FI73468B - SVETSBART STAOL. - Google Patents

Description

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Weldable steel

The present invention relates to Metallurgy and deals in more detail to high-strength hit-5 stainless steels for the production of heavy-duty structures to be used in low temperatures and corrosive environments, such as floating drilling units and hulls for nuclear icebreakers.

10 In the light of the fact that such steels are used in the manufacture of critical, heavy-duty components and units, they must meet a number of binding requirements. These requirements are as follows: These types of steels must have excellent strength properties together with satisfactory weldability and highly resistant to brittle fractures. For example, the steel used in the fabrication of the ice cladding of a nuclear icebreaker is expected to stop the rapidly developing crack over its entire thickness range at stresses not lower than 0.5 of the yield point and at temperatures as low as -50 ° C.

In the case of floating drilling units operating at temperatures of -30 ° C to -40 ° C and fatigue load 11a, the critical crack size at which brittle fracture may occur must be much larger than the actual crack size at which the body may lose its load-bearing capacity.

Such steels must be corrosive to seawater and resistant to mechanical effects.

They are expected to be highly malleable and machinable in a variety of machining and molding processes in metallurgical, machine building and shipbuilding equipment.

The steels used in the construction of heavy-duty structures, such as icebreaker hulls and offshore and offshore installations, differ in their strength levels depending on how critical a given piece is and under what conditions it is intended to operate.

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High-strength weldable steels of categories D32, E32, D36 and E36 are known and are widely used in shipbuilding. The chemical composition and mechanical properties of these steels meet the standards of the International 5 Association of Classification Societies.

The workability and weldability of these steels are satisfactory, however, at temperatures below -30 ° C at thicknesses of more than 30 mm and with cyclic, vibration and dynamic loads they are unable to stop dynamic cracks at stresses greater than 0.5 of the yield point. The steels in question are still deficient in that their strength properties are not compatible with the weight requirements given to the structures. In many cases, the strength of the structure can only be improved by increasing the thickness of the steel used in the structure, but increasing the thickness increases the weight of the structure and affects the brittle fracture toughness of the steel.

Raex Polor welded steels of categories E27, E32 and E36 have been widely used in Finland. The strength properties of such steels 20 are excellent (cf. Shipbuilding Steels for Arctic Conditions, the Maritime Journal of Finland, No. 3, 1983). The chemical composition of these steels is shown in Table 1.

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Table 1 No. Steel class C Si 1 2 3 4 5 1 Raex E27 Polor <0.18 0.1-0.3 2 Raex E32 Polor <0.18 0.1-0.3 3 Raex E36 Polor <0 , 18 0.1-0.3

Table 1 (continued) 10 No. Mn Cu Ce 5 6 7 1 0.6 to 1.6 0.1 to 0.3 0.005 to 0.10 15 2 0.9 to 1.6 0.10 to 0, 35 0.005 - 0.10 3 1.1 - 1.6 0.1 - 0.3

Table 1 (continued) No. Ni_AI_S_P_Nb_Fe _ 20 _8_9_10_11_12_13 1 - ^ 0.0 2 <0.02 <0.035 - For equilibrium 2 - 0.02 - 0.06 <0.02 <0.035 0.002 - 0.050 3 <0.4 0.06 <0.03 <0.30 0.04 25 In thickness ranges up to 30 min, such steels are widely used in the construction of Arctic ships, however, their guaranteed yield strength is not higher than 352 MPa.

Due to their limited strength, such steels must be 40 to 70 mm thick if they are used for plating nuclear icebreakers.

However, this increases the weight and draft of the vessel and affects its behavioral characteristics.

In addition, increasing the thickness makes the steel 35 more brittle.

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At thicknesses above 30 mm, this type of steel is unable to stop dynamic cracking at stresses above the yield strength of 0.5.

At a temperature of -50 ° C and a thickness of 40 mm up to -5, the critical crack size of these steels is less than 20 mm.

A number of highly durable weldable steels are known for the manufacture of heavy-duty offshore drilling rigs and ship hulls. The composition and physico-mechanical properties of these steels are listed below.

High-strength Wel-Ten steel produced by Nippon Steel Corporation of Japan. The composition of this steel in% by weight is as follows: carbon, ^ 0.16 nickel, ^ 0.60 manganese, 0.90 - 1.50 chromium, <0.30 sulfur, ^ 0.03 molybdenum, 0.30 phosphorus, 4: 0.03 vanadium, <0.10 silicon, ^ 0.15-0.55 iron, to equilibrium.

In the thickness range up to 50 mm, the yield strength of this steel 20 is at least 490 MPa. The impact strength (NDT) shows a zero ductility temperature between -20 ° C and -55 ° C. In the thickness range 50 mm, steel is welded without cracking only when preheated to 75-100 ° C. Judging by its composition, it is on average -25 ° C. In other words, the steel is very strong, containing a limited content of alloying metals, but its formability at low temperatures is insufficient.

Pipeline steel according to Japanese Patent No. 54 to 127,821 is known. The composition of this steel in 30% by weight is as follows: carbon, ^ 0.3 sulfur, 4 0.02 silicon, 0.01-0.80 aluminum 0.10 manganese, 0.5-2.0 calcium, 0.005 to 0.015 chromium, ^ 1.0 molybdenum, ^ 0.15 35 nickel, 1.0 vanadium, 4: 0.10 phosphorus ^ 0.04 niobium, ^ 0.04 iron, equilibrium.

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In the thickness range less than 32 mm, the strength level of this steel is about 440 MPa. Due to the high carbon and chromium content, the steel must be heated to 100 - 150 ° C before welding. Due to its limited strength, limited ncin 5 32 mm thickness range and limited brittle fracture toughness, this steel cannot be used in heavily loaded structures working at temperatures up to -50 ° C.

A number of fine-grained ferrite-perlite-10 steels are known which are used in the manufacture of tanks intended for the transport of liquefied gases kept at a temperature of -50 ° to -55 ° C. These include steels produced in Sweden and Japan based on the recommendations contained in the IMO Code.

15 0X416 steel produced by the Swedish SS AB. The composition of this steel in% by weight is as follows: 0.10 ° C; 0.26 Si; 1.38 Mn; 0.02 -0.06 AI; 0.02 - 0.03 Nb; <0.11 Ni; <: 0.1 Cu; ^ 0.1 Cr; 0.020 P; 0.020 S; the balance.

In the thickness range less than 32 mm, the yield strength of this steel is at least 314 MPa, the specific elongation is at least 50% -50 and the international impact work is at least 35 J (cf. Transactions of the Soviet-Swedish-Nprwegian Symposium in Leningrad in October 1977).

Despite the high level of impact work, the steel is not able to stop dynamic cracks at a temperature of -50 ° C and at stresses higher than 0.5 of the yield point.

The N-Tyt 37 steel produced by the Japanese Nippo Steel Corporation is a high-strength weldable steel used in the manufacture of tanks intended for the transport of liquefied gases kept at temperatures as low as -55 ° C. The composition of this steel in% by weight is in accordance with the IMO code. It is as follows: 0.10 C; 0.24 Si; 1.32 Mn; 0,020P; 0.04 S; 0.52 Ni, Fe equilibrium.

35 In the thickness range 40 mm N-Tyt steel has a yield strength of 430 MPa and a tensile strength of 520 MPa. Its specific elongation is -50 24% and the international impact work is 210 J.

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However, the results of the dynamic crack stopping tests do not fully meet the requirements for the manufacture of steels operating at -30 ° C.

High-strength weldable Armco SSS100 5 steel is known, the composition weight percent of which is as follows: carbon, 0.13 to 0.20 chromium, 0.85 to 1.20 manganese, 0.40 to 0.70 molybdenum, 0.15 - 0.25 phosphorus, max 0.035 titanium, 0.04 - 0.10 sulfur, max. 0.040 copper, 0 to 0.40 10 silicon, 0.10 to 0.35 boron, 0.0015 to 0.0050 iron, to equilibrium (cf. CA Patent No. 753,190).

This steel is produced by Armco Inc. When sheets up to 32 mm thick have been hardened and released at high temperatures, the mechanical properties of this steel are as follows: yield strength: at least 685 MPa; tensile strength: 790 to 930 MPA; specific elongation: at least 16%; alahäviö surface; 20 at least 35%; -40 KV impact work; at least 26 J.

This steel is intended for the manufacture of ships, floating drilling rigs, pressure tanks, etc. Increasing the chromium and molybdenum content to 2.0 and 0.6%, respectively, makes it possible to produce plates up to 150 mm thick with a yield strength of at least 630 MPa. Such steel has high strength and good corrosion resistance in different weather conditions. Prior to welding, the steel according to the above-mentioned CA patent must be heated to a high temperature, which complicates the welding delivery, especially when assembling structures from thick steel parts.

The steel is intended to operate at temperatures above -10 ° C. Its behavior at lower temperatures is unknown.

35 The high-strength weldable 0X6102 steel produced by the Swedish SS AB is known. It is intended for use in the manufacture of 7 73468 structures for mining structures and floating drilling rigs. The composition of this steel in% by weight is as follows: 0.15 ° C; 0.36 Si; 1.25 iin; 0.051 V; 0.022 P, 0.004 S? 0.03 Cr; 0.01 Ni; 5 0.01 Cu, 0.004 N. At a thickness of 25 mm, its yield strength is 530 MPa, -4 0 tensile strength is 610 MPa, the specific elongation is 19% and the KV impact work is 80 J.

Fragile fracture tests show that at a thickness of 25 mm and a temperature below -20 ° C, 10 brittle crystalline fractures clearly appear. Impact tests on cracked samples at temperatures below -20 ° C show a sharp decrease in impact work.

The disadvantages described above do not allow the use of this steel for the construction of structures operating below -30 ° C. 15 High-strength weldable HY-80 and HY-100 steels developed by the United States Steel Corporation, NS-46 (HT-60) steel, developed by the Japanese Nippon Steel Corporation, A 553 (ASTM) steel and known others that behave quite well at temperatures below -30 ° C. An important disadvantage of these steels is their price due to the use of nickel, molybdenum and other rare alloying metals.

Thus, there are currently no high-strength weldable steels that would meet the requirements for heavy-duty structures such as hull plating of nuclear icebreakers operating at temperatures as low as -50 ° C and offshore installations operating below -30 ° C.

It is an object of the present invention to provide a high-strength weldable steel whose physical-mechanical properties overcome the corresponding properties of known steels, which would retain their physical-mechanical properties at temperatures down to -50 ° C under heavy load.

The invention provides a high-strength weldable steel containing carbon, silicon, manganese, ________ - τζ 8 73468 chromium, copper, nickel, molybdenum, aluminum, vanadium and iron, according to the invention, characterized in that its composition in% by weight is as follows: carbon 0.09 to 0.13; 5 pi, 0.20 - 0.40; manganese, 0.45-0.74; chromium, 1.05 - 1.30; copper, 0.20 to 0.65; nickel, 1.05 - 2.20; 10 molybdenum, 0.10-0.18; aluminum, 0.01-0.06; vanadium, 0.01 - 0.03; calcium, 0.005 - 0.050; phosphorus, <0.025; 15 sulfur, <0.025; iron balance

The composition of the steel above ensures reliable behavior of heavily loaded structures at temperatures below -30 ° C, under cyclic and dynamic loads and under the corrosive effect of seawater.

In the thickness range of 10 to 70 mm, the sheet steel described above has the following guaranteed physico-mechanical properties: 25 yield strength: at least 490 MPa; tensile strength: 570 to 710 MPa; specific elongation: 31 - 70 mm thick sheets: about 20% 10 - 30 mm thick sheets: about 18% 30 surface loss: at least -55%; -40 KV impact work: at least 47 J; fiber content at sample fractures at + 20 ° C: not less than -80 °.

In the thickness range 71 to 100 mm, the sheet steel shown above has the following physical and mechanical properties: 9 73468 yield strength: at least 440 MPa; breaking strength: 520 to 650 MPa; specific elongation: at least 19%; surface loss: at least -55%; -30 5 KV impact work: at least 47 J; fiber content at sample fractures at + 20 ° C: at least 65 °.

In the thickness range less than 40 mm, the steel according to the invention with brittle fracture stresses caused by dynamic cracks at 0.7 <{> q 2 3a temperatures up to -50 ° C.

10 In the thickness range less than 60 mm, it stops brittle fracture at temperatures down to -40 ° C. In the thickness range less than 70 mm, it stops brittle fracture at temperatures down to -30 ° C. In the thickness range less than 100 mm, it stops brittle fracture at temperatures down to -25 ° C.

In these respects, the steel of the present invention is superior to all known steels.

The invention also provides an alternative steel composition which differs from the previous one in that the sulfur content is 4 0.008% and the phosphorus content is 4 0.012%.

The physico-mechanical properties of the latter steel are even better. In the case of sheet steel 10 to 70 mm thick, the impact work at -50 ° C is at least 78 J. The specific elongation in the thickness range 31 to 70 mm is at least 21%. In the thickness range 10 - 30 mm, the specific elongation is at least 19% and the surface loss is at least 60%.

The structures welded from the steel according to the invention are resistant to brittle fracture. This new property 30 is also reflected in the area loss' p n of at least 35%.

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With a sulfur content of 0.008% and a phosphorus content of 0.012%, steel stops dynamic cracks more effectively.

In the thickness range less than 50 mm, it is guaranteed that the dynamic cracks stop at stresses at temperatures of 0.7 £ n 0 up to o υ'Δ -50 ° C. In the thickness range of 65 mm, dynamic cracks 10 73468 stop at temperatures down to -40 ° C. In the thickness range of 70 mm, dynamic cracks stop at temperatures down to -35 ° C.

Steel with reduced sulfur and phosphorus content is most preferably used in the manufacture of heavily loaded structures intended to operate at temperatures below -40 ° C.

An important advantage of the steel according to the invention is that in the thickness range less than 50 mm it can be welded using low-hydrogen welding materials without preheating. In this context, it should be emphasized that in the above-mentioned thickness range, HY-80 and Armco SSS100 steels have to be heated before welding, which means considerable energy consumption and the high cost of time-consuming structures.

The steel according to the invention is further advantageous in that it has better corrosion resistance than steels D32, E32 and E36.

The corrosion rate of the steel according to the invention in sea-20 water is 15-30% lower than that of the above-mentioned steels. Similar results are obtained in 14 m / s flowing water.

The excellent physical-mechanical properties of the steel according to the invention are combined with good ductility and machinability, which is extremely important in the manufacture of heavily loaded structures, such as offshore installations, ships, bridges, etc.

The excellent physico-mechanical properties of the steel according to the invention keep its behavior good under extreme conditions such as temperatures down to -50 ° C, heavy dynamic and cyclic loads and corrosive conditions.

The steel of this invention can be used effectively in the construction of various types of ships, including nuclear icebreakers, as well as offshore

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n 73468 to be used at temperatures up to -40 ° C. It can also be used in the manufacture of equipment for the chemical and energy industries.

To ensure all these advantages, the steel composition must be as described above. Changing the concentration of any one component affects the properties of the steel.

For example, reducing the carbon content to less than 0.08% affects the yield strength and tensile strength and can reduce impact work.

10 Increasing the carbon content above 0.15% increases the yield strength and tensile strength, reduces the elongation at break and the impact work, and affects the ductility.

Reducing the concentrations of silicon, manganese, aluminum, anadine, and calcium below the specified limits affects the steel production process and properties such as specific elongation, surface area loss, impact work, and dynamic crack stop ability. Increasing the concentration of these elements above defined levels affects ductility and machinability and reduces elongation and impact work.

Reducing the chromium, copper, nickel, and molybdenum contents below specified levels will affect yield strength and fracture toughness, surface loss, and impact work.

25 Increasing the concentration of these elements above the specified levels affects the weldability, raises the yield strength and reduces the impact work.

The present invention can be better understood by considering the following examples which illustrate the steel composition of the invention and its physical-mechanical properties.

Examples 1 to 5 are tabulated in Table 2.

The steel according to the invention is produced in a conventional manner. The production cycle comprises the following steps: 12 73468 - batch production; - steelmaking in steelmaking furnaces; - ingot casting; - heating the ingots before rolling; 5 - rolling of ingots into sheets; - heat treatment (hardening and emission).

The steel of this invention is produced in an induction furnace or any other type of furnace. The non-oxidizing alloying components, namely nickel, ferromolybdenum and copper, are added to the furnace with an iron charge. Other alloying elements are added before landing when the molten metal is at a temperature of 1,640 to 1,680 ° C. The oxygen scavengers are manganese and silicon, which are added before landing. The final deoxygenation is done in a ladle with aluminum-15 and solicocalcium.

Before lowering, the steel is at a temperature of 1,620 to 1,640 ° C, during casting, the metal is at a temperature of 1,595 to 1,605 ° C.

Prior to rolling, the ingots are heated to 1 220 -1 270 ° C. At the end of rolling, the temperature of the metal is 850 -20 950 ° C.

After rolling, the sheet metal is subjected to a dehydrogenation treatment, for which purpose it is cooled to 250-50 ° C and kept at that temperature for 2-4 hours. The metal is then heated to 650-25670 ° C and held for 6-12 hours, after which it is allowed to cool in air. The dehydration is carried out on sheet metal with a thickness not exceeding 33 mm.

Dehydrogenation treatment is not required in the case of vacuum degassing of steel.

30 The sheet metal is heat treated as follows: - at a temperature of 860 to 900 ° C, it is hardened in water; - it is discharged at 620 to 680 ° C - it is cooled in water.

The steel thus produced was tested with a view to examining its properties.

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Tensile and impact bending tests were performed according to standard methods.

The percentage of fiber in the steel was determined by performing static bending tests on samples with a cross-sectional area of 5 sheets of thickness and a free height equal to three times the thickness, but not less than 100 mm. The samples were 250 to 300 mm long. The% fiber was determined by measuring the plastic fracture area.

Robertson and Esso experiments were performed to determine the dynamic crack-10 stop temperature.

The chemical composition of the steel prepared as described in Examples 1-5 is tabulated in Table 2. The physical and mechanical properties of this steel are listed in Table 3. Its ductility properties are listed in Table 4. The crack cracking properties are listed in Table 5. The corrosion rates in seawater are listed in Table 6.

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Table 2

Chemical composition (% by weight)

Example C Si Mn Cr Ni Co Mo 5 I 2 3 4 5 6 7 8 1 0.08 0r20 0.45 1.05 1.05 0.65 0.10 2 0.09 0.36 0.68 1.27 1.80 0.23 0.14 3 0.11 0.26 0.60 1.23 0.59 0.59 0.10 10 4 0.13 0.40 0.75 1.30 2.20 0, 20 0.18 5 0.10 0.28 0.64 1.05 1.85 0.42 0.15

Table 2 (continued)

Example V AI Ca SPO Fe 15 —-- 9 10 11 12 13 14 15 tel Sci '"" 1 0.01 0.01 0.005 0.008 0.012 escape 2 0.02 0.02 0.028 0.010 0.021 20 3 0.02 0, 03 0.029 0.018 0.024 4 0.03 0.06 0.050 0.025 0.025 5 0.03 0.012 0.036 0.08 0.012 40.002 25 * Oxygen not determined

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Table 3

Physico - mechanical properties

Series Example Thickness Fracture No. mm limit strength 5 _______________________________MPa MPa 1 2 3 ~ 4 '5 1 1 10 542-550 667-686 22 50 504-588 686-699 10 5 5 40 555-596 705-752 44 70 562-591 707-752 55 50 490-559 650-670 6 40 520-540 650-676 15 7 50 520-556 640-652 8 70 520-512 650-658 9 100 510-520 642-628 20 Table 3 (to be continued)

Series Characteristic- Area- Impact work Area- Fiber No. elongation,% loss,% -50 ° C loss breakage and% + 20 ° TZ * C 25 _1__7 8 9 10 1 20.1-22.3 68.5-67.7 155-186 59.4-65.2 100,100 2 20.8-25.6 64.2-66.5 78-96 - 90 5 22.5-24.2 60.1- 62.7 98-112 - 100,100 30 4 21.0-25.5 59.4-65.2 78-97 - 90,100 5 25-24 65-68 196-205 55-55.56 100,100 6 25-24 62 -65 140-151 61-59.64 100,100! «7 3468

Table 3 (continued) 1 6 7 8 9 10 7 23-24 68-69.3 180-204 63-65.60 100,100 5 180-224 8 23-25 63-64 149-186 61-59.60 100,100 9 22- 23 64-69 172-222 56-57,55 100,100 180-224 10_______________ * In the samples, a V-shaped groove in the direction of rolling.

Table 4

Weldability with respect to preheating Temperature, ° C

Steel type Thickness, mm Preheating Temperature, __ 12 3 20 -

Example 5 50 Preheating does not meet the steel requirement 70 Drying the edges before welding. Pre-heating

25 between 50 and 60 ° C

100 Preheating in between

80-100 ° C

HY-80 max. 50 Preheating to 80 ° C 51 - 100 Preheating to 140 ° C

Armco SSS100 up to 30 Preheating to 50 ° C up to 90 Preheating to 150 ° C 17 73468

Table 5

Dynamic distortion stop information

Steel Plate charge Tension counter- Critical incl. Yield point for stopping temperature 5 ___ S_temperature, C ° _ E32 30 0,5 -20 E36 30 0,5 -20 N-Tyt 40 0,5 -30 10 0X602 20 0,5 - 15

Steel according to Example 5 50 0.7 -50 70 0.7 -35 15 Table 6

Corrosion rate in seawater

Steel Corrosion rate, mm / year in standing water 14mm / s in running water 20 --- D32 0.07 0.20 E 36 0.07 0.18

The steel of Example 4 0.055 0.15

Claims (2)

18 73468 High-strength weldable steel containing carbon, silicon, magnesium, chromium, copper, nickel, 5 molybdenum, aluminum, vanadium and iron, characterized in that it has the following composition in weight percent: carbon 0.08 to 0.13 silicon 0.20 to 0.40 10 manganese 0.45 to 0.75 chromium 1.05 to 1.30 copper 0.20 to 0.65 nickel 1.05 to 2.20 molybdenum 0.10 to 0.18 15 aluminum 0.01 to 0.06 vanadium 0.01 to 0.03 calcium 0.005 to 0.050 phosphorus <0.025 sulfur <0.025 20 iron rest. Steel according to Claim 1, characterized in that it contains <0.008% by weight of sulfur and <0.012% by weight of phosphorus.