DE60030175T2 - cutting alloy - Google Patents

Description

State of technology

The The present invention relates to free-cutting alloys that are excellent are in machinability.

alloys have diverse Applications due to a variety of properties. An automatic alloy, which are excellent in machinability is selected in one case for the Improvement of productivity. For example, to improve machinability a free-cutting alloy, which is the machinability improving element such as S, Pb, Se or Bi (hereinafter referred to as the denotes the machinability improving element) contains widely used. In particular, in a case where the machine Machinability due to a precise finish in the Editing or for other reasons especially necessary, not only the content of such the machinability improving element in one Alloy increased, but the elements also become an alloy in combination added.

While S, which for the machinability improvement has been widely used in many cases is added in the form of MnS, due to its addition to a Alloy in a big one Quantity a deterioration of corrosion resistance, thermoformability and the cold workability of the alloy. In addition, one in the Alloy inserted Sulfur component in the environment in the form of a sulfur-containing Gases released in the surrounding areas of the parts easily causes sulfur contamination when the alloy is exposed to air becomes. Therefore, there is a need to prevent the release of sulfur-containing gas (hereinafter referred to as the improvement in the exhaust resistance designated). Elements such as S, Se and Te, however, worsen the magnetic properties in an electromagnetic stainless steel or similar very strong.

Therefore were different proposals submitted: the Mn content is limited, the Cr content in the sulfide will be raised, or, in the case of the presence of S, Ti is combined with S is added to disperse the sulfide in spherical form (see for example JP-A-98-46292 or JP-A-81-16653). The increase of Cr content in the sulfide However, it can greatly reduce the machinability and lead to thermoformability, and therefore such an alloy is in many cases limited in its application.

R. Kiessling et al. "non metallic inclusions in steel ", 1978 concerns sulfide inclusions in steel.

The GB 1 519 313 relates to a stainless steel alloy and a ferrite free cutting steel having excellent machinability and high corrosion resistance.

consequently It is an object of the present invention to provide a free-cutting alloy which is excellent in machinability, showing outstanding properties as an alloy, such as corrosion resistance, Thermoformability and cold formability or specific magnetic Properties which match those of conventional alloys are comparable.

Summary the invention

Around to solve the above mentioned problem is a vitrified alloy of the present invention by a Automate alloy according to claim 1 characterized. "(Ti, Zr)" means one or both of Ti and Zr.

The Machinability of an alloy can be achieved by forming the (Ti, Zr) -based compound described above in a matrix metal phase the alloy can be improved. In addition, by forming this compound in the alloy the formation of compounds, like MnS and (Mn, Cr) S, which easily increases the corrosion resistance and thermoformability of the alloy, prevents or this be prevented, thereby reducing corrosion resistance, hot workability and Cold formability be kept at a sufficiently good level can. This means that according to the present Invention, a vat alloy can be realized, which excellent in machinability, without being useful Alloy properties, such as hardness, corrosion resistance, Thermoformability, cold workability and specific magnetic properties, impaired become.

In addition, a (Ti, Zr) -ba formed in the free-cutting alloy of the present invention is sierte compound distributed in the alloy structure. The machinability of an alloy can be further increased particularly by dispersing or dispersing the compound in an alloy structure. To increase this effect, the particle size of the (Ti, Zr) -based compound as observed in the structure of a polished portion of the alloy is preferably approximately in the range of 0.1 to 30 μm on average, for example, and more For example, an area ratio of the compound in the structure is preferably in the range of 1 to 20%, wherein the particle size is defined by the maximum distance between two parallel lines surrounding a particle to be observed when the parallel lines are drawn to be intersect in an area including the particle to be observed while changing the direction of the parallel lines.

The above-described (Ti, Zr) -based alloy may include at least one compound expressed by the composition formula (Ti, Zr) ₄ (S, Se, Te) ₂ C ₂ (hereinafter also referred to as carbosulfide / selenide) wherein one or more of Ti and Zr may be contained in the compound and wherein one or more of S, Se and Te may be contained in the compound. By forming a compound in the form of the above-described composition formula, not only the machinability of an alloy can be improved, but also the corrosion resistance can be increased.

It should be understood that the identification of a (Ti, Zr) -based compound in an alloy by X-ray diffraction (for example, a diffractometer method), an electron probe microanalysis method (EPMA), and a similar technique can be done. For example, the presence or absence of the compound (Ti, Zr) ₄ (S, Se, Te) ₂ C _{2 can} be confirmed by whether or not a peak corresponding to the compound appears in the diffraction pattern measured by an X-ray diffractometer. In addition, a region in the alloy structure in which the joint is formed can also be determined by comparing between two-dimensional mapping results of characteristic X-ray intensities of Ti, Zr, S, Se, and C by EPMA surface analysis performed on a section structure of the alloy be given.

Short description of drawings

The 1 Fig. 12 is a graph showing an X-ray diffraction pattern of a No. 5 steel sample according to the invention in the experiment of Example 1 (reference);

2 Fig. 12 is a graph showing the EDX analysis results of the No. 2 candidate sample of the second selection invention in Example 2;

3 Fig. 3 is an optical microscope photograph of the steel samples of Nos. 2 and 13 of the second selection invention in Example 2;

4 Fig. 12 is a diagram showing the measurement points for the endurance test in Example 2;

5 Fig. 12 is a graph showing an example of a Schaeffler diagram;

6 Fig. 3 is an optical microscope photograph of the reference steel sample No. 5 in Example 1 (Reference);

7 FIG. 12 is a graph showing the dependencies of the solubility products on the temperature of the components of TiO, TiN, Ti ₄ C ₂ S ₂ , TiC, TiS and CrS in γ-Fe.

preferred embodiments the invention

The present invention is quite concretely applied to an alloy constituted as a stainless steel. In this case, such an alloy preferably contains one or more of Ti and Zr, so that W _Ti + 0.52W _Zr = 0.03 to 3.5 mass% is satisfied, where W _Ti and W _{Zr are} the respective contents in mass. specify% of Ti and Zr; and one or more of S and Te in the respective ranges of 0.01 to 1.0 mass% for S and 0.01 to 0.8 mass% for Se, for a (Ti, Zr) -based compound without any To make deterioration in the stainless steel properties.

Of the Reason why the elements and their contents are so selected as follows:

(1) The Ti and Zr content which is defined such that W _Ti + 0.52W _Zr = 0.03 to 3.5 mass%, wherein W _Ti and W _{Zr are} the respective contents in mass% of Ti and Zr mean

Ti and Zr are indispensable elements for forming a (Ti, Zr) -based compound, which plays a central role in exerting the effect of improving the machinability of a free-cutting alloy according to the present invention. When the value of W _Ti + 0.52W _{Zr is} below 0.03 mass%, the amount of the (Ti, Zr) -based compound is insufficiently formed, whereby the effect of improving the machinability becomes insufficient. On the other hand, when the value is exceeded, the machinability is lowered on the contrary. For this reason, the value of W _Ti + 0.52W _Zr must be suppressed to 3.5 mass% or less. The above effect, which is exhibited when Ti and Zr are incorporated in an alloy, is determined by the sum of the number of atoms (or the sum of the number of moles) irrespective of the kinds of the metals Ti or Zr. Since the ratio between the atomic weights is approximately 1: 0.52, Ti with a smaller atomic weight shows a larger effect at a lower mass. Thus, the value of W _Ti + 0.52W _{Zr represents} a compositional parameter that reflects the sum of the atomic numbers of Zr and Ti contained in an alloy.

(2) One or more off S and Se in the respective ranges of 0.01 to 1 mass% for S and 0.01 to 0.8 mass% for se

S and Se are useful elements for improving machinability. By adding S and Se to an alloy, a compound useful for improving machinability is formed in the alloy structure (for example, a (Ti, Zr) -based compound which is in the form of a compositional formula (Ti, Zr) ₄ (S , Se) ₂ C _{2 is} expressed). Consequently, the contents of S and Se as the upper limit are 0.01 mass%. If the contents are extremely large, there is a possibility that a problem of deterioration of thermoformability occurs, and hence the upper limits must be maintained: the S content is set to 1 mass%, and the Se content becomes 0 , 8 mass% set as respective upper limits. Moreover, S and Se are both preferably added to an alloy in the necessary and sufficient amount to form an alloy machinability improving compound such as the (Ti, Zr) based compound described above. Excessive addition of S results in deterioration of exhaust resistance.

A free-cutting alloy of the present invention, which is formed as a stainless steel, constitutes a martensite-containing stainless steel (hereinafter referred to as second selection invention), wherein the composition of the free-cutting alloy of the present invention is as follows:
The state-of-the-art alloy can contain: 2 mass% or less, including zero, Ni; 9 to 17 mass% Cr; and C, which satisfies the following formulas: 0.375 (W S + 0.4W se ) <W C ≤ 1.5 formula A and 0.125 (W Ti + 0.52W Zr ) <W C ≤ 1.5 formula B, wherein W _C , W _S and W _Se denote the respective contents of C, S and Se in mass% and W _Ti and W _{Zr are} as defined above.

Martensite stainless steel is often used in equipment and parts that require hardness and corrosion resistance properties. Since the hardness of martensitic stainless steel is increased by a quenching heat treatment, there was the case where work was carried out in a calcined state, followed by quenching and annealing, so that workability was improved. However, in this case, stress was generated in the stainless steel by the quenching heat treatment, and therefore, the processing had to be performed in the case after the quenching heat treatment when precision processing was provided. In addition, there has been a problem specific to martensite stainless steels that not only the corrosion resistance, thermoformability and the like but also the quenchability has been deteriorated when the machinability improving elements such as S, Se improve machinability , Pb and Bi were added to the stainless steel. In this way, only insufficient hardness was achieved. It should be understood that martensite-containing stainless steel is a generic term for stainless steels which has a martensite phase in the matrix by a quench heat treatment and Ab Training for the toughening treatment.

When examples for Compositions of martensite-containing stainless steels can be named: corresponding Types of stainless steels, such as SUS 403, SUS 410, SUS 410S, SUS 420J1, SUS 420J2, SUS 429J1, SUS 440C and similar, which all are shown within JIS G 4304. In addition, should be understood in the present invention, heat-resistant martensite steel is such it is handled by the term martensite-containing stainless steel falls. As examples of a composition of heat-resistant martensite steel can corresponding types of steels whose compositions are described in JIS G 4311 and the G 4312 are defined as SUH 1, SUH 3, SUH 4, SUH 11, SUH 600 and SUH 616. However, none of the elements is Ti, Zr, S and Se as essential features of the present invention in the standard expressly mentioned. In this case should be understood that part of the Fe content of each of the Stainless steel types described above by the elements described above in the respective compositions described above. In this way, the martensite-containing stainless steel of the present Invention obtained. While in the description of the present invention, the same JIS numbers These are therefore actually alloys that are used for the present invention, wherein the alloys compositions which defines only one basis in the JIS standards are.

There Martensite-containing stainless steel at a martensite transformation temperature (Ms point) changed and the quenching ability Quenchability depends on the components contained in it Areas of contained components to be given attention. For this reason, the Ranges of components in the content of the above-described (Ti, Zr) -based connection are set such that the the following conditions First, the contents of the components are as much as possible determined such that a (Ti, Zr) -based compound is not in such a surplus is formed that the martensite formation temperature (Ms point) and the quenching ability impaired become. As contained in the (Ti, Zr) -based compound Atoms approximately does not affect the properties of the stainless steel, such as the hardness of the Martensite phase and its quenching ability, exercise, will suppose that the elements obtained by excluding the Amount of elements contained in the (Ti, Zr) based compound from the original in the martensite-containing stainless steel added elements (below as residual elements) stay in solid solution solved in the matrix phase and the residual elements have an influence on the martensite transformation exercise. Accordingly, the ranges of the content of the respective elements preferably adjusted, with the influence on the martensite conversion using a continuous cooling transformation diagram of stainless steel with a composition which results in the composition the rest of the elements is analog, is observed. In particular, the C content in this way set that the above-described formulas A and B are satisfied, there C has a big influence on the martensite transformation. As a result, not only the machinability is improved, but also the hardness after quenching, quenching ability and similar becomes compatible with conventional martensite-containing stainless steels.

below the reason why the components and their contents are described in the second selection invention of the present invention which are formed as martensite-containing stainless steel, selected such and limited are:

(3) 2 mass% or less, including zero, Ni

nickel can be added as needed, as the element for improvement the corrosion resistance, especially in the environment of a reducing acid, effective is. Excess addition reduced but not just the martensite transformation temperature (Ms point), but increased also the stability the austenite phase of the matrix phase to a high degree, thereby It comes to a case in which the amount of martensite needed to ensure the hardness necessary, can hardly be obtained. In addition, the hardness is after the glow large, causing a through the Ni excess caused solid solution hardening effect occasionally features such as the machine Machinability, lowers. For the reason described above the Ni content has an upper limit of 2 mass%.

(4) 9 to 17 mass% Cr

Cr is an indispensable element for ensuring corrosion resistance and is added in an amount of 9 mass% or more. However, when the content exceeds 17 mass%, the phase stability is impaired, and thereby high-temperature brittleness easily occurs, resulting in poor thermoformability. In addition, it is assumed that with increasing salary the cons steadiness or hardness decreases. In particular, when a stainless steel containing Cr in excess undergoes extensive heat treatment at a temperature in the middle range of 400 to 540 ° C, the room temperature resistance is easily lost. Therefore, a Cr content is desirably set in the range of 11 to 15 mass%, and more preferably in the range of 12 to 14 mass%.

Furthermore For example, the vending alloy of the second selection invention of the present Invention, which formed as martensite containing stainless steel is included: 2 mass% or less, including zero, Si; 2 mass% or less, including zero, Mn; 2% by mass or less, including zero, Cu; and 2 mass% or less, including zero, Co. In addition, the Automotive alloys continue to contain one or more of Mo and W in the respective ranges of 0.1 to 4 mass% for Mo and 0.1 to 3 mass% for W included.

below the reason why the elements and their contents are described are defined as follows:

(5) 2 mass% or less, including zero, Si

Si is used as a deoxidizer for Steel added. However, the addition of Si in excess is undesirable because not only the cold workability is deteriorated, but as well the formation of δ-ferrite in the amount increases, whereby the thermoformability of the steel decreases. About that In addition, the Ms point is in excess in the case of a martensite-containing stainless steel. Accordingly the Si content has the upper limit of 2 mass%. In one Case in which cold workability is considered to be particularly important is the Si content is preferably 0.5 mass% or less, including zero, set.

(6) 2 mass% or less, including zero, Mn

Mn acts as a deoxidizer for Stole. additionally there is a need of adding if the machinability is considered to be particularly important, as it is one to increase the machinability in coexistence with S or Se useful Represents connection. On the other hand, it affects cold formability disadvantageous because MnS in particular the corrosion resistance deteriorates, and above In addition, the Ms point decreases sharply in a martensite-containing stainless steel. Therefore, the Mn content has an upper limit of 2 mass%. Especially if the corrosion resistance and the cold formability is considered important, the Mn content preferably to 0.4 mass% or less, including zero, limited.

(7) 2 mass% or less, including zero, Cu

Cu can be added as needed, as the element for improvement the corrosion resistance, especially in the environment of a reducing acid, effective is. Preferably, 0.3 mass% or more is contained by one to achieve a more pronounced effect. In excess, however, not only does the thermoformability, but in a martensite-containing stainless steel the Ms point decreases and the quenching ability is also impaired, whereas it is preferred that the Cu content be 2 mass% or less, including zero, is set. In particular, when the thermoformability than important, it is particularly preferred, the Cu content to 0.5 mass% or less, including zero.

(8) 2 mass% or less, including zero, co

Co is to improve corrosion resistance, especially in the Environment of a reducing acid, effective element and may be additional added to martensite-containing stainless steel as needed since Co increases the Ms point and the quenching ability improved. A content of Co of 0.3 mass% or more is preferable to achieve clearer effects. With excess addition however decreases not only the thermoformability, but the raw material costs climb. Therefore, it is preferable to have the content of Co in the range of 2 mass% or less, including zero. Especially if thermoformability and reduction of raw material costs as is considered to be important Content of Co is more preferably 0.5% by mass or less inclusive of zero.

(9) One or more off Mo and W in the respective ranges of 0.1 to 4 mass% for Mo and 0.1 to 3 mass% for W

There Mo and W the corrosion resistance and increase strength further can, can the elements are added as needed. The lower limits both amount to 0.1%, where their effects are clearly observed are. On the other hand, not only is the thermoformability of excess addition deteriorates but takes in a martensite-containing stainless steel the Ms point is strong, and above In addition, the costs are increased. Therefore, the upper limits of Mo and W are 4 mass% each and 3 mass%.

In the martensite-containing stainless steel described above are the Content of other elements as follows: the stainless steel can contain: 0.05 mass% or less P; and 0.03 mass% O; and 0.05 mass% or less N. Above can out the stainless steels continue one or more of Te, Bi and Pb in the respective areas from 0.005 to 0.1 mass% for Te; 0.01 to 0.2 mass% for Bi; and 0.01 to 0.3 mass% for Pb included. Below is the reason why the Elements and their contents are defined as follows:

(10) 0.05 mass% or less, including zero, P

P is segregated at the grain boundaries and not only increases the intergranular corrosion sensitivity, but also occasionally reduces firmness. Therefore, a P content preferably as low as possible set and amounts 0.05 mass% or less, including zero. Although the P content more preferably 0.03 mass% or less, inclusive of zero, is set, can be a more than necessary reduction in the salary increased in Production costs reflect.

(11) 0.03 mass% or less, including zero, O

O combined with Ti or Zr, which are both constituent elements a useful for improving the machinability Compound, and forms oxides which improve of machinability are not useful. Therefore, should an O content as low as possible held and set to 0.03% by mass as the upper limit become. The O content is preferably 0.01 mass% or less, if applicable an increase the production costs possible is.

(12) 0.05 mass% or less, including zero, N

N combined with Ti or Zr, which are both constituent elements one useful for improving machinability Represent compound, and forms nitrides, which improve machinability are not useful. Therefore, a should N content as low as possible held and set to 0.05% by mass as the upper limit become. The N content is preferably 0.03 mass% or less, including zero, and particularly preferably 0.01% by mass, if this is considered increase the production costs possible is.

(13) One or more of Te, Bi and Pb in the respective ranges of 0.005 to 0.1 Mass% for Te; 0.01 to 0.2 mass% for Bi; and 0.01 to 0.3 mass% for pb

There Te, Bi and Pb further improve machinability can, can the elements are added, if necessary. their Lower limits where the corresponding effects are clearly visible are as follows: 0.005 mass% for Te; 0.01 mass% for Bi and 0.001% by mass for Pb respectively. On the other hand, the upper limits are as follows adjusted: 0.1 mass% Te; 0.2 mass% Bi; and 0.3 mass% Pb, as an excess addition reduces the thermoformability.

Moreover, the machined alloy of the present invention formed as a stainless steel may include one or more of the group consisting of Ca, Mg, B and REM (one or more of the metal elements classified as Group 3A in the Periodic Table of Elements) in the range from 0.0005 to 0.01 mass% for one element or as total content in the case of two or more elements. The elements are useful for improving the hot workability of the steel. The effect of improving the thermoformability obtainable by adding the elements becomes particularly apparent in the range of 0.0005 mass% or higher for one element or as the total content of more than one element in combination. On the other hand, if the elements are added in excess, the effect is saturated and the thermoformability is reduced on the contrary. Consequently, the content of a single element or the total content of the combined elements is set to 0.01 mass% as an upper limit provides. As REM, it is useful to have one or more elements selected from Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu from this standpoint because low-radioactivity elements are easy to handle when used primarily. It is desirable to use the light rare earth elements, particularly La or Ce, from the viewpoint of a clear effect and price. However, there is no problem in interfering with a trace of radioactive rare earth elements such as Th and U, which inevitably remain in a process for separating rare earth elements without being excluded. In addition, rare earth elements not separated out from the standpoint of reducing the raw material cost, such as misch metal (cermet metal) and didymium, can be used.

A Automated alloy of the present invention, which is stainless steel is formed, one or more, selected from the group consisting of Nb, V, Ta and Hf in the respective range of 0.01 to 0.5 Mass% included. Since Nb, V, Ta and Hf have an effect regarding the formation of carbonitrides for the miniaturization of crystalline Particles of steel and to increase have the strength. Consequently, the elements in the respective Content of up to 0.5% by mass may be added and are preferred in 0.01 mass% or more in the range.

A free-cutting alloy of the present invention, which is formed as the above-described stainless steel, may contain a W _SO value which is less than 0.035 mass%, provided that the following test is conducted: an alloy test piece of the free-cutting alloy is prepared such that it has the Having a rectangular prism of size 15 mm in length, 25 mm in width and 3 mm in thickness, the entire surface was polished with a No. 400 emery paper; a silver foil of the size of 10 mm in length, 5 mm in width and 0.1 mm in thickness with a purity of 99.9% or more as S-getter; 0.5 cm ³ of pure water are sealed in a vessel having an inner volume of 250 cm ³ together with the test piece; the temperature in the vessel is raised to 85 ° C and the temperature is then held there for 20 hours; and then the S content is analyzed in mass% in the silver foil, the obtained S content being defined as the W _SO .

A (Ti, Zr) -based compound, which is a feature of the present invention Invention is formed, and in the course of training Added S is added to the stainless steel as a constituent element the (Ti, Zr) -based compound, which is chemically more stable than MnS or similar. And therefore, the amount released into the air from the stainless steel decreases at S from. Consequently, the exhaust resistance of the stainless steel can also can be improved by forming the (Ti, Zr) -based compound.

In this case, when the exhaust resistance test is performed, an S component released from the test piece as the sulfur-containing gas is forced to absorb in the silver foil as a getter, and the sulfur content W _SO in the silver foil is measured quantitative determination of the exhaust gas resistance of the material. An S content absorbed in the silver foil is defined by using the W _SO value and adjusted to 0.035 mass% or less in W _SO . A stainless steel of the present invention, which is controlled such that its W _{SO is} 0.035 mass% or less, scarcely causes sulfur contamination in the environment when exposed to air since the S component released from the stainless steel into the air is extremely low. Therefore, the stainless steel can be preferably used as parts for industrial devices requiring exhaust resistance.

While a factor for determining the exhaust resistance of a material is mainly the composition of the material, it is desirable to fix S as the carbosulfides of Ti and Zr to improve the exhaust resistance of the material. For these purposes, an S content is preferably determined such that a value of W _S / (W _Ti + 0.52W _Zr ) is 0.45 or less, or alternatively a value of W _S / W _{C is} 0.4 or less and W _S / (W _Ti + 0.52W _Zr ) is 0.45 or less, wherein W _S and W _C each represent an S content and a C content. With such a range of matched components, an S content present in chemically unstable conditions can be limited, and thus the exhaust resistance of the matrix metal phase of the stainless steel can be improved.

Examples

The The following experiments were performed to demonstrate the effects of the present Confirm the invention. It should be understood that in the following description the test alloy, which relates to the present invention, as inventive steel or alloy according to the invention or as a selection invention steel or selection invention alloy is designated.

Example 1: ferrite-containing Stainless steel (reference only)

The Effects of an automatic alloy, which as ferrite-containing stainless steel formed (a reference steel) were determined by the following experiment approved. First, 50 kg of steel blocks with corresponding compositions in mass%, as shown in Table 1 are melted in a high frequency induction furnace, and from the molten blocks Ingots made were at a temperature in the range from 1050 to 1100 ° C heated and the bars were in hot State to bars with circular Cross-section of 20 mm diameter shaped. The bars were continue at 800 ° C Warmed for 1 hour, followed by air cooling (annealing or hardening) as a source for Test pieces.

Table 1

While the main inclusions of a reference steel (Ti, Zr) were ₄ (S, Se) ₂ C ₂ , other inclusions such as (Ti, Zr) S and (Ti, Zr) S _{3 were} locally observed in the matrix. In addition, in the sample No. 7 having a high Mn content (Mn, Cr) S, it was observed, though only in trace amounts. An identification method for the inclusions was conducted in the following manner: A test piece in an appropriate amount was obtained from each of the bars. A metal matrix portion of the test piece was dissolved by electrolysis using a methanol solution including tetramethylammonium chloride and acetalacetone at 10% as an electrolytic solution. The electrolytic solution was subjected to filtration after the electrolysis, and compounds not dissolved in the steel were extracted from the filtrate. The extract was dried and subjected to chemical analysis by an X-ray diffraction method with a diffractometer. A compound was identified on the basis of the peaks of the diffraction pattern. A composition of a compound particle in the steel structure was separately analyzed by EPMA, and a compound having a composition corresponding to an X-ray diffraction observed compound was confirmed on the basis of the formation of two-dimensional mapping results. The 1 shows an X-ray diffraction pattern of a number 5 steel by means of a diffractometer, and FIGS 6 is an optical microscope photograph of a steel sample No. 5. Moreover, the samples of Nos. 1 to 14 in Table 1 are steel species corresponding to the reference steel, and the samples of Nos. 15 to 28 are steel species of Comparative Examples.

The The following experiments were carried out on the test pieces described above:

1) thermoformability test

The Assessment of thermoformability was based on the optical Observation performed, depending on whether defects, such as fractures, when thermoforming occur or not. [O] indicates that essentially no Defect in thermoforming occurs, [x] indicates that fractures occur on a large scale Thermoforming were observed, and [Δ] indicates that small fractures occur during Thermoforming occurred.

2) Assessment of the machine workability

The Assessment of machinability was carried out collectively the basis of cutting resistance in machining, the finished surface roughness and the chip shapes. A cutting tool made of cermet is, has been carried out the machining under dry conditions at a Rotation speed of 150 m / min, one cutting depth per Revolution of 0.1 mm and an addition rate per revolution of 0.05 mm used. The cutting resistance in N as a unit was by Measurement of the cutting force formed during machining. The finished surface roughness was measured by a measuring method specified in JIS B 0601, and the value thereof was the roughness (in μm Ra) on the test piece surface machining as an arithmetic mean. Furthermore the chip shapes were optically considered and, if friability or friability was good, the result is given as [G], and, if the friability or friability was bad and all Chips were not separated but partially connected, are the Results given as [B]. When the assessment of chip shapes between [G] and [B], the result is given as [I].

3) Assessment of the exhaust gas resistance

The evaluation of the exhaust resistance was carried out by determining the amount of S released. Specifically, the test pieces used had a shape of a rectangular prism of 15 mm in length, 25 mm in width and 3 mm in thickness, and the entire surface was coated with emery paper of the Number 400 polished. A test piece was placed in a sealed vessel having an inner volume of 250 cm ³ together with a silver foil having a size of 10 mm in length, 5 mm in width and 0.1 mm in thickness and 0.5 cm ³ of pure water and the temperature in the vessel was maintained at 85 ° C for 20 hours. The S content W _SO in the silver foil by the method was measured for the test piece by a combustion type infrared absorption analysis method.

4) Cold formability test

The Evaluation of cold formability was made by measuring the limit strain or limit pressure deformation in a compression or compression test of specimens Numbers 1 to 5 and 13 performed. The test pieces for compression had each the shape of a cylinder with a diameter of 15 mm and a height of 22.5 mm, each one being a piece through a 600 ton oil hydraulic press was compressed to obtain the limit compression, in which the frontal compression is defined as ln (H0 / H) or the natural logarithm of H0 / H, where H0 is the initial height of the test piece represents and H the limit height is what the maximum height represents where no break occurred. The reference alloys the examinees the numbers 1 to 5 possessed confirmed high Limit compression ratios, which were almost equal to the comparison steel specimen of Number 15 and about 20% higher as the comparative steel test piece number 16. Furthermore, they also showed good cold formability on.

5) Assessment of corrosion resistance

The Assessment of corrosion resistance was through a salt spray test carried out. The test pieces were each prepared in such a way that it has the shape of a cylinder with a diameter of 10 mm and a height of 50 mm. The entire surface of each test piece was polished and cleaned with number 400 sandpaper. A test piece became a foggy atmosphere with 5 mass% aqueous NaCl solution 96 hours at 35 ° C exposed. The final Assessment was made visually with the naked eye. As a result became approved, that the steel according to the invention the present invention, a good corrosion resistance retained. The results are shown in Table 2.

Table 2

It has been found, according to Table 2, that the reference steel is comparable in heat moldability, cold formability and corrosion resistance to conventional ferrite-containing stainless steel and is, moreover, better in machinability than conventional ferrite-containing stainless steel. Moreover, it was found from Table 2 that in comparison with the Vergleichsstahlprüflingen the numbers 16 and 18 of the reference steel in terms _SO W is smaller and better in out-gas resistivity. The reason why the steel types of Comparative Alloy Nos. 16 and 18 each had a high W _SO seems to be that a carbosulfide is hard to be formed because the steel species have neither Ti nor Zr, whereas an S content in the matrix is extraordinary is high. In the comparative alloy sample of No. 18, hot workability is poor, and therefore the evaluation of machinability was not performed.

Example 2: Martensite-containing stainless steel

The The following experiment was carried out on a martensite-containing stainless steel and a steel of the second selection invention of the present invention carried out. First, 50 kg steel blocks the composition shown in Table 3 in mass% in one High frequency induction furnace melted to form the respective ingot. The ingots were heated to a temperature in the range of 1050 to Heated to 1100 ° C, so they are in hot Condition forged and rods with each circular Cross section of 20 mm could be formed. The bars were continue to 750 ° C Heated for 1 hour, followed by air cooling, so they passed the test could be subjected.

Table 3

In Table 3 are the specimens the numbers 1 to 19 steels the second selection invention of the present invention, which are formed as martensite-containing stainless steel. Furthermore correspond in the comparative examples, the specimens stainless steel: the specimen of Number 20 corresponds to SUS 410, the candidate corresponds to number 21 SUS 416, the examinee the number 22 corresponds to SUS 420F and the candidate number 23 corresponds SUS 440F. Further candidates Nos. 24 to 26 are stainless steel, i. Reference samples.

While the major inclusions of the inventive steel of the present invention were (Ti, Zr) ₄ (S, Se) ₂ C ₂ , other inclusions such as (Ti, Zr) S and (Ti, Zr) S _{3 were} locally observed in the matrix , Moreover, in the sample No. 9 having a high Mn content (Mn, Cr) S, it was observed, albeit in small amounts. The identification of the inclusions was carried out in the following manner: A test piece in an appropriate amount was obtained from each of the bars. A metal matrix portion of the test piece was dissolved by electrolysis using methanol solution including tetramethylammonium chloride and acetylacetone at 10% as an electrolytic solution. The electrolytic solution was subjected to filtration after the electrolysis, and compounds not dissolved in the steel were extracted from the filtrate. The extract was dried and subjected to chemical analysis by EDX (Energy Dispersive X-ray Spectrometer). A compound was identified on the basis of the peaks of the diffraction pattern. The composition of a compound particle in the steel structure was separately analyzed by EDX, and a compound having a composition corresponding to a compound examined by EDX was confirmed on the basis of the formation of two-dimensional mapping results. The 2 Figure 12 shows the results of the EDX analysis of random inclusions in the steel specimen of the second invention selection number of the present invention number 2. From these results, the formation of a (Ti, Zr) based compound can be inferred. In addition, shows 3 an optical microscope photograph of Stahlprüflingen the second selection invention of the present invention, the numbers 2 and 13th

The The following experiments were carried out on the test piece described above.

1) thermoformability test

The Assessment of thermoformability was based on the optical Observation performed, depending on whether defects, such as fractures, when thermoforming occur or not. While the workability during thermoforming at a level where the processing without problem carried out can be, not just inclusions, but also the quantity As alloying elements increase, there has been a deterioration in the Workability in the test tends to be observed. It was found, that steel species of the present invention, in which one or more Ca, B, Mg and REM were included, good thermoformability compared to steel types in which none of these elements are included were, exhibit.

2) Assessment of the machine workability

The Assessment of machinability was carried out collectively the basis of tool abrasion loss during machining, the finished surface roughness and the chip shapes. A cutting tool made of cermet was prepared for processing under wetting conditions by means of a water-soluble cutting oil at a rotation speed of 120 m / min, a cutting depth per revolution of 0.1 mm and an addition rate per revolution of 0.05 mm used. The tool abrasion loss was on a flank of the cutting tool after 60 minutes machining with μm as a unit the tool abrasion loss measured. The final surface roughness and chip shapes were made by a similar method as in Example 1 (Reference) described method determined.

The following assessments were made using a material which was subjected to treatments in which the material at 980 to 1050 ° C for 30 Minutes, then a quench heat treatment and then annealing treatment by holding at 180 ° C for 1 hour, followed by air cooling was subjected.

3) endurance test

The Measurement of hardness a test piece was measured on a C-scale of Rockwell hardness by means of a Rockwell hardness test, which is specified in JIS Z 2245 performed. The Rockwell hardness was used as an average of the measurements at 5 arbitrary measuring points S on one Circle, which on a cross section of a rod-shaped test piece with circular Section was drawn, obtained, with the circle on the cross section which is a circle representing the relationship of PS = 0.25 PG, where G represents a point approximating the center of the Circle section coincides, P an arbitrary one Point on the outer circumference of the test piece and the point S is on the line segment PG.

4) Assessment of the exhaust gas resistance

The Assessment of the exhaust gas resistance became similar as in Example 1 (Reference) performed.

5) Assessment of corrosion resistance

The Assessment of corrosion resistance was carried out by a method similar to that in Example 1 (reference) is. test pieces were each made to be a shape of a cylinder 15 mm in diameter and 50 mm high. The total surface of each test piece was polished. One of each test piece was polished, and then became the test piece in a thermo-hygrostat at a temperature of 60 ° C and a RH of 90% RH for 168 hours. One Evaluation procedure was such that when finding none Rust the test piece was judged with [A] when locating punctate patches at different points on the test piece the test piece with [B] was judged when red rust occurred in an area an area ratio of 5% or less the test piece was assessed with [C] and when red rust appeared in one Range of greater than an area ratio of 5% the test piece was assessed with [D]. The results are shown in Table 4.

Table 4

Tabelle 2

• * bedeutet "außerhalb des Umfangs der vorliegenden Erfinfung"

It is apparent from Table 4 that while in the stainless steel of the comparative test pieces of Nos. 20 to 23, the hardness is sufficiently ensured, the machinability is poor. It is further found that the samples of Nos. 21 to 23 are inferior in corrosion resistance and exhaust resistance. When comparing a reference steel to a steel according to the second selection invention, it is found that the reference steel has improved machinability, while the steel according to the second selection invention exhibits increased hardness, corrosion resistance and exhaust resistance. The reason why the steel according to the second selection invention is improved in hardness as compared with the reference steel seems to be that the C content satisfies the formulas A and B. Thereby, a C content which forms a (Ti, Zr) -based compound and a C content as an additive satisfy an adjusted balance, thereby sufficiently dispersing a C component in an Fe-based matrix phase. Moreover, the reason why the exhaust resistance has been improved is considered to be that S is excessively added in comparison with the amount of the (Ti, Zr) -based compound which can be formed.

Table 2

• * means "outside the scope of the present invention"

Table 4

Claims (4)

A free-cutting alloy formed as a martensite-containing stainless steel containing: 2 mass% or less, including zero, Ni; 9 to 17 mass% Cr; one or more of Ti and Zr such that W _Ti + 0.52W _Zr = 0.03 to 3.5 mass% is satisfied, wherein W _Ti and W _Zr represent respective amounts in mass% of Ti and Zr; and one or more of S and Se in the respective ranges of 0.01 to 1 mass% for S and 0.01 to 0.8 mass% for Se; and wherein C satisfies the following formulas: 0.375 (W S + 0.4W se ) <W C ≤ 1.5 formula A and 0.125 (W Ti + 0.52W Zr ) <W C ≤ 1.5 formula B, wherein W is _Ti , W is _Zr , W is _C , W is _S and W _{Se is} the respective amounts of Ti, Zr, C, S and Se each in% by mass; and wherein a (Ti, Zr) -based compound containing one or more of Ti and Zr as a metal-element component, wherein C is an indispensable element as a bonding component with the metal-element component, and one or more of S, Se and Te are dispersed in a matrix metal phase; further optionally containing: 2 mass% or less, including zero, Si; 2 mass% or less, including zero, Mn; 2 mass% or less, including zero, Cu; 2 mass% or less, including zero, Co; one or more of Mo and W in the respective ranges of 0.1 to 4 mass% for Mo and 0.1 to 3 mass% for W; 0.05 mass% or less, including zero, P; 0.03 mass% or less, including zero, O; 0.05 mass% or less, including zero, N; one or more of Te, Bi and Pb in the respective ranges of 0.005 to 0.1 mass% for Te; 0.01 to 0.2 mass% for Bi; and 0.01 to 0.3 mass% for Pb; one or more selected from the group consisting of Ca, Mg, B, and REM (one or more of the metal elements classified as Group 3A in the Periodic Table of Elements) in the range of 0.0005 to 0.01 mass% for a Element or total content of more than one element in combination; one or more selected from the group consisting of Nb, V, Ta and Hf in the respective range of 0.01 to 0.5 mass%, the remainder being Fe and unavoidable impurities. The vitrified alloy according to claim 1, wherein W _S / (W _Ti + 0.52W _Zr ) is 0.45 or less, wherein W _S , W _Ti and W _Zr each denote an S content, a Ti content and a Zr content , A vitrified alloy according to any one of claims 1 to 2, wherein the W _SO value representing the amount of S released is less than 0.035 mass% when the following test is conducted: an alloy test piece of the free-cutting alloy is prepared so as to have the Having a rectangular prism of size 15 mm in length, 25 mm in width and 3 mm in thickness, the entire surface was polished with a No. 400 emery paper; a silver foil of the size of 10 mm in length, 5 mm in width and 0.1 mm in thickness with a purity of 99.9% or more as S-getter; 0.5 cm ³ of pure water are sealed in a vessel having an inner volume of 250 cm ³ together with the test piece; the temperature in the vessel is raised to 85 ° C and the temperature is then held there for 20 hours; and then the S content is analyzed in mass% in the silver foil, the obtained S content being defined as the W _SO . Automate alloy according to one of claims 1 to 3, wherein the particle size of the (Ti, Zr) -based compound, as in the structure of a polished Section in the alloy is observed in the range of an average of 0.1 to 30 μm and where furthermore an area ratio of Compound in the structure is in the range of 1 to 20%.