CN109136773A - Low-alloy high-strength bridge Suo Gang continuous casting square billet thermal treatment production process - Google Patents
Low-alloy high-strength bridge Suo Gang continuous casting square billet thermal treatment production process Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
- B22D11/225—Controlling or regulating processes or operations for cooling cast stock or mould for secondary cooling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/34—Methods of heating
- C21D1/42—Induction heating
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- 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
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
The invention discloses a kind of low-alloy high-strength bridge Suo Gang continuous casting square billet thermal treatment production process, by weight percentage include C0.90~1.20, Si0.90~1.10, Mn0.60~0.90, P≤0.01, S≤0.01, Cr0.20~0.40, Nb+V0.60~0.80, Ti0.010~0.015, N0.005~0.015, B0.0005~0.0015.The present invention passes through the titanium nitride particle being precipitated in continuous casting square billet process of setting, the nucleation point of titanium nitride particle and acicular ferrite as new austenite in the austenitization of electromagnetic induction coil heating, and the effect of " pinning " austenite boundaries of particle refines austenite, reduce or eliminate the coarse columanar structure in continuous casting billet, the tissue of refinement is provided for the production of rear process, can be further improved the tissue and performance of final products.
Description
Technical field
The present invention relates to high-strength steel technical field of heat treatment, and in particular to a kind of low-alloy high-strength bridge Suo Gang continuous casting square billet
Thermal treatment production process.
Background technique
Macrostructure in continuous casting billet is made of three crystal zones from outside to inside: tiny equiax crystal band (chill), column crystal
Band, Center Equiaxial Crystal area (see attached drawing 1).Steel slab plasticity is poor for general steel products, this is because adjacent
The crystal boundary of column crystal is more straight, and intercrystalline is bonded to each other secured not as good as equiax crystal, the column especially extended in different directions
Often there is fragile interface in shape crystalline substance junction, therefore, is easy cracking in rolling.Column crystal is also also easy to produce inside in slab and splits
Line, also, coarse column crystal can also continue the tissue and performance for influencing product.With national large bridge build development,
The intensity rank of bridge cable steel wire via previous 1670MPa, 1770MPa and 1860MPa grade develop to 1960MPa and
2000MPa grade, and carried out the research and development of 2500MPa grade bridge cable steel wire.Due to the requirement of bridge cable steel wire
While having high intensity, also to have the requirement (torsion of steel wire, number of bends are greater than 14 times) of high tenacity, this is to bridge Suo Gang
Chemical component, metallographic structure and the mechanical property of wire product all put forward higher requirement.It is " high-intensitive high in order to meet user
The requirement of toughness ", with Japan Kobe, Nippon Steel, Chinese Baosteel, Anshan iron and steel plant, emerging clear special steel etc., iron and steel enterprise is all adopted both at home and abroad at present
With bloom continuous casting (slab cross section edge size is in 200mm~600mm range), (slab is cross-section at small billet for split rolling method
Face edge size is in 100mm~200mm range) after carry out the rolling of bridge rope steel wire rod again, this can be improved in slab
The as-cast structure (tiny equiax crystal+column crystal+equiax crystal) of continuous casting billet can also be changed into and roll state tissue, subtracted by component segregation
Lack column crystal to the tissue of rear process and the influence of performance, refined crystallite dimension, improves the matter such as bridge rope steel wire rod performance
Figureofmerit.
Currently, all using the split rolling method technique of continuous casting blooms when each steel mill's production bridge rope steel wire rod: in ladle
Molten steel crystallizer entered by tundish be frozen into continuous casting blooms, bloom is pulled out crystallizer by pulling-straightening roller, passes through continuous casting
After the secondary cooling zone of machine fan-shaped section, by slab according to Length-fixing cutting.Before split rolling method, continuous casting blooms are packed into and are heated
Furnace is rolled into the size of small billet after being heated to the tissue austenitizing in steel.The production technology there are bloom it is cooling after again
The secondary process for being packed into heating furnace heating, extending the production time, (heating time at least also increases the energy in 100min or more)
Consumption.Currently, the wire rod market competition daytime increasingly, product homogeneity is serious, therefore how preferably to meet user demand,
It promotes user's efficiency, reduce user cost, be the problem of steel production enterprise has to face.
The energy consumption of billet reheat between reduction continuous casting and high line procedures, currently, some steel mills use both at home and abroad
Hot delivery and hot charging and Direct Rolling Technology improve productivity and energy-saving.But whether hot delivery and hot charging or Direct Rolling
Technology, in the production process of heating continuous casting billet austenitizing, traditional method is to use coal, gas, oil, electricity as power supply, passes through spoke
It penetrates, heat is transmitted to continuous casting billet by the modes such as convection current and conduction.Heating device has through continuous oven of shaft furnace, bell furnace etc., leads to
Referred to as external-heat furnace.There are three major defects for external-heat heating: (1) heating time is long, for continuous furnace, continuous casting
Base heating time is mostly 100min or more, time up to a few houres of shaft furnace and bell furnace quasi-periodic heating furnace, production efficiency
It is low, and have surface oxidation and decarburization phenomenon；(2) low efficiency of external-heat furnace, the efficiency of Fuel Furnace are lower than 40~50%, electricity
The efficiency for hindering furnace is 70% or so, also, thermal inertia is big, needs longer starting preheating time.(3) longer heating time meeting
There are the generations of abnormal structure's (such as Wei Shi body) of decarburized layer deepness increase, austenite grain size abnormal growth, burning.Institute
With the production efficiency of external-heat heating furnace, energy-saving and heating process can also be further increased and be improved.
Induction heating technique is since the second half in 20th century, since semiconductor technology, computer control and metal are quick
The development and progress of phase transformation theory is heated, so that the energy conversion efficiency of induction heating increases substantially, reliability increases, can
Realize the automatic control of entire production process.Induction heating is that vortex is generated by inductor alternating magnetic field, and vortex in a metal will
Electromagnetic energy is converted to Joule heat, becomes the ideal chose of heat treatment heating.But since the kelvin effect of induction heating (rises
Temperature concentrates on metallic surface), cause induction heating technique to be chiefly used in the benefit of sheet billet heating or slab surface part
Heat, to obtain the uniformity of temperature.For the lesser continuous casting square billet of cross section edge length-width ratio, how induction heating technique is used
The temperature for improving continuous casting billet entirety is the problem of being of practical significance very much up for solving.
On the other hand, added in steel niobium, vanadium, the alloying elements such as titanium have to the intensity for improving high-intensitive bridge Suo Gang it is certain
It helps.Wherein, a small amount of titanium can form the nanoscale titanium nitride particle for small and dispersed distribution of taking measurements greatly, these Dispersed precipitate grains
Son can pinning austenite grain boundary be mobile in austenite transition process, effectively inhibits thermal stress strength austenite crystal grain length
Greatly.But at 1500 DEG C or more, titanium nitride particle is dissolved in molten steel the temperature of molten steel in steel-making and continuous casting process, even
Titanium nitride particle is not formed during slab cooling, cannot prevent the formation of coarse column crystal.Therefore, how titanium nitride is utilized
" pinning " of particle acts on, and reduces coarse column crystal, and up for solving the problems, such as.
In titanium nitride particle refinement organizational aspects, Chinese invention patent (application number CN200610026267.3, the applying date
2006.04.29 a kind of Fe-Ti-N grain refiner and preparation method thereof of the steel of technical field of metal material) is disclosed, it is described
The component and weight percent of grain refiner are as follows: Fe 35~99.4%, Ti 0.5~50%, N 0.1~15%, the crystal grain
With the TiN particle of Dispersed precipitate in fining agent.Method are as follows: be put into the Ti of 40~99.5% pure iron and 0.5~60% very
Heating fusing, melt temperature are maintained at 1550~1650 DEG C in aerial frequency crucible induction furnace；Lead to nitrogen into vacuum medium frequency induction furnace
Gas makes nitrogen partial pressure in furnace be maintained at 0.01~0.1MPa；Snorkel is inserted into alloy melt nitrogen blowing, reaches the predetermined time
Afterwards, snorkel is extracted out, power-off is cast, after addition is a small amount of using Fe-Ti-N grain refiner obtained by the present invention in the melt of steel, casting
State tissue equiax crystal crystallite dimension greatly reduces, and isometric crystalline region ratio is increased to 60% or more, the thinning effect of grain refiner
Obviously.
In terms of continuous casting billet induction heating, Chinese invention patent application (application number CN201710240071.2, the applying date
2017.4.13 a kind of quick self-adapted temperature control method of continuous casting billet induction heating for simplifying adjusting based on mechanism model) is disclosed,
It is exactly method of the mechanism model referring to finite element induction heating mesh modeling, investigates the electromagnetism coupling of electromagnetic induction heating whole process
It closes, the vortex differentiation such as heat and heat transfer, heat radiation, mechanism model is abstracted and is reduced to " original state " and " final shape
The mapping status equation of state ".Induction heating grid model is mainly established in the patent application, and is checked by data, and fortune is improved
With model repeatable accuracy with higher.
But how reasonable disposition will be carried out between induction heater and continuous casting billet, it reduces or eliminates coarse in continuous casting billet
Columanar structure is the technical issues of needing urgent need to resolve.
Summary of the invention
The purpose of the present invention is to the deficiency of above-mentioned technology, provide it is a kind of efficiency not only can be improved but also can be reduced or
It eliminates at low-alloy high-strength bridge Suo Gang continuous casting square billet heat of the influence of coarse as-cast grain to improve product structural homogenity
Manage production technology.
To achieve the above object, the low-alloy high-strength bridge Suo Gang continuous casting square billet heat treatment production work designed by the present invention
Skill includes the following steps:
1) molten steel completed is smelted by default ingredient, forms continuous casting square billet after carrying out continuous casting；
2) continuous casting square billet controls continuous casting square billet surface temperature and is cooled to 500 by the secondary cooling zone of continuous casting machine fan-shaped segment
~800 DEG C, cooling rate is not more than 200 DEG C/m；
3) continuous casting square billet Jing Guo step 2) is passed sequentially through into multiple electromagnetic induction coils and is heated to 1000~1450 DEG C, made
The tissue of continuous casting square billet is completely reformed into austenite structure；
4) rolling line will be heat-fed after the continuous casting square billet of step 3) is cooled to 500~800 DEG C, or will be by step
Rapid continuous casting square billet 3) is cooled to room temperature rear inventory；
Wherein, low-alloy high-strength bridge rope steel chemical composition includes: by weight percentage
C:0.90~1.20wt%, Si:0.90~1.10wt%, Mn:0.60~0.90wt%, P≤0.01wt%, S≤
0.01wt%, Cr:0.20~0.40wt%, Nb+V:0.60~0.80wt%, Ti:0.010~0.015wt%, N:0.005~
0.015wt%, B:0.0005~0.0015wt%, remaining is Fe and inevitable impurity.
Continuous casting square billet has the precipitation of TiN particle during passing through continuous casting machine fan-shaped segment secondary cooling zone, want according to scale
Cutting continuous casting square billet is sought, when continuous casting square billet surface temperature is cooled to 500~800 DEG C, is heated using electromagnetic induction coil, is heated up
To 1000~1450 DEG C, the tissue in continuous casting square billet steel is completely reformed into austenite structure；It is re-converted into as-cast structure
During austenite, new austenite forming core at TiN particle and acicular ferrite, and the Ovshinsky that TiN particle pinning is new
(high-strength bridge Suo Gang austenite structure crystal boundary figure when see attached drawing 2 being 1000 DEG C has titanium nitride particle at white arrow to body crystal boundary, black
There is no titanium nitride particle at color arrow), preventing austenite from growing (is that titanium nitride particle pinning is high when heating up 1200 DEG C see attached drawing 3
Strong bridge Suo Gang austenite structure crystal boundary figure does not have titanium nitride particle at black arrow), and at TiN particle for nucleation point (see
Attached drawing 4 is the titanium nitride particle subgraph in 583 DEG C of high-strength bridge Suo Gang of observation, has titanium nitride particle at white arrow), promote needle-shaped iron
Ferritic growth (is that 582 DEG C of observation acicular ferrites have titanium nitride at the big figure of titanium nitride particle director, white arrow see attached drawing 5
Particle), make new austenite (see the austenite structure figure refined after 6 induction heating of attached drawing) size be less than original austenite (see
Attached drawing 7 is the austenite figure before induction heating), reduce coarse column crystal inside continuous casting square billet to the tissue of rear process product and
The influence of performance；It is then possible to which 500~800 DEG C of hot delivering technology of CC billets rolling line will be cooled to, room temperature can also be cooled to
Inventory afterwards.
The design of alloy above-mentioned to this is described in detail below:
C: steel is iron-carbon alloy, and carbon is most important component in steel, and phosphorus content directly determines its intensity and plasticity.?
Under cold drawing state, tensile strength is continuously improved with the increase of phosphorus content, is continuously increased with the increase of total draught, and contain
Carbon amounts is higher to be improved faster, and plasticity is then reduced with the increase of phosphorus content.Therefore C:0.90~1.20wt% of the present invention.
Si: silicon is intensified element important in steel, can significantly improve the elastic limit of steel wire after drawing, and can effectively reduce
Strength reduction caused by heat treatment, meanwhile, element silicon can also slow down the broken of drawing process cementite, promote steel wire resultant force
Learn performance.Therefore, to make up intensity notch caused by carbon content reduction, steel wire properties after drawing are promoted, silicone content of the present invention is aobvious
It writes and is higher than traditional axle Suo Gang.Therefore Si:0.90~1.10wt% of the present invention.
Mn: the affinity of manganese and sulphur, oxygen is greater than iron, it is the good deoxidier of steel-making, smelts the vulcanization generated in reaction
Manganese, manganese oxide do not generate adverse effect, manganese and vulcanization symphysis to the cold drawing performance of wire rod and make at the nocuousness that MnS can also mitigate sulphur
With.Manganese also can increase pearlite relative quantity, and pearlite is made to attenuate.So manganese content increase can be such that the intensity of steel wire and hardness mentions
Height, yield limit and the contraction percentage of area also increased.Therefore Mn:0.60~0.90wt% of the present invention.
P, S: p and s belong to harmful element in this steel grade, and phosphorus is easy to produce cold short, and Sulfur capacity is also easy to produce hot-short, and then deteriorates
Steel wire drawing and heat treatment process condition, it is therefore desirable to reduce its content as far as possible.P≤0.01wt% of the present invention, S≤
0.01wt%.
Cr: chromium can refine pearlite lamella, improve finished product intensity of steel wire, but excessively high chromium, can improve wire rod harden ability, lead
Course of hot rolling is caused the abnormal structures such as martensite occur, meanwhile, excessively tiny lamella can reduce wire rod toughness, and then deteriorate steel
The most key index-the twisting property of silk, therefore Cr:0.20~0.40wt% of the present invention.
Nb+V: the nitride of vanadium other microalloys compared with, niobium and vanadium has highly dissoluble, can either roll
Or it is dissolved at a temperature of the normal heating of forging.Normal heating temperature is 900 DEG C to 1150 DEG C, is obtaining the entire of alloying component
In process, it is sufficient to dissolve all vanadium carbonitrides.It is full to be remarkably contributing to estimation for the linear relationship of niobium and vanadium additive amount and intensity
Alloy addition level required for sufficient minimum strength.Nb+V:0.60~0.80wt% of the present invention.
Ti: a small amount of titanium is added in steel can form the nanoscale titanium nitride particle for small and dispersed distribution of taking measurements greatly, these
Dispersed precipitate particle can pinning austenite grain boundary be mobile in austenite transition process, effectively inhibits thermal stress strength Ovshinsky
Body crystal grain is grown up.TiN can promote acicular ferrite nucleating as effective nucleation mass point in cooling procedure simultaneously.But it is excessive
Ti TiN particle is grown up and remelting at high temperature, to lose the inhibiting effect to Austenite Grain Growth.Therefore
Ti:0.010~0.015wt% of the present invention.
N: nitrogen is solid-solution in iron as carbon, forms the solid solution of clearance-type, and solution strengthening is played in steel and aging precipitation is strong
Change effect, it expands γ phase region, formation and stable austenite tissue.When nitrogen content is more than certain limit, the titanium, niobium in Yi Yugang
Equal elements form fine particle, play the role of precipitation strength.Therefore N:0.005~0.015wt% of the present invention.
B: micro boron can inhibit P in the enrichment of crystal boundary in high-carbon steel, and improve the form of field trash, and then can improve line
The cold-forming property of material, but excessive boron can weaken crystal boundary binding force and deteriorate wire rod mechanical property.Therefore B:0.0005 of the present invention
~0.0015wt%.
Further, in the step 1), the specification of continuous casting square billet are as follows: continuous casting square billet cross section edge having a size of 100~
200mm。
Further, in the step 3), the number of electromagnetic induction coil is 1~3, and each electromagnetic induction coil
Length is 2000~5000mm, and the distance between each electromagnetic induction coil and continuous casting square billet surface are 10~300mm.
Further, in the step 3), in order to improve the heating efficiency of continuous casting square billet, the electricity of each electromagnetic induction coil
5000~10000A of intensity of flow, 50~2000Hz of heating frequency, the speed that continuous casting square billet passes through each electromagnetic induction coil are 0.1
~1.0m/min makes continuous casting square billet have time enough to be warming up to 1000~1450 DEG C, it is ensured that continuous casting square billet tissue whole Ovshinsky
Body, and control TiN particle and be not dissolved into austenite again.
Titanium nitride particle is precipitated and the principle of refinement austenite structure:
In the present invention, titanium nitride particle is precipitated in the continuous casting billet solidification later period in the titanium elements in high-intensitive bridge Suo Gang, in Ovshinsky
Shown in the solubility product that TiN is varied with temperature in body phase such as formula (1):
Lg[w(Ti)d·w(N)d]γ=4.35-14890/T (1)
In formula: w (Ti)dWith w (N)dRespectively be dissolved into the mass fraction of Ti and N in austenite: T is temperature at that time, K.
In addition it controls Ti and the ratio of N content is also extremely important.Since undissolved Ti and N carries out mutual with 3.42 mass ratio
Match, as follows:
[w(Ti)t- w (Ti)d]/[w(N)t- w (N)d]=3.42 (2)
In formula: w (Ti) t and w (N) t is respectively Ti and N total mass fraction in steel.By joint type (1) and formula (2), calculate
The beginning Precipitation Temperature of the titanium nitride particle in sample is 1453 DEG C out.Pass through Thermo-calc software for calculation and SSOL4 data
The setting temperature that steel is calculated in library is 1521 DEG C.Therefore, it is distributed in the present invention in order to obtain a large amount of small and disperseds in steel
TiN particle, it is necessary to control heating temperature no more than 1450 DEG C.And the Ti and N content for rationally controlling material, avoid in molten steel
Middle forming quantity is few, size is coarse and titanium nitride particle unevenly distributed.Therefore, it is necessary to according to the requirement control of Ti and N content
System, it is ensured that TiN particle starts Precipitation Temperature lower than solidification of molten steel temperature.
TiN particle is precipitated in the cooling procedure after continuous casting billet solidification, so forming the nanoscale of a large amount of small and disperseds
Particle, average-size are about 30nm.These Dispersed precipitate particles are more stable at high temperature, can promote in induction heating
Forming core at TiN particle, the more austenite of generation quantity.Also, pinning Ovshinsky in austenite transition process occurs in continuous casting billet
Body crystal boundary is mobile, effectively inhibits coarse columnar zone Austenite Grain Growth.TiN particle distribution gets over even dispersion, and size is thinner
Small, quantity is more, then is more obvious to the inhibition of Austenite Grain Growth.
Acicular ferrite is formed and refinement principle:
MnS precipitation makes to form the poor area of manganese element around field trash in steel, and the presence in poor area leads to the Austria for being mingled with surrounding
The decline of family name's body stability, improves the Ae3 temperature of transformation, increases the driving force of ferrite forming core, is conducive to acicular ferrite nucleating；
In addition, TiN particle and acicular ferrite are all body-centered cubic structure, lattice constant is respectively 0.423nm and 0.287nm, they
There is good symbiosis and epibiosis, interface energy can be effectively reduced, promote acicular ferrite nucleating.It is molten around field trash in Nucleation Mechanism
It is conclusive that the low energy interface of prime element composition transfer and precipitate and acicular ferrite promotes ferrite forming core to serve.Cause
This, attachment TiN particle has very strong promotion acicular ferrite nucleating ability.
Austenite grain size is very tiny, this is attributed to the formation of acicular ferrite, then keeps solid with original austenite
Fixed to be orientated and keep wide-angle to grow up toward different directions between each other, these acicular ferrites can be also the forming core of new austenite
In induction heating again after continuous casting square billet is cooling austenite → ferrite → austenite (γ → α → γ) phase transition process occurs for point
Middle refinement columanar structure.
Control the principle of coarse column crystal in continuous casting square billet:
Macrostructure ecto-entad in continuous casting billet is made of three crystal zones: tiny equiax crystal band, column crystal band, center etc.
Axialite band, steel slab plasticity is poor for general steel products, this is because the crystal boundary of adjacent column crystalline substance is relatively more flat
Directly, what intercrystalline was bonded to each other is secured not as good as equiax crystal, and the column crystal junction especially extended in different directions often occurs
Fragile interface.Therefore, cracking is easy in rolling.Column crystal is also also easy to produce underbead crack in slab, and isometric crystalline region does not have
Apparent plane of weakness, intercrystalline hasp obtain very secured thus not easy to crack when hot-working.
Column crystal is to go out crystallizer in slab in continuous casting billet, into what is gradually formed during secondary cooling zone.This hair
The bright method for reducing or eliminating coarse as-cast structure inside continuous casting billet is exactly after the molten steel in slab solidifies completely, to be precipitated TiN
Son forms acicular ferrite.In 500~800 DEG C of ranges, 1000~1450 DEG C are warming up to by electromagnetic induction heating, by continuous casting
Tissue whole austenitizing in square billet.New austenite forming core at titanium nitride particle and acicular ferrite, across former Ovshinsky
The growth of body crystal boundary, then austenite is refined by the pinning effect of titanium nitride particle, new austenite size is less than original austenite, subtracts
The influence of few coarse column crystal.
Electromagnetic inductive heating principle
Electromagnetic induction heating is using self-heating and to heat the induced current generated in high frequency magnetic field caused by conductor.Magnetic field
Inductive loop principle, i.e., by the current induced magnetic field of coil, it is countless that the magnetic field in magnetic metal material can be such that metallic object generates
Small vortex (by effect of the induction coil alternating magnetic field in metal object in electromagnetic field, generate many closed rotations
The object of electric current), since electric current has fuel factor, it can generate heat in a large amount of, be heated at high temperature metal material itself.
For continuous casting blooms, induction heating belongs to the process of Coupled Electromagnetic-Thermal, the mutual shadow of electromagnetic field and temperature field
It rings, electromagnetism rule all follows Maxwell's differential equation group, can be expressed as formula (3) equation group:
In formula:For Laplace operator；D is electric flux density, C/m2；ρ is charge density, C/m3；E is electric field strength, V/
m；B is magnetic induction intensity, Wb/m2；H is magnetic field strength, A/m；J is current density vectors, A/m2；T is time, s.
Electromagnetic field is solved conducive to complex vector magnetic potential gesture method in ANSYS software, vector magnetic is introduced and swears A, vector magnetic arrow is defined as:
The equation group of substitution formula (3), the finite element formula of available solution alternating magnetic field are as follows:
[K+j ω C] { A }={ F } (5)
During the induction heating of continuous casting square billet, the variation in temperature field, which is one, typically has inner heat source three-dimensional unstable state to lead
Thermal process.Heat Conduction Differential Equations can be expressed as formula (6).
Slab belongs to the Unsteady Heat Transfer process with uneven inner heat source, heat source is from electricity in inductor internal operation
Vortex, i.e. power loss of the electromagnetic field in slab, ignore slab axial thermal conductivity, then the unstable state with uneven inner heat source is led
Thermal process:
In formula: T is temperature, K；K is thermal coefficient, W (/mK)；qvFor inner heat source intensity, W/m3；ρdFor density, kg/
m3；C is specific heat capacity, J (/kgK).
Slab belongs to the Unsteady Heat Transfer process of no inner heat source when running into before inductor and between inductor,
Inner heat source item: qv=0, during solution of Temperature, the heat loss of workpiece is mainly caused by thermal convection and heat radiation.Temperature field
Boundary condition analysis can be expressed as formula (7).
In formula: kx、ky、kzThe respectively thermal coefficient in x, y, z direction, W (/mK)；nx、ny、nzRespectively spatial domain three
The direction vector of dimension；αcFor convection transfer rate, W (/m2·K)；αrFor heat emissivity coefficient, W (/m2·K)；Tα、TsRespectively work
Part peripheral environment temperature and workpiece surface temperature, K.
Compared with prior art, beneficial effects of the present invention are as follows:
1) while low alloyed element improves bridge rope steel wire rod mechanical property, conducive to being precipitated in continuous casting square billet process of setting
Titanium nitride particle, titanium nitride particle and acicular ferrite are as new difficult to understand in the austenitization of electromagnetic induction coil heating
The effect of " pinning " austenite boundaries of the nucleation point and particle of family name's body refines austenite, reduces or eliminates in continuous casting billet
Coarse columanar structure provides the tissue of refinement for the production of rear process, can be further improved final products tissue and
Performance
2) heating rate for being conducive to electromagnetic induction coil heating is fast, avoid coarse as-cast structure in rear process into one
Step-length is big, while also shortening heating time, compared with external-heat heating, using the high-temperature residual heat of continuous casting billet, saves blank and exists
The consumed energy during heating；
3) having broken high-intensitive bridge rope steel continuous casting billet must be simplified by the process flow of " two fiery coggings " for iron and steel enterprise
Process, energy-saving and emission-reduction reduce enterprise's production cost, improve the market competitiveness.
Detailed description of the invention
Fig. 1 is continuous casting billet cross section tissue schematic diagram；
Fig. 2 high-strength bridge Suo Gang austenite structure crystal boundary figure when being 1000 DEG C；
Titanium nitride particle pinning high-strength bridge Suo Gang austenite structure crystal boundary figure when Fig. 3 is 1200 DEG C of heating；
Fig. 4 is the titanium nitride particle subgraph in 583 DEG C of high-strength bridge Suo Gang of observation；
Fig. 5 is 582 DEG C of observation acicular ferrites in the big figure of titanium nitride particle director；
Fig. 6 is the austenite structure figure that refines after induction heating；
Fig. 7 is the austenite figure before induction heating.
Specific embodiment
By controlling low-alloy high-strength bridge rope steel chemical composition, heat treatment process parameter is controlled, can more be refined
Tissue more evenly.With reference to the accompanying drawing, the present invention is described in further detail for specific embodiment and comparative example, convenient for more
Be well understood the present invention, but they limiting the invention.
Table 1 is the chemical component list of various embodiments of the present invention and comparative example, and surplus is iron；
Table 2 is various embodiments of the present invention and comparative example electromagnetic induction coil heating process technological parameter list；
Table 3 is that various embodiments of the present invention and comparative example test list.
Table 1 (wt, %)
| Project | C | Si | Mn | P | S | Cr | Nb+V | Ti | N | B |
| Embodiment 1 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.010 | 0.010 | 0.0010 |
| Embodiment 2 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.012 | 0.010 | 0.0010 |
| Embodiment 3 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.015 | 0.010 | 0.0010 |
| Comparative example 1 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.009 | 0.010 | 0.0010 |
| Comparative example 2 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.016 | 0.010 | 0.0010 |
| Comparative example 3 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.012 | 0.010 | 0.0010 |
| Comparative example 4 | 1.01 | 0.96 | 0.65 | 0.008 | 0.007 | 0.35 | 0.61 | 0.012 | 0.010 | 0.0010 |
Table 2
Table 3
Claims (4)
1. a kind of low-alloy high-strength bridge Suo Gang continuous casting square billet thermal treatment production process, it is characterised in that: continuous casting square billet heat treatment
Production technology includes the following steps:
1) molten steel completed is smelted by default ingredient, forms continuous casting square billet after carrying out continuous casting；
2) continuous casting square billet controls continuous casting square billet surface temperature and is cooled to 500~800 by the secondary cooling zone of continuous casting machine fan-shaped segment
DEG C, cooling rate is not more than 200 DEG C/m；
3) continuous casting square billet Jing Guo step 2) is passed sequentially through into multiple electromagnetic induction coils and is heated to 1000~1450 DEG C；
4) it will be heat-fed rolling line after the continuous casting square billet of step 3) is cooled to 500~800 DEG C, or step 3) will be passed through
Continuous casting square billet be cooled to room temperature rear inventory；
Wherein, low-alloy high-strength bridge rope steel chemical composition includes: by weight percentage
C:0.90~1.20wt%, Si:0.90~1.10wt%, Mn:0.60~0.90wt%, P≤0.01wt%, S≤
0.01wt%, Cr:0.20~0.40wt%, Nb+V:0.60~0.80wt%, Ti:0.010~0.015wt%, N:0.005~
0.015wt%, B:0.0005~0.0015wt%, remaining is Fe and inevitable impurity.
2. low-alloy high-strength bridge Suo Gang continuous casting square billet thermal treatment production process according to claim 1, it is characterised in that: institute
It states in step 1), the specification of continuous casting square billet are as follows: continuous casting square billet cross section edge is having a size of 100~200mm.
3. low-alloy high-strength bridge Suo Gang continuous casting square billet thermal treatment production process according to claim 1, it is characterised in that: institute
It states in step 3), the number of electromagnetic induction coil is 1~3, and the length of each electromagnetic induction coil is 2000~5000mm,
The distance between each electromagnetic induction coil and continuous casting square billet surface are 10~300mm.
4. low-alloy high-strength bridge Suo Gang continuous casting square billet thermal treatment production process according to claim 1, it is characterised in that: institute
It states in step 3), 5000~10000A of current strength, the 50~2000Hz of heating frequency of each electromagnetic induction coil, continuous casting square billet
Speed by each electromagnetic induction coil is 0.1~1.0m/min.
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