CN107747033A - Baking hardening hot-dip galvanizing sheet steel of excellent shaping and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of steel plate manufacturing, and in particular relates to a hot-dip galvanized steel plate and a preparation method thereof. Aiming at problems such as poor mechanical properties and poor elongation properties of the hot-dip galvanized steel sheet prepared by the existing method, the invention provides a hot-dip galvanized steel sheet and a preparation method thereof. The chemical composition of the hot-dip galvanized steel sheet of the present invention is: by weight Percent meter C: 0.04～0.08%, Si: 0.01～0.04%, Mn: 0.10～0.40%, P: ≤0.020%, S: ≤0.015%, Als: 0.015～0.050%, B: 0.0010～0.0040% balance For Fe and unavoidable impurities. The preparation method is as follows: after smelting-hot-rolling-acid rolling-hot-dip galvanizing-annealing process, the smelted molten steel is obtained to obtain a hot-dip galvanized steel sheet. The yield strength of the hot-dip galvanized steel sheet prepared by the invention is 220-250 MPa, the tensile strength is 320-380 MPa, the elongation is ≥ 36.0%, n90 ≥ 0.18, r90 ≥ 1.5, BH ≥ 30 MPa, the mechanical properties and formability are excellent, and can meet User requirements for automotive exterior panels.

Description

Excellently formed bake-hardening hot-dip galvanized steel sheet and method for producing the same

technical field

The invention belongs to the technical field of hot-dip galvanized steel sheet production, and in particular relates to a well-formed bake-hardened hot-dip galvanized steel sheet and a preparation method thereof.

Background technique

Baking-hardening hot-dip galvanized steel sheets are widely used in auto parts, which not only require excellent stamping performance and surface appearance quality, but also require certain anti-sag performance and baking hardness to reduce noise during high-speed driving. Production technologies related to bake-hardened steel plates are:

CN 103228808B provides a high-strength bake-hardening cold-rolled steel sheet with excellent bake hardenability, room temperature aging performance and deep drawing processability, and small in-plane anisotropy. The composition is C: 0.0010-0.0040%, Si: 0.005-0.05%, Mn: 0.1-0.8%, P: 0.01-0.07%, S: 0.001-0.01%, Al: 0.01-0.08%, N: 0.0010-0.0050%, Nb: 0.002-0.020%, and Mo: 0.005 ~0.050%, [Mn%]/[P%] is not less than 1.6 and not more than 45, and the amount of solid solution C calculated from [C%]-(12/93)×[Nb%] is not less than 0.0005% and 0.0025 % or less, by controlling the texture of X(222)/{X(110)+X(200)}≥3.0, a bake-hardened cold-rolled steel sheet with low anisotropy and a tensile strength of 300-450 MPa can be obtained. The invention adds P, Nb, Mo and other alloy elements, and the alloy composition is relatively high. At the same time, it has related control requirements for each C, N, Mn, P, Nb and other elements, and the actual smelting control is difficult.

CN 1090246C provides a cold-rolled steel sheet with excellent bake hardenability, including extremely low carbon steel containing Ti and/or Nb, and bake hardened steel containing a specific amount of B, the composition of which is C: 0.0013-0.0070%, Si: 0.001-0.08%, Mn: 0.01-0.9%, P: 0.01-0.10%, S: 0.03% or less, Al: 0.001-0.1%, N: 0.01% or less, Nb: 0.001-0.040%, and Ti: 0.001 ~0.025%, the bake hardening value can be obtained above 50MPa. This invention patent only involves bake hardening and aging resistance, and does not specify other properties. At the same time, C, N, Nb, Ti, Mo, and B in the composition are related and limited, and the actual smelting control is difficult.

CN101994056B relates to an ultra-low carbon bake-hardening steel plate with excellent stamping performance, the base components are: C: 0.0010-0.0030%, Si: 0.035-0.065%, Mn: 0.10-0.17%, P: 0.015-0.025%, S ≤0.010%, Al: 0.015～0.045%, N≤0.0030%, Ti: 0.007～0.014%, where [C%]/[Ti%] is controlled at 0.8～1.2. Through final rolling at 920-945°C, cold-rolling at 75-85% cold rolling reduction, and finally continuous annealing, yield strength 171-235MPa, tensile strength 302-322MPa, elongation after fracture 43.5-47%, r value 2.26~2.58, n value 0.22~0.24, BH value 35~58MPa. This invention only uses micro-titanium treatment, and the alloy cost is relatively low, but its tensile strength is on the low side (less than 340MPa).

CN201280047553.1 discloses a high-strength hot-dip galvanized steel sheet with excellent bake hardenability. 0.100%, S: 0.0001-0.0100%, Al: 0.001-2.00%, N: 0.0001-0.0100%, O: 0.0001-0.0100%. The invention is a high-carbon high-manganese steel, which cannot satisfy high deep drawing performance.

Although the above method can prepare a hot-dip galvanized steel sheet, the yield strength and tensile strength of the hot-dip galvanized steel sheet are low, and the mechanical properties are not good.

Contents of the invention

The technical problem to be solved by the invention is: the hot-dip galvanized steel sheet prepared by the existing method has problems such as poor mechanical properties, poor elongation performance, and high cost.

The technical solution of the present invention to solve the above-mentioned technical problems is: to provide a well-formed bake-hardened hot-dip galvanized steel sheet and its preparation method. The hot-dip galvanized steel sheet has a yield strength of 220-250 MPa, a tensile strength of 320-380 MPa, Rate ≥ 36.0%, n90 ≥ 0.18, r90 ≥ 1.5, BH ≥ 30MPa, strong operability and low cost.

The invention provides a bake-hardened hot-dip galvanized steel sheet with excellent forming, the chemical composition of which is: by weight percentage, C: 0.04-0.08%, Si: 0.01-0.04%, Mn: 0.10-0.40%, P: ≤0.020%, S: ≤0.015%, Als: 0.015-0.050%, B: 0.0010-0.0040%, and the balance is Fe and unavoidable impurities.

Among them, among the above-mentioned bake-hardened hot-dip galvanized steel sheets with excellent formation, the yield strength of the steel sheet is 220-250MPa, the tensile strength is 320-380MPa, the elongation is ≥36.0%, n90≥0.18, r90≥1.5, BH≥30MPa .

The present invention also provides a method for preparing the above-mentioned excellently formed bake-hardened hot-dip galvanized steel sheet, comprising the following steps:

The smelted molten steel is subjected to smelting-hot rolling-acid rolling-hot-dip galvanizing-annealing steps to obtain hot-dip galvanized steel sheets; the hot-rolling includes heating, dephosphorization, rough rolling, finish rolling, laminar cooling and coiling steps.

Wherein, in the preparation method of the above-mentioned excellently formed bake-hardening hot-dip galvanized steel sheet, the starting temperature of the finish rolling in the hot rolling is 1100-1250°C, and the finishing rolling temperature is 880-960°C.

Wherein, in the above-mentioned method for preparing the bake-hardened hot-dip galvanized steel sheet with good shape, the coiling temperature in the hot rolling is 650-750°C.

Wherein, in the preparation method of the above-mentioned excellently formed bake-hardening hot-dip galvanized steel sheet, the cold rolling reduction in the acid rolling process is 50-80%.

Among them, in the preparation method of the above-mentioned excellently formed bake-hardened hot-dip galvanized steel sheet, the annealing process is specifically: cooling from 780-850°C to 440-470°C at a rate of 10-50°C/s, and galvanizing for 7-50°C. 30s, then finally cool to room temperature at a speed of 5-10°C/s.

Wherein, in the preparation method of the above-mentioned excellently formed bake-hardening hot-dip galvanized steel sheet, the dew point temperature of the protective atmosphere in the furnace is -25～-60°C.

Compared with prior art, the beneficial effect of the present invention is:

The present invention provides a bake-hardened hot-dip galvanized steel sheet with excellent formation. The purity of the steel is ensured by strictly controlling the interstitial atoms such as C and N, especially the quantitative composition design of the Si and Mn contents, without adding titanium, and combining the unique A hot-dip galvanized steel sheet with excellent surface quality and excellent formability was prepared by rolling and continuous annealing hot-dip galvanizing process. The yield strength of the steel plate is 220-250MPa, the tensile strength is 320-380MPa, the elongation ≥ 36.0%, n90 ≥ 0.18, r90 ≥ 1.5, BH ≥ 30MPa, which can ensure the tensile strength and elongation at the same time to meet the requirements of automobile outer panel users According to the application requirements, a new hot-dip galvanized steel sheet for automobiles was developed.

Detailed ways

The invention provides a bake-hardened hot-dip galvanized steel sheet with excellent forming, the chemical composition of which is: by weight percentage, C: 0.04-0.08%, Si: 0.01-0.04%, Mn: 0.10-0.40%, P: ≤0.020%, S: ≤0.015%, Als: 0.015-0.050%, B: 0.0010-0.0040%, and the balance is Fe and unavoidable impurities.

Carbon: C determines the strength, plasticity and formability of the steel plate. C is the element with the most obvious solid-solution strengthening effect in steel materials. If the solid-solution C content in steel increases by 0.1%, its strength can be increased by about 450MPa. When the C content is too low, the strength will be low, which is generally not less than 0.02% in steel; when the C content is too high, the plasticity and welding performance of the steel will decrease, and the steel is generally not more than 0.15%. Therefore, the C content in the present invention is 0.04-0.08%.

Silicon: Si can dissolve in ferrite and austenite to improve the strength of steel, its effect is second only to C and P, stronger than Mn, Cr, Ti and Ni and other elements; Si can also inhibit carbonization in ferrite The precipitation of solid solution C atoms can be fully enriched in austenite, thereby improving its stability. However, when the Si content is too high, the surface oxide scale formed by Si in the heating furnace is difficult to remove, which increases the difficulty of phosphorus removal; at the same time, it is easy to enrich the surface to form SiO2 during the annealing process, resulting in surface defects such as missing plating. Therefore, the Si content in the present invention is 0.01 to 0.04%.

Manganese: Mn is a good deoxidizer and desulfurizer, and is also a solid solution strengthening element commonly used in steel. Mn can combine with C to form a variety of carbides to play a role in precipitation strengthening, and can also be dissolved in the matrix to enhance solid solution strengthening. Effect. Mn is easy to combine with S to form a high melting point compound MnS, thereby eliminating or weakening the hot embrittlement phenomenon caused by FeS and improving the hot workability of steel. Mn can improve the stability of austenite and shift the C curve to the right, thus significantly reducing the critical cooling rate of martensite. However, when the Mn content is too high, it is easy to enrich the surface during the annealing process, forming a large amount of manganese compounds, resulting in a decrease in the quality of the surface galvanizing. Therefore, in the present invention, the Mn content is 0.10 to 0.40%.

Aluminum: Al is a common deoxidizer in steel. At the same time, it can form AlN to pin the grain boundary, so as to refine the grains; carbon rich. Therefore, the Al content in the present invention is 0.015-0.050%.

In summary, through the precise control of various components, the present invention has prepared a bake-hardened hot-dip galvanized steel sheet with excellent strength and formability. The steel sheet has a yield strength of 220-250 MPa and a tensile strength of 320-380 MPa. Elongation ≥ 36.0%, n90 ≥ 0.18, r90 ≥ 1.5, BH ≥ 30MPa.

The present invention also provides a method for preparing the above-mentioned excellently formed bake-hardened hot-dip galvanized steel sheet, comprising the following steps:

The smelted molten steel is subjected to smelting-hot rolling-acid rolling-hot-dip galvanizing-annealing steps to obtain hot-dip galvanized steel sheets; the hot-rolling includes heating, dephosphorization, rough rolling, finish rolling, laminar cooling and coiling steps.

Wherein, in the preparation method of the above-mentioned excellently formed bake-hardening hot-dip galvanized steel sheet, in order to prevent warping defects in the hot rolling process and ensure the high-temperature coiling temperature, the finishing rolling start temperature in the hot rolling is 1100-1250 ℃, and the final rolling temperature is 880-960 ℃.

Wherein, in the preparation method of the above-mentioned excellently formed bake-hardening hot-dip galvanized steel sheet, in order to obtain a suitable ferrite and pearlite structure in the hot rolling process, the coiling temperature in the hot rolling is 650-750°C.

Wherein, in the preparation method of the above-mentioned excellently formed bake-hardening hot-dip galvanized steel sheet, the cold rolling reduction in the acid rolling process is 50-80%.

Among them, in the preparation method of the above-mentioned excellently formed bake-hardened hot-dip galvanized steel sheet, the annealing process is specifically: cooling from 780-850°C to 440-470°C at a rate of 10-50°C/s, and galvanizing for 7-50°C. 30s, then finally cool to room temperature at a speed of 5-10°C/s.

Wherein, in the preparation method of the above-mentioned excellently formed bake-hardening hot-dip galvanized steel sheet, the dew point temperature of the protective atmosphere in the furnace during galvanizing is -25 to -60°C.

The following will further explain the specific implementation of the present invention through examples, but it does not mean that the protection scope of the present invention is limited to the scope described in the examples.

Embodiment 1-3 prepares hot-dip galvanized steel sheet with the inventive method

The specific operation steps are as follows:

(1) through common smelting process, prepared the baking hardening steel slab of chemical composition as shown in table 1 below:

Table 1 Chemical composition of bake-hardened hot-dip galvanized steel sheets with excellent formation (wt.%)

Numbering C Si mn P S als B 1 0.06 0.02 0.21 0.007 0.007 0.034 0.0028 2 0.08 0.02 0.30 0.013 0.005 0.029 0.0032 3 0.05 0.01 0.026 0.009 0.006 0.046 0.0029

(2) After the above-mentioned slab is heated, dephosphorized, hot-rolled and laminar-flow cooled, a hot-rolled coil is obtained, wherein each parameter is set as shown in Table 2 below:

Table 2 Main process parameters of hot rolling

Numbering Heating temperature/℃ Finishing temperature/℃ Finishing temperature/℃ Coiling temperature/℃ Hot rolling thickness/mm 1 1220 1040 880～910 650～700 3.00 2 1200 1050 920～950 720～750 4.25 3 1205 1065 930～960 700～730 5.25

(3) After pickling the hot-rolled coils, they are cold-rolled into thin strips, and the cold-rolling reductions of 1#, 2# and 3# are 76.7%, 64.7% and 61.9% respectively.

(4) hot-dip galvanizing and annealing are carried out to the strip steel obtained in step (3), and the hot-dip galvanizing annealing process parameters are as shown in table 3:

Table 3 main process parameters of hot-dip galvanizing annealing

Numbering Annealing temperature/℃ Rapid cooling rate/℃/s Galvanizing time/s Final cooling rate/℃/s 1 796 30 10 4.5 2 823 35 15 7.0 3 845 45 25 8.5

(5) The mechanical properties of the well-formed bake-hardened hot-dip galvanized steel sheet prepared by the above-mentioned process are shown in Table 4 below:

Table 4 Mechanical properties of well-formed bake-hardened hot-dip galvanized steel sheets

From the results of Examples 1 and 2, it can be seen that the bake-hardened hot-dip galvanized steel sheet prepared in the present invention has good mechanical properties, the yield strength is 220-250MPa, the tensile strength is 320-380MPa, and the elongation is ≥36.0 %, n90≥0.18, r90≥1.5, BH≥30MPa, which can meet the requirements of automobile outer panel users. The invention provides a brand-new hot-dip galvanized steel sheet, which has excellent performance, low cost and obvious economic benefits.

Claims (8)

1. the baking hardening hot-dip galvanizing sheet steel of excellent shaping, it is characterised in that chemical composition is：C：0.04~0.08%, Si： 0.01~0.04%, Mn：0.10~0.40%, P：≤ 0.020%, S：≤ 0.015%, Als：0.015~0.050%, B： 0.0010~0.0040% surplus is Fe and inevitable impurity.

2. the baking hardening hot-dip galvanizing sheet steel of excellent shaping according to claim 1, it is characterised in that：Hot-dip galvanizing sheet steel Yield strength is 220~250MPa, tensile strength is 320~380MPa, elongation percentage >=36.0%, n90 >=0.18, r90 >= 1.5、BH≥30MPa。

3. the preparation method of the baking hardening hot-dip galvanizing sheet steel of the excellent shaping described in claim 1 or 2, it is characterised in that bag Include following steps：

Smelting molten steel is rolled through smelting-hot rolling-acid-galvanizing-annealing operation after, obtain hot-dip galvanizing sheet steel；The hot rolling includes Heating, dephosphorization, roughing, finish rolling, section cooling and coiling process.

4. the preparation method of the baking hardening hot-dip galvanizing sheet steel of excellent shaping according to claim 3, it is characterised in that：Institute It is 1100~1250 DEG C to state finish rolling start rolling temperature in hot rolling, and finishing temperature is 880~960 DEG C.

5. the preparation method of the baking hardening hot-dip galvanizing sheet steel of excellent shaping according to claim 3, it is characterised in that：Institute It is 650~750 DEG C to state coiling temperature in hot rolling.

6. the preparation method of the baking hardening hot-dip galvanizing sheet steel of excellent shaping according to claim 3, it is characterised in that：Institute It is 50~80% to state acid to roll cold rolling reduction ratio in process.

7. the preparation method of the baking hardening hot-dip galvanizing sheet steel of excellent shaping according to claim 3, it is characterised in that：Institute Stating annealing operation is specially：440~470 DEG C, zinc-plated 7~30s are cooled to from 780~850 DEG C of speed with 10~50 DEG C/s, then Room temperature is cooled to 5~10 DEG C/s speed eventually.

8. the preparation method of the baking hardening hot-dip galvanizing sheet steel of excellent shaping according to claim 3, it is characterised in that：Institute Protective atmosphere dew-point temperature is -25~-60 DEG C in stove when stating galvanizing.