CN111809107A

CN111809107A - Hot-dip galvanized high-strength IF steel for Ti-series ton barrel and manufacturing method thereof

Info

Publication number: CN111809107A
Application number: CN202010549421.5A
Authority: CN
Inventors: 王金超; 杨维宇; 张嘉华; 宿成; 宋文钟; 班兆东; 刘强
Original assignee: Baotou Iron and Steel Group Co Ltd
Current assignee: Baotou Iron and Steel Group Co Ltd
Priority date: 2020-06-16
Filing date: 2020-06-16
Publication date: 2020-10-23

Abstract

The invention discloses hot-dip galvanized high-strength IF steel for a Ti-series ton barrel and a manufacturing method thereof, wherein P, Si and Mn elements are properly added on an IF steel matrix for solid solution strengthening to ensure the strength, Ti alloy elements are added to eliminate interstitial atoms and realize precipitation strengthening, a proper amount of B elements are added to inhibit P segregation at a grain boundary, so that higher elongation after fracture and lower yield ratio are ensured, meanwhile, the tensile strength is improved, and the characteristics of production equipment capability are combined, so that the yield strength of a finished product is 220-280 MPa, the tensile strength is 340-410 MPa, and the elongation after fracture is more than or equal to 32 percent (tensile test: L & lt/EN & gt: L & gt & lt/EN & gt) through smelting, a 2250mm hot rolling mill, an₀80mm, 20mm), n is greater than or equal to 0.17, r is greater than or equal to 1.5, ensuring lower flexionStrength ratio and good punching performance.

Description

Hot-dip galvanized high-strength IF steel for Ti-series ton barrel and manufacturing method thereof

Technical Field

The invention relates to the technical field of high-strength automobile steel, in particular to hot-galvanized high-strength IF steel for a Ti-series ton barrel and a manufacturing method thereof.

Background

With the development of industrial technologies, energy and environmental issues have become important social issues, and the automobile industry is no exception. Therefore, in the structural performance of modern automobiles, reducing weight and consumption, reducing environmental pollution and improving safety become hot spots of research. Automotive steels are constantly being developed toward higher strength, high strength IF steels, bake-hardened steels, phosphorus (P) -containing steels, High Strength Low Alloy (HSLA) steels, Dual Phase (DP) steels, Complex Phase (CP) steels, transformation induced plasticity (TRIP) steels, and the like.

Because the hot-dip galvanized iron alloy product has better welding performance, coating performance and corrosion resistance, the hot-dip galvanized iron alloy product is widely applied to outer plates of high-grade automobiles, the traditional hard-to-punch parts basically adopt common IF steel, but the weight reduction pace of automobiles is increasingly accelerated, BH steel gradually replaces the common IF steel, but the BH steel cannot be stored for a long time and can be used in a short time, and the BH steel cannot be used for manufacturing parts which are difficult to form. Compared with BH steel, the high-strength IF steel is obtained by adding strengthening elements on the basis of common IF mild steel, so that the high-strength IF steel has the characteristics of interstitial-free steel, namely the high-strength IF steel has the characteristic of good stamping and forming, and does not have the problem of aging, and therefore, the high-strength IF steel is widely applied to the field of manufacturing automobile outer plates.

Traditional high-strength IF steel is improved in strength by adding solid solution strengthening elements such as P, Si and Mn, however, the addition of the solid solution strengthening elements can reduce the r value while improving the fracture strength (the strength limit is 440MPa) and the yield ratio, and has adverse effects on the formability of the material.

The patent application with the publication number of CN101348884A provides 440MPa niobium-containing high-strength IF steel and a preparation method thereof, and the steel comprises the following chemical components: 0.005-0.007% of C, 0.02-0.03% of Si, 1.2-2.1% of Mn, 0.08% of P, 0.006% of S, 0.003% of N, 0.05-0.11% of Nb, 0.0005-0.002% of B, 0.2-0.5% of Cr, 0.005-0.01% of Ti, 0.01-0.04% of AI, and the balance of Fe and inevitable impurities, wherein the Nb content is as high as 0.05-0.11%, and the raw material cost is high.

The patent application with the publication number of CN103710617A provides 340 MPa-grade hot-galvanized iron alloy high-strength IF steel, the chemical components of the steel are 0.01-0.025% of Nb and 0.005-0.015% of Ti, and the Nb element is added to increase the manufacturing cost.

The high-strength IF steel related by the patent contains expensive Nb element in the manufacturing process, and in order to adapt to the low-cost excellent stamping formability, environmental protection and corrosion resistance of modern steel materials, the low-cost Ti-based ton hot galvanizing steel disclosed by the invention eliminates interstitial atoms and realizes precipitation strengthening by adding Ti alloy element, realizes solid solution strengthening by adding Mn, P and Si elements, inhibits P from segregating at a crystal boundary by adding a proper amount of B element, and has the particularity of a hot galvanizing alloying process. The hot-dip galvanized high-strength IF steel for the ton barrel has excellent stamping forming and corrosion resistance, and accords with the research and development design concept of modern special steel products. The steel grade has high technical content and higher production difficulty.

Disclosure of Invention

The invention aims to provide hot-dip galvanized high-strength IF steel for a Ti-series ton barrel and a manufacturing method thereof, wherein P, Si and Mn elements are properly added on an IF steel matrix for solid solution strengthening to ensure the strength, Ti alloy elements are added to eliminate interstitial atoms and realize precipitation strengthening, a proper amount of B elements are added to inhibit P segregation at a grain boundary, so that higher elongation after fracture and lower yield ratio are ensured, meanwhile, the tensile strength is improved, and the yield strength of a finished product is 220-280 MPa, the tensile strength is 340-410 MPa and the elongation after fracture is more than or equal to 32 percent (tensile test: L & lt/EN & gt: L & gt is combined with the characteristics of production equipment capacity, and is subjected to smelting, 2250mm hot rolling mill, acid pickling continuous rolling unit and continuous annealing₀80mm, 20mm), n is not less than 0.17, r is not less than 1.5, ensuring lower yield ratio and good performanceAnd (4) stamping performance.

In order to solve the technical problems, the invention adopts the following technical scheme:

the invention relates to hot galvanizing high-strength IF steel for a Ti-series ton barrel and a manufacturing method thereof, wherein the hot galvanizing high-strength IF steel comprises the following chemical elements in percentage by mass, C is less than or equal to 0.0030%, Si: 0.06% -0.10%, Mn: 0.65% -0.80%, P: 0.045-0.065%, Ti: 0.040% -0.060%, Als: 0.020% -0.060%, B: 0.0002 to 0.0009 percent of Fe, less than or equal to 0.015 percent of S, less than or equal to 0.0050 percent of O, less than or equal to 0.0050 percent of N, and the balance of Fe and inevitable impurities.

Further, C is less than or equal to 0.0025%, Si: 0.07-0.10%, Mn: 0.70% -0.80%, P: 0.045-0.065%, Ti: 0.045% -0.055%, Als: 0.030-0.050%, B: 0.0002 to 0.0009 percent of Fe, less than or equal to 0.010 percent of S, less than or equal to 0.0050 percent of O, less than or equal to 0.0045 percent of N, and the balance of Fe and inevitable impurities.

A manufacturing method of hot galvanizing high-strength IF steel for a Ti-series ton barrel comprises a steel making process, a hot rolling process, a cold rolling process, a zinc plating process and an annealing process.

Further, the steel-making process comprises the following steps: the molten iron is subjected to desulfurization pretreatment and then is smelted in a converter, the content of S in the molten iron fed into the converter is controlled within 0.005 percent, the sulfur increase in the smelting process is reduced, the converter achieves the required range by controlling P, S components at the end point through double slag, the carbon-oxygen content at the end point is controlled to be proper, and the tapping temperature of the converter is controlled within the range of 1630-1700 ℃; preventing molten steel from being overoxidized, adding ferromanganese for alloying in the process of converter tapping, and adding lime and modifier for top slag modification after tapping; and (2) carrying out vacuum decarburization treatment in an RH furnace, adding a deoxidizing agent and aluminum component according to the oxygen determination condition after decarburization is finished, circulating for 4-6 minutes, adding ferrotitanium, ferroniobium, manganese metal, micro-carbon ferrosilicon and ferrophosphorus alloy to adjust the components, ensuring vacuum circulation for more than 5-10 min after the components are adjusted, and ensuring that the component temperature of molten steel meets the production requirement after the vacuum treatment is finished and the continuous casting superheat degree is 30-45 ℃.

Further, the hot rolling process comprises the following steps: heating a plate blank → descaling with high pressure water → a constant width press → rolling with an E1R1 roughing mill → rolling with an E2R2 roughing mill → flying shear → descaling with high pressure water → rolling with an F1-F7 finishing mill → cooling with a dense laminar flow → coiling → a pallet transportation system → sampling and inspection; the method is characterized in that the heating temperature of the plate blank is 1170-1220 ℃, the heating time is 115-125 min, the finish rolling temperature is 880-925 ℃, and the coiling temperature is 610-655 ℃.

Further, the cold rolling and galvanizing process comprises the following steps: acid rolling and uncoiling → welding → straightening → acid pickling → drying → trimming → tandem cold rolling → slitting → coiling → off-line inspection → weighing → identification → bundling → packaging → storage → hot galvanizing and uncoiling → welding → inlet loop → cleaning → annealing furnace → zinc pan → post-plating cooling → water quenching → intermediate loop → finisher → straightener → roller coater → drying machine → air cooling device → outlet loop → trimming → surface inspection → oil coating → coiling → bundling and weighing → packaging → storage.

Further, the annealing process parameters are as follows: the outlet temperature of the heating and soaking section is 810-830 ℃, the outlet temperature of the slow cooling section is 675-685 ℃, the temperature of the fast cooling section is 460-480 ℃, the temperature of the zinc pot is 460-470 ℃, and the temperature of the steel strip at the top of the cooling tower is 240-250 ℃; the elongation of the temper mill is 0.6-1.2%.

Compared with the prior art, the invention has the beneficial technical effects that:

the steel for the market ton barrel generally adopts a Nb-Ti component system, wherein the addition of Nb element refines grains and increases the product strength, but the product cost is often much higher than that of Ti alloy element. The invention is different from other products in the market, adopts Ti alloy elements to eliminate interstitial atoms, adds P, Si and Mn and B elements, realizes low yield ratio, high strength and elongation after fracture of the finished product performance by controlling hot rolling, acid rolling and annealing processes, and reduces the production cost of the product.

Drawings

The invention is further illustrated in the following description with reference to the drawings.

FIG. 1 shows the metallographic structure of the finished steel;

FIG. 2 is a fracture morphology diagram under an electron microscope of finished steel;

fig. 3 is a photograph of the punched out object.

Detailed Description

1. Smelting process

1.1KR desulfurization: adopt KR molten iron desulfurization technique, require that the terminal point sulphur content is within 0.002% after the deep desulfurization, KR desulfurization is through mechanical stirring method desulfurization, adds the desulfurizer to the molten iron, makes the sulphur in desulfurizer and the molten iron take place the sulphur content in the desulfurization reaction takes place to take off the molten iron in continuous stirring, thoroughly takes off the desulfurization sediment totally after the desulfurization is accomplished, prevents that high sulphur sediment from mixing into the converter and leading to the resulfurization. The temperature stability of the molten iron entering the converter is controlled, the temperature of the molten iron is ensured to be above 1300 ℃, the smelting process control of the converter is facilitated to be stabilized, and the hit rate of the end point temperature of the converter is improved.

1.2 converter smelting:

adding scrap steel into the molten iron of the converter according to the Si content, ensuring the heat balance in the smelting process, wherein the smelting steel is high-P steel, and the adding amount of lime is less; according to the temperature control in the smelting process of the converter, slag materials such as dolomite, iron shot, briquettes and the like and iron-containing materials are added into the smelting process to stabilize the temperature in the smelting process, so that the content of MgO in the slag is met, and the serious corrosion of a furnace lining is avoided. The tapping temperature of the converter is controlled within the range of 1630-1700 ℃. Preventing molten steel from being over oxidized, adding ferromanganese for alloying in the process of converter tapping, and adding lime and modifier for top slag modification after tapping.

1.3RH vacuum treatment: the RH refining furnace carries out decarburization treatment according to the in-place components and the temperature of molten steel, RH decarburization is the most important decarburization link in the production of ultra-low carbon steel, the decarburization is carried out for 10min under the condition that the vacuum degree is less than 2mbar, ferrophosphorus is added to adjust the phosphorus content in the molten steel after the vacuum treatment is started, a deoxidizer and the component aluminum are added according to the oxygen determination condition after the decarburization is finished, and the components are adjusted by adding alloys such as ferrotitanium, ferroniobium, metal manganese, micro-carbon ferrosilicon, ferrophosphorus and the like after circulation is carried out for 3-4 min. And after the components are adjusted, vacuum degassing circulation is ensured for 5-10 min, the homogenization of the temperature components of the molten steel is ensured, the floating of inclusions in the molten steel is facilitated, and the cleanliness of the molten steel is improved.

1.4 continuous casting: the continuous casting has constant drawing speed, protects the casting, prevents the secondary oxidation of molten steel and avoids the secondary oxidation of steel quality of the molten steel. The drawing speed is controlled according to different sections by adopting the constant drawing speed, the proper superheat degree of pouring is controlled, the superheat degree is controlled to be 25-35 ℃ in the pouring process, the steel is prevented from being cooled in the molten steel pouring process, floating of inclusions is facilitated, and multi-furnace pouring is realized.

2 Hot rolling process

A step-by-step heating furnace is adopted to heat a casting blank (the heating process is shown in table 1), double-frame R1 and R2 are adopted for rough rolling, the rough rolling mode is 3+3, the finish rolling adopts a continuous rolling process of F1-F7, the finish rolling temperature is 900 +/-15 ℃, the austenite single-phase region rolling is ensured, the coiling temperature is 640 +/-15 ℃, the normal precipitation of carbonitride is ensured, the deep drawing performance is improved, and the specific hot rolling process is shown in table 2.

TABLE 1 casting blank heating System

TABLE 2 Rolling Process

3 annealing process

The annealing adopts a vertical continuous annealing furnace, and the furnace is cooled by adopting a mixed protective atmosphere of reducing atmosphere and nitrogen and hydrogen. The temperature of the heating section and the soaking section is 825 ℃, the complete recrystallization of crystal grains is ensured, the control condition of the temperature of the outlet of each section of the heating furnace is shown in table 3, and the control conditions of different thicknesses of the elongation of the temper mill are shown in table 4.

TABLE 3 annealing Process

TABLE 4 temper mill elongation

4 example analysis

4.1 Steel making composition

The actual slab chemistry (mass percent) is shown in table 5 below, according to the above steelmaking process requirements.

Table 5 example chemical composition wt. -%)

4.2 Hot Rolling Properties

According to the above design chemical composition and hot rolling process, the hot rolled plate tensile properties at room temperature are shown in Table 6, and the test methods are described in GB/T228.1 and GB/T229.

TABLE 6 Hot Rolling tensile Properties

4.3 Final Properties

And (3) cold rolling and annealing are carried out on the basis of the hot rolling performance, the room-temperature tensile mechanical property of the finished product is shown in Table 7, the metallographic structure is equiaxed ferrite, the grain size is 10.5 grade, and the structure appearance is shown in figure 1. The appearance of the fracture with more pits under the scanning of an electron microscope is shown in figure 2.

TABLE 7 tensile Properties of the finished product

4.4 actual effect after stamping

The stamping formability meets the requirements of users, and the picture of the stamped product is shown in figure 3.

In conclusion, the product meets the requirements through performance inspection and various performances used by users.

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.

Claims

1. A hot galvanizing high-strength IF steel for a Ti series ton barrel is characterized in that: the mass percentage of chemical elements is less than or equal to 0.0030 percent, Si: 0.06% -0.10%, Mn: 0.65% -0.80%, P: 0.045-0.065%, Ti: 0.040% -0.060%, Als: 0.020% -0.060%, B: 0.0002 to 0.0009 percent of Fe, less than or equal to 0.015 percent of S, less than or equal to 0.0050 percent of O, less than or equal to 0.0050 percent of N, and the balance of Fe and inevitable impurities.

2. The hot-dip galvanized high-strength IF steel for a Ti-based ton drum according to claim 1, wherein: c is less than or equal to 0.0025%, Si: 0.07-0.10%, Mn: 0.70% -0.80%, P: 0.045-0.065%, Ti: 0.045% -0.055%, Als: 0.030-0.050%, B: 0.0002 to 0.0009 percent of Fe, less than or equal to 0.010 percent of S, less than or equal to 0.0050 percent of O, less than or equal to 0.0045 percent of N, and the balance of Fe and inevitable impurities.

3. The method for manufacturing the hot-dip galvanized high-strength IF steel for the Ti-based ton barrels as claimed in claim 1 or 2, comprising a steel-making process, a hot-rolling process, a cold-rolling process, a galvanizing process and an annealing process.

4. The manufacturing method according to claim 3, characterized in that: the steelmaking process comprises the following steps: the molten iron is subjected to desulfurization pretreatment and then is smelted in a converter, the content of S in the molten iron fed into the converter is controlled within 0.005 percent, the sulfur increase in the smelting process is reduced, the converter achieves the required range by controlling P, S components at the end point through double slag, the carbon-oxygen content at the end point is controlled to be proper, and the tapping temperature of the converter is controlled within the range of 1630-1700 ℃; preventing molten steel from being overoxidized, adding ferromanganese for alloying in the process of converter tapping, and adding lime and modifier for top slag modification after tapping; and (2) carrying out vacuum decarburization treatment in an RH furnace, adding a deoxidizing agent and aluminum component according to the oxygen determination condition after decarburization is finished, circulating for 4-6 minutes, adding ferrotitanium, ferroniobium, manganese metal, micro-carbon ferrosilicon and ferrophosphorus alloy to adjust the components, ensuring vacuum circulation for more than 5-10 min after the components are adjusted, and ensuring that the component temperature of molten steel meets the production requirement after the vacuum treatment is finished and the continuous casting superheat degree is 30-45 ℃.

5. The manufacturing method according to claim 3, characterized in that: the hot rolling process comprises the following steps: heating a plate blank → descaling with high pressure water → a constant width press → rolling with an E1R1 roughing mill → rolling with an E2R2 roughing mill → flying shear → descaling with high pressure water → rolling with an F1-F7 finishing mill → cooling with a dense laminar flow → coiling → a pallet transportation system → sampling and inspection; the heating temperature of the plate blank is 1170-1220 ℃, the heating time is 115-125 min, the finish rolling temperature is 880-925 ℃, and the coiling temperature is 610-655 ℃.

6. The manufacturing method according to claim 3, characterized in that: the cold rolling and galvanizing process comprises the following steps: acid rolling and uncoiling → welding → straightening → acid pickling → drying → trimming → tandem cold rolling → slitting → coiling → off-line inspection → weighing → identification → bundling → packaging → storage → hot galvanizing and uncoiling → welding → inlet loop → cleaning → annealing furnace → zinc pan → post-plating cooling → water quenching → intermediate loop → finisher → straightener → roller coater → drying machine → air cooling device → outlet loop → trimming → surface inspection → oil coating → coiling → bundling and weighing → packaging → storage.

7. The manufacturing method according to claim 3, characterized in that: the annealing process parameters are as follows: the outlet temperature of the heating and soaking section is 810-830 ℃, the outlet temperature of the slow cooling section is 675-685 ℃, the temperature of the fast cooling section is 460-480 ℃, the temperature of the zinc pot is 460-470 ℃, and the temperature of the steel strip at the top of the cooling tower is 240-250 ℃; the elongation of the temper mill is 0.6-1.2%.