DE102008048050A1 - Easily cutting ferritic stainless steel has manganese that forms sulphide in zirconium-series sulphide replaced by zirconium - Google Patents

Abstract

The easily cutting ferritic stainless steel has manganese that forms sulphide in zirconium-series sulphide replaced by zirconium. The steel comprises of not greater than 0.2 weight percent of carbon, 0.01 to 5 weight percent of silicon, 0.01 to 2.5 weight percent of manganese, 0.01 to 0.5 weight percent of sulfur, not greater than 5 weight percent of nickel, 7.5 to 30 weight percent of chromium, not greater than 5 weight percent of molybdenum, not greater than 0.05 weight percent of nitrogen, not greater than 0.015 weight percent of oxygen. The stainless steel also comprises of not greater than 0.30 weight percent of titanium, and 0.01 to 1 weight percent of zirconium and the remaining percentage of iron and unavoidable purities.

Description

The The invention relates to a ferritic stainless steel machine.

One ferritic stainless steel, which is a high alloy steel, is hard to cut, although it has excellent corrosion resistance having.

In In the recent past, ferritic stainless steel became available Widely used for parts of electric lighting equipment used. Because parts, for safety reasons Dimensional accuracy require precise finishing, or complex shaped parts are difficult to machine, However, in such a case it is necessary that the ferritic stainless steel is machinable.

consequently is added as a machinable component S to the steels. When S is added to a steel, MnS becomes in the form of inclusions produced in the steel, reducing the machinability of the steel when cutting the steel due to a stress concentration effect for the inclusions is improved.

however has steel in which MnS inclusions are formed, the problem of deterioration of high corrosion resistance on which the strongest feature of stainless steel is.

in the Case of stainless steel becomes part of Cr which contained in steel is so incorporated into a sulfide that the part of Cr is replaced by a Part Mn is replaced.

Even though Cr has a lower tendency than Mn to form a sulfide, is a part, as much Cr is contained in a stainless steel of Cr introduced into the sulfide in such a way that the part of Cr is replaced by Mn (the degree of replacement of the share depends on Mn and Cr in the steel).

Therefore is conventionally in view of the emphasis of Corrosion resistance limits the amount of Mn added, to reduce the concentration of Mn in the sulfide and the concentration of Cr in the sulfide (i.e., high Cr content), whereby the sulfide in the form of (Mn, Cr) S is produced positively.

On This is done by decreasing the Mn concentration when increasing the Cr concentration in the sulphide the (Mn, Cr) S is chemically more stable, whereby the corrosion resistance is increased. On the other hand, the machinability can be greatly deteriorated become.

The rounder and larger the sulfide, the better the machinability of the steel. In view of this fact, MnS has a relatively round and large spindle shape, whereby good machinability is given as in 1A shown.

On the other hand, as in 1B (Mn, Cr) S has an elongated strand shape and is therefore difficult to machine by machine ((Mn, Cr) S has a high elongation capability in hot rolling in the rolling direction).

Thus, from the point of view that the shape of the sulfide is important, an attempt has been made to add Ti, which has a greater tendency for sulfide bonding than Mn, to a steel to make the steel machinable (see, e.g. JP-A-2005-139531 ).

If however, Ti is added to the steel can be two kinds of Inclusions, TiS and MnS (strictly speaking (Mn, Cr) S), depending on the composition of the steel in the steel be generated.

The reason for this is as follows:
MnS has a crystal structure of the NaCl type (cubic crystal structure) in the steel as in 2A while TiS has a NiAs (hexagonal crystal structure) crystal structure in the steel, as in FIG 2 B shown.

Accordingly because MnS and TiS do not produce the same kind of sulfide in the steel can, two types of sulfides, TiS and MnS, in the steel generated.

In other words, although the sulfide is formed by adding Ti to the steel, MnS is still generated and remains in the steel (though in the case of lack of addition of Mn, only TiS is generated can not add Mn from the industrial cost point of view).

Although TiS, which is a chemically stable substance, does not specifically deteriorate the corrosion resistance of the steel and has a relatively round shape as in FIG 1C In this case, the TiS can not sufficiently improve the machinability of the steel due to its small size.

on the other hand the MnS remaining in the steel deteriorates the corrosion resistance, as described above.

In addition, the reveal JP-A-2001-355048 . JP-A-2005-60812 and JP-A-2001-98352 each machinable stainless steels.

In particular, the JP-A-2001-355048 Ferritic machinable stainless steel, according to which invention contains 0.005 to 0.015% O in the steel as stated in claim 5, and 0.005 to 0.3% Zr is contained in the steel as stated in claim 7.

However, the JP-A-2001-355048 a technique according to which coarse MnO-Cr ₂ O ₃ -based deoxidized products are generated upon solidification, and O is positively added as a useful element to improve machinability, which is in light of the underlying technical idea of the This invention differs.

In addition, the reveals JP-A-2001-355048 Also, a technique in which Zr is added to improve the machinability and cold forgeability by uniformly and finely dispersing a sulfide in addition to the production of carbonitride. However, this technique is also different from the present invention in that the document does not have the technical idea of the invention that Zr-based sulfide in which part of the sulfide-forming Mn is substituted by Zr is generated.

The JP-A-2005-60812 also discloses a ferritic, machinable, stainless steel which according to that teaching contains more than 0.05%, but 0.15% or less of P and 0.03% or less of O in the steel, as stated in claim 1, and 0.8% or less of Zr is contained in the steel as stated in claim 3.

Although the present invention does not preclude the addition of P, the content of P according to the present invention is completely different from the content of P according to the present invention JP-A-2005-60812 , and the importance of adding O according to the JP-A-2005-60812 is completely different from that of the present invention in that O is included according to the former for the purpose of forming an oxide which forms a core when a sulfide is produced so as to improve machinability.

Further differs, although according to claim 3 of the JP-A-2005-60812 Zr is contained in this claim 3 Zr JP-A-2005-60812 in its function fundamental to the Zr of the present invention, and thus the technical idea of the JP-A-2005-60812 different from that of the present invention.

JP-A-2001-98352 discloses a machinable stainless steel having excellent surface finish and high corrosion resistance, wherein in this invention 0.005 to 0.04% O is contained in the steel as stated in claim 1, and according to claim 3, 1.00% or less Zr is contained in the steel ,

However, the JP-A-2001-98352 a technique in which O is positively included as an element useful for improving machinability, and Zr is included for the purpose of improving corrosion resistance and hot workability by forming a nitride, which is a concept different from the present invention.

Under In the above circumstances, it is an object of the invention, a ferritic, machinable, stainless steel with both good indicate machinability as well as good corrosion resistance, which properties were previously considered to be hardly compatible.

• 1. Ferritischer, zerspanbarer, rostfreier Stahl, aufweisend (Angaben in Massen-%): C: ≤ 0,200%, Si: 0,01 bis 5,00%, Mn: 0,01 bis 2,50%, S: 0,05 bis 0,50%, Ni: ≤ 5,0%, Cr: 7,5 bis 30,0%, Mo: ≤ 5,0%, N: ≤ 0,050%, O: ≤ 0,0150%, Ti: ≤ 0,30%, und Zr: 0,01 bis 1,00%, wobei der Rest aus Fe und unvermeidlichen Verunreinigungen besteht und wobei ein Zr-basiertes Sulfid in einer solchen Form in dem Stahl ausgebildet wird, dass ein Teil von sulfidbildendem Mn durch Zr substituiert wird.
• 2. Ferritischer, zerspanbarer, rostfreier Stahl, aufweisend (ausgedrückt in Massen-%): C: ≤ 0,200%; Si: 0,01 bis 5,00%; Mn: 0,01 bis 2,50%; S: 0,01 bis 0,50%; Ni: ≤ 5,0%; Cr: 7,5 bis 30,0%; Mo: ≤ 5,0%; N: ≤ 0,050%; O: ≤ 0,0150%; Ti: ≤ 0,30%; Zr: 0,01 bis 1,00%, und mindestens ein Element, das ausgewählt ist aus der Gruppe, die aus folgendem besteht: Pb: 0,01 bis 0,30%, Bi: 0,01 bis 0,15%, Te: 0,01 bis 0,30%, Se: 0,01 bis 0,40% Sn: 0,01 bis 0,10% P: 0,01 bis 0,05%, und B: 0,001 bis 0,03%, wobei der Rest Fe und unvermeidbare Verunreinigungen sind, wobei ein Zr-basiertes Sulfid in einer solchen Form, dass ein Teil von sulfidbildendem Mn durch Zr substituiert wird, im Stahl ausgebildet wird.
• 3. Ferritischer, zerspanbarer, rostfreier Stahl nach Punkt 1 oder 2, welcher die folgenden Gleichungen (1) und (2 erfüllt: 0,1 ≤ [Mn]/[Zr] ≤ 50 (1) 300 × [O] – [Zr] ≤ 4,0 (2)wobei [Mn], [Zr] und [O] in den obigen Gleichungen den Anteil an Mn in Massen-%, den Anteil an Zr in Massen-% bzw. den Anteil an O in Massen-% darstellen.
• 4. Ferritischer, zerspanbarer, rostfreier Stahl nach einem der Punkte 1 bis 3, welcher darüber hinaus, in Massen-%, mindestens ein Element enthält, das aus der Gruppe ausgewählt ist, welche aus folgendem besteht: W: 0,01 bis 0,50%, und Cu: 0,01 bis 0,50%.
• 5. Ferritischer, zerspanbarer, rostfreier Stahl nach einem der Punkte 1 bis 4, welcher darüber hinaus, in Massen-%, mindestens ein Element enthält, das aus der Gruppe ausgewählt ist, welche aus folgendem besteht: Al: 0,01 bis 3,00%, V: 0,01 bis 0,30%, und NB: 0,01 bis 0,30%
• 6. Ferritischer, zerspanbarer, rostfreier Stahl nach einem der Punkte 1 bis 5, welcher darüber hinaus, in Massen-%, mindestens ein Element enthält, das aus der Gruppe ausgewählt ist, welche aus folgendem besteht: Mg: 0,0001 bis 0,0100%, Ca: 0,0001 bis 0,0100%, und REM: 0,0001 bis 0,0100%, wobei REM mindestens eines der Metallelemente ist, die als Gruppe 3A im Periodensystem der Elemente klassifiziert sind.

In order to achieve the above object, the following items 1 to 6 are proposed according to the invention:

• 1. Ferritic, machinable, stainless steel, containing (in% by mass): C: ≤ 0.200%, Si: 0.01 to 5.00%, Mn: 0.01 to 2.50%, S: 0.05 to 0.50%, Ni: ≤ 5.0%, Cr: 7.5 to 30.0 %, Mo: ≤ 5.0%, N: ≤ 0.050%, O: ≤ 0.0150%, Ti: ≤ 0.30%, and Zr: 0.01 to 1.00%, the balance being Fe and and wherein a Zr-based sulfide is formed in such a form in the steel that a part of sulfide-forming Mn is substituted by Zr.
• 2. Ferritic, machinable, stainless steel, having (expressed in mass%): C: ≤ 0.200%; Si: 0.01 to 5.00%; Mn: 0.01 to 2.50%; S: 0.01 to 0.50%; Ni: ≤ 5.0%; Cr: 7.5 to 30.0%; Mo: ≤ 5.0%; N: ≤ 0.050%; O: ≤ 0.0150%; Ti: ≦ 0.30%; Zr: 0.01 to 1.00%, and at least one member selected from the group consisting of: Pb: 0.01 to 0.30%, Bi: 0.01 to 0.15%, Te: 0.01 to 0.30%, Se: 0.01 to 0.40% Sn: 0.01 to 0.10% P: 0.01 to 0.05%, and B: 0.001 to 0.03 %, the remainder being Fe and unavoidable impurities, wherein a Zr-based sulfide in such a form that a part of sulfide-forming Mn is substituted by Zr is formed in the steel.
• 3. Ferritic, machinable, stainless steel according to item 1 or 2, which satisfies the following equations (1) and (2): 0.1 ≤ [Mn] / [Zr] ≤ 50 (1) 300 × [O] - [Zr] ≤ 4.0 (2) wherein [Mn], [Zr] and [O] in the above equations represent the content of Mn in mass%, the content of Zr in mass% and the proportion of O in mass%, respectively.
• A ferritic machinable stainless steel according to any one of items 1 to 3, which further contains, in mass%, at least one element selected from the group consisting of: W: 0.01 to 0, 50%, and Cu: 0.01 to 0.50%.
• A ferritic machinable stainless steel according to any one of items 1 to 4, which further contains, in mass%, at least one element selected from the group consisting of: Al: 0.01 to 3, 00%, V: 0.01 to 0.30%, and NB: 0.01 to 0.30%
• A ferritic machinable stainless steel according to any one of items 1 to 5, which further contains, in mass%, at least one element selected from the group consisting of Mg: 0.0001 to 0, 0100% Ca: 0.0001 to 0.0100%, and REM: 0.0001 to 0.0100%, wherein REM is at least one of the metal elements classified as Group 3A in the Periodic Table of the Elements.

In this regard, the steel according to item 1 above preferably contains the following (in% by mass):
C: ≤ 0.050%,
Si: 0.01 to 3.00%,
Mn: 0.01 to 2.00%,
S: 0.10 to 0.45%,
Ni: ≤ 3.0%,
Cr: 12.0 to 28.0%,
Mo: ≤ 3.0%,
N: ≤ 0.040%,
O: ≤ 0.0100%,
Ti: ≤ 0.20%, and
Zr: 0.05 to 0.80%,
and, more preferably, contains (in% by mass):
C: <0.030%,
Si: 0.01 to 2.00%,
Mn: 0.01 to 1.80%,
S: 0.20 to 0.43%,
Ni: ≤ 2.0%,
Cr: 12.5 to 25.0%,
Mo: ≤ 2.5%,
N: ≤ 0.030%,
O: 0.0080%,
Ti: <0.05%, and
Zr: 0.05% or more, but 0.60% or less.

In addition, the steel according to item 2 preferably contains the following (in% by mass):
C: ≤ 0.050%,
Si: 0.01 to 3.00%,
Mn: 0.01 to 2.00%,
S: 0.01 to 0.45%,
Ni: ≤ 3.0%,
Cr: 12.0 to 28.0%,
Mo: ≤ 3.0%,
N: ≤ 0.040%,
O: ≤ 0.0100%,
Ti: ≦ 0.20%,
Zr: 0.05 to 0.80%,
Pb: 0.02 to 0.25%,
Bi: 0.03 to 0.15%, and
Te: 0.02 to 0.28%,
and, most preferably, contains the following (in% by mass):
C: <0.030%,
Si: 0.01 to 2.00%,
Mn: 0.01 to 1.80%,
S: 0.01 to 0.43%,
Ni: ≤ 2.0%,
Cr: 12.5 to 25.0%,
Mo: ≤ 2.5%,
N: ≤ 0.030%,
O: <0.0080%,
Ti: <0.05%,
Zr: 0.05 to 0.60%,
Pb: 0.05 to 0.20%,
Bi: 0.05 to 0.15%, and
Te: 0.04 to 0.26%.

The 1A to 1D Figure 13 are schematic views showing forms of sulfide-based inclusions.

The 2A and 2 B are views showing crystal structures of sulfide-based inclusions.

3 Fig. 10 is a view showing microscopic photographs for Example 1, Comparative Example 3, Comparative Example 8 and Comparative Example 12.

below The present invention will be described in detail.

In The following description is all mass-based percentages equal to the weight percentages.

basic idea the invention is to specify a ferritic stainless steel, which has a given composition with good machine Workability or corrosion resistance by action a Zr-based sulfide, in the steel on such Is formed, that a part of the sulfide-forming Mn by Zr is substituted by adding Zr under the condition that the amount of O is at a certain limit or below is limited.

Zr is an element with a higher tendency for sulfide formation as Mn and forms the sulfide by binding to S when Zr is added to the steel on the condition that the amount of O is limited to a certain limit or below becomes.

in this connection As Zr forms ZrS, it becomes the same cubic crystal structure of the NaCl type, such as MnS, and the lattice constants of the two Inclusions are very close to each other (ZrS: 5.25 nm and MnS: 5.22 nm), the Zr dissolved in MnS to give a (Mn, Zr) S inclusion (strictly speaking: (Mn, Cr, Zr) S inclusion) so that part of the Mn in MnS (strictly speaking: (Mn, Cr) S) by Zr is replaced.

The inventors of the present invention remarked that (Mn, Zr) S, in which Zr is dissolved, exists in the form of a relatively round and long spindle in the steel after hot rolling, as in 1D shown.

additionally The (Mn, Zr) S inclusion was found to be chemically stable is and maintains a good corrosion resistance of the steel can.

Accordingly shows the ferritic stainless steel of the present invention both good machinability and good Corrosion resistance, which hardly compatible with each other seem to be.

According to the present invention, the same kind of sulfide together with Mn and Cr are designed so that the added Zr in MnS (strictly speaking: (Mn, Cr) S) is dissolved by adding it for a part of the Mn is used.

If Ti is added to the steel, a TiS sulfide is replaced by the Ti alone is formed so that MnS remains separate from this TiS sulfide. in the Contrary to this case, it is according to the present Invention possible, the problem of deterioration of To solve corrosion resistance due to MnS, because MnS does not stay in the steel.

According to the present invention, for effectively forming the (Mn, ZR) S inclusion, it is preferable to restrict the content of Mn, Zr and O in the steel, so that the following equations (1) and (2) are satisfied. 0.1 ≤ [Mn] / [Zr] ≤ 50 (1) 300 × [O] - [Zr] ≤ 4.0 (2)

(In the above equations (1) and (2), [Mn], [Zr] and [O] represent the content Mn in mass%, the content of Zr in% by mass or the content of O in mass%).

The Equation (1) is intended to express the ratio of the content of Mn to Specify the content of Zr in the steel. By specifying the contents of Mn and Zr according to equation (1) it is possible the machinability and corrosion resistance ferritic stainless steel to maintain beneficial and effective and even to reinforce.

In addition, according to the invention, the ratio [Mn] / [Zr] preferably has the following order of magnitude: 0.5 ≤ [Mn] / [Zr] ≤ 10, and especially preferred: 0.5 ≤ [Mn] / [Zr] ≤ 5.

The equation (2) above is intended to specify the contents of O and Zr in the steel and has the following meaning: Zr is an element with a high Tendency to oxide formation. If O is contained in the steel, that is added Zr not usefully used for the formation of the sulfide, since it is bound to O That is, the (Mn, Zr) S inclusion, which is of interest according to the present invention is not to be effectively formed.

Consequently is the ratio according to the present invention between the content of O and Zr limited to that to fulfill the above equation (2).

According to the invention, the ratio between the content of O and Zr is preferably: 300 × [O] - [Zr] ≤ 3.5, especially preferred: 300 × [O] - [Zr] ≤ 2.5, and most preferably: 300 × [O] - [Zr] ≤ 2.0.

When Next, the reason for the limitation will be described below of elements according to the invention.

C: ≤ 0.200%

C is an interstitial element that helps increase the strength. Meanwhile, since C is also a carbide-forming element, carbides can be produced when the proportion of C is excessive to exceed 0.200%. Among all these carbides, since Cr ₂₃ C _{6 is} a Cr-containing carbide and Cr contributes to the improvement of corrosion resistance and is contained in steel, the generation of Cr ₂₃ C _{6 may} lead to a deterioration of corrosion resistance. In addition, the carbides produced in the steel (for example, CR ₂₃ C ₅ , ZrC, TiC, etc.) are very hard, which may lead to deterioration of the machinability of the steel containing these carbides.

Si: 0.01 to 5.00%

Si is a ferrite-forming element and must account for 0.01% or more to maintain a ferritic phase. On the other hand, an addition amount of Si exceeding 5.00% may be added. promote the formation of a σ-phase, resulting in a significant deterioration of hot workability and mechanical Machinability can lead.

Mn: 0.01 to 2.50%

Mn is an element with a high tendency to form a sulfide, and exists in the case of a general span S-steel as MnS inclusion.

In a stainless steel such as the invention Steel, (Mn, Cr) S is substituted with Cr instead of Mn formed in MnS, which has a NaCl-type crystal structure (because the proportion of Cr in the steel is high). Therefore, if the Proportion of Mn is excessive, the Mn concentration in (Mn, Cr) S high (excessive content on Mn), resulting in a significant deterioration of corrosion resistance and can lead to outgassing.

S: 0.05 to 0.50% (according to the above Point 1) or 0.01 to 0.50% (according to the above point 2)

S is an important element, which as one for the improvement the machinability effective element is added and which according to the invention in the amount of 0.05% or more must be added. On the other hand, the excessive Addition of S significantly deteriorate the hot workability, and therefore the upper limit for the addition of S is 0.50%.

If however, machinability steels that are not only S, but also owed to other machinable elements, lent can, the lower limit for the addition of S to 0.01% be set.

Ni: ≤ 5.0%

Ni is preferably added as it is for the improvement the corrosion resistance of stainless steel in acidic atmosphere is effective.

on the other hand causes excessive addition of Ni an increase in costs. In addition, Ni prevents a Austenitic element is that for stabilizing an austenite phase contributes, the excessive addition of Ni exceeding 5.0% that a single ferrite phase is obtained, resulting in a deterioration of hot workability and the corrosion resistance can lead. A preferred lower limit for Ni is 0.05%.

Cr: 7.5 to 30.0%

Cr is an important element that makes a big contribution to Improvement of corrosion resistance and strength makes, and is according to the invention in one Order of 7.5% or more added.

on the other hand leads the excessive addition of Cr, which exceeds 30.0%, to an increased Amount of Cr carbonitrides, resulting in a significant decrease in Lead corrosion resistance of stainless steel can, and in addition, since the Cr carbonitrides very hard, the machinability of the steel, which these Containing carbonitrides worsens. additionally is in a stainless steel such as the invention Steel (Mn, Cr) S with the substitution of Cr for a Mn element formed in MnS, which has a NaCl-type crystal structure (since the content Cr in the steel is high). Therefore, if the salary Cr is excessive, the content of Cr in (Mn, Cr) S excessively, resulting in a significant Deterioration of machinability lead Although, corrosion resistance and outgassing behavior be improved.

Mo: ≤ 5.0%

Not a word is an element that makes a big contribution to the improvement the corrosion resistance provides. A preferred lower one Limit for Mo is 0.05%.

on the other hand Mo can promote the precipitation of a σ-phase, resulting in a significant deterioration of hot workability and machinability, and therefore the addition amount for Mo is set to 5.0% or less.

N: ≤ 0.050%

N is an interstitial element which contributes to increase the strength. On the other hand, if the content of N is excessive, nitrides may be generated. Among all of these, Cr ₂ N is a nitride containing Cr, which contributes to the improvement of corrosion resistance and is contained in the steel, so that the production of Cr ₂ N may lead to a deterioration of corrosion resistance. Moreover, nitrides (for example, Cr ₂ N, ZrN, TiN, etc.) produced in the steel are very hard, which may result in deterioration of the machinability of the steel containing these nitrides, and therefore the upper one Limit of its amount to 0.050%.

O: ≤ 0.0150%

O exists as an oxide or the like in the steel. Because O the corrosion resistance and the like deteriorates, it is preferable to O by a Reduce deoxidation during the manufacturing process. On the other hand, excessive Reductions of O lead to an increase in costs, and therefore, the addition amount thereof is to the above upper one Limit or less.

Ti: ≤ 0.30%

Ti is an element that helps to improve corrosion resistance contributes.

on the other hand causes the excessive addition of Ti, which has a high tendency to nitride formation, a tendency form hard and coarse TiN and is from the point of view the machinability disadvantageous.

About that In addition, the excessive addition may occur Ti, since Ti also has a strong tendency to form sulfides, lead to the production of a Ti sulfide. Because the Ti sulfide a sulfide other than MnS, which is a NiAs-type sulfide the addition of Ti does not contribute to the control of the composition a MnS sulfide. Accordingly, the generation of the Ti sulfide lead to a relative reduction in the amount of (Mn, Cr, Zr) S, this is of interest for steel according to the invention is.

Zr: 0.01 to 1.00%

Zr is an important element for the invention. Zr, which has a strong tendency to form sulfides, forms (Mn, Zr) S (strictly speaking: (Mn, Cr, Zr) S since the invention relates to stainless steel) by having Mn in MnS (having a NaCl-type crystal structure ) is substituted. Although it is known that it is effective to increase the Cr concentration in MnS to improve the corrosion resistance of the sulfide, (Mn, Cr) S having a high concentration of Cr has a strong tendency to form a strand form, and its machinability is worse than that of MnS. On the other hand, (Mn, Cr, Zr) S, in which Zr is contained in the NaCl-type sulfide, can keep the sulfide in the form of a spindle while at the same time improving the corrosion resistance. However, the excessive addition of Zr may lead to an excessive concentration of Zr in (Mn, Cr, Zr) S, thereby increasing the hardness of the sulfide, which may lead to a reduction in the improvement of machinability. 0.1 ≤ [Mn] / [Zr] ≤ 50 (1)

Zr, which has a strong tendency to form sulfides, forms (Mn, Zr) S (strictly speaking: (Mn, Cr, Zr) S, since the invention is stainless Steel) by substitution of Mn into MnS (which is a Having crystal structure of the NaCl type). Although it is known that it is effective to increase the Cr concentration in MnS, to improve the corrosion resistance of the sulfide, For example, (Mn, Cr) S with a high concentration of Cr has a strong Tendency to form a strand form, and its machine Machinability is lower than that of MnS. on the other hand can (Mn, Cr, Zr) S, in which Zr is dissolved in the sulfide of the NaCl type, obtained the sulfide in the form of a spindle, while the Improvement of corrosion resistance is obtained resulting in a sulfide with good machinability.

however can the excessive addition of Zr in the Steel to an excessive Zr concentration lead in (Mn, Cr, Zr) S, whereby the hardness of the Sulfides is increased, resulting in a reduction in the improvement which can lead to machinability. For the purpose controlling the composition of the sulphide was found that the corrosion resistance with the machinability can be compatible if the relationship between the Mn concentration and the Zr concentration in the steel is controlled so that the equation (1) is adhered to.

If [Mn] / [Zr] is less than 0.1, the Zr concentration in (Mn, Cr, Zr) S-excessive, reducing the hardness of the sulfide is increased, resulting in a reduction of Improvement of machinability can lead.

On the other hand, when [Mn] / [Zr] is larger than 50, the Mn concentration in (Mn, Cr, Zr) S becomes excessive, which can lead to a significant deterioration of corrosion resistance and outgassing. 300 × [O] - [Zr] ≤ 4.0 (2)

Zr, which also has a strong tendency to oxide formation forms then oxide, if much O contained in the liquid steel and the sufficient amount of Zr necessary for the formation of (Mn, Zr) S (taken in the same way: (Mn, Cr, Zr) S, since the invention is stainless Steel) with substitution of Mn into MnS (which has a crystal structure of NaCl type), according to the invention is of interest, necessary, can in some cases can not be obtained. To prevent this, it is preferable carried out a deoxidizing treatment in steel. D. h., it is possible by satisfying equation (2), to secure the sufficient amount of Zr necessary for training of (Mn, Zr) S (strictly speaking: (Mn, Cr, Zr) S, since the invention stainless steel) with substitution of Mn in MnS (which has a crystal structure of NaCl type) is required.

If the value of 300 × [O] - [Zr] less than 4.0 is not possible, it is sufficient (Mn, Zr) S, in which Mn in MnS (which has a crystal structure of the NaCl type) is substituted by Zr due to excessive Content of O and insufficient content of Zr.

Pb: 0.01 to 0.30%, Bi: 0.01 to 0.15%, Te: 0.01 to 0.30%, Se: 0.01 to 0.40%, Sn: 0.01 to 0.10%, P: 0.01 up to 0.05% and B: 0.001 to 0.03%

These Elements are machinable elements which indicate machinability in a form different from that of the sulfide different. Therefore, if at least one of these elements in the steel, the proportion of S is 0.01 to 0.50%. On the other hand, the excessive addition these elements to a deterioration of hot workability to lead.

W: 0.01 to 0.50% and Cu: 0.01 to 0.50%

These Elements can be added to the corrosion resistance to improve. On the other hand, the excessive Adding these elements to a deterioration of hot workability to lead.

Al: 0.01 to 3.00%, V: 0.01 to 0.30% and Nb: 0.01 to 0.30%

These Elements which can fix carbonitrides can be added to improve the corrosion resistance. On the other hand, the excessive addition these elements lead to a reduction in hot workability. In this regard, the amount of Al is preferably 0.01 to 0.30%.

Mg: 0.0001 to 0.0100%, Ca: 0.0001 to 0.0100% and REM: 0.0001 to 0.0100%

These Elements that can fix carbonitrides can added to improve corrosion resistance become. On the other hand, the excessive Adding these elements to a reduction in hot workability to lead.

About that In addition, as REM elements are used, which has a low radiation activity because of their ease of handling. For example it is favorable to use at least one element as REM, which is selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Especially it is from the standpoint of a clearer expression of the above To prefer effects and product costs, light elements of to use rare earths, especially La or Ce. It is acceptable if a small amount of radioactive elements of rare earths (for example, Th, U, etc.), which in the course of the separation of the rare Earth remains contained in the steel. In addition, you can not from the point of view of reducing raw material costs separable elements of rare earths such. B. Mischmetall, Didym and the like can be used.

below Examples of the invention will be described in detail.

150 kg of steel ingots, which have content compositions according to Table 1 and Table 2 were mixed in a high frequency induction furnace melted, heated to 1100 to 1200 ° C and as materials a ring bar mold with an outer diameter of 20 mm and materials of an angled rod shape of a portion of FIG. 30 mm × 60 mm processed by hot forging.

The materials were then heated to 780 ° C for 4 hours each and air for the following tests annealed.

I. hot workability

to Evaluation of hot workability became a defect level (such as Breakage points) when hot forging in five stages divided: Class A (no defect) to Class E (very large Fractures: forging impossible) (A> B> C> D> E), when viewed with the naked eye.

II. Rotary test

annular, plate-like samples were subjected to machine turning subjected to the following test conditions and the flank wear of a tool after 60 minutes of cutting was measured.

<Test conditions>

• Tool: cermet
• Cutting speed: 120 m / min.
• Feed: 0.05 mm / revolution
• Depth: 0.1 mm
• Cutting oil: water-soluble

III. outgassing

in the Steel contained S reacts with water or the like under one certain condition to produce hydrogen sulfide gas. If Parts of ferritic stainless steel inside a sealed Space, the hydrogen sulfide gas produced corrodes others Parts in the sealed room. This phenomenon is not desirable and therefore, generation of the hydrogen sulfide gas by outgassing examined.

The rod-shaped samples (diameter 10 mm × 50 mm L), Ag foil (10 mm × 5 mm × 0.1 mm) and 0.5 ml of pure water were placed in a sealed container, and then, after the container was over 20 Hours at 85 ° C, the discoloration of the Ag film (ie, the degree of formation of Ag ₂ S) was examined. The outgassing property was evaluated for classification by classifying the Ag films without decolorization as Class A and that with significant decolorization (effecting a large outgassing amount) as Class E (ie, A>B>C>D> E). The Ag film acted as a getter in producing S-containing gas, and as S absorbed as a constituent, a surface of the Ag film became black due to generation of silver sulfide (Ag ₂ S).

IV. Corrosion resistance

According to the salt spray test, which in JIS 22371 Specimens (diameter 10 mm x 50 mm L) were placed in a salt spray atmosphere (5% aqueous solution of sodium chloride at 35 ° C) for 96 hours for testing. Those without rust were classified in class A and those whose entire surface was rotted were assigned to class E (ie A>B>C>D> E).

Respective test results are shown in Tables 3 and 4. Table 3 hot workability turning test outgassing corrosion resistance Examples 1 B 78 B B 2 B 85 B B 3 B 77 B B 4 B 73 B B 5 B 89 B B 6 B 79 B B 7 B 53 B B 8th B 58 B B 9 B 61 B B 10 B 63 B B 11 B 71 B B 12 B 73 B B 13 A 65 B A 14 B 81 B A 15 B 82 B A 16 B 79 B A 17 B 78 B A 18 B 75 B A 19 A 72 B A 20 B 76 B A 21 B 74 B A 22 B 54 B B 23 B 59 B A 24 B 61 B A 25 B 74 B A 26 B 58 B A 27 B 56 B B 28 A 65 B A 29 B 81 B A 30 B 82 B A 31 B 79 B A 32 B 78 B A 33 B 72 B A 34 A 58 B A 35 B 61 B A Table 4 Comparative Examples 1 B 132 B e 2 e 142 B C 3 A 77 e e 4 A 153 A B 5 e 69 e e 6 D 78 B D 7 B 82 D e 8th D 129 A B 9 D 131 B B 10 B 142 B D 11 B 152 B e 12 B 119 C B 13 B 134 B B 14 B 121 B B

V. Form of the sulfide

In Examples of the invention and comparative examples were sulfide forms, which were produced in the steel, examined.

to Examination of sulfide forms were measurements for example 1 as a representative example of the invention and comparative examples 3, 8 and 12 executed.

The measurements were carried out as follows:
A longitudinal portion of a 1 / 2R size part of a rod-shaped sample was mirror-polished and observed in the range of 100,000 μm ² at 400 magnification of an optical microscope among 10 fields of view, and then the shape of the sulfide was analyzed by image analysis.

3 shows microscopic photographs for Example 1, Comparative Example 3, Comparative Example 8 and Comparative Example 12. In 3 For example, the maximum absolute length of the sulfide is the length of a sulfide having the largest absolute length among 10 fields, and the average size ratio of the sulfide refers to an average acicular ratio of all the sulfides (including NaCl type, NiAs type, etc.). which exist in the 10 fields of view.

A method of identifying inclusions was performed as follows:
An appropriate amount of sample size was taken from each annular rod and its metal matrix portion was electrolyzed using a methanol solution containing tetramethylammonium chloride and 10% acetylacetone as the electrolyte. Next, a non-soluble mixture contained in the steel was extracted by filtering molten electrolyte, drying and analyzing using X-ray diffractometry to specify a mixture over a peak appearing in the diffraction profile. In addition, the composition of mixture particles in a steel structure was analyzed using a separate EPMA, and it was confirmed by a two-dimensional image that a mixture (compound) having a composition corresponding to that mixture observed by the X-ray diffractometry was formed.

Out From the above results, it can be seen that Comparative Example 1 had a low corrosion resistance, since the Content of C is the upper limit of C according to the Invention exceeded that Comparative Example 2 a low hot workability, since the amount of Si is the upper limit exceeded according to the invention, and that Comparative Example 3 is a bad Ausgasverhalten and a bad corrosion resistance showed, as the amount at Mn and the value of equation (1) the upper limits according to Invention exceeded.

It can also be seen that Comparative Example 4 shows severe tool wear and showed a poor machinability because the amount of S was lower than the lower limit of S according to the invention and that Comparative Example 5 had poor hot workability, poor outgassing behavior and low corrosion resistance since the amount of C is the upper limit of C exceeded according to the invention.

It is also seen that the Comparative Example 6 a small Hot workability and poor corrosion resistance As the amount of Ni is the upper limit of Ni according to the Invention exceeded that of Comparative Example 7 a poor outgas ratio and poor corrosion resistance showed that the amount Cr was lower than the lower limit of Cr according to the invention and that the comparative example 8 bad hot workability and bad machine Machinability showed that the amount of Cr is the upper limit for Cr exceeded according to the invention.

It It can also be seen that Comparative Example 9 is a poor one Hot workability and poor machinability showed that the amount of Mo is the upper limit for Mo according to the Invention exceeded, and that the Comparative Example 10, poor machinability and low corrosion resistance because the amount of N is the upper limit of N according to the Invention exceeded.

It It can also be seen that Comparative Example 11, which is the Equation (2) was not enough, a bad machine Machinability and low corrosion resistance showed that the amount of O is the upper limit for O according to the Invention exceeded, and that the Comparative Example 12 had a poor machinability as the amount Ti is the upper limit for Ti according to Invention exceeded.

It It can also be seen that Comparative Example 13 is a poor one Machinability showed that the amount of Zr was the upper one Limit for Zr according to the invention exceeded.

About that In addition, it can also be seen that the comparative example 14 a high tool wear and a bad machine Machinability, because although that machinability containing improving element in a form different from sulfide was, the amount of S was less than the lower limit for S according to the invention.

in the By contrast, it can be seen from the results of Tables 3 and 4, that all examples of the invention with respect to the respective Features excellent sections.

In in this regard, Examples 22-35 showed, though these examples Compared to Examples 1 to 21, a small amount of Cr contained in the steel and the amount of Cr in the sulfide (Mn, Cr, Zr) S thus, was low, high corrosion resistance.

This This is because ZrS is insoluble in water and corrosion resistance (MnS is water soluble and degraded the corrosion resistance) is not affected and therefore the influence on the corrosion resistance even then not big if the amount of Cr in the sulfide is low.

About that In addition, examples showing Pb, Bi, Te, Se, Sn, P or B, good machinability and high Corrosion resistance when the amount of S is more than 0.01% amounted to. This is because these elements are machinability in a form other than a sulfide.

Even though the invention in detail and with reference to their specific embodiments it is obvious to a person skilled in the art that that various changes and modifications are made without leaving their protected area.

The invention is based on Japanese Patent Application 2007-243067 , filed on 19 September 2007, and at the Japanese Patent Application 2008-235819 , filed Sep. 15, 2008, the contents of which are incorporated herein by reference.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - JP 2005-139531 A [0012]
• - JP 2001-355048 A [0019, 0020, 0021, 0022]
• - JP 2005-60812 A [0019, 0023, 0024, 0024, 0025, 0025, 0025]
• - JP 2001-98352 A [0019, 0026, 0027]
• - JP 2007-243067 [0108]
• - JP 2008-235819 [0108]

Cited non-patent literature

• - JIS 22371 [0089]

Claims (6)

Ferritic, machinable, stainless steel, having (in% by mass): C: ≤ 0.200%, Si: 0.01 to 5.00%, Mn: 0.01 to 2.50%, S: 0.05 to 0.50%, Ni: ≤ 5.0%, Cr: 7.5 to 30.0%, Mo: ≤ 5.0%, N: ≤ 0.050%, O: ≦ 0.0150%, Ti: ≦ 0.30%, and Zr: 0.01 to 1.00%, the rest being Fe and inevitable Impurities, and wherein a Zr-based sulfide in such a form that a part of sulfide-forming Mn by Zr is substituted, is formed in the steel. Ferritic, machinable, stainless steel, comprising (expressed in mass%): C: ≤ 0.200%; Si: 0.01 to 5.00%; Mn: 0.01 to 2.50%; S: 0.01 to 0.50%; Ni: ≤ 5.0%; Cr: 7.5 to 30.0%; Mo: ≤ 5.0%; N: ≤ 0.050%; O: ≤ 0.0150%; Ti: ≦ 0.30%; Zr: 0.01 to 1.00%, and at least one item selected is from the group consisting of: Pb: 0.01 to 0.30% Bi: 0.01 to 0.15%, Te: 0.01 to 0.30%, se: 0.01 to 0.40% Sn: 0.01 to 0.10% P. 0.01 to 0.05%, and B: From 0.001 to 0.03%, the remainder being Fe and unavoidable impurities are, wherein a Zr-based sulfide in such a form, that a part of sulfide-forming Mn is substituted by Zr, is formed in steel. A ferritic machinable stainless steel according to claim 1 or 2, which satisfies the following equations (1) and (2): 0.1 ≤ [Mn] / [Zr] ≤ 50 (1) 300 × [O] - [Zr] ≤ 4.0 (2) wherein [Mn], [Zr] and [O] in the above equations represent the content of Mn in mass%, the proportion of Zr in mass% and the proportion of O in mass%. Ferritic, machinable, stainless steel after one of claims 1 to 3, which furthermore, in Mass%, contains at least one element that is from the group is selected, which consists of the following: W: 0.01 to 0.50%, and Cu: 0.01 to 0.50%. A ferritic, machinable stainless steel according to any one of claims 1 to 4, which further contains, in mass%, at least one element selected from the group consisting of the following Al: 0.01 to 3.00%, V: 0.01 to 0.30%, and NB: 0.01 to 0.30% Ferritic, machinable, stainless steel after one of claims 1 to 5, which furthermore, in Mass%, contains at least one element that is from the group is selected, which consists of the following: mg: 0.0001 to 0.0100%, Ca: 0.0001 to 0.100%, and REM: 0.0001 up to 0.0100%, where REM is at least one of the metal elements which are classified as Group 3A in the Periodic Table.