on the above findings. Further, a preferred embodiment of the present invention will be described in detail. In the following description, a preferred embodiment of the present invention will be described as the present invention. Hereinafter, each requirement of the present invention will be described in detail. In the bar-shaped steel material of the present invention, the "bar-shaped steel material" includes "bar steel", "wire rod", "steel wire", "shaped wire", "shaped bar steel", and the like.

[0011] 1. Average particle diameter of nitrides in the outermost surface layer to the surface layer 200 μm of the steel material In the bar-shaped steel material according to the present invention, the average particle diameter of nitrides in the outermost surface layer to the surface layer 200 μm of the steel material is controlled. Specifically, the average particle diameter of nitrides in the outermost surface layer to the surface layer 200 μm of the steel material is set to 0.1 μm or more. When the average particle diameter of nitrides in the outermost surface layer to the surface layer 200 μm of the steel material is less than 0.1 μm, it is difficult for recrystallization and grain growth to occur during hot forging due to fine nitrides, and fine grains and strains remain, resulting in a decrease in soft magnetic properties. Further, the fine nitrides themselves suppress the movement of magnetic walls, resulting in a decrease in soft magnetic properties. The average particle diameter of the nitrides is more preferably 1.0 μm or more, and even more preferably more than 5.0 μm. On the other hand, when the average particle diameter of nitrides in the outermost surface layer to the surface layer 200 μm of the steel material becomes too large, forging cracks starting from the surface layer of the steel material during hot forging occur. Therefore, the average particle diameter of nitrides in the outermost surface layer to the surface layer 200 μm of the steel material is preferably 30 μm or less. Note that the nitrides include carbonitrides.

[0012] The average particle diameter of the nitrides can be measured in at least one field of view at a magnification of 400 in the L cross-section (the cross-section including the center line of the bar-shaped steel material) of the bar-shaped steel material in the position part (the region with a depth from the outermost surface to the surface layer 200 μm) from the outermost surface layer to the surface layer 200 μm of the steel material. The nitrides in the observation field of view are identified using FE-SEM / ESD, and the average value of the equivalent circle diameters of the nitrides in the same field of view can be calculated.

[0013] 2. Amount of dissolved N in steel In the bar-shaped steel material according to the present invention, the amount of dissolved N in the steel is controlled. Specifically, the amount of dissolved N in the steel is set to 0.020% by mass or less. When the amount of dissolved N in the steel exceeds 0.020% by mass, it is difficult to recrystallize and grain-grow during hot forging, and fine grains and strain remain, resulting in deterioration of soft magnetic properties. This is also because the soft magnetic properties deteriorate due to lattice strain caused by the dissolved N itself. The amount of dissolved N in the steel is more preferably 0.015% by mass or less, and even more preferably 0.01% by mass or less. On the other hand, if the amount of dissolved N in the steel becomes too small, the strength deteriorates. Therefore, the amount of dissolved N in the steel is preferably 0.00001% by mass or more. In the steel of the present invention, since the crystal structure is ferritic steel, the amount of dissolved N in the steel corresponds to the amount of dissolved N in the ferrite phase.

[0014] The amount of dissolved N in the steel is determined by subjecting the bar-shaped steel material to electrolytic extraction residue, extracting nitrides, measuring the amount of N in the nitrides (N pre ), and measuring the amount of dissolved N in the steel (=N 0 ) from the difference from the amount of alloy N (N 0 -N pre ).

[0015] 3. Chemical Composition The reasons for limiting each element are as follows. In the following description, "%" for the content means "% by mass".

[0016] C: 0.001 to 0.030% C increases the strength of the steel material. Therefore, the C content is set to 0.001% or more. However, if C is contained in excess, the average particle diameter of the nitrides and the amount of dissolved N in the steel deviate from the scope of the present invention, and the soft magnetic properties deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. Therefore, the C content is set to 0.030% or less. The C content is preferably 0.020% or less, and more preferably 0.015% or less.

[0017] Si: 0.01 to 4.00% Si is included as a deoxidizing element to improve soft magnetic properties. Therefore, the Si content is 0.01% or more, preferably 0.10% or more. However, if Si is contained in excess, the average particle size of the nitride and the amount of dissolved N in the steel deviate from the scope of the present invention, and the soft magnetic properties deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. Therefore, the Si content is 4.00% or less. The Si content is preferably 3.00% or less, more preferably 1.50% or less.

[0018] Mn: 0.01 - 2.00% Mn improves the strength and soft magnetic properties of the steel material. Therefore, the Mn content is 0.01% or more, preferably 0.05% or more. However, if Mn is contained in excess, the average particle size of the nitride and the amount of dissolved N in the steel deviate from the scope of the present invention, and the soft magnetic properties deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. Furthermore, the corrosion resistance may decrease. Therefore, the Mn content is 2.00% or less. The Mn content is preferably 1.00% or less, more preferably 0.50% or less.

[0019] Ni: 0.01 - 4.00% Ni improves the toughness and soft magnetic properties of the steel material. Therefore, the Ni content is 0.01% or more, preferably 0.05% or more. However, if Ni is contained in excess, the average particle size of the nitride and the amount of dissolved N in the steel deviate from the scope of the present invention, and the soft magnetic properties deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. Therefore, the Ni content is 4.00% or less. The Ni content is preferably 3.00% or less, more preferably 1.00% or less, and even more preferably 0.50% or less.

[0020] Cr: 8.0 - 35.0% Cr improves corrosion resistance and soft magnetic properties. Therefore, the Cr content should be 8.0% or more. It is more preferable that the Cr content be 10.0% or more. However, if the Cr content is insufficient or excessively contained, the average particle size of the nitride and the amount of dissolved N in the steel deviate from the scope of the present invention, and the soft magnetic properties deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. The Cr content should be 35.0% or less. It is preferably 21.0% or less, and more preferably 20.0% or less.

[0021] Mo: 0.01 - 5.00% Mo improves corrosion resistance and soft magnetic properties. Therefore, the Mo content should be 0.01% or more. However, if Mo is excessively contained, the average particle size of the nitride and the amount of dissolved N in the steel deviate from the scope of the present invention, and the soft magnetic properties deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. Therefore, the Mo content should be 5.00% or less. It is preferably 3.00% or less, more preferably 2.00% or less, and even more preferably 1.50% or less.

[0022] Cu: 0.01 - 2.00% Cu improves corrosion resistance and soft magnetic properties. Therefore, the Cu content should be 0.01% or more, and preferably 0.05% or more. However, if Cu is excessively contained, the average particle size of the nitride and the amount of dissolved N in the steel deviate from the scope of the present invention, and the soft magnetic properties deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. Therefore, the Cu content should be 2.00% or less. It is preferably 1.00% or less, more preferably 0.80% or less, and even more preferably 0.40% or less.

[0023] N: 0.001 - 0.030% N improves the strength of the steel material and is an element that forms nitrides. Therefore, the N content should be 0.001% or more, preferably 0.002% or more. However, if N is contained in excess, the soft magnetic properties will deteriorate, the amount of dissolved N will increase, and recrystallization and grain growth during hot forging will be suppressed. For this reason, the N content should be 0.030% or less, preferably 0.025% or less, and more preferably 0.020% or less.

[0024] Al: 7.000% or less Al promotes deoxidation and has the effect of improving the inclusion cleanliness level. In addition, the addition of Al enhances the soft magnetic properties. However, if Al is contained in excess, the effect will saturate, the average particle size of the nitrides and the amount of dissolved N in the steel will deviate from the scope of the present invention, and the soft magnetic properties will deteriorate. Also, recrystallization and grain growth during hot forging will be suppressed. Furthermore, toughness will decrease due to coarse inclusions. For this reason, the Al content should be 7.000% or less, preferably 3.000% or less, more preferably 0.100% or less, and even more preferably 0.020% or less. On the other hand, in order to obtain the above effects, the Al content is preferably 0.001% or more.

[0025] In addition to the above elements, the bar-shaped steel material according to the present invention contains one or more elements selected from Ti: 0.001% or more and Nb: 0.001% or more within the following component ranges. These elements are the main elements constituting the nitrides and need to be controlled because they are related to the average particle size of the nitrides, the amount of dissolved N, and recrystallization and grain growth during hot forging. For the elements among Ti and Nb that are not selected above, they may not be contained or may be contained within the following component ranges.

[0026] Ti: 0 - 2.00% Ti has the effect of enhancing the strength and soft magnetic properties of steel materials. Also, Ti forms nitrides and is related to the amount of dissolved N. Furthermore, since Ti reduces the amount of dissolved N and C and forms relatively coarse nitrides, it promotes recrystallization and grain growth during hot forging. Also, it suppresses the formation of Cr carbides and the formation of Cr-deficient layers. As a result, it has the effect of preventing intergranular corrosion. For this reason, the Ti content is set to 0.001% or more. However, if Ti is contained in excess, the average particle size of the nitrides deviates from the scope of the present invention and the soft magnetic properties deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. For this reason, the Ti content is set to 2.00% or less. It is preferable that the Ti content is 1.00% or less, more preferably 0.50% or less, even more preferably 0.50% or less, and still more preferably 0.25% or less.

[0027] Nb: 0 to 2.00% Nb has the effect of enhancing the strength and soft magnetic properties of steel materials. Also, Nb forms nitrides and is related to the amount of dissolved N. Furthermore, since it forms carbonitrides, it suppresses the formation of Cr carbides and the formation of Cr-deficient layers. As a result, it has the effect of preventing intergranular corrosion. For this reason, the Nb content is set to 0.001% or more. However, if Nb is contained in excess, the average particle size of the nitrides deviates from the scope of the present invention and the soft magnetic properties deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. For this reason, the Nb content is set to 2.00% or less. It is preferable that the Nb content is 1.00% or less, more preferably 0.80% or less, even more preferably 0.60% or less.

[0028] In addition to the above elements, the bar-shaped steel material according to the present invention may contain one or more elements selected from B, V, W, Ga, Co, Sn, Sb, and Ta as necessary.

[0029] B: 0 to 0.1% B has the effect of enhancing the soft magnetic properties of the steel material. Also, B forms nitrides and is related to the amount of dissolved N. Therefore, the B content should be 0.0001% or more. However, if B is contained in excess, the soft magnetic properties will deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. Therefore, the B content should be 0.10% or less. The B content is preferably 0.02% or less, and more preferably 0.01% or less.

[0030] Sn: 0~2.50% Since Sn has the effect of improving corrosion resistance and soft magnetic properties, it may be contained as required. However, if Sn is contained in excess, the soft magnetic properties will deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. Furthermore, the toughness decreases due to grain boundary segregation of Sn. Therefore, the Sn content should be 2.50% or less. The Sn content is more preferably 1.00% or less, and even more preferably 0.20% or less. On the other hand, in order to obtain the above effects, the Sn content is preferably 0.0001% or more, and more preferably 0.05% or more.

[0031] V: 0~2.0% Since V has the effect of improving soft magnetic properties, it may be contained as required. However, if V is contained in excess, the soft magnetic properties will deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. Therefore, the V content should be 2.0% or less. The V content is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.1% or less. On the other hand, in order to obtain the above effects, the V content is preferably 0.001% or more.

[0032] W: 0~3.0% Since W has the effect of improving corrosion resistance, it may be contained as necessary. However, if W is contained in excess, the soft magnetic properties will deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. Furthermore, toughness decreases due to coarse carbonitrides. For this reason, the W content should be 3.0% or less. The W content is preferably 2.0% or less, and more preferably 1.5% or less. On the other hand, in order to obtain the above effects, the W content is preferably 0.05% or more, and more preferably 0.10% or more.

[0033] Ga: 0 to 0.05% Since Ga has the effect of improving corrosion resistance, it may be contained as necessary. However, if Ga is contained in excess, the hot workability will deteriorate. For this reason, the Ga content should be 0.05% or less. On the other hand, in order to obtain the above effects, the Ga content is preferably 0.0004% or more.

[0034] Co: 0 to 2.50% Since Co has the effect of improving the strength and soft magnetic properties of the steel material, it may be contained as necessary. Also, adding an appropriate amount of Co increases the saturation magnetic flux density, thereby enhancing the soft magnetic properties. However, if Co is contained in excess, the soft magnetic properties will deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. For this reason, the Co content should be 2.50% or less. The Co content is preferably 1.00% or less, and more preferably 0.80% or less. On the other hand, in order to obtain the above effects, the Co content is preferably 0.05% or more, and more preferably 0.10% or more.

[0035] Sb: 0 to 2.5% Since Sb has the effect of improving corrosion resistance, it may be contained as necessary. However, if Sb is contained in excess, the soft magnetic properties will deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. Therefore, the Sb content should be 2.5% or less. It is more preferable that the Sb content be 1.0% or less, and even more preferable that it be 0.2% or less. On the other hand, in order to obtain the above effects, it is preferable that the Sb content be 0.01% or more, and more preferably 0.05% or more.

[0036] Ta: 0 to 2.5% Since Ta has the effect of improving corrosion resistance, it may be contained as necessary. However, if Ta is contained in excess, the soft magnetic properties will deteriorate. Also, recrystallization and grain growth during hot forging are suppressed. Therefore, the Ta content should be 2.5% or less. It is preferable that the Ta content be 1.5% or less, and more preferable that it be 0.9% or less. On the other hand, in order to obtain the above effects, it is preferable that the Ta content be 0.01% or more, more preferably 0.04% or more, and even more preferably 0.08% or more.

[0037] In addition to the above elements, the bar-shaped steel material according to the present invention may contain one or more elements selected from Ca, Mg, Zr, and REM as necessary. Ca: 0 to 0.05% Mg: 0 to 0.012% Zr: 0 to 0.012% REM: 0 to 0.05% Ca, Mg, Zr, and REM may be contained as necessary for deoxidation. However, if each of these elements is contained in excess, the soft magnetic properties will deteriorate. Also, toughness will decrease due to coarse inclusions. Therefore, Ca shall be 0.05% or less, Mg shall be 0.012% or less, Zr shall be 0.012% or less, and REM shall be 0.05% or less. The Ca content is preferably 0.010% or less, more preferably 0.005% or less. Mg is preferably 0.010% or less, more preferably 0.005% or less. Zr is preferably 0.010% or less, more preferably 0.005% or less. REM is preferably 0.010% or less. On the other hand, in order to obtain the above effects, it is preferable that Ca is 0.0002% or more, Mg is 0.0002% or more, Zr is 0.0002% or more, and REM is 0.0002% or more. The Ca content is more preferably 0.0004% or more, even more preferably 0.001% or more. The Mg content is preferably 0.0004% or more, even more preferably 0.001% or more. The Zr content is more preferably 0.0004% or more, even more preferably 0.001% or more. The REM content is more preferably 0.0004% or more, even more preferably 0.001% or more. Note that REM is a general term for 17 elements including Y and Sc among the 15 elements of lanthanoids. One or more of these 17 elements can be contained in steel, and the REM content means the total content of these elements.

[0038] In addition to the above elements, the bar-shaped steel material according to the present invention may contain one or more elements selected from Pb, Se, Te, Bi, S, and P as necessary. Pb: 0 to 0.30%, Se: 0 to 0.80%, Te: 0 to 0.30%, Bi: 0 to 0.50%, S: 0 to 0.50%, P: 0 to 0.30%, Pb, Se, Te, Bi, S, and P may be contained as necessary for machinability. However, if each of these elements is contained in excess, the soft magnetic properties will deteriorate. Also, the toughness will deteriorate. For this reason, Pb shall be 0.30% or less, Se shall be 0.80% or less, Te shall be 0.30% or less, Bi shall be 0.50% or less, S shall be 0.50 or less, and P shall be 0.30 or less. The Pb content is preferably 0.1% or less, and more preferably 0.05% or less. The Se content is preferably 0.1% or less, and more preferably 0.05% or less. The Te content is preferably 0.1% or less, and more preferably 0.05% or less. The Bi content is preferably 0.1% or less, and more preferably 0.05% or less. The S content is preferably 0.1% or less, and more preferably 0.05% or less. The P content is preferably 0.1% or less, and more preferably 0.05% or less. On the other hand, in order to obtain the above effects, it is preferable that Pb is 0.0001% or more, Se is 0.0001% or more, Te is 0.0001% or more, Bi is 0.0001% or more, S is 0.0001% or more, and P is 0.0001% or more. The Pb content is more preferably 0.0004% or more, and even more preferably 0.001% or more. The Se content is more preferably 0.0004% or more, and even more preferably 0.001% or more. The Te content is more preferably 0.0004% or more, and even more preferably 0.001% or more. The Bi content is more preferably 0.0004% or more, and even more preferably 0.001% or more. The S content is more preferably 0.0001% or more, and even more preferably 0.0002% or more. The P content is more preferably 0.0004% or more, and even more preferably 0.001% or more.

[0039] In the chemical composition of the steel material of the present invention, the balance is Fe and impurities. Here, "impurities" means components that are mixed in due to raw materials such as ores and scraps and various factors in the manufacturing process when the steel material is industrially manufactured, and are allowed within a range that does not adversely affect the present invention.

[0040] Examples of impurities include O, Zn, H, etc. Although it is preferable to reduce impurities, when they are contained, it is desirable that O, Zn, and H be 0.01% or less.

[0041] 4. Manufacturing Method A preferred manufacturing method of the electromagnetic stainless steel (stainless steel bar-shaped steel material) according to the present invention will be described. The stainless steel bar-shaped steel material according to the present invention can obtain the above-described effects as long as it has the above-described configuration regardless of the manufacturing method. For example, the stainless steel bar-shaped steel material according to the present invention can be stably obtained by the following manufacturing method.

[0042] In the stainless steel bar-shaped steel material according to the present invention, steel having the above chemical composition is melted, and after casting a slab having a predetermined diameter, hot or warm bar and wire rolling is performed by inclined rolling, rough rolling, intermediate rolling, and finish rolling, and heat treatment of the bar-shaped steel material is performed. Thereafter, pickling or the like is appropriately performed as necessary.

[0043] 4-1. Slab Heating Temperature It is preferable to control the slab heating temperature during hot rolling of the bar-shaped steel material. The slab heating temperature changes the average particle diameter of nitrides and the fraction of dissolved N in the steel. For this reason, the slab heating temperature affects soft magnetic properties. Also, it is related to recrystallization and grain growth in hot forging. When the slab heating temperature exceeds 1400°C, nitrides are likely to dissolve, and the amount of dissolved N increases. As a result, soft magnetic properties deteriorate. Also, the average particle diameter of nitrides becomes small, recrystallization and grain growth in hot forging are suppressed, and soft magnetic properties deteriorate. Therefore, the slab heating temperature should be 1400°C or less, preferably 1300°C or less, and more preferably 1200°C or less. On the other hand, when the slab heating temperature is less than 600°C, shear deformation is promoted in the subsequent hot rolling process, coarse nitrides are fragmented, fine nitrides are formed, and the average particle diameter of nitrides becomes small, so recrystallization and grain growth in hot forging are suppressed, and soft magnetic properties deteriorate. Therefore, the slab heating temperature should be 600°C or more. The slab heating temperature is preferably 700°C or more, and more preferably 800°C.

[0044] 4-2. Inclined Rolling Speed The inclined rolling speed particularly contributes to the fracture behavior of nitrides in the outermost layer to the 200-μm surface layer of the steel material, changes the average particle size of nitrides in the outermost layer to the 200-μm surface layer of the steel material, is also related to the precipitation amount of nitrides, changes the amount of dissolved N, and affects the soft magnetic properties, so it is necessary to control. When the inclined rolling speed exceeds 3.0 / s, the nitrides in the outermost layer to the 200-μm surface layer of the steel material are fractured during inclined rolling, and the average particle size of the nitrides becomes smaller. As a result, recrystallization and grain growth during hot forging are suppressed, and the soft magnetic properties deteriorate. Therefore, the inclined rolling speed should be 3.0 / s or less, preferably 2.0 / s or less, and more preferably 1.0 / s or less. On the other hand, when the inclined rolling speed is less than 0.1 / s, the precipitation amount of nitrides decreases and the amount of dissolved N increases, so the magnetic properties deteriorate. Therefore, the inclined rolling speed should be 0.1 / s or more, preferably 0.2 / s or more, and more preferably 0.3 / s or more. The inclined rolling speed (average strain rate) ( / s) is calculated as follows from the diameter D of the steel material 0 before inclined rolling and the diameter D of the steel material after inclined rolling, and the inclined rolling time t (s). Inclined rolling speed = 2ln(D 0 / D) / t

[0045] 5. Electromagnetic parts The electromagnetic parts using the stainless steel bar-shaped steel material of the present invention are, for example, cores such as injectors and solenoid valves and connectors. Since the bar-shaped steel material used as the material has excellent soft magnetic properties, effects such as "improvement of magnetic attraction force", "miniaturization of parts", and "improvement of responsiveness" can be achieved. In addition, since it has excellent soft magnetic properties even without magnetic annealing, it is possible to manufacture the parts with high production and low cost.

[0046] Hereinafter, the present invention will be described more specifically by way of examples. However, these are examples of the present invention, and the present invention is not limited to these examples.

Examples

[0047] Steel having the chemical compositions described in Tables 1 to 3 was melted. In Table 3, the numerical values deviating from the present invention are underlined. When melting the steel, AOD melting, which is an inexpensive melting process for stainless steel, was assumed, and it was melted in a 100 kg vacuum melting furnace and cast into a slab with a diameter of 180 mm. Thereafter, it was made into a stainless steel bar-shaped steel material with a diameter of 20.0 mm under the following manufacturing conditions.

[0048] The conditions are described below. Specifically, the cast slab was heated, and inclined rolling, rough rolling, intermediate rolling, and finish rolling were performed, followed by heat treatment to produce a bar wire (bar-shaped steel material) with a diameter of 20.0 mm. Also, the slab heating temperature and the inclined rolling speed were set to 1000 °C and 0.6 / s, which are the conditions of No. 62 in Table 4. For the obtained bar wire (bar-shaped steel material), the average particle diameter of nitrides, the amount of dissolved N in the steel, and the soft magnetic properties were evaluated.

[0049]

Table 1

[0050]

Table 2

[0051]

Table 3

[0052] Next, in order to examine the possibility of omitting magnetic annealing by hot forging, a warm hot compression test (specimen: φ10×17 mm, heating temperature: 900 °C, heating time: 3 min, compression ratio: 60%, strain rate: 10 / s, cooling rate after compression: 0.5 °C / s) simulating hot forging was performed using the obtained bar-shaped steel material, and the soft magnetic properties were evaluated using the test specimen after the compression test. Also, the hot forging crack susceptibility was evaluated by changing only the compression ratio under the above conditions. The results are summarized in Tables 1 to 3 below. These measurements were performed according to the following procedure. The warm hot compression test conditions are an example, and the heating conditions, compression ratio, strain rate, cooling rate after compression, or heat treatment after compression, etc. are not limited to the above examples.

[0053] The average particle diameter of the nitride was measured at least once in a 400-fold field of view at the position from the outermost surface to 200 μm below the surface (the region with a depth from the outermost surface to 200 μm below the surface) in the L cross-section of the bar-shaped steel material (the cross-section including the center line of the bar-shaped steel material). Then, the nitride in the observation field of view was identified using FE-SEM / ESD, and the average value of the equivalent circle diameter of the nitride in the same field of view was calculated. If the average particle diameter of the nitride was more than 5.0 μm and 30 μm or less, it was rated as ◎◎; if it was 1.0 to 5.0 μm, it was rated as ◎; if it was 0.1 to 1.0 μm, it was rated as ○; if it was less than 0.1 μm, it was rated as ×. When the bar-shaped steel material of the present invention was used, it was rated as ◎◎, ◎, and ○, and was excellent in the average particle diameter of the nitride.

[0054] Regarding the amount of dissolved N in the steel, electrolytic extraction residue was performed on the bar-shaped steel material to extract the nitride, and the amount of N in the nitride (N pre ) was measured. From the difference from the amount of alloy N (N 0 ), the amount of dissolved N in ferrite (= N 0 - N pre ) was measured. If the amount of dissolved N in the steel was 0.00001 to 0.01% by mass, it was rated as ◎◎; if it was 0.01 to 0.015% by mass, it was rated as ◎; if it was 0.015 to 0.020% by mass, it was rated as ○; if it was more than 0.020% by mass, it was rated as ×. When the bar-shaped steel material of the present invention was used, it was rated as ◎◎, ◎, and ○, and was excellent in the amount of dissolved N in the steel.

[0055] Regarding the soft magnetic properties, the coercive force (A / m) was measured. A ring-shaped test piece with a thickness of 3 mm, an outer diameter of 10 mm, and an inner diameter of 8 mm was prepared from the sample after the warm compression test, and the coercive force was measured. If the coercive force was 5.0 A / m or less, it was rated as ◎◎; if it was 10 A / m or less, it was rated as ◎; if it was 15 A / m or less, it was rated as ○; if it was more than 15 A / m, it was rated as ×. When the bar-shaped steel material of the present invention was used, it was rated as ◎◎, ◎, and ○, and was excellent in the soft magnetic properties.

[0056] The hot forging crack susceptibility was determined by the presence or absence of cracks on the end face in a hot upset compression test. Test pieces with a diameter of φ10×15 mm were prepared, the compression ratio was changed at room temperature, the test pieces were compressed, the side surfaces of the test pieces after the test were observed, the presence or absence of cracks was determined, and the hot forging crack susceptibility was evaluated from the magnitude of the compression ratio without cracks. If the compression ratio was 80% or more, it was rated as ◎◎; if 70% or more, it was rated as ◎; if 60%, it was rated as 〇; and if less than 60%, it was rated as ×. When the bar-shaped steel material of the present invention was used, it was rated as ◎◎, ◎, and 〇, and it had excellent hot forging crack susceptibility.

Example

[0057] Subsequently, using the steel type R shown in Table 1, a bar-shaped steel material with a diameter of 13 mm was produced under the conditions described in Table 4. The history other than the slab heating temperature and the inclined rolling speed was the same as in Example 1 above. For the produced bar wire (bar-shaped steel material), the average particle diameter of the nitride, the amount of dissolved N in the steel, the soft magnetic properties, and the hot forging crack susceptibility were measured by the above-described methods. The results are summarized and shown in Table 4 below. In Table 4, numerical values deviating from the preferred production conditions of the present invention are underlined. Similarly, using the steel type N shown in Table 1, a bar-shaped steel material with a diameter of 13 mm was produced under the conditions described in Table 5. The results are summarized and shown in Table 5.

[0058]

Table 4

[0059]

Table 5

Industrial Applicability

[0060] According to the present invention, a bar-shaped steel material excellent in soft magnetic properties can be obtained, which is extremely useful industrially.

Claims

1. The chemical composition is by mass percentage, C: 0.001 to 0.030%, Si: 0.01 to 4.00%, Mn: 0.01 to 2.00%, Ni: 0.01 to 4.00%, Cr: 8.0 to 35.0%, Mo: 0.01 to 5.00%, Cu: 0.01 to 2.00%, N: 0.001 to 0.030%, Al: 7.000% or less, furthermore Ti: 0 to 2.00%, Nb: 0 to 2.00%, containing one or more selected from Ti: 0.001% or more and Nb: 0.001% or more, B: 0 to 0.1%, Sn: 0 to 2.50%, V: 0 to 2.0%, W: 0 to 3.0%, Ga: 0 to 0.05%, Co: 0 to 2.50%, Sb: 0 to 2.5%, Ta: 0 to 2.5%, Ca: 0 to 0.05%, Mg: 0 to 0.012%, Zr: 0 to 0.012%, REM: 0 to 0.05%, Pb: 0 to 0.30%, Se: 0 to 0.80%, Te: 0 to 0.30%, Bi: 0 to 0.50%, S: 0 to 0.50%, P: 0 to 0.30%, the balance being Fe and impurities, an electromagnetic stainless steel bar for warm forging, wherein the average particle size of nitrides in the outermost surface layer to the surface layer 200 μm of the steel material is 0.1 to 30 μm and the amount of dissolved N in the steel is 0.020 mass% or less.

2. The chemical composition further comprises, by mass percentage, B: 0.0001 to 0.1%, Sn: 0.0001 to 2.5%, V: 0.001 to 2.0%, W: 0.05 to 3.0%, Ga: 0.0004 to 0.05%, Co: 0.05 to 2.5%, Sb: 0.01 to 2.5%, and Ta: 0.01 to 2.5%, containing one or more selected from the electromagnetic stainless steel bar for warm forging according to Claim 1.

3. The chemical composition further comprises, by mass percentage, Ca: 0.0002 to 0.05%, Mg: 0.0002 to 0.012%, Zr: 0.0002 to 0.012%, and REM: 0.0002 to 0.05%, containing one or more selected from the electromagnetic stainless steel bar for warm forging according to Claim 1 or Claim 2.

4. The chemical composition further comprises, by mass percentage, Pb: 0.0001 to 0.30%, Se: 0.0001 to 0.80%, Te: 0.0001 to 0.30%, Bi: 0.0001 to 0.50%, S: 0.0001 to 0.50%, P: 0.0001 to 0.30%, containing one or more selected from the electromagnetic stainless steel bar for warm forging according to any one of Claims 1 to 3.

5. An electromagnetic component using the electromagnetic stainless steel bar for warm forging according to any one of claims 1 to 4.

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