CN102851622B - Superhigh-strength high-toughness steel plate for ocean engineering and production method thereof - Google Patents

Abstract

The invention discloses a superhigh-strength high-toughness steel plate for ocean engineering and a manufacturing method thereof. The superhigh-strength high-toughness steel plate comprises the following chemical components in percentage by weight: 0.06-0.10% of C, 0.20-0.40% of Si, 1.10-1.65% of Mn, at most 0.010% of P, at most 0.0020% of S, 0.030-0.050% of Nb, 0.020-0.060% of V, 0.006-0.015% of Ti, 0.60-1.30% of Ni, 0.30-0.60% of Cr, 0.20-0.60% of Cu, 0.40-0.60% of Mo, 0.020-0.040% of Alt, and the balance of Fe and inevitable impurities. The production method comprises the following steps: smelting in a converter, rolling on a Steckel reversing mill, and finally carrying out hardening and tempering heat treatment by a TMCP (thermomechanical rolling process) technique. The steel plate has favorable properties: the tensile strength is 770-840 MPa, the yield strength is 710-800 MPa, the elongation percentage is 16-19%, the -40 DEG C low-temperature lateral impact and low-temperature ageing impact properties are greater than or equal to 90J, and the cold bending resistance is qualified; and thus, the steel plate has the advantages of ultrahigh strength, excellent low-temperature impact and low-temperature ageing impact properties, and stable production technique.

Description

A kind of ultra-high-strength/tenacity steel plate for ocean engineering and production method thereof

Technical field

The invention belongs to iron and steel domain, especially a kind of ultra-high-strength/tenacity steel plate for ocean engineering and production method thereof.

Background technology

Continually developing of the mankind makes land Nonrenewable resources increasingly exhausted, and ocean day by day becomes the precious deposits that meet various countries' needs.Marine oil and gas industry, Marine Tourism industry, modern marine fishery, maritime transportation had become four large mainstay industries of current marine economy already, and wherein marine oil and gas industry is the maximum marine industries in the whole world.And have a extensive future as the supporting structure thing marine engineering equipment of offshore oil and gas drilling operation, growth momentum is powerful.Derived and the further developing of oceanographic engineering auxiliary facility of coming by marine engineering equipment manufacture, to pull Marine Engineering Steel to more high strength development, as the equipment ocean platform crane as offshore platform and boats and ships and other items handling and personnel's conveying, as arm and turntable, need the above high-strength steel of 690MPa, this high-strength steel has the high-intensity while at needs, also need certain cold resistant climate, be different from common high-strength machined steel.At present, domestic have some iron and steel enterprises to obtain the following Marine Engineering Steel of 550MPa level to have obtained in the world main surveying society and authenticate, and product is introduced to the market.But the 690Mpa level Marine Engineering Steel of ultrahigh-intensity high-toughness, in the market substantially taking import as main.In order further to meet the needs of market and iron and steel enterprise's product diversification, the development of high value added product 690Mpa level Marine Engineering Steel is imperative with exploitation.

Produce Marine Engineering Steel and conventionally smelt by two kinds of methods of electric furnace or converter, carry out strand with die casting or continuous cast method.Consider the low cost of producing Marine Engineering Steel by the mode that converter smelting, continuous casting are produced, and produce custom in order to adapt to numerous domestic steel production enterprise.It is 220mm that the present invention selects continuously cast bloom, produces 690Mpa level Marine Engineering Steel, and finished steel plate thickness is thick between 40～80mm.Produce the low compression ratio steel of 40～80mm for 220mm, the quality of continuously cast bloom, the control of inclusion and harmfully seem particularly important without plain control.In addition, Marine Engineering Steel, due to its Service Environment abominable, requires steel not only to have superstrength, high tenacity and has in addition certain strain aging.As a rule, the intensity of steel is higher, the more difficult raising of plasticity and low-temperature flexibility.In order to have increased substantially intensity and the low-temperature flexibility, ageing of Marine Engineering Steel, and the good plasticity matching with it, need rational alloying, pass through reasonable process, make steel obtain desirable tissue morphology, could meet steel can apply under severe ocean environment.

The patent of the existing production method that relates to Marine Engineering Steel, is mainly to obtain steel plate for ocean engineering by controlled rolling and controlled cooling or heat treating method, and concrete production method is as follows:

Chinese patent CN 102400043 provides a kind of large thickness steel plate for oceaneering and production method thereof, it passes through microalloying, by electrosmelting, the vacuum deaeration of VD stove, pull into 330mm thick stock, carry out subsequently two stage rolling, finally carry out modifier treatment, the large thickness steel plate for oceaneering that to have obtained steel plate thickness be 150mm, yield strength more than 460MPa, tensile strength between 530～650MPa, the ballistic work excellence of-40 DEG C.But this steel grade low strength, and be electrosmelting, production capacity is lower.

Chinese patent CN 101709432 discloses a kind of steel for large-thickness hardening and tampering ocean platform, and in steel, carbon component is designed to 0.16～0.18%, by electrosmelting, the vacuum-treat of VD stove, sends into LF and processes, subsequently casting.No explanation is not cast in which way, has obtained the superstrength of large thickness, high tenacity Marine Engineering Steel.But because steel plate is thicker, carbon component is designed to 0.16～0.18% in steel, and add a large amount of alloy that affects welding property and microalloy element, carbon equivalent is higher, worsens the welding property of steel plate.

Chinese patent CN 102392192 provides the thick low compression ratio steel plate for ocean engineering of a kind of 80mm and manufacture method, adopts cooling controlling and rolling controlling process in conjunction with normalizing treatment, and finally organizing rank is ferrite and perlite.Because carbon and manganese content in its steel is relatively high, from the organization chart providing, there is certain banded structure.And intensity is lower, yield strength is between 360 ~ 370 MPa.

Summary of the invention

In view of above the deficiencies in the prior art, consider superstrength, high tenacity, weldability and the producibility of steel plate for ocean engineering, the object of this invention is to provide a kind of ultra-high-strength/tenacity steel plate for ocean engineering and production method thereof, the method is by rational chemical composition design, the reasonable compression ratio TMCP technology controlling and process of rolling sequence, and rational hardening and tempering process, obtain the strong steel plate for ocean engineering of superelevation of excellent performance.

The object of the invention is to be achieved through the following technical solutions:

A kind of ultra-high-strength/tenacity steel plate for ocean engineering, it is characterized in that: the chemical composition of this superstrength steel plate for ocean engineering by weight percentage, C:0.06～0.10%, Si:0.20～0.40%, Mn:1.10～1.65%, P :≤0.010%, S :≤0.0020%, Nb:0.030～0.050%, V:0.020～0.060%, Ti:0.006～0.015%, Ni:0.60～1.30%, Cr:0.30～0.60%, Cu:0.20～0.60%, Mo:0.40～0.60%, Alt:0.020～0.040%, surplus is Fe and inevitable impurity.

Be one of key factor affecting continuously cast bloom internal soundness and High Strength Steel Plate performance due to the chemical composition of steel, the present invention, in order to make described steel obtain excellent over-all properties, limits the chemical composition of described steel, and reason is:

C: carbon is the principal element that affects superstrength steel mechanical property, by the intensity of gap solid solution raising steel, improves the hardening capacity of steel.When the lower intensity of carbon content is low, work as too high levels, there is the shortcoming of toughness and weldability variation.In addition, when carbon content is between 0.10～0.13% time, steel, in peritectoid district, increases to smelt and controls difficulty, thus in the present invention carbon content control 0.06～0.010%.

Si: silicon is the bioelement of deoxidation in steel making, also have certain solution strengthening effect, but silicone content is too high, and plate surface quality and toughness are existed to considerable influence, therefore in the present invention be limited to silicon in 0.20～0.40% scope.

Mn: manganese, to thinning microstructure, improves intensity and toughness favourable.In quenched and tempered steel, can increase the hardening capacity of steel, and with low cost.When manganese too high levels, can in actual production, cause continuous casting slab segregation.For steel of the present invention, in order to adapt to produce on Steckel mill, manganese content is controlled in 1.10～1.50% scope.

Nb: the solute effect of dragging of trace niobium and the pinning effect of niobium to austenite grain boundary, all suppress the austenitic recrystallize of deformation, and form precipitate in the time of the tempering of cooling or modifier treatment, thereby the intensity of making and toughness are all improved.In steel of the present invention, DeGrain when addition is less than 0.030%, toughness drop while being greater than 0.050%, promotes continuously cast bloom to produce surface crack, in addition welding property is also had to deterioration effect.Therefore, content of niobium should be controlled in 0.030～0.050% scope.

V: vanadium is the good reductor of steel.In steel, add the vanadium can thinning microstructure crystal grain, improve intensity and toughness.When tempering or when cooling after welding, form carbide, be conducive to gain in strength.DeGrain when addition is less than 0.020%, while being greater than 0.060%, the toughness of steel and weldability reduce.Therefore, content of vanadium should be controlled in 0.020～0.060% scope.

Ti: titanium is the nitrogen element being used for fixing in steel, under proper condition, titanium, nitrogen form titanium nitride, stop steel billet grain growth in heating, rolling, welding process, improve the toughness of mother metal and welded heat affecting zone.Titanium is lower than 0.006% time, and nitrogen fixation effect is poor, and while exceeding 0.015%, nitrogen fixation effect reaches capacity, and superfluous titanium can make the toughness of steel worsen.Therefore in the present invention, in conjunction with nitrogen in steel content span of control in actual production, by titanium Composition Control 0.006～0.015%.

Ni: nickel can improve intensity, toughness, patience and the erosion resistance in air, seawater and some acid of steel in steel.Nickel can suppress carbon precipitation from austenite, reduces grain boundary carbide and separates out tendency, significantly reduces intergranular carbide quantity.But nickel increased content in steel, production cost can significantly increase, therefore nickel content is controlled at 0.60～1.30% in the present invention.

Cr, Cu: chromium and copper are the elements that improves steel hardenability, can suppress polygonal ferrite and pearlitic formation, promote low temperature to organize bainite or martensitic transformation, is the element that quenched and tempered steel often adds.But Cr and Cu too high levels will affect the toughness of steel, and cause temper brittleness, and in the present invention, chromium content is controlled at 0.30～0.60%, and copper content control is 0.20～0.60%.

Mo: improve the hardening capacity of steel, can increase cost while interpolation in a large number, and reduce toughness and weldability.When tempering, form carbide particle, be conducive to precipitation strength.Generally be limited in 0.40～0.60%.

Al: aluminium is a kind of important deoxidant element in steelmaking process, even if add micro-aluminium in molten steel, also can effectively reduce the inclusion content in steel, and crystal grain thinning.But too much aluminium, can promote continuously cast bloom to produce surface crack, and producing inner aluminium is inclusion, reduces slab quality, and therefore, Holo-Al content should be controlled at 0.020～0.040%.

Impurity element in steel, as S, P etc., can grievous injury described in the low-temperature flexibility of steel and the nearly weld metal zone of welding, increase continuous casting slab segregation degree.Therefore, sulphur, phosphorus content should be controlled at respectively≤0.0020% and≤below 0.010%.And control other inevitable impurity element and control respectively as follows as O, N, H, As, Pb, Sn, Sb: O≤0.0018%, N≤0.0040%, H≤0.00015%, As≤0.012%, Pb≤0.010%, Sn≤0.010%, Sb≤0.010%.

A production method for ultra-high-strength/tenacity steel plate for ocean engineering, is characterized in that this production method comprises following operation:

Smelt continuous casting process: adopt molten iron pretreatment desulfurizing-converter smelting-LF refining-RH vacuum-treat-hello calcium line-quiet stirring-sheet billet continuous casting.After desulfurization is processed, in molten iron, carbon content control is [S]≤0.002%, and the control of converter terminal temperature is 1600 DEG C-1660 DEG C, to LF temperature 1540-1600 DEG C, adopts the deoxidation of aluminium deoxidation method.In LF stove, the residence time is greater than 30 minutes.Adopt atmosphere in micro-pressure operation control bag.RH vacuum-treat, condition of high vacuum degree (≤5.0mbar) lower hold-time of condition >=25 minute.After RH vacuum breaker, feed pure calcium line processing, line feeding length 180-220 rice.Calcium line carries out quiet stirring, the quiet treatment time >=12min that stirs after processing.Carry out subsequently continuous casting.Middle bag temperature is controlled at above 10～15 DEG C of liquidus temperature.After continuously cast bloom cutting, with the hot continuously cast material lower berth upper cover of other heat (batch) numbers, stacking slow cooling is more than 72 hours.

Rolling technology: adopt cooling controlling and rolling controlling process, roll front continuous blank heating temperature between 1200 DEG C～1220 DEG C, adopt austenite recrystallization district and the two-stage control rolling of austenite non-recrystallization district, every time draft >=12% of roughing, 1050 ~ 1100 DEG C of roughing finishing temperatures, roughing becomes the intermediate blank of 1.5～2.5 times of finished product thicknesses; Finish rolling start rolling temperature is 830～870 DEG C, rolls rear employing laminar flow cooling, 600～650 DEG C of final cooling temperatures, 8～15 DEG C/s of rate of cooling, air cooling subsequently.

Thermal treatment process: the steel plate after air cooling is heated again, and Heating temperature is at Ac ₃on 30～80 DEG C carry out austenite phase region quench treatment, quenching temperature is at 900～920 DEG C, Quenching Soaking Time is 2min/mm × thickness of slab, after quenching, steel plate has obtained uniform hardening lath martensite, original austenite grains is tiny, after quenching, 600～630 DEG C of tempering, tempering insulation time is (1.5～2.5) min/mm × thickness of slab+30min.

The present invention, by reasonable component control, utilizes reasonably to depress than the TMCP technology of distribution system and quenching-and-tempering process to have obtained a kind of superstrength Marine Engineering Steel, is organized as tempered sorbite, and sheet interlayer spacing is comparatively tiny, and original austenite grain is tiny.Steel of the present invention has superstrength, has excellent in low temperature toughness, plasticity is higher.The ultrahigh-strength steel specific performance obtaining by the present invention is: tensile strength is 770～840MPa, and yield strength is 710～800MPa, and unit elongation is 16～19% ,-40 DEG C of low temperature transverse impacts and low temperature aging impact property >=90J, and cold-bending property is good.Meet the E690 of the surveying society steel authentication requestings such as DNV, CCS, ABS, and there is mass production condition, stable processing technique, the feature such as workable.

Tool of the present invention has the following advantages:

1, the present invention adapt to numerous domestic for Iron and Steel Production converter smelting, continuous casting mode produce Marine Engineering Steel.It is 220mm that the present invention selects continuously cast bloom, produces 690Mpa level Marine Engineering Steel, and finished steel plate thickness is thick between 40～80mm, and compression ratio is low, reduces rolling cost.Be conducive to instruct the exploitation of other large thickness, the similar steel grade of low compression ratio simultaneously.

2, under the prerequisite of the TMCP technique of utilizing rational chemical composition design mode and be easy to realize aborning, by the modified heat treating method of off-line, need not increase other special process, other any equipment, just can obtain the Marine Engineering Steel of low compression ratio high-intensity high-tenacity.

3,, by simple quenching process, the segregation that former continuously cast bloom center is existed is further alleviated.Adjusted temper, and obtained soft or hard phase rational Match in iron and steel village material, and gave full play to the strengthening effect of the microalloy element that steel has little time to separate out in TMCP process, and made the tensile strength of steel increase, unit elongation rises, and low-temperature impact toughness improves.

4, manufacture method of the present invention, by modified thermal treatment, more close than the modified thermal treatment temp interval of conventional steel plate, be convenient to plan as a whole tissue with other steel grade and produce, save the industrial scheduling time.

5, manufacture method of the present invention, for ultrahigh-strength steel plates manufacture like this, by Nb micro-alloying technology, expand between the non-recrystallization zone of austenite, finishing temperature can be carried out at higher temperature, reduce intermediate blank time of staying temperature, reduce rolling pass, faster production rhythm, saves the energy, shorten the production cycle, reduce production costs.

Brief description of the drawings

Fig. 1 is embodiment 2 60mm ultra-high-strength/tenacity Marine Engineering Steel As rolled through-thickness 1/4 tissue topographies of place, is organized as bainite structure.

Fig. 2 is embodiment 2 60mm ultra-high-strength/tenacity Marine Engineering Steel quenched and tempered state through-thickness 1/4 tissue topographies of place, is organized as tempered sorbite tissue.

Embodiment

According to production technique of the present invention, smelt altogether two heats, smelting flow process is that hot metal pretreatment → converter smelting → LF stove refining → RH vacuum-treat → continuous caster continuous casting → casting blank stacking slow cooling → strand inspection → strand judgement → strand is checked and accepted.After desulfurization is processed, in molten iron, carbon content control is [S]≤0.002%, and blowing rear converter terminal temperature is respectively 1601 and 1620 DEG C, to 1551,1569 DEG C of LF difference temperature, adopts the deoxidation of aluminium deoxidation method.40～50 minutes residence time in LF stove.Adopt atmosphere in micro-pressure operation control bag.RH vacuum-treat, condition of high vacuum degree (≤5.0mbar) the lower hold-time of condition is 30 minutes.After RH vacuum breaker, feed pure calcium line processing, 200 meters of line feeding length.Calcium line carries out quiet stirring after processing, and the quiet treatment time 15min that stirs, carries out continuous casting subsequently.Middle bag temperature is controlled at above 10～15 DEG C of liquidus temperature.After continuously cast bloom cutting, Cross Section of CC Billet is 220mm × 2260mm, and with the hot continuously cast material lower berth upper cover of other heat (batch) numbers, stacking slow cooling more than 72 hours, expands hydrogen as much as possible.Through macroscopic examination, there is slight segregation in slab internal soundness, flawless, bubble, other defect such as is mingled with, and surface quality is good.The two stove embodiment main chemical compositions of smelting are as shown in table 1.

The main chemical compositions (wt%) of table 1 embodiment of the present invention

Embodiment C Si Mn P S Nb Ti Ni Cr Cu Mo V Alt Embodiment 1,2 0.065 0.25 1.63 0.0080 0.0015 0.036 0.013 1.25 0.56 0.20 0.45 0.045 0.0039 Embodiment 3,4 0.095 0.26 1.48 0.0057 0.0010 0.030 0.015 0.90 0.29 0.29 0.48 0.032 0.0030

Adopt rolling on cooling controlling and rolling controlling process plate of moderate thickness Steckel mill, roll front continuous blank heating temperature between 1200 DEG C～1220 DEG C, and ensure steel plate time inside furnace, total time inside furnace is 220～264 minutes, adopt austenite recrystallization district and the two-stage control rolling of austenite non-recrystallization district, every time draft >=12% of roughing, 1050 ~ 1100 DEG C of roughing finishing temperatures, roughing becomes the intermediate blank of 1.5～2.5 times of finished product thicknesses; Finish rolling start rolling temperature is 830～870 DEG C, rolls rear employing laminar flow cooling, 600～650 DEG C of final cooling temperatures, 8～15 DEG C/s of rate of cooling, air cooling subsequently.

Table 2 rolling process for cooling parameter list

On quenching press and tempering stove, embodiment is carried out to modifier treatment subsequently, steel plate is heated again, quenching temperature is between 900～920 DEG C, and Quenching Soaking Time is 2min/mm × thickness of slab.In quenching, reheating object is that material is carried out to abundant austenitizing, material is obtained and evenly wait axle Ao Shishi body crystal grain.As far as possible its alloy is dissolved, use subsequently water quenching, form low-carbon (LC) lath martensite.After quenching, 580～630 DEG C of tempering, tempering time is (1.5～2.5) min/mm × thickness of slab+30min.Thermal treatment concrete technology parameter is as shown in table 3.

Table 3 heat treatment process parameter table

Embodiment is organized as bainite after hot rolling, after modifier treatment, is organized as uniform tempered sorbite.Fig. 1 is through-thickness 1/4 place's metallographic structure pattern after embodiment 2 60mm ultra-high-strength/tenacity Marine Engineering Steel hot rollings, is organized as bainite structure.Fig. 2 is again through modified through-thickness 1/4 tissue topography of place after embodiment 2 60mm ultra-high-strength/tenacity Marine Engineering Steel hot rollings, be organized as tempered sorbite tissue, under metaloscope, can be observed tempered sorbite organization regulation, sorbite sheet interlayer spacing is comparatively tiny.Original austenite grain is tiny, even, and average original austenite grain size is between 20～30 μ m.

The plate stretch performance obtaining according to technique of the present invention is as shown in table 4, and low temperature impact properties is as shown in table 5 and low temperature aging performance is as shown in table 6.The results of property of the embodiment of the present invention is good, and wherein the tensile strength of material is 770～840MPa, and yield strength is 710～800MPa, and unit elongation is 16～19% ,-40 DEG C of low temperature transverse impacts and low temperature aging impact property >=90J, and cold-bending property is good.Meet the E690 of the surveying society steel authentication requestings such as DNV, CCS, ABS, and there is mass production condition, stable processing technique, the feature such as workable.

The plate stretch performance obtaining after the modified thermal treatment of table 4 embodiment of the present invention

The sheet material low temperature impact properties obtaining after the modified thermal treatment of table 5 embodiment of the present invention

Embodiment Thickness of slab/mm Position Temperature/DEG C Impact 1/J Impact 2/J Impact 3/J Average/J Embodiment 1 40 Laterally -40 190 205 174 190 Embodiment 2 60 Laterally -40 168 60 138 122 Embodiment 3 60 Laterally -40 78 90 110 93 Embodiment 4 80 Laterally -40 183 99 93 125

The sheet material low temperature aging impact property obtaining after the modified thermal treatment of table 6 embodiment of the present invention

Embodiment Thickness of slab/mm Position Temperature/DEG C Timeliness impacts 1 Timeliness impacts 2 Timeliness impacts 3 Average Embodiment 1 40 1/4 is longitudinal -40 61 183 111 98 Embodiment 2 60 1/4 is longitudinal -40 219 228 242 230 Embodiment 3 60 1/4 is longitudinal -40 224 210 230 221 Embodiment 4 80 1/4 is longitudinal -40 210 248 215 224

Claims (1)

1. a production method for ultra-high-strength/tenacity steel plate for ocean engineering, is characterized in that this production method comprises following operation:

Smelt continuous casting process: adopt molten iron pretreatment desulfurizing-converter smelting-LF refining-RH vacuum-treat-hello calcium line-quiet stirring-sheet billet continuous casting technique; After desulfurization is processed, the control of Sulfur Content in Hot Iron content is [S]≤0.002%, and the control of converter terminal temperature is 1600 DEG C-1660 DEG C, to LF temperature 1540-1600 DEG C, adopts the deoxidation of aluminium deoxidation method; In LF stove, the residence time is greater than 30 minutes; Adopt atmosphere in micro-pressure operation control bag; RH vacuum-treat, vacuum tightness≤5.0mbar lower hold-time of condition >=25 minute; After RH vacuum breaker, feed pure calcium line processing, line feeding length 180-220 rice; Calcium line carries out quiet stirring after processing, and the quiet treatment time >=12min that stirs, carries out continuous casting subsequently; Middle bag temperature is controlled at above 10～15 DEG C of liquidus temperature; After continuously cast bloom cutting, with hot continuously cast material lower berth upper cover, stacking slow cooling is more than 72 hours; The chemical composition of this continuously cast bloom by weight percentage, C:0.06～0.10%, Si:0.20～0.40%, Mn:1.10～1.65%, P :≤0.010%, S :≤0.0020%, Nb:0.030～0.050%, V:0.020～0.060%, Ti:0.006～0.015%, Ni:0.60～1.30%, Cr:0.30～0.60%, Cu:0.20～0.60%, Mo:0.40～0.60%, Alt:0.020～0.040%, surplus is Fe and inevitable impurity; Impurity element control in the chemical composition of this steel plate is as follows: O≤0.0018%, N≤0.0040%, H≤0.00015%, As≤0.012%, Pb≤0.010%, Sn≤0.010%, Sb≤0.010%;

Rolling technology: adopt cooling controlling and rolling controlling process, roll front continuous blank heating temperature between 1200 DEG C～1220 DEG C, adopt austenite recrystallization district and the two-stage control rolling of austenite non-recrystallization district, every time draft >=12% of roughing, 1050 ~ 1100 DEG C of roughing finishing temperatures, roughing becomes the intermediate blank of 1.5～2.5 times of finished product thicknesses; Finish rolling start rolling temperature is 830～870 DEG C, rolls rear employing laminar flow cooling, 600～650 DEG C of final cooling temperatures, 8～15 DEG C/s of rate of cooling, air cooling subsequently;

Thermal treatment process: the steel plate after air cooling is heated again, and Heating temperature is at ferrite Ovshinsky body equilibrium phase height Ac ₃on carry out austenite phase region quench treatment, quenching temperature is at 900～920 DEG C, Quenching Soaking Time is 2min/mm × thickness of slab, after quenching, steel plate has obtained uniform hardening lath martensite, original austenite grains is tiny, after quenching, 600～630 DEG C of tempering, tempering time is (1.5～2.5) min/mm × thickness of slab+30min; Obtain ultra-high-strength/tenacity steel plate for ocean engineering.