CN115896612A - Low-carbon equivalent weathering steel with yield strength of 500MPa and production method thereof - Google Patents

Abstract

The invention belongs to the field of medium plate production, and relates to low-carbon equivalent weathering steel with yield strength of 500MPa and a production method thereof. The invention designs that the carbon content is 0.09-0.12, the carbon equivalent Ceq is less than or equal to 0.45, the whole Cr-Ni-Cu-Ti series microalloying technology with low C, low Mn and low Cr is adopted, the expensive Mo alloy is not required to be added through the component design, the production cost is reduced, meanwhile, the high-temperature condition precipitation of the titanium compound during the blank rolling is adopted, the austenite crystal growth in the rolling process is prevented, and the comprehensive performance of the material is improved through fine grain strengthening and precipitation strengthening; the heat treatment link is not needed in the production flow, and the weathering steel with 500MPa grade yield strength and excellent low-temperature impact and welding performance can be obtained through controlled rolling and heap cooling.

Description

Low-carbon equivalent weathering steel with yield strength of 500MPa and production method thereof

Technical Field

The invention belongs to the field of medium plate production, and relates to low-carbon equivalent weathering steel with yield strength of 500MPa and a production method thereof.

Background

The weathering resistant steel is also called atmospheric corrosion resistant steel, which is characterized in that elements such as Cu, cr, ni and Mo are added on the basis of plain carbon steel, so that a compact oxide film with good adhesion with base metal is formed between a rust layer of the steel and a base, oxygen and water in the atmosphere are prevented from permeating into the base steel, and the corrosion of the base steel is slowed down. Compared with common steel, the weathering steel has stronger atmospheric corrosion resistance, can be directly used in atmospheric environment without painting, and has better corrosion resistance along with the increase of atmospheric exposure age. With the rapid development of high-rise buildings and cross-sea bridges, the application prospect of the high-strength weathering steel is increasingly wide. The welding of high-rise buildings and sea-crossing bridges is generally about open air, the construction environment is poor, the measures of heat preservation and slow cooling after welding are difficult to implement, and the weather-resistant steel added with elements such as Cu, cr, ni and Mo which increase the carbon equivalent has great influence on the quality of open-air welding products.

Patent No. CN201510247401.1 introduces a production process of low-carbon weathering steel, which adopts Cr-Ni-Cu system component design with low C, low Mn and medium Cr, improves the hardness and corrosion resistance of steel by adding Sb element, but the application of Sb element in steel is not mature, on the other hand, the improper treatment of Sb element increases the brittleness of steel and deteriorates the performance of steel.

The patent CN201811338543.9 introduces a production process of low-carbon microalloyed Q690-grade high-strength weather-resistant steel, and a V-N-Cr-Ni-Cu-Mo series microalloying technology, so that on one hand, the addition of V and Mo precious alloys increases the production cost, on the other hand, the application of the addition of nitrogen in molten steel in steel is immature, the control is improper, and N is easy to form nitrides with Al, nb, ni and other elements in the steel, so that cracks can be formed on the surface or under the skin of a casting blank, and the surface quality of the casting blank is influenced.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

Aiming at the problems, the invention aims to provide the low-carbon equivalent weathering steel with the yield strength of 500MPa and the production method thereof, which adopts the Cr-Ni-Cu-Ti series microalloying technology with low C, low Mn and low Cr, reduces the production cost by not adding precious Mo alloy through component design, simultaneously prevents austenite grains from growing in the rolling process by adopting the high-temperature precipitation of titanide during blank rolling, and improves the comprehensive performance of the material through fine grain strengthening and precipitation strengthening.

The invention also aims to provide a production method of the low-carbon equivalent weathering steel with the yield strength of 500 MPa.

In order to achieve the purpose, the invention adopts the technical scheme that: low-carbon equivalent weathering steel with yield strength of 500MPa and raw material thereofThe production method has the advantages that the thickness of the steel plate is 12-60 mm, the carbon equivalent Ceq is less than or equal to 0.45, the carbon content is less than or equal to 0.12, the steel plate has good welding performance, the atmospheric corrosion resistance index I is more than or equal to 6.5, and the corrosion rate is 1.3-1.43 g/m ² H-40 ℃ KV2 type impact energy of 140-190J; comprises the following chemical components in percentage by mass (unit, wt%):

c:0.09 to 0.12, si: 0.30-0.40, mn:1.20 to 1.40, P: less than or equal to 0.015, S: not more than 0.005, cr is 0.35-0.50, cu:0.18 to 0.25, 0.15 to 0.30 of Ni, ti:0.055 to 0.075, and the balance Fe and residual elements.

Regarding the component design, it is to be noted that:

c is a main strengthening element in steel, the steel plays roles of structure strengthening and precipitation strengthening, the ductile-brittle transition temperature is increased along with the increase of the C content, and the welding performance is poor, so the C content needs to be controlled to be less than or equal to 0.12, and preferably 0.09-0.12;

cr is combined with carbon to form a chromium-carbon compound, has the characteristics of fine and uniform distribution, and has the effect of improving strength;

ni is the most effective element for improving the low-temperature toughness of steel and reducing the brittle transition temperature, and the higher the Ni content is, the better the impact toughness of the steel at extremely low temperature is; meanwhile, three elements of Ni, cr and Cu are added, so that a compact protective film with strong adhesiveness is formed on the surface of the steel, corrosion is prevented from diffusing and developing inwards, and a substrate below the rust layer is protected to slow down the corrosion speed of the steel;

ti has the function of fixing N in molten steel, reduces the plasticity reduction transition temperature of steel, improves the thermoplasticity of steel billets, weakens the sensitivity of cracks generated on the steel billets, simultaneously has the functions of refining grains and precipitation strengthening, and has the characteristics of dispersion distribution of C and N compound precipitation particles of Ti, thereby pinning dislocation and playing a strong role in strengthening; in addition, ti is relatively cheap, and a proper amount of Ti can be added to replace the expensive Mo alloy.

The production method comprises the steps of converter smelting, LF refining, VD vacuum refining, continuous casting, heating, controlled rolling and stack cooling;

the controlled rolling process adopts two-stage rolling, wherein the rolling temperature of one stage is 1000-1100 ℃, the controlled rolling process adopts high-temperature low-speed high-pressure rolling, the pass reduction rate is 12-15%, the steel is dried in the air by 2-2.5 times the thickness of a finished product, ti, N and S form a compound of TiN and Ti 4C 2S 2, the controlled rolling process has very high precipitation temperature, and the controlled rolling process can prevent austenite grains from growing to be large at high temperature so as to refine initial grains during rolling, and the fine grain strengthening and precipitation strengthening effects are obvious under the conditions of low C and low Mn; the second-stage rolling temperature is 820-880 ℃, the pass reduction is more than or equal to 15%, the rolled steel plate is subjected to ACC laminar cooling, the water inlet temperature is more than or equal to 750 ℃, and the red return temperature is 550-600 ℃;

in the process of the cooling by heaping, the temperature of the rolled steel plate in a slow cooling pit is more than or equal to 400 ℃, the slow cooling time is 36-48 hours, the height of a slow cooling stack is controlled to be 1.5-2 m, and the upper surface and the lower surface of the steel plate are strictly forbidden to be exposed in the air.

The steel grade obtained by the scheme has the advantages of low production cost, simple rolling operation process, no need of quenching and tempering treatment, atmospheric corrosion resistance, good comprehensive performance of obdurability, good low-temperature impact performance and easy realization of industrial production, and in the material design, the carbon equivalent is less than or equal to 0.45, the carbon content is less than or equal to 0.12, the steel grade has good weldability, and the welding is carried out after the material is preheated.

Drawings

FIG. 1 is a metallographic structure picture of a 40mm thick 500MPa low-carbon equivalent weathering steel plate obtained by an embodiment of the invention

Detailed Description

The low-carbon equivalent weather-resistant steel plate with the yield strength of 500MPa and the thickness of 12-60 mm and the production method thereof comprise the following chemical components in percentage by mass (unit, wt%):

c:0.09 to 0.12, si: 0.30-0.40, mn:1.20 to 1.40, P: less than or equal to 0.015, S: not more than 0.005, cr is 0.35-0.50, cu: 0.18-0.25, ni 0.15-0.30, ti:0.055 to 0.075, the others are Fe and residual elements, the carbon equivalent Ceq is less than or equal to 0.45, and the atmospheric corrosion resistance index I is more than or equal to 6.5.

The production process is mainly controlled as follows:

1) The requirements of converter smelting process points

The molten iron in the converter is subjected to pre-desulfurization treatment, and the content of S in the molten iron is less than or equal to 0.015 percent. By adopting the low-pull carburization and dephosphorization process, the tapping P is less than or equal to 0.01 percent, and the tapping C is less than or equal to 0.04 percent. After tapping, a slag blocking cone is used for blocking slag, and the thickness of converter slag is controlled to be below 30mm so as to avoid slag return P; after the molten steel arrives at the argon station, 200kg of lime is added into the molten steel in advance, and argon is blown for 5min for stirring.

2) Point requirements of LF refining process

Large amount of slag is adopted for slagging, 100 tons of LF refining furnace, and the dosage of single furnace lime is 800-900 Kg. The white slag is kept for 30-40 min, and the content of S is controlled to be less than or equal to 0.005 percent. Adding ferroboron in the second heating process after the white slag is formed. Adding a steel aluminum wire of 2.0m/t to the station, wherein the process deoxidizer adopts aluminum particles and calcium carbide, the dosage of the aluminum particles is controlled to be 30-60 Kg, and the white slag is kept for 15-18 min;

3) VD vacuum refining process point requirement

The pressure maintaining time is controlled according to 12-15 min under the pressure less than or equal to 67Pa, soft blowing is carried out for 3-5 min after vacuum breaking, and then a crane ladle is prepared for leaving the station.

4) Continuous casting

And the continuous casting link is well protected for pouring, and the superheat degree is controlled according to 5-20 ℃.

5) Essential point of heating process

The first heating temperature is less than or equal to 950 ℃, the second heating temperature is 1210-1230 ℃, the temperature of the soaking section is 1200-1220 ℃, and the heating time is 11-13 min/cm.

6) The key points of the rolling and ACC laminar cooling process

Two-stage rolling is adopted, wherein the starting rolling temperature of one stage is 1000-1100 ℃, high-temperature low-speed high-pressure rolling is adopted, the pass reduction rate is 12-15%, and the finished product thickness is 2-2.5 times that of steel airing; the two-stage rolling temperature is 820-880 ℃, the pass reduction is more than or equal to 15%, the crystal grains are fully crushed, and the crystal grains are prevented from growing. And performing ACC laminar cooling on the rolled steel plate, wherein the water inlet temperature of the steel plate is more than or equal to 750 ℃, and the red returning temperature is 550-600 ℃.

7) Key point of slow cooling process

The temperature of the rolled steel plate entering a slow cooling pit is more than or equal to 400 ℃, and the slow cooling time is 36-48 hours. The height of the slow cooling stack is controlled to be 1.5-2 m, and the upper surface and the lower surface of the steel plate are strictly forbidden to be exposed in the air.

TABLE 1 chemical composition and mass percent of low carbon equivalent weathering steel plate of each example

Remarking: carbon equivalent Ceq = C + Mn/6+ (Cr + Mo + V)/5 + (Ni + Cu)/15

Corrosion performance index I =26.01 (% Cu) +3.88 (% Ni) +1.20 (% Cr) +1.49 (% Si) +17.28 (% P) -7.29 (% Cu) (% Ni) -9.10 (% Ni) (% P) -33.39 (% Cu) ²

TABLE 2 mechanical Properties of the Low carbon equivalent weathering steel sheets of each example

TABLE 3 Corrosion resistance of the low carbon equivalent weathering steel sheets of each example

Periodic infiltration corrosion test is adopted, and the test conditions are as follows:

sample size: 4 × 45 × 60mm

Solution: 0.01mol/L NaHSO3 solution with the initial PH value of 4.4-4.8;

temperature: 45 +/-2 ℃;

relative humidity: 70. + -.5% RH;

in the test tank, 1.5L of solution in the tank is taken out every 24h, and 2L of NaHSO3 solution of 0.02mol/L is added. Acid washing according to the chemical method of GB/T16545 (1L acid washing solution preparation method: 500ml deionized water, 500ml hydrochloric acid, 3.5g hexamethylenetetramine)

Through reasonable chemical composition design and production process control, the low-carbon equivalent weather-resistant steel plate with the thickness of 12-60 mm and the yield strength of 500MPa is successfully developed. The carbon equivalent is less than or equal to 0.45, the yield strength is 520-550 MPa, the tensile strength is 630-660 MPa, and the elongation is 23.0-25.0%; -40 ℃ K _V2 The type impact power is 140 to 190J, and the corrosion rate is 1.3 to 1.43g/m ² ·h。

Claims (2)

1. The low-carbon equivalent weathering steel with the yield strength of 500MPa and the production method thereof are characterized in that the thickness of the steel plate is 12-60 mm, and the steel plate comprises the following chemical components in percentage by mass (unit, wt%): c:0.09 to 0.12, si: 0.30-0.40, mn:1.20 to 1.40, P: less than or equal to 0.015, S: not more than 0.005, 0.35-0.50 of Cr, cu: 0.18-0.25, ni 0.15-0.30, ti: 0.055-0.075, and the others are Fe and residual elements;

the carbon equivalent Ceq is less than or equal to 0.45, the atmospheric corrosion resistance index I is more than or equal to 6.5, and the corrosion rate is 1.3-1.43 g/m ² ·h，-40℃K _V2 The type impact energy is 140 to 190J.

2. The method for producing the low carbon equivalent weathering steel with yield strength of 500MPa according to claim 1, characterized by comprising the following steps: smelting in a converter, LF refining, VD vacuum refining, continuous casting, heating, controlled rolling and stack cooling;

the controlled rolling process adopts two-stage rolling, wherein the rolling temperature of the first stage is 1000-1100 ℃, the high-temperature low-speed high-reduction rolling is adopted, the pass reduction rate is 12-15%, the finished product thickness is 2-2.5 times that of steel airing, the rolling temperature of the second stage is 820-880 ℃, the pass reduction is more than or equal to 15%, the rolled steel plate is subjected to ACC laminar cooling, the water inlet temperature is more than or equal to 750 ℃, and the red return temperature is 550-600 ℃;

in the process of the cooling by heaping, the temperature of the rolled steel plate in a slow cooling pit is more than or equal to 400 ℃, the slow cooling time is 36-48 hours, the height of a slow cooling stack is controlled to be 1.5-2 m, and the upper surface and the lower surface of the steel plate are strictly forbidden to be exposed in the air.

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