Background technology
Because many parts of the large-scale steel structures such as building, bridge are exposed to outdoor throughout the year, atomospheric corrosion is serious, and cause the life-span of structure short, waste of material is serious; Weathering steel can improve opposing weather-resistance more than one times, thus can extend the life-span of steel construction, also saves material, remarkable in economical benefits.At present, the industry such as building and bridge extensively adopts weathering steel to be used for the construction of key position.
Weathering steel can be roughly divided into two classes by the height of Cr content:
A kind of is the high Cr type weathering steel of Cr content >=2.5%; High Cr type weathering steel also contains the Cu of 0.2 ~ the 0.5% and Ni of 0.2 ~ 1.0% usually to meet the balance requirement of high strength and low-temperature impact toughness; And Cr exists disadvantageous effect to welding property, the thermal weld stress amount interval of bearing of high Cr type weathering steel is narrow, and between 15 ~ 30kJ/cm, otherwise the impelling strength of welded heat affecting zone worsens, and affects the security of total.In industrial practice, also need the strict weld preheating of execution and postweld heat treatment system to guarantee the quality of welding joint, its preheating temperature, according to formulae discovery, significantly reduces welding procedure efficiency.
Be the low Cr type weathering steel between Cr content 0.3 ~ 1.0%, low Cr type weathering steel contains the Mn of >=0.8% usually, the Cu of >=0.2%, the Ni of >=0.2%, and appropriate Mo.Compared with high Cr type weathering steel, because Cr content significantly reduces, and low-carbon (LC) or Ultra-low carbon Composition Design, the welding property of low Cr type weathering steel is increased, is in particular in: carbon equivalent reduces, welding chill sensitive is reduced, preheating temperature is reduced, carbon equivalent reduction decreases hardenability index, and the thermal weld stress amount that steel plate can be born is increased to about 50kJ/cm, still there is the problem that heat input is lower.According to measuring and calculating, for the opposite joint of thickness 40mm steel plate, adopt heat input be 20 and 50kJ/cm submerged arc welding about need 24 and 13 passages; And welding can be completed by single pass during heat input 372kJ/cm, efficiency can improve more than 5 times.
But so far, existing weathering steel technology can't meet the requirement of high heat-input amount welding (>=100kJ/cm).
Summary of the invention
For the deficiencies in the prior art, the object of this invention is to provide a kind of weathering steel adapting to the welding requirements of high heat-input amount, and the impact property of welded heat affecting zone can be guaranteed; Steel grade of the present invention adopts the low manganese Composition Design of low carbon low silicon, control oxygen level after feed calcium line smelting technology, and thermomechanical controlled rolling and controlled cooling model (saving the manufacturing process such as direct quenching, slow cooling) technique, target finished steel plate can be obtained; Yield strength >=the 420MPa of finished steel plate, tensile strength >=550MPa ,-40 DEG C of Charpy-V impact power >=183J, at-20 DEG C of Charpy-V impact power >=47J of the welded heat affecting zone of thermal weld stress amount 200 ~ 600kJ/cm condition lower steel plate.Finished steel plate is keeping, on excellent mechanical property and weather resistance basis, also possessing the requirement adapting to the welding of high heat-input amount, excellent combination property.
For achieving the above object, present invention employs following technical scheme:
A kind of can high heat-input amount welding weather-resistant steel plate, it is characterized in that, the chemical composition of this steel plate is by weight percentage: C0.02 ~ 0.06%, Si<0.10%, Mn0.40 ~ 0.80%, Ni0.35 ~ 0.85%, Cr0.35 ~ 0.85%, Cu0.35 ~ 0.85%, Ti0.005 ~ 0.02%, Al<0.01%, N0.0015 ~ 0.0060%, P≤0.009%, S≤0.005%, Ca0.003 ~ 0.010%, B0.0005 ~ 0.005%, and surplus is Fe and inevitable impurity;
Also should meet: Ti >=3.42N, Mn+Ni≤1.2,1.0≤Cr+Ni+Cu≤2.0 simultaneously
The welding cold crack sensitivity coefficient of this steel grade
Pcm=C+Si/30+(Mn+Cu+Cr)/20+Mo/15+Ni/60+V/10+5B≤0.16;
The production method of this weathering steel comprises the following steps:
In smelting procedure, adopt converter, electric furnace or vacuum induction furnace smelting, alloy to add complete, and oxygen level adds calcium line after meeting 30 ~ 100ppm, molten steel per ton adds calcium line 0.2 ~ 0.3kg, then taps, is cast into slab; In heating, rolling process, slab after heating and thermal insulation, carry out thermomechanical controlled rolling, wherein the rolling temperature of recrystallization zone is between 1050 ~ 1150 DEG C, the rolling temperature of non-recrystallization zone between 820 ~ 920 DEG C, total rolling draft >=70% of rolling sequence; In refrigerating work procedure, after rolling completes, directly enter cooling water equipment, be cooled to go out water-air cooling to room temperature between 450 ~ 600 DEG C, can finished steel plate be obtained;
In described heating process, slab heating temperature controls at 1150 ~ 1200 DEG C, is incubated 2 ~ 2.5 hours;
In described rolling process, non-recrystallization zone single pass draft >=15%;
In described refrigerating work procedure, speed of cooling is 10 ~ 30 DEG C/s.
Select to illustrate to the effect of component contained in the present invention and consumption below:
C: directly affect the intensity of steel plate, low-temperature flexibility and welding property, the minimizing of C content simultaneously also can improve the low-temperature impact toughness of steel plate; But C content too low (<0.02%) can cause the reduction of armor plate strength; And can reduce higher than 0.08% base metal tenacity and HAZ toughness.Therefore C content is 0.02 ~ 0.06%.
Si: the effect usually playing deoxidation in smelting process, and the intensity that can improve steel plate in finished steel plate, its content is often >=0.20%; But the low-temperature flexibility of the grievous injury of Si meeting simultaneously steel plate and welding property, under the condition of weld heat input >=50kJ/cm, Si can promote the formation of M-A constituent element, damage the low-temperature flexibility of Plate Welding heat affected zone.In steel grade of the present invention, Si is as harmful element, and its content controls below 0.10%.
Mn: the hardening capacity that effectively can improve steel on the one hand, and play the effect of solution strengthening and fining ferrite grains, therefore its content >=0.40%; Mn too high levels then can bring difficulty to the continuous casting operation of steel but then, and can form large-sized MnS and be mingled with, thus worsens center segregation, brings harm to the core structure of steel plate and performance, its content should≤1.70%.Consider in steel grade and added the more alloying element guaranteeing steel grade weather resistance, for reducing Pcm further to improve welding property, Mn content is 0.40 ~ 0.80%.
Cr: most important effect is in the present invention the weather resistance improving steel grade, because it can form fine and close oxide compound at surface of steel plate, thus can improve atmospheric corrosion resistance ability; But too high levels can have a negative impact to the welding property of steel plate simultaneously.Therefore, Cr content is 0.35 ~ 0.85%.
Cu: be the most cheap element improving steel plate weather resistance, obvious for the corrosive effect improving opposing industrial atmosphere or marine atmosphere.When Cu too high levels, continuously cast bloom can be made on the one hand to produce brittle crack, affect plate quality; Increase welding cold crack sensitivity on the other hand, thus reduce the weldability of steel plate.When Cr and Cu compound is added, opposing atomospheric corrosion effect is more obvious.Therefore, Cu content is 0.35 ~ 0.85%.
Ni: be one of effective element improving steel plate weather resistance, its add-on does not have corrosion-resistant effect when being less than 0.10%, but too high levels can cause steel plate oxide skin to be difficult to remove, plate surface quality can be affected on the one hand, on the other hand owing to being noble element, too high levels significantly can increase cost.Meanwhile, Ni effectively can also suppress the Surface Crack Problems of the continuously cast bloom introduced because Cu adds.Therefore, Ni content is 0.35 ~ 0.85%.
Ti: be combined with N and generate the higher TiN particle of high-temperature stability, can suppress austenitic grow up (temperature≤1350 DEG C) like this, thus improve the low-temperature flexibility in steel plate and HAZ district thereof, thus improves welding property, and therefore its content wants >=0.005%; But when content is more than 0.02%, can cause the reduction of HAZ district toughness, therefore Ti content is 0.005 ~ 0.02%, and Ti >=3.42 × N.
Al: introduce as impurity element, first by acid-soluble for Al(state) content be limited in less than 0.01%, thus decrease the quantity of aluminate in steel grade, and the titaniferous amount that can increase to a certain extent in oxide inclusion, thus the effect reached alumina inclusion modification, can indirectly promote Intragranular Acicular Ferrite forming core, improve welding property; In addition the minimizing of dissolved aluminum, decreases the generation of crystal boundary ferrite side plate, is also beneficial to the raising of low-temperature flexibility.
P: bring adverse influence can to the toughness of mother metal and the toughness of HAZ as impurity element, so its content should lack as much as possible, its content controls≤0.009%.
S: be form MnS thus the element that ductility is reduced.For ensureing the Z-direction performance of slab, its content controls≤0.005%.
Ca: the important element in the present invention, on the one hand can cleaning molten steel, can effectively reduce alumina type and be mingled with; Can form the oxysulfide of a certain amount of calcium on the other hand in molten steel, this type impurity can serve as the heterogeneous nucleating agent of austenite Intragranular Acicular Ferrite forming core in phase in version process, thus favourable to low-temperature impact toughness.Steel grade of the present invention is in experience Thermal Cycle process, and this type impurity can be induced and be inspired Intragranular Acicular Ferrite forming core, thus reduces the formation of grain boundary ferrite or upper bainite lath, thus can improve the low-temperature impact toughness of welded heat affecting zone.Its content controls 0.003 ~ 0.010%.
B: effectively can improve hardening capacity, thus can refinement steel plate tissue improve intensity.But in the present invention, the compound interpolation of main employing Ca and B controls the phase in version behavior of steel plate in Thermal Cycle process, both suppressed the generation of boundary Wei Shi body ferrite, ferrite side plate and lath of bainite, thus be the oxysulfide performance promotion Intragranular Acicular Ferrite forming core creation prerequisite of calcium.Its content controls 0.0005 ~ 0.005%.
N: in order to ensure the surface quality (surface crack) of continuously cast bloom, control below 0.0060%.Meanwhile, low N content also can reduce the tough sex chromosome mosaicism that the solid solution N embrittlement in HAZ brings.Also the Ti of trace is with the addition of in the present invention, one of object forms TiN particle, can block that continuously cast bloom (~ 1200 DEG C insulation 2 hours) in Furnace Production Process is austenitic grows up, thus reach fining ferrite grains size, and then improve the object of intensity.Therefore the preferred content of N is 0.0015 ~ 0.0060%, and Ti >=3.42N.
Compared with the existing technology, beneficial effect of the present invention is at least:
(1) steel plate of the present invention is redesigned by composition, smelting and rolling technology, obtains the weather-resistant steel plate possessing high strength, superior low temperature impelling strength, weather resistance and excellent welding performance; Compare with existing steel grade, the welding property of steel plate of the present invention is excellent, on the basis can exempting weld preheating and postweld heat treatment, the thermal weld stress amount that general steel plate can bear is risen to 200 ~ 600kJ/cm from existing 50kJ/cm level;
(2) weld task that electro-gas (enclosed) welding single pass or multiple-wire submerged-arc welding single pass complete 40mm thickness steel plate can be realized, welding efficiency can be made to improve more than 5 times than adopting conventional steel plates, remarkable in economical benefits, is specially adapted to the large welded structures such as boats and ships, ocean platform field;
(3) steel plate yield strength >=420MPa, tensile strength >=550MPa, unit elongation >=22% ,-40 DEG C of ballistic work >=183J, under thermal weld stress amount 200 ~ 600kJ/cm condition ,-20 DEG C of ballistic work >=47J of heat affected zone, can meet the efficient welding requirement of high heat-input amount.
Embodiment
Below in conjunction with the drawings and the specific embodiments, technical scheme of the present invention is described further.
Embodiment 1:
After adopting vacuum induction furnace smelting, each alloying element to add, meet after 30 ~ 100ppm until oxygen level, molten steel per ton adds the calcium line of 0.2 ~ 0.3kg, is then cast into steel ingot, forges into the steel billet that thickness is 220mm.This steel billet contains (weight percent): C0.03, Si0.08, Mn0.77, P0.007, S0.004, Cr0.45, Cu0.35, Ni0.35, Ti0.013, N0.0035, B0.004, Ca0.003, Al0.007, and surplus is Fe and inevitable impurity.This steel grade cool attenuation FACTOR P cm=0.137; Weather-proof index I=6.10.
Heating of plate blank is incubated 2 hours to 1200 DEG C, and then start thermomechanical controlled rolling and cooling, recrystallize rolling temperature is between 1100 ~ 1150 DEG C, and rolling pass is followed successively by 220 → 200 → 180 → 150 → 120 → 100mm; Unhydrated cement rolling temperature is 860 ~ 900 DEG C, and rolling pass is followed successively by 100 → 80 → 64 → 50 → 40mm; Roll the rear water tank that directly enters into cool, leaving water temperature(LWT) is 550 DEG C, and speed of cooling is 18 DEG C/s, and then air cooling is to room temperature, and namely obtained thickness is the finished steel plate of 40mm.
The yield strength of steel plate is 460MPa, and tensile strength is 585MPa, and unit elongation is 25%, and-40 DEG C of ballistic work measured values are 285/300/295J, and mean value is 293J.Steel plate tissue is made up of acicular ferrite and a small amount of bainite, sees Fig. 1; Steel plate weather resistance is in table 1.
Slag Welding test is carried out to 40mm Plate Steel, welding current 320A, voltage 50V, welding speed 0.43mm/s, electrode swing rate 4.8mm/s, heat input 372kJ/cm.Tissue and the impact property of the steel plate hot zone of influence are shown in Fig. 2 and table 2.
Embodiment 2:
After adopting vacuum induction furnace smelting, each alloying element to add, meet after 30 ~ 100ppm until oxygen level, molten steel per ton adds the calcium line of 0.2 ~ 0.3kg, is then cast into steel ingot, then forges into steel billet.This slab contains (weight percent): C0.04, Si0.06, Mn0.72, P0.008, S0.004, Cr0.40, Cu0.35, Ni0.35, Ti0.016, N0.0032, B0.003, Ca0.0045, Al0.008, and surplus is Fe and inevitable impurity.This steel grade cool attenuation FACTOR P cm=0.136; Weather-proof index I=6.11.
Heating of plate blank is incubated 2 hours to 1200 DEG C, and then start thermomechanical controlled rolling and cooling, recrystallize rolling temperature is between 1100 ~ 1150 DEG C, and rolling pass is followed successively by 240 → 200 → 170 → 150 → 120mm; Unhydrated cement rolling temperature is 860-900 DEG C, and rolling pass is followed successively by 120 → 102 → 85 → 71 → 60mm → 50mm; Roll the rear water tank that directly enters into cool, leaving water temperature(LWT) is 550 DEG C, and speed of cooling is 18 DEG C/s, and then air cooling is to room temperature, and namely obtained thickness is the finished steel plate of 50mm.
The yield strength of steel plate is 455MPa, and tensile strength is 564MPa, and unit elongation is 26%, and-40 DEG C of ballistic work measured values are 304/312/324J, and mean value is 313J.Steel plate tissue is made up of acicular ferrite and a small amount of bainite; Steel plate corrosion performance is in table 1.
Slag Welding test is carried out to 50mm Plate Steel, welding current 340A, voltage 52V, welding speed 0.33mm/s, electrode swing rate 4.8mm/s, heat input 535kJ/cm.The impact property of the steel plate hot zone of influence is in table 2.
As can be seen here, weather-resistant steel plate of the present invention is on the basis keeping the intensity of common grade weather-resistant steel plate, low-temperature flexibility and weather resistance, and welding property obtains remarkable lifting; Weld preheating and postweld heat treatment can be exempted, and thermal weld stress amount can be adapted to up to the welding requirements of 200 ~ 600kJ/cm and can guarantee-20 DEG C of Charpy-V impact power >=47J of heat affected zone.The present invention can high heat-input amount welding weather-resistant steel plate can be applicable to the fields such as building, bridge, ocean platform.
The weather resistance of table 1 embodiment steel plate
Steel grade |
Relative corrosion rate |
Embodiment 1 |
0.43 |
Embodiment 2 |
0.42 |
Comparative example Q345B |
1.0 |
The impelling strength of the slag Welding joint heat affected zone that table 2 embodiment obtains