FI97398B - Use of stainless martensite steel for suction rollers in the manufacture of paper - Google Patents

Description

97398

Use of martensitic stainless steel for suction rolls in papermaking.

The present invention relates to improvements in stainless marzentite steels and in particular to stainless maraging steel which is a suitable consumable for cases where high corrosion fatigue strength and high corrosion resistance are required, for example for suction rolls in the paper industry, seawater pumps and various other devices.

For example, suction rolls used in the paper industry are exposed to white liquor and must therefore have very good corrosion resistance and very good corrosion-15 wear fatigue strength. Materials with excellent properties include stainless ferrite austenitic duplex steel, stainless steel, and the like, but these materials generally have poor machinability.

Because these materials are particularly poor to work with drills, they are very difficult to machine with a rotary drill and cannot usually be used.

Thus, stainless martensitic steels are commonly used in the manufacture of suction rolls in the paper industry, a typical example of which is JIS SCSI, because these steels have excellent drill machinability and are inexpensive. In addition, these materials have the problem of poor stability when used on machine members. For example, their applicability in terms of corrosion resistance and fatigue strength is not entirely satisfactory in corrosive environments containing chlorine ions. Especially when used in conditions where the stresses are repetitive, the material deteriorates rapidly, allowing failures such as roll breakage.

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In particular, paper mills in particular have been operating in recent years. at club speed, at a lower pH and at a higher 97398 2 S2032 ion concentration and therefore in an increasingly corrosive environment in the presence of white liquor. Therefore, it is necessary that the material used is increasingly better in terms of corrosion resistance and corrosion fatigue strength.

The present invention provides a new material that meets this requirement.

The main object of the present invention is to provide 10 martensitic stainless steels having high corrosion fatigue strength and excellent corrosion resistance, and having a composition of more than 0 to 0.06% C, more than 0 to 2.0% Si, more than 0 to no more than 2.0%

Mn, 3,0 to 6,0% Ni, 14 to 17% Cr, 1 to 3% Mo, 0,5 to 1,5% Cu 15 with iron and unavoidable impurities, use in suction rolls for papermaking under corrosive conditions chloride ions.

The martensitic steel 20 used in accordance with the present invention has high corrosion fatigue strength and excellent corrosion resistance, and is particularly suitable as a material for making paper industry suction rolls, chemical equipment, pump components and seawater treatment equipment used in corrosive environments, including there are chlorine ions.

The content of the present stainless steel components is limited as above for the following 30 reasons.

·· C: more than 0 - not more than 0,06% C is an austenite-forming element and is present in solid solution in the austenite phase to strengthen the structure. However, as it is more and more present, C forms Cr carbide and consumes chromium, which contributes to the corrosion resistance, thus reducing the corrosion resistance. In addition, any large amounts of Cr carbide released will impair toughness. The upper limit of C should be 0.06%.

5 Si: more than 0 - not more than 2.0%

Si acts as a counteroxidant when steel is melted. However, when silicon is present in large quantities, it becomes brittle and otherwise degrades the properties of the material, resulting in an upper limit of 10 and is 2.0%.

Mn: more than 0 - not more than 2.0%

Like silicon, Mn acts as a counteroxidant and also traps sulfur (S) when the steel is smelted. However, the large amount of manganese present lowers the corrosion resistance, and for this reason the upper limit is 2.0%.

Ni 3.0 - 6.0% 20

Ni is an austenite-forming element that forms the austenitic phase remaining in microstructures to effectively improve toughness and corrosion resistance. Suction sleeves for papermaking are generally large rolls with a diameter of more than 1 meter and a wall thickness of 100 mm when cast and are usually made by centrifugal casting. When a conventional SCS1 material was used to cast such rolls, various problems such as cracking during casting occurred in the casting process. Nickel mu-30 chicken improves castability. In addition, when a suitable amount of nickel is present, this promotes the formation of the correct amount of residual austenitic: * phase, which in turn ensures better toughness and makes the steel solidify with a better composition. To ensure these advantages, at least 3.0% nickel must be present, while the presence of a higher amount of nickel generates too much residual austenite and thus leads to an undesired result. As a result, 97398 4 costs increase because nickel is an expensive element. The Ni content should therefore not exceed 6.0%.

Cr: 14 - 17% 5

Cr, which is a ferrite-forming element, is an essential element for providing better strength because it forms a ferrite phase and gives stainless steel corrosion resistance. To ensure high strength and good corrosion resistance, the Cr content must be at least 14%. However, the presence of a high amount of Cr increases the amount of ferrite phase in the microstructure, which impairs corrosion resistance and toughness. The upper limit should therefore be 17%. The Cr content happens to be closely related to the concentrations of carbon and nickel as austenite-forming elements and to the molybdenum content as a ferrite-forming element. In view of this, it is suitable to limit the Cr content according to the invention to between: 14 and 17%.

20 Mo: 1 - 3%

Mo is very effective in improving corrosion resistance, especially against pitting. The effect is insufficient if the Mo content is less than 1%, while a Mo-25 content of more than 3% leads to lower toughness and higher costs. The upper limit should therefore be 3%.

Cu: 0.5 - 1.5% 30 Cu improves the general corrosion resistance and can provide a reinforced austenitic solid solution. In particular, copper and molybdenum can be used synergistically to achieve even better resistance to general corrosion (as shown in the example below). The stainless steel according to the present invention is very important because this steel contains various components in good balance and also contains copper and molybdenum, which provide a synergistic effect and considerably improve the resistance to general corrosion. To fully guarantee this effect, at least 0.5% copper should be present. On the other hand, too high a Cu content 5 lowers the toughness, so the upper limit should be 1.5%.

The stainless steel used in accordance with the present invention contains the above-mentioned elemental components. The rest is the elemental-10 impurities that inevitably come into the iron and steel. These impurities include P, S, and others that inevitably enter the steel when it is produced by smelting. These impurities may be present if the amount of impurity is within the range normally allowed for said types of steels.

The purpose of the example below is to describe in detail the improvements that can be made in the corrosion resistance and corrosion fatigue strength of the martensitic stainless steel used according to the invention.

Example

Using a high frequency induction furnace, 25 alloys of different compositions were prepared and these were cast by centrifugal casting into ingots. Table 1 gives the chemical compositions of test pieces made from ingots.

The specimens were heat treated (cooling in air at 1050 ° C, tempering at 650 ° C) and subjected to a ·. * General corrosion test and a corrosion-fatigue strength test. The results are given in Table 2. The tests were performed by the following methods.

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For the general corrosion test, the specimens were immersed in boiling 5% sulfuric acid for 6 hours and the corrosion loss per square meter was checked every hour.

5 The corrosion-fatigue strength test was performed in a liquid having

Ph was 3.5 and containing 100 ppm Cl and 1000 ppm C042 ions using an Ono rotating bending fatigue tester at 3000 rpm and a loading stress of 18 kg / mm2. The number of repeated cycles required to break the specimen was determined.

Table I

Sample 1 5 _Chemical composition (wt%) * _ no. C_Si_Mn_Cr_Ni_Mo_Cu 1 0.05 0.37 0.68 11.77 0.48 0.02 2 0.05 0.52 0.80 11.95 0.53 0.58 3 0.05 0.41 0.72 16 .00 6.13 2.03 20 4 0.05 0.42 0.81 16.12 5.01 2.11 1.01 * Remaining iron and unavoidable impurities.

Table 2 25 Specimen Corrosion loss Corrosion fatigue strength no ._ (g / m2. H) _ (number of cycles) _ 1 1 060 1.1 x 1 07 2 780 1.2 x 1 O7 30 3 520 3.0 x 1 07 4 50 9.1 x 107

Table 1 shows sample no. 1 standard JIS SCS1 material, specimens no. 2 and 3 are reference materials made for comparison with the stainless steel according to the invention, and sample no. 4 is a stainless steel according to the invention.

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The results in Table 2 show that the corrosion loss of the stainless steel for use according to the invention is much lower than that of the conventional material and the reference material and that it has excellent overall corrosion resistance.

From the fatigue strength determined in the corrosive environment, it can be stated that the strength of the stainless steel intended for use according to the invention is about 7 times that of the specimens no. 1 and 2 and about 3 times that of sample no. 3 compared.

These excellent properties are believed to be due to the synergistic effect of molyb-15 dene and copper.

The stainless steel of the present invention has excellent corrosion resistance and corrosion-fatigue strength and is therefore a very suitable material for papermaking rolls, chemical equipment, pump components, seawater treatment equipment and the like where such properties are required.

Claims (3)

97398 Claim stainless steels with high corrosion fatigue strength and excellent corrosion resistance, 5 having a composition in weight percent of more than 0 to 0.06% C, more than 0 to 2.0% Si, more than 0 to 2.0% Mn , 3.0 to 6.0% Ni, 14 to 17% Cr, 1 to 3% Mo, 0.5 to 1.5% Cu with the remainder being iron and unavoidable impurities, use in suction rolls for papermaking under corrosive conditions with chloride ions. «I» il m h mu i. «Ju i 97398 Användning av rostfritt martensitstäl, som uppvisar stor corrrosionsutmattningshällfasthet och utmärkt korrosions-5 beständighet, och vars sammansättning som viiktprocent är 0. högst 0,06% C, över 0 - högst 2% Si, 0 to 2% Mn, 3.0 to 6.0% Ni, 14 to 17% Cr, 1 - 3% Mo, 0,5 - 1,5% Cu, Medan resten är järn och oundvikliga föroreningar, för sugvalsar i papperstillverkningen i frätande förhällanden, 10 där kloridjoner förekommer.