TW202000943A - Free-cutting S-containing martensitic stainless steel - Google Patents

Abstract

This free-cutting S-containing martensitic stainless steel includes, in terms of mass%: C: 0.08 to 0.70%; Si: 0.01 to 1.0%; Mn: 0.1 to 1.50%; S: 0.15 to 0.60%; P: 0.010 to 0.050%; Cr: 10 to 16%; N: 0.005 to 0.15%; Al: 0.004% or less; Mg: 0.0020% or less; O: 0.007 to 0.030%; Ni: 0 to 1.0%; and Mo: 0 to 3.0%, with a remainder including Fe and unavoidable impurities, wherein (Mn,Cr)(S,O) inclusions containing 0.5 mass% or more of O are included.

Description

Ma Tian loose iron series S quick-cut stainless steel

Field of invention The invention relates to a Matian loose iron system S-cutting stainless steel (Matian loose iron system S-cutting stainless steel). This case claims priority based on Japanese Patent Application No. 2018-112652, which was filed in Japan on June 13, 2018, and the contents are cited here.

Background of the invention Among parts such as OA equipment and electronic equipment, precision parts manufactured by cutting not only require chip handling during cutting, but also require high dimensional accuracy and good surface properties of the cutting surface. The materials that can be requested are: SUS420F containing 0.15% or more of S, or Ma Tian loose iron series free-cutting stainless steel containing Pb, Se, Te alone or in combination to further improve machinability (Patent Documents 1 to 3) .

On the other hand, in response to the market demand for stopping the addition of Pb, a field-hard bulk iron-based free-cutting stainless steel that contains Bi or Sn and has a second phase mainly composed of Cu dispersed (Patent Documents 4 and 5) has been proposed.

However, with the inventions described in Patent Documents 1 to 5, it is impossible to produce products that can satisfy manufacturability and surface properties after cutting. Especially for the above precision parts system requirements: under the industrial cutting conditions of cutting speed ≧20m/min, cutting amount ≧0.05mm, feed rate ≧0.005mm/rev, it has the accuracy and excellent resistance of surface roughness Ra≦0.50μm Tool wearability.

Prior technical literature Patent Literature Patent Document 1: Japanese Patent Publication No. 7-56064 Patent Document 2: Japanese Patent Laid-Open No. 2001-152298 Patent Document 3: Japanese Patent No. 5135918 Patent Document 4: Japanese Patent Publication No. 6194696 Patent Document 5: Japanese Patent Publication No. 4502519

Summary of the invention Problems to be solved by invention The present invention was made in view of the above circumstances, and the object is to provide a Matian bulk iron S-cutting stainless steel, which can obtain an excellent surface roughness (Ra): 0.50 μm or less under the industrial cutting processing conditions of precision parts The precision, tool wear resistance and manufacturability are also excellent, and it does not contain Pb.

Means to solve the problem In one aspect of the present invention, it is understood that by controlling trace components, the composition of inclusions can be controlled, and by uniformly dispersing MnS, machinability can be improved, and in particular, surface roughness after cutting can be improved. Detailed knowledge and insights are as follows.

In order to improve the surface roughness, it is effective to make the built-up edge of the cutting edge of the tool smaller during cutting. If a chip edge is generated on the cutting edge, irregularities that are different from the cutter contour of the tool will occur during cutting, so the surface roughness will deteriorate. In one aspect of the present invention, the aspect ratio of the inclusions in the steel is reduced to suppress the formation of cutting edge.

First, the trace components are controlled in the casting stage to produce granular sulfide-based inclusions (sinite type). In one aspect of the present invention, the sulfide-based inclusions are (Mn, Cr) (S, O)-based inclusions or (Mn, Cr, Ca, REM) (S, O, Te)-based inclusions, and their characteristics It is to make the trace elements solid dissolve in the sulfide inclusions to improve the deformation resistance of the inclusions, and the aspect ratio becomes smaller. In addition, generally, rod-shaped sulfides (eutectic forms) are generated in the casting stage, but such inclusions have a large aspect ratio and a non-uniform morphology, thus causing deterioration in surface roughness.

One aspect of the present invention is based on the above knowledge and the gist of the invention is as follows. [1] A Ma Tian loose iron series S quick-cut stainless steel, characterized by Contains the following elements in mass%: C: 0.08~0.70%, Si: 0.01~1.0%, Mn: 0.1~1.50%, S: 0.15~0.60%, P: 0.010~0.050%, Cr: 10~16%, N: 0.005~0.15%, Al: 0.004% or less, Mg: 0.0020% or less, O: 0.007~0.030%, Ni: 0~1.0%, Mo: 0~3.0%, Ca: 0~0.003%, Te: 0~0.024%, REM: 0~0.003%, B: 0~0.02%, Nb: 0~1.00%, Ti: 0~1.00%, V: 0~0.50%, Ta: 0~0.5%, W: 0~0.5%, Co: 0~1.00%, Zr: 0~0.020%, Cu: 0~3.0%, Sn: 0~0.5%, Sb: 0~0.5%, and Ga: 0~0.0050%, and The remainder consists of Fe and impurities; and Contains (Mn, Cr) (S, O)-based inclusions, and the (Mn, Cr) (S, O)-based inclusions contain 0.5 mass% or more of O. [2] The Ma Tian loose iron series S free-cutting stainless steel as in [1], which contains one or more of the following elements in mass %: Ca: 0.0005~0.003%, Te: 0.010~0.024%, and REM: 0.0005~0.003%. [3] As in [1] or [2], Ma Tian loose iron series S fast-cut stainless steel, which contains (Mn, Cr, Ca, REM) (S, O, Te) series inclusions, the (Mn, Cr, Ca , REM) (S, O, Te) inclusions contain 0.3 mass% or more of Ca, 1 mass% or more of Te, and 0.3 mass% or more of any one or more elements of REM. [4] As in any one of [1] to [3], the Ma Tian loose iron series S free-cutting stainless steel contains one or more elements selected from the following mass %: B: 0.0001~0.02%, Nb: 0.05~1.00%, Ti: 0.05~1.00%, V: 0.05~0.50%, Ta: 0.1~0.5%, W: 0.1~0.5%, Co: 0.05~1.00%, Zr: 0.001~0.020%, Cu: 0.1~3.0%, Sn: 0.005~0.5%, Sb: 0.005~0.5%, and Ga: 0.0005 to 0.0050%. [5] As in any one of [1] to [4], the Ma Tian loose iron system S free-cutting stainless steel, wherein the aspect ratio of the aforementioned (Mn, Cr) (S, O) inclusions is 4.0 or less. [6] As in [3] or [4], the Ma Tian loose iron series S fast-cut stainless steel, wherein the aspect ratio of the aforementioned (Mn, Cr, Ca, REM) (S, O, Te) series inclusions is 4.0 or less.

Invention effect In one aspect of the present invention, a Ma Tian loose iron series S free-cutting stainless steel can be prepared, which does not contain Pb that will adversely affect the environment, and has a surface roughness (Ra ): Excellent surface accuracy of 0.50 μm or less, and also excellent tool wear resistance and manufacturability. In addition, the Matian loose iron series S free-cutting stainless steel according to the aspect of the present invention can be used as materials for precision parts such as OA equipment and electronic equipment that require machinability and corrosion resistance, or shafts, screws, and bolts, for example. And other parts.

Forms for carrying out the invention The Ma Tian loose iron series S free-cutting stainless steel of this embodiment has a chemical composition containing C: 0.08 to 0.70%, Si: 0.01 to 1.0%, Mn: 0.1 to 1.50%, S: 0.15 to 0.60%, P in mass %. : 0.010~0.050%, Cr: 10~16%, N: 0.005~0.15%, Al: 0.004% or less, Mg: 0.0020% or less, O: 0.007~0.030%, Ni: 0~1.0%, Mo: 0~ 3.0%, Ca: 0 to 0.003%, Te: 0 to 0.024%, REM: 0 to 0.003%, B: 0 to 0.02%, Nb: 0 to 1.00%, Ti: 0 to 1.00%, V: 0 to 0.50 %, Ta: 0 to 0.5%, W: 0 to 0.5%, Co: 0 to 1.00%, Zr: 0 to 0.020%, Cu: 0 to 3.0%, Sn: 0 to 0.5%, Sb: 0 to 0.5% And Ga: 0~0.0050%, and the rest is composed of Fe and impurities, and contains (Mn, Cr) (S, O)-based inclusions, the (Mn, Cr) (S, O)-based inclusions contain 0.5 O with mass% or more. In addition, the Ma Tian loose iron series S free-cutting stainless steel of this embodiment may also contain (Mn, Cr, Ca, REM) (S, O, Te) series inclusions, the (Mn, Cr, Ca, REM) (S, O, Te)-based inclusions contain 0.3% by mass or more of Ca, 1% by mass or more of Te, and 0.3% by mass or more of any one or more elements of REM. In addition, the aspect ratio of (Mn, Cr) (S, O)-based inclusions in the Ma Tian loose iron-based S free-cutting stainless steel of the present embodiment may be 4.0 or less. In addition, in the Ma Tian bulk iron S quick-cut stainless steel of this embodiment, the aspect ratio of (Mn, Cr, Ca, REM) (S, O, Te)-based inclusions may be 4.0 or less. Hereinafter, each requirement of this embodiment will be described.

C: 0.08～0.70% The C system is necessary to obtain the Ma Tian scattered iron structure after quenching to obtain high strength. Therefore, the C content is set to 0.08% or more. In addition, from the viewpoint of machinability, the C content may be 0.12% or more. On the other hand, if an excessive amount of C is contained, coarse carbides are generated during annealing, which promotes the formation of cutting edge chips during cutting and further deteriorates the accuracy of the cutting surface. Therefore, the C content is set to 0.70% or less. And it should be below 0.40%.

Si: 0.01~1.0% The Si system is included for deoxidation. Therefore, the Si content is set to 0.01% or more. The Si content may be 0.05% or more. On the other hand, if Si is greater than 1.0%, when hot rolling stainless steel to make rods and wires, scale formation will be promoted during rolling delay, and hot rolling defects will be generated, so the Si content is set to 1.0% the following.

Mn: 0.1~1.50% Mn is the following element: it will form inclusions together with Cr to improve machinability, especially surface accuracy. Therefore, the Mn content is set to 0.10% or more. On the other hand, if the Mn content is greater than 1.50%, the composition ratio of Mn/Cr in the inclusions becomes high, the inclusions stretch and the aspect ratio becomes large. Therefore, the Mn content is set to 1.50% or less. The Mn content may also be 1.40% or less, and may also be 1.10% or less.

S: 0.15～0.60% S will form sulfide-based inclusions, and the stress will concentrate on the inclusions during cutting. In addition, when the chips are generated, cracks are generated in the shear deformation zone system starting from the inclusions, and the growth of the edge of the chip accumulation can be suppressed. Therefore, the accuracy of the steel cutting surface will be improved. In order to obtain this effect, the S content is made 0.15% or more. The S content may also be 0.20% or more. On the other hand, if it contains more than 0.60% of S, the hot workability significantly deteriorates. Therefore, the S content is set to 0.60% or less. The S content can also be set to 0.40% or less.

P: 0.010～0.050% P will segregate at the grain boundary, reducing the ductility of the material during cutting and improving the surface accuracy. Therefore, the P content is set to 0.010% or more. The P content can also be 0.020% or more. On the other hand, if the P content exceeds 0.050%, the manufacturability is significantly deteriorated. Therefore, the P content is set to 0.050% or less.

Cr: 10~16% Cr forms sulfide-based inclusions together with Mn. In particular, by optimizing the composition ratio (Mn/Cr) of Mn and Cr in the inclusions, the aspect ratio of the inclusions can be controlled. In order to reduce the aspect ratio to improve the accuracy of the cutting surface, the Cr content needs to be set to 10% or more. The Cr content may also be 12% or more. However, if a large amount of Cr is contained, the composition ratio of Mn/Cr in the inclusions becomes too small, the inclusions become easy to stretch, and the aspect ratio becomes large. Therefore, the Cr content is set to 16% or less. The Cr content may be 15% or less.

N: 0.005～0.15% N will dissolve in the matrix, and in the cutting temperature zone will embrittle the matrix and increase the strength of the product. Therefore, the N content is set to 0.005% or more. And it is preferable to contain N in an amount greater than 0.02%. However, if it contains more than 0.15% of N, it will cause significant deterioration of manufacturability due to the formation of pores or deterioration of hot workability. Therefore, the N content is set to 0.15% or less. The N content can also be 0.12% or less.

Al: 0.004% or less The Al-based is used as a deoxidizing element, and in order to form a hard Al-based oxide with low oxidation, it is necessary to generate a rod-shaped sulfide (eutectic type). Therefore, the Al content is set to 0.004% or less. The Al content can be less than 0.003% or less than 0.002%. In this embodiment, to exhibit the effect, it is preferable to contain Al in an amount of 0.001% or more.

Mg: 0.0020% or less The Mg system is used as a deoxidizing element, and in order to form a hard Mg system oxide with low oxidation, it is necessary to generate a rod-shaped sulfide (eutectic type). Therefore, the Mg content is set to 0.0020% or less. The Mg content can be below 0.0010% or less than 0.0005%. In this embodiment, to exhibit the effect, it is preferable to contain Mg in an amount of 0.0001% or more. By containing both Al and Mg in an amount in the range of the present embodiment, granular sulfide-based inclusions (polarized type) can be generated, thereby improving machinability.

O: 0.007～0.030% O will coarsen the deoxidation products during solidification, and generate granular sulfide-based inclusions (polarized type), thereby improving machinability. Therefore, the O content is set to 0.007% or more. The O content may also be 0.012% or more. Moreover, it may be 0.016% or more. However, if O is contained in an amount greater than 0.030%, hard inclusions are increased to deteriorate machinability, so the O content is set to 0.030% or less.

In addition to the above-mentioned elements, the Ma Tian loose iron system S free-cutting stainless steel of this embodiment is composed of Fe and impurities. However, within the range that does not hinder the effects of the technical features of this embodiment, elements other than the above may optionally contain the elements described below. The reason for limitation is described below. The lower limit of these elements is 0%.

Ni: 0～1.0% Ni will also be included because it will increase the hardness of the material through solid solution strengthening, prevent the formation of edge chips, and further improve the surface accuracy during cutting. At this time, the Ni content is preferably 0.1% or more. However, if it is greater than 1.0%, it will be hardened, resulting in loss of tool life. Therefore, the Ni content is set to 1.0% or less. The Ni content may also be 0.8% or less. And the Ni content can also be 0%.

Mo: 0～3.0% Mo is an element that improves corrosion resistance and may also be included. However, if it contains a large amount of Mo, it will be hardened and the life of the tool will be reduced. Therefore, the Mo content is set to 3.0% or less. The Mo content may also be 2.0% or less. On the other hand, in order to obtain the above effect, the Mo content is preferably 0.1% or more. The Mo content can also be 0%.

Ca: 0~0.003% Ca may generate granular sulfide-based inclusions (macromorphic type) to further improve machinability, and therefore may also be included. In addition, it also has the effect of softening oxide-based inclusions and improving tool life, so it may be included. To obtain these effects, it should be more than 0.0005%. However, if it contains more than 0.003% Ca, the effect will reach saturation, but it will reduce the hot workability. Therefore, the Ca content is set to 0.003% or less. The Ca content is 0.001% or more and more preferably 0.002% or less. The Ca content can also be 0%.

Te: 0～0.024% Te is used in this embodiment to improve machinability, especially important elements required to improve the accuracy of the cutting surface, and therefore may also be included. By dissolving Te in the inclusions by 1% by mass or more, the deformation of the inclusions is suppressed, and the aspect ratio becomes smaller. As a result, the growth of the cutting edge of the cutting edge is suppressed, and the accuracy of the cutting surface is improved. When containing Te, the Te content is preferably 0.010% or more. On the other hand, if it contains more than 0.024% of Te, not only the effect is saturated, but also MnTe is formed around the inclusions, which significantly deteriorates the manufacturability. Therefore, the Te content is set to 0.024% or less. The Te content can also be 0.015% or less. Te content can also be 0%.

REM: 0~0.003% Like the Ca, the REM system generates granular sulfide-based inclusions (macromorphic type), and further improves machinability, so it may be included. In addition, it also has the effect of softening oxide-based inclusions and improving tool life, so it may be included. When REM is contained, it should be set to 0.0005% or more. However, if it contains more than 0.003% of REM, not only its effect is saturated, but also a part of the inclusions will generate hard REM oxysulfide, resulting in reduced tool life. Therefore, the REM content is set to 0.003% or less. The REM content is preferably 0.001% or more and 0.002% or less. The REM content can also be 0%.

According to the general definition, REM (rare earth element) refers to the two elements of scandium (Sc) and yttrium (Y) and the 15 elements (lanthanides) from lanthanum (La) to lutetium (Lu) in the periodic table . It may contain one kind alone or a mixture of two or more kinds.

B: 0~0.02% B is an element used to improve hot workability, and may be included to obtain a stabilizing effect. However, if an excessive amount of B is contained, the compound of B will precipitate and deteriorate the hot workability, so the B content is set to 0.02% or less. The B content should be below 0.015%. On the other hand, in order to obtain the above effect, the B content is preferably 0.0001% or more, and the B content is preferably 0.0002% or more. The B content can also be 0%.

Nb: 0~1.00% Ti: 0~1.00% V: 0~0.50% Ta: 0～0.5% W: 0～0.5% Nb, Ti, V, Ta, and W have the effect of forming carbonitrides to improve corrosion resistance, and therefore may be contained. However, if a large amount of these elements are contained, machinability deteriorates, so the Nb content is set to 1.00% or less, and the Ti content is set to 1.00% or less. The V content is 0.50% or less, the Ta content is 0.5% or less, and the W content is 0.5% or less. On the other hand, in order to obtain the above effect, the Nb content is preferably 0.05% or more, the Ti content is preferably 0.05% or more, and the V content is preferably 0.05% or more. Also, the Ta content is preferably 0.1% or more, and the W content is preferably 0.1% or more. Nb, Ti, V, Ta and W can also be 0%.

Co: 0~1.00% Co will increase the toughness of the matrix, so it can also be included. However, if an excessive amount of Co is contained, it becomes hard and deteriorates machinability, so the Co content is set to 1.00% or less. The Co content can also be 0.60% or less. On the other hand, in order to obtain the above effects, the Co content is preferably 0.05% or more. Co can also be 0%.

Zr: 0～0.020% Zr has an effect of increasing strength, so it may be contained. However, if a large amount of Zr is contained, the toughness is reduced, so the Zr content is set to 0.020% or less. On the other hand, in order to fully obtain the effect of improving strength, the Zr content is preferably 0.001% or more. Zr can also be 0%.

Cu: 0～3.0% Cu will increase the hardness of the material through solid solution strengthening, prevent the formation of edge cutting edge, and further improve the surface accuracy during cutting, so it may also be included. However, even if it contains more than 3.0%, the effect is still saturated, and slab cracking or the like may occur to deteriorate the manufacturability, so the Cu content is made 3.0% or less. On the other hand, in order to obtain the above effect, the Cu content is preferably 0.1% or more. Cu can also be 0%.

Sn: 0~0.5% Sb: 0~0.5% Since Sn and Sb coexist with sulfide which deteriorates the corrosion resistance, the deterioration of the corrosion resistance is suppressed, and therefore may be contained. However, if more than 0.5% of Sn and Sb are contained, the manufacturability is deteriorated, so the content of Sn and Sb is set to 0.5% or less, respectively. The content of Sn and Sb can also be less than 0.3%. On the other hand, in order to obtain the above effects, the Sn and Sb contents are preferably 0.005% or more. The content of Sn and Sb can also be more than 0.010%. In addition, the content of Sn and Sb can also be 0%.

Ga: 0~0.0050% Ga may contain more than 0.0005% in order to improve cold workability. However, if Ga is greater than 0.0050%, the forgeability will deteriorate. Therefore, the upper limit of the Ga content is preferably 0.0050% or less. Ga may also be 0%.

In this embodiment, the Ma Tian loose iron S free-cutting stainless steel may inevitably contain Pb and Se, but the Pb content must be controlled to less than 0.03% and the Se content to less than 0.02%.

In addition, the term “impurity” refers to materials mixed from ore, scrap, or manufacturing environment as raw materials when manufacturing steel in industry, and it can be tolerated to the extent that it does not adversely affect the steel of this embodiment. Thing.

In this embodiment, it is important to control the composition of inclusions. If the deformation resistance of the inclusions is increased, the aspect ratio of the inclusions can be kept small even after rolling the Matian loose iron S-cut stainless steel of this embodiment into a wire rod. As a result, the formation of cutting edge chips can be suppressed, and high dimensional accuracy and good surface properties can be obtained during cutting.

To control the composition of the inclusions, the amount of deoxidizing components such as Al and Mg is controlled below the upper limit of the content of the present embodiment when melting steel in the refining step, thereby increasing the oxygen content in the molten steel. In addition, at the time of actual machine manufacturing, in AOD (or VOD), the basicity of slag CaO/SiO _{2 is} preferably set to 1.8 or less, and preferably set to about 1.5. After the above refining is completed, the oxygen content in the molten steel can be increased by the operation without adding deoxidizing components such as Al and Mg at all. Thereby, (Mn, Cr)(S, O)-based inclusions containing 0.5% by mass or more of O can be generated as granular sulfide-based inclusions (polarized type). At this stage, the aspect ratio of the inclusions is 4.0 or less, and preferably 3.0 or less. Even if the stainless steel that has generated inclusions is rolled in the subsequent hot rolling step under the condition that the total hot rolling reduction ratio (the total reduction ratio of hot rolling delay) is more than 95%, the inclusions will not Deformation, and the aspect ratio can be controlled below the target, that is, below 4.0, and should preferably be controlled below 3.0. If the aspect ratio is greater than 4.0, the machinability is reduced when cutting into parts, etc., which is not good. The length-to-width ratio of inclusions should be 1 or more. When the aspect ratio of the inclusions is less than 1, the inclusions will be difficult to extend and very hard inclusions, and it is presumed that they will cause cracks or surface scratches during manufacturing.

In addition, if one or more elements of Ca, Te, and REM are contained, (Mn, Cr, Ca, REM) (S, O, Te)-based inclusions can be generated, which contains 0.3% by mass or more Ca, 1% by mass or more of Te, and 0.3% by mass or more of REM composite inclusions of one or more elements. The aspect ratio of the generated inclusions is 4.0 or less, and preferably 3.0 or less. The deformation resistance of the composite inclusions is high, so even if the rolling delay is performed under the condition that the reduction ratio of the hot rolling is more than 95% in the subsequent hot rolling step, the inclusions will not be deformed, but the inclusions The aspect ratio is controlled below 4.0 and preferably below 3.0, so that the machinability can be greatly improved. If the aspect ratio is greater than 4.0, the machinability will be reduced, which is not good. The length-to-width ratio of inclusions should be 1 or more.

The Matian loose iron series S free-cutting stainless steel of the present embodiment may be a steel material after casting, or may be a wire material obtained by hot rolling a steel material, or may be obtained by further cold drawing a wire material The steel wire may also be a forged material obtained by forging a cast steel material or a hot-rolled wire material. The steel, wire, steel wire or forged material is steel with the chemical composition of this embodiment, and contains (Mn, Cr) (S, O)-based inclusions or (Mn, Cr, Ca, REM) (S, O, Te) are inclusions. In addition, (Mn, Cr) (S, O)-based inclusions or (Mn, Cr, Ca, REM) (S, O, Te)-based inclusions contained in steel are relatively less deformable inclusions, so In any of the above stages, those with an aspect ratio of 4.0 or less.

In addition, by containing one or more elements of Ca, Te, and REM, (Mn, Cr, Ca, REM) (S, O, Te) inclusions are generated, but even in this case, The Ma Tian loose iron series S free-cutting stainless steel of this embodiment may still contain (Mn, Cr) (S, O) series inclusions.

The (Mn, Cr) (S, O)-based inclusions containing 0.5% or more of O include all Mn, Cr, S, and O, and the O concentration is 0.5% or more. Also, the so-called (Mn, Cr, Ca, REM) (S, O, Te)-based inclusions include all Mn, Cr, S and O, and contain 0.3% or more of Ca, 1% or more of Te and 0.3% Inclusions of one or more elements in the above REM. In addition, (Mn, Cr, Ca, REM) (S, O, Te)-based inclusions may also contain 0.5% or more of O. The content of O and Te in the inclusions is preferably 10% or less. The contents of Ca and REM in the inclusions are preferably 20% or less.

The composition of these inclusions was analyzed using an energy dispersive X-ray analysis device (EDS) attached to a scanning electron microscope (SEM). When all Cr, Mn, S, and O are detected from inclusions specified by SEM and contain 0.5% by mass or more of O, the inclusions are designated as (Mn, Cr) (S, O)-based inclusions. In addition, all of Mn, Cr, S, and O were detected from the inclusions specified by SEM, and one or more of 0.3 mass% Ca, 1 mass% or more Te, and 0.3 mass% or more REM were detected or In the case of two or more elements, the inclusion is designated as (Mn, Cr, Ca, REM) (S, O, Te) based inclusions. Whether these inclusions are mixed can be analyzed by specifying more than 10 inclusions, and the results can be used to confirm whether the inclusions are mixed.

In addition, the aspect ratio of the inclusions is based on the sample already provided for SEM-EDS. Observed with an optical microscope, the 10 field of view is taken at a magnification of 100 times, and the image analysis method is used to determine the external contact with the inclusions. The length direction in the rolling direction is horizontal (horizontal Feret diameter) and the length length perpendicular to the rolling direction (vertical Ferret diameter). Calculate the ratio of the horizontal Ferret diameter/vertical Ferret diameter of each inclusion as the aspect ratio, and take the average of the aspect ratios of all inclusions as the aspect ratio of the sample. When the above two kinds of inclusions are contained, the aspect ratio of all the inclusions may be averaged.

As described above, the Mata loose iron S free-cutting stainless steel of the present embodiment contains S as a free-cutting element and is excellent in machinability. After the steel is made into a steel wire, for example, it can be suitably used as a material for precision parts such as OA equipment and electronic equipment that require machinability and corrosion resistance, or a material for parts such as screws and bolts. Examples

150kg of alloy raw material is melted in a vacuum furnace, and the amount of deoxidizing components such as Al and Mg is controlled below the upper limit of the content of the present embodiment, thereby performing in a mold with a diameter of 200 mm in a state where the oxygen content in the molten steel is high Casting. After that, it was heated at 1200°C, followed by hot forging and processing up to a diameter of 70 mm. Next, it was annealed (air-cooled) at 780°C for 1 hour and peeled to a diameter of 66 mm. Next, it is processed into a diameter of 10 mm by hot extrusion equivalent to rolling of bar steel. Then pickling was carried out, followed by annealing again at 780°C for 1 hour, and air cooling (5°C/sec) (total hot rolling reduction rate: 98%). Next, cold wire drawing was performed up to φ6 mm, and the obtained wire rod was again held in a furnace at 780°C for 3 minutes to perform strand annealing (cooling system rapid cooling). Finally, the wire was processed with a draw bench to obtain a cold drawn bar with a diameter of 5.5 mm. Using this cold drawn bar as a material for evaluation, each evaluation test was carried out. In addition, in the steel compositions shown in Tables 1 to 3, Pb is less than 0.03% and Se is less than 0.02%.

After embedding the aforementioned wire material in the resin so that the longitudinal cross section including its center line can be observed, and performing mirror polishing, the inclusion is analyzed by an energy dispersive X-ray analyzer (EDS) attached to a scanning electron microscope (SEM) Composition. When all Cr, Mn, S, and O are detected from inclusions specified by SEM and contain 0.5% by mass or more of O, the inclusions are designated as (Mn, Cr) (S, O)-based inclusions. In addition, all of Mn, Cr, S, and O were detected from the inclusions specified by SEM, and one or more of 0.3 mass% Ca, 1 mass% or more Te, and 0.3 mass% or more REM were detected or In the case of two or more elements, the inclusion is designated as (Mn, Cr, Ca, REM) (S, O, Te) based inclusions. Whether these inclusions are mixed is determined by analyzing more than 10 inclusions, and the result confirms whether the inclusions are mixed. Table 4 and Table 5 show the composition ratio of inclusions.

The aspect ratio of the inclusions is based on the samples already provided for SEM-EDS. Observed with an optical microscope, the 10 field of view is photographed at a magnification of 100 times, and the external analysis of the inclusions and rolling is determined by image analysis The diameter length in the direction is horizontal (horizontal ferret diameter) and the diameter length perpendicular to the rolling direction (vertical ferret diameter). Calculate the ratio of the horizontal Ferret diameter/vertical Ferret diameter of each inclusion as the aspect ratio, and take the average of the aspect ratios of all inclusions as the aspect ratio of the sample. The results are shown in Table 6 and Table 7. In addition, in Table 6 and Table 7, when the two types of inclusions are included, the value obtained by averaging the aspect ratios of all the inclusions is described as the aspect ratio of the sample.

The surface roughness after cutting the outer circumference of the wire rod was evaluated by the average roughness (Ra) of the center line of the cutting surface. The cutting is turning. The tool is made of cemented carbide P type and the blade R is 0.4mm. The cutting speed is 50m/min, the feed rate is 0.02mm/rev, and the knife consumption is 0.1mm. Cutting with cloth cutting oil (mineral oil).

The surface roughness Ra is measured with a sample after 15 minutes of turning. For the measurement system, a contact-type roughness measuring machine was used to measure 5 points at a reference length of 2.5 mm, and the average value was used as the measured value. In this embodiment, when the surface roughness Ra is 0.50 μm or less, it is judged as good. The results are shown in Table 6 and Table 7.

In addition, the tool life is evaluated based on the time until the average wear of the clearance surface reaches 0.2mm. If the average wear of the clearance surface is less than 0.2mm under 15 minutes of processing, it is considered to have reached the life. That is, when the average wear of the clearance surface under 15 minutes of processing is less than 0.2 mm, it is estimated that the tool life is long and the machinability is excellent. When the average wear of the clearance surface is more than 0.2 mm under 15 minutes of processing, it is estimated that the tool life is short and the machinability is poor. The results are shown in Table 6 and Table 7.

Manufacturability is evaluated by high temperature tensile test. A hot ductility evaluation test piece having a diameter of 10 mm was taken from the center of the forged material having a diameter of 70 mm and the middle of the surface along the length of the round bar. The manufacturability was evaluated by the reduction in area after tensile fracture under the conditions of a test temperature of 1000° C. and a tensile speed of 10 mm/sec. The shape of the test piece at this time was φ10mm×100mm. The manufacturability is regarded as achieving manufacturability with a reduction in area at 1000°C of 50% or more. That is, when the reduction ratio at 1000° C. is 50% or more, it is evaluated as excellent in manufacturability. When the reduction in area at 1000°C is less than 50%, it is estimated that the manufacturability is poor. The results are shown in Table 6 and Table 7.

[Table 1]

[Table 2]

[table 3]

[Table 4]

[table 5]

[Table 6]

[Table 7]

Samples No. 1 to 49 are inventive steels (inventive examples), and sample Nos. 50 to 65 are comparative steels (comparative examples). The * mark in the table indicates that the value is outside the range of this embodiment. Supplementary explanation of the inclusion composition in Table 4 and Table 5, that is, No.25~37 and 63~65 containing any one or more elements of Ca, Te and REM contain (Mn, Cr)(S , O) inclusions and (Mn, Cr, Ca, REM) (S, O, Te) inclusions. In addition, when two kinds of inclusions are included, the aspect ratios of (Mn, Cr)(S, O)-based inclusions and (Mn, Cr, Ca, REM)(S, O, Te)-based inclusions are both Below 4.0. Also, in Nos. 59, 60 and 62, the oxygen content in the inclusion composition is less than 0.5% by mass. In addition, No. 59, 60, and 62 do not contain (Mn, Cr) (S, O)-based inclusions with an aspect ratio of 4.0 or less. In No. 52, the amount of Mn is outside the scope of this embodiment. In No. 55, the amount of Cr is outside the scope of this embodiment. In addition, these Nos. 52 and 55 do not contain (Mn, Cr) (S, O)-based inclusions with an aspect ratio of 4.0 or less. Samples other than the above contain (Mn, Cr) (S, O)-based inclusions with an aspect ratio of 4.0 or less.

The No. 1 to No. 49 of the steel of the present invention is to control the composition of the inclusions of the Matian loose iron series S free-cutting stainless steel, so that the surface roughness Ra after cutting is 0.50 μm or less, and the tool wear is also reduced Less than 0.2mm to achieve the target tool life benchmark. In addition, the manufacturability is also the same, and the reduction in area at 1000° C. is 50% or more to achieve the manufacturability standard. On the other hand, No. 50 to No. 65 of the comparative steel did not satisfy the prescribed range of the embodiment, and did not satisfy any of the characteristics.

As can be seen from the examples, according to the present embodiment, it is possible to produce a Sada free-cutting stainless steel which does not contain highly toxic Pb and the like, and is excellent in machinability and manufacturability.

Industrial availability The Mata loose iron series S free-cutting stainless steel of this embodiment can be used, for example, as a material for precision parts such as OA equipment and electronic equipment that require machinability and corrosion resistance, or parts such as shafts, screws, and bolts.

Claims (6)

A Ma Tian loose iron series S quick-cut stainless steel, characterized by: Contains the following elements in mass%: C: 0.08~0.70%, Si: 0.01~1.0%, Mn: 0.1~1.50%, S: 0.15~0.60%, P: 0.010~0.050%, Cr: 10~16%, N: 0.005~0.15%, Al: 0.004% or less, Mg: 0.0020% or less, O: 0.007~0.030%, Ni: 0~1.0%, Mo: 0~3.0%, Ca: 0~0.003%, Te: 0~0.024%, REM: 0~0.003%, B: 0~0.02%, Nb: 0~1.00%, Ti: 0~1.00%, V: 0~0.50%, Ta: 0~0.5%, W: 0~0.5%, Co: 0~1.00%, Zr: 0~0.020%, Cu: 0~3.0%, Sn: 0~0.5%, Sb: 0~0.5%, and Ga: 0~0.0050%, and The remaining part is composed of Fe and impurities, and Contains (Mn, Cr) (S, O)-based inclusions, and the (Mn, Cr) (S, O)-based inclusions contain 0.5 mass% or more of O. If the Ma Tian loose iron series S fast-cut stainless steel of claim 1, it contains one or more of the following elements in mass %: Ca: 0.0005~0.003%, Te: 0.010~0.024%, and REM: 0.0005~0.003%. If claim 1 or claim 2 of the Ma Tian loose iron series S free-cutting stainless steel, which contains (Mn, Cr, Ca, REM) (S, O, Te) series inclusions, the (Mn, Cr, Ca, REM) The (S, O, Te)-based inclusions contain 0.3% by mass or more of Ca, 1% by mass or more of Te, and 0.3% by mass or more of any one or more elements of REM. For any of the claims 1 to 3, the Ma Tian loose iron series S quick-cut stainless steel contains one or more elements selected from the following by mass %: B: 0.0001~0.02%, Nb: 0.05~1.00%, Ti: 0.05~1.00%, V: 0.05~0.50%, Ta: 0.1~0.5%, W: 0.1~0.5%, Co: 0.05~1.00%, Zr: 0.001~0.020%, Cu: 0.1~3.0%, Sn: 0.005~0.5%, Sb: 0.005~0.5%, and Ga: 0.0005 to 0.0050%. According to any one of claim 1 to claim 4, the Ma Tian loose iron series S fast-cut stainless steel, wherein the aspect ratio of the aforementioned (Mn, Cr) (S, O) inclusions is 4.0 or less. As in claim 3 or claim 4, the Ma Tian loose iron series S free-cutting stainless steel, in which the aspect ratio of the aforementioned (Mn, Cr, Ca, REM) (S, O, Te) series inclusions is 4.0 or less.