HU191191B - Weldable durable construction-steel with big solidity - Google Patents

Abstract

The strength and toughness of the steel according to the invention is greater than that of structural steel commonly used for similar purposes, and can also be well machined by cold and hot-work processes, mechanical and heat-resistant, and resistant to atmospheric corrosion without preheating and preheating. The steel composition is as follows: C = 0.003-0.05% Mn = 1.5-2.0% Si = max. 0.35% P = max. 0.025% S = max. 0.010% Nb = 0.08-0.12% Al = max. 0.12% Cr = 0-2% Mo = 0.3-0.5% N = max. 0.018% -1-

Description

The present invention relates to a high-strength, tough and weldable structural steel comprising hot and cold forming tubes containing manganese, molybdenum tubes containing chromium alloys and aluminum and niobium micro alloys.

Recently, the strength requirements for metal structures, especially for tank piping materials, have increased significantly, particularly for weight loss. Equipment for the chemical, petroleum and energy industries, various hall structures, vehicles are generally made by welding, forged or rolled rods, profiles and sheet materials. Load bearing, stiffness and durability are essential requirements for such equipment.

By increasing the load-bearing capacity and durability, the structure is easier to breathe with adequate plastic deformation capability. A further requirement is fracture safety, which can be achieved by providing adequate fracture toughness. However, fracture safety is generally not taken into account today when selecting the material. The design material characteristic for static stress is the value of the yield point minus the safety factor. However, this safety factor is now known to be inadequate and insufficient to determine the breakdown safety of the structure. Fracture safety is assumed to be the fault of the most unfavorable position and size - cracking, unheated gas bladder, inclusions, etc. and calculated based on the quasi-static fracture toughness of the material. Assuming propagating fracture, fracture stopping is assured in a similar manner, but based on dynamic fracture toughness. The property of the material is also referred to as fracture mechanical properties.

An important characteristic of structural materials used in technical practice is the economic indicator, which is the ratio of the allowable stresses to the unit price. Obviously, this index can be increased if we can produce high-slip steel cheaply. Of course, other factors need to be taken into account to determine cost-effectiveness. These include transport and technology costs, where weight loss also plays an important role.

Several grades of steel have been developed to meet, at least in part, the above requirements. These steels contain manganese and silicon as well as many other alloys that are sorted according to the desired purpose. Such steels are described, for example, in U.S. Patent Nos. 2,157,305, 2,320,185, 2,407,338, United States Patent Nos. 4,137,104, and U.S. Pat. No. 1,491,729. These steels usually contain copper and / or nickel in addition to the alloying elements listed in order to achieve the listed properties.

However, the complexity of the requirements listed and the relative contradictions of the individual conditions have not yet enabled all the requirements to be met at the same time. The simultaneous increase in strength and toughness has so far been limited, the materials often cracked after welding and are generally quite expensive due to the high number of alloying ring.

The object of the present invention is to provide a high-strength weldable structural steel which has greater strength and toughness than structural steels commonly used for similar purposes, and is well machined by both cold and hot forming processes, resistant to mechanical and thermal fatigue and corrosion resistance. cs can usually be welded without preheating.

This problem was solved by the discovery that increasing the strength in iron-based alloys can be solved by anti-slip effects of the crystal lattice, e.g. At the same time, the deformability can be controlled by reducing the particle size, increasing the number of sliding planes, providing deformable particle boundaries, and preventing the formation of large brittle phases.

In this way, the favorable properties of a given alloy can be ensured by optimum selection of the amount of each dressing clcmck.

In the present case, the object of the present invention is solved by providing the alloy according to the invention with 0.003-0.05% by weight of carbon, 1.5-2.0% by weight of manganese, up to 0.35% by weight of silicon, up to 0.015% by weight of phosphorus, 0.01% by weight. sulfur, 0.08 to 0.12% by weight of niobium, 0 to 2% by weight of chromium, up to 0.12% by weight of aluminum, 0.3 to 0.5% by weight of molybdenum, air up to 0.018% by weight of nitrogen and residues. partly contains iron.

The alloy thus formed fulfills the above mentioned conditions: at the same time with high strength and toughness! has both a hot and cold base and, apart from special sizes, can be welded without preheating. In addition, it is resistant to atmospheric corrosion.

Further details of the invention are given by way of exemplary embodiments.

The steel of the present invention was prepared in four different doses. Their chemical composition is

Table 1 shows By way of comparison, Table 1 shows several conventional and standard steels in the same category.

Test specimens were prepared from the variants of the steel of the invention shown in Table 1 for mechanical testing. The results of the mechanical tests are shown in Tables 2,3 and 4. The tables show the appropriate properties of the materials standardized for similar purposes as shown in Table 1, except that the strengths of such tests are not known for other steels.

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Table 1

Chemical composition (% by weight)

Signal c Mn Ski P S Mo cr Al. V Ni Cu Cb Nb Β N 1 0.03 1.52 0.30 0.10 0,008 0.45 0.20 0.08 - - - 0.09 - 0.013 2 0.04 1.74 0.32 0.011 0,007 0.48. 0.25 0.12 - - 0.09 - 0.009 3 0.05 1.83 • 0.35 0,013 0,008 0.48 0.40 0.10 - - - 0.10 - 0.013 I ⁴ 0.05 1.78 0.34 0,015 0.01 0.40 0.90 0.12 -, - - 0.11 - 0.007

MS 6280

E 420 E E 460 E o, l8 0.18 1.7 1.7 0.15 to 0 35 0.15 to 0 50 0.03 0.03 0.1 0.03 0.3 0.4 0.3 1.5 0.3 mikroölvözött alloyed 1.5 0.3 SVENKST STAL 0 χ 602 0.12 1.35 0.3 0.02 0,004 0.15 0.05 - - 0x812 0.13 1.35 0.3 0.02 0,004 - - - 0.05 - - 0,002

IPSO Canada

5 0,047 1.69 0,021 0,012 0,016 0.25 - 0.21 0.25 0,058 - - LS-x 70 ± 0.007 ± 0.12 ± 0.006 ± 0.003 ± 0.003 ± 0.02 - ± 0.06 ± 0.03 ± 0.01 5 0.042 1.61 0.042 0.011 0,014 0.24 - 0.21 0.21 0.062 - - LS-x65 ± 0.01 0.09 ± 0.012 ± 0.002 ± 0.003 ± 0.02 - - - ± 0.03 ± 0.4 ± 0.009

Table 2

Results of tensile tests at room temperature

Sample yield point Rpo.2 (N / mm ² ) tensile strength R _m (N / mm ² ) elongation at break A ₅ (%) contraction Z (%) 1.1 560 799 17.2 59.0 1.2 564 799 17.0 57.7 · 1.3 564 796 16.4 56.5 2.1 570 786 17.8 58.0 2.2 570 788 17.8 57.2 2.3 568 810 17.2 58.0 3.1 638 762 16.3 60.4 3.2 640 762 16.4 58.2 3.3 640 760 16.4 58.4 4.1 560 820 18.2 58.4 4.2 562 820 15.3 59.3 4.3 560 814 17.2 56.4 E 420 E 420 510-680 19 E 460 Ft 460 550-730 17 - 0x602 490 590-5 'O 16 - 0x812 690 780-930 16 - 5 LS - x65 518 ± 16 ± 637? 4 33 ± 2 - 5 LS - x70 522 ±! 6 667 ± 77 31 ± 2 -

Note: 3 3 test specimens were used to test the material for batches 1-4.

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Table 3

Tests for hot silicaria

Sample Temperature (° C) yield point R _p0 , 2 (N / mnf) tensile strength Rm (N / inm ² ) elongation at break A ₅ (%) contraction Z (%) I / I 200 628 755 17.0 59.2 1/2 250 598 726 17.0 56.0 1/3 300 * 558 775 16.5 54.2 1/4 350 596 814 19.0 56.2 1/5 '400 573 794 16.4 55.0 1/6 450 549 755 16.4 55.0 1/7 500 541 669 15.5 54.3 2/1 200 630 780 17.0 55.3 2/2 250 628 726 17.2 54.7 2/3 300 625 730 17.4 55.3 2/4 350 570 610 17.0 54.7 2/5 400 565 605 17.0 55.2 2/6 450 580 615 17.4 55.0 2Π 500 562 610 18.2 55.0 3/1 200 620 680 17.2 58.2 3/2 250 620 684 17.4 58.4 3/3 300 615 680 17.0 55.2 3/4 350 610 670 17.6 '59 2 3/5 400 625 665 17.2 56.4 3/6 450 580 642 17.4 54.3 3/7 500 575 638 17.0 53.0 4/1 200 580 664 17.0 57.4 4/2 250 578 664 17.6 57.2 4/3 300 578 662 17.4 59.4 4/4 350 560 644 17.4 58.0 4/5 400 540 620 19.2 58.2 4/6 450 545 620 18.2 57.4 4/7 500 520 580 17.0 54.2

Table 4 Ülővizsgálat Signal test temperature (C ·) Seated work KV (J) 1/1 + 20 110.4 1/2 108.6 2/1 120.0 2/2 122.2 3/1 120.8 3/2 130.2 4/1 115.4 4/2 116.9 1/3 ± 0 100.2 1/4 107.0 2/3 118.0 2/4 114.0 3/3 113.0 3/4 118.4 4/3 110.2 4/4 112.0 1/5 -20 68.4 1/6 ' 66.8

Signal test temperature (C) Impact KV ü) 2/5 84.2 2/6 84.4 3/5 -20 66.8 3/6 64.0 4/5 80.2 4/6 74.2 1/7 -40 42.4 1/8 44.6 2/7 54.0 2/8 50.2 3/7 . 53/1 · 3/8 44.8 4/7 60.8 4/8 64.2 E 420 E -50 > 27 E 460 E -50 '> 27 OX 602 -60 > 39 OX 812 -40 > 39 5 LS-X 65 -43 + 04 + 16 5 LS - X 70 - 18 77 ±! 5

-4Ί

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When comparing the data in the above tables with those of the steels disclosed in the prior art patents, it can be seen that some of the mechanical properties of the steels according to the invention are generally better than those of the prior art. they have significantly better properties in terms of use, ie they fulfill the requirements listed in the introduction to a large extent.

The steel of the present invention is cold-drawn and heat-hard, and can be machined well by conventional cold and hot forming processes.

The resistance of the material to mechanical and thermal fatigue is not excellent in bulk welding processes without pre-heating. It is well-resistant to atmospheric corrosion and is known as so-called "corrosion" during normal enamelling processes. can be applied without risk of white peeling.

The steel sheet according to the invention has isotropic properties.

The above favorable properties were achieved by selecting the alloying elements from theoretical analyzes by cs experiments. The mechanism of action of the alloying elements we employ is described below.

In the structural steel type we propose, molybdenum exerts its most significant effect by delaying the time of conversion of austenite, so that the tissue structure of the naturally occurring product becomes needle ferritic by extending the incubation time. Mo inhibits the polygonization of the particles. Mo-free steels of similar composition have a coarse-grained structure with polygonal ferrite and nearly 100 wt.% Of lithium with a Mo content of about 0.5%.

Mo has a granular abrasive effect as, like other substitutional alloys, it prevents the recrystallization of deformed austenite and thus forms a refined ferritic substructure. The resulting fine granular, perlite-free tissue structure is reinforced by a substitution dressing. The critical alloys of the substitutional alloys are increased in proportion to their atomic percentages.

Thus, Mo dissolved in α-iron alters the properties by increasing the α or lattice parameter due to the difference in the atomic radius of the noble element.

r _FE = 1.27 Å and r _Mo = 1.40 Å. Other space requirements of dissolved atoms result in greater "roughness" of the sliding planes. The slip resistance increases, and the translational trigger voltage increases. However, the deformability and toughness are similar to non-ferrous metals in the solid solution because the substitutional alloying elements do not deprive the solvent metal crystals of their sliding planes. 9 atomic percent Mo increases the yield strength by 160 N / mm ² for steel.

The creep limit of steel is most strongly increased by Mo and Cr, and high-flow steel up to about 600 'C is a better alloying element of air. The fatigue stresses at T <atan increase Mo the best.

It is known that the elements to the left of the iron in the periodic table are carbide-forming, the more strongly the higher the period number and the less the d electron shell is filled. Mo is thus more potent carbide-forming than Mn or Cr, but less so than W, V, Nb, Ti, Zr or Hf.

Mo-like alloying elements are similar to Mo's listed properties so far. Higher nickel content also results in a high tensile strength structure in air-cooled steels.

Mo itself has the ability to exert a complex effect that can only be produced by more alloying elements and has the unique property of reducing reversible softening aging. If Cr-Ni steels are exposed to temperatures of 500-600 ° C for extended periods of time, their toughness will be significantly reduced. The developed hot-solid steel type is also recommended for applications where the operating temperature is around 500-600 ° C. We chose Mo as a base alloy, as opposed to the previous U.S. Patent Nos. 2,407,338 and US 3,386,862, U.S. 1084,231 and US 2,157,305. alloys in which the base alloy has various nickel and copper added in significant amounts.

Manganese, nickel, tungsten, and the like, alloy steel alloys, the greater the solubility in austenite, the greater the time to the beginning and the end of the conversion. The effect of manganese is stronger than that of nickel: 2% by weight of Mo corresponds to about 4% by weight of nickel.

Mn is soluble in iron. The potency of the substitutional solid solution according to the mechanism of action already described for Mo is three times greater than that of molybdenum. The manganese content we specify at a maximum of 2% by weight results in a strength increase of about 120 N / mm ² .

Manganese also contributes significantly to inhibiting the conversion to polygonal ferrite, and this effect is exerted by molibdcnncl. It also decreases the tendency for early Nb (C, N) precipitation in austenite with molybdenum. It also has a clear effect on toughness.

Even with a maximum of 2% by weight of chromium, the creep limit of the developed steel type is significantly higher than that of either normalized ferrite perlite or refined steels.

However, chromium is only alloyed when we need steel with high creep strength.

Chromium, molybdenum and manganese have a very strong effect in the needle-spherical rather than perlite or martensitic transformation. It exerts its strength enhancing effect as a substitutional and carbide-forming alloying element.

Up to 0.35% by weight of silicon in the steel is allowed. In large quantities, it is very damaging to the mechanical properties of steel. Forms polygonal ferrylet, highly localizing slip lines.

Not only does it increase the brittle transition temperature, but it also reduces the yield point. Its effect is only in the addition of an additional alloying element, nickel, molybdenum or manganese

191 191 can be balanced. This is also the case with the alloys disclosed in the patents mentioned above.

Carbon (iron carbide) and carbides of various carbide-forming alloys have previously played a major role in increasing the strength of steels. Technological advances have made it possible to develop low-carbon steels, which have brought about a quality change. These steels have excellent toughness, strength, weldability and formability, but do not provide strength enhancement in the conventional way. An increase in carbon content (C> 0.05 wt.) Increases the strength and reduces the toughness.

Generally, a rise in carbonate content of greater than 0.05 lmcg% results in an increase in the content of perl of 8 llccg per 0.1%. 10 mass perlite of 17 N / m ^{2 2} cl raises the yield point, but also increases the transition temperature by 50 C 'and significantly reduces the maximum impact work. The amount of carbon is therefore kept at the minimum value required to produce the precipitates of niobium carbonitride at cs0.05% w / w. The knbbon-niobium ratio is always less than 1.

Niobium is also an effective microalloy of thymerite steels:

refines the ferrite particles and forms an intermetallic phase.

Its refining effect also strongly depends on the temperature and duration of austenitization. The properties of low Nb (0.04 wt) steels do not change with the austenitization temperature.

For steels with a higher Nb content (> 0.04 wt.), The austenitization temperature has to be determined very accurately, with austenitization at 1180 ° C without significantly reducing the toughness. A lowering of the austenitization temperature below this will sharply reduce the yield point. When austenitized at 1120 ° C, the mechanical properties of the steel are similar to those of the low Nb content, so the excess alloying element is added unnecessarily. The effect of Nb on the yield point varies with the ferrite size. For a particle size of 0 µg, for a particle size of Nb 10 Å, an increase in yield strength of 250 Nmm ^{J is obtained} , while for a particle size of 0.05 mass, for a particle size of 120 N, an increase of 120 N / mm ^{2 is obtained} . It exerts its effect by precipitating Nb (C, N). Namely, Nb forms carbonitrides depending on the amount of carbon and nitrogen in the steel. The size, volume and spacing of these particles are decisive for the mechanical properties of steel. The particles may precipitate in the ferrite during the α-γ conversion of the austenite.

The austenitic fine coarse particles of 100-2000 A have very little effect on increasing the strength.

In the ferrite phase, the secretion of Nb (C, N) depends on the thermodynamic conditions, the diffusion capability of the alloying atoms, the degree of supercooling, and the condition of crystal germ formation.

The size of the precipitates produced increases with the temperature and the firing time.

One of the functions of the alloyed Mn is to reduce the precipitation in the austenite. It has this effect together with molybdenum, with a larger amount of niobium remaining in solution in the austenite to produce Nb (C, N) precipitates in the ferrite.

Sulfur is extremely harmful to toughness! properties. Increasing inclusions will greatly reduce toughness. However, the incidence of inclusions to the transition temperature is not so obvious. As the sulfur content increases, the depreciation of the striker will be much greater in the transverse direction than in the longitudinal direction. Anisotropy (the mechanical properties of steel give different values in the tilt and longitudinal direction) severely limits the usefulness of the steel, because the structure can only be designed on the basis of the most unfavorable veins in the three directions of space. Some patents have attempted to reduce anisotropy by adding zirconium, cerium, and other rare earth metals, but the result is not clear enough. Although anisotropy is reduced, but 0.15 weight percent zirconium can increase the brittle transition temperature by 50 ° C. Therefore, we follow the procedure of adjusting the sulfur content to 0.01 wt.

The amount of nitrogen in the alloy affects the dissolution of Nb (C, N) in the austenite by changing the C-N ratio in the Nb (C, N) phase. Its solubility in austenite decreases with increasing volume. As a result, early Nb (C, N) precipitations are formed in the austenitic state, so they are detrimental to a certain amount (N> 0.01 wt.) By reducing the amount of niobium that is then required for Nb (C, N) precipitation in ferrite. .

At higher N contents, the strain on the steel is reduced. Nitrogen is present in unwanted impurities in the thymerite steel in excess of the amount required for Nb (C, N) precipitation. If the nitrogen content is significantly higher than 0.1 weight, the toughness-toughness will be adversely affected! and balance. At this point, as the amount of niobium carbonitride precipitates on the thymerrylbn, a microstructure containing large amounts of polygonal ferrite is formed. Therefore, the nitrogen content should be kept to the lowest possible level.

From the foregoing it can be seen that by restricting the individual ingots to stricter limits than usual, and by the application of properly selected alloys, very good steels can be produced.

The composition of the present invention achieves a higher strength and toughness of the steel than previously used weldable structural steels for similar purposes. In steel, contaminants are formed in the most favorable form from a close morphological point of view, the steel is cold-drawn, hot-solid, good by the usual cold and hot forming processes! machinable, excellent mechanical and thermal fatigue resistance.

In welding, even without preheating, the tendency to crack is considerably lower than that of hitherto used perlite materials. It is resistant to atmospheric corrosion and can be enamelled without the slightest risk of lacquering in the usual enamelling process.

The steel plate has isotropic properties.

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Table 5

Sample Chemical composition (%) C Mn Si S P Mo Nb cr A is 0.05 1.9 0.32 0.01 0.02 0.45 0.10 1.9 B, 0.03 1.5 0.30 0.006 0.01 0.42 0.08 0.2

Table 6

Mechanical properties

Sample flow tensile elongation contra-impact work hardening help

Rp.oifN / R _m A _s (%) Z (%) kV (J) mm ² ) (N) mm ²

THE 640 850 13 55 45 (-20 'C) B 510 812 21 63 44 (-70 'C)

These favorable properties are provided to a greater or lesser extent by all steels in the range described, but some properties within the range may be shifted in the desired directions. For example, a high strength alloy can be created, but its use is recommended only at ambient temperatures down to -20 ° C. Alternatively, steel may be formed which provides one and a half times the conventional yield point, but the tough-brittle transition temperature is already about -70 ° C. The above is illustrated in Tables 5 and 6, where the chemical composition and mechanical properties of two steels with extreme properties are shown.

Claims (1)

Claims 1. High strength, tough, weldable structural steels, manganese, molybdenum and chromium alloys, as well as aluminum and niobium micro alloys, which can be hot and cold formed, characterized in that: 0.03-0.05% by weight of carbon, 1.4-2.0 tömegszá- vol manganese, at most 0.35 by weight of silicon, at most 0,015 % by weight of phosphorus, at most 0,010 weight percent smear, 0.08 to 0.12% by weight of niobium, 0 to 2.0 chromium by weight, at most 0.12 aluminum by weight, 0.3-0.5 % by weight of molybdenum, at most 0,018 nitrogen oxides and the remainder contains iron.