Summary of the invention
First problem to be solved by this invention provides a kind of high-strength hot rolled steel plate, its objective is and make it both have high strength, have good cold shaping performance and high low-temperature impact toughness again, when satisfying vehicle structure safety (particularly low-temperature region use) needs, can satisfy the process for stamping and forming requirement in the vehicle structure manufacturing processed again.
To achieve these goals, the technical scheme that the present invention takes is: this high-strength hot rolled steel plate that is provided, based on the low-carbon high-manganese Clean Steel, in described low-carbon high-manganese Clean Steel, add the Nb micro alloying element, and also add the Ca of trace.
The weight percent of the chemical ingredients of described high-strength hot rolled steel plate is: C:0.08%~0.10%; Si:0.10%~0.25%; Mn:1.30%~1.50%; P :≤0.015%; S :≤0.008%; Nb:0.020%~0.030%; Ca:0.0010%~0.0030, all the other are iron and remaining trace impurity.
Described high-strength hot rolled steel plate, its material add Al when smelting, make its total amount at the weight percent of body material be: 0.015%~0.050%.
Second problem that the present invention will solve provides the manufacture method of above-mentioned high-strength hot rolled steel plate, and its goal of the invention is identical with technique scheme.
Described manufacture method of having added the high-strength hot rolled steel plate of Nb micro alloying element and micro-Ca is to adopt the manufacture method of controlled rolling and controlled chilling on continuous rolling process, and its technological process and technology content are:
(a), hot metal pretreatment: molten iron is carried out desulfurization handle;
(b), converter smelting: molten iron is taken off P, Si, C and Alloying Treatment;
(c), furnace rear refining: adopt dark sulfur removal technology and molten steel Alloying Treatment and add the iron calcium line through the LF stove and carry out inclusion modification and handle;
(d), continuous casting: molten steel after refining is protected casting by continuous caster, becomes slab;
(e), slab heating: send hot continuous mill after the heating of strand cold charge;
(f), roughing: rolling by the roughing unit behind the high-pressure water descaling, roughing adopts 5~7 passages rolling, also adopts high-pressure water descaling between the roughing passage; Roughing is after middle stay-warm case send finishing train;
(g), finish rolling: adopt 7 passages rolling by finishing train, control pass deformation and rolling temperature;
(h), laminar flow cooling: the speed of cooling that adopts the control of laminar flow cooling mode to roll the back steel plate;
(i), batch: by the coiling temperature of above laminar flow cooling control steel plate.
Be some necessary technical in above-mentioned each processing step below:
In above-described step (d), slab thickness is 230mm~250mm.
In step (e), slab heating temperature is 1180~1220 ℃.
In step (f), carry out 5~7 roughing after, the roughing temperature out is 1020~1060 ℃; Intermediate blank thickness requirement after the roughing guarantees that the finish rolling draft is 〉=80%.
In step (g), 860~890 ℃ of finishing temperatures
In step (h), the laminar flow speed of cooling is 15~35 ℃/s;
In step (i), coiling temperature is 580~620 ℃.
The present invention adopts technique scheme, by the rational chemical proportioning, adopts converter smelting, refining, continuous caster protection casting and cooling controlling and rolling controlling process, obtains that steel is pure, the even tiny hot continuous rolling coiled sheet of high comprehensive performance, grain fineness number.
Above-mentioned composition design and rolling and process for cooling control promote that on the one hand the part globular carbide forms, and gain in strength, and reduce either pearlite occurred simultaneously; The 2nd, promote the more tiny and dispersion of pearlite colony.This tissue helps obtaining high strength, high cold shaping performance and good low temperature impact properties.
Implement this technology and on the 2250mm hot rolling line, produce high-strength hot-rolled vehicle structure steel plate, the stable easily control of chemical ingredients, the rolling technology control stabilization, product stable mechanical property, surface quality are good.The performance index of product are respectively: the hot-rolled steel sheet tensile strength of production is 545~580MPa, yield strength is 455~495MPa, unit elongation is 27~33%, reflection intensity and the cold shaping integrated performance index---strength and ductility product (is TS * EL, the product of tensile strength and unit elongation) in 15950~18810MPa% scope ,-60 ℃ of summers of 5mm * 10mm * 55mm sample than V-type ballistic work greater than 97J.Steel plate has high-intensity have simultaneously good cold shaping performance and higher low-temperature impact toughness, satisfies the forming technology requirement in the vehicle structure making processes when satisfying vehicle structure safety (particularly low-temperature region use) needs.Kept simultaneously good welding property again.
That uses product success that the technology of the present invention produces is applied to make high strength automobile structures such as vehicle beam, longeron, axle housing, frame member.
Embodiment
Below in conjunction with accompanying drawing, by description to embodiment, to application, the manufacturing process and product of the concrete composition of the specific embodiment of the present invention such as product, performance, effect, product and manipulate method etc., be described in further detail, to help those skilled in the art that general plotting of the present invention, detailed technical scheme are had more complete, accurate and deep understanding, help it and better and more easily realize the present invention.
The present invention is a kind of high-strength hot rolled steel plate, is mainly used in high strength automobile structure steel plate materialses such as vehicle beam, longeron, axle housing, frame member, is basic composition with the low-carbon high-manganese Clean Steel.On this basis, in order to solve the problem that exists at the described present known technology of this specification sheets background technology part and to overcome its defective, realization makes this steel plate both have high strength, have the goal of the invention of good cold shaping performance and high low-temperature impact toughness again, the present invention has also taked following technical scheme:
This high-strength hot rolled steel plate provided by the present invention adds the Nb micro alloying element in described low-carbon high-manganese Clean Steel, also add the Ca of trace.
The topmost effect of Nb is a crystal grain thinning.On the one hand, the NbC particle of separating out in the continuous casting and solidifying process can be organized only austenite crystal and grows up refinement initial austenite grain-size when strand heats; On the other hand, the Nb and deformation induced tiny Nb (C, the N) particle that distributes along the substructure border of separating out of hot rolling that are solid-solubilized in the course of hot rolling in the austenite can be organized only austenite recrystallization, thereby enlarge the non-recrystallization district, and the tiny Nb that separates out (C, N) particle can be used as the forming core core of ferrite transformation, improve the ferrite transformation nucleation rate, be beneficial to the ferrite crystal grain refinement.
In the low-carbon high-manganese Clean Steel, add the Nb micro alloying element, the Ca that adds trace, by the manufacture method of controlled rolling and controlled chilling, this method can obtain high strength, high tenacity and good cold shaping performance by grain refining reinforcement, precipitation strength on continuous rolling process.
The thickness specification of above-mentioned steel plate is 3.0mm~10.0mm, is applicable to automotive frame, automobile axle housing, vehicle frame and other structural part, and cost is low than Nb, V, Ti combined microalloying steel.
Embodiment one:
In the specific implementation, the weight percent of controlling the chemical ingredients of described high-strength hot rolled steel plate is: C:0.08%~0.10%; Si:0.10%~0.25%; Mn:1.30%~1.50%; P :≤0.015%; S :≤0.008%; Nb:0.020%~0.030%; Ca:0.0010%~0.0030%, all the other are iron and remaining trace impurity.
The effect of each above-mentioned alloying element and be respectively to effect of material performance:
The increase of C:C content can increase the intensity of material, but the plasticity of steel and plasticity reduce; Mn has certain influence to the obdurability of steel.
Mn:Mn content is on the low side, strength degradation; And the Mn too high levels, steel plate easily forms banded structure, thereby influences the cold shaping and the welding property of steel, reduces low temperature impact properties.
Si: add an amount of Si in the steel, can increase the solution strengthening effect, but Si is too high, the surface of steel plate iron scale is difficult for removing, the surface easily forms the tiny crack that oxide compound is pressed into, thereby harmful to plasticity, Si content is controlled at and helps obtaining good surface quality below 0.25%.
Take all factors into consideration and through experimental verification, C% is 0.08~0.10 in control, and Si% is 0.10~0.25, and Mn% is in 1.30~1.50 scope.
Nb: the effect of described Nb is also very big with rolling and process for cooling relation in front, utilizes the effect of the performance Nb that controlled rolling and controlled cooling technology can be maximum, reduces the add-on of Nb, reduces cost.The content span of control of taking all factors into consideration design Nb is 0.020%~0.030%.
S:S easily forms the MnS inclusion in steel, MnS is deformed into strip or sheet in rolling, causes the anisotropy of steel plate to increase; The velocity of diffusion of P in α-Fe and γ-Fe is little, easily forms segregation, thereby improves the banded structure rank.
P: P segregation and MnS are mingled with meeting reduction steel plate cold shaping performance and low-temperature impact toughness in the steel.
Therefore as far as possible P%, S% content in the steel are controlled at low scope, and in steel, add proper C a, the inclusion of S is carried out denaturing treatment.
Embodiment two
Described high-strength hot rolled steel plate for improving its toughness, can also add an amount of Alt.Its material adds Al when smelting, make its total amount at the weight percent of body material be: 0.015~0.050.Alt refers to the total content of aluminium in the steel, comprises the aluminium of solid solution in the steel and the aluminium in the nonmetallic inclusionsin steel.
As shown in Figure 2, this figure is the displaing micro picture of the weave construction of the related high-strength hot rolled steel plate among the present invention.Shown this microstructure is a rational chemical and by obtain tiny and uniform of suitable processing method and ferrite+pearlitic structure of being reinforced, helps obtaining high strength, high cold shaping performance and good low temperature impact properties.
By rational chemical design, adopt converter smelting, refining, continuous caster protection casting and cooling controlling and rolling controlling process, obtain that steel is pure, the even tiny hot continuous rolling coiled sheet of high comprehensive performance, grain fineness number.Composition design among the present invention and rolling and process for cooling control promote that on the one hand the part globular carbide forms, and gain in strength, and reduce either pearlite occurred simultaneously; The 2nd, promote the more tiny and dispersion of pearlite colony.
Following table 1 is the example of every performance of the chemical ingredients of this high-strength hot rolled steel plate provided by the invention and product:
Table 1: the chemical ingredients of high-strength hot-rolled vehicle structure steel plate of the present invention and mechanical property example
Remarks: the impact toughness value J system in the table 1 adopts the observed value of 5mm * 10mm * 55mm sample.
The present invention has proposed the technical scheme of corresponding method of manufacture also at the high-strength hot rolled steel plate that has added Nb and Ca.
Provide the exemplifying embodiment of this manufacture method below:
Embodiment three:
As shown in Figure 1, described manufacture method is to adopt the manufacturing process of controlled rolling and controlled chilling on continuous rolling process, and it is rolling to be to produce at the 2250mm hot rolling line, and its technological process and technology content are:
(a), hot metal pretreatment: molten iron is carried out desulfurization handle;
(b), converter smelting: molten iron is taken off P, Si, C and Alloying Treatment;
(c), furnace rear refining adopts dark sulfur removal technology and molten steel Alloying Treatment and adds the iron calcium line through the LF stove and carries out the inclusion modification processing;
(d), continuous casting: molten steel after refining is protected casting by continuous caster, becomes slab;
(e), slab heating: the strand cold charge send hot continuous mill after going into the stove heating;
(f), roughing: rolling by the roughing unit behind the high-pressure water descaling, roughing adopts 5~7 passages rolling, also adopts high-pressure water descaling between the roughing passage; Roughing is after middle stay-warm case send finishing train;
(g), finish rolling and finish to gauge: adopt 7 passages rolling by finishing train, control pass deformation and rolling temperature;
(h), laminar flow cooling: the speed of cooling that adopts the control of laminar flow cooling mode to roll the back steel plate;
(i), batch: by the coiling temperature of above laminar flow cooling control steel plate.
Technical scheme design of the present invention is: add the Nb micro alloying element in the low-carbon high-manganese Clean Steel, the Ca that adds trace, by the manufacture method of controlled rolling and controlled chilling, this method can obtain high strength, high tenacity and good cold shaping performance by refinement reinforcement, the precipitation strength of crystal grain on continuous rolling process.
In above-mentioned step (c), adopt and to feed calcium line at the LF stove and handle molten steel technology, can change MnS, Al than being mingled with sex change in further to steel under the low condition to reach in sulphur content
2O
3Deng the non-metallic inclusion form, inclusion is fully floated, be mingled with content thereby reach to reduce in the Finished Steel, improve the comprehensive mechanical property of steel plate.
According to technique scheme and specific embodiment, realized the goal of the invention of proposition in this specification sheets summary of the invention part, the defective of prior art and the problem of existence have been overcome, have outstanding substantial characteristics, can obtain the beneficial effect introduced in this specification sheets summary of the invention, existing relatively disclosed technology obtained tangible technical progress, thereby the present invention has possessed novelty and creativeness.
The present invention also considers following factor in order to obtain comprehensive performance in the selection of technology, and realizes that by different embodiment wherein said step all refers to the processing step in embodiment three:
Embodiment four:
Molten steel after refining is protected casting by continuous caster.
In described step (d), slab thickness is 230mm~250mm.
The selection of slab thickness, main consideration has suitable rolling reduction for follow-up rolling technology, can play the effect of strengthening crystalline structure.
Embodiment five:
In described step (e), slab heating temperature is 1180~1220 ℃.
Slab heating temperature is selected 1180~1220 ℃ can guarantee the complete solid solution of Nb microalloy element, and it is thick to suppress the strand austenite structure, and favourable Nb separating out in subsequent process.Send 2250mm hot continuous mill after the heating of strand cold charge.
Embodiment six:
Coming out of the stove between high pressure descaling water and the roughing of back, the employing of high pressure descaling water can guarantee the steel plate favorable surface quality before the high pressure descaling water and finish rolling.
In described step (f), carry out 5~7 roughing after, the roughing temperature out is 1020~1060 ℃; Intermediate blank thickness requirement after the roughing guarantees that the finish rolling draft is 〉=80%.Entering finishing mill through stay-warm case is rolled.
Stay-warm case in the middle of using guarantees that intermediate blank temperature end to end is even, so that the mechanical property of finished product length direction remains in the less fluctuation range.
Embodiment seven:
In described step (g), 860~890 ℃ of finishing temperatures.
Finishing temperature and reduction system are selected, and suitable finishing temperature and reduction system can better be brought into play the effect of Nb microalloying.Nb enlarges non-recrystallization district scope, and the non-recrystallization temperature is moved on the high-temperature zone, increases the finish rolling draft, improves non-recrystallization district deflection, helps obtaining tiny ferrite crystal grain, improves the intensity and the toughness of steel.Finishing temperature is preferably 870~890 ℃, and intermediate blank thickness is determined according to finished product different thickness specification, preferably satisfied finish rolling draft 〉=80%.
Embodiment eight:
In described step (h), the laminar flow speed of cooling is 15~35 ℃/s.
Roll the back and adopt cooling fast, grain-size is tiny behind the ferrite transformation, and suppressing carbon niobium nitride particle separates out at austenite, promote it more in process of cooling and the ferrite when batching, to separate out, precipitation particles is more tiny, obtain good refined crystalline strengthening and precipitation strength, the perlite banded structure is avoided in cooling fast simultaneously.Tiny and uniform ferrite+the pearlitic structure of final acquisition.
Embodiment nine:
In described step (i), coiling temperature is 580~620 ℃.
The coiling temperature optimum valuing range is 590~600 ℃.
Implement this technology and produce high-strength hot-rolled vehicle structure steel plate at the 2250mm hot rolling line, the STEELMAKING PRODUCTION cost of alloy is lower, the stable easily control of chemical ingredients, and the rolling technology control stabilization, product stable mechanical property, surface quality are good.
The quality technology parameter of the hot-rolled steel sheet product of producing is:
Tensile strength is 545~580MPa;
Yield strength is 455~495MPa;
Unit elongation is 27%~33%;
The tensile strength of reflection intensity and cold shaping integrated performance index and the product of unit elongation (strength and ductility product, TS * EL) in 15950~18810MPa% scope;
-60 ℃ of summers of 5mm * 10mm * 55mm sample than V-type ballistic work greater than 97J.
Steel plate has high-intensity have simultaneously good cold shaping performance and high low-temperature impact toughness, satisfies the forming technology requirement in the vehicle structure making processes when satisfying vehicle structure safety (particularly low-temperature region use) needs.That uses product success that the technology of the present invention produces is applied to make high strength automobile structures such as vehicle beam, longeron, axle housing, frame member.
In conjunction with the accompanying drawings the present invention has been carried out exemplary description above; obviously specific implementation of the present invention is not subjected to the restriction of aforesaid way; as long as adopted the improvement of the various unsubstantialities that method of the present invention design and technical scheme carry out; or design of the present invention and technical scheme are directly applied to other occasion without improving, all within protection scope of the present invention.