CN103194675A - Low-carbon hot-rolled full-ferrite based steel with ultrahigh strength and ultrahigh reaming ratio and preparation method thereof - Google Patents

Abstract

The invention provides low-carbon hot-rolled full-ferrite based steel with ultrahigh strength and ultrahigh reaming ratio and a preparation method thereof. According to the microstructure of the steel, a large number of nano-scale second-phase carbide particles are uniformly distributed on a matrix structure of single-phase ferrite, and the nano-scale particles have a strong precipitation strengthening role, so that the steel has ultrahigh strength while the steel has good extensibility and ultrahigh reaming ratio of the single-phase ferrite. Molten steel meeting a set ingredient control range is smelted through a vacuum induction furnace, and casting blanks are formed through casting. The casting blanks are subjected to forging and heating and are then subjected to hot-rolling, water-cooling and coiling, and the prepared nanoparticle-strengthened ultrahigh-strength steel has the final properties that the tensile strength is 700-800 MPa, the extensibility is 19-24% (A50 gage length), and the reaming ratio is over 100%. According to the low-carbon hot-rolled full-ferrite based steel with ultrahigh strength and ultrahigh reaming ratio and the preparation method thereof, the production process is simple, and the operation is feasible, so that the steel can be applied to the production of automotive chassis and suspension systems.

Description

Low-carbon (LC) hot rolling pure ferrite based ultra-high strength superelevation hole expansibility steel and preparation method thereof

Technical field

Present technique relates to a kind of low-carbon (LC) hot rolling pure ferrite based ultra-high strength superelevation hole expansibility steel and preparation method thereof, it is mainly concerned with a kind of superstrength of preparation, the single-phase ferritic steel of the hot rolling of high hole expansibility, interpolation Ti and Mo element can guarantee that single-phase ferritic steel under the condition with good forming property, possesses the intensity of superelevation in soft steel.

Background technology

Traditional FMDP(ferrite+martensite dual-phase steel) there is the widely different two-phase interface of deformability in, in forming process, easily at perforate position cracking, influences reaming.With the martensitic phase ratio, as the bainite of second phase flange tensile property and fracture toughness property are all had favorable influence, have high hole expansibility, yet unit elongation is lower.

Compare with other polyphase structures such as ferrite+bainite etc., single-phase ferrite has favorable extensibility and high hole expansibility concurrently, has excellent forming property.On the basis that keeps the excellent forming property of ferrite, increase the intensity of ferritic steel, be an important directions of the high reaming steel development of modern high strength.

Development along with nanosecond science and technology, nano material shows special advantages such as high strength, high rigidity and high tenacity aspect mechanical property, nano material and nanotechnology are applied in the ferrous materials design, utilize the precipitation strength of nano-scale precipitated phase and stop the grain growth technology, on the basis that keeps the excellent forming property of ferrite, be expected to increase substantially intensity and the toughness of structure iron.Separating out the NANOHITEN steel capital that hot rolling super-high strength steel and Japanese JFE develop as National Taiwan University poplar sage leader's seminar and the nanoparticle of Sinosteel Corporation cooperative development is the high hole expansibility ferrite base of this superstrength steel.

The present invention is by adding titanium and molybdenum element in the single-phase ferritic steel of low-carbon (LC), and at high-temperature final rolling, the high temperature isothermal batches and makes the carbide particle of separating out a large amount of nano-scales at ferrite matrix after the water-cooled, thereby guaranteeing that single-phase ferrite has under the condition of favorable forming property, can obtain higher intensity.The low-carbon (LC) hot rolling pure ferrite based ultra-high strength steel that can obtain to have high hole expansibility so.

Summary of the invention

The objective of the invention is to utilize the method for nano-scale carbide precipitation strength, produce a kind of hot rolled ferrite super-high strength steel with favorable forming property.

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

A kind of low-carbon (LC) hot rolling pure ferrite based ultra-high strength superelevation hole expansibility steel, its chemical ingredients mass percent is:

C 0.01～0.1%；

Si 0.01～0.2%；

Mn 0.1～0.4%；

P ≤0.01%；

S ≤0.01%；

N ≤0.01%；

Ti 0.01~0.2%；

Mo 0.01~0.2%。

The preparation method that the present invention adopts high temperature soaking, high-temperature final rolling and high temperature to batch, it comprises the steps:

1) a kind of low-carbon (LC) hot rolling pure ferrite based ultra-high strength superelevation hole expansibility steel, its chemical ingredients mass ratio is: C%:0.01～0.1, Si%:0.01～0.2, Mn%:0.1～0.4, P% :≤0.01, S% :≤0.01, N% :≤0.01, Ti%:0.01 ~ 0.2, Mo%:0.01 ~ 0.2.All the other are Fe and unavoidable impurities; Smelt, cast and forge into steel billet by mentioned component;

2) steel billet is through 1250 ~ 1300 ℃ of heating, be incubated soaking in 1～2 hour after, at A _R3The finish to gauge of above high-temperature zone, finishing temperature are at 880 ℃～950 ℃, and water-cooled is cooled to 600～700 ℃ then, and cooling rate is at 30 ~ 50 ℃/s, and high temperature batches, and coiling temperature is chilled to room temperature with stove at 600 ℃～700 ℃ behind insulation 1 ~ 2h;

3) with step 2) steel billet that obtains after the heat insulation carries out hot rolling, and the hot rolling draft obtains final hot-rolled product between 80%～90%, and this product is widely used in automotive seat, vehicle structure stiffener etc.

Further: steel billet is through 1250 ℃ of heating of high temperature in the described step 2, and more than the insulation 1.5h, the high-temperature final rolling temperature is 950 ℃; Coiling temperature is 600 ~ 620 ℃.When finishing temperature was 950 ℃, it such as was organized as at ferrite of axle, and the ferrite that distortion is elongated does not have.

To utilize high temperature to batch to separate out a large amount of nano-scale carbide are the present invention is guaranteeing that ferritic steel itself well under the prerequisite of plasticity, improves the principal character of its intensity.

The content requirement of each element and effect:

C:Cization thing forming element, with Ti and Mo element when the high temperature isothermal batches so that (Ti, Mo) form of C is separated out, and plays strong precipitation strength effect.The content of carbon can not be too high, and the too high alligatoring that then has perlite generation and carbide can make the plasticity variation.

Si:Si is a kind of effective solution strengthening element, and when the Si too high levels, separating out of meeting accelerated carbonation thing makes the carbide alligatoring, makes the forming property variation.

Mn:Mn is strong molten strengthening element, when the Mn too high levels, has segregation or hard forms mutually, makes the plasticity variation.

P:P is the solution strengthening element, when the P too high levels, has segregation and occurs, and makes the plasticity variation.

S:S is harmful element, and S content is more low more good, when S content is higher, can make the plasticity variation.

N:N content is more low more good, when N content is higher, can make the nitride alligatoring, makes the plasticity variation.

Ti:Ti and C play the effect of strong precipitation strength in conjunction with forming tiny carbide, when greatly improving the intensity of steel, can not influence the plasticity of steel.

Mo:Mo can suppress growing up of the second phase carbide particle when separating out with Ti and C formation carbide, make that the carbide precipitate particle is more tiny, makes the effect of precipitation strength more remarkable.

Beneficial effect of the present invention:

1) possesses excellent comprehensive mechanical properties.The tensile strength of the steel grade that the present invention relates to is 700-820MPa, and unit elongation is at 19%-24%, and hole expansibility is more than 100%.Because the massfraction of C is 0.01%～0.1%, does not specially add Si, therefore also possesses good weldability.

2) operation feasible, equipment is simple.The present invention adopts conventional smelting and steel rolling equipment, and the hot rolling technology simple and feasible, and present most of industrial production line all can be produced at existing equipment.

3) application prospect is extensive.The high hole expansibility hot rolled ferrite steel that the present invention prepares has high intensity when guaranteeing favorable forming property, it is applied on automobile chassis or the suspension system, and prospect is considerable.

4) its desirable chemical ingredients proportioning can be used traditional hot rolling technology, the final tissue that is organized as pure ferrite, and pearlitic structure disappears basically, and the carbon in the composition alloy is separated out with the nano level second phase particulate forms basically.

Description of drawings:

Fig. 1 is the thermal treatment process synoptic diagram;

Fig. 2 is the stress-strain(ed) curve synoptic diagram;

Fig. 3 separates out the topographic profile synoptic diagram for the nano-scale carbide.

Embodiment

The chemical ingredients given according to table 1 adopts electromagnetic induction furnace vacuum melting, the blank forging of casting become steel billet, to carry out subsequent technique.Fig. 1 is the thermal treatment process synoptic diagram.

Table 1 is the mass percent of each composition

Table 1

Numbering	C	Si	Mn	Ti	Mo	S	P	N	Surplus
										1#	0.040	0.090	1.70	0.12	0.16	0.0040	0.0070	0.004	Fe and inevitable impurity
2#	0.046	0.080	1.48	0.11	0.21	0.0047	0.0070	0.005	Fe and inevitable impurity
										3#	0.043	0.088	1.57	0.10	0.26	0.0066	0.0029	0.005	Fe and inevitable impurity

Hot rolling technology is for being heated to forging stock 1250 ℃ of insulations 1.5 hours, hot rolling on 350mm two roller hot rollss, 6 passages of hot rolling obtain thickness and are the latten about 2～6mm, total deformation is 80%～90%, and its open rolling and finishing temperature are respectively 1150 ℃ and 950 ℃.

Cooling rate water-cooled with 30 ~ 50 ℃/s after the finish to gauge arrives coiling temperature, and the present invention has adopted three kinds of different coiling temperatures, 600 ℃, 650 ℃ and 700 ℃.Batch isothermal 1-2h at process furnace, cool to room temperature then with the furnace, can obtain hot-rolled product.Fig. 2 is the stress-strain(ed) curve synoptic diagram; Fig. 3 separates out the topographic profile synoptic diagram for the nano-scale carbide.

The mechanical property of the corresponding composition 1# of different technical parameters is as shown in table 2:

Table 2 is the mechanical property of main technologic parameters 1# composition correspondence

Table 2

Coiling temperature/℃	Yield strength/Mpa	Tensile strength/Mpa	Yield tensile ratio	Unit elongation
					600	715	750	0.95	19.4
650	610	665	0.92	20.6
					700	580	615	0.94	23.3

Claims (3)

1. low-carbon (LC) hot rolling pure ferrite based ultra-high strength superelevation hole expansibility steel, its chemical quality per-cent is as follows:

C 0.01～0.1%；

Si 0.01～0.2%；

Mn 0.1～2%；

P ≤0.01%；

S ≤0.01%；

N ≤0.01%；

Ti 0.01~0.2%；

Mo 0.01~0.2%。

2. the preparation method of a kind of low-carbon (LC) hot rolling pure ferrite based ultra-high strength superelevation hole expansibility steel as claimed in claim 1, it comprises the steps:

1) a kind of low-carbon (LC) hot rolling pure ferrite based ultra-high strength superelevation hole expansibility steel, its chemical ingredients mass ratio is: C%:0.01～0.1, Si%:0.01～0.2, Mn%:0.1～2, P% :≤0.01, S% :≤0.01, N% :≤0.01, Ti%:0.01 ~ 0.2, Mo%:0.01 ~ 0.2; All the other are Fe and unavoidable impurities; Smelt, cast and forge into steel billet by mentioned component;

2) steel billet is through 1250 ~ 1300 ℃ of heating, be incubated soaking in 1～2 hour after, at A _R3The finish to gauge of above high-temperature zone, finishing temperature are at 880 ℃～950 ℃, and water-cooled is cooled to 600～700 ℃ then, and cooling rate is at 30 ~ 50 ℃/s, and high temperature batches, and coiling temperature is chilled to room temperature with stove at 600 ℃～700 ℃ behind insulation 1 ~ 2h;

3) with step 2) steel billet that obtains after the heat insulation carries out hot rolling, and the hot rolling draft is between 80%～90%; , obtaining final hot-rolled product, this product is widely used in automotive seat, vehicle structure stiffener etc.

3. the preparation method of a kind of low-carbon (LC) hot rolling pure ferrite based ultra-high strength superelevation hole expansibility steel as claimed in claim 2 is characterized in that: steel billet is through 1250 ℃ of heating of high temperature in the described step 2, and more than the insulation 1.5h, the high-temperature final rolling temperature is 950 ℃; Coiling temperature is 600 ~ 620 ℃.

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