CN103215504B - Production method of easily formable high-strength medium-thick steel plate - Google Patents

Abstract

The invention relates to a production method of an easily formable high-strength medium-thick steel plate. The method comprises the following process steps: converter steelmaking, ladle furnace refining, vacuum treatment vacuum treatment, continuous casting, heating, rolling, pre-straightening, on-line quenching and tempering heat treatment. The mass percent composition of the steel is as follows: C = 0.07-0.09, Si = 0.15-0.30, Mn = 1.55-1.80, P <= 0.015, S <= 0.005, Nb + V + Ti <= 0.10, Cr + Mo <= 0.5, Alt= > 0.020, and Pcm <= 0.23. The Q800F steel plate with a thickness of 200mm produced by the method is good in cold bending, and the cold bending property of the steel plate real object meets the easily forming requirement of users; the yield ratio of the steel plate is smaller than 0.92, and the uniform elongation rate is larger than 8%, which meets the use requirements of relevant designs; the product of strength and elongation is increased by more than 35%, the capacity of resisting dynamic loading of the high strength steel plate is increased, and the equipment safety is improved; through hot charging and on-line quenching of the continuous casting, the production cost is reduced; and with the component design in which Pcm is smaller than 0.23%, the welding properties welding property of the high strength steel plate is improved.

Description

A kind of production method of easy-formation high-strength medium plate

Technical field

The invention belongs to steel-smelting technology, is the production method of the high-strength steel plate of a kind of easy-formation.

Background technology

Along with the development of metallurgical industry, the production of surrender more than 550MPa High Strength Steel Plate there occurs huge change, from traditional quench in furnace+tempering (i.e. RQ+T) technological development to TMCP, TMCP+T, DQ+T, Q+P, Q+P+T, particularly rolled rear online direct quenching ((Direct Quenching in recent years, be called for short DQ)) technique obtains significant progress, is widely used in the production of High Strength Steel Plate.

The High Strength Structural Steel of present DQ explained hereafter is compared with the High Strength Structural Steel of other explained hereafter, significantly can reduce alloying element content when mechanical property is suitable and reduce carbon equivalent, improve the processing performance such as welding, receive efficient, material-saving, the energy-conservation and multiple effect that lowers consumption; When roughly the same composition, compared with other techniques higher, the plasticity of armor plate strength and toughness better, routine inspection all can meet the requirement of technical qualification of delivering goods.But in actual use, the yield tensile ratio of steel plate is high, particularly steel plate cold bending cracking causes processability poor, and user proposes quality objection in a large number, the high strength structure plate that refusal uses DQ to produce.

Carefully analyze discovery, the high tensile steel plate dislocation desity of DQ explained hereafter is high, yield strength is high, causes yield tensile ratio high.Delivery requirements cold-bending property verifies as narrow clod wash sample, and the requirement of the actual use of user is cold roll forming is wide clod wash; Find evenly to extend low during steel plate stretching inspection, stretching fracture be ductile rupture really but there is layering, be typical brittle rupture with layered face.

Thick High Strength Steel Plate delivery technical qualification in low yield strength ratio Q800F: chemical composition requires as table 1, factory can add wherein one or more alloying elements as required, maximum value should meet in table and specifies, its content should be reported in quality certificate, a kind of crystal grain thinning element in Nb, Ti, V, Al at least should be added in steel, wherein the minimum of at least one element is 0.015%(is Als for Al), also Alt substitute for Al s can be used, now minimum is 0.018%, CEV=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15; Mechanical property requirements is as table 2, and tension test is applicable to horizontal sample, and shock test is applicable to longitudinal test piece, when yield phenomenon is not obvious, adopts Rp _0.2.

Table 1 thickness≤50mmQ800F steel chemical composition requires (%)

Table 2 thickness≤50mmQ800F steel mechanical property requirement

DQ explained hereafter High Strength Steel Plate patent is as Chinese patent application 200910046581.1 " a kind of ultrafine crystal bainite high-strength steel and manufacture method thereof ", 201010101815.0 " a kind of low cost yield strength 700MPa Micro Alloying process high tensile steel plate and manufacture method thereof ", 201210011762.2 " the easy welding high-strength steel plate of low yield strength ratio and preparation technologies thereof ", 201110181602.8 " adopting the method for direct quenching explained hereafter petroleum storage tank steel plate for ultra ".Wherein first three items is TMCP explained hereafter High Strength Steel Plate, and latter one what adopt is DQ+T explained hereafter High Strength Steel Plate, but causes that steel plate yield tensile ratio is high, steel plate uniform elongation is low containing B in steel plate composition, cold roll forming cracking.

In a word, the high tensile steel plate that traditional direct quenching+tempering process (DQ+T) is produced has following shortcoming: all containing B element in steel plate composition, steel plate hardening capacity is good, produce armor plate strength high, impact high, unit elongation is higher, but evenly extend < 7%, steel plate yield tensile ratio > 0.96; Steel plate yield tensile ratio is high, is difficult to the actual operation requirements meeting related design; Steel plate evenly extends low, and during steel plate stretching test, demixing phenomenon appears in fracture, and user thinks that steel plate exists demixing phenomenon; Steel plate is qualified according to standard regulation inspection by sampling clod wash, but wide clod wash and actual steel plate bending major part cracking, i.e. cold roll forming poor performance; Steel plate rolls speed of cooling > 35 DEG C/s in rear traditional DQ technique, causes yield tensile ratio uncontrolled.

Summary of the invention

This patent purport has the production method providing the high-strength steel plate of a kind of easy-formation, and producing thickness is thick High Strength Steel Plate in 8 ~ 30mm easy-formation, easily welding, low yield strength ratio Q800F, meets the demand of the manufacturing such as engineering machinery, mine equipment.

Technical scheme of the present invention:

A production method for the high-strength steel plate of easy-formation, its processing step is converter steelmaking → ladle furnace refining → vacuum-treat → continuous casting → heating → rolling → pre-straightening → press quenching → tempering heat treatment.It is characterized in that:

The percent mass of steel consists of: C=0.07 ~ 0.09, Si=0.15 ~ 0.30, Mn=1.60 ~ 1.80, P≤0.015, S≤0.005, Nb+V+ Ti≤0.10, Cr+ Mo≤0.50, Alt >=0.020, Pcm≤0.23.

Main technological steps is:

A. converter steelmaking: molten steel sulfur content controls at S≤0.020%, temperature >=1250 DEG C, slag is taken off totally before entering converter by molten iron; Converter terminal control objectives is that C-T coordinates tapping P≤0.015%, S≤0.020%; Slag-stopping tapping slag is thick≤50mm, tapping time 4 ~ 7min; Tapping 1/5 adds alloy, and tapping 2/5 adds alloy; Squeeze into Al line after tapping and be no less than 250 ~ 300m deoxidation.

B. ladle furnace refining: LF stove control molten steel conduction time >=20min, total argon blowing time >=40 minute, white slag hold-time >=15min; Feed Al line and adjust Alt, molten steel goes out to stand firm oxygen≤5ppm; Feed SiCa line or FeCa line 400 ~ 700m during departures, carry out the operation of soft blow argon to molten steel before departures, soft argon blowing time should be greater than 5min; VD stove controls molten steel and enters the omnidistance Argon of VD stove, total argon blowing time >=35 minute; Vacuumize target 0.5 below tor, the hold-time is not less than 15min; Molten steel goes out the soft blow of VD stokehold and is greater than 12 minutes, continuous casting platform temperature 1555 ~ 1565 DEG C in departures.

C. continuous casting: target molten steel overheat 15 DEG C, liquidus temperature 1517 DEG C, middle bag representative temperature 1527-1537 DEG C; It is 1.3 m/min, 1.2m/min, 1.0m/min, 0.8 m/min. that the maximum pulling rate of slab thickness 180 mm, 220mm, 260mm, 300mm is respectively.

D. rolling: process furnace heating zone temperature 1210 ~ 1240 DEG C, soaking zone temperature 1200 ~ 1220 DEG C, slab adopts the heating of hot charging stove, rate of heating 6 ~ 10min/cm; Roughing stage start rolling temperature>=1050 DEG C, finishing temperature>=980 DEG C, workpiece thickness is more than or equal to 3 times of finished product thicknesses, stage rolling adopts large reduction system, has continuous 2 percentage pass reduction>=15% after ensureing broadening; Finish rolling stage start rolling temperature 880 ~ 1000 DEG C, finishing temperature 830 ~ 920 DEG C, several percentage pass reduction>=13% before finish rolling.

E. press quenching: open cold temperature >=800 DEG C, final cooling temperature≤160 DEG C, cooling rate 25 ~ 35 DEG C/s.

F. tempering heat treatment: tempering temperature 630 ~ 650 DEG C, tempering time (thickness of slab+70) min, air cooling.

Patent of the present invention possesses the High Strength Steel Plate feature of easy-formation, is organized as tempering ferrite bainite+tempering acicular ferrite+a small amount of tempering granular bainite.Its know-why is the speed of cooling controlling press quenching, the dislocation desity of steel plate after reduction press quenching, thus the yield tensile ratio reducing yield strength, reduction steel plate; The content that B element improves acicular ferrite after steel plate quenching is not added in steel, thus even extension when increasing substantially steel plate deformation; The raising of even extension and dislocation desity reduce the possibility decreasing steel plate Transverse Cracks when cold roll forming; The Composition Design of below Pcm0.23%, improves the welding property of steel plate, and this steel plate can normal weld under the condition of not preheating and low preheating; Hot-cast base directly fills and press quenching reduces the fuel consumption of heating; The measures such as significantly reduction, the removal of out-line quenching operational path, the direct shove charge of hot-cast base of alloy, significantly reduce the production cost of steel plate.

Therefore, compared with the high-strength steel technology of existing DQ explained hereafter, the present invention has the following advantages: the wide clod wash of steel plate 200mm is intact, and steel plate cold-bending property in kind meets the requirement of user's easy-formation; Steel plate yield tensile ratio is less than 0.92, and uniform elongation is greater than 8%, meets the service requirements of relevant design; Strength and ductility product improves more than 35%, improves High Strength Steel Plate opposing Dynamic Loading ability, improves the security of equipment; Hot charging and the press quenching of continuously cast bloom reduce production cost; The Composition Design of below Pcm0.21%, improves the welding property of High Strength Steel Plate.

Accompanying drawing explanation

Fig. 1, Fig. 2 are respectively Q800F steel metallographic structure figure, the stress strain curve figure that the inventive method is produced.

Embodiment

Embodiment 1:20mmQ800F Plate Production method

The chemical constitution of steel is as table 3.

Table 3 20mm Q800F steel plate composition actual achievement (%)

Chemical Composition	C	Si	Mn	P	S	Nb+V+ Ti	Cr+ Mo	Alt	Pcm	CEV
											Actual achievement	0.07	0.21	1.68	0.014	0.002	0.067	0.45	0.032	0.22	0.52

Main technological steps:

A. molten steel sulfur content S≤0.020%, temperature >=1250 DEG C, must take off slag totally before molten iron enters converter.Converter terminal control objectives: C-T coordinates tapping, P 0.012%, S 0.015%; Strict slag-stopping tapping, slag is thick≤50mm, tapping time 7min, tapping 1/5 adds alloy, and tapping 2/5 adds alloy; Al line 290m deoxidation is squeezed into after tapping.

B. molten steel is at LF stove 22min conduction time, total argon blowing time 42min, white slag hold-time 16min.Feed Al line and adjust Alt, argon station process molten steel terminates Als0.042%, and molten steel goes out to stand firm oxygen 4ppm.Fe-Ca line is fed, feed quantity 530m during departures.The operation of soft blow argon is carried out to molten steel, soft argon blowing time 6min before departures.Molten steel entered VD stove and namely opens omnidistance Argon, the total argon blowing time of VD stove 37 minutes.Vacuumize 0.4 tor, hold-time 16min.The compositions such as C, Si, Mn in molten steel are finely tuned.Molten steel goes out VD stokehold soft blow 15min.The upper continuous casting platform temperature 1562 DEG C of molten steel departures.

C. tundish temperature 1528 DEG C, pulling rate 1.0m/min.Continuous casting becomes 260X2280 section slab.

D. process furnace heating zone temperature controls at 1230 ~ 1240 DEG C, and soaking zone temperature controls at 1210 ~ 1220 DEG C.Hot slab rate of heating 9min/cm. stage start rolling temperature 1060 DEG C, finishing temperature 990 DEG C.Workpiece thickness 75mm, continuous 2 percentage pass reduction >=18%, finished product thickness 20mm. stage start rolling temperature 910 DEG C, finishing temperature 870 DEG C.

E. press quenching: open cold temperature 850 DEG C, speed of cooling 33 DEG C/s, final cooling temperature 68 DEG C.

F. tempering temperature 640 DEG C, tempering time 90 min, air cooling.

Actual measurement sample plate property: yield strength 852MPa, tensile strength 928MPa, yield tensile ratio 0.92, unit elongation 19.5%, uniform elongation 9.1%, the wide clod wash of 200mm (D=3a, 180 °) intact ,-60 DEG C of ballistic work Kv ₂mean value 218J.

Embodiment 2:30mmQ800F Plate Production method

The chemical constitution of steel is as table 4.

Table 4 30mm Q800F steel plate composition actual achievement (%)

Chemical Composition	C	Si	Mn	P	S	Nb+V+ Ti	Cr+ Mo	Alt	Pcm	CEV
											Actual achievement	0.08	0.23	1.67	0.013	0.003	0.110	0.93	0.034	0.23	0.59

Main technological steps:

A. molten steel sulfur content S≤0.020%, temperature >=1250 DEG C, must take off slag totally before molten iron enters converter.Converter terminal control objectives: C-T coordinates tapping, P 0.013%, S 0.016%; Strict slag-stopping tapping, slag is thick≤50mm, tapping time 6min, tapping 1/5 adds alloy, and tapping 2/5 adds alloy; Al line 300m deoxidation is squeezed into after tapping.

B. molten steel is at LF stove 22min conduction time, total argon blowing time 44min, white slag hold-time 16min.Feed Al line and adjust Alt, argon station process molten steel terminates Als0.039%, and molten steel goes out to stand firm oxygen 4ppm.Fe-Ca line is fed, feed quantity 580m during departures.The operation of soft blow argon is carried out to molten steel, soft argon blowing time 6min before departures.Molten steel entered VD stove and namely opens omnidistance Argon, the total argon blowing time of VD stove 37 minutes.Vacuumize 0.4 tor, hold-time 16min.The compositions such as C, Si, Mn in molten steel are finely tuned.Molten steel goes out VD stokehold soft blow 17min.The upper continuous casting platform temperature 1560 DEG C of molten steel departures.

C. tundish temperature 1530 DEG C, pulling rate 1.0m/min.Continuous casting becomes 260 X 2280 section slabs.

D. process furnace heating zone temperature controls at 1220 ~ 1230 DEG C, and soaking zone temperature controls at 1200 ~ 1220 DEG C.Hot slab rate of heating 8.5min/cm. stage start rolling temperature 1050 DEG C, finishing temperature 980 DEG C.Workpiece thickness 90mm, continuous 2 percentage pass reduction >=19%, finished product thickness 30mm. stage start rolling temperature 880 DEG C, finishing temperature 860 DEG C.

E. press quenching: open cold temperature 830 DEG C, speed of cooling 26 DEG C/s, final cooling temperature 59 DEG C.

F. tempering temperature 630 DEG C, tempering time 100min, air cooling.

Actual measurement sample plate property: yield strength 848MPa, tensile strength 932 MPa, yield tensile ratio 0.91, unit elongation 20.2%, uniform elongation 9.4%, the wide clod wash of 200mm (D=3a, 180 °) intact ,-60 DEG C of ballistic work Kv ₂mean value 216J.

Claims (1)

1. a production method for the high-strength steel plate of easy-formation, processing step is converter steelmaking → ladle furnace refining → vacuum-treat → continuous casting → heating → rolling → pre-straightening → press quenching → tempering heat treatment, it is characterized in that:

The percent mass of steel consists of: C=0.07 ~ 0.09, Si=0.15 ~ 0.30, Mn=1.60 ~ 1.68, P≤0.015, S≤0.005, Nb+V+ Ti≤0.10, Cr+ Mo≤0.50, Alt >=0.020, Pcm≤0.23, and all the other are Fe and inevitable impurity element; Steel plate is organized as tempering ferrite bainite+tempering acicular ferrite+tempering granular bainite;

Critical process step is:

A .converter steelmaking: molten steel sulfur content controls at S≤0.020%, temperature>=1250 DEG C, slag is taken off totally before entering converter by molten iron; Converter terminal control objectives is that C-T coordinates tapping P≤0.015%, S≤0.020%; Slag-stopping tapping slag is thick≤50mm, tapping time 4 ~ 7min; Tapping 1/5 adds alloy, and tapping 2/5 adds alloy; Squeeze into Al line after tapping and be no less than 250 ~ 300m deoxidation;

B .ladle furnace refining: LF stove control molten steel conduction time>=20min, total argon blowing time>=40 minute, white slag hold-time>=15min; Feed Al line and adjust Alt, molten steel goes out to stand firm oxygen≤5ppm; Feed SiCa line or FeCa line 400 ~ 700m during departures, carry out the operation of soft blow argon to molten steel before departures, soft argon blowing time should be greater than 5min; VD stove controls molten steel and enters the omnidistance Argon of VD stove, total argon blowing time>=35 minute; Vacuumize target 0.5 below tor, the hold-time is not less than 15min; Molten steel goes out the soft blow of VD stokehold and is greater than 12 minutes, continuous casting platform temperature 1555 ~ 1565 DEG C in departures;

C .continuous casting: target molten steel overheat 15 DEG C, liquidus temperature 1517 DEG C, middle bag representative temperature 1527-1537 DEG C; It is 1.3 m/min, 1.2m/min, 1.0m/min, 0.8 m/min that the maximum pulling rate of slab thickness 180 mm, 220mm, 260mm, 300mm is respectively;

D .rolling: process furnace heating zone temperature 1210 ~ 1240 DEG C, soaking zone temperature 1200 ~ 1220 DEG C, slab adopts the heating of hot charging stove, rate of heating 6 ~ 10min/cm; Roughing stage start rolling temperature>=1050 DEG C, finishing temperature>=980 DEG C, workpiece thickness is more than or equal to 3 times of finished product thicknesses, stage rolling adopts large reduction system, has continuous 2 percentage pass reduction>=15% after ensureing broadening; Finish rolling stage start rolling temperature 880 ~ 1000 DEG C, finishing temperature 830 ~ 920 DEG C, several percentage pass reduction>=13% before finish rolling;

E .press quenching: open cold temperature>=800 DEG C, final cooling temperature≤160 DEG C, cooling rate 25 ~ 35 DEG C/s;

F .tempering heat treatment: tempering temperature 630 ~ 650 DEG C, tempering time (thickness of slab+70) min, air cooling.