FI73469B - HOEGHAOLLFAST, SVETSBART STAOL FOER FRAMSTAELLNING AV FASONGJUTSTYCKEN. - Google Patents

Description

High-strength weldable steel for the manufacture of shaped lamps 1 73469

The present invention relates to metallurgy and, more particularly, to high-strength, weldable steels for high-stress, shaped mass castings intended for use in low-temperature, heavily stressed structures. Examples of these critical structures are the basic or supporting pillars of self-supporting drilling platforms, in which case ingots made of this steel can be used as connecting parts.

In view of the highly critical nature and the difficult operating conditions, the following requirements are imposed on steels of this class: increased strength together with satisfactory weldability and good resistance to brittleness; good casting properties and good processability (machinability) in metallurgy, mechanical engineering and the shipbuilding industry.

In Japan, high-strength Cr-Ni-Mo-V steel STC-80 with a chemical composition of no more than the following mass percentages is used in the production of complex ingots with a complex structure, specially designed for self-supporting drilling rig connecting supports: C - 0.18; Si - 0.40; Mn - 1.0; Cu - 0.4; Ni - 2.5; Cr -0.6; Mo - 0.5; V - 0.08; and S and P - 0.020 (each).

Steel STC-80 is hardened to a thickness of 80-100 mm and after heat treatment its mechanical properties are as follows: 30 yield strength, MPa at least 700 tensile strength, MPa at least 800 relative elongation,% at least 15-50 impact energy, KV, J at least 35 surface sector reduction,% at least 35.

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The steel can be satisfactorily welded.

However, the above properties are obtained for this steel only in ingots with a wall thickness of up to 80-100 millimeters. With an ingot wall thickness of up to 5 mm, for example up to 200 millimeters, the hardening of this steel is no longer guaranteed and thus the required temperature-viscosity margin (Journal of Petsoleum Technology, July, 1980).

In the Federal Republic of Germany, low-alloy steel of the "Koesch GS Ark 10" grade with a chemical composition (percentage by mass) of: C not more than 0,15, Si - 0,150 - 0,50, Mn - 0 is used for the connecting parts of self-propelled drilling rigs; 85-1.70, Ni-0.90-1.20, S not more than 0.010, P not more than 0.020 Castings with a wall thickness of up to 15,500 mm give values of mechanical properties: yield strength - not less than 280 MPa, tensile strength - not less than 460 MPa, relative elongation - at least 30%, area reduction -50 at least 15%, impact energy, KV - at least 27 J. The weldability of this steel is satisfactory, (cf. Hoesch 20 Estel Huttenverkskontor GMBH, Berhardstrasse 23 D - 4000, Dortmund , West Germany, from Stahl und Eisen 102 (1982) No. 14).

In the United Kingdom, low-alloy steel with a yield strength of at least 320 MPa and a composition in weight percent of the following is used for these purposes: C - up to 0.18; Si - 0.10-0.50; Mn - 1.2-1.6; Ni up to -0.5; Mn down to -0.2; V - up to 0.08, Nb - up to 0.4 (Iron Age Metals Working Intern., 1982, 21.6).

However, Hoesch GS Ark and CSNB grade steel 30 cannot be used for heavily loaded ingots used at low temperatures (down to -30 ° C) due to its low strength and insufficient temperature-viscosity margin.

In Finland, grade 35 Vaculok F 60 is used for critical values, the chemical composition of which is as follows (mass

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3 73469%): C - 0.10-0.16, Si - 0.20-0.5; Μη - 0.90-1.20;

Cr - 1.10-1.40; Ni - 2.30-2.70; Mo - 0.25-0.40; Ai - 0.020, P - up to 0.020; S - not more than 0.010; Cu - not more than 0.25. The mechanical properties of the steel are as follows: 5 yield strength, MPa at least 590 tensile strength, MPa at least 720 relative elongation,% at least 15 area reduction,% at least 50 -40 impact energy, KV, J at least 30 10 (cf. "Rauma-Repola" company book).

This steel achieves the required level of strength and ductility, but is not sufficiently yielding at temperatures below 0 ° C.

Well-known grades HY-80 15 and HY-100 are used in several states for die castings for critical uses. The mechanical strength and formability of these steels are good enough to achieve proper performance at temperatures below 0 ° C. However, these steels achieve the required level of mechanical strength and ductility only in ingots with a wall thickness of up to 152 millimeters.

Of the prior art high-strength steels disclosed in the literature, which most closely correspond to the steel of the present invention in composition, are improved weldable steels (cf. USSR Invertor's Certificate No. 505738, Cl. C 22 C 38/00, 1974). with the following composition in percentage by mass: carbon 0.10-0.15 silicon 0.20-0.42 30 manganese 0.30-0.55 chromium 1.20-1.70 nickel 1.40-1.80 copper 0.40-0.65 molybdenum 0.20-0.10 35 vanadium 0.08-0.15 4 73469 cerium 0.02-0.10 aluminum 0.02-0.08 calcium 0.015-0.04 iron the rest.

5 The hardenability of this steel is insufficient in ingots with a wall thickness of up to 200 mm and thus its formability, especially at temperatures below 0 ° C, is insufficient.

The present invention is directed to the development of high-strength, weld-10 type steel for die casting by appropriately selecting alloying components having good casting properties and high formability at low temperatures up to thicknesses of 200 mm.

This object is achieved by means of a high-strength weldable steel for die casting, which steel contains carbon, silicon, manganese, chromium, nickel, copper, molybdenum, vanadium, cerium, aluminum, calcium and iron and is characterized in that it contains the following components: vina in percentage by mass: 20 carbon 0.09-0.13 silicon 0.15-0.30 manganese 0.50-1.00 chromium 0.40-0.70 nickel 4.00-4.80 25 copper 1.50 -2.00 molybdenum 0.25-0.35 vanadium 0.02-0.05 cerium 0.010-0.030 aluminum 0.010-0.035 calcium 0.005-0.08 sulfur less than 0.012 phosphorus less than 0.012 iron remainder.

The steel of the present invention guarantees complete hardenability throughout its thickness in ingots having I! 5 73469 wall, thickness up to 200 mm and the following mechanical properties: yield strength, MPa not less than 600 area reduction,% not less than 45 -50 5 impact energy, KV, J not less than 80

The amount of fibrous component in samples with a cross - section of 200 x 200 mm at 20 ° C is at least 100%.

The copper and nickel content in the steel of the present invention 10 has been increased to ensure complete hardenability throughout its thickness in ingots having a wall thickness of up to 200 mm. Copper also improves the flowability of steel. In addition, the increased concentration of nickel and copper in the steel causes an increase in the temperature-15 reserve of the workability of the steel, i.e. improving the resistance of steel to brittleness fractures. The contents of chromium and vanadium in the steel are limited compared to the prior art steel grade to improve its weldability.

After heat treatment, the level of strength, malleability-20 and formability properties of the steel is required, thus guaranteeing good performance in cast parts under periodic, dynamic loading conditions and the effect of seawater. The steel of the present invention can be welded to thicknesses of up to 70 mm at low temperatures without prior preheating in cases where austenitic electrodes are used; in cases where low-alloy electrodes are used, it is necessary to preheat to 60-80 ° C.

The machinability and other handling properties of the steel of the present invention are good in the fabrication steps associated with the fabrication of heavily loaded structures, for example, for support columns of self-supporting drilling rigs.

These properties of the steel of the present invention can only be guaranteed by accurately determining the proportions of ingredients to be added to the steel composition. By way of derogation from the limits set for at least 6 73469 components, steel with the above characteristics cannot be produced.

For example, if the carbon content is lower than shown, the tensile load properties and hardenability are reduced.

If the carbon content is higher than 0.13%, this causes an increase in the strength of the steel and a decrease in the deformation and forging properties, as well as a decrease in the hardenability, which is undesirable.

10 Reducing the concentrations of silicon, manganese, aluminum, vanadium, calcium or cerium below the above limits will have a detrimental effect on the grainability of the steel during the metallurgical stages of production and on the deformation and malleability properties of the steel. By increasing the concentrations of the above-mentioned elements above the above-mentioned limits, the weldability and processability of the steel deteriorate.

When the contents of chromium, copper, nickel and molybdenum in the steel are lower than the above-mentioned amounts, the hardenability of the steel and its deformation and forging properties of its tensile stress deteriorate. Increasing their concentrations above the above-mentioned upper limit impairs the weldability of the steel, improves its strength, but lowers forging.

In order that the present invention may be better understood, the following are some specific examples showing the composition of the steel, its mechanical and casting properties. Examples 1-15 are shown in Tables 1 and 2.

Steel ingots from the new steel 30 of the present invention are prepared according to a method comprising the steps of: preparing a batch of tl 7 73469; steel smelting in smelting units; pouring steel into castings; ingot cleaning; 5 previous heat treatment; removal of debris, casting heads and the like by cutting; pre-machining (if required); inspection of ingot quality to detect internal and external defects; 10 ingot welding repair; final heat treatment.

The steel is smelted in an electric furnace.

Non-oxidizing alloying ingredients, namely nickel, ferromolybdenum and copper, are added to the furnace together with the iron charge. The other alloying ingredients are added to the furnace prior to steel removal by draining into a ladle at a molten steel temperature of 1640-1680 ° C. The pre-deoxidation of the steel is carried out by means of aluminum, manganese and silicon in a furnace. The final deoxidation - modification of the steel with calcium, silicon calcium 20 and ferroserium - is carried out in a ladle.

Before the steel is drained, its temperature is 1620 -164 ° C. The casting of the metal into the molds is carried out at a metal temperature of 1580-1600 ° C.

It is advantageous if the steel is subjected to a vacuum treatment outside the furnace.

Shaking of the ingots out of the molds is performed at a temperature of 650-500 ° C, the ingots are then transferred to an oven heated to 600-550 ° C and an anti-flocculation treatment is performed according to the following scheme: slow cooling from 600-550 ° C to 300 ° C temperature, holding at 300 ° C for 10 hours, slow heating to 620-640 ° C, holding for 24 hours, after which the ingots are cooled in an oven.

The ingots are subjected to a pre-heat treatment according to the following scheme: 8 73469 1. homogenization at 1160 ° C 2. tempering at 600-620 ° C 3. normalization at 920-960 ° C 4. tempering at 620-640 ° C 5 Final ingots the heat treatment is performed according to the following scheme: 1. Water cooling from 880-910 ° C 2. Temperature at 620-640 ° C, water cooling. After the heat treatment, ingots with a cross-section of 10,200 x 200 cm and ingots were cut into samples for testing, with the samples being cut across the entire thickness of the ingot and ingot.

The determination of the mechanical and casting properties of the steel was performed following the following standard procedures. The 15% crack in the fibers was determined by testing the static deflection of the samples with a cross section of 200 x 200 mm. The amount of fibrous component was determined by the area of the flexible crack.

The critical brittleness temperature (T ^) was determined to perform a series of 20-bar impact tests on V-notched samples at temperatures ranging from + 20 ° C to 120 ° C. The evaluation criterion for determining the T ^ value is the presence of a 50% crystalline (brittle) component in the cracks of the samples.

Tables 1 and 2 show the chemical composition, description of the crack type, mechanical tensile strength, impact energy at + 20 ° C and -50 ° C, critical brittleness temperature, casting properties and weldability (analyzed by carbon equivalent) for five annealing of the steel of the present invention and three annealing. Inventor's Certificate 30 No. 505738 Cl. 22 C 39/00, 1974.

The values in these tables indicate that said USSR Inventor's Certificate No. 505738 steel in ingots with a thickness of up to 200 mm does not guarantee complete hardenability over the entire thickness and thus the required level of ductility and malleability, in particular below 0 ° C.

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9 73469 side temperatures. It follows from the above that the use of this steel in die castings with a wall thickness of up to 200 mm is impossible, because during use these castings are subjected to considerable static, svkli-5 and impact stresses at temperatures up to -30 ° C.

The steel of the present invention can be completely hardened throughout its thickness in ingots having a wall thickness of up to 200 mm and having good strength and ductility with good resistance to brittleness at temperatures below 10 ° C.

table 1

For example, mass fraction of elements,% 12 No Carbon Silicon Man- Chromium Nik- Kupa- Molybganic gelide 12 545 6 7 Q 9 I. Steel according to the invention 20 1 I 0.09 0.15 0.50 0.40 4.00 1.50 0.25 2 2 0; 11 0.23 0.75 0.62 4.50 1.71 0.52 3 3 0.15 0.50 1.00 0.70 4.80 2 .00 0.55 4 4 0.12 0.20 0.91 0.60 4.51 1.95 0.27 25 5 5 0.10 0.29 0.99 0.57 4.50 1.96 0 .29 2. Steel in accordance with USSR Inventor's Certificate No. 505738 6 0.10 0.20 0.32 1.20 1.44 0.41 0.22 30 7 0.12 0.51 0.45 1.50 1.60 0.52 0.25 8 0.15 0.41 0.54 1.70 1.79 0.65 0.50 10 73469

Table 1 continues

No Vana- Alu- Calcium Serium Sulfur Phosphorus Iron diamine mine 5 _ 10 11 12 13 14 15 16 I. Steel according to the invention 1 Oy02 0j010 0.005 0.010 0.008 0.005 remaining 10 2 0j02 Oy021 0.010 0.019 0; 012 0.003 remaining 3 0.05 0r035 0.080 0j030 0; 011 0.003 rest 4 Oy04 0y012 0y025 0.011 0; 005 0.010 rest 5 0703 Oy030 0; 035 Oy025 0; 008 0.007 rest 15 2. Steel according to USSR Inventor's Certificate No. 505738 6 0y03 0.020 0; 015 0; 022 0; 008 0; 006 remaining 2Q 7 0.12 0.052 0.020 0; 045 0.012 0.005 remaining 8 0.14 0.073 0.040 0.050 0.014 0.008 remaining

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11 73469

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Table 2 continues

No. Critical Casting properties at 1Q0 ° C 5 brittleness- Linear- Fracture Shrinkage Liquid- Carbon flux- temperature resistance volume flow valence oq shrinkage accumulation- λ mm ^ Cvunits ^ nuclear, aperture-yfs * f kg and 1 0 TT cf vp »/ en no nn 12 i3 ή 15 n -noo 1; 84 50 ^ 0 2f1 180 0; 42 2 -noo n? 84 51 ^ 0 2; 2 n70 oy57 3 -noo n? 82 50 ^ 0 zf2 177 0; 65 4 -noo n ^ 83 52 jo 2 ^ n 185 of57 20 5 -noo n ^ 8? 51 yo ZjZ n82 o ^ 57 Steel according to USSR Inventor's Certificate 6 0 1779 52; o 2; o neo or57 7 0 1; 75 51; 0 2.1 185 o; 64 25 8 -20 1; 81 50; 0 2; 3 175 0; 72

Note. 1. Test specimens were cut to the full thickness of the ingot.

2. Ingots with a cross section of 200 x 200 mm 30 were heat treated under the same conditions.

3. Test results are averages of 3-5 values.

4. The carbon equivalent is calculated by the formula: c, -1,1, - = c + iy, sI + -? Mn + -7rtNi + | cr-4Mo + i V.

units 24 6 40 5 4 14

Claims (1)

High-strength weldable steel for die-casting, containing carbon, silicon, manganese, chromium, nickel, copper, molybdenum, vanadium, cerium, aluminum, calcium and iron, characterized in that it contains the following constituents in the following percentages by weight: carbon - 0.013 silicon 0.15 to 0.30 10 manganese 0.50 to 1.00 chromium 0.40 to 0.70 nickel 4.00 to 4.80 copper 1.50 to 2.00 molybdenum 0.25 to 0, 35 15 vanadium 0.02 - 0.05 cerium 0.010 - 0.030 aluminum 0.010 - 0.035 calcium 0.005 - 0.08 sulfur less than 0.012 20 phosphorus less than 0.012 iron balance