CN107119228B - A kind of 700~800MPa of tensile strength grades of hot rolling high-strength light dual phase steels and its manufacturing method - Google Patents

A kind of 700~800MPa of tensile strength grades of hot rolling high-strength light dual phase steels and its manufacturing method Download PDF

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CN107119228B
CN107119228B CN201710465292.XA CN201710465292A CN107119228B CN 107119228 B CN107119228 B CN 107119228B CN 201710465292 A CN201710465292 A CN 201710465292A CN 107119228 B CN107119228 B CN 107119228B
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steel
dual phase
800mpa
tensile strength
hot rolling
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CN107119228A (en
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谭文
韩斌
黄全伟
张剑君
沈继胜
孙宜强
朱万军
刘继雄
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Wuhan Iron and Steel Co Ltd
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    • 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
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Abstract

The present invention discloses a kind of 700~800MPa of tensile strength grades of hot rolling high-strength light dual phase steels and its manufacturing method.The mass percent of the material chemical component of the steel is C:0.20~0.50%, Mn:2.00~6.00%, Al:4.0~9.0%, Si:0.30~1.00%, P≤0.015%, S≤0.010%, N≤0.008%, it further include at least one of Cr, Ti, V, Mo, Nb, Ca, Ni, Cu or several, and 0.8≤(15C+0.5Mn)/(Al+Si)≤1.20, remaining is Fe and inevitable impurity.The microstructure of steel of the present invention is ferrite+martensitic structure or ferrite+martensite+residual austenite body tissue, pass through steel-smelting continuous casting-hot rolling-annealing process flow, steel obtained show good intensity and toughness, 700~900MPa of tensile strength, elongation percentage >=20%, yield tensile ratio≤0.80 can be applied to automobile structure or reinforcer etc. and need favorable forming property and high-strength thinned position.

Description

A kind of 700~800MPa of tensile strength grades of hot rolling high-strength light dual phase steels and its manufacture Method
Technical field
The invention belongs to automobile steel production technical fields, and in particular to a kind of 700~800MPa of tensile strength grades of hot rollings High-strength light dual phase steel and its manufacturing method.
Background technique
In recent years, with the propulsion of energy-saving and emission-reduction technology of vehicles, automotive light weight technology becomes a kind of development trend.Thin gauge is high Strong steel is one of developing direction of light weight material in automobile, and in thin gauge high-strength steel, since ferrite+martensite two-phase is high Strong steel have good strong plasticity, low yield strength ratio, high initial work hardening rate, good baking hardenability and be used widely. Conventional ferrite+martensite dual-phase steel is generally made of 70%~90% ferrite and 10~30% martensite, is mainly adopted With the carbon for adding 0.08~0.20% and the alloying elements such as a certain amount of Si, Cr, Mn, Cu are added, and pass through complicated bosher Skill controls the ratio of ferrite and martensite in steel, to reach strong modeling proportion and low yield strength ratio, traditional dual phase steel it is anti- Tensile strength can cover 500~1000MPa.
Compared with cold-rolled biphase steel, hot-rolled dual-phase steel can not only reduce cold rolling, annealing, rewinding during Plate Production Etc. processes, but also can avoid the steel processing hardening after cold rolling, reduce abrasion and rebound to mold during part punching Amount.However currently, the high-strength hot-rolled dual-phase steel for producing and applying both at home and abroad is still based on cold rolling.Therefore, high-strength hot is developed Dual phase steel is rolled for the application range of expansion hot-rolled dual-phase steel, and automotive sheet " with hot Dai Leng " is promoted to have great importance.
Since conventional ferrite+martensite dual-phase steel density is generally in 7.80g/cm3More than, therefore, loss of weight mainly leads to It crosses and improves intensity to realize being thinned for automobile component, and when auto parts and components are thinned to a certain extent, thickness continues to be thinned then The rigidity that its auto parts and components can be reduced thus limits the loss of weight potential of auto parts and components.In addition, traditional dual phase steel due at Divide and technology controlling and process narrow range, control ability especially cooling capacity require height, general device is difficult to reach requirement.
Summary of the invention
In order to overcome the drawbacks of the prior art, present invention aim to provide a kind of 700~800MPa of tensile strength Grade hot rolling high-strength light dual phase steel and its manufacturing method.There is the hot rolling high-strength light dual phase steel good strong modeling proportion to bend with low Strong ratio, and ingredient and technology controlling and process wider range, manufacturing process flow are simple, especially cooling and annealing process, it can shape At a certain amount of ferrite and martensitic structure, and guarantee good intensity and toughness.
To achieve the above object, the present invention provides a kind of 700~800MPa of tensile strength grades of hot rollings high-strength light dual phase steel, The mass percent of the material chemical component of the steel be C:0.20~0.50%, Mn:2.0~6.0%, Al:4.0~9.0%, Si:0.30~1.00%, P≤0.015%, S≤0.010%, N≤0.008% further include Cr, Ti, V, Mo, Nb, Ca, Ni, Cu At least one of or a kind of, the mass percent of the above element are as follows: Cr:0.10~1.0%, Ti:0.03~0.20%, V: 0.01~0.15%, Mo:0.10~1.00%, Nb:0.03~0.15%, Ca:0.0001~0.10%, Ni:0.05~ 2.0%, Cu:0.10~1.50%, remaining is Fe and inevitable impurity, and above-mentioned element meets 0.8≤(15C+ simultaneously 0.5Mn)/(Al+Si)≤1.20。
Preferably, in the chemical component of the hot rolling high-strength light dual phase steel, the mass percent of C is 0.20~ The mass percent that the mass percent of 0.40%, Al are 4.5~7.0%, S is controlled 0.005% hereinafter, the quality percentage of N Than controlling below 0.006%.
Preferably, in the chemical component of the hot rolling high-strength light dual phase steel, 1.00≤(15C+0.5Mn)/Al of satisfaction≤ 1.15。
Preferably, in the chemical component of the hot rolling high-strength light dual phase steel, the mass percent of V is 0.02~ 0.15%.
Preferably, in the chemical component of the hot rolling high-strength light dual phase steel, the mass percent of Ni is 0.05~ 2.0%.
The effect of each element and main technique in the present invention:
C:C plays solution strengthening in steel, can be with the carbide formers shape such as Ti, Nb, V, Zr, Mo in steel At MC fine particle, plays the role of precipitation strength and refinement crystal grain, improve the intensity of steel.But C content is excessively high to reduce steel The toughness and welding performance of material.Therefore, the mass percent of C controls in the range of 0.20%~0.50% in steel of the present invention, Preferred scope is 0.20~0.40%.
Mn:Mn plays solution strengthening and stable austenite in steel.Mn content is too low, and invigoration effect is too small, Ovshinsky Body is unstable；Mn too high levels are easy to form macrosegregation in strip mid-depth, reduce toughness of products, hold in forming process Easily lead to cracking.Therefore, the mass percent of Mn controls in the range of 2.0~6.0% in steel of the present invention.
Al:Al is lightweight element, since its atomic mass is small and bigger than iron atom radius, can effectively reduce the close of steel Degree, therefore be the main adding elements of lightweight dual phase steel；Al can also play the role of solution strengthening, and Al can in phase transition process Effectively inhibit the formation of carbide, to effectively inhibit the formation of P etc..Al constituent content is excessively high to will form FeAl intermetallic Object reduces steel toughness.Therefore, the mass percent of Al controls preferred scope in the range of 4.0-9.0% in steel of the present invention It is 4.5~7.0%.
Si:Si plays solution strengthening effect in steel.Si content is too low, and solid solution strengthening effect is unobvious；But Si too high levels Also can Surface Quality have an adverse effect.Therefore, the mass percent of Si is controlled 0.30~1.00% in steel of the present invention In range.
P:P is the impurity element in steel, easily generates segregation in crystal boundary, influences the toughness of product, thus its content it is more low more It is good.According to practical controlled level, should control below 0.015%.
S:S is the impurity element in steel, easily generates segregation in crystal boundary, and form the FeS of low melting point with the Fe in steel, reduces The toughness of steel, when steel-making, should sufficiently remove, and should control 0.010% hereinafter, preferred scope is S≤0.005%.
N:N is the impurity element in steel, reduces the toughness of steel, is easy to form AlN and TiN, content mistake with Al, Ti in steel Height easily forms coarse AlN and TiN, therefore reduces its content as far as possible, should control 0.008% hereinafter, preferred scope be N≤ 0.006%.
C, Al, Mn constituent content need to meet 0.8≤(15C+0.5Mn)/(Al+Si)≤1.20 in the present invention.When 0.8≤ When (15C+0.5Mn)/(Al+Si)≤1.20, it is ensured that form a certain amount of ferrite and martensitic structure in steel, guarantee steel Performance, and the welding performance of steel can be effectively improved.Preferably, 1.00≤(15C+0.5Mn)/Al≤1.15.
Cr:Cr is solution strengthening element, and the intensity of steel can be improved and improve the harden ability of steel, Cr content Tai Gaoyi shape At carbide, the toughness of steel is reduced, therefore, the mass percent of Cr is controlled 0.10~1.00% in steel of the present invention.
Ti:Ti plays the role of solution strengthening in steel, and TiC and TiN are formed in conjunction with C, N in steel, and it is strong to play precipitation The effect of change.But Ti too high levels will increase the manufacturing cost of steel.Therefore, the mass percent control of Ti exists in steel of the present invention 0.03~0.20%.
Nb:Nb plays the role of solution strengthening in steel, and NbC and NbN are formed in conjunction with C, N in steel, and it is strong to play precipitation The effect of change.But Nb too high levels will increase the manufacturing cost of steel.Therefore, the mass percent control of Nb exists in steel of the present invention 0.02~0.15%.
V:V plays the role of solution strengthening in steel, and VC and VN are formed in conjunction with C, N in steel, plays precipitation strength Effect.But the excessively high manufacturing cost that will increase steel of V content.Therefore, in steel of the present invention the mass percent control of V 0.01~ 0.15%, preferred scope is 0.02~0.15%.
Mo:Mo plays the role of solution strengthening in steel, and MoC is formed in conjunction with the C in steel, plays the work of precipitation strength With.But Mo too high levels will increase the manufacturing cost of steel.Therefore, in steel of the present invention the mass percent control of Mo 0.10~ 1.00%.
Ca: the calcium of certain content can improve the state of steel inclusion, to be conducive to improve the toughness of steel.Therefore, originally The mass percent of Ca is controlled 0.0001~0.10% in invention steel.
Ni:Ni is solution strengthening element, and the inoxidizability and corrosion resistance of steel, but Ni price can be improved in the Ni of certain content Valuableness, therefore, 0.10~2.0%, preferred scope is 0.05~2.0% for the mass percent control of Ni in steel of the present invention.
Cu:Cu plays the role of solution strengthening and precipitation strength in steel, but the excessively high Surface Quality of Cu generates unfavorable shadow It rings, and due to expensive, the mass percent of Cu is controlled 0.10~1.50% in steel of the present invention.
The present invention provides a kind of manufacturing method of 700~800MPa of tensile strength grades of hot rollings high-strength light dual phase steel, including Following steps:
1) it smelts；
2) it casts: Al in used covering slag2O3And SiO2Mass percent Al2O3/SiO2>=1.0, pulling rate 1.0 ~10.0m/min, 15~50 DEG C of the degree of superheat；
3) heating of plate blank: 5~50 DEG C/min of the rate of heat addition, 1100~1250 DEG C of slab tapping temperature, heating time 10~ 200min；
4) hot rolling: 850~950 DEG C of hot rolling finishing temperature；
5) cooling is batched: cooling rate >=15 DEG C/s, coiling temperature≤200 DEG C；
6) it anneals: 600~800 DEG C of annealing temperature, annealing time 1~for 24 hours.
Specifically, the modes such as ingot casting, thin-belt casting rolling, sheet blank continuous casting, conventional slab CC machine can be used in slab when continuous casting Production.
It is middle that slow cooling is carried out using insulation cover specifically, when cooling, cooling rate≤50 DEG C/min, slab from insulation cover into When entering to heat stove heating, slab charging temperature >=200 DEG C；Cooling, two sections of coolings or multistage are cooling using leading portion for the type of cooling.
Specifically, when annealing, using bell-type annealing, 650~750 DEG C of annealing temperature, 1~10h of annealing time.
It is using the reasons why above-mentioned manufacturing process:
When casting, due in steel contain high Al, and Al easily with SiO in covering slag2It reacts, so as to cause continuous casting height There is surface quality problems, therefore Al in aluminum steel2O3/SiO2≥1.0.Suitable pulling rate and the degree of superheat are conducive to Surface Quality of Steel Billet With the control of internal soundness.
The thermal expansion coefficient of steel is improved since a large amount of Al being added in steel.It is excessively high that rate is added, easily causes continuous casting Base generates cracking because internal stress is excessive；Addition rate is too low, and heating time is too long, causes skin decarburization serious, crystal grain in steel It is coarse, reduce the toughness of steel.Therefore the rate of heat addition of the present invention is 5~50 DEG C/min.
Tapping temperature is at 1100~1250 DEG C in the present invention, because element in steel is difficult to expanding, steel when heating temperature is low Middle uniformity is poor, and the too low slab plasticity of temperature reduces, and resistance of deformation increases, and is easy to produce side and splits problem；And temperature is too high It is easy to cause decarburization serious and coarse grains, reduces steel toughness.
Heating time of the invention is 10~200min, because heating time is too short, the poor temperature uniformity of slab, and alloy Elements diffusion is insufficient；And heating time is too long, be easy to cause steel slab surface decarburization serious.
850~950 DEG C of finishing temperature of the invention causes austenite grain coarse because finishing temperature is excessively high, reduces steel Material toughness；And finishing temperature is too low, resistance of deformation will increase, and board rolling is caused to crack.
After hot rolling of the present invention in strip cooling procedure, strip cooling rate >=15 DEG C/s, coiling temperature≤200 DEG C.Because Strip cooling rate is too low, carbide precipitate in steel, reduces the content of martensite in steel.Coiling temperature is excessively high, increases and analyses in steel The risk of carbide out, the same content for reducing martensite in steel, to reduce the intensity of steel.
Strip uses bell-type annealing after hot rolling of the present invention, is conducive to the disperse educt K carbide in ferrite and martensite, Play the role of improving intensity and toughness.Annealing temperature is too low and annealing time is too short, martensite cannot be made effectively to be softened, Toughness cannot be significantly improved；Annealing temperature is excessively high and overlong time, increases K Carbide Precipitation size, to reduce Intensity and toughness.
The present invention is designed by reasonable ingredient, using carbon, silicon, manganese, aluminium basic element combination chromium, titanium, niobium, vanadium and molybdenum The chemical composition that solution strengthening element selectively adds, Steelmaking-continuous casting-hot rolling-annealing process flow, is bent The steel product matched than low, compression strength and elongation percentage by force.The microstructure of steel of the present invention be ferrite+martensitic structure or Ferrite+martensite+residual austenite body tissue.And by a large amount of theory analysis and it is demonstrated experimentally that meet 0.8≤(15C+ 0.5Mn)/(Al+Si)≤1.20 is equipped with suitable simply and effectively cooling and annealing process, just can guarantee in steel and formed centainly The ferrite and martensitic structure of amount, effectively improve the welding performance of steel.
The beneficial effects of the present invention are: 1) present invention manufacture obtain invite high-strength light steel to have 700~800MPa's Tensile strength, 20% or more elongation percentage, and yield tensile ratio are less than 0.80, density 7.50g/cm3Hereinafter, being reduced than conventional dual phase steel 6.0% or more, have good loss of weight potentiality, the manufacture suitable for automobile structure and reinforcer.2) this manufacturing approach craft Process is short, and simple production process is easy, without complicated cooling control technique and controls equipment, not additional equipment investment.
Detailed description of the invention
Fig. 1 is the metallograph of 1 steel of the embodiment of the present invention.
Specific embodiment
The present invention will be further explained by examples below, but does not limit the present invention.It is all without departing substantially from the present invention The change of design or equivalent substitute are included within protection scope of the present invention.
Table 1 is the chemical component (wt%) of steel of the embodiment of the present invention, and table 2 is the system of various embodiments of the present invention and comparative example steel Technological parameter is made, table 3 is the performance of various embodiments of the present invention steel.
Various embodiments of the present invention produce according to the following steps:
Technical process: → bell-type is batched in smelting → molding or continuous casting → heating or soaking → rolling → section cooling → Annealing → finished product；And traditionally process produces in comparative example, no annealing steps.Wherein technological parameter is referring to table 2.
It can be seen that product tensile strength of the invention from the performance of 3 embodiment steel of table and reach 700~800MPa, extend Rate is more than 20%, and yield tensile ratio is lower than 0.80, density 7.50g/cm3Hereinafter, density ratio routine steel grade reduces by 6.0% or more；Comparison Example steel grade density ratio routine steel grade only reduces by 0.6%, and elongation percentage is lower than product of the present invention.

Claims (7)

1. a kind of 700~800MPa of tensile strength grades of hot rollings high-strength light dual phase steel, the mass percent including chemical component are C:0.20~0.50%, Mn:2.00~6.00%, Al:6.5~9.0%, Si:0.30~1.00%, P≤0.015%, S≤ 0.010%, N≤0.008% further includes at least one of Cr, Ti, V, Mo, Nb, Ca, Ni, Cu or several, the above element Mass percent are as follows: Cr:0.10~1.0%, Ti:0.03~0.20%, V:0.02~0.15%, Mo:0.10~1.00%, Nb:0.03~0.15%, Ca:0.0001~0.10%, Ni:0.05~2.0%, Cu:0.10~1.50%, remaining is for Fe and not Evitable impurity, and meet 0.8≤(15C+0.5Mn)/(Al+Si)≤1.14 simultaneously；The yield tensile ratio of the dual phase steel is less than 0.80, microstructure is ferrite and martensitic structure or ferrite+martensite+residual austenite body tissue.
2. 700~800MPa of tensile strength grades of hot rollings high-strength light dual phase steel according to claim 1, it is characterised in that: Mass percent C:0.20~0.40%, Al:6.5~7.0%, S≤0.005%, N≤0.006%.
3. 700~800MPa of tensile strength grades of hot rollings high-strength light dual phase steel according to claim 1, it is characterised in that: In the chemical component of the hot rolling high-strength light dual phase steel, meet 1.00≤(15C+0.5Mn)/Al≤1.14.
4. 700~800MPa of tensile strength grades of hot rollings high-strength light dual phase steel according to claim 1, it is characterised in that: The mass percent of the Ni is 0.10~2.0%.
5. a kind of manufacturing method of 700~800MPa of tensile strength grades of hot rollings high-strength light dual phase steel as described in claim 1, The following steps are included:
1) it smelts；
2) it casts: Al in used covering slag2O3And SiO2Mass percent Al2O3/SiO2>=1.0, pulling rate be 1.0~ 10.0m/min, 15~50 DEG C of the degree of superheat；
3) heating of plate blank: 5~50 DEG C/min of the rate of heat addition, 1100~1250 DEG C of slab tapping temperature, heating time 10~ 200min；
4) hot rolling: 850~950 DEG C of hot rolling finishing temperature；
5) cooling is batched: cooling rate >=15 DEG C/s, coiling temperature≤200 DEG C；
6) it anneals: 600~800 DEG C of annealing temperature, annealing time 1~for 24 hours.
6. the manufacturing method of 700~800MPa of tensile strength grades of hot rolling high-strength light dual phase steels according to claim 5, special Sign is: when the casting, it is raw that the modes such as ingot casting, thin-belt casting rolling, sheet blank continuous casting, conventional slab CC machine can be used in slab It produces.
7. the manufacturing method of 700~800MPa of tensile strength grades of hot rolling high-strength light dual phase steels according to claim 5, special Sign is: when the annealing, using bell-type annealing, and 650~750 DEG C of annealing temperature, 1~10h of annealing time.
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