Stainless steel and carbon steel composite steel bar with low contact potential difference, high strength and high corrosion resistance and manufacturing method of stainless steel and carbon steel composite steel bar

Abstract

The invention relates to a low-contact-potential-difference high-strength high-corrosion-resistance stainless steel and carbon steel composite reinforcing steel bar and a manufacturing method thereof, the low-contact-potential-difference high-strength high-corrosion-resistance stainless steel and carbon steel composite reinforcing steel bar comprises a carbon steel reinforcing steel bar and a stainless steel layer wrapping the surface of the carbon steel reinforcing steel bar, and the carbon steel reinforcing steel bar comprises, by weight, 0.01%-0.08% of C, 0.05%-0.4% of Si, 0.50%-1.70% of Mn, 0.020%-0.040% of Al, 0.25%-0.8% of Cr, 0.18%-0.6% of Cu, 0.2%-0.8% of Ni, 0.001%-0.02% of Ti and the balance Fe and other inevitable impurities; and the self-corrosion potential difference between the carbon steel reinforcement and the stainless steel layer is less than 0.25 V. The potential difference (smaller than 0.25 V) between the carbon steel reinforcement and the stainless steel layer is reduced, end face galvanic corrosion is greatly reduced, the galvanic corrosion rate of the carbon steel at the end of the composite reinforcement is close to that of common reinforcement, and good corrosion resistance is achieved; and the stainless steel and the carbon steel are effectively compounded in a metallurgical bonding mode, so that the problem of difficult connection is solved.

Description

Technical Field

[0001] The invention relates to the technical field of composite steel bar manufacturing, and in particular to a stainless steel carbon steel composite steel bar with low contact potential difference, high strength and high corrosion resistance, and a manufacturing method thereof. Background Art

[0002] Among the existing steel materials, there are many types of composite materials, most of which are composite plates combining carbon steel and stainless steel, including explosive composite plates, rolled composite plates, mechanically bonded or brazed composite plates; in recent years, stainless steel carbon steel composite steel bars have an outer layer of stainless steel and an inner layer of carbon steel. Because they have the corrosion resistance of stainless steel and the strength of carbon steel as well as the cost advantages, they have very broad application prospects in the ocean and coastal areas.

[0003] However, when carbon steel and stainless steel come into contact, there is a potential difference, which results in galvanic corrosion. As we all know, the corrosion potential difference indicates the tendency of galvanic corrosion. The greater the difference in corrosion potential between the two metals in the use environment, the greater the possibility that the anode metal will be damaged by accelerated corrosion when forming a galvanic pair. Although the self-corrosion potential difference between carbon steel and stainless steel is not much different, when the service environment is an ion-rich solution, the corrosion current of carbon steel will increase, and the corrosion of carbon steel will increase exponentially.

[0004] Chinese patent CN106964649A discloses a method for preparing highly corrosion-resistant bimetallic composite steel bars, which uses carbon steel round bars as the core, assembles them into corrosion-resistant alloy tubes after surface treatment, and then heats and rolls them to obtain bimetallic composite steel bars. The process disclosed in this patent is similar to that disclosed in Chinese patent CN107933013A, and the latter is more specific in the implementation method. Only by improving the process, steel bars with better strength and corrosion resistance are obtained, but there is no improvement in the self-corrosion potential difference between carbon steel and stainless steel.

[0005] Chinese patent CN104910509B discloses a method for continuously producing a polypropylene tape wrapped around a steel bar to form a composite steel bar, producing a polypropylene-steel composite, wherein the polypropylene tape is wound in a circumferential direction to completely wrap the steel bar in the inner layer, the polypropylene is heated to melt, and after cooling, the polypropylene completely wraps the steel bar. The composite steel bar is wrapped by an organic material, which is quite different from the composite steel bar metallurgically combined with stainless steel and carbon steel.

[0006] Chinese patent CN104357745A discloses a composite steel bar with a yield strength of ≥600MPa and a production method. Although it is called composite steel bar, it is actually a general steel bar, not a steel bar made of stainless steel and carbon steel, so it does not involve the problem of corrosion potential difference. Moreover, the carbon content in the steel bar exceeds the national standard.

[0007] Chinese patent CN107933013A discloses a stainless steel / carbon steel vacuum composite steel bar and its manufacturing process, which mainly realizes the welding of stainless steel and carbon steel and the vacuum of the pores between stainless steel and carbon steel through a vacuum electron beam, and then obtains stainless steel / carbon steel rolled composite steel bars by heating and rolling; this is a general basic rolling composite method, which does not involve composition design and material strength design, etc.

[0008] Chinese patent CN112598723B discloses a method, device and storage medium for identifying the thickness of stainless steel coated steel bars; and Chinese patent CN111141671A discloses a galvanic corrosion simulation test device and method for composite steel bar coating and core material; the above patents are all method patents for the application or detection of stainless steel carbon steel composite steel bars.

[0009] Based on the above patents, there are few studies on stainless steel / carbon steel in existing composite steel bars, and no one has conducted relevant research on how to reduce the potential difference between stainless steel and carbon steel through composition and process control. Summary of the invention

[0010] The purpose of the present invention is to provide a stainless steel-carbon steel composite steel bar with low contact potential difference and high corrosion resistance and a manufacturing method thereof, which can reduce the potential difference between the carbon steel bar and the stainless steel layer (less than 0.25V), greatly reduce the end face galvanic corrosion, and the carbon steel galvanic corrosion rate at the end of the composite steel bar is similar to that of ordinary steel bars, and has good corrosion resistance; and through metallurgical bonding, the stainless steel and carbon steel bars are effectively composited, thereby solving the problem of connection difficulties.

[0011] To achieve the above object, the technical solution of the present invention is:

[0012] A low contact potential difference, high strength and high corrosion resistance stainless steel carbon steel composite steel bar, comprising a carbon steel bar and a stainless steel layer wrapped on the surface of the carbon steel bar, wherein the carbon steel bar comprises the following components by weight: C: 0.01-0.08%, Si: 0.05-0.4%, Mn: 0.50-1.70%, Al: 0.020-0.040%, Cr: 0.25-0.8%, Cu: 0.18-0.6%, Ni: 0.2-0.8%, Ti: 0.001-0.02%, and the remainder comprises Fe and other unavoidable impurities;

[0013] The self-corrosion potential difference between the carbon steel reinforcement and the stainless steel layer is less than 0.25V.

[0014] Furthermore, the balance of the carbon steel bar is Fe and other inevitable impurities.

[0015] Furthermore, other inevitable impurities in the carbon steel bar include P≤0.015%, S≤0.008%, and N≤0.008%.

[0016] Furthermore, the stainless steel is 316L stainless steel, and its components by weight percentage are: C≤0.03%, Si≤0.75%, Mn≤2.0%, P≤0.045%, S≤0.030%, Ni: 10.00~14.00%, Cr: 16.00~18.00%, Mo: 2.00~3.00%, N: 0.02~0.20%, and the remainder includes Al and other inevitable impurities.

[0017] In the chemical composition design of carbon steel described in the present invention:

[0018] C: is beneficial to strength, plays a role of solid solution strengthening in steel, and can significantly improve the strength of steel, but too high a C content is not conducive to the corrosion resistance of steel. Therefore, the present invention adopts a low-carbon design to control the C content to 0.01-0.08%.

[0019] Si: Adding silicon to steel can improve the purity and deoxidation of steel, and also support the strength. Silicon plays a role in solid solution strengthening in steel, but high silicon content is not conducive to welding performance. Therefore, the present invention controls the Si content to 0.05-0.4%.

[0020] Mn: It improves the strength of steel by solid solution strengthening and is the most important and economical strengthening element in steel to compensate for the strength loss caused by the reduction of C content. Therefore, the Mn content of the present invention is controlled to be 0.50-1.70%.

[0021] S and P: Sulfur and phosphorus are harmful elements in steel, which seriously damage the plasticity and toughness of the steel plate. They are both unavoidable impurity elements. The present invention requires P≤0.015% and S≤0.008%.

[0022] Al: a strong deoxidizing element. In order to ensure that the oxygen content in the steel is as low as possible, the aluminum content in the present invention is controlled within the range of 0.02-0.04%.

[0023] Ti: Ti is a strong carbide-forming element. Adding a small amount of Ti to steel is beneficial to fix the N in the steel. The formed TiN can refine the original austenite grain size. The titanium content of the present invention is controlled at 0.001-0.02%.

[0024] Ni: can effectively reduce the potential and improve the corrosion resistance of steel. Adding nickel to quenched and tempered steel can greatly improve the low-temperature impact toughness of steel. Considering the economic efficiency, the nickel content of the present invention is controlled at 0.2-0.8%.

[0025] Cr: can effectively reduce the potential and improve the corrosion resistance of steel; can form a dense oxide layer and reduce the corrosion rate. The chromium content of the present invention is controlled at 0.25-0.8%.

[0026] Cu: It can effectively reduce the potential and form a dense oxide layer, and is a common additive element for corrosion-resistant steel. The copper content of the present invention is controlled at 0.18-0.8%.

[0027] In order to ensure the corrosion resistance of the outer layer, 316L stainless steel is used. Its composition range is the requirements of the industry standard GB / T4237-2009, and its composition weight percentage is: C≤0.03%, Si≤0.75%, Mn≤2.0%, P≤0.045%, S≤0.030%, Ni: 10.00~14.00%, Cr: 16.00~18.00%, Mo: 2.00~3.00%, N: 0.02~0.20%, and the balance includes Al and other inevitable impurities. In order to ensure that the composite steel bar has high corrosion resistance, the thickness of the stainless steel layer of the composite steel bar is required to be greater than 0.2mm (the thickness of the stainless steel layer of the longitudinal interface and the cross section must be greater than 0.2mm).

[0028] Stainless steel carbon steel composite steel bar, the outer layer is stainless steel, the inner layer is carbon steel, and the carbon steel on its end face has no isolation protection. When connected with stainless steel, it will make protection very difficult due to electrochemical corrosion. When designing the carbon steel composition, it is necessary to consider adding corrosion-resistant elements and reducing the self-corrosion potential. Since the C element combines with Cr to form CrC, which affects the corrosion resistance, the present invention adopts a low-carbon design with a carbon content similar to that of austenitic stainless steel. In addition, reducing the C content can reduce the carbon gradient between carbon steel and stainless steel, and prevent the carbon steel from being accelerated due to the large C gradient. In addition, Cr, Cu, and Ni elements are added in a coordinated manner. Cr forms CrO in the early stage of oxidation and promotes the density of the rust layer, which can play an effective anti-corrosion inhibitory role; Cu and Ni are elements that improve the stability of the carbon steel matrix, and Ni can effectively reduce the potential and reduce the self-corrosion rate; Cu can promote the density of the rust layer, supplement Cr, and reduce the potential effect than Ni. The effects of Cr, Cu, and Ni are mainly based on the addition of Cr and Ni. When the amount of Cr and Ni is slightly less, the amount of Cu can be increased for supplementation. The obtained carbon steel has a self-corrosion potential of -0.55V to -0.45V, and the self-corrosion potential difference between carbon steel and stainless steel is less than 0.25V, which reduces the corrosion rate of carbon steel at the end of the composite steel bar, and the galvanic corrosion rate of carbon steel at the end of the composite steel bar is similar to that of ordinary steel bars.

[0029] The present invention also provides a method for manufacturing the low contact potential difference, high strength and high corrosion resistance stainless steel carbon steel composite steel bar, comprising the following steps:

[0030] 1) Assembly

[0031] The surfaces of stainless steel and carbon steel bars are cleaned, and then fixed and assembled, welded to obtain composite billets, and vacuumed to ensure that the vacuum degree of the stainless steel and carbon steel bars combined surface is ≤0.1Pa;

[0032] 2) Heating

[0033] The composite blank is heated at a temperature of 1080 to 1250°C and a heating time of 50 to 120 minutes;

[0034] 3) Rolling

[0035] Rough rolling and finishing rolling are carried out in sequence, and the finishing rolling inlet temperature is 800-1000°C;

[0036] 4) Cooling

[0037] After rolling, water cooling is carried out and the temperature of the upper cooling bed is 800-1000℃.

[0038] In the manufacturing method of the present invention:

[0039] Stainless steel and carbon steel composite steel bars have stainless steel outer layer and carbon steel inner layer. The manufacturing technology is very complex and requires many key technologies, such as outer stainless steel coating technology, surface cleaning technology, composite layer homogenization technology, etc. The surfaces of stainless steel plates and carbon steel square billets are cleaned. At this time, there are no non-matrix components such as oxides, water, grease, etc. on the surfaces of stainless steel plates and carbon steel. The treatment methods include but are not limited to machining, polishing, sandblasting, laser treatment, etc. After treatment, the billets are fixed and assembled. After assembly, the billets are welded into billets that can be rolled into steel bars. The welding methods here include conventional welding methods such as arc welding and laser welding. After welding, vacuum treatment is performed to ensure that the bonding surface of stainless steel and carbon steel bars is close to a vacuum state, and the vacuum degree is less than or equal to 0.1Pa.

[0040] The heating temperature of the composite billet is 1080-1250℃, and the heating time is 50-120min. The temperature system is mainly formulated considering the influence of two aspects, one is the performance of stainless steel, and the other is the mechanical properties related to the specifications. The heating time is related to the heating temperature. Since the thermal conductivity of stainless steel is low, the heating time needs to be longer. The high heating temperature can reduce the time in the furnace.

[0041] In order to combine the performance of stainless steel and carbon steel bars during the rolling process, the finishing rolling entrance temperature and the upper cooling bed temperature must be strictly controlled at 800-1000℃. The rolling temperature and the upper cooling bed temperature must not be lower than 800 degrees to ensure that the stainless steel layer is not in the temperature range that easily produces σ ferrite during rolling. In the temperature range of 800-1000 degrees, for the same specification, the lower the temperature control, the higher the strength, but the elongation performance will decrease if the temperature is too low; the rolling temperature for specifications with small diameters is selected to be higher, and the rolling temperature for specifications with large diameters needs to be slightly lower to ensure that the grains of the carbon steel substrate are not too large and to ensure good mechanical properties. The microstructure of the obtained carbon steel bar is uniform ferrite + pearlite, and the grain rating is 8-12.

[0042] The composite steel bar has a yield strength of 450-650MPa, a tensile strength of 560-700MPa, a total elongation At≥19%, and a maximum force elongation≥11%.

[0043] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0044] The present invention is a composite steel bar, the surface layer of which is stainless steel, which has good corrosion resistance, can withstand chloride ion environment, and greatly improve the service life of reinforced concrete. The core structure carbon steel bar is designed with a low-carbon component. On the one hand, the carbon gradient between carbon steel and stainless steel is reduced to prevent the accelerated corrosion of carbon steel caused by the large C gradient. On the other hand, micro-alloy corrosion-resistant elements such as Ni, Cr, and Cu are added in a coordinated manner to effectively reduce the self-corrosion potential and increase the density of the rust layer, thereby solving the problem of severe galvanic corrosion at the end of the composite steel bar prepared from carbon steel and stainless steel. The galvanic corrosion rate of the carbon steel at the end is similar to that of ordinary steel bars.

[0045] Based on the component design, the present invention realizes the complete metallurgical combination of carbon steel and stainless steel through heating, controlled rolling and other metallurgical technologies, and has both the corrosion resistance of stainless steel and the strength of carbon steel. It can solve the essential pain point of easy corrosion of carbon steel, meet the corrosion resistance requirements of reinforced concrete structures in harsh environments, have the advantages of high corrosion resistance, good mechanical properties, simple construction, and have great economic and social benefits. It can also solve the pain point of severe galvanic corrosion at the ends of composite steel bars during construction. The composite steel bars obtained by the present invention have a yield strength of 450-650MPa, a tensile strength of 560-700MPa, a total elongation At≥19%, and a maximum force elongation≥11%. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The figure is a process flow chart of an embodiment of the present invention.

[0047] Figure 2 This is a cross-sectional view of the composite steel bar described in the present invention.

[0048] Figure 3This is a cross-sectional photograph of the composite steel bar according to Example 1 of the present invention.

[0049] Figure 4 This is a metallographic photograph of the cross-section carbon steel of the composite steel bar in Example 1 of the present invention.

[0050] Figure 5 This is an enlarged view of the cross section of the composite steel bar in Example 1 of the present invention. DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with specific embodiments and drawings. However, this description does not constitute an improper limitation on the technical solution of the present invention.

[0052] The composition of 316L stainless steel used in the embodiment of the present invention is shown in Table 1, and the balance includes Fe and other inevitable impurities. The composition of carbon steel bars used in the embodiment of the present invention and the composition of ordinary threaded steel bars used in the comparative example are shown in Table 2, and the balance includes Fe and other inevitable impurities.

[0053] The manufacturing process of the embodiment of the present invention is shown in Figure 1 , the process parameters are shown in Table 3.

[0054] Comparative Example 1 is an ordinary threaded steel bar, and its typical chemical composition weight percentage is: C: 0.22-0.25%, Si: 0.45-0.55%, Mn: 1.35-1.45%, P≤0.035%, S≤0.035%, V: 0.030-0.045%, Ceq<0.55, and the rest includes Fe and other unavoidable impurities.

[0055] Comparative Example 2 uses ordinary threaded steel bars as the core and is covered with 316L stainless steel on the outer layer.

[0056] Figure 2 It is a cross-sectional view of the composite steel bar of the present invention. Figure 3 This is a cross-sectional view of the composite steel bar of Example 1 of the present invention. It can be seen from the figure that the carbon steel bar and the stainless steel are well composited with no cracks and no separation areas. Figure 4 This is a photo of the metallographic structure of the carbon steel rebar in Example 1 of the present invention. The metallographic structure of the carbon steel rebar is ferrite+pearlite, and the grain size is 8 to 12 levels.

[0057] Depend on Figure 5 It can be seen that the thickness of the composite steel bar stainless steel layer obtained by the present invention is greater than 0.2 mm.

[0058] Corrosion rate measurement experiment: referring to the standard “JB / T7901-1999 Metal Materials Laboratory Uniform Corrosion Full Immersion Test Method”, the simulated solutions used include: NaCl 13000mg / L, KCl 50mg / L, CaCl2 400mg / L, MgCl2 460mg / L, Na2SO4 1000mg / L, NaHCO3 1000mg / L, the solution pH is 6.5±0.3, the solution is static and has no flow rate.

[0059] Comparative Example 1 is an ordinary steel bar, whose strength is similar to that of the composite steel bar of the present invention, but its toughness is worse than that of the present invention. Moreover, the outer layer of the composite steel bar of the present invention has a layer of stainless steel, and its circumferential corrosion resistance is much better than that of Comparative Example 1. Moreover, the carbon steel corrosion rate at the end of the composite steel bar of the present invention is even lower than the corrosion rate of ordinary carbon steel bars, that is, the cross-section corrosion problem can be ignored when using the composite steel bar of the present invention.

[0060] Comparative Example 2 uses ordinary steel bars as the core and is coated with stainless steel on the outer layer. The obtained composite steel bar has mechanical properties close to those of the composite steel bar described in the present invention, but its cross-section corrosion rate is high and the cross-section corrosion is serious.

[0061] As can be seen from Table 4, through the carbon steel component designs 1-5 with low potential difference, in the process of measuring the corrosion rate of the ends of the composite steel bars, the carbon steel corrosion rate of the ends of the composite steel bars obtained in the embodiment of the present invention is even lower than the corrosion rate of the ordinary carbon steel bars, while the carbon steel corrosion rate of the ends of the composite steel bars using ordinary carbon steel as the inner core is much higher than that of the ordinary steel bars.

[0062] That is, the low potential difference design of the present invention can effectively reduce the acceleration of galvanic corrosion on carbon steel.

[0063] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

[0064]

[0065]

[0066]

Claims

1. A low contact potential difference, high strength and high corrosion resistance stainless steel carbon steel composite steel bar, comprising a carbon steel bar and a stainless steel layer wrapped on the surface of the carbon steel bar; the weight percentage of the components of the carbon steel bar is: C: 0.01-0.08%, Si: 0.05-0.4%, Mn: 0.50-1.70%, Al: 0.020-0.040%, Cr: 0.25-0.8%, Cu: 0.18-0.6%, Ni: 0.2-0.8%, Ti: 0.001-0.02%, and the balance includes Fe and other inevitable impurities; The self-corrosion potential difference between the carbon steel reinforcement and the stainless steel layer is less than 0.25V.

2. The low contact potential difference, high strength and high corrosion resistance stainless steel carbon steel composite steel bar according to claim 1, characterized in that: The balance of the carbon steel bar composition is Fe and other inevitable impurities.

3. The low contact potential difference, high strength and high corrosion resistance stainless steel carbon steel composite steel bar according to claim 1 or 2, characterized in that: Other inevitable impurities in the carbon steel bar include P≤0.015%, S≤0.008%, and N≤0.008%.

4. The low contact potential difference, high strength and high corrosion resistance stainless steel carbon steel composite steel bar according to claim 1, 2 or 3, characterized in that: The carbon steel bar has a microstructure of uniform ferrite+pearlite, and a grain rating of 8 to 12.

5. The low contact potential difference, high strength and high corrosion resistance stainless steel carbon steel composite steel bar according to claim 1, 2, 3 or 4, characterized in that: The self-corrosion potential of the carbon steel reinforcement is -0.55V to -0.45V.

6. The low contact potential difference, high strength and high corrosion resistance stainless steel carbon steel composite steel bar according to any one of claims 1 to 5, characterized in that: The thickness of the stainless steel layer on the surface of the carbon steel bar is greater than 0.2 mm.

7. The low contact potential difference, high strength and high corrosion resistance stainless steel carbon steel composite steel bar according to claim 1 or 6, characterized in that: The stainless steel layer is 316L stainless steel, and its components by weight percentage are: C≤0.03%, Si≤0.75%, Mn≤2.0%, P≤0.045%, S≤0.030%, Ni: 10.00-14.00%, Cr: 16.00-18.00%, Mo: 2.00-3.00%, N: 0.02-0.20%, and the remainder includes Al and other inevitable impurities.

8. The low contact potential difference, high strength and high corrosion resistance stainless steel carbon steel composite steel bar according to claim 1, 6 or 7, characterized in that: The self-corrosion potential of the stainless steel layer is -0.4V to -0.3V.

9. The method for manufacturing a low contact potential difference, high strength and high corrosion resistance stainless steel carbon steel composite steel bar according to any one of claims 1 to 8, characterized in that: The steps include: 1) Assembly The surfaces of stainless steel and carbon steel bars are cleaned, and then fixed and assembled, welded to obtain composite billets, and vacuumed to ensure that the vacuum degree of the stainless steel and carbon steel bar bonding surface is ≤0.1Pa; 2) Heating The composite blank is heated at a temperature of 1080 to 1250°C and a heating time of 50 to 120 minutes; 3) Rolling Rough rolling and finishing rolling are carried out in sequence, and the finishing rolling inlet temperature is 800-1000°C; 4) Cooling After rolling, water cooling is carried out, and the temperature of the upper cooling bed is 800-1000℃.

10. The manufacturing method according to claim 9, characterized in that: The composite steel bar has a yield strength of 450-650 MPa, a tensile strength of 560-700 MPa, a total elongation At≥19%, and a maximum force elongation≥11%.

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