CN102534384B - Cr-free high-performance weatherable bridge steel and preparation method thereof - Google Patents

Abstract

The invention belongs to the manufacture field of low alloy steel, in particular to Cr-free high-performance weatherable bridge steel and a preparation method thereof. The Cr-free high-performance weatherable bridge steel provided by the invention contains the following chemical ingredients in percent by mass: 0.02-0.05% of C, 0.20-0.30% of Si, 0.6-1.00% of Mn, no more than 0.02% of P, no more than 0.010% of S, 0.20-0.40% of Cu, 0.30-0.80% of Ni, 0.04-0.07% of Nb, 0.005-0.015% of Ti, no more than 0.02% of Al and the balance of Fe and impurities. The Cr-free high-performance weatherable bridge steel provided by the invention is formed by adopting two-stage rolling, wherein the rolling temperature of rough rolling in a first stage is 1,050-1,070 DEG C, the rolling temperature of fine rolling in a second stage is 900-950 DEG C, and the temperature for final rolling is 800-850 DEG C. The Cr-free high-performance weatherable bridge steel provided by the invention has excellent comprehensive mechanical properties and welding properties, does not contain the toxic element Cr, and meanwhile, has excellent resistance to atmospheric marine corrosion.

Description

A kind of without Cr high-performance weatherable bridge steel and preparation method thereof

Technical field

The invention belongs to low alloy steel and make the field, be specifically related to a kind of without Cr high-performance weatherable bridge steel and preparation method thereof.

Background technology

Along with the development of china natural resources saving type and friendly environment society, the erosion resistance of Bridge Steel more and more comes into one's own, and develops anti-corrosion Bridge Steel, can not only prolong the whole service life of bridge, and can reduce the total expenses of bridge in useful life period.The China mainland shoreline reaches 18; 000km; the coastland is the developed area normally; along with these regional bridge constructions especially developing rapidly of bridge spanning the sea construction; the construction of different types of rridges has also driven the demand to Bridge Steel; these engineerings are when having strengthened the Bridge Steel demand; performance to Bridge Steel is also had higher requirement; not only require to have higher intensity; toughness and good welding property; the also requirement that has has certain solidity to corrosion; meanwhile; existing common corrosion-resisting steel shows in the use experience of coastland; its surface can not form protective rust, stops atomospheric corrosion further to occur, and does not bring into play its due atmospheric corrosion resistance.Therefore, material supplier author has proposed high-performance steel (High Performance Steel both at home and abroad, HPS) concept, high performance steel refers to that mainly a certain of material or several the more traditional steel of performance improve, except possessing higher-strength, the welding property of steel and low-temperature flexibility, especially corrosion resistance nature has a more substantial increase.

The patent No. is that 200510045624.6 Chinese patent relates to the low alloy steel field, a kind of corrosion-resisting steel is disclosed, the alloying constituent of this corrosion-resisting steel and weight percent content are: C:0.12-0.21, Si:0.2-2.0, Mn:0.7-2.0, S≤0.036, P≤0.034, Cu:0.10-0.40, Al＜0.2, all the other are iron and trace impurity, by the Partial Elements content of simple adjustment Q235 ordinary low-carbon steel, in the situation that changes Q235 steel manufacturing condition, produce and have good atmospheric corrosion resistance, the economic corrosion-resisting steel of comprehensive mechanical property, but this type of anti-corrosion steel grade is because of Cu, the too high interpolation of Al element causes inconvenience to its continuous casting and Rolling Production operation, difficulties in its industrialization process is more, and is not easy to solve.

The patent No. is that the Chinese patent of 200810046963.X is for the shortcoming of the welding property of the high remarkably influenced steel of carbon content, a kind of corrosion-resisting steel that adopts the Ultra-low carbon design is disclosed, its impelling strength, weldability and atmospheric corrosion resistance are better, but a large amount of alloying elements such as Cr, Mo etc. have been added during this type of weathering steel design, on the one hand Cr serious harm people healthy under+6 valency states has huge toxicity; On the other hand, the interpolation of the alloying element such as Mo has increased production cost.

Patent CN 102127710 A (201110086804.4) are under the prerequisite of not adding noble metal Cr element, reasonable control by alloying element, make steel have good mechanical property and corrosion resistance nature, reduced production cost, but carbon content higher (0.06%-0.16%) during this type of steel design is higher to welding process requirement, affects its welding property, and its intensity is relatively low, is equivalent to the Q345 rank.

Patent CN 102021495 A (201010592034.6) disclose a kind of 420MPa high tenacity Weather-resistance bridge steel, its intensity, toughness, weldability, corrosion resisting property are good, but the Cr constituent content is higher, reach 0.25%-0.40%, Cr serious harm people healthy under+6 valency states easily produces toxicity; On the other hand, added 0.0002～0.003% boron in the steel, boron easily produces segregation at crystal boundary, causes the slab surface crack defective, to steel-making and the rolling inconvenience that causes.

Summary of the invention

Problem for existing corrosion-resistant steel existence, the present invention is a kind of without Cr high-performance weatherable bridge steel and preparation method thereof, and purpose provides a kind of lower cost and has good comprehensive mechanical property, welding property and do not contain the marine atmosphere corrosion-resisting steel of toxic element Cr.

Realize a kind of without the Cr high-performance weatherable bridge steel of the object of the invention, its chemical constitution is by mass percentage: C 0.02～0.05%, Si 0.20～0.30%, Mn 0.6～1.00%, P≤0.02%, S≤0.010%, Cu 0.20～0.40%, Ni 0.30～0.80%, and Nb 0.04～0.07%, and Ti 0.005～0.015%, Al≤0.02%, surplus is Fe and impurity, its yield strength 〉=450MPa, tensile strength 〉=535MPa, unit elongation 〉=28%,-40 ℃ of lower Charpy merit 〉=270J, welding cold crack sensitivity FACTOR P cm≤0.115, erosion resistance index I 〉=6.13.

Prepare above-mentionedly without the Cr high-performance weatherable bridge steel, carry out according to following steps:

At first melting chemical constitution is by mass percentage: C 0.02～0.05%, Si 0.20～0.30%, Mn 0.6～1.00%, P≤0.02%, S≤0.010%, Cu 0.20～0.40%, Ni 0.30～0.80%, Nb 0.04～0.07%, and Ti 0.005～0.015%, Al≤0.02%, surplus is the molten steel of Fe and inevitable impurity, it is poured into a mould, form steel ingot, the steel ingot forge hot is become steel billet, to heating steel billet to 1150～1200 ℃, insulation 30-60min makes its abundant austenitizing, and so that the abundant solid solution of the microalloy element in the steel;

Then adopt two stage rolling, first paragraph is roughing, 1050～1070 ℃ of start rolling temperatures, the accumulative total draft is at least 50%, and subordinate phase is finish rolling, start rolling temperature 900-950 ℃, 800～850 ℃ of finishing temperatures, the accumulative total draft is at least 70%, and rolling rear speed of cooling water spray with 15-16 ℃/s is cooled to 480～550 ℃, and then air cooling is to room temperature.

Compared with prior art, characteristics of the present invention and beneficial effect are:

In order to make weathering steel have higher intensity and corrosion resistance nature, have simultaneously good impelling strength and welding property, the present invention adopts the mode of compound interpolation alloying element, obtain best effect with less alloying element, reach cost-benefit maximization, main alloy element content of the present invention is based on following principle:

C exists with the interstitial atom form in steel, to improve the most economic element of hardness of steel, but the C too high levels can worsen low-temperature flexibility and the welding property of steel, the Ultra-low carbon design limit formation of pearlitic structure and other carbide, be conducive to the formation of single bainite structure, the galvanic corrosion of having avoided potential difference between the out-phase and having caused is conducive to improve the erosion resistance of steel, thus the present invention to design carbon content be 0.02～0.05%;

Si plays the effect of solution strengthening in steel, can improve the intensity of steel, but too high low-temperature flexibility and the welding property that can reduce steel of Si content, Si is conducive to the formation of fine and close rusty scale in addition, can improve the atmospheric corrosion resistance of steel, it is 0.20～0.30% that the present invention adopts the content of Si;

Mn is highly malleablized element important in the steel, in steel, play the effect of solution strengthening, can reduce simultaneously the phase transition temperature of steel, the size of crystal grain in the refinement steel, improve the low-temperature flexibility of steel, but can increase during too high levels steel continuous casting produce in the middle of the trend of segregation, in steel, form banded structure, the homogeneity of impact tissue, thus the present invention to adopt the content of Mn be 0.6～1.00%.

The P element can the Effective Raise steel atmospheric corrosion resistance, but the P element also is a kind of element that is easy to segregation, make the part of steel produce serious segregation, can reduce plasticity and the toughness of steel, especially very harmful to low-temperature flexibility, simultaneously, because bridge construction is to the large span future development, the thickness of steel plate is also increasing, and for guaranteeing the welding property of steel, is difficult for usually improving by increasing P unit the corrosion resistance nature of steel, P should be controlled at below 0.04%, remedy the weathering resistance loss of energy by adding other alloying element, P content is controlled at lower level among the present invention, P≤0.02%;

S is the harmful element in the steel, and the sulfide of generation not only has a strong impact on the mechanical property of steel, but also can worsen the atmospheric corrosion resistance of steel, therefore the S content in the steel should be controlled at lower level, S among the present invention≤0.010%;

Cu is the very important alloying element of atmospheric corrosion resistance that improves steel, can improve the intensity of steel simultaneously, but during too high levels, easily cracks when heating steel billet or hot rolling, worsens the surface of steel plate performance, can worsen simultaneously the welding property of steel, produces easily hot-short; The Cu of Xiang Gangzhong adding about 0.2% can significantly improve the corrosion resistance nature of steel, improves simultaneously the intensity of steel by solution strengthening, and it is little less than 0.55% pair of welding performance hazards to contain the Cu amount, so the content of Cu is Cu 0.20～0.40% among the present invention;

Ni is the important alloying element that improves the anti-sea atmosphere corrosion performance of weathering steel.In addition, the crystal grain that Ni can the refinement steel improves the low-temperature flexibility of steel, effectively stops the hot-short check crack that causes of Cu, and Ni content is designed to 0.30～0.70% in the steel of the present invention;

Nb has a very important role in the controlled rolling and controlled cooling process of steel, the effective austenitic recrystallize of delayed deformation, suppress Austenite Grain Growth, improve austenite recrystallization temperature, to obtain tiny crystal grain, simultaneously, Nb is strong carbonitride forming element, can play the effect of precipitation strength in steel; Ti is strong carbonitride forming element, and the carbonitride energy effectively pin austenite grain boundary of Ti suppresses the alligatoring of austenite crystal, be conducive to crystal grain thinning, improve intensity and the low-temperature flexibility of steel, Nb content of the present invention is designed to Nb 0.04～0.07%, and Ti content is designed to 0.005～0.015%.

The present invention adopts the Ultra-low carbon design, has improved the welding property of steel, has reduced carbide formation, has obtained single uniform formation, improves atomospheric corrosion performance and the low-temperature flexibility of steel; Add trace alloying element Nb and Ti, the establishment Austenite Grain Growth, depress greatly by high temperature, refine austenite crystal grain finally obtains tiny grain structure, improve intensity and the low-temperature flexibility of steel, Bridge Steel good mechanical performance of the present invention, its yield strength 〉=455MPa, tensile strength 〉=535MPa, unit elongation 〉=25% ,-40 ℃ of low-temperature impact work 〉=270J.

Preparation method of the present invention utilizes controlled rolling and controlled cooling (TMCP) manufacturing process, adopts two stage rolling, and first paragraph is roughing, 1050～1070 ℃ of start rolling temperatures, and accumulative total draft 〉=50%, purpose is the refine austenite crystal grain that makes steel; Subordinate phase is rolling to be finish rolling, start rolling temperature 900-950 ℃, and 800～850 ℃ of finishing temperatures, accumulative total draft 〉=70%, purpose produces a large amount of dislocations by the hot rolling thinning microstructure, increases the nucleation site of precipitated phase, promote precipitated phase to separate out, after rolling, do not need thermal treatment, can supply with hot-rolled state, effectively guaranteed delivery cycle, reduce production cost, and overcome the deficiency of steel plate specification heat-treated stove restriction.

In sum, steel grade of the present invention design is not being added under the prerequisite of valuable but poisonous element Cr, guarantee good welding property by the lower carbon content of control, and by rational element design and Composition Control, the synergy of utilizing alloying element to add guarantees that steel grade has good anti-sea atmosphere corrosion performance, and guaranteeing that this marine atmosphere corrosion-resisting steel is guaranteeing anti-sea atmosphere corrosion performance, high strength, under the prerequisite of excellent in toughness, the cost of control alloying element, the phenomenon such as avoid cracking in process of production, make it to be suitable for suitability for industrialized production, in steel-making, simple and easy to control in continuous casting and the Rolling Production process, of the present inventionly be applicable to application requiring such as bridge under the atmospheric marine environment without Cr marine atmosphere corrosion-resisting steel product.

Embodiment

Embodiment 1

At first adopt 200kg vacuum induction melting test steel, the molten steel that chemical constitution is as shown in table 1 is cast thereafter, forms steel ingot, and this steel ingot cogging and forge hot become the steel billet of section 80 mm * 80 mm, with heating steel billet to 1200 ℃, and insulation 30min;

Then adopt two stage rolling schemes as shown in table 2, first paragraph is roughing, 1070 ℃ of start rolling temperatures, accumulative total draft 50%, subordinate phase is finish rolling, 950 ℃ of start rolling temperatures, 840 ℃ of finishing temperatures, accumulative total draft 70%, rolling rear speed of cooling water spray with 16 ℃/s is cooled to 507 ℃, and then air cooling is to room temperature.

Embodiment 2

At first adopt 200kg vacuum induction melting test steel, the molten steel that chemical constitution is as shown in table 1 is cast thereafter, forms steel ingot, and this steel ingot cogging and forge hot become the steel billet of section 80 mm * 80 mm, with heating steel billet to 1200 ℃, and insulation 30min;

Then adopt two stage rolling schemes as shown in table 2, first paragraph is roughing, 1060 ℃ of start rolling temperatures, accumulative total draft 50%, subordinate phase is finish rolling, 950 ℃ of start rolling temperatures, 830 ℃ of finishing temperatures, accumulative total draft 70%, rolling rear speed of cooling water spray with 15 ℃/s is cooled to 530 ℃, and then air cooling is to room temperature.

The chemical ingredients of table 1 embodiment of the invention 1 and 2 steel (mass percent, %)

Grade of steel	C	Si	Mn	P	S	Ni	Mo	Cr	Cu	Nb	Ti	Al	Surplus
														Embodiment 1	0.045	0.25	0.71	0.02	0.007	0.65	-	-	0.30	0.065	0.012	0.016	Fe and impurity
Embodiment 2	0.03	0.22	0.75	0.02	0.007	0.42	-	-	0.31	0.06	0.01	0.014	Fe and impurity

Table 2 embodiment of the invention 1 and 2 hot rolling scheme

Grade of steel	Heating temperature (℃)	The roughing start rolling temperature (℃)	Finish rolling begin temperature (℃)	Finishing temperature (℃)	Speed of cooling (℃/s)	Final cooling temperature (℃)
							Embodiment 1	1200	1070	950	840	16	507
Embodiment 2	1200	1060	950	830	15	530

Table 3 is mechanical property, welding property and corrosion resistance nature data of the high-performance weatherable bridge steel of the embodiment of the invention 1 and 2 preparations, scaling index I calculation formula is the Legault-Leckie formula of revising among the standard A STM G101-01 of American Society Testing and Materials in the table, its value is larger, erosion resistance is stronger, and calculation formula is:

I=26.01(%Cu)+3.88(%Ni)+1.20(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Ni)(%Cu)-9.10(%Ni)(%P)-33.39(%Cu)(%Cu)

In addition, welding cold cracking sensitivity coefficient calculation formula is:

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

The mechanical property of table 3 embodiment of the invention 1 and 2 steel and compared steel, welding property and corrosion resistance nature data

Grade of steel	Yield strength (MPa)	Tensile strength (MPa)	Unit elongation	-40 ℃ of low-temperature impact works (J)	Welding cold crack sensitivity FACTOR P cm	Corrosion resistance index I
							Embodiment 1	475	558	0.280	279	0.115	6.50
Embodiment 2	455	535	0.329	318	0.097	6.13

As can be seen from Table 3, yield strength 〉=the 455MPa of the high-performance weatherable bridge steel of the present invention's preparation, tensile strength 〉=535MPa, unit elongation 〉=28%,-40 ℃ of lower Charpy merit 〉=279J, welding cold crack sensitivity FACTOR P cm≤0.115, erosion resistance index I 〉=6.13, above data show that steel of the present invention has good mechanical property, especially have excellent low-temperature flexibility; Have simultaneously good welding property and atmospheric corrosion resistance welding property.

In order better to characterize the corrosive nature of high-performance weather-proof steel of the present invention under the marine atmosphere condition, adopt the dried wetted perimeter method of soaking that the corrosion resistance nature of embodiment is tested, its result is as shown in table 4, and Xiang Gangzhong adds an amount of Ni element, can improve the anti-sea atmosphere corrosion performance of steel.

The steel of table 4 embodiment of the invention 1 and 2 preparations Corrosion results under the chloride ion-containing environment compares

Grade of steel	252 cycle depth of corrosion (μ m)
		Embodiment 1	125.0
Embodiment 2	131.5

Embodiment 3

At first adopt 200kg vacuum induction melting molten steel, chemical constitution is by mass percentage: C 0.02%, Si0.30%, Mn 1.00%, and P 0.18%, and S 0.010%, Cu 0.20%, and Ni 0.30%, and Nb 0.04%, Ti 0.015%, and Al 0.02%, and surplus is Fe and impurity, thereafter cast, form steel ingot, this steel ingot cogging and forge hot become the steel billet of section 80 mm * 80 mm, with heating steel billet to 1150 ℃, insulation 60min;

Then adopt two stage rolling schemes as shown in table 2, first paragraph is roughing, 150 ℃ of start rolling temperatures, accumulative total draft 55%, subordinate phase is finish rolling, 900 ℃ of start rolling temperatures, 800 ℃ of finishing temperatures, accumulative total draft 70%, rolling rear speed of cooling water spray with 16 ℃/s is cooled to 480 ℃, and then air cooling is to room temperature.

Yield strength is 465MPa, and tensile strength is 542MPa, and unit elongation is that 29% ,-40 ℃ of lower Charpy merits are 280J, and welding cold crack sensitivity FACTOR P cm is 0.099, and erosion resistance index I is 6.33.

Embodiment 4

At first adopt 200kg vacuum induction melting molten steel, chemical constitution is by mass percentage: C 0.05%, and Si 0.20%, Mn 0.6%, and P 0.02%, S0.008%, Cu 0.40%, and Ni 0.80%, and Nb 0.07%, Ti 0.005%, and Al 0.015%, and surplus is Fe and inevitable impurity, thereafter cast, form steel ingot, this steel ingot cogging and forge hot become the steel billet of section 80 mm * 80 mm, with heating steel billet to 1200 ℃, insulation 30min;

Then adopt two stage rolling schemes as shown in table 2, first paragraph is roughing, 1060 ℃ of start rolling temperatures, accumulative total draft 50%, subordinate phase is finish rolling, 920 ℃ of start rolling temperatures, 850 ℃ of finishing temperatures, accumulative total draft 72%, rolling rear speed of cooling water spray with 16 ℃/s is cooled to 550 ℃, and then air cooling is to room temperature.

Its yield strength is 482MPa, and tensile strength is 538MPa, and unit elongation is that 28% ,-40 ℃ of lower Charpy merits are 270J, and welding cold crack sensitivity FACTOR P cm is 0.105, and erosion resistance index I is 6.21.

Claims (2)

1. one kind without the Cr high-performance weatherable bridge steel, its chemical constitution is by mass percentage: C 0.02～0.05%, Si 0.20～0.30%, Mn 0.6～1.00%, P≤0.02%, S≤0.010%, Cu 0.20～0.40%, Ni 0.30～0.80%, and Nb 0.04～0.07%, and Ti 0.005～0.015%, Al≤0.02%, surplus is Fe and impurity, its yield strength 〉=450MPa, tensile strength 〉=535MPa, unit elongation 〉=28%,-40 ℃ of lower Charpy merit 〉=270J, welding cold crack sensitivity FACTOR P cm≤0.115, erosion resistance index I 〉=6.13.

2. one kind prepares the method without the Cr high-performance weatherable bridge steel as claimed in claim 1, it is characterized in that carrying out according to following steps:

At first melting chemical constitution is by mass percentage: C 0.02～0.05%, and Si 0.20～0.30%, and Mn 0.6～1.00%, P≤0.02%, S≤0.010%, Cu 0.20～0.40%, Ni 0.30～0.80%, and Nb 0.04～0.07%, and Ti 0.005～0.015%, Al≤0.02%, surplus is the molten steel of Fe and inevitable impurity, and it is poured into steel ingot, and the steel ingot forge hot is become steel billet, to heating steel billet to 1150～1200 ℃, insulation 30-60min;

Then adopt two stage rolling, first paragraph is roughing, 1050～1070 ℃ of start rolling temperatures, the accumulative total draft is at least 50%, and subordinate phase is finish rolling, start rolling temperature 900-950 ℃, 800～850 ℃ of finishing temperatures, the accumulative total draft is at least 70%, and rolling rear speed of cooling water spray with 15-16 ℃/s is cooled to 480～550 ℃, and then air cooling is to room temperature.