CN103468902B - Method for improving through-thickness characteristics of thickness-specification high-strength steel - Google Patents
Method for improving through-thickness characteristics of thickness-specification high-strength steel Download PDFInfo
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- CN103468902B CN103468902B CN201310372863.7A CN201310372863A CN103468902B CN 103468902 B CN103468902 B CN 103468902B CN 201310372863 A CN201310372863 A CN 201310372863A CN 103468902 B CN103468902 B CN 103468902B
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Abstract
The invention discloses a method for improving through-thickness characteristics of thickness-specification high-strength steel. The method comprises the following steps: smelting, continuous casting, slab reheating, descaling, rough rolling, finish rolling, cooling, hot straightening and hot thermal treatment, wherein the initial rolling temperature of the rough rolling is 1213-1245 DEG C, the pressing-down rate of at least two gates is more than 25%, the thickness of a middle blank is 1.8-2.5 times of that of a product plate blank, the first gate is rolled initially at the rough rolling stage, and a rack descaling device is adopted for descaling the first gate after steel revolving; the initial rolling temperature of the finish rolling is 861-875 DEG C, the final rolling temperature is 821-838 DEG C, the effective rolling gate number at the finish rolling stage is not more than seven, the rack descaling device is adopt for descaling the first gate at the finish rolling stage; the final cooling temperature is 540-600 DEG C, and the cooling speed is 10-14 DEG C/s. The method can improve the through-thickness characteristics of the 60-80 mm thickness high-strength steel plate, even that of the Q550D high-strength steel plate.
Description
Technical field
The present invention relates to hot rolling and thermal treatment plate of moderate thickness technical field, specifically, relate to a kind of method improving think gauge high-strength steel thickness directional properties.
Background technology
Hi-Stren steel is widely used in all kinds of engineering machinery, particularly 550MPa grade high-strength steel for engineering machinery, is widely used in Electric Motor Wheel and stirs car, mine truck, excavator, dozer, all kinds of lifting machine, coal mine hydraulic supporting etc.These engineering machinery service conditions are harsh, therefore require that steel for engineering machinery has higher intensity, good low-temperature flexibility, good anti-fatigue performance, good cold forming capability, good welding property and good thickness directional properties etc.Particularly thickness directional properties, the use properties of thick steel plates in remarkably influenced.Current, to thick steel plates, particularly the investigation of the thickness directional properties of Q550D steel plate is not harsh.In actual production, the thickness direction relative reduction in area of thick steel plates only can reach 10-20%.Along with engineering machinery more and more maximize, high efficiency, to thick steel plates, particularly the demand of Q550D steel plate also gets more and more, simultaneously to thick steel plates, particularly the performance requriements of Q550D steel plate is also harsh gradually, and its thickness directional properties also will receive publicity.
Prior art is all in most cases take optimized alloy design, control inclusion, the mode such as compression ratio, normalizing treatment that increases to promote think gauge high-strength steel thickness directional properties.
Summary of the invention
Technical problem to be solved by this invention is to provide a kind of method improving think gauge high-strength steel thickness directional properties, can improve the thickness directional properties of 60mm-80mm think gauge High Strength Steel Plate, particularly the thickness directional properties of Q550D high-strength steel.
Technical scheme of the present invention is as follows:
Improve a method for think gauge high-strength steel thickness directional properties, comprising: smelting, continuous casting, slab reheat, de-scaling, roughing, finish rolling, cooling, hot straightening and thermal treatment, wherein; The start rolling temperature of described roughing is 1213-1245 DEG C, 2 percentage pass reductions are had at least to be greater than 25%, the thickness of intermediate blank be the 1.8-2.5 of the thickness of finished product slab doubly, rough rolling step open rolling first passage, turn steel after the first passage take frame scale removal equipment to carry out de-scaling; The start rolling temperature of described finish rolling is 861-875, and finishing temperature is 821-838 DEG C, and the finish rolling stage, effective rolling pass number was no more than 7 roads, and finish rolling stage open rolling first passage takes frame scale removal equipment to carry out de-scaling; The final cooling temperature of described cooling is 545-598 DEG C, and the speed of described cooling is 10-14 DEG C/s.
Further: the Tapping Temperature of Bof of described smelting is 1620-1660 DEG C, the vacuum tightness of vacuum outgas is 0.20 ~ 0.25Kpa, dark vacuum time > 10min.
Further: the molten steel overheat of described continuous casting is 15-50 DEG C, the speed of cast is 0.8-1.2m/min, C class center segregation≤2.0 grade of continuously cast bloom, middle crack≤1.5 grade, center porosity≤1.0 grade.
Further: described slab reheats and comprises heating zone and soaking zone, the temperature that described slab reheats is 1220-1260 DEG C, described in time of reheating be 360-400 minute, the time of described soaking zone is 50-80 minute.
Further: described thermal treatment process is tempering process, the temperature of described tempering is 680-700 DEG C, and the time of described tempering is 30-50 minute.
Further: the thickness of described think gauge high-strength steel is 60mm-80mm.
Further, the mass percentage producing the chemical composition of the material of the described think gauge high-strength steel obtained comprises: C0.06-0.10%, Si0.15-0.40%, Mn1.5-1.8%, P≤0.015%, S≤0.005%, Als >=0.020%, Nb0.035-0.060%, V0.035-0.070%, Ti0.008-0.015%, Cr0.30-0.60%, Mo0.15-0.25%, and surplus is Fe and other impurity.
Technique effect of the present invention is as follows:
1, of the present inventionly 60mm-80mm think gauge High Strength Steel Plate, the particularly thickness directional properties of Q550D High Strength Steel Plate can be improved.
2, the average section shrinking percentage of think gauge High Strength Steel Plate of the present invention reaches 43%, and minimum cross section shrinking percentage is 38%, reaches Z35 rank.
Accompanying drawing explanation
Fig. 1 is the metallograph (thickness specification 80mm) of the embodiment of the present invention 3.
Embodiment
Production technique of the present invention is based on TMCP (Thermo Mechanical Control Process, thermomechanical Controlling Technology) and temper technique.Its key step comprises: smelting, continuous casting, slab reheat, de-scaling, roughing, finish rolling, cooling, hot straightening and thermal treatment.Preferred embodiment of the present invention selects the slab of think gauge Q550D high-strength steel as original slab.The percent mass of the chemical composition of original slab is: C0.06-0.15%, Si0.15-0.50%, Mn1.4-1.8%, P≤0.015%, S≤0.005%, Als (dissolved aluminum) 0.0200.045%, Nb0.035-0.050%, V0.035-0.070%, Ti0.008-0.015%, Cr0.15-0.40%, Mo0.10-0.20%, surplus is Fe and inevitable impurity.
Specific embodiment is as follows:
Step S1: smelt
Molten iron need carry out dark desulfurization through pre-treatment, then carries out converter smelting.Adopt single slag technique to smelt, low carbon ferromanganese and silumin deoxidation alloying, tapping pushing off the slag, ensure a catch carbon success, Tapping Temperature of Bof controls at 1620-1660 DEG C.Molten steel carries out LF external refining after converter smelting, and this stage, to molten steel gold conjugate, guarantees alloy hit.RH operation mainly carries out vacuum outgas, ensureing significantly to reduce the gas contents such as hydrogen, oxygen, nitrogen under the prerequisite that liquid steel temperature is stable, reducing obnoxious flavour to the disadvantageous effect of Molten Steel Cleanliness, does not add in principle or add alloy less treatment stage of RH.The vacuum tightness of vacuum outgas is 0.20 ~ 0.25Kpa, dark vacuum time > 10min.
Step S2: continuous casting
Smelt successful molten steel to deliver to casting machine and carry out continuous casting, control molten steel overheat 15-50 DEG C.Continuous caster is straight curved type continuous caster, detailed process and state modulator as follows: use low-carbon high-manganese steel alloy covering slag, bits will keep dry; Middle bag uses alkaline hollow particle carbon-free covering agent; Keep constant speed cast, pouring speed controls at 0.8-1.2m/min; Carry out molding casting, guard against secondary oxidation of steel and air-breathing nitrogen pick-up; Strand macroscopic examination result should meet C class center segregation≤2.0 grade, middle crack≤1.5 grade, center porosity≤1.0 grade.
Step S3: slab reheats
When continuous casting of molten steel becomes base, temperature is cooled to spend cool to room temperature again 1200 from more than 1500 degree more, and slab reheats and refers to that slab is elevated to degree more than 1200 from room temperature again, the heat-processed that temperature raises again.
Slab reheats process to carry out in pusher-type furnace or walking beam furnace.The formulation reheating temperature depends on the solubleness of alloying element.Heat-processed requires suitable temperature and rational time, promotes abundant dissolving and composition, the homogeneous microstructure of alloying element.Generally, the solvent temperature of alloying element carbon (nitrogen) compound is about 1150 DEG C-1200 DEG C.In order to promote the abundant dissolving of alloying element carbon (nitrogen) compound, and consider on-the-spot actual production conditions, the process that reheats of the present invention comprises heating zone and soaking zone, because heating zone slab internal-external temperature difference is very large, needs finally to carry out soaking even to ensure board briquette.What slab reheated reheats temperature is 1220-1260 DEG C, and rethermalization time is 360-400 minute, wherein soaking time 50-80 minute.
Step S2: dephosphorization
Slab can generate severe oxidation iron sheet reheating surface in process, and therefore, slab needs after coming out of the stove to carry out de-scaling to eliminate its scale on surface.Slab adopts high-pressure water descaling, requires that de-scaling pressure is not less than 18MPa.
Step S3: roughing
Slab is delivered to roughing mill and is carried out roughing after de-scaling.Roughing is divided into three phases: truing phase, broadening stage and high temperature extend the stage.Truing phase eliminates the defect such as uneven of steel slab surface, and promotes that slab thickness is even.Width of plate slab is mainly increased to finished width by the broadening stage.It is generally acknowledged, truing phase and broadening stage can not produce obviously impact to plate property.The high temperature extension stage will give full play to mill capacity, realizes powerful large pressure, with minimum road number of times, slab is rolled workpiece thickness, and promotion austenite crystal repeatedly recrystallize, with crystal grain thinning, requires that roughing high temperature extends stage effective rolling pass number and is no more than 8 roads.The start rolling temperature of roughing of the present invention is 1213-1245 DEG C, has at least 2 percentage pass reductions to be greater than 25%, and the thickness of intermediate blank is 1.8-2.5 times of the thickness of finished product slab.Rough rolling step open rolling first passage, turn steel after the first passage frame scale removal equipment must be taked to carry out de-scaling, high temperature extend the stage carry out de-scaling flexibly depending on surface of steel plate situation, ensure plate surface quality.
Step S4: finish rolling
The finish rolling stage is from intermediate blank temperature drops to after austenite Unhydrated cement.Slab is rolled into through rough rolling step and the roller-way after intermediate blank between roughing mill and finishing mill carries out swing treats temperature, and intermediate blank temperature is transported to finishing mill and carries out finish rolling stage rolling after being reduced to finish rolling stage start rolling temperature scope.Finish rolling stage open rolling first passage must take frame scale removal equipment to carry out de-scaling, de-scaling is carried out flexibly depending on surface of steel plate situation in the finish rolling operation of rolling, ensure plate surface quality, do not allow to carry out dephosphorization after steel plate thickness is less than 20mm, prevent frame de-scaling water from being started by steel plate and cause industrial accident.The finish rolling stage carries out at austenite Unhydrated cement, and the distortion of this stage builds up, and promotes austenite crystal " flattening " on the one hand, forms a large amount of dislocation on the other hand at austenite crystal intragranular, increases ferrite crystal grain nucleation site, crystal grain thinning.Require that finish rolling stage effective rolling pass number is no more than 7 roads.The effect of Nb element significantly suppress austenite crystal recrystallize, improve austenite Unhydrated cement temperature, consider that the steel plate of finished product is thicker, after finish to gauge, steel billet temperature is too high simultaneously, finish rolling start rolling temperature of the present invention is 861-875 DEG C, and finishing temperature is 821-838 DEG C.
Step S5: cooling
The present invention adopts acceleration cooling system (ACC) to control Cooling Process for Steel Plate Based.Steel plate is after controlled rolling, austenite crystal is elongated in " flattening ", intra-die accumulation has a large amount of dislocation and born of the same parents' shape substructure, deformed austenite " excessively cold " under larger cooling rate effect, promote cenotype under larger phase driving force effect in deformed austenite and grain boundaries forming core, form the bainite structure of fine uniform.The final cooling temperature 545-598 DEG C of cooling of the present invention, speed of cooling 10-14 DEG C/s.Carry out in accelerating cooling process at steel plate, in order to ensure steel plate integral head, afterbody, edge and plate body homogeneous temperature, need to adopt and cover end to end and edge-masking, general head shadow 0-2.0m, afterbody covers 0-2.5m, edge-masking 0-2.0m, control steel plate return red rear bulk temperature poor≤50 DEG C.
Step S6: hot straightening
Steel plate out needs to carry out hot straightening process afterwards from ACC and has good profile to make steel plate, considers steel plates straightening difficulty and thermal straightening machine ability, requires that steel plates straightening temperature is 400-1000 DEG C.If steel plate a time can not leveling, multi-pass can be adopted to align, but be no more than 3 passages in principle, steel plate roughness≤6mm/2m.The specification that steel plate after hot straightening becomes to require by shearing post-treatment.
Straightening temperature is greater than 1000 DEG C, and temperature is too high, and straightener cannot work, because straightener cooling itself is limited in one's ability, straightener can be scorched, and after the very high aligning of temperature, steel plate also can be out of shape, and loses the meaning of aligning.Temperature is too hard lower than 400 DEG C of steel plates, and thermal straightening machine also meeting limited in one's ability " is rectified motionless ".Straightening temperature determines primarily of steel plate final cooling temperature, and steel plate just starts aligning after about about 1 minute after going out ACC, general straightening temperature 20-30 DEG C lower than whole cold red temperature.
Step S7: thermal treatment
Thermal treatment process is tempering process.Tempering can eliminate the internal stress of steel plate, promotes low carbon in steel shellfish
Family name's body matrix recovers, and promotes the decomposition on martensite (M)/austenite (A) island in steel simultaneously and makes carbide dispersion be distributed on low-carbon bainite (B) matrix, promotes the toughness of steel plate.The tempering temperature of thermal treatment process of the present invention is 680-700 DEG C, and tempering time is 30-50 minute.
To the steel plate sampling after thermal treatment, inspection.The finished product warehouse-in be up to the standards, delivery.
Because production technique is very little to the composition influence of steel plate materials, the mass percentage of the chemical composition of the material of the think gauge high-strength steel therefore obtained is: C0.06-0.15%, Si0.15-0.50%, Mn1.4-1.8%, P≤0.015%, S≤0.005%, Als >=0.020%, Nb0.035-0.050%, V0.035-0.070%, Ti0.008-0.015%, Cr0.15-0.40%, Mo0.10-0.20%, surplus is Fe and inevitable impurity.
The thickness of the think gauge high-strength steel of finished product is 60mm-80mm.
Embodiment 1-6
The slab of the plan rolling by smelting, after continuous casting through reheating, de-scaling, roughing, finish rolling, be rolled into certain thickness steel plate, the processing parameter of heating, roughing and finish rolling is in table 1, and the processing parameter of cooling and tempering is in table 2, and its mechanical property is in table 3.Fig. 1 is the metallograph (thickness specification 80mm) of the embodiment of the present invention 3.
The processing parameter of the heating of table 1 embodiment 1-6, roughing and finish rolling
The cooling of table 2 embodiment 1-6 and the processing parameter of tempering
The mechanical property of table 3 embodiment 1-6
As can be seen from embodiment, present invention employs suitable rate of cooling and promote steel plate deformation, austenite phase transformation; Have employed higher tempering temperature, promote steel plate M/A to decompose and the recovery of bainite matrix; Have employed suitable tempering time, promote the distribution of steel plate carbide dispersion.
In sum, the average section shrinking percentage of think gauge high-strength steel of the present invention reaches 43%, and minimum cross section shrinking percentage is 38%, reaches Z35 rank.
Claims (7)
1. improve a method for think gauge high-strength steel thickness directional properties, it is characterized in that, comprising: smelting, continuous casting, slab reheat, de-scaling, roughing, finish rolling, cooling, hot straightening and thermal treatment, wherein; The start rolling temperature of described roughing is 1213-1245 DEG C, 2 percentage pass reductions are had at least to be greater than 25%, the thickness of intermediate blank be the 1.8-2.5 of the thickness of finished product slab doubly, rough rolling step open rolling first passage, turn steel after the first passage take frame scale removal equipment to carry out de-scaling; The start rolling temperature of described finish rolling is 861-875, and finishing temperature is 821-838 DEG C, and the finish rolling stage, effective rolling pass number was no more than 7 roads, and finish rolling stage open rolling first passage takes frame scale removal equipment to carry out de-scaling; The final cooling temperature of described cooling is 545-598 DEG C, and the speed of described cooling is 10-14 DEG C/s.
2. the method improving think gauge high-strength steel thickness directional properties as claimed in claim 1, it is characterized in that: the Tapping Temperature of Bof of described smelting is 1620-1660 DEG C, the vacuum tightness of vacuum outgas is 0.20 ~ 0.25KPa, dark vacuum time > 10min.
3. the method improving think gauge high-strength steel thickness directional properties as claimed in claim 1, it is characterized in that: the molten steel overheat of described continuous casting is 15-50 DEG C, the speed of cast is 0.8-1.2m/min, C class center segregation≤2.0 grade of continuously cast bloom, middle crack≤1.5 grade, center porosity≤1.0 grade.
4. the method improving think gauge high-strength steel thickness directional properties as claimed in claim 1, it is characterized in that: described slab reheats and comprises heating zone and soaking zone, the temperature that described slab reheats is 1220-1260 DEG C, the described time reheated is 360-400 minute, and the time of described soaking zone is 50-80 minute.
5. the method improving think gauge high-strength steel thickness directional properties as claimed in claim 1, it is characterized in that: described thermal treatment process is tempering process, the temperature of described tempering is 680-700 DEG C, and the time of described tempering is 30-50 minute.
6. the method improving think gauge high-strength steel thickness directional properties as claimed in claim 1, is characterized in that: the thickness of described think gauge high-strength steel is 60mm-80mm.
7. the method improving think gauge high-strength steel thickness directional properties as claimed in claim 1, it is characterized in that, the mass percentage producing the chemical composition of the material of the described think gauge high-strength steel obtained comprises: C 0.06-0.10%, Si 0.15-0.40%, Mn 1.5-1.8%, P≤0.015%, S≤0.005%, Als >=0.020%, Nb 0.035-0.060%, V 0.035-0.070%, Ti 0.008-0.015%, Cr0.30-0.60%, Mo 0.15-0.25%, surplus is Fe and other impurity.
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| CN103831296B (en) * | 2014-02-21 | 2017-05-24 | 内蒙古包钢钢联股份有限公司 | Method for improving single-pass reduction rate at moderate-thickness plate rough rolling high-temperature extending stage |
| CN103805863B (en) * | 2014-02-24 | 2016-04-20 | 内蒙古包钢钢联股份有限公司 | The production technique of high-strength high-toughness steel plate |
| CN105734426A (en) * | 2014-12-10 | 2016-07-06 | 新疆八一钢铁股份有限公司 | Production process for Q235B steel plate |
| CN105463170B (en) * | 2015-11-12 | 2017-10-13 | 内蒙古包钢钢联股份有限公司 | The production method of 36Kg grades of offshore platform steel plates |
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| CN102691000A (en) * | 2012-06-18 | 2012-09-26 | 内蒙古包钢钢联股份有限公司 | Steel plate for engineering machinery and rolling and heat treatment technologies thereof |
| CN102747278A (en) * | 2012-07-02 | 2012-10-24 | 山西太钢不锈钢股份有限公司 | Manufacturing method of steel plate for pressure vessel |
| CN103014282A (en) * | 2012-12-21 | 2013-04-03 | 首钢总公司 | Production method of high-strength and good-low-temperature-toughness wind power steel plate |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102691000A (en) * | 2012-06-18 | 2012-09-26 | 内蒙古包钢钢联股份有限公司 | Steel plate for engineering machinery and rolling and heat treatment technologies thereof |
| CN102747278A (en) * | 2012-07-02 | 2012-10-24 | 山西太钢不锈钢股份有限公司 | Manufacturing method of steel plate for pressure vessel |
| CN103014282A (en) * | 2012-12-21 | 2013-04-03 | 首钢总公司 | Production method of high-strength and good-low-temperature-toughness wind power steel plate |
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