CN103667880A - High hole expansion steel plate with tensile strength of 440MPa and manufacturing method thereof - Google Patents

Abstract

The invention discloses a high hole expansion steel plate with tensile strength of 440MPa and a manufacturing method thereof. The high hole expansion steel plate comprises the following chemical components by weight percent: 0.05-0.1% of C, 0.1-0.6% of Si, 0.9-1.8% of Mn, less than or equal to 0.02% of P, less than or equal to 0.005% of S, 0.015-0.060% of Al, less than 0.0050% of Ca, and the balance of Fe and inevitable impurities, wherein ([C]*[Mn]) is less than or equal to 0.1, ([P]+10[S]) is less than or equal to 0.04, the thickness of the obtained steel plate is 1.6-6.0 mm, the arithmetic product of the tensile strength TS and the hole expansion rate lambda of the steel plate is greater than or equal to 44000MPa%, and the requirement for steel used for a chassis or a complex stamping part in the automobile industry is met.

Description

A kind of tensile strength 440MPa level high-chambering steel plate and manufacture method thereof

Technical field

The present invention relates to high reaming steel, particularly a kind of tensile strength 440MPa level high-chambering steel plate and manufacture method thereof, product has good reaming and flanging forming characteristic.

Background technology

Hot rolling and hot rolling acid-cleaning plate are widely used in automobile chassis, wheel and body structure part, and they account for 28% left and right of automobile steel.Intensity and the rigidity that by auto parts flange and the design of local reaming shape, can improve part, reach autobody sheet attenuate and light-weighted object.The reaming performance of steel plate is relevant with composition, intensity and the homogeneity of structure of steel plate, and traditional 440MPa steel plate has the hole expansibility of carbon manganese Solid Solution Strengthened Steel and low-alloy precipitation strength steel between 50～70%.Along with Automobile Design improves day by day to the requirement of chassis structure, part forming is more complicated, the flange of steel plate and reaming performance requriements are increased, conventional carbon manganese Solid Solution Strengthened Steel and low-alloy precipitation strength steel plates of steel structure difficulty or ease meet automobile chassis, the requirement of cantilever part forming, and high reaming steel has become one of important kind for autobody sheet.

Chinese patent CN101353757 adopts the reaming steel of low carbon component production tensile strength 440MPa, owing to adopting 600 ℃ of coiling temperatures, to carbon manganese steel hot-rolled sheet, often has banded structure, causes steel plate hole expansibility to decline.Add a small amount of niobium titanium alloy and be conducive to improve intensity, increase production cost simultaneously.

Patent WO200928515 adopts C, Si, Mn to add a small amount of Nb, Ti alloying element, can production tensile strength at the above reaming steel of 490MPa, hot rolling must adopt the two-part laminar flow type of cooling, in laboratory, can more accurately simulate two-stage cooling controls, obtain good test-results, but in hot rolling is produced, in hot rolling, strip speed changes greatly, cannot measure the steel billet temperature of air cooling section again, adopt two-stage cooling model to control laminar flow cooling, the fluctuation of steel plate actual temperature is large, easily causes coil of strip head, middle and end performance inconsistency very large.

Japanese Patent JP2006063394 discloses a kind of hot rolling high-chambering steel, carbon content 0.20～0.48%, and its tensile strength is also >=440MPa, but its hole expansibility is only >=70%, and also to carry out the anneal of 640 ℃ after hot rolling.

Summary of the invention

The object of the present invention is to provide a kind of tensile strength 440MPa level hot rolling high-chambering steel plate and manufacture method thereof, the armor plate strength of acquisition and hole expansibility product TSx λ >=44000MPa%, meet automotive industry chassis and complicated stamping steel demand.

For achieving the above object, technical scheme of the present invention is:

A kind of tensile strength 440MPa level high-chambering steel plate, its chemical component weight per-cent is: C:0.05～0.1%, Si:0.1～0.6%, Mn:0.9～1.8%, P≤0.02%, S≤0.005%, Al:0.015～0.060%, Ca < 0.0050%, and all the other are Fe and inevitable impurity; Wherein, ([C] * [Mn])≤0.1, ([P]+10[S])≤0.04, armor plate strength and hole expansibility product TSx λ >=44000MPa%.

High-chambering steel plate thickness of the present invention is 1.6～6.0mm.

In Composition Design of the present invention:

C: be used to form enough carbide reinforced phases, to guarantee the intensity rank of steel, C too low strength does not reach requirement, and the too high carbide precipitate particle of C is unfavorable for greatly steel plate reaming performance.In addition, for carbon manganese steel, carbon in steel and manganese interact, pearlitic structure formation and distribution is had to certain influence, carbon manganese too high levels, [C] * [Mn] product is large, easily produces the mutually thick and perlite banded structure of perlite, the present invention controls the coupling of carbon manganese content, requires ([C] * [Mn])≤0.1.

Si: play solution strengthening effect in carbon manganese steel, carrying the high-intensity unit elongation that simultaneously improves steel plate, improve the plasticity of steel plate, suitable silicone content should be greater than 0.3%, the negative impact that adds silicon is that silicon height easily makes surface of steel plate produce the surface imperfection such as red iron sheet, can not the requirement of targeted customer's great surface quality.

Mn: be solution strengthening element, lower than the undercapacity of 0.9% steel, crossing high Mn content will increase perlite phase ratio, and high Mn content causes slab manganese component segregation, is the one of the main reasons of Banded Structure of Steel Plate, and the reaming performance of the deteriorated steel plate of banded structure meeting.In the present invention, the manganese content of manganese the best should be below 1.5%.

P: phosphorus is the impurity element in steel, content should be more low better, crosses high phosphorus amount and can cause intensity higher, and in casting process, phosphorus can aggravate slab component segregation simultaneously, causes tissue odds even, needs to control, and the present invention requires P≤0.02%.

S: sulphur is the impurity element in steel, S easily forms MnS in steel, and steel medium sulphide content quantity and form directly affect the hole expansibility of steel plate, and S must, lower than 0.005%, be preferably lower than 0.003%.Tramp element quantity and form have a great impact the reaming performance of steel plate, and particularly strip sulfide inclusion easily causes crackle to occur in distortion, require the overall control of phosphorus sulphur in ([P]+10[S])≤0.04.

Al: be the deoxidant element in steel, reduce oxide inclusion, pure steel in steel, be conducive to improve the forming property of steel plate.Al:0.02～0.06%, unsuitable too low, but affect continuous casting when too high, produce.

Ca: can change the form of steel medium sulphide content, improve plasticity and the toughness of steel plate, molten steel calcium of the present invention be processed, and controlled Ca < 0.0050%.

The manufacture method of tensile strength 440MPa level high-chambering steel plate of the present invention, comprises the following steps:

1) smelt, cast

By following compositions smelting, continuous casting, become slab, its chemical component weight per-cent is: C0.05～0.1%, Si:0.1～0.6%, Mn:0.9～1.8%, P≤0.02%, S≤0.005%, Al:0.015～0.060%, Ca < 0.0050%, and all the other are Fe and inevitable impurity; ([C] * [Mn])≤0.1, ([P]+10[S])≤0.04; Wherein, adopt the desulfurization of LF stove to process, molten steel sulphur content is less than 0.003%;

2) hot rolling

1180～1250 ℃ of continuous casting steel billet Heating temperatures, 840～880 ℃ of finishing temperatures, 450～550 ℃ of coiling temperatures;

3) cooling

After slab finish rolling completes, adopt the conventional laminar flow type of cooling of one-part form cooling, behind cooling metal sheets to 450～550 ℃, batch, wherein, speed of cooling is greater than 30 ℃/s;

4) pickling

Naturally cool to 50 ℃ of following coils of hot-rolled steel by pickling unit the iron scale at hot hydrochloric acid soln removal steel plate, pickled plate is coated with oil treatment through rinsing, after extracting, drying.

In manufacture method of the present invention, molten steel is by converter smelting, and LF stove is processed, and guarantees that S content is lower than 0.003%, and carry out Ca processing and improve oxide morphology, in hot rolling technology, Heating temperature is 1180～1250 ℃, and finishing temperature is 820～880 ℃, adopt the conventional one-part form type of cooling, cooling to be greater than the speed of cooling of 30 ℃/s, steel plate batches at 450～550 ℃ of temperature, and coil of strip batches rear air cooling to room temperature.Coiler plate excess Temperature, causes armor plate strength to decline, and meanwhile, tissue odds also causes steel plate hole expansibility to reduce.Coiling temperature is too low, causes armor plate strength to raise, and unit elongation declines.Preferably coiling temperature scope is at 480～540 ℃.

Steel roll temperature before pickling is less than 60 ℃, is preferably lower than 50 ℃, and steel roll temperature is too high, easily causes surface of steel plate waist folding defect.After uncoiling of steel plate, by heating hydrochloric acid soln (70～85 ℃ of Acidwash solution temperature), remove the iron scale of surface of steel plate, after pickling, steel plate, through water rinse, oven dry, batches after painting slushing oil.

This hot-rolled high-strength high-chambering steel plate provided by the invention, tensile strength reaches 440MPa, and hole expansibility is greater than 100%.Composition, containing Nb, Ti, without thermal treatment, does not reduce costs; After hot rolling, without complex control cooling technology, with general laminar flow cooling technology, just can realize, be easy to produce.This steel plate has good reaming performance, forming property, cold-forming property, is mainly used in automobile chassis Irregular Shaped Parts shaping processing.

Hole expansibility evaluation method, calculates hole expansibility (λ: unit is %) in the steps below.Get in the hot rolling or pickled plate of 150 * 150mm, as initial stage aperture (d[1]), the punching of opening diameter 10mm, is used the circular cone drift of 60 ° of drift angles to expand this punching.The aperture when crackle that mensuration punching partly produces connects thickness of slab (d[2]), by following formula, calculate hole expansibility.In the present invention, λ is more than 85% for qualified.

Hole expansibility (λ)=and [(d[2]-d[1])/d[1]] * 100%

The metallographic structure of the high reaming steel of tensile strength 440MPa level of the present invention is mainly ferrite, bainite content trace.What realize high hole expandability is mainly to rely on following several respects:

1, adopt the desulfurization of LF stove to process, reduce molten steel S content, and then reduce the quantity that is mingled with of steel plate, and process by Ca, rectangular MnS is mingled be converted into spherical CaS to be mingled with, the nonmetal inclusion that to reduce MnS be representative is without to the successional destruction of matrix.

2, reasonably hot rolling technology is controlled, and adopts suitable C, Mn content and ratio, can make the homogeneous microstructure of material, prevents banded structure and center segregation, slows down the susceptibility that steel plate ftractures in local deformaton process.

Accompanying drawing explanation

Fig. 1 is the typical metallographic structure photo of the embodiment of the present invention 1 steel plate.Homogeneous microstructure, segregation-free band and banded structure.

Embodiment

Below in conjunction with embodiment and accompanying drawing the present invention will be further described book.

Table 1 is the chemical composition of embodiment of the present invention steel, and table 2 is depicted as the mechanical property of embodiment of the present invention steel.

Embodiment of the present invention sample is processed by converter smelting, the desulfurization of LF stove, 1180～1250 ℃ of continuous casting, continuous casting steel billet Heating temperatures, finishing temperature is 820～880 ℃, 450～550 ℃ of coiling temperatures, hot-rolled sheet is cooling to be greater than the speed of cooling of 30 ℃/s, steel plate batches at 450～550 ℃ of temperature, and coil of strip batches rear air cooling to room temperature.The commercial material that comparative example 1, comparative example 2 steel are same level.

The typical metallographic structure of steel plate as shown in Figure 1, is organized as uniform ferrite.

Table 1 unit: weight percent

?	C	Si	Mn	P	S	Al	Nb	Ti	Ca
										Embodiment 1	0.05	0.20	1.70	0.018	0.0010	0.055	?	?	0.003
Embodiment 2	0.06	0.60	1.25	0.010	0.0030	0.021	?	?	0.0015
										Embodiment 3	0.07	0.50	1.40	0.015	0.0012	0.030	?	?	0.002
Embodiment 4	0.09	0.15	1.00	0.007	0.0032	0.045	?	?	0.003
										Comparative example 1	0.06	0.03	0.66	0.011	0.0040	0.040	0.017	0.001	?
Comparative example 2	0.08	0.10	1.20	0.014	0.0040	0.022	0.006	0.003	0.003

Table 2

?	Slab heating temperature ℃	Finishing temperature ℃	Coiling temperature ℃
				Embodiment 1	1210	850	480
Embodiment 2	1195	865	540
				Embodiment 3	1240	880	520
Embodiment 4	1220	845	505

Table 3

In sum, steel of the present invention carries out match control to carbon manganese content, coordinates the coiling technique of low temperature, can obtain that carbide is tiny, the single ferritic structure of homogeneous microstructure.By the control of sulphur phosphorus total inclusion content and calcium, process, the amount of inclusions and form are managed, improve the reaming performance of steel plate.

Claims (3)

1. a tensile strength 440MPa level high-chambering steel plate, its chemical component weight per-cent is: C:0.05～0.1%, Si:0.1～0.6%, Mn:0.9～1.8%, P≤0.02%, S≤0.005%, Al:0.015～0.060%, Ca < 0.0050%, and all the other are Fe and inevitable impurity; Wherein, ([C] * [Mn])≤0.1; ([P]+10[S])≤0.04; The armor plate strength and the hole expansibility product TSx λ >=44000MPa% that obtain.

2. tensile strength 440MPa level high-chambering steel plate as claimed in claim 1, is characterized in that, described high-chambering steel plate thickness is 1.6～6.0mm.

3. a manufacture method for tensile strength 440MPa level high-chambering steel plate, comprises the following steps:

1) smelt, cast

By following compositions smelting, continuous casting, become slab, its chemical component weight per-cent is: C0.05～0.1%, Si:0.1～0.6%, Mn:0.9～1.8%, P≤0.02%, S≤0.005%, Al:0.015～0.060%, Ca < 0.0050%, and all the other are Fe and inevitable impurity; ([C] * [Mn])≤0.1, ([P]+10[S])≤0.04.; Wherein, adopt the desulfurization of LF stove to process, molten steel sulphur content is less than 0.003%;

2) hot rolling

1180～1250 ℃ of continuous casting steel billet Heating temperatures, 840～880 ℃ of finishing temperatures, 450～550 ℃ of coiling temperatures;

3) cooling

After slab finish rolling completes, adopt the conventional laminar flow type of cooling cooling, behind cooling metal sheets to 450～550 ℃, batch, wherein, speed of cooling is greater than 30 ℃/s;

4) pickling

Naturally cool to 50 ℃ of following coils of hot-rolled steel by pickling unit the iron scale at hot hydrochloric acid soln removal steel plate, pickled plate is coated with oil treatment through rinsing, after extracting, drying.

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