CN103215524A - Stainless steel welded pipe with excellent pipe processability and manufacturing method thereof - Google Patents
Stainless steel welded pipe with excellent pipe processability and manufacturing method thereof Download PDFInfo
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Abstract
The invention relates to a stainless steel welded pipe with excellent pipe processability and a manufacturing method thereof. The stainless steel welded pipe comprises the following chemical components in percentage by weight: 0.005 to 0.015 percent of C, 0.005 to 0.015 percent of N, 0.001 to 0.040 percent of P, 0.0005 to 0.030 percent of S, 10.0 to 19.0 percent of Cr, 0.10 to 1.0 percent of Mn, 0.10 to 1.0 percent of Si, 0.05 to 1.50 percent of Mo, 0.05 to 0.60 percent of Cu, 0.001 to 0.020 percent of Al, 0.005 to 0.10 percent of Zr, 0.0003 to 0.0030 percent of B, 0.01 to 0.15 percent of Ce, less than or equal to 0.20 percent of Ni, 0.08 to 0.50 percent of Ti, 0.08 to 0.50 percent of Nb, less than or equal to 0.80 percent and more than or equal to 8*(C+N) of Ti+Nb, less than or equal to 0.60 percent and more than or equal to 8*(C+N) or less than or equal to 0.70 percent and more than or equal to 8*(C+N) of Ti+0.5Nb, and the balance of Fe and inevitable impurities. The stainless steel welded pipe has a single ferritic structure and has an excellent weld joint structure; the width of the weld joint is controlled to be within 50 to 150 percent of the thickness of the plate; the flaring rate of the welded pipe is over 40 percent; the pipe expanding rate reaches 40 to 110 percent; and the pipe processing requirements such as pipe bending, flaring, pipe expanding and the like are completely met.
Description
Technical Field
The present invention relates, in particular, to a stainless steel welded pipe having excellent pipe workability and a method for manufacturing the same; the stainless steel welding pipe material has a single ferrite structure and a good welding line structure, the welding line width is controlled within 50-150% of the plate thickness, the flaring rate of the welding pipe can reach over 40%, the flaring rate can reach 40-110%, and the welding pipe is far higher than 30% of the conventional welding.
Background
With the development of society, stainless steel welded pipes are increasingly applied to various fields of society, people put higher requirements on the service performance of various materials including welded pipe materials, and stainless steel replaces conventional carbon steel welded pipes in various fields. For example, in an exhaust gas purification system in the field of automobile industry, the use of stainless steel welded pipes exceeds 60%. Due to the limitation of the design of the automobile chassis, more welded pipes with larger bent pipe deformation can be used in the design of an exhaust system of an automobile, and a straight pipe needs to be bent to a larger angle, such as 120-90 degrees, in order to meet the local space requirement of the chassis, and particularly, a stainless steel welded pipe becomes a main product for use because of good corrosion resistance and processability.
If the connecting pipe at the front end of the exhaust system adopts a part for expanding the pipe, the manifold can be directly arranged in the connecting pipe, so that the space can be saved, the efficiency can be improved, the connecting pipe with a certain specification needs to be expanded to 200 percent or even higher of the original specification, and the welded pipe material, particularly the welded part, needs to have good pipe processing performance. This all places higher demands on the welded pipe quality, in particular the weld quality.
Aiming at the performance requirements of stainless steel welded pipes for automobiles, the traditional argon arc welding process not only has production quality, particularly the performance of welding seams, which is difficult to meet the requirements of automobile parts, but also has very low production efficiency (the argon arc welding speed is about 1.2 m/min), and can not meet the large-scale production requirements of the automobile industry. In addition, the stainless steel welded pipe for the automobile also considers the use requirements of the service environment on the materials. For example, stainless steel welded pipe for automobile cleaning system has good heat conductivity and lower thermal expansion coefficient, so as to reduce the expansion failure caused by automobile starting as much as possible. In order to obtain the workability as described above, it is difficult for the conventional ferritic stainless steel material to meet the requirements, and ultra-pure ferritic stainless steel with low carbon and nitrogen is considered as the most suitable stainless steel.
At present, the welding mode for most stainless steel welded pipes mainly adopts an argon arc welding process, the technical requirement of the process is not high, the cost is low, but the requirements of high-performance pipe construction are difficult to meet, and if the pipe expansion rate exceeds 100%, the pipe expansion rate exceeds 40%, and even reaches more than 50%. And the required stainless steel welded pipe with high formability can be obtained by adopting laser welding or high-frequency welding and matching with proper welding process parameters. The high-performance stainless steel material and the welding mode become main requirements in the automobile industry.
Disclosure of Invention
The invention aims to provide a stainless steel welded pipe with excellent pipe processability and a manufacturing method thereof for the fields of automobiles, heat exchange and other related industries, and the stainless steel welded pipe has the following main performance indexes: the width of the welding seam is controlled within 50-150% of the plate thickness, the flaring rate of the welded pipe can reach over 40%, and the flaring rate can reach 40-110%, which is far higher than 30% of the conventional welding.
In order to achieve the purpose, the invention adopts the following technical scheme:
a stainless steel welded pipe with excellent pipe processability comprises the following chemical components in percentage by weight: c: 0.005-0.015%, N: 0.005-0.015%, P: 0.001 to 0.040%, S: 0.0005 to 0.030%, Cr: 10.0 to 19.0%, Mn: 0.10 to 1.0%, Si: 0.10 to 1.0%, Mo: 0.05 to 1.50%, Cu: 0.05-0.60%, Al: 0.001-0.020%, Zr: 0.005-0.10%, B: 0.0003-0.0030%, Ce: 0.01-0.15%, Ni is less than or equal to 0.20%, Ti: 0.08 to 0.50%, Nb: 0.08-0.50%, when two of Ti and Nb are added, the following conditions are satisfied: not less than 8 x (C + N) and not more than 0.80% of Ti + Nb, and not less than 8 x (C + N) and not more than 0.5% of Ti + 0.60% of Nb, or when three of Ti, Nb and V are added simultaneously: ti +0.5Nb + V is more than or equal to 8 x (C + N) and less than or equal to 0.70 percent, and the balance is Fe and inevitable impurities; the yield strength of the material reaches over 240MPa, the tensile strength reaches over 400MPa, and the elongation rate exceeds 30 percent; the stainless steel welded pipe has a single ferrite structure and a good weld joint structure, the weld joint width is controlled within 50-150% of the plate thickness, the flaring rate of the welded pipe is more than 40%, and the pipe expansion rate is 40-110%.
The stainless steel welded pipe with excellent pipe processability comprises the following chemical components in the design:
c and N: the stainless steel material used in the present invention is a low carbon and nitrogen ferritic stainless steel, and therefore carbon and nitrogen are particularly interesting control elements in the steel, wherein C and N are both control elements, but need to be controlled in a specified range. The low content of C is not favorable for ensuring the strength of the material, and the high content of C influences the corrosion resistance of the material, so the control range of C is set to be 0.005-0.015%. The N element is useful for improving the quality of continuous casting, but too high content thereof causes deterioration of workability, and the control range of N is set to 0.005% to 0.015%. The existing smelting equipment can easily meet the requirement that the content of carbon and nitrogen is controlled to be less than 0.015 percent and the content of C and N is 0.005 to 0.015 percent. Controlling the C, N upper limit also reduces the amount of stabilizing elements, especially reduces the use of Ti, improves the surface quality of the product and improves the intergranular corrosion performance.
Cr: cr is a main alloying element that improves corrosion resistance and strength. Cr improves the corrosion resistance of stainless steel and improves the local corrosion resistance of the stainless steel, such as atmospheric corrosion resistance, crevice corrosion resistance and the like. Cr increases the strength of steel, but excessively increases the plasticity of steel, which is disadvantageous in formability and weldability. The corrosion performance of the steel is not improved due to too low content, so that the selection range of Cr in the steel is 10.0-19.0%.
Si: si is added into steel to perform the functions of deoxidation and corrosion resistance improvement, and simultaneously, the strength of the material can be further improved. Too low is detrimental to deoxidation and strength enhancement, typically greater than 0.10%. However, if it is too high, it exceeds 1.0%, and the resulting composition is not suitable for molding at ordinary temperature because of its poor workability and toughness. The Si content in the steel of the invention is selected in the range of 0.10% to 1.0% in view of the overall properties.
Mn: mn is a weak austenite element, and can inhibit the harmful effect of sulfur in stainless steel and improve thermoplasticity. Too low is not favorable for improving the thermoplasticity of the alloy, and is not favorable for improving the formability at normal temperature, and too high is not favorable for ensuring the corrosion resistance of the alloy. In the steel, the selection range of Mn content is 0.10-1.0% in order to ensure the strength and plasticity of the steel.
Cu: cu can improve corrosion resistance and processability. Too low a Cu content does not meet the requirement of improving the performance, too high a content causes a stress corrosion tendency, and the upper limit of Cu is not more than 0.60% under the condition of meeting the corrosion and processing performance.
Ni: ni belongs to a control element in the ferritic stainless steel, the amount of Ni brought by scrap steel smelting is reduced as much as possible, and the total amount is not more than 0.30 percent.
V: v is beneficial to improving the strength of the material and can also play a stabilizing role. But the content is not easy to be too high, which can cause the material strength and hardness to be too high, and is not beneficial to forming processing, and in order to improve the material strength, the V in the steel is required to be less than or equal to 0.1 percent.
Zr: zr can combine with free O in steel to improve formability and toughness, too low an effect is not obvious, too high a cost is increased, and workability is deteriorated, and a suitable range of Zr content is: 0.005-0.10 percent.
Mo: mo can improve the chloride ion corrosion resistance and the corrosion resistance in a reducing medium, particularly, a middle pipe and a front pipe at the chassis part can be frequently corroded by high-temperature dissolved salt, and the corrosion resistance can be effectively improved by adding Mo. But the corrosion resistance effect cannot be achieved due to the excessively low addition of Mo, and the minimum addition amount is not less than 0.05 percent. If the addition amount of Mo is too high, the material cost is obviously increased and generally is not more than 1.5 percent.
Al: al is introduced into steel when Al is used as a deoxidizer for stainless steel making. Too high an Al content, in turn, leads to the formation of Al oxides, which leads to a reduction in toughness and an impairment of the surface quality of the product. Therefore, the reasonable range of the Al content in the steel is more than or equal to 0.001 percent and less than or equal to 0.020 percent.
B: b is beneficial to improving the secondary processing performance of the material, such as flaring, pipe expanding, pipe bending and the like of a welded pipe, and the addition amount cannot be lower than 0.0003% to achieve the expected effect, but the tensile elongation and the r value are influenced by excessive addition, so the upper limit is not more than 0.0030%.
Ce: ce is one of the common rare earth elements. The rare earth elements are important elements for improving the structure, refining grains and improving the oxidation resistance. The addition amount of the rare earth element is less than 0.01 percent, the effects of improving the structure and improving the oxidation resistance cannot be achieved, and the addition amount is more than 0.15 percent, so that the defects of slag inclusion and the like are easily caused. Therefore, the ideal addition amount of Ce should be controlled to be between 0.01 percent and 0.15 percent.
Ti and Nb: ti and Nb are mainly used for preventing chromium concentration reduction caused by the formation of chromium carbide by the combination of chromium and carbon in steel, resulting in the reduction of corrosion resistance, particularly causing intergranular corrosion; ti can also combine with sulfur in steel to form TiC2The S compound prevents pitting corrosion caused by MnS. Stainless steel has greater affinity for Ti and nitrogen than for Nb, which has greater affinity for carbon than for Ti. Ti and Nb can improve the strength of the stainless steel at room temperature and high temperature, improve the fatigue resistance, cold formability and welding of the ferritic stainless steel, and the over-high Nb is unfavorable for the brittle transition temperature of the steel. The nitride TiN formed by Ti and nitrogen as an inclusion affects the surface and internal quality of steel, and the nitride NbN formed by Nb and nitrogen reduces the thermoplasticity of steel. TiN formed by Ti in the continuous casting stage can also play a role of nucleation particles, which is beneficial to further improving the proportion of isometric crystals and improving the processing performance. If the Ti content is more than 0.08%, the effect is obvious, and if the Ti content is too high, surface defects are generated, and the Ti content is generally not more than 0.50%. The effect is obvious when the Nb content is more than 0.08 percent, and when the Nb content exceeds 0.50 percent, coarse Fe is formed due to excessive Nb2Nb is not favorable for material formability and welding impact property. Selecting Nb by taking account of C, N contentAnd Ti as stabilizing additive elements, the ranges (weight percent) being selected: ti: 0.08 to 0.50%, Nb: 0.08-0.50%, and when Ti and Nb are added simultaneously, the following conditions are satisfied: ti and Nb are more than or equal to 8 x (C + N) and less than or equal to 0.80 percent, and Ti and Nb are more than or equal to 8 x (C + N) and less than or equal to 0.5 and less than or equal to 0.60 percent. Meanwhile, the effect of V is considered, and the three types of Ti + Nb + V meet the requirements (weight percentage) when being added simultaneously: ti +0.5Nb + V is more than or equal to 8 x (C + N) and less than or equal to 0.70 percent.
P and S: phosphorus and sulfur in ferritic stainless steel seriously affect the corrosion resistance and the processing performance of the stainless steel, and must be strictly controlled, and P is less than or equal to 0.040 percent and S is less than or equal to 0.030 percent. However, considering that the smelting cost is increased by excessively low content, the lower limit is controlled to P not less than 0.001% and S not less than 0.0005%.
Ni: ni is taken as an introduced element, and is not taken as an alloy element due to the introduction of raw material addition, so that the introduction is reduced as much as possible, and the stainless steel can obtain a single ferrite structure, so that the Ni is required to be less than or equal to 0.20 percent.
The method for manufacturing the stainless steel welded pipe with excellent pipe processability comprises the following steps: smelting according to the proportion of the chemical components, and obtaining the stainless steel welded pipe with excellent pipe processability through continuous casting, heating, hot rolling, acid washing, cold rolling, annealing after cold rolling, stripping, looping, pipe making, welding, sizing and saw cutting; wherein,
in the smelting step, electric furnace steelmaking, AOD decarburization and VOD deoxidation are adopted for steelmaking, and Ti is fed with titanium wires after VOD is finished;
in the continuous casting step, the drawing speed of a continuous casting billet in the continuous casting process is 0.9-1.1 m/min, and the continuous casting billet with the isometric crystal proportion not less than 60% is obtained;
in the heating step, the heating temperature is 950-1250 ℃, and the heat preservation time is 180-240 min;
in the hot rolling step, firstly carrying out 5-7 times of rough rolling and removing surface oxide skin, wherein the rough rolling temperature is 1100-900 ℃, and then carrying out 5-7 times of finish rolling, the finish rolling temperature is 1080-750 ℃, and the total reduction rate of the rough rolling and the total reduction rate of the finish rolling are not lower than 85%;
in the cold rolling step, the reduction rate of cold rolling is 60-80%;
in the annealing step after cold rolling, the annealing temperature is 850-1020 ℃, the annealing time is 2-6 min, and a cold-rolled steel plate with the grain size of 6-8 grade and the surface roughness Ra of 0.10-0.50 mu m is obtained;
in the welding step, laser welding or high-frequency induction heating welding is adopted:
when laser welding is adopted, argon is adopted for protection inside and outside a welding part, the welding speed V is 2-10 m/min, the welding power W is 4 KW-12 KW, and the welding power W meets the condition that W is more than or equal to 4+6 multiplied by V/10; one or more pairs of squeezing rollers are used at the welding position, and the squeezing force is not more than 10Kg/cm2。
When high-frequency induction heating welding is adopted, argon or nitrogen is adopted for protection inside and outside a welding position, the welding speed V is 20-100 m/min, the welding frequency is 250-350 KHz, the welding power W is 240-320 KW, the welding power W meets the condition that W is more than or equal to 240+60 XV/100, a pair of horizontal extrusion rollers are adopted for the welding position, the extrusion force is not more than 10Kg/cm2。
Preferably, when laser welding or high-frequency induction heating welding is adopted, the wall thickness of a welded pipe is 0.50-2.50 mm.
Preferably, in the continuous casting step, electromagnetic stirring is adopted in the continuous casting process, and the current of the electromagnetic stirring is 1000-1600A.
Furthermore, temperature-carrying surface polishing is carried out before the continuous casting billet is heated, the polishing starting temperature is not lower than 360 ℃, and the polishing finishing temperature is not lower than 150 ℃.
Further, the sizing step further comprises an annealing step, wherein the annealing temperature is 300-850 ℃, and the annealing time is 1-5 min, so that the processing performance is further improved, such as the pipe expanding performance and the pipe expanding performance are improved.
When the stainless steel welded pipe with excellent pipe processability is subjected to three-step steel making through electric furnace steel making, AOD decarburization and VOD deoxidation, other elements can be added in the previous smelting process, but in consideration of Ti oxidation, Ti element needs to be subjected to titanium wire feeding treatment after VOD is finished, and molten steel meeting the component requirements can be obtained after comprehensive components meet the design requirements.
According to the invention, by controlling the continuous casting billet drawing speed (0.9-1.1 m/min) in the continuous casting process, enhancing electromagnetic stirring (current 1000-1600A) and combining with stabilization elements and other comprehensive processes, the molten steel is subjected to continuous casting to obtain the continuous casting billet, and the medium axicon proportion of the continuous casting billet is not lower than 60%; and (3) carrying out surface grinding with temperature on the continuous casting billet, wherein the grinding starting temperature is not lower than 360 ℃, and the grinding finishing temperature is not lower than 150 ℃. After polishing, the steel strip is sent to a heating furnace with temperature to be heated (950-1250 ℃) and is subjected to heat preservation for a certain time for hot rolling.
The hot rolling of the invention is firstly carried out for 5-7 times of rough rolling (temperature range is 1100-900 ℃) and surface oxide skin is removed, the rough rolling billet is subjected to 5-7 times of finish rolling (temperature range is 1080-750 ℃), and the total reduction rate of the rough rolling and the total reduction rate of the finish rolling are not lower than 85%. The hot rolled coil is directly pickled to obtain the required stainless steel plate. In addition, the continuous casting and the control of the hot rolling state structure are beneficial to inhibiting the structure coarsening of the subsequent welding seam.
The cold rolling process of the invention also ensures a certain rolling reduction rate, which is generally set to 60-80%, and is beneficial to obtaining good comprehensive mechanical properties. After the cold-rolled sheet is rolled, cold rolling annealing is needed, so that the cold-rolled stainless steel can be fully recrystallized, the grain size grade reaches 6-8 grades, and certain surface roughness (Ra is more than or equal to 0.10 mu m and less than or equal to 0.50 mu m) is ensured, thus not only the tube processability is ensured, but also the comprehensive corrosion performance is favorably improved, and the cold-rolled stainless steel product with the comprehensive performance meeting the requirement is obtained.
The cold-rolled stainless steel plate meeting the requirements obtained by the invention is used for preparing stainless steel welded pipes by obtaining the lath with the required specification through splitting. The stainless steel welded pipe can be manufactured by laser welding or high-frequency induction heating welding, and comprises the following specific steps:
the invention is suitable for the width and the thicknessThe stainless steel cold-rolled strip with the required degree is formed into a cylinder shape by roll forming, and then welded into a steel pipe by adopting a laser welding or high-frequency welding mode. When the laser welding processing is adopted, the internal and external argon protection is also adopted, so that the welding line can not be oxidized and slag is not included. The welding speed is 2-10 m/min, one or more pairs of squeeze rollers are adopted at the welding position to ensure that the welding can weld the molten metal together with the welded pipe through the squeeze rollers, and the squeezing force is controlled to be not more than 10Kg/cm2The welding power is 4 KW-12 KW. In order to obtain good welding quality, the welding power W is preferably selected to satisfy W ≧ 4+6 XV/10 (W is KW; V is m/min). When a high-frequency welding mode is adopted for processing, the welding position is protected by internal and external argon or nitrogen, and the welding speed is 20-100 m/min. The frequency of a welding machine is 250-350 KHz, the welding power W is 240-320 KW, and the welding wall thickness is 0.50-2.50 mm. In order to obtain good welding quality, the welding power is preferably selected to satisfy W ≥ 240+60 XV/100 (W is KW; V is m/min). During high-frequency welding, a pair of horizontal extrusion rollers are adopted at the welding position to ensure that the welding can weld the welded pipe by molten metal through the extrusion rollers, and the extrusion force is controlled to be not more than 10Kg/cm2。
The yield strength of the stainless steel welded pipe manufactured by the process can reach over 240 MPa. The tensile strength reaches more than 400MPa, and the elongation rate exceeds 30 percent. The stainless steel welded pipe and the welding line material have single ferrite structure, the welded pipe has good welding line structure, the width of the welding line is controlled within 50-150% of the plate thickness, the flaring rate of the welded pipe can reach more than 40%, and the pipe expansion rate can reach 50-110%.
Compared with the prior art, the invention has the following characteristics:
in the prior art, chinese patent CN1072271C discloses a ferritic stainless steel used in an automobile exhaust device, which comprises the following chemical components by weight percent: c is not more than 0.005%, N is not more than 0.008%, C + N is not more than 0.009%, Si is not more than 0.45%, Mn is not more than 1%, Cr is 10% -12.5%, Nb is 0.05% -0.3%, Ti is 8 x (C + N) -0.3%, and the balance is Fe and inevitable impurities.
European patent EP1930461A1 discloses stainless steel and a welded pipe for an automobile exhaust system, which comprise the following chemical components in percentage by weight: c is less than 0.03%, Si: 1.0% or less, Mn: 1.5% or less, Cr: 10.0-20%, Nb: 0.5% or less, Ni: 0.6% or less, N: 0.03% or less, Ti: 0.05-0.30%, S: 0-0.10%, Mo: 0-1.5%, Al: 0.03-0.12%, Cu 1-2%, V: 0.2% or less, B: 0.0005% -0.02%, O: less than 0.01 percent, and the balance of Fe and inevitable impurities. Nb is more than or equal to 8 x (C + N), and Al- (54/48) O is more than or equal to 0.02% and less than or equal to 0.1%.
Compared with the two prior patents, the stainless steel welded pipe with excellent pipe processability has the chemical composition designed as low as C, N ferrite stainless steel, particularly controls the adding amount of elements for strengthening corrosion performance, such as Mo, Cu, Cr and the like, and simultaneously strengthens the elements for processing performance, such as Mn, Si, V, B and the like. Particularly, compared with the Chinese patent CN1072271C, the invention makes special limitation on the content of C and N, and the lower limit is not lower than 0.005%. The upper limit of the content of C in CN1072271C is 0.005%, which is totally different from the former. The addition of Ni element and higher Cu in EP1930461a1 not only significantly increases the manufacturing cost, but also the excessive Cu greatly causes stress corrosion cracking. Meanwhile, the component design of the invention also considers the oxidation resistance elements of the material, such as Ce, Zr and the like, and mainly aims to meet the requirements of the use of the automobile in the high-temperature environment. In particular, addition of Ti and Nb serves to stabilize and improve corrosion resistance. Meanwhile, Ti can also improve the welding performance and is beneficial to refining the weld joint structure. Nb can improve high temperature stability and formability.
Compared with the prior art, the method can obtain the high-performance stainless steel welded pipe with the thickness of 0.5-2.5 mm and the diameter of 19-75 mm. The base material and the welding seam of the welded pipe material are both single ferrite tissues. Completely meets the pipe processing requirements of bending, flaring, pipe expanding and the like. If necessary, the processing performance can be further improved by annealing, such as the pipe expanding performance and the pipe expanding performance are improved.
Drawings
FIG. 1 is a schematic view of a laser welding process for a stainless steel welded pipe according to the present invention;
FIG. 2 is a schematic view of the high-frequency induction heating welding process of the stainless steel welded pipe of the present invention.
Detailed Description
The technical solution of the present invention is further described in detail with reference to the specific examples below.
The chemical components of the stainless steel welded pipe with excellent pipe processability are shown in the table; the main control process parameters of each example are shown in table 2, the welding process parameters of the stainless steel welded pipes are shown in table 3, and the properties of the obtained stainless steel welded pipes having excellent pipe workability are shown in table 4.
Smelting according to the proportion of chemical components of each embodiment, and obtaining the stainless steel welded pipe with excellent pipe processability through continuous casting, heating, hot rolling, acid washing, cold rolling, annealing after cold rolling, stripping, looping, pipe making, welding, sizing and sawing; wherein,
in the smelting step, electric furnace steelmaking, AOD decarburization and VOD deoxidation are adopted for steelmaking, and Ti is fed with titanium wires after VOD is finished;
in the continuous casting step, the drawing speed of a continuous casting blank in the continuous casting process is 0.9-1.1 m/min, electromagnetic stirring is adopted in the continuous casting process, the current of the electromagnetic stirring is 1000-1600A, and the continuous casting blank with the isometric crystal proportion not lower than 60% is obtained;
further, before heating the continuous casting blank, carrying out surface grinding with temperature, wherein the grinding starting temperature is not lower than 360 ℃, and the grinding finishing temperature is not lower than 150 ℃;
in the heating step, the heating temperature is 950-1250 ℃, and the heat preservation time is 180-240 min;
in the hot rolling step, firstly carrying out 5-7 times of rough rolling and removing surface oxide skin, wherein the rough rolling temperature is 1100-900 ℃, and then carrying out 5-7 times of finish rolling, the finish rolling temperature is 1080-750 ℃, and the total reduction rate of the rough rolling and the total reduction rate of the finish rolling are not lower than 85%;
in the cold rolling step, the reduction rate of the cold rolling is 60 to 80 percent;
in the annealing step after cold rolling, the annealing temperature is 850-1020 ℃, the annealing time is 2-6 min, and a cold-rolled steel plate with the grain size of 6-8 grade and the surface roughness Ra of 0.10-0.50 mu m is obtained;
in the welding step, laser welding or high-frequency induction heating welding is adopted:
when laser welding is adopted, argon is adopted for protection inside and outside a welding position, the welding speed V is 2-10 m/min, one or more pairs of extrusion rollers are adopted for the welding position, and the extrusion force is not more than 10Kg/cm2The welding power W is 4 KW-12 KW, and the welding power W meets the condition that W is more than or equal to 4+6 multiplied by V/10; the manufacturing process path of a welded tube using laser welding is shown in fig. 1.
When high-frequency induction heating welding is adopted, argon or nitrogen is adopted for protection inside and outside a welding position, the welding speed V is 20-100 m/min, a pair of extrusion rollers in the horizontal direction are adopted for the welding position, and the extrusion force is not more than 10Kg/cm2The welding frequency is 250-350 KHz, the welding power W is 240-320 KW, the welding power W meets the condition that W is more than or equal to 240+60 multiplied by V/100, and when high-frequency induction heating welding is adopted, the welding wall thickness is 0.50-2.50 mm. The manufacturing process path of the welded tube using high frequency induction heating welding is shown in fig. 2.
The stainless steel welded pipe with excellent pipe processability, which is obtained in each embodiment of the invention, has the yield strength of over 240MPa, the tensile strength of over 400MPa and the elongation of over 30 percent. The stainless steel welded pipe and the welding line material have single ferrite structure, the welded pipe has good welding line structure, the width of the welding line is controlled within 50-150% of the plate thickness, the flaring rate of the welded pipe can reach more than 40%, and the pipe expansion rate can reach 50-110%. The stainless steel welded pipe is also subjected to industrial trial production, and the effect is good.
Table 1 units: weight percent of
TABLE 2
TABLE 3
TABLE 4
Claims (5)
1. A stainless steel welded pipe with excellent pipe processability comprises the following chemical components in percentage by weight: c: 0.005-0.015%, N: 0.005-0.015%, P: 0.001 to 0.040%, S: 0.0005 to 0.030%, Cr: 10.0 to 19.0%, Mn: 0.10 to 1.0%, Si: 0.10 to 1.0%, Mo: 0.05 to 1.50%, Cu: 0.05-0.60%, Al: 0.001-0.020%, Zr: 0.005-0.10%, B: 0.0003-0.0030%, Ce: 0.01-0.15%, Ni is less than or equal to 0.20%, Ti: 0.08 to 0.50%, Nb: 0.08-0.50%, when two of Ti and Nb are added, the following conditions are satisfied: not less than 8 x (C + N) and not more than 0.80% of Ti + Nb, and not less than 8 x (C + N) and not more than 0.5% of Ti + 0.60% of Nb, or when three of Ti, Nb and V are added simultaneously: ti +0.5Nb + V is more than or equal to 8 x (C + N) and less than or equal to 0.70 percent, and the balance is Fe and inevitable impurities; the yield strength of the material reaches over 240MPa, the tensile strength reaches over 400MPa, and the elongation rate exceeds 30 percent; the stainless steel welded pipe has a single ferrite structure and a good weld joint structure, the weld joint width is controlled within 50-150% of the plate thickness, the flaring rate of the welded pipe is more than 40%, and the pipe expansion rate is 40-110%.
2. A method for manufacturing a stainless steel welded pipe having excellent pipe workability according to claim 1, comprising the steps of: smelting according to the proportion of the chemical components, and obtaining the stainless steel welded pipe with excellent pipe processability through continuous casting, heating, hot rolling, acid washing, cold rolling, annealing after cold rolling, stripping, looping, pipe making, welding, sizing and saw cutting; wherein,
in the smelting step, electric furnace steelmaking, AOD decarburization and VOD deoxidation are adopted for steelmaking, and Ti is fed with titanium wires after VOD is finished;
in the continuous casting step, the drawing speed of a continuous casting billet in the continuous casting process is 0.9-1.1 m/min, and the continuous casting billet with the isometric crystal proportion not less than 60% is obtained;
in the heating step, the heating temperature is 950-1250 ℃, and the heat preservation time is 180-240 min;
in the hot rolling step, firstly carrying out 5-7 times of rough rolling and removing surface oxide skin, wherein the rough rolling temperature is 1100-900 ℃, and then carrying out 5-7 times of finish rolling, the finish rolling temperature is 1080-750 ℃, and the total reduction rate of the rough rolling and the total reduction rate of the finish rolling are not lower than 85%;
in the cold rolling step, the reduction rate of cold rolling is 60-80%;
in the annealing step after cold rolling, the annealing temperature is 850-1020 ℃, the annealing time is 2-6 min, and a cold-rolled steel plate with the grain size of 6-8 grade and the surface roughness Ra of 0.10-0.50 mu m is obtained;
in the welding step, laser welding or high-frequency induction heating welding is adopted:
when laser welding is adopted, argon is adopted for protection inside and outside a welding part, the welding speed V is 2-10 m/min, the welding power W is 4-12 KW, and the welding powerW is more than or equal to 4+6 xV/10; one or more pairs of squeezing rollers are used at the welding position, and the squeezing force is not more than 10Kg/cm2；
When high-frequency induction heating welding is adopted, argon or nitrogen is adopted for protection inside and outside a welding position, the welding speed V is 20-100 m/min, the welding frequency is 250-350 KHz, the welding power W is 240-320 KW, and the welding power W meets the condition that W is more than or equal to 240+60 multiplied by V/100; the welding position adopts a pair of extruding rollers in the horizontal direction, and the extruding force is not more than 10Kg/cm2；
The yield strength of the obtained stainless steel welded pipe with excellent pipe processability reaches over 240MPa, the tensile strength reaches over 400MPa, and the elongation rate exceeds 30 percent; the stainless steel welded pipe has a single ferrite structure and a good weld joint structure, the weld joint width is controlled within 50-150% of the plate thickness, the flaring rate of the welded pipe is more than 40%, and the pipe expansion rate is 40-110%.
3. A method of manufacturing a welded stainless steel pipe having excellent pipe workability according to claim 2, wherein the wall thickness of the welded pipe is 0.50 to 2.50mm when laser welding or high-frequency induction heating welding is employed.
4. A method for manufacturing a welded stainless steel pipe having excellent pipe workability according to claim 2 or 3, wherein in the continuous casting step, electromagnetic stirring is used in the continuous casting process, and the current of the electromagnetic stirring is 1000 to 1600A.
5. A method for manufacturing a stainless steel welded pipe having excellent pipe workability according to claim 2 or 3, wherein warm surface thinning is further performed before the continuous cast slab is heated, and the thinning start temperature is not lower than 360 ℃ and the thinning finish temperature is not lower than 150 ℃.
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| CN106319343B (en) * | 2016-10-10 | 2021-08-17 | 宝钢德盛不锈钢有限公司 | Low-cost high-strength stainless steel and welded pipe manufacturing method thereof |
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