CN102534384A - 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 no Cr high-performance weather-proof 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 no Cr high-performance weather-proof 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, and 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, and 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 CRES shows in the use experience of coastland; Its surface can not form the protectiveness rusty scale, stops atomospheric corrosion further to take place, 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) notion, high-performance steel are meant 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, discloses a kind of CRES, and the alloying constituent of this CRES 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, through the part constituent content of simple adjustment Q235 ordinary low-carbon steel, under the situation that changes Q235 steel manufacturing condition; Produce have good atmospheric corrosion resistance, the economic corrosion-resisting steel of comprehensive mechanical property, but this type of anti-corrosion steel grade causes inconvenience because of the too high interpolation of Cu, Al element to its continuous casting and Rolling Production operation; Difficult point problem in its industrialization process is more, and is not easy to solve.

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

Patent CN 102127710 A (201110086804.4) through the reasonable control of alloying element, make steel have good mechanical performance and corrosion resistance nature under the prerequisite of not adding noble metal Cr element; Reduced production cost; But carbon content higher (0.06%-0.16%) during this type of steel design is higher to welding process requirement, influences 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 H.T. Weather-resistance bridge steel; Its intensity, toughness, weldableness, 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 is prone to toxigenicity; On the other hand, added 0.0002～0.003% boron in the steel, boron is prone to produce segregation at crystal boundary, causes the slab surface crack defective, to steel-making and the rolling inconvenience that causes.

Summary of the invention

Problem to existing corrosion-resistant steel existence; A kind of no Cr high-performance weather-proof Bridge Steel of the present invention and preparation method thereof, purpose provide a kind of lower cost and have good comprehensive mechanical properties, welding property and do not contain the marine atmosphere corrosion-resisting steel of toxic element Cr.

Realize a kind of no Cr high-performance weather-proof Bridge Steel of the object of the invention, its 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%, and Ni 0.30～0.80%; Nb 0.04～0.07%, and Ti 0.005～0.015%, Al≤0.02%, and surplus is Fe and impurity; Its ys>=450MPa, tensile strength>=535MPa, unit elongation>=28%; Under-40 ℃ than ballistic work>=270J, welding cold crack sensitivity FACTOR P cm≤0.115, erosion resistance index I>=6.13.

Prepare above-mentioned no Cr high-performance weather-proof Bridge Steel, carry 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%, and Ni 0.30～0.80%, and Nb 0.04～0.07%; Ti 0.005～0.015%, Al≤0.02%, and surplus is the molten steel of Fe and unavoidable impurities, and it is poured into a mould; Form steel ingot, the steel ingot forge hot is become steel billet, steel billet is heated to 1150～1200 ℃; Insulation 30-60min makes its abundant austenitizing, and makes the abundant solid solution of microalloy element in the steel;

Adopt two stage rolling then, first section 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 back is cooled to 480～550 ℃ with the speed of cooling water spray of 15-16 ℃/s, and air cooling is to room temperature then.

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 good impelling strength and welding property simultaneously; 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; Be to improve the most economic element of hardness of steel, but the C too high levels can worsen the low-temperature flexibility and the welding property of steel, the Ultra-low carbon design limit formation of pearlitic structure and other carbide; Help the formation of single bainite structure; The galvanic corrosion of having avoided potential difference between the out-phase and having caused helps improving 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 the too high low-temperature flexibility and the welding property that can reduce steel of Si content, Si helps 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 a highly malleablized element important in the steel, in steel, plays the effect of solution strengthening, can reduce the phase transition temperature of steel simultaneously; The size of crystal grain in the refinement steel; Improve the low-temperature flexibility of steel, but can increase during too high levels the steel continuous casting produce in the middle of the trend of segregation, in steel, form banded structure; The homogeneity of influence tissue, thus the present invention to adopt the content of Mn be 0.6～1.00%.

The P element can effectively improve the atmospheric corrosion resistance of steel, but the P element also is a kind of element that is easy to segregation, makes the part of steel produce serious segregation; Can reduce the plasticity and the toughness of steel, especially very harmful to low-temperature flexibility, simultaneously; Because bridge construction develops to the large span direction, the thickness of steel plate is also increasing, for guaranteeing the welding property of steel; Be difficult for usually improving the corrosion resistance nature of steel, should P be controlled at below 0.04%, remedy the weathering resistance loss of energy through adding other alloying element through increasing P unit; 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 should the S content in the steel be controlled at lower level, S among the present invention≤0.010%;

Cu is the atmospheric corrosion resistance important alloying element very that improves steel, can improve the intensity of steel simultaneously, but during too high levels, is prone to crack when steel billet heating or hot rolling, worsens the surface of steel plate performance, can worsen the welding property of steel simultaneously, is easy to generate hot-short; The Cu of Xiang Gangzhong adding about 0.2% can significantly improve the corrosion resistance nature of steel, improves the intensity of steel simultaneously through 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; Effectively the austenitic recrystallize of delayed deformation suppresses austenite crystal and grows up, and improves austenite recrystallization temperature; To obtain tiny crystal grain; Simultaneously, Nb is strong carbonitride forming element, can in steel, play the effect of precipitation strength; Ti is strong carbonitride forming element, and the carbonitride of Ti is the pinning austenite grain boundary effectively, suppresses the alligatoring of austenite crystal; Help crystal grain thinning; Improve the 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 the atomospheric corrosion performance and the low-temperature flexibility of steel; Add trace alloying element Nb and Ti, effectively suppress austenite crystal and grow up, depress greatly through high temperature; Refine austenite crystal grain finally obtains tiny grain structure, improves the intensity and the low-temperature flexibility of steel; Bridge Steel good mechanical performance of the present invention, its ys >=455MPa, tensile strength >=535MPa; Unit elongation >=25% ,-40 ℃ of low-temperature impact work >=270J.

Preparing method of the present invention utilizes controlled rolling and controlled cooling (TMCP) ME, adopts two stage rolling, and first section 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 through 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 guarantee delivery cycle, reduced 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 through the lower carbon content of control, and through 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 under the prerequisite of anti-sea atmosphere corrosion performance, HS, excellent in toughness; The cost of control alloying element such as avoids cracking in process of production at phenomenon, makes it to be suitable for suitability for industrialized production; Simple and easy to control in steel-making, continuous casting and Rolling Production process, no Cr marine atmosphere corrosion-resisting steel product of the present invention is applicable to the application requiring such as bridge under the atmospheric marine environment.

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, and steel billet is heated to 1200 ℃, insulation 30min;

Adopt two stage rolling schemes as shown in table 2 then, first section 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 back is cooled to 507 ℃ with the speed of cooling water spray of 16 ℃/s, and air cooling is to room temperature then.

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, and steel billet is heated to 1200 ℃, insulation 30min;

Adopt two stage rolling schemes as shown in table 2 then, first section 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 back is cooled to 530 ℃ with the speed of cooling water spray of 15 ℃/s, and air cooling is to room temperature then.

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 weather-proof 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 big more; Erosion resistance is strong more, 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	Ys (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

Can find out the ys>=455MPa of the high-performance weather-proof Bridge Steel of the present invention's preparation, tensile strength>=535MPa from table 3; Unit elongation>=28%; Under-40 ℃ than ballistic work>=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 excellent mechanical property, especially have excellent low-temperature flexibility; Have good welding property and atmospheric corrosion resistance welding property simultaneously.

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%, and Mn 1.00%, and P 0.18%; S 0.010%, and Cu 0.20%, and Ni 0.30%, and Nb 0.04%; Ti 0.015%, and Al 0.02%, and surplus is Fe and impurity, casts thereafter; Form steel ingot, this steel ingot cogging and forge hot become the steel billet of section 80 mm * 80 mm, and steel billet is heated to 1150 ℃, insulation 60min;

Adopt two stage rolling schemes as shown in table 2 then, first section 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 back is cooled to 480 ℃ with the speed of cooling water spray of 16 ℃/s, and air cooling is to room temperature then.

Ys is 465MPa, and tensile strength is 542MPa, and unit elongation is to be 280J than ballistic work under 29% ,-40 ℃, 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%, and 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 unavoidable impurities, casts thereafter; Form steel ingot, this steel ingot cogging and forge hot become the steel billet of section 80 mm * 80 mm, and steel billet is heated to 1200 ℃, insulation 30min;

Adopt two stage rolling schemes as shown in table 2 then, first section 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 back is cooled to 550 ℃ with the speed of cooling water spray of 16 ℃/s, and air cooling is to room temperature then.

Its ys is 482MPa, and tensile strength is 538MPa, and unit elongation is to be 270J than ballistic work under 28% ,-40 ℃, and welding cold crack sensitivity FACTOR P cm is 0.105, and erosion resistance index I is 6.21.

Claims (2)

1. no Cr high-performance weather-proof Bridge Steel, its 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%, and Ni 0.30～0.80%; Nb 0.04～0.07%, and Ti 0.005～0.015%, Al≤0.02%, and surplus is Fe and impurity; Its ys>=450MPa, tensile strength>=535MPa, unit elongation>=28%; Under-40 ℃ than ballistic work>=270J, welding cold crack sensitivity FACTOR P cm≤0.115, erosion resistance index I>=6.13.

2. method for preparing no Cr high-performance weather-proof Bridge Steel as claimed in claim 1 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%, and Ni 0.30～0.80%, and Nb 0.04～0.07%; Ti 0.005～0.015%, Al≤0.02%, and surplus is the molten steel of Fe and unavoidable impurities, and it is poured into steel ingot; The steel ingot forge hot is become steel billet, steel billet is heated to 1150～1200 ℃, insulation 30-60min;

Adopt two stage rolling then, first section 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 back is cooled to 480～550 ℃ with the speed of cooling water spray of 15-16 ℃/s, and air cooling is to room temperature then.