EA010540B1 - A steel shell for a suction roll and a method of producing a steel product - Google Patents

Abstract

The invention relates to a suction roll shell 9 having a plurality of through holes 7. The shell is made of a stainless ferrite-austenite steel having a micro-structure essentially consisting of 35-65 % by volume of ferrite and 35-65 % by volume of austenite. The steel has a composition containing, among other things, 0.005-0.07 C and 0.15-0.30 N, in % by weight. The invention also relates to a suction roll comprising the inventive suction roll shell and a method of producing a steel product.

Description

The invention relates to a steel jacket for a suction shaft and a method for producing a steel product, in which a piece of steel material is processed by a cutting operation, such as milling, turning and / or drilling.

BACKGROUND OF THE INVENTION

Stainless steel is used in areas where high corrosion resistance is required. High corrosion resistance may be required in high seas environments, in the paper and pulp industries, and in the chemical industry. One example is the suction roll shirts for the paper industry, which are made of stainless steel. One type of stainless steel is the so-called duplex steel, which contains ferrite and austenite. It is known that duplex steels combine high mechanical strength and toughness with good corrosion resistance, in particular in terms of stress corrosion and fatigue corrosion. For corrosion resistance, as well as for mechanical properties such as weldability, it is important that the steel is well balanced in terms of the essential components of austenite and ferrite. In the modern development of duplex steels, it is desirable to have a microstructure containing 35-65% ferrite, with the remainder being austenite. In areas requiring high strength and good corrosion resistance, duplex steels are increasingly competing with traditional austenitic stainless steels. Such steel material is described in published US patent application No. 2003/0172999. The steel material described in this publication is ferritic-austenitic stainless steel with a microstructure essentially consisting of 35-65 vol.% Ferrite and 35-65 vol.% Austenite. The steel in question has a chemical composition containing, in wt.%:

0.005-0.07 C; 0.1-2.0 8ί; 3-8 megapixels; 19-23 Cg; 0.15-0.30 N and 0.5-1.7 N1. Other components may also be included.

Nitrogen is essential for the steel described in US patent application No. 2003/0172999, since nitrogen is the main austenite-forming element and contributes to the strength of the steel, as well as its corrosion resistance. For this reason, it was estimated that the nitrogen content in the steel should be in the range of 0.15 to 0.30%, and preferably in the range of 0.20 to 0.24%. However, it was previously shown that steel types with such a high nitrogen content are characterized by poor machinability.

Most often, stainless steel intended for use in a particular product needs to be subjected to certain types of machining, such as milling, turning or drilling. As such, austenitic and duplex stainless steels are characterized by low machinability, and therefore, various measures are being taken to improve the machinability of stainless steels. It is known that the presence of nitrogen in stainless steel degrades machinability. For example, US Pat. No. 4,769,213 proposes a method for improving machinability by cutting martensitic stainless steels by lowering the carbon and nitrogen contents, so that the total carbon and nitrogen content together is not more than 0.05 wt.%. However, in comparison with duplex steels, martensitic steels have lower corrosion resistance. For austenitic stainless steels, US Pat. No. 5,482,674 proposes to reduce the carbon and nitrogen contents so that neither the carbon content nor the nitrogen content is greater than about 0.035% by weight. It is also known that the addition of sulfur can improve machinability. Accordingly, US Pat. No. 4,784,828 proposes to add sulfur to austenitic stainless steel to improve cutting machinability. It is also claimed that the carbon and nitrogen content should be very low, in aggregate up to 0.065 wt.%. However, compared with duplex steels, austenitic steels have lower strength.

US Pat. No. 4,964,924 proposes the use of martensitic stainless steel in a suction roll. This publication claims that stainless ferritic-austenitic duplex steels are not suitable as materials for suction rolls because they are difficult to drill. Instead, it is suggested that stainless steel suitable for a shirt of suction rolls should be of the martensitic type and, among other substances, contain, in wt.% Carbon, more than 0, but not more than 0.06, silicon more than 0, but not more than 2, Manganese more than 0, but not more than 2, 3-6 nickel, 14-17 chromium, 1-3 molybdenum and copper from 0.5 to 1.5.

The aim of the present invention is to solve the problem by obtaining a steel material that exhibits high strength as well as good corrosion resistance and which, moreover, is suitable for cutting operations without additional processing with the addition of sulfur. It is also an object of the invention to provide a suction roll jacket with good corrosion resistance, which is easy to manufacture by cutting.

Disclosure of invention

The applicant was surprised to find that the steel material of the type described in the aforementioned application for US patent No. 2003/0172999, not only has high strength and good corrosion resistance, but the material in question is also suitable for cutting, such

- 1 010540 as turning, milling and drilling, without the gray treatment of the material in question. The applicant also found that the material in question is particularly suitable as a material for the suction rolls of paper machines, and that manufacturing a jacket of the suction roll from such material is favorable. Accordingly, the invention relates to a jacket of a suction roll of this material. The invention can also be understood as a method of machining, in particular in the manufacture of shells of a suction roll, but also in the manufacture of other products, for example, machine parts, such as shafts. The invention can also be defined in terms of the use of the specified steel as a workpiece in the processing of steel by cutting.

Therefore, the invention relates to a suction roll jacket having a plurality of through holes. The suction roll jacket according to the invention is made of stainless ferritic-austenitic steel, the microstructure of which essentially consists of 35-65 vol.% Ferrite and 3565 vol.% Austenite. The composition of the steel will be described in more detail in the detailed description of the invention.

The invention also relates to a suction shaft including a patentable jacket of a suction shaft.

In a preferred embodiment of the invention, machining involves drilling at least one through hole, and preferably drilling a plurality of holes. In an advantageous embodiment of the invention, the method includes drilling hundreds of thousands of holes. The corresponding drilled length is several kilometers. Cutting may also include turning the outer and inner surfaces of the shirt.

Brief Description of the Drawings

In FIG. 1 shows the bending of a blank for a shirt of a suction shaft.

In FIG. 2 shows a workpiece bent and welded to form a shirt.

In FIG. 3 schematically shows the first stage of processing the shirt shown in FIG. 2.

In FIG. 4 shows a second stage of shirt processing.

In FIG. 5 shows the finished shirt of the suction shaft.

In FIG. 6-9 show the results of comparative tests in which the steel used according to the invention was compared with other steels in terms of machinability.

DETAILED DESCRIPTION OF THE INVENTION

The manufacture of shells for the suction rolls is schematically described below. In FIG. 1 shows a first step in manufacturing a shirt of a suction roll. As shown in FIG. 1, a substantially planar blank 1 is bent between two rollers 2, 3, such a method is known, and a more detailed description is not necessary. After bending to a substantially annular shape, the ends of the workpiece 1 are welded so that the weld joins the workpiece 1 to form segment 9. Then, the multiple segments are joined using circular seams to form a jacket that is heat treated after welding. In FIG. 3 shows how the thus obtained jacket 9 can be subjected to machining operations, such as turning. In FIG. 3 shows a turning tool 5 acting on the surface of a shirt 9. The purpose of the turning is to provide a smooth and uniform surface of the shirt 9. In FIG. 4 schematically shows the next stage of the manufacturing method in which the jacket 9 is drilled with a drill 6, as a result of which the jacket is provided with a series of through holes 7. In FIG. 5 shows the finished shirt 8 of the suction shaft with its annular cylindrical shirt 9 and through holes 7 therein. In FIG. 5 also schematically shows that the ends of the suction shaft jacket 8 can be closed with side covers 10. When the suction shaft jacket 8 is used, its inner side is connected to a vacuum source (not shown), which leads to suction of air from the outside and through the through holes 7. Only a few holes are shown in the drawings. However, it should be understood that in actual applications the number of holes can be very large, such as 100,000 holes or more.

Until now, the shirts of the suction rolls were made of material sold under the name 3KE60 Avesta 8RS. This steel is an austenitic ferritic steel that has been improved in terms of machinability by sulfur treatment and which has the following typical

becoming in ma from.%. FROM 0.02 8ΐ 1,50 SG 18.5 N1 4.90 Mo 2.80 N 0.08 8 0.02

With good results, 3KE60 steel was used for about 30 years to manufacture the shells of the suction rolls and about 10 years ago it was provided with an additive for improved machinability by cutting and the name was changed to 3KE60 8K.O. Currently, steel is called 3ЯЕ60 Avesta 8K.O.

It has been unexpectedly found that there is another ferritic-austenitic steel that has

- 2 010540 in addition, a high nitrogen content and which has equally good or in some respects better machinability, compared with 3KE60 Avesta 8BO steel having improved machinability. This steel has a microstructure consisting essentially of 35-65 vol.% Ferrite and 35-65 vol.% Austenite, and its chemical composition contains, wt.%:

S 0.005

8ΐ 0.1-2.0

Mp 3-8

SG 19-23

N1 0.5-1.7

N 0.15-0.3

Steel, which is particularly suitable for this application, accordingly contains possibly Mo and / or with a total content of not more than 1.0 (Mo + ^ / 2), possibly Cu, up to a maximum of 1.0 Cu, with iron and impurities remaining.

For ferrite and austenite-forming elements in the alloy, i.e. chromium and nickel equivalents, preferably the following conditions are met:

20 <Cr _e 24.5

10 <\ r - where

Cr _e = Cr + 1.581 + Mo + 2T1 + 0.5№ No. _{e1 |} = N1 + 0.5Mn + 30 (C + Ν) + 0.5 (Cu + Co).

In a winning design, the steel contains 0.02-0.05 C. It is suitable if the steel contains 0.18-0.26 N and preferably 20-23 Cg. In a preferred embodiment, the steel contains 0.8-1.70 Νί and more preferably 1.35-1.7 N1.

The steel of this composition is described in published patent application US No. 2003/0172999.

In a particularly advantageous embodiment of the invention, the steel contains 0.22 N 21.5 Cg; 1.5 N1; 0.3 Mo; 5 MP and not more than 0.04 C. Such steel is sold by Oi1okitri 81ash1e88 AB, Vokh 74, 8E-774 22, AUE8TA. Oi1okitri sells this steel under the name ΕΌΧ2101®. The name is a trademark registered in the European Union. Thus, ΕΌΧ2101® steel is particularly suitable for use in a suction roll jacket. Particularly suitable copper and silicon contents are 0.3 Cu and 0.7 81, respectively. For ΕΌΧ2101®, standard values of 0.3 Cu and 0.7 δί (in wt.%) Are used.

Compared, for example, with steel 3KE60 Avesta 8BC. steel of the above type has a relatively high nitrogen content. Since nitrogen is known to tend to degrade machinability, it should be expected that machinability will be worse. However, it unexpectedly turned out that the machinability of the steel used according to the present invention is significantly better than expected.

In FIG. Figure 6 shows the results of a comparative test in which ΕΌΧ2101® steel was compared with two other austenitic steels, with improved machinability called 304O RKOEES® and 316L RKOEES®, respectively. Steel 304b РРОЭЕС® had the following composition, wt.%:

C 0.02

8ΐ 0.5

MP 1.5

SG 18.2

N1 8.4

Mo is essentially absent

N 0.07 δ 0.02

Steel 316b RROEES® had the following composition:

FROM 0.02 8ΐ 0.5 Mp 1,5 SG 17,2 N1 11.2 Mo 2,3 N 0.05 δ 0.02

Since the nitrogen content of both austenitic steels with improved machinability 304b РРОЭЕС® and 316Ь РРОЭЕС® is significantly lower than that of ΕΌΧ2101® steel, one would expect these steels to have better machinability than ΕΌΧ2101® steel. However, in the turning tests, it was shown that for ΕΌΧ2101® steel, with a processing time of 30 minutes and the use of high-speed steel tools, a significantly higher cutting speed was possible compared to the other two steels, as shown in FIG. 6.

- 3 010540

In FIG. 7 shows the results of an additional comparative test for steel ΕΌΧ2101® and steels 304Ь ΡΚΘΌΕΟ® and 316Ь РЕОЭЕС®. In FIG. 7 shows a test with a processing time of 15 minutes, in which the turning was carried out by the cutting edge of the hard alloy. In these circumstances, the cutting speed for ΕΌΧ2101® was achieved, which was slightly lower compared to the other two steels. However, the difference is not significant.

In FIG. Figure 8 shows another test in which ΕΌΧ2101® steel was compared to traditional duplex steel sold under the name 2205. This steel, which is higher alloyed than ΕΌΧ2101®, is standardized (European Committee for Standardization standard - ΕΝ 1.4462) and is used in large number of applications. It has no additives that improve machinability, and it is not used for this type of suction roll casing. Steel 2205 has the following composition:

C 0.02

8ΐ 0,4

MP 1.5

SG 22.2

N1 5.7

Mo 3.1

N 0.17

0.001

In the test, a comparison was made in terms of tool life when milling with a hard alloy cutting edge. As is apparent from FIG. 8, the tool life was significantly longer with ΕΌΧ2101® steel compared to 2005 steel.

Finally, another test is shown in FIG. 9. In the test shown in FIG. 9, ΕΌΧ2101® steel was compared with three other types of steel used for suction roll casings, i.e. 2304 Avesta 8K.6, 3ΒΕ60 Avesta 8RS and 2205 Avesta 8RS. All steels designated 8RS (Grade for Suction Shafts) have improved machinability by adding sulfur. Steel 2304 Avesta 8K.S has the following typical composition:

C 0.02

0.8

MP 1.5

SG 22.7

N1 4.7

Mo 0.3

N 0.09

0.02

Avesta 8RS steel 2205 has the following typical composition:

S 0.017

0.6

Mp 1.35

SG 22.0

N1 5.7

Mo 2.9

N 0.13

0.02

In the test shown in FIG. 9, a comparison was made regarding the cutting speed that can be achieved for a drilled length of 1000 mm without damaging the tool in various materials. As is apparent from FIG. 9, ΕΌΧ2101® is significantly better than 2304 Avesta 8K.6 and 2205 Avesta 8K. C with improved machining, and in this regard it is as good as 3ΒΕ60 Avesta 8PC steel with improved machinability, despite the fact that ΕΌΧ2101® contains significantly more nitrogen than 3ΚΕ60 Avesta 8RS steel. An obvious technical advantage is the ability to achieve machinability by cutting material without the so-called additives that improve machinability by cutting, such as sulfur, as they lead to a number of disadvantages, such as deterioration of rolling ability and deterioration of corrosion resistance.

It should be understood that although the invention has been described with an example of a suction shaft jacket and method, they are simply different aspects of the same invention, since the method according to the invention is suitable for use in the manufacture of a suction shaft jacket according to the invention.

By means of the invention, among other things, the advantage is achieved that the finished shaft jacket gains high corrosion resistance.

Claims (19)

CLAIM 1. Shirt (9) of the suction shaft with many through holes (7), characterized in that this shirt is made of stainless ferritic-austenitic steel, the microstructure of which essentially consists of 35-65 vol.% Ferrite and 35-65 vol. .% austenite, and the chemical composition contains, wt.%: 0.005-0.07 C; 0.1-2.0 8ΐ; 3-8 megapixels; 19-23 Cg; 0.5-1.7 N1; 0.15-0.30 N. 2. Shirt (9) of the suction shaft according to claim 1, characterized in that the steel contains: a) possibly Mo or with a total content of not more than 1.0 (Mo + ^ / 2); b) it is possible Cu, up to a maximum of 1.0 Cu, with the remainder being iron and impurities, and for ferritic austenite-forming elements in the alloy, i.e. chromium and nickel equivalents, the following conditions are met: c) 20 <Cr _ex <24.5 d) 10 <N ^ e ^, where e) Cg. = Cr + 1.581 + Mo + 2T1 + 0.5 g) No. _{e1 |} = N1 + 0.5Mn + 30 (C + Ν) + 0.5 (Cu + Co). 3. The shirt (9) of the suction shaft according to claim 1 or 2, characterized in that the steel contains 0.02-0.05 C. 4. The shirt (9) of the suction shaft according to claim 1 or 2, characterized in that the steel contains 0.18-0.26 Ν. 5. Shirt (9) of the suction shaft according to claim 1 or 2, characterized in that the steel contains 20-23 Cg. 6. Shirt (9) of the suction shaft according to claim 1 or 2, characterized in that the steel contains 0.8-1.70 N1. 7. Shirt (9) of the suction shaft according to claim 1 or 2, characterized in that the steel contains 1.35-1.7 N1. 8. Shirt (9) of the suction shaft according to claim 1 or 2, characterized in that the steel contains 0.22 N 21.5 Cg; 1.5 N1; 0.3 mo; 5 MP, not more than 0.04 C and preferably 0.3 Cu, and preferably 0.7 81. 9. The suction shaft (9), characterized in that it has a shirt (9) of the suction shaft according to any one of claims 1 to 8. 10. A method of obtaining a steel product, which includes providing a steel billet (1, 9) and cutting the billet (1, 9), characterized in that the billet steel (1, 9) is stainless ferritic-austenitic steel, the microstructure of which is essentially , consists of 35-65 vol.% ferrite and 35-65 vol.% austenite, and the chemical composition contains, wt.%: 0.005-0.07 C; 0.1-2.0 81; 3-8 megapixels; 19-23 Cg; 0.5-1.7 N1; 0.15-0.30 N. 11. The method according to claim 10, characterized in that the steel contains: a) possibly Mo or with a total content of not more than 1.0 (Mo + ^ / 2); b) it is possible Cu, up to a maximum of 1.0 Cu, with the remainder being iron and impurities, and for ferritic austenite-forming elements in the alloy, i.e. chromium and nickel equivalents, the following conditions are met: c) 20 <Cr _ex <24.5 d) 10 <N ^ e ^, where e) Cg. = Cr + 1.5 81 + Mo + 2ΤΪ + 0.5№ g) No. _{e1 |} = N1 + 0.5Mn + 30 (C + N + 0.5 (Cu + Co). 12. The method according to claim 11, characterized in that the steel contains 0.02-0.05 C. 13. The method according to claim 11, characterized in that the steel contains 0.18-0.26 N. 14. The method according to claim 11, characterized in that the steel contains 20-23 Cg. 15. The method according to claim 11, characterized in that the steel contains 0.8-1.70 N1. 16. The method according to claim 11, characterized in that the steel contains 0.22 N 21.5 Cg; 1.5 N1; 0.3 Mo; 5 MP, not more than 0.04 C. 17. The method according to any one of paragraphs.10-16, characterized in that the cutting includes drilling at least one through hole (7). 18. The method according to any one of paragraphs.10-17, characterized in that the cutting includes turning. 19. The method according to 17, characterized in that the drilling of at least one through hole (7) is carried out after the previous stage of turning.