CN114854952A - Production method of Q420-grade high-corrosion-resistance high-strength offshore structure steel - Google Patents

Abstract

A production method of Q420-grade high-corrosion-resistance high-strength offshore structure steel comprises the process steps of molten iron pretreatment → converter steel making → external refining LF → vacuum treatment RH → continuous casting → heating → rolling → controlled rolling cooling → tempering → finishing → performance inspection → ultrasonic flaw detection. The method is characterized in that: the steel comprises the following components in percentage by mass: c = 0.03-0.07, Si = 0.15-0.40, Mn = 0.95-1.05, P ≤ 0.020, S ≤ 0.003, Nb = 0.04-0.06, Ti = 0.01-0.02, Als = 0.02-0.05, Cu = 0.30-0.70, Ni = 0.7-1.5, and the balance of Fe and unavoidable impurity elements. The method is suitable for producing the steel with the thickness specification of less than or equal to 60mm and the marine atmospheric corrosion resistance, the yield strength of the steel is more than or equal to 420MPa, the tensile strength of the steel is more than or equal to 540MPa, the low-temperature impact toughness at 60 ℃ below zero, KV2 of the steel is more than or equal to 120J, the low-temperature impact toughness at 1/2 thickness of the steel plate at 60 ℃ below zero, KV2 of the steel is more than or equal to 120J, and the lamellar tearing resistance Z of the steel is more than or equal to 35 percent.

Description

Production method of Q420-grade high-corrosion-resistance high-strength offshore structure steel

Technical Field

The invention belongs to the technical field of metallurgy, and relates to a production method of Q420 grade high-corrosion-resistance high-strength offshore structural steel.

Background

With the development of island foundation construction, cross-sea bridge construction, seaside construction and marine engineering of ships, the demand for offshore structural steel for marine atmosphere and seawater corrosion environment has increased greatly. According to the unique, complex and variable marine corrosion environment of offshore high-humidity heat, high-salt, high-radiation and strong-heat zone storm, the mechanical-corrosion performance of the steel for infrastructure and key engineering is researched, and the steel with high corrosion resistance alloying and tissue structure matched with the steel is developed, so that the method is one of the key directions of the current metallurgical industry research.

CN200510045624.6 discloses a low-alloy weathering steel which can be used as a structural steel for railways, bridges, vehicles and the like which are exposed to the sun for a long time and used under atmospheric conditions. The C content of the steel is 0.12-0.21%, the low-temperature impact property and the welding property of the steel are deteriorated due to the overhigh carbon content, the content of Al which is less than or equal to 0.2% is higher, and a great deal of inconvenience is caused to steel making and rolling.

CN200810046963.X discloses an ultra-low carbon hot-rolled weathering steel with yield strength more than 450 MPa. The steel has the C content of 0.01-0.05%, achieves the ultra-low carbon level, and has higher strength, good low-temperature impact property and welding property; but the Mn content is 1.50-1.90%, a banded structure is easy to generate, and the difference of the mechanical properties is obvious.

The patent of CN201210072989.8 discloses a Cr-free high-performance weather-resistant bridge steel and a preparation method thereof. The steel has lower cost, good comprehensive mechanical property and welding property, and does not contain toxic element Cr. But the Ni content is low, the Ni content is only used for improving the marine atmospheric corrosion resistance of the steel, and the actual marine atmospheric corrosion resistance is weak.

The patent of CN201210027231.2 discloses a high-performance bridge weathering steel containing Mo and a preparation method thereof, which have the characteristics of low cost and low yield ratio, and simultaneously have excellent low-temperature impact toughness, welding performance and atmospheric corrosion resistance, and adopt an ultra-low carbon design. Non-marine atmospheric corrosion resistant steel, ultra-low carbon design and difficult smelting.

The patent CN201210055632.9 discloses a clean corrosion-resistant steel for ocean engineering and its production method, the steel has low Nb content and high P content, which are both unfavorable for the toughness of the parent metal and the welding heat affected zone.

CN201310398905.4 patent discloses steel for welded structure with excellent marine environment corrosion resistance and its manufacturing method, wherein Cu and Mo are added in a large amount, Cu increases casting blank cracks in continuous casting process, Mo increases raw material production cost, and increases hardness after welding and crack sensitivity after welding.

CN201811323097.4 discloses a weather-resistant bridge steel and a smelting process, which are applied to steel structures used in long-term exposure in the atmosphere of railways, vehicles, bridges, towers, photovoltaics, high-speed engineering and the like, and have poor toughness due to high carbon design, so that the requirements of offshore structures cannot be met.

CN202010804029.0 discloses an ultra-thick high-toughness weather-resistant bridge steel plate and a production method thereof, relates to the technical field of manufacturing of ultra-wide weather-resistant bridge steel plates, mainly meets the performance requirements of the ultra-thick weather-resistant bridge steel plate with the thickness of more than or equal to 60mm, and does not relate to the field of marine atmospheric corrosion resistance.

CN202110342322.4 discloses a 420 MPa-grade weather-resistant bridge steel and a production method thereof, which adopt low cost and give consideration to the comprehensive properties of toughness, weather resistance, weldability and the like of the steel, thereby achieving the purposes of low cost and easy industrial production. The steel is industrial atmosphere corrosion resistant steel and non-marine climate resistant steel.

Disclosure of Invention

The invention aims to provide a production method of Q420-grade high-corrosion-resistance high-strength offshore structural steel, which is used for producing steel for island foundation construction, cross-sea bridge construction, seaside construction and marine engineering of ships, wherein the thickness specification of a steel plate is less than or equal to 60mm, the yield strength is more than or equal to 420MPa, the tensile strength is more than or equal to 540MPa, the impact toughness at the low temperature of 60 ℃ below zero, KV2 is more than or equal to 120J, the impact toughness at the low temperature of 60 ℃ below zero at the position with the thickness of 1/2, KV2 is more than or equal to 120J, and the lamellar tearing resistance Z is more than or equal to 35%.

The technical scheme of the invention is as follows:

a production method of Q420-grade high-corrosion-resistance high-strength offshore structural steel comprises the following process steps of molten iron pretreatment → converter steelmaking → external refining LF → vacuum treatment RH → continuous casting → heating → rolling → controlled rolling cooling → tempering → finishing → performance inspection → ultrasonic flaw detection, wherein the chemical composition mass percent of the steel is C = 0.03-0.07, Si = 0.15-0.40, Mn = 0.95-1.05, P is less than or equal to 0.020, S is less than or equal to 0.003, Nb = 0.04-0.06, Ti = 0.01-0.02, Als = 0.02-0.05, Cu = 0.30-0.70, Ni = 0.7-1.5, the balance is Fe and inevitable impurity elements, Pcm is less than or equal to 0.20, and I is more than or equal to 6.0; the key process steps are as follows:

(1) continuous casting: the superheat degree of the molten steel is less than 15 ℃;

(2) rolling: the heating temperature of the heating section of the heating furnace is 1100-1240 ℃, the temperature of the soaking section is 1100-1200 ℃, and the heat preservation time of the soaking section is more than or equal to 30 min; the thickness of the intermediate blank is more than or equal to 2 times of the thickness of the finished product, and a large reduction system is adopted in rough rolling, so that the continuous 3-pass reduction rate after widening is more than or equal to 14 percent; the finish rolling temperature is 700-800 ℃, and the reduction rate of several passes before finish rolling is more than or equal to 10%;

(3) cooling after rolling: directly adding water, wherein the temperature of red returning is 450-570 ℃, and the cooling speed is 7-20 ℃;

(4) and (3) tempering after rolling: tempering at 640-660 ℃ for mm x (2.0-3.5) min/mm, and air cooling.

Wherein: pcm = C + Si/30+ (Mn + Cu + Cr)/20 + Ni/60+ Mo/15+ V/10+5B (%); i =26.01(% Cu) +3.88(% Ni) +1.20(% Cr) +1.49(% Si) +17.28(% P) -7.29(% Ni) (% Cu) -9.10(% Ni) (% P) -33.39(% Cu).

The technical principle of the invention is as follows:

the invention adopts a Ni-Cu alloy design marine atmospheric corrosion environment resistance commonality technology and a low-carbon bainite structure design, adopts simulated corrosion and on-site hanging for 3-5 years of research, establishes a rapid evaluation method of material performance in a whole life cycle, and constructs a material corrosion performance database.

Ni is a relatively stable element, and the addition of Ni can change the self-corrosion potential of the steel to the positive direction, thereby increasing the stability of the steel. The atmosphere exposure test shows that when the Ni content is about 4%, the atmosphere corrosion resistance of the offshore atmosphere corrosion resistant steel can be obviously improved. The Ni enriched in the stable rust layer can effectively inhibit the invasion of Cl < - > ions, promote the generation of a protective rust layer and reduce the corrosion rate of steel. However, the higher Ni content inevitably leads to the increase of the cost of the steel and is not beneficial to the use of industrial mass production, so under the consideration of meeting a certain balance between the ocean weather resistance and the economic efficiency, the research on the use, the processing and the weather resistance of offshore structural steel by about 1.0 percent of Ni content is suitable.

Cu is increasingly added to steel as a strengthening element, especially ultra low carbon steel. After solution treatment of high purity copper-containing steel, the solute atoms of copper are not uniformly distributed in the ferrite matrix, but exist in a non-uniform short-range ordered form. The presence of ordered domains may create advantages for subsequent age precipitation, thereby having an impact on the age-strengthening behavior of the copper-containing steel.

The invention has the beneficial effects that: the key technology of the cooperative regulation and control of the composition design, the metallurgical quality, the microstructure and the material performance of the high-corrosion-resistant alloy is overcome, and the novel alloying offshore structural steel and the matched welding material technology are developed. The low-carbon bainite steel is designed as a serialized structure, the strength is adjusted by adopting the reinforcement of other alloys and micro alloys and combining the rolling and tempering processes, and the steel for island reef infrastructure construction, cross-sea bridge construction, seaside construction and marine engineering of ships is produced, wherein the thickness specification of a steel plate is less than or equal to 60mm, the yield strength is greater than or equal to 420MPa, the tensile strength is greater than or equal to 540MPa, the impact toughness at the low temperature of 60 ℃ below zero, the KV2 is greater than or equal to 120J, the impact toughness at the low temperature of 60 ℃ below zero in the thickness of the steel plate 1/2, the KV2 is greater than or equal to 120J, and the lamellar tearing resistance Z is greater than or equal to 35%.

Drawings

FIG. 1 is a metallographic structure photograph of a steel plate 1/4 having a thickness of 60 mm.

Detailed Description

The present invention will be further described with reference to the following examples.

Example 1: the 60mmQ420 grade high-corrosion-resistance high-strength offshore structure steel plate is produced.

The chemical composition mass percent of the steel is C =0.04, Si =0.24, Mn =1.02, P =0.010, S =0.001, Nb =0.045, Ti =0.018, Als =0.032, Cu =0.42, Ni =1.02, and the balance of Fe and inevitable impurity elements, Pcm =0.14, and I = 6.33; the key process steps are as follows:

(1) continuous casting: the superheat degree of the molten steel is 14 ℃;

(2) rolling: the temperature of a heating section of the heating furnace is 1150-1200 ℃, the temperature of a soaking section is 1180-1200 ℃, and the heat preservation time of the soaking section is 45 min; the thickness of the blank is 300mm, the thickness of the intermediate blank is 120mm, the rough rolling adopts a large reduction system, and the continuous 3-pass reduction rate after widening is 14%, 20% and 20%; the finish rolling temperature is 768 ℃, and the reduction rates of three passes before finish rolling are 10%, 11% and 11%;

(3) cooling after rolling: directly adding water, and cooling at 486 deg.C and 8 deg.C;

(4) and (3) tempering after rolling: tempering at 660 ℃ for 150min, and cooling in air.

The test results of the steel plate properties are shown in Table 1; ultrasonic flaw detection is carried out, and the flaw detection grade I is qualified according to the GB/T2970 standard.

Example 2: production of 20mmQ420 grade high-corrosion-resistance high-strength offshore structure steel plate

The chemical composition mass percent of the steel is C =0.04, Si =0.24, Mn =1.02, P =0.010, S =0.001, Nb =0.045, Ti =0.018, Als =0.032, Cu =0.42, Ni =1.02, and the balance of Fe and inevitable impurity elements, Pcm =0.14, and I = 6.33; the key process steps are as follows:

(1) continuous casting: the superheat degree of the molten steel is 14 ℃;

(2) rolling: the temperature of a heating section of the heating furnace is 1150-1200 ℃, the temperature of a soaking section is 1180-1200 ℃, and the heat preservation time of the soaking section is 35 min; the thickness of the blank is 300mm, the thickness of the intermediate blank is 70mm, the rough rolling adopts a large reduction system, and the continuous 3-pass reduction rate after broadening is 24%, 27% and 27%; the finish rolling temperature is 738 ℃, and the reduction rates of three passes before finish rolling are 12%, 12% and 13%;

(3) cooling after rolling: directly adding water, and returning red at 526 ℃ and cooling at 15 ℃;

(4) and (3) tempering after rolling: tempering at 660 ℃ for 50min, and cooling in air.

The test results of the steel plate properties are shown in Table 2; ultrasonic flaw detection is carried out, and the flaw detection grade I is qualified according to the GB/T2970 standard.

Example 3: production of 48mmQ420 grade high corrosion resistant high strength offshore structure steel plate

The chemical composition mass percent of the steel is C =0.06, Si =0.25, Mn =0.99, P =0.012, S =0.001, Nb =0.058, Ti =0.012, Als =0.025, Cu =0.42, Ni =0.98, and the balance is Fe and inevitable impurity elements, Pcm =0.16, I = 6.33; the key process steps are as follows:

(1) continuous casting: the superheat degree of the molten steel is 12 ℃.

(2) Rolling: the heating temperature of the heating furnace is 1160-1200 ℃, the temperature of the soaking section is 1180-1190 ℃, and the heat preservation time of the soaking section is 32 min.

The thickness of the blank is 260mm, the thickness of the intermediate blank is 110mm, the rough rolling adopts a large reduction system, and the continuous 3-pass reduction rate after widening is 22%, 24% and 24%; the finish rolling temperature is 768 ℃, and the reduction rates of three passes before finish rolling are 11%, 11% and 13%.

(3) Cooling after rolling: directly adding water, and returning red at 506 deg.C and cooling at 10 deg.C.

(4) And (3) tempering after rolling: tempering at 660 ℃ for 12min, and cooling in air.

The test results of the steel plate properties are shown in Table 3; ultrasonic flaw detection is carried out, and the flaw detection grade I is qualified according to the GB/T2970 standard.

Table 1 example 1 test results of steel sheet properties

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Table 2 example 2 test results of steel sheet properties

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Table 3 example 3 test results of steel sheet properties

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Claims (1)

1. A production method of Q420 grade high corrosion resistance high strength offshore structure steel comprises the process steps of molten iron pretreatment → converter steelmaking → external refining LF → vacuum treatment RH → continuous casting → heating → rolling → controlled rolling cooling → tempering → finishing → performance inspection → ultrasonic flaw detection, and is characterized in that: the steel comprises, by mass, C = 0.03-0.07, Si = 0.15-0.40, Mn = 0.95-1.05, P ≤ 0.020, S ≤ 0.003, Nb = 0.04-0.06, Ti = 0.01-0.02, Als = 0.02-0.05, Cu = 0.30-0.70, Ni = 0.7-1.5, and the balance of Fe and inevitable impurity elements, Pcm is ≤ 0.20, and I is ≥ 6.0; the key process steps are as follows:

(1) continuous casting: the superheat degree of the molten steel is less than 15 ℃;

(2) rolling: the heating temperature of the heating section of the heating furnace is 1100-1240 ℃, the temperature of the soaking section is 1100-1200 ℃, and the heat preservation time of the soaking section is more than or equal to 30 min; the thickness of the intermediate blank is more than or equal to 2 times of the thickness of the finished product, and a large reduction system is adopted in rough rolling, so that the continuous 3-pass reduction rate after widening is more than or equal to 14 percent; the finish rolling temperature is 700-800 ℃, and the reduction rate of several passes before finish rolling is more than or equal to 10%;

(3) cooling after rolling: directly adding water, wherein the temperature of red returning is 450-570 ℃, and the cooling speed is 7-20 ℃;

(4) and (3) tempering after rolling: tempering at the temperature of 640-660 ℃ for mm x (2.0-3.5) min/mm of the plate thickness, and air cooling.

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