Mo-containing austenitic stainless steel welding strip and its preparation method and application

Abstract

The present invention belongs to the technical field of stainless steel production and manufacturing, and specifically relates to a Mo-containing austenitic stainless steel welding strip and its preparation method and application. The Mo-containing austenitic stainless steel welding strip of the present invention comprises, by weight percentage: C≤0.020%, 0.2%≤Si≤0.6%, Mn≤2.00%, P≤0.020%, S≤0.010%, 21.00%≤Cr≤22.00%, 13.00%≤Ni≤14.00%, 2.50%≤Mo≤3.00%, 0.03%≤N≤0.08%, Cu≤0.2% and the balance of Fe and inevitable impurities. The Mo-containing austenitic stainless steel welding strip of the present invention adopts one pass of surfacing to replace the original two passes of surfacing in the surfacing process, and the surfacing efficiency is increased by more than 1 times, which is favored by users and has obvious market promotion value.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel production and manufacturing, and specifically relates to a Mo-containing austenitic stainless steel welding strip and a preparation method and application thereof. Background Art

[0002] Stainless steel welding strip is a stainless steel cladding on the surface of ordinary carbon steel to resist high temperature corrosion. It can save more than 90% of stainless steel materials. It is a typical representative of resource-saving stainless steel of cladding composite thinning. In recent years, this technology has developed rapidly and has been widely used in the manufacture of high-temperature and high-pressure hydrogen-resistant containers such as nuclear reaction pressure vessels, refinery hydrogenation reactors, and coal chemical gasifiers. The cladding layer of stainless steel welding strip is in harsh environments such as high temperature, high pressure, and hydrogen for a long time. Its quality is directly related to the safe operation of pressure vessels. Therefore, its quality requirements are very high, mainly manifested in: 1) In order to reduce the sensitivity of hot cracks in the cladding process of stainless steel welding strip, the steel is required to be pure and the welding strip organization contains a certain proportion of ferrite organization; 2) In order to reduce the fluctuation of the quality of the cladding layer, the welding strip is required to have stable composition, stable and moderate mechanical properties, high dimensional accuracy, good surface quality and plate shape, and smooth and burr-free edges after stripping. Therefore, the production process of this type of steel is complex and difficult to manufacture, and it has long relied on imports.

[0003] The surfacing layer is generally divided into two layers. When surfacing is performed on low alloy steel, the first layer is the base layer, using 309L stainless steel welding strip, and the second layer is the corrosion resistant layer, using 316L stainless steel welding strip. The two layers of surfacing are a complete surfacing, and the corrosion resistant layer after surfacing is 316L stainless steel. However, this type of surfacing requires surfacing twice, and the work efficiency is low. For large pressure vessels, it generally takes more than half a month to complete the surfacing. Therefore, on the basis of two-layer surfacing, a single-layer surfacing technology has been developed, that is, using Mo-containing 309Lmo stainless steel welding strips to achieve the effect of the original two surfacings in one surfacing, which can save a lot of time and improve production efficiency. Summary of the invention

[0004] In order to overcome the problems of long working time and low surfacing efficiency faced by the existing stainless steel welding strips using double-layer surfacing, the present invention provides a Mo-containing austenitic stainless steel welding strip and a preparation method and application thereof.

[0005] Specifically, the Mo-containing austenitic stainless steel welding strip of the present invention comprises, by weight percentage, C≤0.020%, 0.2%≤Si≤0.6%, Mn≤2.00%, P≤0.020%, S≤0.010%, 21.00%≤Cr≤22.00%, 13.00%≤Ni≤14.00%, 2.50%≤Mo≤3.00%, 0.03%≤N≤0.08%, Cu≤0.2% and the remainder of Fe and unavoidable impurities.

[0006] The above-mentioned Mo-containing austenitic stainless steel welding strip includes, by weight percentage: 0.015%≤C≤0.020%, 0.3%≤Si≤0.5%, 1.50%≤Mn≤2.00%, P≤0.020%, S≤0.010%, 21.00%≤Cr≤21.50%, 13.50%≤Ni≤14.00%, 2.60%≤Mo≤2.90%, 0.04%≤N≤0.05%, Cu≤0.1% and the remainder of Fe and unavoidable impurities.

[0007] The above-mentioned Mo-containing austenitic stainless steel welding strip has a ferrite number FN of 9-14%.

[0008] On the other hand, the present invention also provides a method for preparing the above-mentioned Mo-containing austenitic stainless steel welding strip, comprising:

[0009] (1) obtaining molten steel with qualified composition through molten iron pretreatment, converter smelting, VOD furnace refining and LF furnace refining;

[0010] (2) continuously casting the molten steel to obtain a continuously cast slab;

[0011] (3) After grinding and heating, the continuous casting slab enters the hot rolling, cold rolling and annealing process, and is stripped to obtain Mo-containing austenitic stainless steel welding strip.

[0012] In the above-mentioned preparation method of Mo-containing austenitic stainless steel welding strip, during the VOD furnace refining process, the vacuum degree of the VOD furnace is less than 2mbar, the furnace entry temperature is ≥1620°C, and the carbon content is removed to below 0.015wt% by blowing oxygen.

[0013] In the above-mentioned preparation method of Mo-containing austenitic stainless steel welding strip, during the LF furnace refining process, the Ca-Si wire is fed at a speed of 4m / t before weak stirring, and Fe-B is added at a rate of 0.3Kg / t of molten steel, and the outlet temperature is controlled at 1500-1510℃.

[0014] In the above-mentioned method for preparing the Mo-containing austenitic stainless steel welding strip, during the continuous casting process, argon gas is blown into the crystallizer for 5 minutes before pouring, the pouring temperature is 1450-1480°C, and the drawing speed is controlled at 0.9-1.1 mm / min.

[0015] In the above-mentioned method for preparing the Mo-containing austenitic stainless steel welding strip, the heating temperature of the continuous casting slab is 1200-1260° C., and the holding time is 180-220 min.

[0016] In the preparation method of the Mo-containing austenitic stainless steel welding strip, the final rolling temperature of hot rolling is ≥1030°C, the deformation rate of the last cold rolling process is controlled at 45-50%; the annealing temperature is 1060-1100°C, and the holding time is 0.3-0.7min.

[0017] On the other hand, the present invention also provides the use of the above-mentioned Mo-containing austenitic stainless steel welding strip in single-layer cladding.

[0018] The technical solution of the present invention has the following beneficial effects:

[0019] (1) The Mo-containing austenitic stainless steel welding strip of the present invention has uniform composition, low content of elements such as C, P, and S, and the ferrite number FN is controlled at 9-14%, which effectively ensures that the ferrite of the cladding metal is 3-8%, which not only ensures the stability of the structure at high temperature, but also avoids the cracking of the cladding metal during the cladding process;

[0020] (2) The Mo-containing austenitic stainless steel welding strip of the present invention adopts one-pass surfacing instead of the original two-pass surfacing (TEQ309L+TEQ316L) in the surfacing process, and the surfacing efficiency is increased by more than 1 times, which is favored by users and has obvious market promotion value. DETAILED DESCRIPTION

[0021] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0022] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0023] In order to achieve the effect of double cladding with single-layer cladding, a lot of work needs to be done on the composition design. It is necessary not only to control the ratio of elements such as Cr, Ni, Mo, and ferrite content of the material to avoid thermal cracks during solidification of the cladding, but also to consider how to avoid cracking of the stainless steel welding strip during the smelting and continuous casting production process. Therefore, the composition design and smelting production of stainless steel welding strip is a comprehensive consideration.

[0024] Specifically, the Mo-containing austenitic stainless steel welding strip of the present invention comprises, by weight percentage, C≤0.020%, 0.2%≤Si≤0.6%, Mn≤2.00%, P≤0.020%, S≤0.010%, 21.00%≤Cr≤22.00%, 13.00%≤Ni≤14.00%, 2.50%≤Mo≤3.00%, 0.03%≤N≤0.08%, Cu≤0.2% and the remainder of Fe and unavoidable impurities.

[0025] Preferably, the above-mentioned Mo-containing austenitic stainless steel welding strip includes, by weight percentage, 0.015%≤C≤0.020%, 0.3%≤Si≤0.5%, 1.50%≤Mn≤2.00%, P≤0.020%, S≤0.010%, 21.00%≤Cr≤21.50%, 13.50%≤Ni≤14.00%, 2.60%≤Mo≤2.90%, 0.04%≤N≤0.05%, Cu≤0.1% and the remainder of Fe and unavoidable impurities.

[0026] The reasons for limiting the content range of the main alloying elements are explained below.

[0027] C is an austenite-forming element. In order to ensure that the C content of the cladding metal after cladding is ≤0.025%, and to consider that the C in the parent material enters the cladding metal and increases the C content of the cladding metal, the C content in the composition system of the stainless steel strip for cladding cannot be higher than 0.020%. However, since C is an austenite-forming element, too low a C content will lead to a reduction in austenite phase, an increase in ferrite content, and poor thermoplasticity of the steel, which is not conducive to subsequent hot rolling production. At the same time, in order to improve the strength of the cladding metal and increase the wear resistance of the cladding metal, a small amount of C needs to be added to more than 0.01% to improve the high-temperature strength of the cladding metal. Therefore, the C content is controlled below 0.020%, and the optimal range is 0.015-0.020%, which can not only meet the ferrite requirements and avoid cracking, but also ensure the strength of the cladding metal and improve wear resistance.

[0028] Si is a ferrite phase forming element. In order to ensure that the Si content of the cladding metal after cladding is ≤1.0%, and considering that high Si will cause solidification cracks, the Si content in the stainless steel welding strip cannot be too high. At the same time, considering that Si is a deoxidizer in the smelting process, it is very helpful to improve the purity of steel. At the same time, Si can also increase the wettability of the cladding metal during the cladding process and improve the aesthetics of the weld. Therefore, the Si content is controlled at 0.2%≤Si≤0.6%, and the optimal range is 0.3%≤Si≤0.5%.

[0029] Mn is an austenite-forming element. In order to ensure that the Mn content of the cladding metal after cladding is ≤2.00%, and considering that Mn can increase the solubility of N in steel, Mn is controlled at the upper limit, i.e., 1.50%≤Mn≤2.00%.

[0030] P and S are easily segregated elements, and their solubility in the ferrite phase is much greater than that in the austenite phase (for example, the solubility of P in the ferrite phase is 2.8%, and only 0.025% in the austenite phase at room temperature). P and S exceeding the solubility will precipitate with Fe, Ni, etc. to form low-melting-point eutectics such as Fe-FeS, Ni-Ni3S2, and Ni-Ni3P, whose melting points are 600-800°C, which is much lower than the melting point of austenite (1300-1360°C), and cracks will be formed under the action of shrinkage stress in the late solidification period. In stainless steel welding strips, they are generally considered as harmful elements, and the lower the control, the better, so P is controlled to be ≤0.020% and S ≤0.010%.

[0031] Cr is a strong ferrite forming element. Cr can form a dense passivation film on the surface of stainless steel to prevent the substrate from being corroded. It is the main element for improving the corrosion resistance of stainless steel. In order to meet the requirement of Cr in the cladding metal between 17.5-19.5%, combined with the calculation of the dilution rate of the welding strip during the cladding process and the burning loss during the cladding process, the Cr content in the stainless steel welding strip should be between 21.00-23.00%. At the same time, considering that too high Cr will lead to an increase in ferrite content, 21.00-22.00% is taken, and the optimal control is 21.00-21.50%.

[0032] Ni is a strong austenite forming element, and its main function is to form and stabilize austenite structure, so that the steel has good plasticity and toughness, and improves the welding performance of the steel. In order to meet the requirement of cladding metal Ni between 11.00-15.00%, combined with the calculation of the dilution rate and cost of the welding strip during the cladding process, the Ni content in the stainless steel welding strip should be between 13.00% ≤ Ni ≤ 14.00%, and the optimal control is 13.50% ≤ Ni ≤ 14.00%.

[0033] Mo is a ferrite-forming element. Its main function is to improve the corrosion resistance of steel in reducing media (such as H2SO4, H3PO4, some organic acids and urea environments), and to improve the steel's resistance to pitting and crevice corrosion. In order to meet the requirement of cladding metal Mo between 2.00-3.00%, combined with the calculation of the dilution rate and cost of the welding strip during the cladding process, the Mo content in the stainless steel welding strip should be between 2.50%≤Ni≤3.00%, and the optimal control is 2.60%≤Ni≤2.90%.

[0034] Cu significantly reduces the hot working properties of stainless steel. Therefore, in the stainless steel welding strip, Cu is controlled to be ≤ 0.2%, and optimally controlled to be ≤ 0.1%.

[0035] N has advantages in saving precious metals, improving material strength and corrosion resistance by replacing nickel with nitrogen, but too much nitrogen reduces the hot workability of the material and is easy to precipitate and form pores during the surfacing process. Therefore, the control range of nitrogen is 0.03-0.08%, and the optimal range is 0.04-0.05%.

[0036] In the Mo-containing austenitic stainless steel welding strip of the present invention, the synergistic effect of various elements not only ensures the stability of the structure at high temperature, but also avoids the cracking of the cladding metal during the cladding process, making it possible to achieve the effect of two cladding processes by one cladding process of the welding strip.

[0037] Furthermore, in order to ensure that the cladding metal does not produce microcracks after cladding and has good structural stability, the ferrite content of the cladding metal should be guaranteed to be 3-8%. According to the influence of the dilution rate in the cladding process, the ferrite content of the stainless steel welding strip should be guaranteed to be 9-14%. When the ferrite content is less than 9%, the ferrite content of the cladding metal may be lower than 3%, and there is a risk of solidification cracks in the cladding process; when the ferrite content is greater than 14%, the cladding metal is prone to the risk of "hydrogen stripping" (under hydrogen conditions, hydrogen enters the cladding layer, causing the cladding layer to strip off the substrate).

[0038] The ferrite content of the welding strip is calculated by the WRC-1992 formula. C, Ni, N, Cu, Mn, Si, Cr, Mo, etc. are input to calculate the ferrite content, among which C, Ni, N, Cu, and Mn are austenite forming elements, and Si, Cr, and Mo are ferrite forming elements.

[0039] On the other hand, the present invention also provides a method for preparing a Mo-containing austenitic stainless steel welding strip, comprising:

[0040] (1) obtaining molten steel with qualified composition through molten iron pretreatment, converter smelting, VOD furnace refining and LF furnace refining;

[0041] (2) continuously casting the molten steel to obtain a continuously cast slab;

[0042] (3) After grinding and heating, the continuous casting slab enters the hot rolling, cold rolling and annealing process, and is stripped to obtain Mo-containing austenitic stainless steel welding strip.

[0043] The main process parameters involved in the method for preparing the Mo-containing austenitic stainless steel welding strip of the present invention are described in detail below, wherein the processes not specified are all carried out according to the prior art.

[0044] Hot metal pretreatment

[0045] The blast furnace molten iron is subjected to three desulfurization treatments (desiliconization, dephosphorization and desulfurization) to ensure that the molten iron P≤0.006wt%, S≤0.025wt%.

[0046] Converter smelting

[0047] Ferromanganese, ferrochrome, nickel plate, ferromolybdenum and other alloys are added to the converter in batches. The [P] in ferromanganese, ferrochrome, nickel plate, ferromolybdenum and other alloys is required to be ≤0.020%, and high-quality auxiliary materials are selected to ensure the purity of the steel.

[0048] Among them, the high-quality auxiliary materials include: crystallizer protective slag, tundish covering agent, tundish water nozzle, etc.

[0049] In the converter, try to add alloy elements to the appropriate range, and add as little alloy as possible to adjust the composition in the LF furnace.

[0050] VOD furnace refining

[0051] During the VOD furnace refining process, the vacuum degree of the VOD furnace is controlled to be less than 2mbar and the furnace inlet temperature is ≥1620℃, thereby achieving the goals of rapid decarburization and denitrification and improving the refining efficiency.

[0052] The carbon content in the molten iron is removed to below 0.015wt% by blowing oxygen.

[0053] LF furnace refining

[0054] In order to ensure that the ferrite content is between 9-14%, the composition needs to be fine-tuned. High carbon ferrochrome is added to adjust the carbon content, nitrogen is blown in the LF furnace to increase nitrogen, and nickel is added to the nickel plate.

[0055] Before weak stirring, the Ca-Si wire is fed at a rate of 4m / t for further deoxidation, and Fe-B is added at 0.3Kg / t of molten steel to improve the hot workability of the steel billet.

[0056] The exit temperature of LF furnace is controlled at 1500-1510℃.

[0057] Slab continuous casting

[0058] A continuous casting machine is used for continuous casting. The specification of the continuous casting slab is 200×1240mm. Before pouring, argon gas is blown into the crystallizer for 5 minutes to exhaust the air and prevent the molten steel from being oxidized.

[0059] During the continuous casting process, the pouring temperature is controlled at 1450-1480℃, the casting speed is controlled at 0.9-1.1mm / min, and the pouring is strictly protected to prevent secondary oxidation of the molten steel.

[0060] Electromagnetic stirring is used to improve the structure of the ingot and enhance hot workability.

[0061] According to the test, the equiaxed crystal ratio of the ingot of the present invention is more than 60%, the ingot has good thermoplasticity, and the edge cracking during the hot rolling coiling process is effectively avoided. Moreover, the surface quality of the ingot is good, which ensures that the surface quality of the steel strip is good after the cold rolling.

[0062] Billet grinding

[0063] The ingot is ground with a grinding wheel, and the grinding rate is 2-3.5%.

[0064] Ingot heating

[0065] The ingot is heated in a heating furnace with the temperature controlled at 1200-1260°C and the holding time at 180-220 minutes, so that the ingot is softened and evenly burned through.

[0066] Hot rolling of cast slab

[0067] Hot rolling is carried out by hot continuous rolling into coils with a thickness of 2.5-3.0 mm. Large deformation and rapid rolling are adopted and the final rolling temperature is ≥1030°C, thereby avoiding cracking of the edges of the steel strip during the hot rolling process.

[0068] Among them, large deformation rapid rolling refers to the process of rolling a 200mm thick continuous casting billet into a 2.5-3mm thick steel strip through 5 rough rolling passes and 7 finish rolling passes.

[0069] Hot rolled coil

[0070] The hot coil is rolled using a 20-roll mill, and the thickness of the steel plate is rolled from 2.5-3.0mm to the finished product thickness of 0.4-0.5mm to ensure the quality of the plate shape.

[0071] Among them, the deformation rate of the last rolling process in the cold hard state is controlled at 45-50%, without annealing, to ensure that the steel strip is in a semi-hard state, which is suitable for long-distance surfacing process.

[0072] Cold coil annealing

[0073] Annealing temperature is 1060-1100℃, and holding time is 0.3-0.7min.

[0074] Striping

[0075] The steel coils are divided into strips according to the width requirements of the user, and attention is paid to the precision control of the knife to ensure that the burrs of the finished product are ≤5%.

[0076] In some preferred embodiments, if the delivery is in a solid solution state, the main process route of the present invention is: molten iron pretreatment + converter + VOD furnace + LF furnace + slab continuous casting + ingot grinding + ingot heating + hot rolling + hot wire solution treatment + cold rolling + cold wire solution treatment + stripping, etc.

[0077] In some other preferred embodiments, if the product is delivered in a semi-cold hard state, the main process route of the present invention is: molten iron pretreatment + converter + VOD furnace + LF furnace + slab continuous casting + ingot grinding + ingot heating + hot rolling + hot wire solution treatment + cold rolling + cold wire solution treatment + cold rolling + stripping, etc.

[0078] The Mo-containing austenitic stainless steel welding strip prepared according to the method of the present invention has good cold plate surface quality and meets performance requirements. After single-layer surfacing by the user, it achieves the effect of the original two-layer surfacing, greatly improving the production efficiency of surfacing.

[0079] Example

[0080] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions. The raw materials used in the following examples are all conventionally purchased.

[0081] Example 1

[0082] For user-ordered steel grade TEQ309LMo, 0.4×50 (mm), solid solution state.

[0083] The designed process route is hot metal pretreatment + 90-ton converter + VOD furnace + LF furnace + slab continuous casting + slab grinding + slab heating + hot rolling + hot wire solution treatment + cold rolling + cold wire solution treatment + stripping, etc. It mainly includes the following steps:

[0084] (1) Hot metal pretreatment: 45 tons of hot metal from a blast furnace was subjected to three desulfurization treatments (desiliconization, dephosphorization and desulfurization). The actual measured values ​​of hot metal P were 0.005% and S were 0.020%.

[0085] (2) Adding alloy to the converter: 2.1 tons of ferromanganese (Mn: 80-87%, C: 0.2%, P: 0.10%), 29 tons of ferrochrome (Cr: 62-72%, C: 6%, P: 0.018%), 12.2 tons of nickel plate (Ni: 99%), 3.5 tons of ferromolybdenum (Mo: 65-75%, C: 0.10%, P: 0.05%), etc. were added in batches. By blowing oxygen for decarburization, the C content was reduced from 0.788% to 0.224%.

[0086] The chemical composition of the steel after the converter is as follows:

[0087] C: 0.224%; Si: 0.159%; Mn: 1.6123%; P: 0.0146%; S: 0.0134%; Cr: 21.23%; Ni: 13.4553%; Mo: 2.6234.00%; Cu: 0.0113%; N: 0.1994%; the rest is Fe and unavoidable impurities

[0088] VOD refining: The vacuum degree of the VOD furnace is 1.5 mbar, the temperature entering the furnace is 1635°C, and the carbon content is reduced to below 0.015% by blowing oxygen.

[0089] The chemical composition of steel after VOD furnace is as follows:

[0090] C: 0.0064%; Si: 0.3308%; Mn: 1.7327%; P: 0.015%; S: 0.0021%; Cr: 21.0684%; Ni: 13.4146%; Mo: 2.6715%; Cu: 0.012%; N: 0.0209%; the rest is Fe and unavoidable impurities. Ferrite number FN: 17.7%.

[0091] LF furnace refining: To ensure that the ferrite content is between 9-14%, the composition needs to be fine-tuned. High carbon ferrochrome is added to adjust the carbon content, nitrogen is blown into the LF furnace to increase nitrogen, and nickel is added to the nickel plate. Before weak stirring, 4m / t of Ca-Si wire is fed, and Fe-B is added at 0.3Kg / t of molten steel. The outlet temperature is controlled at 1503℃.

[0092] The chemical composition of the steel after being tapped from the LF furnace is as follows:

[0093] C: 0.0184%; Si: 0.3402%; Mn: 1.8143%; P: 0.016%; S: 0.001%; ​​Cr: 21.1022%; Ni: 13.5121%; Mo: 2.6117%; Cu: 0.010%; N: 0.0459%; the rest is Fe and unavoidable impurities. Ferrite number FN: 12.6%.

[0094] (5) Slab continuous casting: The continuous casting slab size is 200×1240mm, the pouring temperature is 1455-1465℃, and the casting speed is controlled at 1.0mm / min. The low magnification of the slab shows that the proportion of equiaxed crystals is 65%.

[0095] (6) Ingot grinding: Grinding with grinding wheel, the grinding rate is 2.0%.

[0096] (7) Ingot heating: The ingot is heated in a heating furnace with a temperature of 1220°C and a holding time of 200 min.

[0097] (8) Hot rolling of ingot: The ingot is hot rolled into coils by hot continuous rolling. The thickness of the hot coil is 2.5 mm. Large deformation and rapid rolling are adopted. The final rolling temperature is 1035 °C.

[0098] (9) Hot coil cold rolling: 20-roll rolling is used to roll the steel plate from 2.5 mm to a finished product thickness of 0.4 mm to ensure the quality of the plate shape.

[0099] (10) Cold coil annealing: annealing temperature 1080℃, holding time 0.5min.

[0100] (11) Striping: Strip the steel coil according to the 50mm width requirement to ensure that the burr of the finished product is ≤5%.

[0101] The surface quality of the produced cold plate is good and the performance meets the requirements. After the user's single-layer surfacing, it achieves the effect of the original two-layer surfacing, and the production efficiency is greatly improved.

[0102] Example 2

[0103] For user-ordered steel type TEQ309LMo, 0.5×60 (mm), semi-cold hardened state.

[0104] The designed process route is hot metal pretreatment + 90-ton converter + VOD furnace + LF furnace + slab continuous casting + slab grinding + slab heating + hot rolling + hot wire solution treatment + cold rolling + cold wire solution treatment + cold rolling + stripping, etc. It mainly includes the following steps:

[0105] (1) Hot metal pretreatment: 46 tons of hot metal from blast furnace was subjected to three desulfurization treatments (desiliconization, dephosphorization and desulfurization). The actual measured values ​​of hot metal P were 0.006% and S were 0.018%.

[0106] (2) Adding alloy to the converter: 2.2 tons of ferromanganese (Mn: 80-87%, C: 0.21%, P: 0.11%), 30 tons of ferrochrome (Cr: 62-72%, C: 6%, P: 0.019%), 12.4 tons of nickel plate (Ni: 99%), 3.7 tons of ferromolybdenum (Mo: 65-75%, C: 0.09%, P: 0.04%), etc. were added in batches. By blowing oxygen for decarburization, the C content was reduced from 0.543% to 0.215%.

[0107] The chemical composition of the steel after the converter is as follows:

[0108] C: 0.215%; Si: 0.143%; Mn: 1.7576%; P: 0.0133%; S: 0.0144%; Cr: 21.22%; Ni: 13.4655%; Mo: 2.6124.00%; Cu: 0.0112%; N: 0.1476%; the rest are Fe and unavoidable impurities.

[0109] (3) VOD refining: The vacuum degree of the VOD furnace is 1.4 mbar, the temperature entering the furnace is 1637°C, and the carbon content is reduced to below 0.015% by blowing oxygen.

[0110] The chemical composition of steel after VOD furnace is as follows:

[0111] C: 0.0077%; Si: 0.3422%; Mn: 1.7623%; P: 0.014%; S: 0.0011%; Cr: 21.2333%; Ni: 13.4765%; Mo: 2.6261%; Cu: 0.0113%; N: 0.0243%; the rest is Fe and unavoidable impurities. Ferrite number FN: 17.5%.

[0112] (4) LF furnace refining: To ensure that the ferrite content is between 9-14%, the composition needs to be fine-tuned. High carbon ferrochrome is added to adjust the carbon content, nitrogen is blown into the LF furnace to increase nitrogen, and nickel is added to the nickel plate. Before weak stirring, 4m / t of Ca-Si wire is fed, and Fe-B is added at 0.3Kg / t of molten steel. The outlet temperature is controlled at 1505℃.

[0113] The chemical composition of the steel after being tapped from the LF furnace is as follows:

[0114] C: 0.0185%; Si: 0.3411%; Mn: 1.8290%; P: 0.014%; S: 0.001%; ​​Cr: 21.2222%; Ni: 13.5347%; Mo: 2.6674%; Cu: 0.0111%; N: 0.0476%; the rest is Fe and unavoidable impurities. Ferrite number FN: 13.2%.

[0115] (5) Slab continuous casting: The continuous casting slab size is 200×1240mm, the pouring temperature is 1458-1467℃, and the casting speed is controlled at 1.0mm / min. The low magnification of the slab shows that the proportion of equiaxed crystals is 65%.

[0116] (6) Ingot grinding: Grinding with grinding wheel, the grinding rate is 2.0%.

[0117] (7) Ingot heating: The ingot is heated in a heating furnace with a temperature of 1220°C and a holding time of 200 min.

[0118] (8) Ingot hot rolling: The ingot is hot rolled into coils by hot continuous rolling. The thickness of the hot coil is 3.0 mm. Large deformation and rapid rolling are adopted. The final rolling temperature is 1038 °C.

[0119] (9) Hot coil cold rolling: 20-roll rolling is adopted, from 3.0 mm to the middle thickness of 0.95 mm, to ensure the quality of the plate shape.

[0120] (10) Cold coil annealing: annealing temperature 1080℃, holding time 0.5min.

[0121] (11) Cold rolling of cold coil: rolling from 0.95 mm thickness to 0.5 mm finished product thickness, with a cold rolling deformation rate of 47%.

[0122] (12) Striping: Strip the steel coil according to the 60mm width requirement to ensure that the burr of the finished product is ≤5%.

[0123] The surface quality of the produced cold plate is good and the performance meets the requirements. After the user's single-layer surfacing, it achieves the effect of the original two-layer surfacing, and the production efficiency is greatly improved.

[0124] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be understood as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to these embodiments should be deemed to be included in the scope of the claims of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined in the claims.

Claims

1. A Mo-containing austenitic stainless steel welding strip, characterized in that: Calculated by weight percentage: C≤0.020%, 0.2%≤Si≤0.6%, Mn≤2.00%, P≤0.020%, S≤0.010%, 21.00%≤Cr≤22.00%, 13.00%≤Ni≤14.00%, 2.50%≤Mo≤3.00%, 0.03%≤N≤0.08%, Cu≤0.2% and the balance of Fe and unavoidable impurities; The Mo-containing austenitic stainless steel welding strip is prepared by the following method: (1) obtaining molten steel with qualified composition through molten iron pretreatment, converter smelting, VOD furnace refining and LF furnace refining; (2) continuously casting the molten steel to obtain a continuously cast slab; (3) grinding and heating the continuously cast slab, and then hot rolling, cold rolling and annealing to obtain a Mo-containing austenitic stainless steel welding strip through stripping; During the continuous casting process, argon gas is blown into the crystallizer for 5 minutes before pouring, the pouring temperature is 1450-1480℃, and the pulling speed is controlled at 0.9-1.1mm / min; the heating temperature of the continuous casting slab is 1200-1260℃, and the holding time is 180-220min; the final rolling temperature of hot rolling is ≥1030℃, and the deformation rate of the last rolling process of cold rolling is controlled at 45-50%; the annealing temperature is 1060-1100℃, and the holding time is 0.3-0.7min; Wherein, the ferrite number FN in the Mo-containing austenitic stainless steel welding strip is 9-14%.

2. The Mo-containing austenitic stainless steel welding strip according to claim 1, characterized in that: Calculated by weight percentage: 0.015%≤C≤0.020%, 0.3%≤Si≤0.5%, 1.50%≤Mn≤2.00%, P≤0.020%, S≤0.010%, 21.00%≤Cr≤21.50%, 13.50%≤Ni≤14.00%, 2.60%≤Mo≤2.90%, 0.04%≤N≤0.05%, Cu≤0.1% and the balance of Fe and unavoidable impurities.

3. The method for preparing the Mo-containing austenitic stainless steel welding strip according to any one of claims 1 to 2, characterized in that: include: (1) After hot metal pretreatment, converter smelting, VOD furnace refining and LF furnace refining, molten steel with qualified composition is obtained; (2) continuously casting the molten steel to obtain a continuously cast slab; (3) After grinding and heating, the continuous casting slab enters the hot rolling, cold rolling and annealing process, and is stripped to obtain Mo-containing austenitic stainless steel welding strip.

4. The method for preparing the Mo-containing austenitic stainless steel welding strip according to claim 3, characterized in that: During the VOD furnace refining process, the vacuum degree of the VOD furnace is less than 2mbar, the furnace entry temperature is ≥1620℃, and the carbon content is reduced to below 0.015wt% by blowing oxygen.

5. The method for preparing the Mo-containing austenitic stainless steel welding strip according to claim 3, characterized in that: During the LF furnace refining process, the Ca-Si wire is fed at a rate of 4m / t before weak stirring, and Fe-B is added at a rate of 0.3 Kg / t of molten steel. The outlet temperature is controlled at 1500-1510℃.