JP2022027527A - 630 MPa GRADE HIGH CORROSION-RESISTANT WEATHER-RESISTANT STEEL AND METHOD FOR PRODUCING THE SAME - Google Patents

Abstract

To provide a weather-resistant steel that has a novel composition and a good weather-resistant effect.SOLUTION: Provided is a 630 MPa grade high corrosion-resistant weather-resistant steel that is characterized in containing, in weight percentage, the following chemical composition: C≤0.12%, Si:2.20 to 3.00%, Mn≤1.50%, P:0.005 to 0.030%, S≤0.015%, Cr:2.90 to 3.70%, Ni:0.10 to 0.40%, Cu:0.20 to 0.60%, Als≥0.010%, balance Fe and unavoidable impurities.SELECTED DRAWING: None

Description

The present invention belongs to the technical field of ferrous metallurgy, and particularly relates to a 630 MPa grade high corrosion resistant weathering steel and a method for producing the same.

Steel corrosion is a widespread and serious problem in all areas of the country's economy and defense construction. According to statistics, in some industrialized countries, the economic loss caused by corrosion accounts for 2% -4% of its GDP, and atmospheric corrosion is the main form of corrosion of steel structures and all. It accounts for about half of the corrosion loss. Therefore, it is very significant for the research and development of weathering steel. Weathering steel, also known as atmospheric corrosion resistant steel, is a low alloy steel having good corrosion resistance in the atmosphere. Based on numerous domestic and international studies, when weathering steel is exposed to the atmosphere for extended periods of time, a layer of dense, well-adhered oxidation products is formed on its surface, forming a steel matrix from external corrosive substances. Is generally believed to significantly improve the corrosion resistance of weathering steel. Weathering steel is mainly used in rolled materials and vessels in China, but in some developed countries, including the United States and Japan, it is more widely used in steel structural buildings and urban facilities in exposed fashion. Weathering steel is most commonly used to build bridges in the United States, where exposed steel is widely used, with more than 500 buildings built of exposed weathering steel. Since 1965, exposed weathering steel has been used in Japan for exterior components such as building roofs, louvers, steel ribs, and exterior panel lamps.

As the field of application of weathering steel is expanding more and more, it is necessary to develop more kinds of weathering steel to meet the needs of the market.

The technical problem to be solved by the present invention is to develop a weathering steel having a novel composition and a good weathering effect.

In order to solve the above technical problems, the technical solution provided by the present invention is, by weight percentage, the following chemical composition: C ≦ 0.12%, Si: 2.20 to 3.00%, Mn ≤ 1.50%, P: 0.005 to 0.030%, S ≤ 0.015%, Cr: 2.90 to 3.70%, Ni: 0.10 to 0.40%, Cu: 0 To provide a 630 MPa grade high corrosion and weathering steel containing 20-0.60%, Als ≧ 0.010%, balance Fe and unavoidable impurities.

Preferably, the chemical composition of the 630 MPa grade high corrosion resistant weather resistant steel is C: 0.06 to 0.08%, Si: 2.60 to 2.80%, Mn: 0.85 to 1. 00%, P: 0.010 to 0.025%, S ≦ 0.007%, Cr: 3.30 to 3.50%, Ni: 0.20 to 0.30%, Cu: 0.28 to 0 .38%, Als: 0.015 to 0.050%, balance Fe and unavoidable impurities.

The atmospheric corrosion resistance index I of the 630 MPa grade high corrosion resistance weathering steel is 13.02 to 14.13.

The relative Q355B corrosion rate of 630 MPa grade high corrosion and weathering steel is 25% or less.

The 630 MPa grade high corrosion and weathering steel has a yield strength of 630 to 690 MPa, a tensile strength of 900 to 980 MPa, an elongation A of 18% or more, and an impact value of 60 J or more at −40 ° C.

The present invention further provides a method for producing a 630 MPa grade high corrosion and weathering steel, comprising the following steps:
Hot metal desulfurization-converter refining-LF-RH-LF-slab continuous casting-hot rolling-laminer cooling-coiling.

The present invention further provides the use of 630 MPa grade high corrosion and weathering steel, which is exposed to the open air in hot and humid regions in the field of construction or bridge construction or vehicle manufacturing.

The present invention has the following advantageous effects:
The present invention provides a high chromium weathering steel with a novel composition, the atmospheric corrosion resistance index I reaching 13.02 to 14.13, which is about twice as high as 6.0. Yes, thus achieving excellent air corrosion resistance of the product. In addition to good air corrosion resistance, low maintenance cost, long product life, and reduced risk of full cycle cost, environmental pollution, and corrosion destruction accidents, the high corrosion resistant weathering steel of the present invention is also hot and humid. It can be exposed to the outside air in the area, can be widely used in the fields of construction, bridge construction, or vehicle manufacturing, and has good utility value.

In the present invention, in terms of weight percentage, the following chemical compositions: C ≤ 0.12%, Si: 2.20 to 3.00%, Mn ≤ 1.50%, P: 0.005 to 0.030%, S. ≦ 0.015%, Cr: 2.90 to 3.70%, Ni: 0.10 to 0.40%, Cu: 0.20 to 0.60%, Als ≧ 0.010%, balance Fe and inevitable A 630 MPa grade high corrosion resistant weathering steel containing impurities is provided.

Preferably, the chemical composition of the 630 MPa grade high corrosion resistant weather resistant steel is C: 0.06 to 0.08%, Si: 2.60 to 2.80%, Mn: 0.85 to 1. 00%, P: 0.010 to 0.025%, S ≦ 0.007%, Cr: 3.30 to 3.50%, Ni: 0.20 to 0.30%, Cu: 0.28 to 0 .38%, Als: 0.015 to 0.050%, balance Fe and unavoidable impurities.

Among the components of the weathering steel described above, C is an effective reinforcing element in the steel, and an increase in carbon content may improve the strength of the steel. However, excessive carbon content can result in the following defects: many coarse and brittle carbide particles are formed in the steel, reducing the plasticity and toughness of the steel; segregation zones occur in the center of the steel sheet. , The bending performance and formability of steel are reduced, the weld carbon equivalent is increased, and the welding process is adversely affected. Therefore, according to the design of the present invention, C is 0.12% or less, preferably 0.06 to 0.08%.

Among the components of the above weathering steel, Mn having a strong solid solution strengthening effect can significantly lower the phase transformation temperature of the steel and make the fine structure of the steel finer. Mn is an important strengthening and toughening element. However, the addition of excess Mn may cause slab cracks in the continuous casting process, resulting in a decrease in the welding performance of the steel. Therefore, according to the design of the present invention, Mn is 1.50% or less, preferably 0.85 to 1.00%.

Among the components of the above weathering steel, S may form sulfide inclusions and reduce the performance of the steel. On the other hand, pitting corrosion may propagate during corrosion, which may adversely affect the corrosion performance. Therefore, according to the design of the present invention, S is 0.015% or less, preferably 0.007% or less.

Among the components of the above weathering steel, Al is added to the steel as a deoxidizing agent. However, if the Al content is excessive, nitrogen oxides are likely to precipitate at the austenite grain boundaries, which may lead to the formation of slab cracks. Therefore, according to the design of the present invention, Al is 0.010% or more, preferably 0.015 to 0.050%.

In the present invention, the content of Si, P, Cu, Cr and Ni in the steel is determined by the content of the elements C, Mn, S and Al for the purpose of improving the atmospheric corrosion resistance of the weather resistant steel. After that, Annex D for Weathering Structural Steels (GB / T4171-2008) "Guide to Evaluate the Atmospheric Corrosion Steel Resistance of Low Alloy Steel" Air Corrosion 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 is determined according to the formula.

The air corrosion resistance index of the present invention can reach about twice the specified value, and the corresponding defects that can be caused by the high content of Si and Cr elements are mainly smelted and controlled. It can be avoided by mutual cooperation of rolling and controlled cooling processes.

The addition of Cu to the steel is beneficial for the formation of a dense, well-bonded amorphous oxide (hydrocarbyl oxide) protective layer on the surface of the steel with obvious corrosion resistance. In addition, Cu and S form insoluble sulfides, which counteract the harmful effects of S on the corrosion resistance of the steel. However, since the melting point of Cu is lower than the heating temperature of the slab, if the Cu content is too high, the precipitated Cu gathers at the austenite grain boundaries in the liquid state, and a certain amount of the precipitated Cu is heated or hot-rolled. Sometimes it can cause cracks. In addition, according to the calculation formula of the air corrosion resistance index I, if the Cu content is too high or too low, the calculated value of the air corrosion resistance index I becomes small. Therefore, according to the design of the present invention, Cu is 0.20 to 0.60%, preferably 0.28 to 0.38%.

The addition of Ni to the steel significantly improves the corrosion resistance of the steel; while the elements Ni and Cu form a Ni-containing Cu-rich phase, which remains in the outer oxide layer in a solid state. Thus, the chances of enriching Cu in the matrix and forming a liquid Cu-rich phase are reduced, thus avoiding the development of high temperature brittle defects. Therefore, the Ni / Cu content in the steel is generally controlled to 1/2 or more. However, when the Ni content is excessive, the adhesion of the oxide scale increases and hot rolling defects are formed on the surface when pressed on the steel. Ni is a noble metal, and if the Ni content is excessive, the cost of the steel alloy will increase significantly. Therefore, according to the design of the present invention, Ni is 0.10 to 0.40%, preferably 0.20 to 0.30%.

According to the calculation formula of the air corrosion resistance index I, when the content of Si, P and Cr is large, the I value is greatly increased, and excellent air corrosion resistance can be achieved.

Si has a high solid solubility in the steel, which helps to refine the rust layer structure and reduce the overall corrosion rate of the steel. However, if the Si content is excessive, descaling during rolling becomes difficult, leading to deterioration of welding performance. Therefore, according to the design of the present invention, Si is 2.20 to 3.00%, preferably 2.60 to 2.80%.

P can effectively improve the atmospheric corrosion resistance of steel. The combined use of P and Cu in steel may exhibit better compositional effects, but excessive P content significantly reduces the plasticity and low temperature toughness of the steel. Therefore, according to the design of the present invention, P is 0.005 to 0.030%, preferably 0.010 to 0.025%.

Cr has a significant effect on improving the passivation ability of steel and helps to form a dense passivation film or rust preventive layer on the surface of the steel. Concentration of Cr in the rust layer can effectively improve the selective transfer characteristics of the rust layer to the corrosive medium. However, if the Cr content is excessive, the manufacturing cost becomes high. Therefore, according to the design of the present invention, Cr is 2.90 to 3.70%, preferably 3.30 to 3.50%.

Based on the preferred composition, the air corrosion resistance index I of the highly corrosion resistant weathering steel reaches 13.02 to 14.13, which is about twice as high as 6.0, and thus the product is excellent. Atmospheric corrosion resistance can be achieved.

The 630 MPa grade high corrosion and weathering steel has a yield strength of 630 to 690 MPa, a tensile strength of 900 to 980 MPa, an elongation A of 18% or more, and an impact value of 60 J or more at −40 ° C.

In the smelting process of high corrosion and weathering steel of the present invention, a large amount of alloy is added, the temperature drop in the smelting process is large, and large alloy carburizing and heat carburizing occur; at the same time, the large temperature drop is insufficient for ferrochrome. May cause a smelting effect and severe adhesion of the insert tube in the RH process. Therefore, the general mode "converter smelting-> LF-> RH-> slab continuous casting" cannot meet the production needs of this steel grade.

Therefore, the present invention further provides a method for producing a highly corrosion-resistant weathering steel, which comprises the following steps:
Hot metal desulfurization-converter refining-LF-RH-LF-slab continuous casting-hot rolling-laminer cooling-coiling.

The double LF process is used in the above-mentioned smelting process of the highly corrosion-resistant weathering steel of the present invention. Despite the inevitable increase in production costs, the addition of the LF process can efficiently control temperature, carbon, and effective use of alloys (no phenomenon of alloy loss due to adhesion of insert tubes) and sulfur refining. It is more advantageous in that it significantly reduces production risk. Table 1 shows the main technical means and control goals adopted in each process. In particular, the ferrochrome charged into the first LF process is reduced by 0.15% according to the lower limit of the composition, and the other alloying elements charged into the first LF are due to the low content and oxidizability. Instead, these alloying elements are first constructed after RH decarburization and deoxidation and fine-tuned after being charged into the second LF.

In the hot rolling and laminar cooling process of high corrosion and weathering steel, the slabs are hot-fed and hot-loaded, or immediately laminated and slowly cooled, at an emission temperature of 1240-1280 ° C. 24. It will be supplied to the furnace within an hour. The total length of rough rolling is completely descaled; the initial rolling temperature of finish rolling is 1020 ° C or lower, and the final rolling temperature is 810 to 850 ° C. The cooling water between the plurality of mill stands is completely closed, the sparse cooling is laminar cooling, and the coiling temperature is 580 to 620 ° C.

For steels with high alloy content, slabs are prone to edge crack defects after long-term stacking and at low furnace temperatures; therefore, slabs are hot-fed and hot-loaded or laminated immediately. , Slowly cooled and charged into the furnace within 24 hours.

Steels with a high silicon content may turn into firelite (Fe ₂ SiO ₄ ) having a melting point of 1173 ° C. between the iron oxide skin layer and the matrix during prolonged heating in the furnace. An effective way to eliminate or alleviate the scaling difficulties of silicon-containing steels is to raise the discharge temperature so that the surface temperature of the slab is higher than the melting point of Fe ₂ SiO ₄ during coarse descaling. The FeO / Fe ₂ SiO ₄ anchor is not formed when it is in the liquid state, thus facilitating scaling.

The cooling water between the mill stands is completely closed to reduce the rolling speed, thus reducing the cooling rate; at the same time, to reduce the cooling rate, sparse cooling is referred to as laminar cooling. Due to the high hardenability of high Cr steel, martensite structures that adversely affect the toughness and plasticity of the product are likely to appear at high cooling rates.

In the present invention, the method for producing a highly corrosion-resistant weathering steel is not limited to the above method, and a weathering steel having an air corrosion resistance index I of more than 6 can be smelted by another rational method.

The present invention further provides the use of highly corrosion and weathering steel, which is exposed to the open air in hot and humid areas in the field of construction or bridge construction or vehicle manufacturing.

Hereinafter, specific embodiments of the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited to these embodiments.

Examples and Comparative Examples High corrosion-resistant weathering steel is manufactured by conventional smelting, controlled rolling and controlled cooling processes, and a cycle press-fit corrosion test method for railway weathering steel (Test Method for Cycle Inspection and Corrosion of). Corrosion resistance was tested according to Rollway Weather-restance Steel (TB / T2375). Table 2 shows specific components of the highly corrosion-resistant weathering steel and the atmospheric corrosion resistance index I in Comparative Example 1 (ordinary weathering steel Q450NQR1) and Comparative Example 2 (low alloy high-strength steel Q355B).

From Examples and Comparative Examples, the atmospheric corrosion resistance index I of the high corrosion resistance weathering steel of the present invention is more than twice that of 6.0, which is much larger than that of ordinary weathering steel and low alloy high strength steel. It can be seen that high corrosion and weathering steel can achieve excellent air corrosion resistance. Steel products can be exposed to the open air in hot and humid areas, which reduces coating and rust removal costs, corrosion damage and environmental pollution, and has good potential applications.

Claims (7)

A 630 MPa grade high corrosion and weathering steel with the following chemical composition: C ≤ 0.12%, Si: 2.20 to 3.00%, Mn ≤ 1.50%, P: 0. 005 to 0.030%, S ≦ 0.015%, Cr: 2.90 to 3.70%, Ni: 0.10 to 0.40%, Cu: 0.20 to 0.60%, Als ≧ 0 A 630 MPa grade high corrosion and weathering steel characterized by containing 010%, balance Fe and unavoidable impurities. The chemical composition is C: 0.06 to 0.08%, Si: 2.60 to 2.80%, Mn: 0.85 to 1.00%, P: 0.010 to 0. 025%, S ≦ 0.007%, Cr: 3.30 to 3.50%, Ni: 0.20 to 0.30%, Cu: 0.28 to 0.38%, Als: 0.015 to 0 The 630 MPa grade high corrosion and weather resistant steel according to claim 1, which contains 050%, a balance Fe and unavoidable impurities. The 630 MPa grade high corrosion resistant weathering steel according to claim 1, wherein the atmospheric corrosion resistance index I of the high corrosion resistant weathering steel is 13.02 to 14.13. The 630 MPa grade high corrosion resistant weathering steel according to claim 1, wherein the relative Q355B corrosion rate of the high corrosion resistant weathering steel is 25% or less. Claim 1 is characterized in that the highly corrosion-resistant weathering steel has a yield strength of 630 to 690 MPa, a tensile strength of 900 to 980 MPa, an elongation A of 18% or more, and an impact value of 60 J or more at −40 ° C. 630 MPa grade high corrosion resistance weathering steel according to the above. The method for producing a 630 MPa grade high corrosion-resistant weathering steel according to any one of claims 1 to 5.
A manufacturing method comprising: hot metal desulfurization-converter refining-LF-RH-LF-slab continuous casting-hot rolling-laminar cooling-coiling. The use of the 630 MPa grade high corrosion resistant weathering steel according to any one of claims 1 to 5, wherein the high corrosion resistant weathering steel is used in a hot and humid region in the field of construction, bridge construction or vehicle manufacturing. Used, characterized by being exposed to.