CN104372246A - 400 MPa-grade tungsten-containing corrosion-resistant twisted steel and preparation method thereof - Google Patents

Abstract

The invention provides a 400 MPa-grade tungsten-containing corrosion-resistant twisted steel and a preparation method thereof. The twisted steel comprises the following components (wt%): basic components: 0.03-0.05% of C, 0.3-0.6% of Si, 0.6-1.2% of Mn, less than or equal to 0.01% of P, less than or equal to 0.01% of S, 8.0-10.0% of Cr and 1.0-2.0% of W; optional ingredients: v is 0.04-0.10%, RE is 0.01-0.05%, or the combination of two of the above two; the balance of Fe and inevitable impurities. The invention has the advantages that the seawater corrosion resistance of the steel bar can be improved by more than 4 times compared with the common thread steel bar, the performance is stable, the structure is mainly ferrite and bainite, the good strength and plasticity are ensured, and the invention can be widely applied to reinforced concrete building structures in marine environment.

Description

A 400MPa grade tungsten-containing corrosion-resistant threaded steel bar and its preparation method

technical field

The invention relates to the field of alloy steel, in particular to a 400MPa grade tungsten-containing corrosion-resistant threaded steel bar and a preparation method thereof.

Background technique

Coastal and marine structures such as sea-crossing bridges, breakwaters, trestles and harbor wharfs have long been in the harsh environment of seawater erosion. Therefore, the durability of marine concrete structures has become increasingly prominent, and reliable anti-corrosion measures should be taken. As the main structural material, steel bars are widely used in concrete structures, and their corrosion in seawater is an important factor for the corrosion of reinforced concrete structures.

The seawater corrosion environment can be divided into five zones from the sea level down, namely, the marine atmosphere zone, the splash zone, the tidal range zone, the full immersion zone and the sea soil zone. Among them, the worst corrosion conditions are the salt-rich splash zone and the oxygen-rich tidal zone on the surface of the seawater film. The electrochemical anti-corrosion measures of zinc sacrificial anode can protect the steel bars in the full immersion zone and sea soil zone to a certain extent, but it cannot prevent the corrosion of steel bars in the splash zone and tidal zone. However, if the coating method is used, there is a hidden danger that the coating material will deteriorate year by year and peel off from the steel bar, which will accelerate the occurrence of local corrosion. Therefore, the effective anti-corrosion measure of steel bars in the marine environment is the design of its own alloying composition. By adding an appropriate amount of alloying elements, it changes in structure, structure and electrochemical properties, thereby slowing down or preventing corrosion.

In recent years, a lot of research and development have been carried out on seawater corrosion-resistant steel at home and abroad. Foreign countries often increase the content of corrosion-resistant elements such as Cr, Ni, and Mo to enhance the rust resistance, pitting resistance and crack resistance of steel in seawater environments. corrosive. However, due to the large addition of expensive metal elements such as Ni and Mo, the cost of these steel materials is too high to be widely used in engineering. Such as the USNN08354 (23Cr-35Ni-7.5Mo-0.2N) super stainless steel developed by Japan, its Ni and Mo element content has reached more than 40%. In China, the corrosion resistance of steel is mostly improved by compounding small amounts of elements such as Cu, P, Cr, Ni, Nb, V, etc., but the improvement is relatively limited. For example, the patent authorization announcement number of Guangxi Shenglong Metallurgy Co., Ltd. is CN102321849B, and the patent named "a preparation method of nickel-chromium alloy steel" contains Ni 0.05-3.0%, Cr 0.05-6.0%, Nb or V0.0 ~0.25%, the weather resistance is only better than Corten A.

Contents of the invention

The present invention aims to provide a 400MPa level tungsten-containing corrosion-resistant threaded steel bar and its preparation method. The structure is mainly ferrite and bainite. Through the composite action of Cr and W elements, it has excellent seawater corrosion resistance. Meet the durability needs of marine concrete structures.

To achieve the above object, the present invention takes the following technical solutions:

A 400MPa grade tungsten-containing corrosion-resistant threaded steel bar, characterized in that it contains the following components calculated by weight percentage: C 0.03-0.05%, Si 0.3-0.6%, Mn 0.6-1.2%, P ≤ 0.01%, S ≤ 0.01%, Cr 8.0～10.0%, W 1.0～2.0%; optional components: V 0.04～0.10%, RE 0.01～0.05%, any one or a combination of two; the rest is Fe and unavoidable impurities .

Based on the above composition scheme, after pre-desulfurization of molten iron, molten iron, scrap steel and tungsten elements are added to the electric furnace and then side-blown oxygen smelting is carried out until the carbon content in the molten steel is less than 0.06%, and the phosphorus content is less than 0.01%. The temperature of the steel is less than 1680°C. Add Si and Mn alloy elements for alloy deoxidation when the steel is tapped to 1/4, add carbon powder and slagging material; add Cr alloy elements and use RH vacuum refining for decarburization, and then use LF furnace Refining and deoxidizing until the oxygen content in the molten steel is 0.002% to 0.005%; after deoxidizing, add other alloy elements, heat the molten steel to a temperature of 1590-1620°C, add conventional covering agents, and send it to the continuous casting process to pour into billets. Protective pouring is used during billet continuous casting to prevent breakout. The heating temperature of the continuous casting slab in the soaking section of the heating furnace is 1150-1200°C. After rough rolling and intermediate rolling, it is finished rolling at 950-1050°C. Water penetration is prohibited after rolling, air cooling on the cooling bed at 930-980°C, trimming and shearing, and packing into storage. The corrosion resistance of this 400MPa-grade tungsten-containing corrosion-resistant threaded steel bar is more than 4 times higher than that of ordinary HRB400 steel bars. At the same time, its yield strength is > 400MPa, tensile strength > 650MPa, elongation after fracture > 21%, and the maximum total elongation Rate > 9%.

The mechanism and effect of component among the present invention:

C is an important strengthening element. It mainly exists in the form of carbides in steel, which plays the role of precipitation strengthening and grain refinement. However, C and Cr have a great affinity and can form a series of complex carbides with chromium. The generation of carbides increases the strength and hardness of steel, but also reduces the corrosion resistance of steel. In addition, too high C content will reduce the plasticity and toughness of steel, and deteriorate the weldability of steel. In order to ensure good corrosion resistance of steel grades, the range of C content in the present invention is selected as 0.03-0.05%.

Si is an important reducing agent and deoxidizer, adding silicon to steel can significantly improve the elastic limit, yield point and tensile strength of steel. The combination of silicon and molybdenum, tungsten, chromium, etc. has a certain effect on improving corrosion resistance and oxidation resistance, but increasing the silicon content will reduce the weldability of steel. The range of Si content in the present invention is selected as 0.3-0.6%.

Mn is a good deoxidizer and desulfurizer. It mainly plays a solid solution strengthening role in steel. It is an important tough element and is also an austenite forming element. Excessive manganese content will significantly improve the hardenability of steel and reduce the hardness of steel. plasticity and weldability. In terms of corrosion resistance, the role of manganese is not obvious. The range of Mn content in the present invention is selected as 0.6-1.2%.

S and P are harmful impurity elements in the steelmaking process, and are easy to form harmful inclusions in steel, reducing the toughness and plasticity of steel. Some weathering steels are designed with Cu-P series components, but their corrosion resistance performance is limited, and phosphorus is easy to segregate at the grain boundaries, which increases the brittleness of the steel. 0.01% range.

Cr is an important element to improve the oxidation resistance and corrosion resistance of steel, and promotes the formation of a stable passivation film on the surface of steel under a suitable environment, thereby improving the corrosion resistance of steel. However, the effect of chromium in non-oxidizing medium is not as good as that of molybdenum and nickel. Adding chromium alone cannot greatly improve the seawater corrosion resistance of steel, and it is easy to increase the tendency of pitting corrosion. The range of Cr content in the present invention is selected as 8.0-10.0%.

W is a rare high-melting point metal with stable chemical properties. It does not react with air and water at room temperature. When it is not heated, any concentration of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid and aqua regia has no effect on tungsten. When the temperature rises When the temperature reaches 80°-100°C, among the above-mentioned acids, except hydrofluoric acid, other acids have a weak effect on tungsten. Its high temperature strength and creep resistance, as well as thermal conductivity, electrical conductivity and electron emission performance are good. In addition to being widely used in the manufacture of cemented carbide, it is also used as an alloy additive. Tungsten alloy electroplating technology is being widely used in oilfield equipment to prevent its corrosion wear and tear. The range of W content in the present invention is selected as 1.0-2.0%.

V is a microalloying element that can precipitate V(C,N) compounds during the rolling process, prevent the growth of austenite and ferrite grains, and have strong precipitation strengthening and fine grain strengthening effects. Significantly improve the strength of steel, thereby making up for the defect of insufficient strength caused by low carbon content. The range of V content in the present invention is selected as 0.04-0.10%.

The addition of a proper amount of rare earth to steel can significantly improve the overall corrosion resistance of steel. The role of rare earth in purifying molten steel, modifying inclusions, improving microstructure and grain boundary conditions is an important material science reason for the improvement of corrosion resistance of steel. . Solid solution of rare earth in steel increases the polarization resistance and self-corrosion potential of steel matrix, which is beneficial to improve the corrosion resistance of steel matrix. The range of RE content in the present invention is selected as 0.01-0.05%.

The feature of the present invention is that on the basis of the traditional corrosion-resistant element Cr, W element with stable chemical properties is added, and at the same time, rare earth elements that can purify molten steel are added, and the seawater corrosion resistance of steel bars is significantly improved through the composite action of several elements. performance. The corrosion test of the cycle shows that the seawater corrosion resistance of the produced steel bar can be improved by more than 4 times compared with the ordinary threaded steel bar. Its microstructure is mainly ferrite and bainite, and its yield strength>400MPa, tensile strength>650MPa, elongation after fracture>21%, maximum total elongation>9%, to ensure good strength and plasticity . The smelting process of the invention is simple to operate, and the rolling process has no complicated requirements compared with ordinary threaded steel, and can be popularized and used on a large scale in various environments.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with several examples, but these examples are by no means limiting the present invention. Any changes made by those skilled in the art in the implementation of the present invention under the inspiration of this specification will fall within the scope of the claims.

The components of Examples 1-3 and Comparative Examples are calculated by weight percentage, as shown in the table below, and the balance is Fe.

Table 1 embodiment 1-3 and comparative example composition (wt.%)

C Si mn Cr W V RE P S comparative example 0.231 0.541 1.452 — — — — 0.0086 0.0052 Example 1 0.031 0.492 1.152 9.016 1.374 — 0.027 0.0068 0.0032 Example 2 0.038 0.476 0.856 9.537 1.677 0.079 0.015 0.0073 0.0029 Example 3 0.045 0.526 0.698 8.812 1.843 0.062 — 0.0081 0.0043 Example 4 0.049 0.526 0.605 8.121 1.132 0.095 0.046 0.0069 0.0027

Example 1

The reinforcing bar of the present embodiment, each component is as shown in table 1, and its preparation method is:

The hot metal is desulfurized by the KR method to ensure that the sulfur content in the steel is controlled below 0.01%. Electric furnace smelting, using side blowing for decarburization and dephosphorization, smelting at 1655°C until the carbon content in molten steel is less than 0.05%, and the phosphorus content is less than 0.01%, tapping, adding ferrosilicon, Silicon-manganese alloy deoxidation, adding carbon powder and slagging material; after adding Cr alloy elements, use RH vacuum refining at 1625 °C to carry out oxygen blowing decarburization, and then use LF refining at 1595 °C to deoxidize until the oxygen content in molten steel is 0.002%, add W and other alloying elements after deoxidation; after refining, adopt protective casting, and continuously cast into 150mm×150mm billets; Single-strand rolling, the rolling specification is ∮22mm, the starting rolling temperature is 1040°C, after rough rolling and intermediate rolling, the finish rolling temperature is 980°C, no water penetration after finish rolling, the temperature of the upper cooling bed is 960°C, and the temperature of the upper cooling bed is 960°C. After cooling to room temperature, the threaded steel bar can be obtained by trimming and shearing.

Example 2

The reinforcing bar of the present embodiment, each component is as shown in table 1, and its preparation method is:

The hot metal is desulfurized by the KR method to ensure that the sulfur content in the steel is controlled below 0.01%. Electric furnace smelting, using side blowing for decarburization and dephosphorization, smelting at 1665°C until the carbon content in molten steel is less than 0.06%, and the phosphorus content is less than 0.01%, tapping, and adding ferrosilicon, Silicon-manganese alloy deoxidation, adding carbon powder and slagging material; after adding Cr alloy elements, use RH vacuum refining at 1635 °C to carry out oxygen blowing decarburization, and then use LF refining at 1605 °C to deoxidize until the oxygen content in molten steel is 0.002%, add W and other alloying elements after deoxidation; after refining, adopt protective casting, and continuously cast into 150mm×150mm billets; Single-strand rolling, the rolling specification is ∮22mm, the starting rolling temperature is 1050°C, after rough rolling and intermediate rolling, the finish rolling temperature is 1000°C, no water penetration after finish rolling, the temperature of the upper cooling bed is 950°C, and it is naturally rolled on the cooling bed After cooling to room temperature, the threaded steel bar can be obtained by trimming and shearing.

Example 3

The reinforcing bar of the present embodiment, each component is as shown in table 1, and its preparation method is:

The hot metal is desulfurized by the KR method to ensure that the sulfur content in the steel is controlled below 0.01%. Electric furnace smelting, using side blowing for decarburization and dephosphorization, smelting at 1675°C until the carbon content in the molten steel is less than 0.06%, and the phosphorus content is less than 0.01%, tapping, adding ferrosilicon, Silicon-manganese alloy deoxidation, adding carbon powder and slagging material; after adding Cr alloy elements, use RH vacuum refining at 1645 °C to carry out oxygen blowing decarburization, and then use LF refining at 1615 °C to deoxidize until the oxygen content in molten steel is 0.002%, add W and other alloying elements after deoxidation; after refining, adopt protective casting, and continuously cast into 150mm×150mm billets; Single-strand rolling, the rolling specification is ∮22mm, the starting rolling temperature is 1060°C, after rough rolling and intermediate rolling, the finish rolling temperature is 1010°C, no water penetration after finish rolling, the temperature of the upper cooling bed is 950°C, and the temperature of the upper cooling bed is 950°C. After cooling to room temperature, the threaded steel bar can be obtained by trimming and shearing.

Example 4

The reinforcing bar of the present embodiment, each component is as shown in table 1, and its preparation method is:

The hot metal is desulfurized by the KR method to ensure that the sulfur content in the steel is controlled below 0.01%. Electric furnace smelting, using side blowing for decarburization and dephosphorization, smelting at 1660°C until the carbon content in molten steel is less than 0.06%, and the phosphorus content is less than 0.01%, tapping, and adding ferrosilicon, Silicon-manganese alloy deoxidation, adding carbon powder and slagging material; after adding Cr alloy elements, use RH vacuum refining at 1630°C to carry out oxygen blowing decarburization, and then use LF refining at 1610°C to deoxidize until the oxygen content in molten steel is 0.002%, add W and other alloying elements after deoxidation; after refining, adopt protective casting, and continuously cast into 150mm×150mm billets; Single-strand rolling, the rolling specification is ∮22mm, the starting rolling temperature is 1045°C, after rough rolling and intermediate rolling, the finishing rolling temperature is 990°C, no water penetration after finishing rolling, the temperature of the upper cooling bed is 955°C, and it is naturally rolled on the cooling bed After cooling to room temperature, the threaded steel bar can be obtained by trimming and shearing.

comparative example

The reinforcing bar of this comparative example is common HRB400, each component is shown in Table 1, and its preparation method is:

The hot metal is desulfurized by the KR method to ensure that the sulfur content in the steel is controlled below 0.01%. Converter smelting, decarburization and dephosphorization are carried out by top and bottom double blowing. During the tapping process, protective gas is used to stir the molten steel at a pressure of 0.5MPa. Powder and slagging materials; after smelting, protective pouring is used to continuously cast billets of 150mm×150mm; the heating temperature of the billet in the soaking section of the heating furnace is 1200 ° C, and the continuous rod and wire rolling mill is used for single-wire rolling. The specification is ∮22mm, the starting rolling temperature is 1040°C, after rough rolling and intermediate rolling, the finish rolling temperature is 980°C, no water penetration after finish rolling, the upper cooling bed temperature is 950°C, naturally cooled to room temperature on the cooling bed, finishing Cut to obtain threaded steel bars.

Effect experiment example

For proving effect of the present invention, get the steel bar of system in embodiment 1-3 and comparative example and carry out following experiment:

1. Experimental method:

1.1 Mechanical performance test: refer to "GB1499.2-2007 Steel for Reinforced Concrete Part II: Hot-rolled Ribbed Steel Bar".

The yield strength (R _0.2 ), tensile strength (Rm) and elongation after fracture (A) of steel bars were measured.

1.2 Corrosion resistance test

1.2.1 Weekly immersion corrosion test: refer to the "Draft for Solicitation of Corrosion Test Methods for Steel Bars in Chloride Ion Environment" proposed by the China Iron and Steel Industry Association in May 2012 and drafted by the General Iron and Steel Research Institute and the Metallurgical Industry Information Standard Research Institute. .

The sample is a cylinder of ∮18mm×50mm;

The test solution is a sodium chloride solution with an initial concentration of (0.34±0.009) mol·L-1 (mass fraction 2.0%±0.05%). The specific test conditions are:

Temperature: 45℃±2℃

Humidity: 70%±10%RH

Solution pH value: 6.5～7.2

Test time: 360h

Each cycle: 60min±5min, of which soaking time: 12min±2min

The maximum temperature of the sample surface after baking: 70℃±10℃

1.2.2 Salt spray corrosion test: refer to "GBT10125-1997 Artificial Atmosphere Corrosion Test Salt Spray Test".

The sample is a sample piece of 3mm×20mm×40mm;

The test solution is (50±5)g·L ^-1 (5.0%±0.5%) sodium chloride solution. The specific test conditions are:

Temperature: 35℃±2℃

Solution pH value: 6.5～7.2

Test time: 360h

2. Experimental results

The mechanical property of the steel bar of table 2 embodiment 1-3 and comparative example

The relative corrosion rates in Table 2 are all based on the comparative example, and the corrosion rate of the comparative example is set as 1. As can be seen from Table 2, the corrosion resistance of the 400MPa grade steel bar produced by the design composition and preparation method of the present invention has been improved by more than 4 times compared with ordinary HRB400 steel bars, and its elongation after breaking > 21%, and the maximum force total elongation rate>9%, while obtaining excellent corrosion resistance, ensure high strength and good elongation of hot-rolled steel bars, which can meet the durability requirements of reinforced concrete structures in marine environments.

Claims (3)

1. the anti-corrosion Twisted Steel of 400MPa level tungstenic, is characterized in that, comprises the following component calculated according to weight percent: C 0.03 ~ 0.05%, Si 0.3 ~ 0.6%, Mn 0.6 ~ 1.2%, P≤0.01%, S≤0.01%, Cr 8.0 ~ 10.0%, W 1.0 ~ 2.0%; Optional component: V 0.04 ~ 0.10%, RE 0.01 ~ 0.05%, in the combination of any one or two kinds; All the other are Fe and inevitable impurity.

2. the anti-corrosion Twisted Steel of 400MPa level tungstenic according to claim 1, it is characterized in that, the more common HRB400 reinforcing bar of corrosion resisting property all improves more than 4 times, its yield strength > 400MPa simultaneously, tensile strength > 650MPa, elongation after fracture > 21%, maximum, force percentage of total elongation > 9%.

3. the production method of the anti-corrosion Twisted Steel of 400MPa level tungstenic according to claim 1, is characterized in that, comprise following production stage:

(1) molten iron KR desulfurization → electrosmelting → RH vacuum refinement → LF external refining → small billet protection continuous casting;

(2) continuously cast bloom is heated to 1150 ~ 1200 DEG C in process furnace, through roughing, in roll after, 950 ~ 1050 DEG C of finish rolling, after rolling, do not wear water;

(3) 930-980 DEG C of upper cold bed air cooling → multi-length shear shearing → packaging and warehousing.