CN115505846B - 303 free-cutting stainless steel wire rod with high surface quality and manufacturing method thereof - Google Patents
303 free-cutting stainless steel wire rod with high surface quality and manufacturing method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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Abstract
The 303 free-cutting stainless steel wire rod with high surface quality comprises the following components in percentage by mass: c:0.015% -0.150%, mn: 1.00-3.00%, si:0.20 to 1.00 percent, P is less than or equal to 0.045 percent, S:0.15 to 0.35 percent of Cr: 17.00-19.00%, ni: 8.00-10.00%, cu:1.50 to 3.50 percent, and the balance of Fe and other unavoidable impurities; and simultaneously satisfies: mn/S is more than 8.2; the casting blank high-temperature ferrite mass ratio delta-F=3.0-7.0%; carbide precipitation temperature T M23C6 The temperature is less than or equal to 950 ℃. The tensile strength of the free-cutting stainless steel wire rod is less than or equal to 590MPa, the elongation after fracture is more than or equal to 40%, and the area shrinkage is more than or equal to 50%.
Description
Technical Field
The invention belongs to the technical field of stainless steel production, and particularly relates to a 303 free-cutting stainless steel wire rod with high surface quality and a manufacturing method thereof.
Background
In recent years, with the rapid development of the industries of automobiles, precise instruments and automatic lathes, the use amount of free-cutting stainless steel is increasing year by year. 303 is a free-cutting stainless steel developed by adding free-cutting elemental sulfur on the basis of the S30400 austenitic stainless steel chemical composition. At present, the manufacturing flow of the 303 stainless steel wire rods produced by domestic manufacturers is generally as follows: the surface of the 303 stainless steel wire rod passing through the manufacturing flow is easy to have the phenomena of skin tilting and 'spots'.
Off-line solid solution of stainless steel wire rods generally requires heating the wire rods from room temperature to around 1050 ℃ for a period of time to allow the deleterious second phase to dissolve well in the matrix and then rapidly cool to achieve the desired structure and properties. This process is time consuming and has a high heat loss.
The 303 stainless steel wire rod is easy to segregate due to high S element content, the surface of the wire rod is easy to form a skin-tilting defect, the skin-tilting is easy to form a pit defect after drawing and grinding processing by a customer, and the quality of a finished product is influenced. 303, when the casting blank is solidified, because the solid solubility of the S element in austenite is lower than that of ferrite, when ferrite is transformed into austenite in the solidification process, the S element is precipitated and accumulated to a grain boundary, and S element grain boundary segregation occurs. When the temperature of a casting blank is lower than 1004 ℃, eutectic reaction is carried out, fe-FeS eutectic is distributed at a grain boundary, in the hot working process of heating temperature being higher than the melting point, the Fe-FeS eutectic is melted, the grain boundary is broken when the steel is rolled and pressed, thermal embrittlement occurs, and the skin tilting defect is formed.
After the off-line solid solution process, mixed crystal defects are easy to occur on the surface of the 303 stainless steel wire rod, and the coarse crystal position of the wire rod is softer than the fine crystal position of the wire rod, so that pit defects are easy to occur at the coarse crystal position of the subsequent processing surface, and the quality of a finished product is influenced. The mixed crystal 303 was produced in an off-line solid solution process, and the analysis and laboratory solid solution simulation were performed on the 303 wire rod having the mixed crystal defect, and the results were as follows:
(1) Metallographic analysis of the offline solid solution 303 "plaque" wire rod found: fine (as shown in fig. 1) and coarse (as shown in fig. 2) grain sites have larger sulfide sizes, more rounded morphology, and a smaller number than coarse grain sites.
(2) A solid solution simulation experiment of the 303 wire rods in a muffle furnace shows that the formation of offline solid solution 'spots' has a direct relation with the solid solution time and the solid solution temperature. At a solution time of 90min and a solution temperature of 900-1060 ℃, after the temperature reached 1000 ℃, the tissue began to appear "spots" (see fig. 3-5). And after 1000 c, the sulfide starts to undergo polymerization growth (see fig. 6 to 8). That is, it is explained that the polymerization growth of sulfide is a cause of "plaque". When the temperature is 1000 ℃, the solid solution time is found to be within 20 minutes, and no 'spot' exists in 303. After more than 20min, the tissue began to grow abnormally (FIGS. 9-11). The above phenomenon illustrates that the solid solution temperature and time directly affect 303 "mottle". The existing off-line solid solution furnace can control the solid solution temperature, but the furnace time is generally 90-150 min, so that short-time solid solution is difficult to realize, and the phenomenon of 'spots' cannot be overcome.
The reason why 303 "plaque" is generated is described above: 303 is subjected to off-line solid solution, heat preservation is carried out for 90-150 min, and sulfide is polymerized and grown. The difference in the number, size and morphology of the sulfides at different positions causes the difference in the effect of the sulfides on tissue pinning, so that the tissue growth conditions at different positions are different, and thus "flower spots" are generated.
Chinese patent CN114453413a discloses a rolling method of a sulfur-containing free-cutting stainless steel wire rod, wherein the chemical components of the 303Cu stainless steel in the patent are as follows by mass percent: less than or equal to 0.05 percent of C, less than or equal to 3.00 percent of Mn, less than or equal to 1.00 percent of Si, less than or equal to 0.006 percent of P, and S:0.24 to 0.30 percent of Cr: 17.00-19.00%, ni: 8.00-10.00%, cu:1.80 to 3.50 percent, mo is less than or equal to 0.60 percent, N is less than or equal to 0.040 percent, and the balance is Fe and unavoidable impurities; the soaking section temperature range of the heating furnace is 1270-1290 ℃. The wire rod is covered with a heat preservation cover after spinning, and a water explosion device is added at the outlet of the heat preservation cover, so that the link of an offline solid solution process is reduced, and the problem of mixed crystal caused by offline solid solution is avoided; the grain size grade obtained by the patent is 9.5-10 grade.
Chinese patent CN101435057a discloses a "novel low-cost free-cutting stainless steel 303B and its manufacturing process", which stabilizes the austenitic structure by increasing the Mn element content to 9-11% and decreasing the Ni element content to 3-4%, reducing the cost.
Chinese patent CN102319736a discloses a rolling method of tin-containing free-cutting steel, which reduces the cooling rate by controlling the stelmor cooling line, effectively eliminates the residual stress in the rolled piece, and improves the cold drawing yield.
Chinese patent CN1669685a discloses a "rolling method of tin-containing free-cutting steel", which adopts a process of controlling the heating temperature, heating rate and finishing temperature of a heating furnace, so as to effectively avoid the thermal embrittlement phenomenon of the tin-containing free-cutting steel in the rolling process.
Chinese patent CN105234170a discloses a "rolling method for large-size free-cutting steel", which improves the defects of large-size wire rod ear shape, scab and oxide skin thickness by controlling the heating temperature, the start rolling temperature and the cooling rate of a heating furnace.
Chinese patent CN113787094a discloses a rolling method of a high-carbon free-cutting steel wire rod, which reduces the phenomenon of local net-shaped carbide of a casting blank caused by carbon segregation by setting a higher heating furnace temperature.
The above patents related to free-cutting steel and controlled rolling and cooling technologies mainly aim at the influences of composition design, structure, residual stress, hot shortness and surface defects of free-cutting stainless steel and carbon steel, and do not relate to a manufacturing method of the 303 free-cutting stainless steel controlled rolling and cooling technology with high surface quality.
Disclosure of Invention
The invention aims to provide a 303 free-cutting stainless steel wire rod with high surface quality and a manufacturing method thereof, wherein the free-cutting stainless steel wire rod has no 'spot' defect, good surface quality, lower production cost and good performance, the tensile strength of the stainless steel wire rod is less than or equal to 590MPa, the elongation after fracture is more than or equal to 40%, and the area shrinkage is more than or equal to 50%.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
the 303 free-cutting stainless steel wire rod with high surface quality comprises the following components in percentage by mass: c:0.015% -0.150%, mn: 1.00-3.00%, si:0.20 to 1.00 percent, P is less than or equal to 0.045 percent, S:0.15 to 0.35 percent of Cr: 17.00-19.00%, ni: 8.00-10.00%, cu:1.50 to 3.50 percent, and the balance of Fe and other unavoidable impurities; and simultaneously satisfies:
Mn/S＞8.2；
the casting blank high-temperature ferrite mass ratio delta-F=3.0-7.0%;
δ-F＝((Cr+Mo+1.5*Si+18)/(Ni+30*C+30*N+0.5*Mn+36)+0.262)*161-161；
carbide precipitation temperature T M23C6 ≤950℃；
T M23C6 ＝594+3950*C+20*Si+1.4*Mn+8*Cr-1.4*Ni-300*N+16.7*Cu。
Further, the balance is Fe and other unavoidable impurities.
Preferably, C is less than or equal to 0.08wt%.
The microstructure of the free-cutting stainless steel wire rod disclosed by the invention is austenite, high-temperature ferrite and sulfide.
The tensile strength of the free-cutting stainless steel wire rod is less than or equal to 590MPa, the elongation after fracture is more than or equal to 40%, and the area shrinkage is more than or equal to 50%.
In the design of the components of the 303 free-cutting stainless steel wire rod with high surface quality, the invention comprises the following steps:
mn: mn element is austenite forming element, and Mn content in a certain range can improve the thermoplasticity of steel; too high a Mn content can reduce the formability of the material, thereby affecting hot rolled surface quality; too low a Mn content may cause S element segregation in 303; the Mn content is increased, the Mn/S value is increased, and the S element segregation is reduced. Therefore, the Mn content is controlled to be 1.00-3.00% in the invention.
S: s mainly improves the cutting performance of steel in 303, S and manganese form manganese sulfide inclusions, and the cutting scraps are promoted during cutting, so that the lubricating effect is achieved, and the cutter abrasion is reduced. However, too high S can cause notch effect of stress concentration at the manganese sulfide inclusion, increase rolling difficulty and reduce corrosion resistance. Therefore, the S content is controlled to be 0.15-0.35 percent in the invention.
Mn/S value: since the affinity of Mn and S is greater than that of Fe and S, the improvement of Mn/S can reduce S element dissolved into austenite, and can also reduce the content of S element precipitated from grain boundary, namely effectively reduce the segregation of S element. Analysis of segregation degree of 303 casting blanks shows that: when Mn/S is less than 8.2, S element segregation in 303 casting blanks is aggravated (see figure 12), fe-FeS eutectic is easy to form and is distributed at crystal boundaries, the Fe-FeS eutectic is melted in the hot working process of heating temperature being higher than melting point, the crystal boundaries are broken when steel is rolled and pressed, hot embrittlement occurs, and a skin tilting defect is formed. Thus controlling Mn/S > 8.2.
delta-F value: the high-temperature ferrite content of the cast slab in 303 can reduce segregation of S element, but the higher the high-temperature ferrite content, the worse the plasticity of 303. Analytical description via line manufacture 303: when the delta-F value is less than 3.0%, the segregation of the S element is serious (see figure 13), fe-FeS eutectic is easy to form and is distributed at the grain boundary, hot embrittlement occurs during rolling, and skin warping defects are formed; when the delta-F value is more than 7.0%, although the S element segregation in the steel is weakened, the surplus high temperature ferrite in the steel deteriorates the plasticity of 303, so that the rolling is liable to crack. Thus controlling the delta-F value to be 3.0-7.0%.
T M23C6 Value: the carbide in the stainless steel is separated out, so that the Cr content in the steel is reduced, and the corrosion resistance of the stainless steel is reduced. Carbide precipitation temperature the carbide precipitation temperature formula is obtained by calculating the carbide precipitation temperatures of 303 of different components and combining laboratory solid solution simulation with the calculation result of thermal mol-Calc thermodynamic software (see fig. 14) as a guide. Because the heating device on the Steyr air cooling line of the production line is limited by the condition, the minimum temperature before the wire rod leaves the water cooling unit of the heating device is 950 ℃, the T is required M23C6 ≤950℃。
The invention relates to a manufacturing method of a high-surface-quality 303 free-cutting stainless steel wire rod, which comprises the following steps:
1) Smelting and casting
Smelting and casting into casting blanks according to the components;
2) Heating
The heating temperature is controlled to 1250-1300 ℃ and the heating time is 3.0-5.0 h;
3) Rolling
Controlling the initial rolling temperature of rough rolling to 1100-1250 ℃, the finish rolling inlet temperature to 1000-1150 ℃ and the total deformation rate of finish rolling to be less than or equal to 60%;
4) Cooling
The spinning temperature of the spinning machine is controlled to be 1000-1100 ℃, the speed of a Steyr roller way is controlled to be 8-25 m/min, the cooling rate of a wire rod on the Steyr roller way is controlled to be less than or equal to 60 ℃/min, the temperature of a wire rod water cooling unit is controlled to be 950-1020 ℃, and the temperature of a water cooling unit is controlled to be less than or equal to 200 ℃.
Preferably, in the step 1), the heating temperature of the casting blank is 1260-1290 ℃.
Preferably, in the step 2), the heat preservation cover covers the discharge port of the heating furnace to the roughing mill set and the middle roller way of the roughing mill set, so that the roughing start temperature is 1100-1250 ℃ and the finishing mill inlet temperature is 1000-1150 ℃; the rear water tank of the finishing mill group is opened for 2 groups, the opening degree of the valve of the water tank is controlled to be 80-100%, and the spinning temperature of the spinning machine is controlled to be 1000-1100 ℃. The inlet temperature of the finishing mill and the total deformation rate of finish rolling are required to meet the relation of grain size grades: d is less than or equal to 9.0, d=24.23-0.00366×t Finish rolling -19.955*ε Finish rolling Wherein T is Finish rolling For finishing mill inlet temperature, ε Finish rolling The total deformation rate of the finishing mill group.
Preferably, in the step 3), the stelmor wire insulation cover is completely closed, the heating device is started, and the wire rod cooling rate is controlled to be 30-50 ℃/min; the operation speed of the Steyr wire roller path is 8-16 m/min; after the wire rod is out of the heat preservation cover, the temperature of the wire rod before entering the water cooling unit is controlled to be more than or equal to 950 ℃.
In the manufacturing method of the 303 free-cutting stainless steel wire rod with high surface quality, disclosed by the invention:
the heating temperature of the heating furnace is controlled to 1250-1300 ℃, so that the sulfide is ensured to be fully spheroidized and uniformly distributed, good high-temperature plasticity is obtained, and a proper inlet temperature is provided for a finishing mill.
The initial rolling temperature of rough rolling is controlled to be 1100-1250 ℃, the finish rolling inlet temperature is controlled to be 1000-1150 ℃, and the total deformation rate of a finishing mill is controlled to be less than or equal to 60 percent so as to obtain coarser austenite structure.
The spinning temperature of the spinning machine is controlled to be 1000-1100 ℃, the speed of a Steyr roller way is controlled to be 8-25 m/min, the cooling rate is controlled to be less than or equal to 60 ℃/min, a heat insulation cover is covered before the outlet of the spinning machine reaches a waterfall unit, the temperature of a wire rod outlet heat insulation cover water cooling unit is 950-1020 ℃, and the temperature of the wire rod outlet water cooling unit is less than or equal to 200 ℃. So as to realize short-time online solid solution, avoid abnormal growth of crystal grains and ensure the performance of the wire rod.
In the step 1), the heating temperature of the casting blank is 1260-1290 ℃, and the influence of the heating temperature on the form of the casting blank sulfide is studied (fig. 15-18), so that the casting blank sulfide grows up gradually along with the increase of the temperature, and the spheroidization is also better.
In the step 2), the heat preservation cover is covered from the discharge port of the heating furnace to the roughing mill set and from the roughing mill set to the middle roller way of the middle roller way, so that the heat loss of rolled pieces is reduced, and the roughing start temperature is 1100-1250 ℃ and the finishing mill inlet temperature is 1000-1150 ℃.
In the step 2), the rear water tank of the finishing mill group is opened for 2 groups, the opening degree of the valve of the water tank is controlled to be 80-100%, the rapid temperature rise of rolled pieces caused by rapid rolling speed is reduced, and the spinning temperature of a spinning machine is controlled to be 1000-1100 ℃.
In the step 2), the inlet temperature of the finishing mill and the total deformation rate of the finishing mill need to satisfy the relation of grain size level: d=24.23-0.00366×t Finish rolling -19.955*ε Finish rolling ≤9.0。
The grain size grade formula is obtained by fitting based on the actual sampling analysis grain sizes of rolled lines with different finish rolling inlet temperatures and different finish rolling mill total deformation.
In the step 3), the operation speed of the stelmor wire roller is 8-16 m/min, so that the wire rod is slowly cooled in the heating device and the heat preservation cover, and the recrystallization time is prolonged to reduce the tensile strength and improve the elongation.
In the step 3), after the wire rod is discharged from the heating device and the heat preservation cover, the front temperature of the wire rod water cooling unit is controlled to be more than or equal to 950 ℃, carbide precipitation is avoided, and corrosion resistance is improved.
Compared with the prior art, the invention has the advantages that:
1. in the existing 'GB/T4356 stainless steel wire rod' standard, the Y12Cr18Ni9Cu stainless steel comprises the following chemical components in percentage by mass: less than or equal to 0.150 percent of C, less than or equal to 3.00 percent of Mn, less than or equal to 1.00 percent of Si, less than or equal to 0.200 percent of P, more than 0.150 percent of S and more than 0.150 percent of Cr: 17.00-19.00%, ni: 8.00-10.00%, cu:1.50 to 3.50 percent, and the balance of Fe and unavoidable impurities. In Chinese patent CN114453413A, namely the rolling method of the sulfur-containing free-cutting stainless steel wire rod, the chemical components of the 303Cu stainless steel are as follows in percentage by mass: less than or equal to 0.05 percent of C, less than or equal to 3.00 percent of Mn, less than or equal to 1.00 percent of Si, less than or equal to 0.006 percent of P, and S:0.24 to 0.30 percent of Cr: 17.00-19.00%, ni: 8.00-10.00%, cu:1.80 to 3.50 percent, mo is less than or equal to 0.60 percent, N is less than or equal to 0.040 percent, and the balance is Fe and unavoidable impurities. In the existing '303 Cu free-cutting stainless steel wire rod production practice' literature, mn/S is controlled to be about 8.0.
The composition of the invention accords with the range of Y12Cr18Ni9Cu steel in GB/T4356 stainless steel wire rod, and the Mn/S of the composition is more than 8.2 and delta-F is restrained: 3.0 to 7.0 percent, reduces the hot rolling apparent skin warping defect caused by S element segregation, and the surface quality of the obtained wire rod is good.
2. In the existing '303 Cu free-cutting stainless steel wire rod production practice' literature, the heating temperature interval is 1200-1350 ℃; in the prior 'production practice of stainless steel wires 303Cu and 302 HQ', the heating temperature range of 303Cu is 1180-1300 ℃; in the Chinese patent CN114453413A rolling method of the sulfur-containing free-cutting stainless steel wire rod, the temperature interval of a soaking section is 1270-1290 ℃.
According to the invention, the heating temperature 1260-1290 ℃ is controlled, the temperature selection range of the heating furnace is optimized, the execution target of the heating furnace is more definite, the spheroidization of sulfides is ensured, and the heat energy loss caused by the overhigh heating temperature is avoided.
3. In the prior Chinese patent CN114453413A rolling method of the sulfur-containing free-cutting stainless steel wire rod, the grain size grade is 9.5-10 grade; the grain size grade of the 303Cu wire rod through the off-line solid solution process reaches 7.0-8.0 grade, and the local grain size reaches 1.0 grade.
The invention obtains the wire rod with the grain size grade less than or equal to 9.0 grade by controlling the finish rolling inlet temperature to 1000-1150 ℃ and the total deformation rate of the finish rolling to be less than or equal to 60 percent, and the wire rod has the mechanical property equivalent to the wire rod with offline solid solution.
4. In the prior Chinese patent CN114453413A rolling method of sulfur-containing free-cutting stainless steel wire rods, the wire rods are covered with a heat preservation cover after spinning, and a water explosion device is added at the outlet of the heat preservation cover.
The invention installs the heating device, the heat preservation cover and the water-cooling unit on the Steyr roller way, and controls the front temperature of the wire rod water-cooling unit in the cooling process to be more than T through constraint components M23C6 The wire rod obtained by the method has corrosion resistance equivalent to that of wire rods subjected to offline solid solution.
5. In the existing '303 Cu free-cutting stainless steel wire rod production practice' document, the 303Cu stainless steel wire rod needs to undergo an off-line solid solution process to generate mixed crystals; in the prior Chinese patent CN114453413A rolling method of the sulfur-containing free-cutting stainless steel wire rod, the off-line solid solution process is omitted for 303Cu, and the produced 303Cu wire rod has no mixed crystal, and the mechanical property of the invention is equivalent to the off-line solid solution property.
The invention omits an off-line solid solution process, and the 303 wire rods produced by the controlled rolling and cooling technology avoid the defects of large aggregation length of manganese sulfide and no 'spot' of the wire rods, and the wire rods obtained by the invention have good apparent mass; meanwhile, solid solution loss is reduced, production efficiency is improved, and cost is saved.
The invention has the beneficial effects that:
(1) The invention is characterized by restraining the alloy composition relation: mn/S is more than 8.2; delta-F (%): 3.0 to 7.0, reducing the skin warping defect caused by S element segregation and improving the surface quality of the wire rod.
(2) According to the invention, through a rolling and cooling control technology, an offline solid solution process of the wire rod is omitted, the defect of 'spots' caused by offline solid solution of tissues is avoided, the surface quality of the wire rod is improved, the solid solution loss is reduced, the production efficiency is improved, and the cost is saved.
(3) The invention uses the carbide precipitation temperature T M23C6 And the temperature is less than or equal to 950 ℃, the alloy composition relation and the temperature before the wire rod water cooling unit in the hot rolling process are restrained, the carbide precipitation temperature is ensured to be lower than the temperature before the wire rod water cooling unit, and carbide precipitation is avoided.
(4) The invention ensures that the grain size grade of the finished wire rod product meets D less than or equal to 9.0 by controlling the inlet temperature of the finishing mill and the total deformation rate of the finishing mill, and ensures that the mechanical property is equivalent to the wire rod produced by offline solid solution.
Drawings
FIG. 1 shows the morphology of manganese sulfide at the fine grain location of a solid solution 303 stainless steel coil;
FIG. 2 shows the morphology of manganese sulfide at the coarse grain location of a solid solution 303 stainless steel coil;
FIG. 3 is a structure of a 303 stainless steel coil muffle furnace simulated 950 ℃ solid solution for 1.5 h;
FIG. 4 is a structure of a 303 stainless steel wire rod muffle furnace simulated 1000 ℃ solid solution for 1.5 h;
FIG. 5 is a structure of a 303 stainless steel coil muffle furnace simulated 1040 ℃ solid solution for 1.5 h;
FIG. 6 is a sulfide morphology of a 303 stainless steel coil muffle furnace simulated 950 ℃ solid solution for 1.5 h;
FIG. 7 is a sulfide morphology simulated by a 303 stainless steel coil muffle furnace at 1000 ℃ for 1.5h in solid solution;
FIG. 8 is a sulfide morphology of 303 stainless steel coil muffle furnace simulated 1040 ℃ solid solution for 1.5 h;
FIG. 9 is a diagram of a 303 stainless steel coil muffle furnace simulated 1000 ℃ solid solution for 10 min;
FIG. 10 is a drawing of a 303 stainless steel coil muffle furnace simulated 1000 ℃ solid solution for 20 min;
FIG. 11 is a drawing of a 303 stainless steel coil muffle furnace simulated 1000 ℃ solid solution for 30min structure;
FIG. 12 is a graph of the effect of Mn/S of 303 stainless steel wire rods on S element segregation;
FIG. 13 is a graph of the effect of delta-F on S element segregation of 303 stainless steel wire rods;
FIG. 14 is a calculated phase diagram of 303 stainless steel wire rod free cutting stainless steel;
FIG. 15 shows the morphology of inclusions in the green body of example 2 of the 303 stainless steel wire of the present invention after a temperature of 1200℃has been maintained for 0.5 hour;
FIG. 16 is a drawing showing the morphology of inclusions after heat preservation of the square billet of example 2 of the 303 stainless steel wire rods of the present invention at 1230℃for 0.5 hour;
FIG. 17 shows the morphology of inclusions after 1260℃for 0.5 hours of heat preservation of the square billet of example 2 of the 303 stainless steel wire rod of the present invention;
FIG. 18 shows the morphology of inclusions in the square billet of example 2 of the 303 stainless steel wire rod of the present invention after heat preservation at 1290℃for 0.5 hours;
FIG. 19 is a drawing showing the carbide precipitation of example 3 of the stainless steel wire of the present invention 303;
FIG. 20 is a carbide precipitation profile for stainless steel coil comparative example 3 at 303;
FIG. 21 is a microstructure of example 4 of a 303 stainless steel coil of the present invention;
FIG. 22 is a microstructure of 303 stainless steel coil comparative example 4;
FIG. 23 is a photograph of a macroscopically defect free surface of a stainless steel coil of example 4 of the present invention 303;
FIG. 24 is a photograph of 303 stainless steel coil comparative example 4 macroscopic surface highlights;
fig. 25 is a macroscopic surface skin-lifting picture of comparative example 6 of 303 stainless steel wire rods.
Detailed Description
The invention is further described below with reference to examples and figures.
The composition index of the examples and comparative examples of the present invention is shown in Table 1, and the balance contains Fe and other unavoidable impurities; the manufacturing process of the embodiment of the invention is shown in Table 2; the mechanical properties, corrosion resistance and grain size scale index of the examples and comparative examples are shown in Table 3.
Mechanical property test of materials according to GB/T228.1 section 1 of Metal Material tensile test: room temperature test methods.
Spot corrosion rate test of materials according to GB/T17897-2016 method for stainless steel ferric trichloride spot corrosion test, the test solution was 6% FeCl 3 +0.16% HCl solution at a test temperature of 35.+ -. 1 ℃.
The detection of the structure grain size of the material is carried out according to GB/T6394-2017 metal average grain size determination method.
Example 1 was compared to comparative example 1, example 1 finishing mill inlet temperature 1124 ℃, comparative example 1 finishing mill inlet temperature 980 ℃, example 1 grain size grade 8.5, and comparative example 1 grain size grade 9.5. Comparative example 1 has a low finish rolling temperature, and therefore has a grain size grade of > 9.0.
Example 2 has a total deformation of 58.9% in the finishing mill of example 2, 53.8% in the finishing mill of comparative example 2, a grain size grade of 8.5 in example 2, and a grain size grade of 9.5 in comparative example 2, as compared to comparative example 2. The finishing mill of comparative example 2 has a low total deformation rate, so the grain size grade is > 9.0 grade.
Example 3 compared with comparative example 3, the temperature before the water-cooling unit of example 3 is 998 ℃ higher than the carbide precipitation temperature 865 ℃, the temperature before the water-cooling unit of comparative example 3 is 902 ℃ lower than the carbide precipitation temperature 930 ℃, obvious carbide precipitation exists in comparative example 3, no carbide precipitation exists in example 3 as shown in FIG. 19, and the comparison is carried outExample 3 shows a more white dotted carbide precipitate as shown in fig. 20. The pitting rate of example 3 was 32.3 g/(m) 2 * h) Comparative example 3 was 43.5 g/(m) 2 * h) The corrosion resistance is worse. The presence of carbides reduces the corrosion resistance.
Examples 4-9 the off-line solid solution process was omitted from examples 4-9 as compared to comparative examples 4-6, and comparative examples 4-6 were subjected to the off-line solid solution process. The wire rods of examples 4 to 9 were apparent without "mottle", without carbide precipitation, and with a grain size grade of 9.0, and the wire rods of comparative examples 4 to 6 were free from carbide precipitation, but had apparent defects of skin lifting and "mottle". The microstructure uniformity of example 4 is shown in fig. 21, the "mottle" phenomenon of the microstructure of comparative example 4 is shown in fig. 22, the apparent absence of the "mottle" defect of the wire rod of example 4 is shown in fig. 23, and the apparent "mottle" phenomenon of the wire rod of comparative example 4 is shown in fig. 24. Examples 4-9 have similar mechanical and corrosion resistance properties as comparative examples 4-6, as shown in Table 3.
Examples 4-6 and comparative examples 3, 4 were compared, examples 4-6 satisfying Mn/S > 8.2, comparative examples 3, 4 having Mn/S < 8.2, the difference in Mn/S ratio was such that the skin-lifting defective rates of examples 4-6 were 3.4%, 3.5% and 2.5%, respectively, and the skin-lifting defective rates of comparative examples 3, 4 were 18.7% and 19.1%, respectively.
Examples 7-9 in comparison with comparative examples 5, 6, examples 5, 6 satisfy the delta-F values: from 3.0 to 7.0%, the delta-F values of comparative examples 5 and 6 were < 3.0, the delta-F values were such that the skin-lifting failure rates of examples 7 to 9 were 4.0%, 3.0% and 3.2%, the skin-lifting failure rates of comparative examples 5 and 6 were 14.3% and 16.5%, and the apparent skin lifting of comparative example 6 was as shown in FIG. 25.
In conclusion, the invention effectively avoids carbide precipitation temperature through a controlled rolling and cooling technology, ensures that the grain size level is less than or equal to 9.0 level, reduces the rate of defective tilting, eliminates the problem of surface 'spots' generated in the off-line solid solution process, and obtains 303 wire rods with high surface quality; moreover, the invention omits the off-line solid solution process, and the wire rod performance is equivalent to that of the wire rod subjected to the off-line solid solution process.
The foregoing is illustrative of the embodiments of the present invention and the related analysis, but not limiting the scope of the invention, and all equivalent exchanges made by the content of the present invention or direct or indirect application in the related technical field are included in the scope of the present invention.
Claims (9)
1. The 303 free-cutting stainless steel wire rod with high surface quality comprises the following components in percentage by mass: c:0.015% -0.150%, mn: 1.00-3.00%, si:0.20 to 1.00 percent, P is less than or equal to 0.045 percent, S:0.15 to 0.35 percent of Cr: 17.00-19.00%, ni: 8.00-10.00%, cu:1.50 to 3.50 percent, and the balance of Fe and other unavoidable impurities; and simultaneously satisfies:
Mn/S＞8.2；
the casting blank high-temperature ferrite mass ratio delta-F=3.0-7.0%;
δ-F＝((Cr+Mo+1.5*Si+18)/(Ni+30*C+30*N+0.5*Mn+36)+0.262)*161-161；
carbide precipitation temperature T M23C6 ≤950℃；
T M23C6 ＝594+3950*C+20*Si+1.4*Mn+8*Cr-1.4*Ni-300*N+16.7*Cu。
2. The high surface quality 303 free-cutting stainless steel wire rod of claim 1, wherein the balance is Fe and other unavoidable impurities.
3. The high surface quality 303 free-cutting stainless steel wire rod according to claim 1, wherein C is less than or equal to 0.08wt%.
4. The high surface quality 303 free-cutting stainless steel wire rod of claim 1 or 2, wherein the microstructure of said free-cutting stainless steel wire rod is austenite + high temperature ferrite + sulfide.
5. The high surface quality 303 free-cutting stainless steel wire rod of claim 1, 2 or 3, wherein said free-cutting stainless steel wire rod has a tensile strength of 590MPa or less, a post-fracture elongation of 40% or more, and a reduction in area of 50% or more.
6. The method of manufacturing a high surface quality 303 free cutting stainless steel wire rod as claimed in claim 1 or 2 or 3 or 4, comprising the steps of:
1) Smelting and casting
Smelting and casting into a cast strand according to the composition of claim 1 or 2;
2) Heating
The heating temperature is controlled to 1250-1300 ℃ and the heating time is 3.0-5.0 h;
3) Rolling
Controlling the initial rolling temperature of rough rolling to 1100-1250 ℃, the finish rolling inlet temperature to 1000-1150 ℃ and the total deformation rate of finish rolling to be less than or equal to 60%; the inlet temperature of the finishing mill and the total deformation rate of finish rolling are required to meet the relation of grain size grades: d is less than or equal to 9.0, d=24.23-0.00366×t Finish rolling -19.955*ε Finish rolling Wherein T is Finish rolling For finishing mill inlet temperature, ε Finish rolling The total deformation rate of the finishing mill group;
4) Cooling
The spinning temperature of the spinning machine is controlled to be 1000-1100 ℃, the speed of a Steyr roller way is controlled to be 8-25 m/min, the cooling rate of a wire rod on the Steyr roller way is controlled to be less than or equal to 60 ℃/min, the temperature of a wire rod water cooling unit is controlled to be 950-1020 ℃, and the temperature of a water cooling unit is controlled to be less than or equal to 200 ℃.
7. The method for manufacturing a high surface quality 303 free-cutting stainless steel wire rod according to claim 5, wherein in step 1), the billet heating temperature is 1260 to 1290 ℃.
8. The method for manufacturing the 303 free-cutting stainless steel wire rod with high surface quality according to claim 5, wherein in the step 2), a heating furnace discharge port is connected to a roughing mill set and is roughed to a middle roller way cover heat preservation cover of a middle rolling mill set, and the roughing mill start rolling temperature is ensured to be 1100-1250 ℃ and the finishing mill inlet temperature is ensured to be 1000-1150 ℃; the rear water tank of the finishing mill group is opened for 2 groups, the opening degree of the valve of the water tank is controlled to be 80-100%, and the spinning temperature of the spinning machine is controlled to be 1000-1100 ℃.
9. The method for manufacturing a high surface quality 303 free-cutting stainless steel wire rod according to claim 5, wherein in step 3), the stelmor wire insulation cover is completely closed, the heating device is opened, and the wire rod cooling rate is controlled to be 30-50 ℃/min; the operation speed of the Steyr wire roller path is 8-16 m/min; after the wire rod is out of the heat preservation cover, the temperature of the wire rod before entering the water cooling unit is controlled to be more than or equal to 950 ℃.
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| CN101397633B (en) * | 2007-09-30 | 2010-08-11 | 宝山钢铁股份有限公司 | Sulphur and copper-containing free-cutting stainless steel and preparation method thereof |
| KR102015510B1 (en) * | 2017-12-06 | 2019-08-28 | 주식회사 포스코 | Non-magnetic austenitic stainless steel with excellent corrosion resistance and manufacturing method thereof |
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| KR102268906B1 (en) * | 2019-07-17 | 2021-06-25 | 주식회사 포스코 | Austenitic stainless steel with imporoved strength and method for manufacturing the same |
| CN114453413B (en) * | 2022-01-12 | 2024-02-27 | 山东工业职业学院 | Rolling method of sulfur-containing free-cutting stainless steel wire rod |
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| CN114990444B (en) * | 2022-06-16 | 2024-03-19 | 浙江青山钢铁有限公司 | Sulfur-containing tellurium-containing free-cutting 304 stainless steel and preparation method thereof |
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