FI122143B - Procedure for the manufacture of a high-strength galvanized profile product and profile product - Google Patents

Description

Method for the manufacture of high strength galvanized molded product and molded product

Background of the Invention

The present invention relates to a process for the preparation of a high-strength galvanized molded product having a composition by weight of C: 0.04-0.10%,

Si: <0.03%

Mn: 0.3-1.2% 10 Nb: 0.015-0.10%

Ti: <0.03% N: <0.01% P: <0.02% S: <0.02% 15 Al: 0.01 - 0.08% V: <0.05% with iron remaining , inevitable impurities and residues.

The invention also relates to a high-strength molded article having the above composition and excellent hot-dip galvanizing.

For example, structural solutions in the construction, transportation and lifting equipment industries tend to use stronger grades of steel, since high-strength steels can achieve structural weight savings and thus reduce product manufacturing, fuel and ___ transport costs, among other things. In addition, steel structures must be protected against corrosion, whereby hot dip galvanizing is used as an effective and economical way to apply a zinc coating that protects the steel surface against corrosion. Zinc coating protects i g steel for hundreds of years, depending on the environment and the thickness of the layer.

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However, the use of hot-dip galvanizing in the coating of high-strength structural tubes is problematic due to various brittle phenomena such as molten metal brittleness at the corners of the cold-formed g 30 molded products, which have been subjected to residual stresses after cold forming. Exposure of the hot-formed zinc die to the hot-formed zinc die results in a crack in the inner corner of the traditional high-strength steel form products. Post-bending back elongation provides a local tensile stress peak in the inner corner of the bend, which also increases the risk of molten metal embrittlement.

Residual stresses in the cold formed steel formulation can be removed by post-molding heat treatment or surface modification, but is not advantageous in industrial scale production requiring additional work.

In addition to the residual stress on the molten metal brittle, the other important factors are the composition of the molten zinc bath and the properties of the steel. At worst, the wrong steel composition causes tearing in the corners of the molded product during the hot galvanizing step. Thus, the production of high-strength galvanized steel formwork has been a problem model and yield strengths have traditionally remained in the order of 355 MPa.

It is known to increase the strength of steel by increasing the carbon or alloy content, but increasing the carbon or alloy content increases the hot-dip galvanizing of the steel. One way to estimate the resistance of steel to hot dip galvanizing is to calculate the LME index of the steel: LME = 201-370C-22Si-51Mn-35P + 33S-28Cu-22Ni-87Cr-15 123Mo-275V-182Nb-82Ti-24AI + 1700N-155000B the index value indicates an increased tendency for molten metal brittleness. High alloying in the index is observed to increase the tendency for molten metal brittleness. Further, the high carbon equivalent of steel increases the brittleness of the molten metal.

Japanese Patent Publication JP8232041 discloses a steel composition for forming a thick-walled, strong and galvanized structural tube having a carbon content of C of 0.04 to 0.12%, <0.05% Si, 0.2 to 2.0% Mn, and 2 or more of the following alloys <0.08% Nb, < 0.08% V and <0.05% Ti. According to the publication, <0.05% Si improves resistance to w brittleness. Further, according to Euronorm 10025-2, steel with a silicon content of 0.03 to 0.05% is poorly galvanized, as it moves through the so-called Sandell i c3 25 zone, where the thickness of the zinc layer increases uncontrollably. According to the reference publication The dielectric strength of the galvanized galvanized structural tube is up to 460MPa and this is. high strength classes (greater than 460MPa) and high impact strength according to the invention are not achieved by teaching according to JP8232041. Further, the publication does not teach to control the additive concentrations of O) o zinc bath to achieve better zinc sealing, whereby the success of hot galvanizing of the structural tube is uncertain.

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BRIEF DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a hot dip galvanizing die for high yield strengths from 460 MPa to 600M Pa, which withstands the stress caused by hot dip galvanized molten metal. Another object of the invention is to provide a novel process 5 for the preparation of a high-strength and galvanized steel formwork in which the steel does not require significant amounts of anti-galvanizing and cost-increasing alloying elements. Further, post-cold forming stress relief effects or other post-treatment steps need not be performed.

According to the invention, it has surprisingly been found that by direct quenching the steel of said composition achieves a high-strength steel with good impact strength properties with excellent hot-dip galvanizing properties.

To accomplish this, the method according to the invention is characterized by what is mentioned in the characterizing part of independent claim 1. Preferred embodiments of the process according to the invention are set forth in claims 2 to 7. The hot-dip galvanizing preparation of the invention 15 is characterized by what is defined in the characterizing part of independent claim 8. Preferred embodiments of the hot-sealable mold preparation of the invention are set forth in claims 9-16.

The major advantages of the process according to the invention are that it enables hot-dip galvanized high-strength steel with excellent impact strength. Further, wet quenching speeds up production throughput without having to wait for the coil to cool.

5 The major advantages of the steel mold preparation according to the invention are that it has a high

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Tough hair combined with good impact resistance and can be excellently hot zinced.

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BRIEF DESCRIPTION OF THE DRAWINGS

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The figure shows the main steps of the method according to the invention.

00 00 g Figure 2 shows a shaped product according to the invention, a square ° structural tube.

Fig. 4 shows a shaped article according to the invention which is a square structural tube; and

Figure 3 shows another rectangular structural tube 1 of the shaped article according to the invention.

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DETAILED DESCRIPTION OF THE INVENTION

The following describes in detail the steps of the method according to the invention, of which the steps relevant to the invention are shown in Figure 1.

After austenitizing annealing, the steel billet is hot-rolled at a temperature of 950 to 1280 ° C to a thickness of typically 25 to 50 mm, from where it is immediately transferred to a strip mill where it is rolled into a strip having a final thickness of 2 to 14 mm. Preferably, the final thickness of the steel strip is at least 4 mm. It is also recommended that the final thickness should not exceed 12.5 mm.

The number of stitches in a strip mill is typically 5 to 7. In strip milling, the last-15 stitching is carried out at a temperature in the range of 760 to 960 ° C, preferably in the range of 850 to 920 ° C, especially if the strip is relatively thin, whereby the rolling forces remain lower.

After the last stitch, the steel strip will be extinguished directly within 15 seconds. At the start of direct quenching, the temperature of the steel strip should be at least 700 ° C. Swamp-20 fire extinguishing is carried out by water quenching with a quench rate of 30-150 ° C / sec, preferably up to a maximum of 120 ° C / sec. The direct quenching is carried out at temperatures up to 300 ° C, preferably up to 100 ° C. Immediately after the direct shutdown, the steel strip is wound up. The winding temperature can thus occur in the temperature range of 30 to cv 300 ° C. Preferably, the initial winding temperature is up to 100 ° C, because when winding 25 steels at temperatures above 100 ° C may form a discontinuous vapor mattress on the steel surface which complicates the process.

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As a result of said thermomechanical treatment, the microstructure of the steel is homogeneous and consists of a power phase, preferably low carbon ferrite and / or low carbon bainite. The power phase is typically greater than 90%. Thus, there is very little carbon rich bainite and / or glacial asenite and / or martensite as very small carbon rich islands. It is also essential that the microstructure does not contain large granules at all, which makes the steel's ductility properties particularly good considering the strength of the steel.

Preferably, the rate of direct quenching is not more than 120 ° C / sec, since this provides the steel 5 with a microstructure that provides the steel with particularly good mechanical properties, including good impact strength.

Preferably, the final quenching temperature of the direct quenching is not more than 100 ° C, since then a quenching strip is obtained after quenching, whereby the edges are also flat and flat.

Preferably, the steel strip is directly quenched directly to the winding temperature and coiled.

The treatment of the steel strip is preferably thermomechanical, whereby after direct quenching there is no post-heat treatment, such as discharge, in which the steel is heated and then allowed to cool. The steel product produced by the process has good mechanical properties without the need for cost-intensive post-heat treatment. Emissions do not significantly improve the mechanical properties of the steel product and complicate the process.

After winding, the steel strip is cold-formed to the desired shape. If necessary, the steel strip may be stripped and / or cut to suitable dimensions. Cold forming is carried out by known profile and / or tubing processes, however, preferably cold forming is accomplished by roll forming from standard cross-sections between several pairs of rolls.

In the roll forming process, the shape of the molded product is formed at each step of the pair of rolls. In the case of a closed profile, the profile is welded lengthwise. Typically, the final step is to cut the continuous mold preparation to the desired extent. Alternatively, the molded article may be a cold formed die. Residual stresses remain in the mold as a result of the molding of the yoke.

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After cold forming before hot galvanizing, the steel can undergo the necessary oo steps, such as cleaning and pickling to achieve successful galvanization.

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In hot dip galvanizing, the steel piece is lifted into a zinc bar with a molten zinc temperature of about 450 ° C. The additive concentrations of the zinc bath according to the invention should preferably be limited for lead Pb <0.02%, tin Sn <0.02% and bismuth Bi, since they have been found to increase their tendency towards molten metal brittleness. Zinc reacts with steel to form a protective coating against corrosion. After a sufficient holding time, the high-strength galvanized molding is removed from the kettle and cooled.

It will be apparent to one skilled in the art that at least some of the benefits of direct quenching for a product may be realized to the disadvantage even without the immediate contact of quenching with strip rolling. Thus, the product of the invention is characterized by what is defined in independent claim 8.

The following describes in more detail the geometry and composition of the product of the invention.

Cooling can be accomplished in known ways, for example in the air.

In other words, hot dip galvanizing 14 uses zinc pot additive contents of lead Pb <0.02% and tin Sn <0.02%.

The corners of the galvanized moldings were examined from the images taken with a metal microscope and it was surprisingly found that the increase in strength to the steel by direct quenching allows the hot-dip galvanizing of the high-strength moldings without corner bends.

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x The following table 1 shows test examples (steels 1, 2) of the strength values measured from cold formed cc structural tubes and their geometrical parameters. Figures 2 ° and 3 show graphically the shapes of structural tubes, o 05 o 25 ^ ___ CV ter®s The position of sample _T__B__H (B + H) / 2T R / T RP02 RM A5 ChV-20 ChV-40 ChV-60 __mm mm mm__mm MPa MPa% J / cm2 J / cm2 J / cm2__ _1__6 200 200 33.3 2.0 497 565 23.1 151 - 132 Page 1 | 6 | 2001 33.3. 2.0 498 56θ | 23.θ | 164 - 118 Bottom 7 1 I 6 I Idol 1001 16.7 2.0 551 607 | 16.81 - I - I 137 I Bottom _1__6 120 80 16.7 2.0 550 580 19.0 - 162 - Bottom _2__6 200 200 33.3 2.0 558 623 20.6 146 - 131 Page _2__6 200 200 33.3 2.0 563 624 20.3 158 - 146 Bottom _2__6 100 100 16.7 2.0 585 641 15.9 161 __-__ Sole _2__6 120 80 16.7 2.0 600 537 15.8 166 Sole R1 _6 200 100 25.0 4.0 675 732 18.0 75 Sole R1 _6 200 100 25.0 2.5 675 732 18.0 75 Sole R1 _6 200 100 25.0 1.5 675 732 18.0 75 Sole R2 _6 150 150 25.0 2.5 562 627 21.0 118 Bottom R2 6 I 15θ | 150 25.0 4.0 562 627 \ 21.o | 118 - - Bottom ~

Table 1. The strength and ductility properties of steels in hot dip galvanizing tests R1 and R2 are reference examples of structural tubes of the corresponding strength level raised by the alloying materials without direct quenching.

The galvanized structural tubes (steels 1 and 2) were examined with a metal microscope and no distortion caused by molten metal brittleness was detected in their corners. It is further seen from the table that the invention provides a galvanizing molded product having a strength of up to 460-600 MPa and an impact strength of at least 120 J / cm 2, even at low temperatures of -60 ° C. The yield strength range of the steel form preparation of the invention is preferably 460-580 MPa.

The steel compositions of the hot-dip galvanizing tests are shown in the following Table 2, in which the alloying compounds which are residual are indicated by a dashed line.

steel C SI MN PS AL NB V CU CR Nl N MO Tl 1 0.06 0.01 0.73 0.008 0.008 0.021 0.026 0.01 0.035 0.041 0.049 0.0045 0.013 0.002 2 0.06 0.01 1.01 0.004 0.007 0.037 0.048 0.005 0.045 0.025 0.049 0.0044 0.006 0.001 3 0.05 0.01 0.50 0.008 0.003 0.03 0.039 0.01 _______ 0.015 ^ R1 0.06 0.19 1.3 0.01 0.004 0.03 0.015 0.013 0.011 0.035 0.044 0.006 0.003 0.08 ^ R2 0.05 0.17 1.38 0.009 0.003 0.023 0.037 0.076 0.03 0.028 0.041 0.007 0.002 0.002 ~ g 15 Table 2. Compositions of Tested Steels 00 ^ Table it is found that the alloying constituents important in the invention are C, Si, Μη, P, S, Al and £ Nb. In addition, vanadium V <0.05% or titanium alloy Ti <0.03% may be used. suuksina. The general level of alloying material in the steel is low, which contributes to the success of hot-dip galvanizing. In particular, the concentrations of silicon Si, vanadium V and manganese Mn have been significantly reduced to achieve the steel quality of the invention.

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Steel has a low carbon content of C 0.04 - 0.10% which is beneficial in terms of impact strength, edging and weldability. The low carbon equivalent of steel (C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15) also positively affects good weldability.

The silicon content of the steel is chosen in the range of SiO 0.03%, whereby the steel is a so-called lower silicon steel. The zinc layer then becomes thin (<90 µm) and has good adhesion. Further, the 5 lower steels achieve good gloss on the zinc surface when hot galvanized and low silicon prevents the tendency to molten metal brittleness. The low silicon content is thus likely to improve the hot-dip galvanizing of the steel.

Manganese Mn, 0.3 to 1.2% is used. 0.3% is required as a minimum to provide the required strength to the steel, while too high a concentration has been found to impair the impact strength of the 10 in the case of direct quenched steels. The manganese content is preferably 0.4-0.9% to ensure impact strength.

Niobi Nb is an effective strength enhancing alloy and must be doped in 0.015-0.10%. Preferably, niobium Nb is doped at a maximum of 0.08%.

Vanadium V is added as a strength enhancing compound, but its content must be limited to 15 V <0.05% as vanadium has been found to impair weldability and impact strength.

The concentration of phosphorus P must be limited to P <0.02 in order to maintain good galvanizing properties. Preferably, the phosphorus content is limited together with silicon Si, whereby preferably P (%) + Si (%) <0.04%.

Sulfur S is present in low concentrations in steel and its content is sought to be limited due to its harmful properties S ^ 0.02.

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^ Aluminum Al is used to seal steel in concentrations of 0.01 to 0.08%, o c3 Copper Cu, chromium Cr, nickel Ni and molybdenum Mo are not required to be mixed with the invention | and their content remains inevitable.

oo 25 Direct quenching has achieved high strength with respect to alloying although the steel o o microstructure is predominantly low carbon ferrite and / or bainite, with no significant ™ amounts of carbon-rich martensite or carbon-rich bainite. Preferably, the predominant phase is ferrite, with the microstructure preferably being almost completely ferritic, and in addition it contains small amounts of bainite and / or martensite and / or residual austenite in very low carbon islets.

The invention provides a solution, for example, for the production of high-strength pulsed structural tubes according to Figs. 2 and 3 which, when hot-dip galvanized, the strength of the formulation. Molten metal brittleness can also occur at angles> 90 °, but preferably at angles <120 °. From Table 1, it is observed that the invention works with outer radii of up to R = 2T, so it can be stated that the invention also works in high strengths with outer radii of R = 2-4T. The outer corner radii are measured as shown in Figs. 2 and 3 from the ul-corner of the profile.

Increasing the material strength T can increase the degree of deformation hardening of the molded product 16, 18, which increases the brittleness of the molten metal. In the case of rectangular structural tubes, the deformation hardening degree of the molded product can be estimated by the formula (B + H) / 2T, where a lower numerical value means a higher deformation hardening degree. Further, increasing the material strength makes it difficult to quench the steel rapidly during direct quenching, whereby the excessively thick strip does not provide a uniformly firm material while the core is softer than the surface. Therefore, the material thickness of the mold 20 according to the invention is 2 to 14 mm, but preferably 4 to 12.5 mm.

The molded product of the invention 16,18 refers to a cold formed steel product having at least one corner cold formed. Preferably, the molded article comprises at least one corner having an outer radius of curvature of ≤ 5T, and preferably additionally one or C 1 -C. . multiple angles <120 °. Preferably, the

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The preparation is an elongated form preparation and most preferably is a closed

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such as a structural tube.

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h- The above invention is illustrated by examples. In view of the foregoing, it should be noted that the present invention can be practiced in many ways within the scope of the appended claims.

Claims (19)

1. A process for the manufacture of a high-pour, hot-dip galvanized profile product, the composition of which is 0: 0.04-0.10% Si: <0.03% Mn: 0.3-1.2% Nb: 0.015-0 10% Ti: <0.03% N: <0.01% P: <0.02% S: <0.02% AI: 0.01-0.08% V: <0.05%, while the ether is iron, inevitable impurities or residues , in which method one rolls an element in a band rolling mill, such that the rolling temperature of the blank at the last caliber is 760-960 ° C, characterized in that the method comprises the following steps, where: 20 with a cooling rate of 30-150 ° C / s to a temperature of not more than 300 ° C, whereby the direct leakage is carried out no later than 15s after the last caliber, - the actuator is flushed at a temperature of 20-300 ° C; - cold profiles the ground profile product of the grounding belt; and - hot-dip galvanizes the cold-profile rack profile product. A method according to claim 1, characterized in that the final temperature at direct extinguishing is at most 100 ° C. 3. Method according to claim 1, characterized in that the machining cuu of the adjusting belt is thermomechanical, whereby no annealing is performed after the direct extinguishing. Method according to claim 1, characterized in that in the case of cold testing the filing profiles the outer curvature of at least one corner to a value i R = 2-4T, where R is the radius of curvature and T is the blank thickness. oo § 5. Process according to claim 4, characterized in that profile rolling is used as a cold and profiling process. CM 14 6. A method according to claim 5, characterized in that a profile roll is rolled, in which the closure of the profile is achieved by longitudinal joint welding. Process according to claim 1, characterized in that the content of additives in the zinc crucible is limited during hot galvanizing: - lead Pb ^ 0.02% and tin Sn <0.02%. 8. High-pour profile hot-dip galvanized product, where the product thickness of the product is 2-14mm, and where the composition of the profile product expressed in weight percent is: C: 0.04-0.10% Si: <0.03% Mn: 0.3-1.2% Nb: 0.015-0.10% Ti: <0.03% N: <0.01% P: <0.02% S: <0.02% AI: 0.01-0.08% V: <0.05%, while the ether is uniform, inevitable impurities or residues , characterized in that the steel is produced by direct quenching of rails from belt rolling, whereby the tensile strength of the steel profile product is 460-600 MPa and impact toughness at least 120J / cm2 (measured as Charpy V-60). Profile product according to claim 8, characterized in that the profile product is hot-dip galvanized. The profile product according to claim 8, characterized in that the tensile strength of the profile product is 460-580 MPa. (M £ 11. Profile product according to claim 8, characterized in that the value of ° the outer curvature of one or more corners in the profile product R = 2-4T, where R is 00 ™ the radius of curvature and T is the blank thickness. 12. Profile product according to claim 11, characterized in that the profile product has one or more curved angles of a size of <120 °. 00 The profile product according to claim 8, characterized in that the profile product is a closed profile. A profile product according to claim 13, characterized in that the closed profile is a square or rectangular shaped structural pipe. 15 15. Profile product according to claim 8, characterized in that the microstructure of the site is substantially ferritic. The profile product according to claim 8, characterized in that the thickness of the profile product is 4-12.5 mm. δ (M i CD O oo (M X and CL h- · 00 00 o O) o o (M