CN117867414A - High Mo content weathering steel and preparation method thereof - Google Patents
High Mo content weathering steel and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a high Mo content weathering steel and a preparation method thereof, comprising the following components in percentage by mass: 0.20 to 0.55 percent of Mo, 0.2 to 0.5 percent of Si, 0.4 to 0.6 percent of Cu, 0.005 to 0.02 percent of P, 0.5 to 1.3 percent of Cr, 0.3 to 0.75 percent of Ni, 0.2 to 0.3 percent of Ti and the balance of Fe. The invention has obvious grain refinement in the hot rolling process, is a ferrite structure or ferrite and pearlite structure, has excellent mechanical property and corrosion resistance, and has simple preparation method, no need of subsequent treatment such as annealing after the hot rolling is finished, and is simple and easy to implement, and test results show that: the effect of carbide precipitation strengthening is 350-460 MPa, the yield strength is 860-975 MPa, and the elongation after breaking is 19.5-23.4%.
Description
Technical Field
The invention relates to the technical field of steel, in particular to weather-resistant steel with high Mo content and a preparation method thereof.
Background
The transmission tower is the main bearing part of power transmission, and the long-term hot dip galvanization of transmission tower is anticorrosive, has 3 problems: (1) Acid washing and galvanization can cause water, gas and soil pollution, and harm human health; (2) The galvanization cost accounts for about 25% of the body cost, and zinc (Zn) metal is consumed at the same time; (3) The full life cycle anticorrosion of the pole tower can not be realized by galvanization, secondary anticorrosion is needed, the high-altitude operation difficulty is high, the cost is high, and the quality is difficult to guarantee. In coastal and industrial atmospheric corrosion environments, the galvanized towers are put into operation for 10 years to carry out secondary corrosion prevention, and the secondary corrosion prevention is complex in structure and large in edge dead angles of iron towers due to high-altitude operation, so that the secondary corrosion prevention effect is poor, the average corrosion prevention service life is 5-10 years, the galvanized towers are repeatedly painted in heavy corrosion areas for only 3-5 years, the operation and maintenance cost is high, the manpower and material resources cannot be guaranteed, and the safe and stable operation of a power grid is seriously endangered.
The weathering steel is a new material which can realize self corrosion prevention by adding corrosion-resistant alloy elements in the steel smelting process to form a stable rust layer on the surface of a metal matrix, and has been used as a pole tower material in recent years. The weathering steel pole tower is provided with the anti-corrosion layer, the anti-corrosion layer is more compact along with the increase of the service life, and the anti-corrosion performance can be better, but the mechanical performance and the anti-corrosion performance of the weathering steel at present still need to be improved.
Disclosure of Invention
The invention mainly aims to provide the weathering steel with high Mo content and better mechanical property and corrosion resistance and the preparation method thereof.
In order to achieve the above purpose, the invention provides a high Mo content weathering steel, which comprises the following components in percentage by mass: 0.20 to 0.55 percent of Mo, 0.2 to 0.5 percent of Si, 0.4 to 0.6 percent of Cu, 0.005 to 0.02 percent of P, 0.5 to 1.3 percent of Cr, 0.3 to 0.75 percent of Ni, 0.2 to 0.3 percent of Ti and the balance of Fe.
Further, the alloy material further comprises any one or any combination of more than two of C0.87-0.92%, mn 1.68-1.83%, nb 0.01%, V0.03%, S0.0037-0.01%, N0.0043-0.0069% and Zr 0.0025% by mass percent.
Further, the structure of the weathering steel with high Mo content is ferrite structure or ferrite+pearlite structure.
Further, the grain size of the weathering steel with high Mo content is 3-8 μm.
The invention also provides a preparation method of the weather-resistant steel with high Mo content, which comprises the following steps:
(1) Smelting
Smelting raw materials to obtain molten steel;
(2) Casting blank molding
Casting the molten steel by adopting a continuous casting process to obtain a continuous casting blank;
(3) Hot continuous rolling
Rolling the continuous casting blank by adopting a hot continuous rolling process, wherein the hot continuous rolling process comprises the following conditions: preheating and preserving the temperature at 1250 ℃ for 1.5 hours; the initial rolling temperature is 1150 ℃, and the final rolling temperature is 900 ℃; and 6 times of hot continuous rolling are adopted, after the final pass of deformation, cooling is carried out at the speed of 30-50 ℃/s, coiling is carried out at the temperature of 600-650 ℃, and isothermal treatment is carried out for 1-3 hours.
Further, the smelting condition is that the tapping temperature of the converter is 1600-1700 ℃ and the temperature of the refining furnace is 1500-1580 ℃.
Further, the deformation amount per pass is 15-65%, and the total deformation amount is 90%.
In the invention, the addition of Mo element can play roles of precipitation strengthening, fine grain strengthening, tissue stability enhancement and corrosion resistance improvement, and the addition of Ti element has the maximum precipitation strengthening effect. The method is specifically as follows:
(1) Precipitation strengthening: the Mo element is an element that is soluble in ferrite and can raise the ferrite recrystallization temperature, thereby strengthening the ferrite structure and improving the heat resistance and creep strength of the steel. It is capable of forming MC or M with carbon 2 The C-type diffuse precipitated phase improves the strength of the steel by pinning dislocation and preventing dislocation movement (strength is mainly improved by the action of precipitation strengthening).
(2) Fine grain strengthening: in microalloyed steel, mo can prevent C, N atoms in austenite from diffusing, and delay the precipitation of carbonitride in austenite, so that more microalloyed elements are reserved in ferrite to precipitate, and the strength of the steel is improved. Meanwhile, mo element can also increase nucleation position of the precipitated phase, so that the size of the precipitated phase is finer and the distribution is more uniform. Mo element is dissolved in the austenite matrix in a solid solution way, so that recovery and recrystallization of deformed austenite can be obviously inhibited, dislocation and deformed energy storage at high temperature are reserved, and grains are thinned. The fine grain strengthening of the ferrite structure in the steel can increase the strength of the steel and improve the toughness of the steel.
(3) Tissue stability: the Mo element can improve the hardenability of the steel and increase the depth of the quenched layer. When tempering brittle elements such as Mn, cr and the like exist in the steel, the addition of Mo element forms fine Mo 2 C phase or Fe 2 Mo phase, increases the secondary hardening effect and improves the tempering stability of steel.
(4) Mo also improves the corrosion resistance of the steel, especially the seawater corrosion resistance. Mo is an advantageous element in the aspect of corrosion resistance of weathering steel, and makes the rust layer on the surface of the weathering steel substrate more compact and compact, and has certain partial polymerization at the defect position in the rust layer, so that the rust layer is more complete. In weathering steel rust layers, mo is usually present in the form of hexavalent platinates, acidsMoO with greater stability in a more aggressive environment 3 In the form of a gel. The corrosion resistance of the steel can be obviously improved by independently adding 0.20 to 0.55 percent of Mo into the steel, and the synergistic effect can be better exerted when the Mo is added together with other corrosion resistant elements.
The beneficial effects of the invention are as follows:
the invention has obvious grain refinement in the hot rolling process, is a ferrite structure or ferrite and pearlite structure, has excellent mechanical property and corrosion resistance, and has simple preparation method, no need of subsequent treatment such as annealing after the hot rolling is finished, and is simple and easy to implement, and test results show that: the effect of carbide precipitation strengthening is 350-460 MPa, the yield strength is 860-975 MPa, and the elongation after breaking is 19.5-23.4%.
Drawings
FIG. 1 is a process diagram of a hot continuous rolling process for high Mo weathering steel;
FIG. 2 is a simulated circuit diagram of an electrochemical impedance spectrum;
FIG. 3 is a graph showing the variation of the electrochemical parameter Rt with cycle time for different Mo contents;
FIG. 4 is a graph showing the electrochemical parameters Rrust with the cyclic period of different Mo contents;
FIG. 5 is a ferrite texture chart of the weathering steel having high Mo content obtained in example 1;
FIG. 6 is a schematic diagram showing the distribution of the nano-sized carbide precipitation morphology in the weathering steel of FIG. 5 with high Mo content.
Detailed Description
The present invention will be described in further detail with reference to specific examples. Those of ordinary skill in the art will be able to implement the invention based on these descriptions. In addition, the embodiments of the present invention referred to in the following description are typically only some, but not all, embodiments of the present invention. Therefore, all other embodiments, which can be made by one of ordinary skill in the art without undue burden, are intended to be within the scope of the present invention, based on the embodiments of the present invention.
The raw materials used in the examples of the present invention are all commercially available or available to those skilled in the art unless specifically stated otherwise; the methods used in the examples of the present invention are those known to those skilled in the art unless specifically stated otherwise.
Example 1
Preparation of weathering steel with high Mo content, cooling mode and influence of coiling temperature on steel performance
The high Mo content weathering steel of example 1, which contains the components shown in table 1 and the balance Fe in mass percent, was prepared by the following steps:
(1) Smelting
Smelting the raw materials under the smelting condition that the tapping temperature of a converter is 1600 ℃ and the temperature of a refining furnace is 1500 ℃ to obtain molten steel;
(2) Casting blank molding
Casting the molten steel by adopting a continuous casting process to obtain a 60mm thick continuous casting blank plate;
(3) Hot continuous rolling
Rolling the continuous casting blank by adopting a hot continuous rolling process, wherein the hot continuous rolling process comprises the following conditions: preheating and preserving the temperature at 1250 ℃ for 1.5 hours; the initial rolling temperature is 1150 ℃, and the final rolling temperature is 900 ℃; adopting 6-pass hot continuous rolling, wherein the deformation of each pass is 15-65%, the deformation of each pass is controlled as shown in figure 1, cooling at the speed of 30 ℃/s after the deformation of the last pass, coiling at the temperature of 600 ℃ and carrying out isothermal treatment for 1h, wherein the ferrite structure diagram of the prepared weather-resistant steel with high Mo content is shown in figures 5 and 6, the steel structure is a ferrite structure, the grain size is 3-8 mu m, and the fine grain strengthening effect exerted by the grain size is detailed; the quantity of carbide precipitated in ferrite is dense, and the grain size of carbide is mainly concentrated at 2-6nm, so that the maximum precipitation strengthening effect can be achieved.
Based on the example 1, the performance data of the steels prepared by adopting two different cooling modes of water cooling and oil cooling and coiling isothermal temperatures of 600, 625 and 650 ℃ are shown in the table 2, the steels of the comparative examples 1-3 comprise the components shown in the table 1 and the balance of Fe in percentage by mass, the preparation method is the same as that of the example 1, and the performance data are also shown in the table 2.
TABLE 1 chemical composition Table (wt%)
| Numbering device | C | Mn | Si | Ti | Mo | Cu | Cr | Ni | P | Nb | V | Zr | S | N |
| Example 1 | 0.092 | 1.83 | 0.32 | 0.20 | 0.21 | 0.50 | 0.64 | 0.42 | 0.0110 | 0.01 | 0.03 | 0.0025 | 0.0037 | 0.0043 |
| Comparative example 1 | 0.093 | 1.80 | 0.30 | 0.21 | -- | 0.50 | 0.70 | 0.60 | 0.0152 | 0.01 | 0.03 | -- | 0.0031 | 0.0031 |
| Comparative example 2 | 0.092 | 1.78 | 0.31 | 0.10 | 0.05 | 0.51 | 0.69 | 0.58 | 0.0132 | 0.01 | 0.03 | -- | 0.0022 | 0.0021 |
| Comparative example 3 | 0.092 | 1.82 | 0.33 | 0.22 | 0.10 | 0.52 | 0.71 | 0.63 | 0.0114 | 0.01 | 0.03 | 0.0026 | 0.0022 | 0.0033 |
TABLE 2 influence of different cooling modes and coiling isothermal temperatures on mechanical properties of steels
| Numbering device | Cooling mode | Coiling isothermal temperature/°c | Yield strength/Mpa | Tensile Strength/Mpa | Yield ratio | Elongation percentage |
| Example 1 | Oil cooling | 600 | 943 | 975 | 0.97 | 18.1 |
| Example 1 | Oil cooling | 625 | 825 | 860 | 0.96 | 19.3 |
| Example 1 | Oil cooling | 650 | 713 | 749 | 0.95 | 20.4 |
| Example 1 | Water cooling | 600 | 961 | 992 | 0.97 | 18.2 |
| Example 1 | Water cooling | 625 | 847 | 893 | 0.95 | 19.7 |
| Example 1 | Water cooling | 650 | 742 | 781 | 0.95 | 20.2 |
| Comparative example 1 | Water cooling | 600 | 753 | 803 | 0.94 | 19.5 |
| Comparative example 2 | Water cooling | 600 | 794 | 841 | 0.94 | 18.3 |
| Comparative example 3 | Water cooling | 600 | 801 | 859 | 0.93 | 17.5 |
As can be seen from the above table, the cooling mode and the coiling temperature have obvious influence on the mechanical properties of the steel, and in general, the highest yield strength of example 1 is 943MPa, the tensile strength is 975MPa, the elongation after break is 18.1%, while the highest yield strength is 961MPa, the tensile strength is 992MPa, the elongation after break is 18.2% and the mechanical properties are improved to a certain extent by adopting the oil cooling mode. The different cooling coiling temperatures in comparative example 1, low temperature coiling was found to be advantageous for mechanical property improvement, and was specifically shown in: in the case of water cooling, the yield strength of the steel was 961MPa, the tensile strength was 992MPa, the elongation after break was 18.2% when the coiling temperature was 600 ℃, and the yield strength of the steel was 742MPa, the tensile strength was 781MPa, and the elongation after break was 20.2% when the coiling temperature was 650 ℃. As can be seen from comparative example 3, the mechanical properties of the steel are improved to some extent with the addition of Mo content.
Examples 2 to 4
Preparation of weathering steel with high Mo content and influence of different Mo and Ti contents on steel performance
The high Mo content weathering steels of examples 2 to 4, comprising the components shown in table 2 and the balance Fe, were prepared by the following steps in mass percent:
(1) Smelting
Smelting the raw materials under the smelting condition that the tapping temperature of a converter is 1700 ℃ and the temperature of a refining furnace is 1580 ℃ to obtain molten steel;
(2) Casting blank molding
Casting the molten steel by adopting a continuous casting process to obtain a 60mm thick continuous casting blank plate;
(3) Hot continuous rolling
Rolling the continuous casting blank by adopting a hot continuous rolling process, wherein the hot continuous rolling process comprises the following conditions: preheating and preserving the temperature at 1250 ℃ for 1.5 hours; the initial rolling temperature is 1150 ℃, and the final rolling temperature is 900 ℃; and 6-pass hot continuous rolling is adopted, the deformation of each pass is 15-65%, the deformation of each pass is controlled as shown in figure 1, after the final pass is deformed, the final pass is cooled at a speed of 45 ℃/s by adopting a water cooling mode, and coiling and isothermal treatment are carried out for 1h at a temperature of 600 ℃.
The steels of comparative examples 4 to 6 were prepared in the same manner as in example 3, except that the steels contain the components shown in Table 2 and the balance Fe in mass percent.
The mechanical properties of the steels obtained in each example and comparative example are shown in Table 4.
TABLE 3 chemical composition Table (wt%)
TABLE 4 influence of different Mo and Ti contents on the mechanical properties of high-strength weathering steel
| Numbering device | Cooling mode | Isothermal temperature/°c | Yield strength/MPa | Tensile strengthdegree/MPa | Yield ratio | Elongation percentage |
| Example 2 | Water cooling | 600 | 951 | 982 | 0.97 | 18.2 |
| Example 3 | Water cooling | 600 | 998 | 1062 | 0.94 | 20.1 |
| Example 4 | Water cooling | 600 | 979 | 1033 | 0.95 | 19.3 |
| Comparative example 4 | Water cooling | 600 | 851 | 903 | 0.94 | 18.7 |
| Comparative example 5 | Water cooling | 600 | 783 | 838 | 0.93 | 20.4 |
| Comparative example 6 | Water cooling | 600 | 712 | 803 | 0.89 | 22.3 |
As can be seen from the above table, the contents of Ti and Mo have a remarkable effect on the mechanical properties of weathering steel, and in examples 2 to 3, when the Ti content is 0.20wt%, the Mo content is increased from 0.21wt% to 0.38wt%, the isothermal temperature of the weathering steel is 600℃under water cooling, the yield strength is increased by 47MPa, and the tensile strength is increased by 80MPa. The Mo content in examples 3 to 4 was increased to 0.55wt% and a small range of decrease in mechanical properties was observed, the yield strength was decreased by 19MPa and the tensile strength was decreased by 29MPa. The strength of the examples was maintained at 950MPa or more in the longitudinal comparative examples 2 to 4 and comparative examples 4 to 6, while the strength of the comparative examples was maintained at 800MPa or less, so that it was found that the addition and the proportion of Ti and Mo were important in the influence on the mechanical properties of weathering steel.
Corrosion resistance performance evaluation
The adopted corrosion resistance evaluation method comprises the following steps: the electrochemical device is tested by adopting an electrochemical resistance method, and consists of a common three-electrode system, wherein a platinum sheet is used as a counter electrode, a Saturated Calomel Electrode (SCE) is used as a reference electrode, and a stainless steel substrate is used as a working electrode. The polarization curve and ac impedance spectrum of the sample were measured thereby. The alternating current impedance test is carried out in 0.5% NaCl (mass fraction) aqueous solution, the amplitude is 10mV, the electrochemical device with the frequency range of 10 < -2 > to 106 is composed of a common three-electrode system, a platinum sheet is used as a counter electrode, a Saturated Calomel Electrode (SCE) is used as a reference electrode, and a stainless steel substrate is used as a working electrode. The polarization curve and ac impedance spectrum of the sample were measured thereby. The AC impedance test was performed in a 0.5% NaCl aqueous solution with an amplitude of 10mV and a frequency in the range of 10-2 to 106HZ. The polarization curve was also tested under the same conditions, and the scan speed was 5 mV.min-1. The data for the ac impedance spectra were fitted using ZSimpwin software and the fitting circuit is shown in fig. 2. Wherein Rs is the resistance of the electrolyte; rr is the resistance of the rust layer; cr is a capacitor formed by a rust layer and a system solution; cd is a capacitor formed by the steel matrix and electrolyte penetrating into the rust layer; rt is the charge transfer resistance of the dissolution reaction of the steel matrix; rw is the Warburg impedance.
The weathering steels provided in examples 2-4 and comparative examples 4-6 were investigated using a dry/wet alternating accelerated corrosion test method, the infiltration solutions were NaCl solutions of different concentrations, the solution temperatures were 45.+ -. 2 ℃ in the test chamber, and the relative humidity was 70.+ -. 10% RH. One cycle period was 60min, dry/wet alternate cycle test 1: the wet-out time was 12.+ -. 1.5min and the dry time was 48.+ -. 1.5min, i.e. dry/wet ratio=4:1, and the results are shown in Table 5.
Table 5 comparison of the corrosion resistance of examples and comparative examples under two different corrosion conditions
As can be seen from the above table, examples 2 to 4 have not only high strength and toughness mechanical properties but also excellent corrosion resistance as compared with comparative examples 4 to 6, and the corrosion rate in the 240-hour immersion test of 0.045mol/L NaCl ranges from 1.2 to 2.1g/m 2 H, when the concentration of the etching solution is increased to 0.450mol/L, the variation range of the accelerated etching rate is 8.9-10.2 g/m 2 H. The corrosion rates of the comparative examples vary from 4.9 to 5.2g/m, respectively 2 H and 26.3 to 30.4g/m 2 H. As can be seen from the table, the average accelerated corrosion rate of the weathering steel of the example with high Mo content is only 32% to the average corrosion rate of the comparative example40 percent, the weathering steel with high Mo content has excellent corrosion resistance.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (7)
1. The weather-resistant steel with high Mo content is characterized by comprising the following components in percentage by mass: 0.20 to 0.55 percent of Mo, 0.2 to 0.5 percent of Si, 0.4 to 0.6 percent of Cu, 0.005 to 0.02 percent of P, 0.5 to 1.3 percent of Cr, 0.3 to 0.75 percent of Ni, 0.2 to 0.3 percent of Ti and the balance of Fe.
2. The high Mo content weathering steel according to claim 1, further comprising any one or any combination of two or more of C0.87 to 0.92%, mn 1.68 to 1.83%, nb 0.01%, V0.03%, S0.0037 to 0.01%, N0.0043 to 0.0069% and Zr 0.0025% in terms of mass%.
3. The high Mo content weathering steel according to claim 1 or 2, characterized in that the structure of the high Mo content weathering steel is a ferrite structure or a ferrite + pearlite structure.
4. The high Mo content weathering steel according to claim 1 or 2, characterized in that the grain size of the high Mo content weathering steel is 3-8 μm.
5. The method for producing a high Mo content weathering steel according to any one of claims 1 to 4, characterized by comprising the steps of:
(1) Smelting
Smelting raw materials to obtain molten steel;
(2) Casting blank molding
Casting the molten steel by adopting a continuous casting process to obtain a continuous casting blank;
(3) Hot continuous rolling
Rolling the continuous casting blank by adopting a hot continuous rolling process, wherein the hot continuous rolling process comprises the following conditions: preheating and preserving the temperature at 1250 ℃ for 1.5 hours; the initial rolling temperature is 1150 ℃, and the final rolling temperature is 900 ℃; and 6 times of hot continuous rolling are adopted, after the final pass of deformation, cooling is carried out at the speed of 30-50 ℃/s, coiling is carried out at the temperature of 600-650 ℃, and isothermal treatment is carried out for 1-3 hours.
6. The method for producing a weathering steel having a high Mo content as claimed in claim 5, wherein the smelting condition is a converter tapping temperature of 1600 to 1700 ℃ and a refining furnace temperature of 1500 to 1580 ℃.
7. The method for producing a weathering steel having a high Mo content as claimed in claim 5 wherein the deformation per pass is 15 to 65% and the total deformation is 90%.
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