CN105420632A - Q690CF hot-rolled steel plate and preparation method thereof - Google Patents

Abstract

The invention discloses a Q690CF hot-rolled steel plate and a preparation method thereof. The Q690CF hot-rolled steel plate is composed of, by mass, 0.05%-0.08% of C, 0.22%-0.30% of Si, 1.6%-2.0% of Mn, 0.2%-0.35% of Al, 0.10%-0.35% of Cr, 0.20%-0.35% of Mo, 0.1%-0.4% of Ni, 0.15%-0.3% of Cu, 0.025%-0.045% of Nb, 0.01%-0.03% of V, 0.005%-0.03% of Ti, 0-0.010% of P, 0-0008% of S, the balance Fe and unavoidable impurities. The preparation method comprises the steps of smelting, pretreatment, hot rolling, multi-pass rough rolling and finish rolling and rapid cooling. The hot-rolled steel plate is high in strength and good in low-temperature toughness and welding property, and non-preheating welding is achieved. The preparation cost is low and the technique is simple.

Description

A kind of Q690CF hot-rolled steel sheet and preparation method thereof

Technical field

The invention belongs to high-strength steel production technology development field, particularly a kind of Q690CF hot-rolled steel sheet and preparation method thereof.

Background technology

In recent years, Steel Structure Work all develops to maximization, lightweight, high-parametersization, as Longspan Bridge, large sized hydropower station, heavy engineering machinery etc.This claimed structure steel has more high strength, better toughness, plasticity and welding property.Heavy construction is built and is adopted High Strength Structural Steel, means and can reduce raw materials cost, lightening material weight while meeting high-load condition.But High Strength Structural Steel often brings the reduction of toughness.In addition, for high-strength hardened and tempered steel, the interpolation of a large amount of alloying element can its welding property of severe exacerbation.Especially, under low_input_power amount, high-strength steel welding joint easily forms welding cold cracking and destroys the structural integrity of Engineering System.In order to prevent the formation of welding cold cracking, need to carry out weld preheating process to steel plate, and welding crack sensitivity means that several Pcm is larger, preheating temperature is higher.But the increase of preheating procedure not only have impact on production efficiency, increases energy consumption, and welding operating mode can be caused to be deteriorated, property of welded joint is unstable, even can affect the safety military service performance of structural part.Therefore, develop a kind of low-welding crack-sensitive high-strength steel without the need to preheating and have social and economic benefits.

Along with the development of thermomechanical control techniques (TMCP) and micro-alloying technology, all kinds of high-level steel grade all adopts micro-alloying technology to reduce alloying element total content, armor plate strength is improved further with precipitation strength mechanism, utilize TMCP technology fining austenite grains, the high dislocation density of deformed austeaite is conducive to the intensity improving phase-change product, microstructure proportioning is accurately controlled in conjunction with On-line accelerated cooling (ACC) technique, the thought of ' with water for alloy ' can reduce alloying element content, remarkable reduction raw materials cost, also ensure that low-welding crack-sensitive index simultaneously, improve the weldability of steel plate.

Low welding crack sensitivity steel, in the world also known as CF (CrackFree) steel, is that a class has low-carbon-equivalent, low Pcm value, the steel grade of welding property excellence, it is generally acknowledged to weld under not preheating or low preheating condition also not occur crackle; In order to improve its intensity further, need equally to adopt TMCP and micro-alloying technology; YB/T4137 ferrous metallurgy industry standard also specifies that its supply of material state has TMCP, TMCP+ tempering or modifier treatment.

At present, more existing patents of invention about low welding crack sensitivity steel plate, but often only relate to the lower steel grade of intensity rank (if yield strength is at about 550MPa) in these patents of invention, general needs adopts extra thermal treatment process to improve its toughness, this mode of production not only increases production cost, and reduces production efficiency.Single invention patent also relates to the manufacture of yield strength 690MPa level hot rolled steel plate, but needs in its composition to add more B element, and ' boron is crisp ' phenomenon is very difficult to expect and control.Now published Patents is illustrated as follows.

Patent CN101476080A, CN101812634A, CN104195429A all have employed and roll rear off-line hardening and tempering process (quenching+tempering) and prepare low-welding crack-sensitive High Strength Steel Plate, complex manufacturing, and production efficiency is low.As described in latter two patents, (be greater than 700MPa) when target tensile strength is higher, Composition Design also needs to add a certain amount of B to improve the hardening capacity of steel plate, ensures its tensile strength.

Patent CN1932063A, CN101096738A, CN102888571A all have employed and roll rear high tempering (600 ~ 650 DEG C) technique, and tempering time is longer.Obviously, the same energy consumption of this mode of production is large, is unfavorable for enhancing productivity.In addition, this target steel grade yield strength rank involved by three patents is far below 690MPa.

For patent CN101481774A, CN101353759A, although these two patents all adopt TMCP technique to prepare low welding crack sensitivity steel, the steel grade yield strength rank involved by it is only 500MPa and 550MPa rank.Patent CN101418418A " yield strength 690MPa level low-crackle sensitive steel and manufacture method thereof " relate to the High Strength Construction Steel that yield strength is greater than 690MPa, but in example component system, great majority have employed higher Nb (0.06 ~ 0.08%), high V (0.04 ~ 0.12%), and with the addition of 0.001 ~ 0.002%B.High microalloy element content, adds somewhat to cost; B element is a kind of element of easy segregation, the crisp phase Fe of boron ₂₃(CB) ₆precipitation the impelling strength of steel plate can be caused unstable, the B content of welding base metal is higher simultaneously, improves the hardenability of heat affected zone, increases the proneness that welding cold cracking is formed.

From upper analysis, rarely patent relates to the exploitation that yield strength is the low welding crack sensitivity steel plate of 690MPa rank at present; But, under the growth requirement of the structural steel for weldings such as large-scale engineering machinery, ensure that the weldability of High Strength Steel Plate and the safety military service performance of welding product are particularly crucial, therefore, a kind of low welding crack sensitivity steel of high-intensity high-tenacity must be developed.In order to solve this difficult problem, the present invention will provide a kind of novel Composition Design, adopts TMCP+ rapid cooling technique to prepare the low-welding crack-sensitive hot-rolled steel sheet of high comprehensive performance.

Summary of the invention

For the deficiencies in the prior art, the invention provides a kind of Q690CF hot-rolled steel sheet and preparation method thereof.Based on multicomponent microalloying technology, chemical composition reasonable in design, by two-stage control rolling and On-line accelerated cooling technology, prepares the hot-rolled steel sheet that comprehensive mechanical property is excellent.

Q690CF steel refers to that yield strength is superior to 690MPa and has a class steel grade of low-welding crack-sensitive.

Q690CF hot-rolled steel sheet of the present invention, chemical composition is by mass percentage: C:0.05 ~ 0.08%, Si:0.22 ~ 0.30%, Mn:1.6 ~ 2.0%, Al:0.2 ~ 0.35%, Cr:0.10 ~ 0.35%, Mo:0.20 ~ 0.35%, Ni:0.1 ~ 0.4%, Cu:0.15 ~ 0.3%, Nb:0.025 ~ 0.045%, V:0.01 ~ 0.03%, Ti:0.005 ~ 0.03%, P≤0.010%, S≤0.008%, surplus is Fe and inevitable impurity.

Q690CF hot-rolled steel sheet of the present invention, welding crack sensibility indices P cm value is not more than 0.20%.

Q690CF hot-rolled steel sheet of the present invention, area percentage composition >=90% of bainite type ferrite and acicular ferrite in microstructure, bainite and ferritic width of sheet are distributed in 0.1 ~ 0.7 μm.

Q690CF hot-rolled steel sheet of the present invention, mechanical property is: 750MPa >=yield strength (Rp0.2) >=690MPa, 940MPa >=tensile strength (Rm) >=810MPa, 22.5% >=unit elongation (A) >=17%, 250J >=-20 DEG C impact absorbing energy (Akv) >=180J, yield tensile ratio (Rp0.2/Rm)≤0.93.

Q690CF hot-rolled steel sheet of the present invention, the thickness range of hot-rolled finished product steel plate is 12 ~ 25mm.

In Q690CF hot-rolled steel sheet of the present invention, chemical composition proportion design is described in detail:

C: be topmost solid solution element in soft steel, even can super saturated solid solution in the bainite matrix of high dislocation density, play the effect of solution strengthening; In addition, be also combined with strong carboritride forming element and form the tiny precipitated phase of disperse, play the effect of precipitation strength; But the increase of carbon content obviously can worsen the welding property of steel, is also unfavorable for impelling strength, therefore in the present invention carbon content control 0.05 ~ 0.08%.

Si: be one of important element of deoxidation in steel-making, can ferrite matrix be solid-solution in steel, play the effect of solution strengthening, cementite can also be suppressed to separate out simultaneously, but too much add membership to worsen plasticity, improve ductile-brittle transition temperature, therefore its content controls is 0.22 ~ 0.30%.

Mn: be stable austenite element, can effectively reduce Ar3 temperature, promotes bainitic transformation, refinement microstructure, and improve intensity and can improve toughness to a certain extent, especially under low-carbon (LC) condition, the solution strengthening effect of Mn is more remarkable.But Mn too high levels can reduce the toughness of steel, and be unfavorable for the cold cracking performance of anti-welding of steel, consider, Mn content fixes on 1.6 ~ 2.0%.

Al: be important deoxidant element during steel-making equally, can also reduce steel grade N content, form AlN and stop AUSTENITE GRAIN COARSENING, but when Al adds too much, can affect plate surface quality, therefore its content should 0.2 ~ 0.35%.

Cr, Mo: the hardening capacity that all can improve steel, its displacement is solid-solution in ferrite, the effect of alternative Mn element, compound is added and is optimized its strengthening effect effect, but Cr, Mo all can improve Pcm value, too much can cause deteriorated weldability, also can increase cost simultaneously, therefore its content should control 0.10 ~ 0.35% respectively, and 0.20 ~ 0.35%.

Ni, Cu:Ni significantly can improve the low-temperature flexibility of steel, but it is expensive; Cu can play the effect of precipitation strength, but easily causes crystal boundary thermal crack, and the two compound is added can eliminate the effect that grain-boundary crack caused by Cu can reach highly malleablized simultaneously, its content respectively 0.1 ~ 0.4%, 0.15 ~ 0.3%

Nb, V, Ti: all belong to strong carboritride forming element, Nb can improve austenitic recrystallize final temperature, fining austenite grains size; Ti and N forms TiN, effectively can organize the alligatoring of austenite crystal, also can improve the impelling strength of mother metal welded heat affecting zone simultaneously; The disperse educt of VC or V (CN) can efficient hardening phase-change product phase; The micro-compound interpolation of three can produce ' co precipitation strengthening effect ', improve the obdurability of steel plate simultaneously, if too high levels, understand alligatoring precipitated phase and cause obdurability to reduce, therefore its content controls respectively at Nb:0.025 ~ 0.045%, V:0.01 ~ 0.03%, Ti:0.005 ~ 0.03% is optimum.

P, S: belong to impurity element, easy segregation damages obdurability in crystal boundary, and P, S content of the present invention controls as P≤0.010%, S≤0.008%.

Pcm: welding crack sensibility indices P cm is the important indicator assessing steel grade weldability based on chemical composition design, Pcm is less, and the weldability of steel is better, it is generally acknowledged, when Pcm is not more than 0.20%, steel grade can weld under not preheating condition also can not produce welding cold cracking.Putting before this, optimizing chemical composition proportioning and can improve obdurability.

The compound of the strong carbonitride-forming elements (Nb, V, Ti) of polynary, trace is added, between different element, ' competition ' is in conjunction with C, atom N and form the tiny and precipitated phase of disperse, as based on the composite carbon nitrogen compound of Nb or V, strong ' pinning ' effect of tiny precipitated phase effectively hinders dislocation motion, plays ' co precipitation strengthening effect ' hot-rolled steel sheet; And if only add separately a certain microalloy element, the increase of its content, will certainly alligatoring precipitated phase, improve not obvious to intensity, and toughness can be worsened; Meanwhile, strong carboritride element and other substitutional elements, as the compounds such as Mn, Mo are added, be conducive to the hardening capacity improving steel plate, collaborative promotion bainitic transformation.

The preparation method of Q690CF hot-rolled steel sheet of the present invention, adopts the quick process for cooling of TMCP+ directly to prepare hot-rolled steel sheet, comprises the steps:

Step 1, melting:

By Q690CF hot-rolled steel sheet chemical composition, electric furnace or converter smelting, smelting temperature is 1550 ~ 1670 DEG C, and is cast into steel ingot or strand;

Step 2, pre-treatment:

Steel ingot or strand are heated to 1150 ~ 1200 DEG C, soaking time 60 ~ 120min;

Step 3, hot rolling:

Adopt two-stage control rolling:

The start rolling temperature of roughing is 1050 ~ 1120 DEG C, multi-pass rolling, and accumulative percentage pass reduction is 45 ~ 60%, and finishing temperature is 1000 ~ 1080 DEG C, and obtaining workpiece thickness is 40 ~ 75mm;

The start rolling temperature of finish rolling is 810 ~ 860 DEG C, multi-pass rolling, and accumulative percentage pass reduction is 60 ~ 80%, and finishing temperature is not less than 780 DEG C, and obtaining steel plate thickness is 12 ~ 25mm;

Step 4, cools fast:

Adopt laminar flow accelerating cooling mode, steel plate begins to cool down temperature and is not less than 750 DEG C, and speed of cooling is 15 ~ 30 DEG C/s, and final cooling temperature controls between 350 ~ 500 DEG C, and then air cooling is to room temperature, obtains finished product Q690CF hot-rolled steel sheet.

In above-mentioned steps 3, the finishing temperature of finish rolling is not less than 780 DEG C, is because significantly increase the entanglement dislocation desity produced by mechanical deformation in austenite, be unfavorable for improving toughness, in addition, finishing temperature is too low can form strain induced ferrite tissue, reduces intensity; In step 4, steel plate begins to cool down temperature and is not less than 750 DEG C, is because when steel plate has just entered water, and grain boundary ferrite tissue appears in the uneven local that causes of speed of cooling, destroys the homogeneity of rolling rear mechanical property of steel plate.

Compared with prior art, beneficial effect of the present invention is:

(1) Q690CF hot-rolled steel sheet of the present invention, does not add B element, and be easy to the homogeneity ensureing hot-rolled steel sheet mechanical property, utilize the synergistic effect between alloying element, the least possible interpolation noble element, reduces raw materials cost simultaneously.

(2) Q690CF hot-rolled steel sheet of the present invention, it is the low-welding crack Q690CF hot-rolled steel sheet of high-strong toughness coupling, the stable mechanical property at each position of hot-rolled steel sheet, there is high strength, good low-temperature toughness and welding property, without preheating welding can be realized, meet the welding demand of heavy construction structure completely; Can be applicable to the operating mode of the service condition such as low temperature, heavy duty harshness, as prepared the components such as large-scale low-temperature storage tank, pressure steel pipe of hydropower station, mining machinery.

(3) preparation method of Q690CF hot-rolled steel sheet of the present invention, adopts TMCP technique directly to prepare high tough hot-rolled steel sheet, and without the need to any thermal treatment process after rolling, production technique is simple, and significantly save energy, enhances productivity and reduce manufacturing cost.

Accompanying drawing explanation

Fig. 1 is the microstructure picture of the Q690CF hot-rolled steel sheet cross section of embodiment 2;

Fig. 2 is the meticulous panel construction photo of the Q690CF hot-rolled steel sheet microstructure of embodiment 2.

Embodiment

Carry out more full and accurate description to specific embodiments of the invention by reference to the accompanying drawings, these embodiments are only be described embodiment of the present invention, do not impose any restrictions scope of the present invention.

The mass percent of three kinds of chemical compositions of table 1 embodiment of the present invention 1 ~ 7

	C	Si	Mn	Al	Cr	Mo	Cu	Ni	Nb	V	Ti	S	P	*
															1	0.063	0.25	1.83	0.03	0.10	0.21	0.22	0.3	0.04	0.01	0.02	0.004	0.008	Surplus
2	0.058	0.30	1.70	0.029	0.23	0.20	0.23	0.2	0.03	0.028	0.005	0.003	0.005	Surplus
															3	0.07	0.22	1.68	0.034	0.20	0.22	0.18	0.18	0.04	0.022	0.028	0.003	0.007	Surplus

Note: * is Fe and inevitable impurity.

The Pcm value of three kinds of chemical compositions of table 2 embodiment of the present invention 1 ~ 7

Sequence number	1	2	3
				Pcm	0.199	0.195	0.200

Note: Pcm=C+Si/30+Mn/20+Cu/20+Cr/20+Ni/60+Mo/15+V/10+5B

Embodiment 1

The preparation method of Q690CF hot-rolled steel sheet of the present invention, comprises the steps:

Step 1, melting:

Press No. 1 Q690CF hot-rolled steel sheet chemical composition in table 1, electrosmelting, smelting temperature is 1670 DEG C, is cast into the steel ingot that thickness is 110mm;

Step 2, pre-treatment:

By Heating Steel Ingots to 1200 DEG C, soaking time 80min;

Step 3, hot rolling:

Adopt two-stage control rolling:

The start rolling temperature of roughing is 1080 DEG C, 3 passes, and accumulative percentage pass reduction is 55%, and finishing temperature is 1060 DEG C, and obtaining workpiece thickness is 50mm;

Roller-way carries out finish rolling, 7 passes after temperature is to 860 DEG C, and accumulative percentage pass reduction is 76%, and finishing temperature is 800 DEG C, and obtaining steel plate thickness is 12mm;

Step 4, cools fast:

Adopt laminar flow accelerating cooling mode, steel plate begins to cool down temperature and is not less than 750 DEG C, and speed of cooling is 26 DEG C/s, and it is 480 DEG C that final cooling temperature controls, and then air cooling is to room temperature, obtains finished product Q690CF hot-rolled steel sheet.

Embodiment 2

The preparation method of Q690CF hot-rolled steel sheet of the present invention, comprises the steps:

Step 1, melting:

Press No. 1 Q690CF hot-rolled steel sheet chemical composition in table 1, converter smelting, smelting temperature is 1560 DEG C, is cast into the strand of 130mm;

Step 2, pre-treatment:

Strand is heated to 1150 DEG C, soaking time 120min;

Step 3, hot rolling:

Adopt two-stage control rolling:

The start rolling temperature of roughing is 1100 DEG C, 3 passes, and accumulative percentage pass reduction is 46%, and finishing temperature is 1050 DEG C, and obtaining workpiece thickness is 70mm;

Roller-way carries out finish rolling, 6 passes after temperature is to 840 DEG C, and accumulative percentage pass reduction is 69%, and finishing temperature is 810 DEG C, and obtaining steel plate thickness is 22mm;

Step 4, cools fast:

Adopt laminar flow accelerating cooling mode, steel plate begins to cool down temperature and is not less than 750 DEG C, and speed of cooling is 18 DEG C/s, and it is 400 DEG C that final cooling temperature controls, and then air cooling is to room temperature, obtains finished product Q690CF hot-rolled steel sheet.

Embodiment 3

The preparation method of Q690CF hot-rolled steel sheet of the present invention, comprises the steps:

Step 1, melting:

Press No. 2 Q690CF hot-rolled steel sheet chemical compositions in table 1, converter smelting, smelting temperature is 1600 DEG C, is cast into the strand that thickness is 110mm;

Step 2, pre-treatment:

Strand is heated to 1180 DEG C, soaking time 60min;

Step 3, hot rolling:

Adopt two-stage control rolling:

The start rolling temperature of roughing is 1070 DEG C, 2 passes, and accumulative percentage pass reduction is 45%, and finishing temperature is 1000 DEG C, and obtaining workpiece thickness is 60mm;

Roller-way carries out finish rolling, 7 passes after temperature is to 830 DEG C, and accumulative percentage pass reduction is 77%, and finishing temperature is 790 DEG C, and obtaining steel plate thickness is 14mm;

Step 4, cools fast:

Adopt laminar flow accelerating cooling mode, steel plate begins to cool down temperature and is not less than 750 DEG C, and speed of cooling is 20 DEG C/s, and final cooling temperature is 430 DEG C, and then air cooling is to room temperature, obtains finished product Q690CF hot-rolled steel sheet.

Embodiment 4

The preparation method of Q690CF hot-rolled steel sheet of the present invention, comprises the steps:

Step 1, melting:

Press No. 2 Q690CF hot-rolled steel sheet chemical compositions in table 1, electrosmelting, smelting temperature is 1650 DEG C, is cast into the steel ingot that thickness is 130mm;

Step 2, pre-treatment:

By Heating Steel Ingots to 1150 DEG C, soaking time 120min;

Step 3, hot rolling:

Adopt two-stage control rolling:

The start rolling temperature of roughing is 1050 DEG C, 3 passes, and accumulative percentage pass reduction is 48%, and finishing temperature is 1000 DEG C, and obtaining workpiece thickness is 68mm;

Roller-way carries out finish rolling, 6 passes after temperature is to 850 DEG C, and accumulative percentage pass reduction is 71%, and finishing temperature is 800 DEG C, and obtaining steel plate thickness is 20mm;

Step 4, cools fast:

Adopt laminar flow accelerating cooling mode, steel plate begins to cool down temperature and is not less than 750 DEG C, and speed of cooling is 15 DEG C/s, and final cooling temperature is 380 DEG C, and then air cooling is to room temperature, obtains finished product Q690CF hot-rolled steel sheet.

Embodiment 5

The preparation method of Q690CF hot-rolled steel sheet of the present invention, comprises the steps:

Step 1, melting:

Press No. 3 Q690CF hot-rolled steel sheet chemical compositions in table 1, converter smelting, smelting temperature is 1600 DEG C, is cast into the strand that thickness is 110mm;

Step 2, pre-treatment:

Strand is heated to 1200 DEG C, soaking time 60min;

Step 3, hot rolling:

Adopt two-stage control rolling:

The start rolling temperature of roughing is 1120 DEG C, 3 passes, and accumulative percentage pass reduction is 55%, and finishing temperature is 1080 DEG C, and obtaining workpiece thickness is 50mm;

Roller-way carries out finish rolling, 7 passes after temperature is to 860 DEG C, and accumulative percentage pass reduction is 76%, and finishing temperature is 810 DEG C, and obtaining steel plate thickness is 12mm;

Step 4, cools fast:

Adopt laminar flow accelerating cooling mode, steel plate begins to cool down temperature and is not less than 780 DEG C, and speed of cooling is 30 DEG C/s, and final cooling temperature is 500 DEG C, and then air cooling is to room temperature, obtains finished product Q690CF hot-rolled steel sheet.

Embodiment 6

The preparation method of Q690CF hot-rolled steel sheet of the present invention, comprises the steps:

Step 1, melting:

Press No. 3 Q690CF hot-rolled steel sheet chemical compositions in table 1, converter smelting, smelting temperature is 1580 DEG C, is cast into the strand that thickness is 110mm;

Step 2, pre-treatment:

Strand is heated to 1200 DEG C, soaking time 60min;

Step 3, hot rolling:

Adopt two-stage control rolling:

The start rolling temperature of roughing is 1100 DEG C, 3 passes, and accumulative percentage pass reduction is 45%, and finishing temperature is 1080 DEG C, and obtaining workpiece thickness is 60mm;

Roller-way carries out finish rolling, 6 passes after temperature is to 820 DEG C, and accumulative percentage pass reduction is 73%, and finishing temperature is 790 DEG C, and obtaining steel plate thickness is 16mm;

Step 4, cools fast:

Adopt laminar flow accelerating cooling mode, steel plate begins to cool down temperature and is not less than 780 DEG C, and speed of cooling is 24 DEG C/s, and final cooling temperature is 410 DEG C, and then air cooling is to room temperature, obtains finished product Q690CF hot-rolled steel sheet.

Embodiment 7

The preparation method of Q690CF hot-rolled steel sheet of the present invention, comprises the steps:

Step 1, melting:

Press No. 3 Q690CF hot-rolled steel sheet chemical compositions in table 1, converter smelting, smelting temperature is 1630 DEG C, is cast into the strand that thickness is 130mm;

Step 2, pre-treatment:

Strand is heated to 1200 DEG C, soaking time 80min;

Step 3, hot rolling:

Adopt two-stage control rolling:

The start rolling temperature of roughing is 1100 DEG C, 2 passes, and it is 46% that accumulative passage presses down rate, and finishing temperature is 1050 DEG C, and obtaining workpiece thickness is 70mm;

Roller-way carries out finish rolling, 6 passes after temperature is to 830 DEG C, and accumulative percentage pass reduction is 64%, and finishing temperature is 820 DEG C, and obtaining steel plate thickness is 25mm;

Step 4, cools fast:

Adopt laminar flow accelerating cooling mode, steel plate begins to cool down temperature and is not less than 750 DEG C, and speed of cooling is 17 DEG C/s, and final cooling temperature is 400 DEG C, and then air cooling is to room temperature, obtains finished product Q690CF hot-rolled steel sheet.

The microsturcture of Q690CF hot-rolled steel sheet prepared by embodiment 2 is shown in Fig. 1, as seen from the figure, microstructure is mainly tiny bainite type ferrite and acicular ferrite, and the meticulous panel construction of its microstructure is shown in Fig. 2, and width of sheet mean sizes is 0.3 μm.

The mechanical property of the Q690CF hot-rolled steel sheet that each embodiment obtains is in table 3.

The mechanical property of the Q690CF hot-rolled steel sheet of table 3 embodiment of the present invention 1 ~ 7

Embodiment	H(mm)	Rp0.2(MPa)	Rm(MPa)	A(％)	Rp0.2/Rm	Akv(-20℃/J)
							1	12	700	815	18.2	0.86	224，233，214
2	22	730	875	17.8	0.85	192，187，196
							3	14	725	890	17.5	0.84	188，190，182
4	20	750	910	17.2	0.82	181，193，186
							5	12	735	860	18	0.85	220，198，206
6	16	740	905	17.3	0.82	192，181，189
							7	25	715	865	17.4	0.83	190，215，182

Note: H represents steel plate thickness; Rp0.2 represents yield strength; Rm represents tensile strength; A represents unit elongation, and Akv represents-20 DEG C of impact absorbing energies.

As can be seen from embodiments of the invention result, ensure that Pcm value is not more than the condition of 0.20% in example steel grade chemical composition, TMCP technique is adopted directly to prepare the hot-rolled steel sheet of high-intensity high-tenacity, mechanical property meets yield strength completely and is greater than 690MPa, low-temperature impact absorbs merit and is greater than 180J (-20 DEG C), and each monodrome is highly stable.

The experiment of single pass plate welding is carried out to the steel grade that the embodiment of the present invention 3 obtains, thermal weld stress is 1.08kJ/mm, be about 15 DEG C in room temperature, without any preheating condition under weld, postwelding measures the vickers hardness number of heat affected zone, its maximum hardness is 310HV, is less than the critical hardness value 350HV easily occurring welding cold cracking, shows that this steel grade has good welding property, in room temperature, without implementing little heat input weldprocedure under any preheating condition.

The steel grade obtained the embodiment of the present invention 2 carries out little iron and grinds experiment, be about 15 DEG C in room temperature equally, without any preheating condition under weld, groove type adopts oblique Y type groove, retain 2mm gap, when adopting thermal weld stress amount to be 1.30kJ/mm, welding cold cracking rate is 0; But when heat input is 0.9kJ/mm, a small amount of crackle appears in the localized heat zone of influence, show that the minimum thermal input that this steel grade can adopt under without preheating, room temperature condition should near 1kJ/mm.

Claims (4)

1. a Q690CF hot-rolled steel sheet, is characterized in that, the chemical composition of described hot-rolled steel sheet is by mass percentage: C:0.05 ~ 0.08%, Si:0.22 ~ 0.30%, Mn:1.6 ~ 2.0%, Al:0.2 ~ 0.35%, Cr:0.10 ~ 0.35%, Mo:0.20 ~ 0.35%, Ni:0.1 ~ 0.4%, Cu:0.15 ~ 0.3%, Nb:0.025 ~ 0.045%, V:0.01 ~ 0.03%, Ti:0.005 ~ 0.03%, P≤0.010%, S≤0.008%, surplus is Fe and inevitable impurity; The welding crack sensibility indices P cm value of described hot-rolled steel sheet is not more than 0.20%.

2. Q690CF hot-rolled steel sheet according to claim 1, it is characterized in that, area percentage composition >=90% of bainite type ferrite and acicular ferrite in the microstructure of described hot-rolled steel sheet, bainite and ferritic width of sheet are distributed in 0.1 ~ 0.7 μm.

3. Q690CF hot-rolled steel sheet according to claim 1, it is characterized in that, described hot-rolled steel sheet, mechanical property is: 750MPa >=yield strength >=690MPa, 940MPa >=tensile strength >=810MPa, 22.5% >=unit elongation >=17%, 250J >=-20 DEG C impact absorbing energy >=180J, yield tensile ratio≤0.93.

4. Q690CF hot-rolled steel sheet according to claim 1, is characterized in that, comprise the following steps:

Step 1, melting:

By Q690CF hot-rolled steel sheet chemical composition, electric furnace or converter smelting, smelting temperature is 1550 ~ 1670 DEG C, and is cast into steel ingot or strand;

Step 2, pre-treatment:

Steel ingot or strand are heated to 1150 ~ 1200 DEG C, soaking time 60 ~ 120min;

Step 3, hot rolling:

Adopt two-stage control rolling:

The start rolling temperature of roughing is 1050 ~ 1120 DEG C, multi-pass rolling, and accumulative percentage pass reduction is 45 ~ 60%, and finishing temperature is 1000 ~ 1080 DEG C, and obtaining workpiece thickness is 40 ~ 75mm;

The start rolling temperature of finish rolling is 810 ~ 860 DEG C, multi-pass rolling, and accumulative percentage pass reduction is 60 ~ 80%, and finishing temperature is not less than 780 DEG C, and obtaining steel plate thickness is 12 ~ 25mm;

Step 4, cools fast:

Adopt laminar flow accelerating cooling mode, steel plate begins to cool down temperature and is not less than 750 DEG C, and speed of cooling is 15 ~ 30 DEG C/s, and final cooling temperature controls between 350 ~ 500 DEG C, and then air cooling is to room temperature, obtains finished product Q690CF hot-rolled steel sheet.