CN113444975A - Pre-heating-free high-strength hydroelectric steel with low carbon equivalent weight of 600MPa grade before welding and manufacturing method thereof - Google Patents

Pre-heating-free high-strength hydroelectric steel with low carbon equivalent weight of 600MPa grade before welding and manufacturing method thereof Download PDF

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CN113444975A
CN113444975A CN202110752773.5A CN202110752773A CN113444975A CN 113444975 A CN113444975 A CN 113444975A CN 202110752773 A CN202110752773 A CN 202110752773A CN 113444975 A CN113444975 A CN 113444975A
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隋轶
王昭东
邓想涛
韩严法
周成
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Northeastern University China
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Abstract

The invention belongs to the technical field of microalloy steel production, and discloses a preheating-free low-carbon equivalent 600 MPa-grade high-strength hydroelectric steel before welding and a manufacturing method thereof. The method can be used for producing the steel plate with the thickness of 20-60mm, the carbon equivalent of the product is not more than 0.42%, the yield strength reaches more than 490MPa, the tensile strength reaches more than 600MPa, preheating is not carried out before welding, the welded joint has good toughness, and the impact energy of the welded joint at-40 ℃ is not less than 80J.

Description

Pre-heating-free high-strength hydroelectric steel with low carbon equivalent weight of 600MPa grade before welding and manufacturing method thereof
Technical Field
The invention belongs to the field of microalloy steel, and particularly relates to preheating-free low-carbon equivalent 600MPa grade high-strength hydroelectric steel before welding and a manufacturing method thereof.
Background
With the development of hydropower equipment towards high parameter, light weight and large scale, the demand of the hydropower industry on the steel plate for the high-strength and high-toughness machinery is increasing. The traditional high-strength steel plate is usually produced by an off-line quenching and tempering (Q-T) process, namely, a solid solution strengthening mechanism and a precipitation strengthening mechanism are adopted to improve the strength, so that the content of carbon and alloy elements in the steel is higher, and the problem caused by the higher content is that the subsequent welding processing is difficult. Welding is an important forming method for subsequent machining of the steel plate, the tendency of cold cracks in the welding process is increased along with the increase of the strength grade and the plate thickness of the steel plate, and the softening and the embrittlement of a welding heat affected zone are very easy to cause brittle fracture of a welding joint and induce catastrophic accidents. In order to avoid the problems, manufacturers mostly adopt a mode of improving preheating temperature and strictly controlling a welding process, preheating before welding is an effective measure for preventing cold cracks, hot cracks and hardening structures in a heat affected zone, all preheating modes can increase energy consumption and improve welding cost, and the welding process is strictly controlled to further reduce welding efficiency.
Application No. 201910119979.7 discloses a preheating-free large-thickness low-carbon equivalent 500MPa grade high-strength steel before welding and a manufacturing method thereof, wherein a TMCP process is adopted for rolling, an off-line tempering process is not adopted, and a welding process is not explained.
Application No. 201810916605.3 discloses a strategic oil storage tank steel plate based on oxide metallurgy and a manufacturing method thereof, wherein the yield strength grade is 500MPa, the impact energy at minus 20 ℃ is more than or equal to 80J, but the impact energy index at minus 40 ℃ is more than or equal to 80J is not mentioned.
The preparation method of the fine oxide dispersion steel of application number 200910187463.2 refers to the preparation of the oxide dispersion steel by spraying fine oxide powder in a tundish, but does not refer to specific steel types, strength grades and impact energy, and is different from the oxide metallurgy mode of the invention in a ladle refining furnace.
Disclosure of Invention
The invention discloses a preheating-free low-carbon equivalent 600 MPa-grade high-strength hydroelectric steel before welding and a manufacturing method thereof, wherein a low-C- (Mn + Ni + Cr + Mo + Cu) - (Nb + Ti + V) -B component system is adopted as a basis, and a high-melting-point fine oxide is formed in the steel by adjusting the addition sequence of deoxidized alloy, so that austenite crystal grains in the steel are effectively refined, coarsening of crystal grains in a welding heat affected zone is reduced, fine acicular ferrite with large-angle crystal grain orientation is induced and generated in a steel matrix and the welding heat affected zone, and a hardening structure is avoided, so that preheating-free welding before welding is realized, the welding process is wide, the energy of a welding line is less than or equal to 100KJ, and Akv at-40 ℃ in the welding heat affected zone is more than or equal to 80J.
The technical scheme of the invention is as follows:
the preheating-free high-strength hydroelectric steel with low carbon equivalent of 600MPa before welding comprises the following components in percentage by mass: c: 0.06-0.10, Si: 0.05-0.20, Mn: 1.40-1.70, P: less than or equal to 0.013, S: not more than 0.008, Nb: 0.02 to 0.06, Cr: 0.05 to 0.15, Mo: 0.10 to 0.30, Ni: 0.10 to 0.30, V: 0.02 to 0.04, Cu: 0.05 to 0.2, Ti: 0.005-0.02, B: 0.0005 to 0.0013, Mg 0.0010 to 0.0040, Al: 0.003 to 0.008 percent, and the balance of Fe and inevitable impurities, wherein the carbon equivalent Ceq is less than or equal to 0.42 percent; wherein Ceq ═ Ceq (%) ═ C + Mn/6+ Si/24+ Ni/40+ Cr/5+ Mo/4+ V/14 is less than or equal to 0.42%.
The chemical composition design of the invention mainly considers the following:
c: when the C is less than or equal to 0.06 percent, other elements for improving hardenability are added to improve the strength, so that the cost is increased. When the carbon content in the steel is below 0.10 percent, the influence of the carbon equivalent of the steel on the cold crack sensitivity is not large, and the content of C is controlled to be 0.06 percent to 0.10 percent.
Si: si is a basic element in steel, and is usually added into the steel in the form of ferrosilicon alloy as a deoxidizing element, so that the strength of the steel can be improved, and the content of the Si-Si alloy is controlled to be 0.05-0.20%.
Mn: mn is a basic element in steel, is usually used as a deoxidizer and a desulfurizer, is added into the steel in the form of Mn-Fe alloy, can be dissolved in ferrite to form a solid solution with the iron, can improve the hardenability and can improve the strength of the steel, and the Mn content is controlled to be 1.40-1.70 percent in the invention.
P: p is an impurity element in the steel grade. The main harm of P to the steel plate parent metal is cold brittleness, and the content of P is limited to P less than or equal to 0.013 percent.
S: s is mainly an impurity element in the steel, but S in the steel can be attached to the periphery of the composite oxide or nitride in the form of MnS, so that the nucleation and growth of a steel matrix and acicular ferrite in a welding heat affected zone are promoted, and the content of the S is controlled to be less than or equal to 0.008 percent;
ni: ni can improve the strength, low-temperature toughness and elongation of the matrix, and the content of Ni is controlled to be 0.10-0.30 percent in the invention.
Cr: cr is a weak carbide forming element, but the composite addition of Cr, Ni, Mo, Cu and the like can improve the hardenability of the steel plate and the strength of the steel plate, and the content of Cr is controlled to be 0.05-0.15 percent.
Mo: mo can effectively improve the strength of steel and can improve the high-temperature tempering stability of the parent metal, and the content of Mo is controlled to be 0.10-0.30 percent.
V: the role of V in steel is mainly precipitation strengthening. The V is precipitated in a V (C, N) form in the tempering process and improves the strength of the steel plate, and the content of V is controlled to be 0.02-0.04 percent in the invention.
Nb: nb is combined with the controlled rolling process through microalloying to fully refine the crystal grains of the parent metal, and is combined with precipitation strengthening and dislocation substructure strengthening effects to achieve the purpose of improving the comprehensive performance of the parent metal, and the content of the Nb-Cu-in combination with the combination of the micro alloying and controlled rolling process is controlled rolling technology to fully refine the crystal grains of the base metal grains of the purpose of the base metal, so as to achieve the aim of improving the comprehensive performance of improving the purpose of improving the comprehensive performance of improving the comprehensive performance of the purpose of the base metal.
B: b makes the proeutectoid ferrite not easy to nucleate, thereby an acicular ferrite structure and a multi-orientation bainite structure can be obtained in a larger cooling speed range, the strength of the steel grade is improved, and the low-temperature toughness is improved at the same time, wherein the content of B is controlled to be 0.0005-0.0013 percent.
Ti: the proper Ti content can be compounded with other deoxidizing elements to obtain a great amount of small-sized oxides and nitrides of Ti, and the Ti content is controlled to be 0.005-0.02 percent in the invention.
Mg: the Mg can promote nodularization of strip MnS series inclusions, and the proper amount of Mg and the proper adding sequence can lead the inclusions to be micronized, wherein the Mg is controlled to be 0.0010-0.0040 percent.
Al: the Al and N are combined to improve the strength of the steel plate, and a proper amount of Al is beneficial to forming Ti compounds, and if the Al and N are more than 0.003 percent, the toughness is deteriorated; in the invention, Al is controlled to be 0.0030-0.008%.
Cu: the Ar3 temperature can be reduced to obtain refined ferrite grains, and the strength of the steel can be improved, and the corrosion resistance and the weather resistance can be improved. In the invention, Cu is controlled to be 0.05-0.2.
The invention discloses a manufacturing method of a high-strength hydroelectric steel with low carbon equivalent of 600MPa without preheating before welding, which comprises the working procedures of smelting, continuous casting, heating, controlled rolling, quenching and heat treatment.
(1) Adopting a converter-ladle refining furnace-vacuum circulating degassing refining furnace/vacuum decarburization furnace continuous casting process to prepare a continuous casting billet with the components; the thickness of the continuous casting slab is 230-300 mm, the addition sequence of the deoxidized alloy in the ladle refining furnace-vacuum cycle degassing refining furnace/vacuum decarburization furnace, Mn and Si combined deoxidation and oxygen content control
Less than or equal to 130ppm, adding Ti alloy for deoxidation, then adding Al alloy for deoxidation, then adding Mg alloy for deoxidation, controlling the adding interval time of each element to be less than or equal to 10min, then entering a vacuum circulating degassing refining furnace/vacuum decarburization furnace process, and finally completing the process, wherein the gas content [ H ] in the steel is less than or equal to 2ppm, the [ O ] is less than or equal to 10ppm, and the [ N ] is less than or equal to 60 ppm.
(2) The heating temperature of the casting blank is 1140-1160 ℃; the rolling process comprises a complete recrystallization rolling stage and a non-recrystallization rolling stage: the temperature of the complete recrystallization rolling stage is controlled to be 1050-1100 ℃, and the total rolling reduction rate is 30-50%; the temperature of the non-recrystallization rolling stage is controlled to be 800-860 ℃, and the total rolling reduction rate is 50%.
(3) The quenching temperature is 880-910 ℃, the heat preservation time is 60-90 min, the tempering temperature is 610-630 ℃, and the tempering heat preservation time coefficient is 2-3 min/mm.
The invention has the beneficial effects that:
(1) the invention discloses a preheating-free low-carbon equivalent 600 MPa-grade high-strength hydroelectric steel before welding and a manufacturing method thereof, wherein a low-C- (Mn + Ni + Cr + Mo + Cu) - (Nb + Ti + V) -B component system is adopted as a basis, and a high-melting-point fine oxide is formed in the steel by adjusting the addition sequence of deoxidation alloy, so that austenite crystal grains in the steel are effectively refined, coarsening of the crystal grains in a welding heat affected zone is reduced, and fine acicular ferrite with large-angle crystal grain orientation is induced and generated in a steel matrix and the welding heat affected zone, so that a hardening structure is avoided, and preheating-free welding before welding is realized, and the welding process is wide.
(2) Can realize preheating-free welding, and has the energy of welding line less than or equal to 100KJ and the impact energy of-40 ℃ in a welding heat affected zone more than or equal to 80J.
Drawings
FIG. 1 is a photograph of crack sensitivity of an example. (a) The surface crack rate is zero, and (b) the fracture surface crack rate is zero.
Detailed Description
The following examples are intended to illustrate the invention in detail, and are intended to be a general description of the invention, and not to limit the invention.
Examples 1 and 2 use a 230mm thick continuous casting slab, example 3 uses a 300mm continuous casting slab, examples 1, 2 and 3 jointly deoxidize Mn and Si in a ladle refining furnace, oxygen content is controlled to be 100ppm, Ti alloy is added for deoxidation, then Al alloy is added for deoxidation, Mg alloy is added for deoxidation, the addition interval of each element is controlled to be 9 minutes, then the process enters a vacuum cycle degassing refining furnace/vacuum decarburization furnace, finally, gas content [ H ]2ppm, [ O ]10ppm, [ N ]50ppm is finished, and the components, rolling process and heat treatment process of examples 1, 2 and 3 are shown in the table.
Chemical composition of the examples
Element(s) C Si Mn P S Ni Cr Mo V
Example 1 0.06 0.12 1.50 0.010 0.003 0.15 0.10 0.20 0.03
Example 2 0.08 0.10 1.45 0.013 0.004 0.18 0.13 0.16 0.04
Example 3 0.09 0.06 1.48 0.012 0.005 0.20 0.06 0.25 0.03
Element(s) Cu Nb Ti Al B Mg N O H
Example 1 0.10 0.03 0.010 0.003 0.0008 0.0020 0.0043 0.0008 0.0001
Example 2 0.06 0.04 0.013 0.008 0.0010 0.0015 0.0054 0.0009 0.0001
Example 3 0.12 0.02 0.012 0.005 0.0010 0.0038 0.0048 0.0009 0.0001
Rolling Process of examples
Figure BDA0003145586910000061
Quenching and tempering process of examples
Quenching temperature DEG C Holding time min Tempering temperature DEG C Tempering and heat preservation time coefficient min/mm
Example 1 880 70 610 2.0
Example 2 890 80 615 2.5
Example 3 900 90 620 2.8
Mechanical Properties of examples
Figure BDA0003145586910000062
Welding Process and Performance of the examples
Figure BDA0003145586910000063
Figure BDA0003145586910000071
Crack sensitivity test of examples
Ambient temperature deg.C Preheating temperature deg.C Fracture rate Rate of surface cracking
Example 1 15 Without preheating 0 0
Example 2 25 Without preheating 0 0
Example 3 10 Without preheating 0 0

Claims (8)

1. The preheating-free high-strength hydroelectric steel with the low carbon equivalent weight of 600MPa before welding is characterized by comprising the following components in percentage by mass: c: 0.06-0.10, Si: 0.05-0.20, Mn: 1.40-1.70, P: less than or equal to 0.013, S: not more than 0.008, Nb: 0.02 to 0.06, Cr: 0.05 to 0.15, Mo: 0.10 to 0.30, Ni: 0.10 to 0.30, V: 0.02 to 0.04, Cu: 0.05 to 0.2, Ti: 0.005-0.02, B: 0.0005 to 0.0013, Mg 0.0010 to 0.0040, Al: 0.003 to 0.008 percent, and the balance of Fe and inevitable impurities, wherein the carbon equivalent Ceq is less than or equal to 0.42 percent; wherein Ceq ═ Ceq (%) ═ C + Mn/6+ Si/24+ Ni/40+ Cr/5+ Mo/4+ V/14 is less than or equal to 0.42%.
2. The pre-weldable preheating-free low-carbon equivalent 600 MPa-grade high-strength hydroelectric steel according to claim 1, wherein the hydroelectric steel contains magnesium-titanium composite inclusions, and the particle size of the magnesium-titanium composite inclusions is 0.01-2.0 μm.
3. The pre-weldable preheating-free low-carbon equivalent 600MPa grade high-strength hydroelectric steel according to claim 2, wherein inclusions with the particle size of 2.0um or less in magnesium-titanium composite inclusions in the hydroelectric steel account for 85% of the total inclusions.
4. The method for manufacturing the pre-weldable preheat-free low-carbon equivalent 600MPa grade high-strength hydroelectric steel according to any one of claims 1 to 3, which is characterized by comprising the following steps:
(1) adopting a converter-ladle refining furnace-vacuum cycle degassing refining furnace/vacuum decarburization furnace continuous casting process to prepare a continuous casting billet according to the components of the hydroelectric steel; the thickness of the continuous casting billet is 230-300 mm;
(2) the heating temperature of the casting blank is 1140-1160 ℃; the rolling process comprises a complete recrystallization rolling stage and a non-recrystallization rolling stage: controlling the temperature at 1050-1100 ℃ in the complete recrystallization rolling stage; the temperature of the non-recrystallization rolling stage is controlled to be 800-860 ℃, and the total rolling reduction rate is 50%;
(3) the quenching temperature is 880-910 ℃, the heat preservation time is 65-90 min, the tempering temperature is 610-630 ℃, and the tempering heat preservation time is 2-3 min/mm.
5. The method for manufacturing a preholdering-free low-carbon equivalent 600MPa grade high-strength hydroelectric steel before welding according to claim 4, wherein the total reduction rate in the complete recrystallization rolling stage in the step (2) is 30-50%.
6. The process for producing a high-strength hydroelectric steel having a preholdening-free low carbon equivalent of 600MPa grade according to claim 4, wherein the total reduction rate in the non-recrystallization rolling stage of the step (2) is 50%.
7. The method for manufacturing a high-strength hydroelectric steel having a preheldable, non-preheated, low carbon equivalent weight of 600MPa grade according to claim 4, wherein in the step (1), the addition sequence of the deoxidation alloy in the ladle refining furnace is as follows: performing combined deoxidation on Mn and Si, controlling the oxygen content to be less than or equal to 130ppm, adding Ti alloy for deoxidation, then adding Al alloy for deoxidation, adding Mg alloy for deoxidation, controlling the adding interval time of each element to be less than or equal to 10min, and then entering a vacuum cycle degassing refining furnace/vacuum decarburization furnace process, wherein the gas content [ H ] after the final steel is finished is less than or equal to 2ppm, the [ O ] is less than or equal to 10ppm, and the [ N ] is less than or equal to 60 ppm.
8. The method for manufacturing the high-strength hydroelectric steel with the preheating-free low carbon equivalent weight of 600MPa level before welding according to claim 4, wherein the yield strength of the obtained high-strength hydroelectric steel is more than 490MPa, the tensile strength is more than 600MPa, preheating is not performed before welding, a welding joint has good toughness, and the impact energy of a heat affected zone of the welding joint is not less than 80J at minus 40 ℃.
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