JP7233481B2 - 660 MPa class high corrosion resistant weathering steel and method for producing the same - Google Patents

Description

The present invention belongs to the technical field of ferrous metallurgy, and more particularly relates to a 660 MPa class high corrosion-resistant weathering steel and a method for producing the same.

The damage of steel corrosion to national economy and national defense construction is a common and serious problem. Economic losses due to steel corrosion account for 2% to 4% of GDP in some developed countries, according to statistics. Atmospheric corrosion is the predominant form of corrosion in steel structures and accounts for approximately half of all corrosion losses. Therefore, atmospheric corrosion is very important for the research and development of weathering steel.

Weathering steel, also known as atmospheric corrosion resistant steel, is a low alloy steel that has good corrosion resistance in the atmosphere. Based on numerous studies at home and abroad, after long-term exposure to the atmosphere, a dense and well-adhered layer of oxidation products is formed on the surface of weathering steel to protect the steel from external corrosive substances. It is believed to isolate the matrix, thereby greatly improving the corrosion resistance of weathering steels.

In China, weathering steel is mainly used for rolling stock and containers. In developed countries such as the United States and Japan, weathering steel is more widely used in steel-framed buildings and public facilities. In the United States, a major use of weathering steel is in building bridges, and the use of exposed steel is expanding, with over 500 buildings made of exposed weathering steel. In Japan, since 1965, exposed weathering steel has been used for exterior components such as building roofs, blinds, steel ribs and exterior panel lamps. In order to meet market demands, it is necessary to develop weathering steel with good corrosion resistance.

A technical problem to be solved by the present invention is to provide a 660 MPa class high corrosion-resistant and weather-resistant steel.

The technical solution used in the present invention to solve the above technical problems is the following chemical composition: C≤0.12 wt%, Si: 2.20-3.00 wt%, Mn≤1 .50% by weight, P: 0.060-0.150% by weight, S≦0.015% by weight, Cr: 2.90-3.70% by weight, Ni: 0.10-0.40% by weight, Cu : 0.20 to 0.60% by weight, Als≧0.010% by weight, and the balance being Fe and unavoidable impurities.

Preferably, the 660 MPa class high corrosion-resistant weathering steel has the following chemical composition: C: 0.06-0.08 wt%, Si: 2.60-2.80 wt%, Mn: 0.85-1. 00 wt%, P: 0.080 to 0.120 wt%, S ≤ 0.007 wt%, Cr: 3.30 to 3.50 wt%, Ni: 0.20 to 0.30 wt%, Cu: 0.28 to 0.38% by weight, Als: 0.015 to 0.050% by weight, balance Fe and unavoidable impurities.

Furthermore, the atmospheric corrosion resistance index I of the 660 MPa class high corrosion resistance weathering steel is 14.10 to 15.51.

Furthermore, the 660 MPa grade high corrosion resistant weathering steel has a yield strength of 660-740 MPa, a tensile strength of 940-1040 MPa, an elongation A of 18% or more, and an impact value of 27 J or more at -40°C.

The present invention also provides a method for producing a 660 MPa class highly corrosion-resistant and weather-resistant steel, comprising:
A method is provided that includes the steps of hot metal desulfurization → converter smelting → LF → RH → LF → slab continuous casting → hot rolling → laminar cooling → coiling.

The present invention also provides the use of 660 MPa class high corrosion resistant weathering steel in the field of building, bridge construction or vehicle manufacturing, the high corrosion resistant weathering steel can be exposed to hot and humid areas.

The effects of the present invention are as follows.

The present invention has a yield strength of 660-740 MPa, a tensile strength of 940-1040 MPa, an elongation A of 18% or more, an impact value of 27 J or more at −40° C., 14.10-15.51 which is twice 6.0 and a corrosion rate of 20% or less against Q355B, a new composition of 660 MPa class high corrosion resistant weathering steel. The 660 MPa class high corrosion resistant weathering steel of the present invention provides good atmospheric corrosion resistance, reduced future maintenance costs, long product life, cost savings over the entire cycle, and reduced risk of environmental pollution and corrosion failure accidents. As such, it is capable of exposure to hot and humid areas and is therefore widely used in the fields of architecture, bridge construction or vehicle construction, demonstrating broad applicability.

The present invention has the following chemical composition: C ≤ 0.12 wt%, Si: 2.20-3.00 wt%, Mn ≤ 1.50 wt%, P: 0.060-0.150 wt%, S ≦0.015 wt %, Cr: 2.90 to 3.70 wt %, Ni: 0.10 to 0.40 wt %, Cu: 0.20 to 0.60 wt %, Als≧0.010 wt % , balance Fe and unavoidable impurities.

Preferably, the 660 MPa class high corrosion-resistant weathering steel has the following chemical composition: C: 0.06-0.08 wt%, Si: 2.60-2.80 wt%, Mn: 0.85-1. 00 wt%, P: 0.080 to 0.120 wt%, S ≤ 0.007 wt%, Cr: 3.30 to 3.50 wt%, Ni: 0.20 to 0.30 wt%, Cu: 0.28 to 0.38% by weight, Als: 0.015 to 0.050% by weight, balance Fe and unavoidable impurities.

C is an effective strengthening element in steel, and increasing the carbon content can improve the strength of steel. However, the excessive content of carbon can lead to the following consequences: many coarse and brittle carbide particles are produced in the steel, reducing the plasticity and toughness of the steel; , reducing its bending performance and formability; increasing the weld carbon equivalent and adversely affecting the welding process. Therefore, according to the design of the present invention, C is 0.12% or less, preferably 0.06-0.08%.

Mn can significantly lower the phase transformation temperature of steel and refine its microstructure due to its strong solid-solution strengthening effect. Mn is an important strengthening and toughening element. However, excessive Mn addition can cause slab cracks during the continuous casting process, resulting in poor weldability of the steel. Therefore, according to the design of the present invention, Mn is 1.50% or less, preferably 0.85-1.00%.

S can form sulfide inclusions and degrade steel performance; at the same time, it can propagate pitting corrosion during corrosion and adversely affect corrosion performance. Therefore, according to the design of the present invention, S is 0.015% or less, preferably 0.007% or less.

Al is added to steel as a deoxidizer. However, when the Al content is excessive, nitrogen oxides tend to precipitate at the austenite grain boundaries, and slab cracks may occur. Therefore, according to the design of the present invention, Als is not less than 0.010%, preferably 0.015-0.050%.

In the present invention, the contents of Si, P, Cu, Cr and Ni in steel are determined for the purpose of improving the atmospheric corrosion resistance of weathering steel. Later, the resistance of Annex D "Guide to Evaluate the Atmospheric Corrosion Resistance of Low Alloy Steels" to Weathering Structural Steels (GB/T4171-2008) Atmospheric 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 .

The addition of Cu to steel promotes the formation of a dense, well-adhered amorphous oxide (hydrocarbyl oxide) protective layer on the steel surface with outstanding corrosion resistance. Furthermore, the insoluble sulfides produced by Cu and S counteract the detrimental effects of S on the corrosion resistance of steel. However, when the Cu content is excessive, the melting point of Cu is lower than the heating temperature of the billet, so the precipitated Cu gathers at the austenite grain boundaries in the liquid phase state, and a certain amount of the precipitated Cu is lost during heating or heat. It may cause cracks during inter-rolling. According to the calculation formula of the atmospheric corrosion resistance index I, the calculated value of the atmospheric corrosion resistance index I becomes small when the Cu content is too low or too high. Therefore, according to the design of the present invention, Cu is 0.20-0.60%, preferably 0.28-0.38%.

The addition of Ni to the steel significantly improves the corrosion resistance of the steel; on the other hand, the elements Ni and Cu form a Cu-rich phase containing Ni, which is solid-state in the outer oxide layer. It remains to avoid the occurrence of hot brittleness defects by reducing the chances of enrichment of Cu in the matrix and formation of liquid Cu-rich phases. Therefore, the Ni/Cu content in steel is generally controlled to 1/2 or more. However, excessive Ni content increases the deposition of oxide scales and hot rolling defects are formed on the surface when pressed into steel. Furthermore, Ni is a noble metal and excessive Ni content significantly increases the cost of the steel alloy. Therefore, according to the design of the present invention, Ni is 0.10-0.40%, preferably 0.20-0.30%.

P can effectively improve the atmospheric corrosion resistance of steel. Combined use of P and Cu in steel can exhibit good compositional effects, but an excessive content of P significantly reduces the plasticity and low-temperature toughness of steel. Therefore, according to the design of the present invention, P is 0.060-0.150%, preferably 0.080-0.120%.

Cr has a significant effect on improving the passivation ability of steel and helps form a dense passivation film or antirust layer on the surface of steel. Enrichment of Cr in the rust layer can effectively improve the selective transmission properties of the rust layer to corrosive media. However, excessive Cr content increases manufacturing costs. Therefore, according to the design of the present invention, Cr is 2.90-3.70%, preferably 3.30-3.50%.

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

Based on the preferred composition, the atmospheric corrosion resistance index I of the 660 MPa class high corrosion resistance weathering steel can reach 14.10-15.51, which is twice 6.0, so that the product has excellent atmospheric resistance. achieve corrosiveness;

According to the present invention, the corrosion rate of 660 MPa class high corrosion resistance and weathering steel is 20% or less with respect to the corrosion rate of Q355B.

According to the present invention, the 660 MPa class high corrosion resistant weathering steel has a yield strength of 660-740 MPa, a tensile strength of 940-1040 MPa, an elongation A of 18% or more, and an impact value of 27 J or more at -40°C.

The present invention also provides a method for producing a 660 MPa class highly corrosion-resistant and weather-resistant steel, comprising:
A method is provided that includes the steps of hot metal desulfurization → converter smelting → LF → RH → LF → slab continuous casting → hot rolling → laminar cooling → coiling.

In the above method for producing 660 MPa class high corrosion-resistant weathering steel, the parameters of each process are controlled according to Table 1.

In the method of producing 660 MPa class high corrosion resistance and weathering steel, a large amount of alloy is added in the smelting process, so the temperature drops greatly, causing alloy carburization and heat carburization; It can cause poor melting effect and severe adhesion of the insertion tube in the RH process. Therefore, the general method of "converter smelting → LF → RH → slab continuous casting" cannot meet the production needs of this steel grade.

The double LF process is used as a smelting process for 660 MPa class high corrosion resistant weathering steel. The addition of the LF process has the advantage that the temperature, carbon and alloy can be used effectively (without the alloy loss phenomenon due to adhesion of the insertion tube) and sulfur refining, despite the inevitable increase in production costs. It is more advantageous in that it can be controlled efficiently and significantly reduces production risks. The table shows the main technical measures and control targets adopted in each process. The ferrochromium in the first charge in the LF process is reduced by 0.15% depending on the lower composition limit, and the other alloying elements in the first charge in the LF are due to their low content and oxidizing properties. not configured. These alloying elements are first made up after RH decarburization and deoxidization and fine-tuned after the second charge to LF.

In the hot rolling and layer cooling process of 660 MPa grade high corrosion resistant weathering steel, the casting billet is either hot fed and hot charged, or immediately layered and slowly cooled, discharged at 1240-1280 ° C. The furnace is fed within 24 hours at temperature. Descaling the total length of rough rolling; the initial rolling temperature of finish rolling is 1020°C or less, and the final rolling temperature is 810-850°C. The cooling water between multiple mill stands is completely closed, loose cooling is laminar cooling, and the coiling temperature is 580-620°C.

For steels with high alloy content, billets are prone to edge crack defects after long-term lamination and at low furnace temperatures, so the billets are either hot-fed and hot-charged, or immediately laminated and slow-rolled. and cooled and charged into the furnace within 24 hours.

Steels with high silicon content can transform into fayalite (Fe ₂ SiO ₄ ) with 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 mitigate the scaling difficulties of silicon- _containing steels is to increase the discharge temperature so that the surface temperature of the slab during rough descaling is above the melting point of _Fe2SiO4 , FeO /Fe ₂ SiO ₄ anchors are prevented from being formed in a liquid phase state, so that they can be easily removed. The cooling water between multiple mill stands is completely closed to reduce the rolling speed and reduce the cooling speed; Due to the high hardenability of high Cr steels, when the cooling rate is high, a martensitic structure is likely to appear, which adversely affects the toughness and plasticity of the product.

Specific embodiments of the present invention are further described with reference to examples and comparative examples.

EXAMPLES AND COMPARATIVE EXAMPLES 660 MPa grade high corrosion resistant weathering steels were produced by conventional smelting process and controlled rolling and cooling process, respectively, and subjected to the Test Method for Cycle Infiltration of railway weathering steel. and Corrosion of Railway Weather-resistance Steel (TB/T2375) for Q355B. Table 2 shows the specific composition and atmospheric corrosion resistance of the 660 MPa class high corrosion resistant weathering steel of the present invention, the normal weathering steel Q450NQR1 of Comparative Example 1, and the low alloy high strength steel Q355B of Comparative Example 2.

From the examples and comparative examples, the atmospheric corrosion resistance index I of the 660 MPa class high corrosion resistance weathering steel is twice 6.0, and the atmospheric corrosion resistance index I of the normal weathering steel and the low alloy high strength steel It can be seen that it is much larger than I and exhibits excellent atmospheric corrosion resistance. High corrosion resistance weathering steel can be exposed to hot and humid areas, which reduces coating and rust removal costs, corrosion failure accidents and environmental pollution, and can be applied to buildings, bridges, vehicles and other fields. , showing good prospects for applications.

Claims (6)

The following chemical composition: C : 0.06-0.12 % by mass , Si: 2.20-3.00% by mass , Mn : 0.85-1.50 % by mass , P: 0.060-0.150 % by mass , S≦0.015% by mass , Cr: 2.90 to 3.70% by mass , Ni: 0.10 to 0.40% by mass , Cu: 0.20 to 0.60% by mass , Al: 0 A 660 MPa class high corrosion resistant weathering steel characterized by comprising 0.010 to 0.050 % by mass, the balance being Fe and unavoidable impurities. The following chemical composition: C: 0.06-0.08% by mass , Si: 2.60-2.80% by mass , Mn: 0.85-1.00% by mass , P: 0.080-0.120 % by mass , S≦0.007% by mass , Cr: 3.30 to 3.50% by mass , Ni: 0.20 to 0.30% by mass , Cu: 0.28 to 0.38% by mass , Al : 0 015-0.050% by mass , the balance being Fe and unavoidable impurities. 3. The 660 MPa class high corrosion resistant weathering steel according to claim 1 or 2, wherein the atmospheric corrosion resistance index I of the 660 MPa class high corrosion resistant weathering steel is 14.10 to 15.51. The 660 MPa class high corrosion resistant weathering steel has a yield strength of 660 to 740 MPa, a tensile strength of 940 to 1040 MPa, an elongation A of 18% or more, and an impact value of 27 J or more at -40 ° C. The 660 MPa class high corrosion-resistant weathering steel according to any one of claims 1 to 3. 5. The method according to any one of claims 1 to 4, characterized by including the steps of hot metal desulfurization → converter smelting → LF → RH → LF → slab continuous casting → hot rolling → laminar cooling → coiling. A method for producing 660 MPa class high corrosion-resistant and weather-resistant steel. 5. The 660 MPa class high corrosion-resistant weathering steel is used in the fields of architecture, bridge construction or vehicle manufacturing, and can be exposed to hot and humid regions. Use of 660 MPa class high corrosion resistance weathering steel described in .