CN101967604B - Boron-nitrogen composite microalloyecd steel allowing for high heat input welding and manufacturing method - Google Patents

Abstract

The invention discloses boron-nitrogen composite microalloyecd steel allowing for high heat input welding and a manufacturing method, which belong to the technical field of microalloyecd steel. The steel comprises the following chemical components: 0.04 to 0.09 percent of C, 1.00 to 1.80 percent of Mn, 0.10 to 0.50 percent of Si, less than or equal to 0.010 percent of S, less than or equal to 0.015 percent of P, 0.10 to 0.30 percent of Mo, 0.03 to 0.10 percent of V, 0.005 to 0.030 percent of Ti, 0.010 to 0.025 percent of N, 0.0005 to 0.0025 percent of B, less than or equal to 0.015 percent of Al, and the balance of Fe and inevitable impurities. The ratio of the boron content and nitrogen content of the steel meets the condition that 2N-15B is more than or equal to 0.010 and less than or equal to 0.018 and the condition that Ti+V+10B is more than or equal to 4.525N-0.002. The production is organized by adopting a process including electric furnace or converter smelting, external refining, continuous casting, rolling and tempering in turn. The steel has the advantages that: the steel yield strength is more than or equal to 550MPa; the tensile strength is more than or equal to 670MPa; the elongation is more than or equal to 18 percent; the charpy impact power (-40 DEG C) is more than or equal to 200J; when the welding heat input is 45 to 80Kj/cm, the charpy impact power (-40 DEG C) of areas close to seams is more than or equal to 47J; and the process is simple and convenient.

Description

A boron-nitrogen composite microalloy steel capable of welding with high heat input and its manufacturing method

technical field

The invention belongs to the technical field of micro-alloy steel, and in particular provides a boron-nitrogen composite micro-alloy steel which can be welded with high heat input and a manufacturing method.

Background technique

Nitrogen-enhanced steel generally refers to low-carbon vanadium-nitrogen microalloyed steel with a nitrogen content above 0.01 wt%. Nitrogen addition in this type of steel, combined with the third-generation TMCP technology, can optimize the precipitation of V-N particles in austenite and ferrite, significantly refine the ferrite grains, increase the precipitation strengthening increment, and simultaneously improve the steel strength and toughness. In addition, under the premise of maintaining a certain strength level, the carbon content in the steel can be appropriately reduced while increasing nitrogen, so that the steel is not preheated before welding or preheated at a lower temperature to avoid the formation of weld near the seam area. cold crack. At present, vanadium-nitrogen microalloy technology has been widely used in products such as weldable high-strength steel bars, profiles, plates, and hot-rolled strip steel.

However, experimental studies have shown that when the above-mentioned nitrogen-increased steel is welded with a heat input of ≥45kj/cm (corresponding to t _8/5 ≥30s), due to the near-seam area of the steel (corresponding peak temperature is around 1350°C) , VN particles promote the transformation of a large number of coarse grain boundary ferrite, and the MA islands formed by the subsequent transformation have higher hardness, larger size and lower dispersion. When the multiphase structure composed of them is subjected to impact load, microcracks tend to nucleate directly at the interface between soft and hard phases in the form of microcleavage, and microcracks are easy to propagate in coarse ferrite grains, and finally form Fracture morphology characterized by quasi-cleavage or cleavage is essentially brittle fracture, and the impact energy at -40°C is generally lower than 27J.

How to suppress the embrittlement tendency of the near-seam zone of nitrogen-enriched steel under high heat input welding conditions is an important problem faced by vanadium-nitrogen microalloying technology at present. One possible way is to break through the traditional microalloying idea of this type of steel, add a small amount of boron to the nitrogen-increased steel, and form a favorable boron and nitrogen content in the steel by reasonably controlling the range and ratio of the boron content and the nitrogen content. Distribution. Among them, a part of boron exists in the form of solid solution, and during continuous cooling after welding, the solid solution boron non-equilibrium segregates at the austenite grain boundary near the seam to inhibit the formation of coarse grain boundary ferrite; part of boron and Part of the nitrogen combines to form boron nitride particles, and the other part of nitrogen combines with vanadium to form VN particles. Both particles promote the formation of intragranular ferrite and limit the coarsening of granular bainite. That is, through the boron-nitrogen composite microalloying technology, to control the continuous cooling structure transformation in the near-slit area, obtain refined intragranular ferrite and granular bainite, suppress the embrittlement tendency of the M-A island hard phase, and finally make this Boron-nitrogen composite microalloy nitrogen-increased steel can also obtain good impact toughness near the seam when welding with high heat input.

At present, from the literature and patents published at home and abroad, it can also be seen that steel contains a certain amount of boron and nitrogen at the same time. Such as R.J.Glodowski in "N Strain aging in ferritic steels" (Wire J.Int., 28 (2005) 1: 70) and Yuan Hui et al. , 2005, (6): 21-23) introduced that the nitrogen content in electric furnace steel is relatively high, generally the highest content can be close to 0.01wt%. If nitrogen in the electric furnace production line exists in the form of free nitrogen, it will produce Strain aging embrittlement reduces drawability. If an appropriate amount of boron is added to the steel to combine boron with nitrogen to fix the free nitrogen in the steel, the processing performance of the wire can be improved. But this is different from the microalloying method and the purpose to be achieved in this application.

Another example is the patent "weldable structural steel components and its manufacturing method" (application number 200380103645.8) applied by the French company Crusoe in China, which proposes to control the boron and nitrogen in the steel within the range of 5-100ppm and ≤250ppm respectively. And the limitation on boron content and nitrogen content (ppm) also meets B≥1/3×N+0.5. However, the purpose of this patented technology is to improve the hardenability of steel to obtain a martensite-bainite structure, so the ratio of boron and nitrogen is required to be as high as possible.

Another example is the patent "Ultra-high-strength three-phase steel with excellent low-temperature toughness" (application number 99814735.4) applied by ExxonMobil Upstream Research Corporation in China, which proposes to control the boron and nitrogen in the steel to 4-20ppm and ≤ 20～50ppm. If the steel involved in this patent technology is to be welded, its disadvantage is that the N content is low, and the number of VN and BN particles formed is relatively small, which cannot significantly promote the formation of intragranular ferrite in the near-slit area and limit bainite growth of ferrite.

Another example is the Japanese patent "JP-A-62-190016" which proposes a method of using TiN and BN to refine the ferrite near the seam. The disadvantage of this patented technology is that the ratio of boron to nitrogen is low. When welding with high heat input, sufficient solid-solution boron segregation occurs at the austenite grain boundary near the seam, and the coarse grain boundary cannot be effectively suppressed. The formation of ferrite will still cause coarse grain embrittlement.

Another example is the Japanese patent "JP-A-59-159968" which proposes a method of improving the toughness of the near-fracture zone by using grain boundary solid-solution boron to prevent reticular coarse grain boundary ferrite. The disadvantage of this method is that the ratio of boron to nitrogen is too high. When welding with high heat input, it will still promote the formation of coarse granular bainite and cannot suppress the local embrittlement caused by M-A islands.

Another example is the Chinese patent "A Production Method for Hot-Rolled Steel Coils of Strong and Tough Steel" (Application No. 200710035787.5), which proposes to control the boron and nitrogen in the steel at 0.0015-0.0060% and 0.010-0.018%, respectively. However, if the steel is to be welded, its shortcoming is that there is no restriction on the ratio of boron content to nitrogen content, and it is still possible to make the ratio between the two higher or lower, so that high heat input welding is close to Coarse grain boundary ferrite or coarse granular bainite, or the coexistence of coarse grain boundary ferrite and coarse granular bainite are formed in the fracture zone, resulting in significantly insufficient impact toughness.

To sum up, the technologies involved in the existing relevant patents and documents either have low nitrogen content in the steel and are not nitrogen-increased steels, or the ratio of boron to nitrogen is improper, or the ratio of boron to nitrogen has not been adjusted. The limitation is different from the method proposed in this application to improve the impact toughness of nitrogen-enhanced steel in high heat input welding near seam by reasonably controlling the range and ratio of boron content and nitrogen content.

Contents of the invention

The object of the present invention is to provide a boron-nitrogen composite microalloy steel that can be welded with high heat input and its manufacturing method, which solves the problem that either the nitrogen content in the steel is low, it does not belong to nitrogen-enriched steel, or the proportion of boron and nitrogen is improper, Either there is no limitation on the ratio of boron and nitrogen.

The chemical composition of the boron-nitrogen composite microalloy steel welded by high heat input of the present invention is (wt%): C: 0.04～0.09, Mn: 1.00～1.80, Si: 0.10～0.50, S: ≤0.010, P: ≤0.015, Mo: 0.10-0.30, V: 0.03-0.10, Ti: 0.005-0.030, N: 0.010-0.025, B: 0.0005-0.0025, Al: ≤0.015, and the balance is Fe and unavoidable impurities.

The relationship between boron content (wt%) and nitrogen content (wt%) is limited so that the ratio between them meets the requirements of 0.010≤2N-15B≤0.018 and Ti+V+10B≥4.525N-0.002.

The manufacturing method of the present invention completes the manufacturing process according to the technological route of electric furnace or converter smelting, out-of-furnace refining, continuous casting, rolling and tempering treatment. Control the following technical parameters in the process:

Steel smelting and continuous casting methods: add compound deoxidizer to the ladle and bottom blow argon for pre-deoxidation during the tapping process of the converter; at the CAS station, add aluminum from the dipping hood to the ladle for deep deoxidation, and control The content of acid-soluble aluminum in molten steel is ≤0.015%, and vanadium-nitrogen alloy is added to make the vanadium content and nitrogen content in the water close to the target value, and argon is blown at the same time to improve the deoxidation effect and composition uniformity; at the LF station, first Make white slag, carry out deep desulfurization and target composition adjustment, and then feed calcium wire, titanium wire and boron wire in sequence, and blow argon at the same time to make the composition uniform. The steel is sent to the continuous casting table; the continuous casting process adopts the whole process of protective pouring.

Steel rolling: the heating temperature of the billet in the soaking furnace is 1150-1200°C, and the heating time is 4-8 hours; the starting rolling temperature is 1100-1150°C, the final rolling temperature is 850-900°C, the total rolling The rate is 70% to 90%; the steel plate after final rolling has a cooling start temperature of 770 to 820°C in the ACC section, a cooling rate of 10 to 30°C/s, and a return temperature of 480 to 550°C; After staying for 30 seconds, heat straightening is carried out. If the plate shape is good, heat straightening can be carried out directly.

In addition, a tempering treatment is carried out on the rolled steel plate. The key points of the process include: the tempering temperature is 550-600°C, and the tempering time is 1min/mm×plate thickness (mm)+30min.

Since the chemical composition of the steel is the key factor affecting the microstructure and impact toughness of the welding near-seam area, the present invention controls the coarse-grain embrittlement and the local embrittlement caused by M-A islands in the welding near-seam area of high-heat input nitrogen-increased steel. The chemical composition of the above-mentioned steel, especially the chemical composition of the microalloying elements, is specially limited, the main reasons are:

1. Carbon is the main element affecting the welding performance of steel. When the carbon content is higher than 0.09%, it is easy to form high-carbon M-A islands in the welding near seam area, with high hardness and large quantity, causing local embrittlement and reducing impact toughness . However, when the carbon content is less than 0.04%, it is difficult to make the steel achieve the required strength. Therefore, the carbon content should be controlled within the range of 0.04-0.09%.

2. Manganese delays the transformation of austenite to ferrite in the welding near-seam area, which is beneficial to refine the structure and improve the impact toughness. When the content of manganese is less than 1.00%, the above effects are not significant, and the strength of the steel is low. When the manganese content is higher than 1.80%, obvious band segregation is easy to form inside the steel plate, which will not disappear even after high temperature heating during welding, thereby locally forming a hardened structure near the seam and reducing impact toughness. Therefore, the manganese content should be controlled within the range of 1.00-1.80%.

3. Silicon promotes the formation of M-A islands in the near seam area, which increases the tendency of embrittlement. Therefore, the content of silicon should not be higher than 0.50%. However, since silicon is one of the most effective deoxidizing elements in steelmaking, when the silicon content is lower than At 0.10%, molten steel is easily oxidized. Therefore, the silicon content should be controlled within the range of 0.10-0.50%.

4. Sulfur and phosphorus seriously damage the toughness of steel and welding near seam. Therefore, the content of sulfur and phosphorus should be controlled below ≤0.010% and ≤0.015%, respectively.

5. Molybdenum inhibits the formation of coarse grain boundary ferrite in the near seam area of high heat input welding, which is beneficial to improve low temperature toughness. When the molybdenum content is lower than 0.10%, the above effects are not significant; however, when the molybdenum content is higher than 0.30%, the granular bainite in the near-fracture zone is developed and the amount is too large, which reduces the low-temperature toughness. Therefore, the molybdenum content should be controlled at 0.10-0.30%.

6. Vanadium combines with nitrogen in the steel to form VN particles, and the precipitation of VN particles in austenite can increase the nucleation rate of ferrite and refine the structure; the precipitation of VN particles in ferrite has significant Precipitation strengthening. When the content of vanadium is less than 0.03%, the above-mentioned effect of vanadium is not significant. However, with the increase of vanadium content, the number of M-A island brittle phases in the weld near seam area increases, which reduces the impact toughness, and its content should not exceed 0.10%. Therefore, the vanadium content should be controlled at 0.03-0.10%.

7. A small amount of titanium and nitrogen combine to form TiN, which can effectively inhibit the coarsening of the original austenite grains near the welding seam and improve the low-temperature toughness. Its content should not be less than 0.005%. But too much titanium, on the one hand, is easy to form coarse inclusions during the solidification process of molten steel, reducing the impact toughness of the steel and the heat-affected zone of welding; The precipitation strengthening effect, its content should not exceed 0.030%. Therefore, the appropriate titanium content should be controlled at 0.005-0.030%.

8. Aluminum is an important deoxidizing element in the steelmaking process. Even if a small amount of aluminum is added to the molten steel, it can effectively reduce the content of inclusions in the steel and refine the grains. But too much aluminum will also "take away" too much nitrogen in the steel, which is not conducive to the effect of TiN, but also weakens the precipitation strengthening effect of vanadium. Therefore, the aluminum content should be controlled below 0.015%.

9. Nitrogen is a key microalloying element in the steel. To effectively utilize the effects of VN and TiN at the same time, there must be enough N in the steel to cooperate with V and Ti, and its content should not be lower than 0.010%. However, excessive nitrogen addition level, in addition to negative effects on continuous casting operation and slab quality, also forms free nitrogen in steel, increasing aging brittleness of steel and welding heat-affected zone, and its content should be controlled at 0.025% Hereinafter, micro-chemical elements such as Ti, V, B, etc. are used to fix. In addition, as the level of nitrogen increase increases, the amount of coarse grain boundary ferrite in the near seam region tends to increase when welding with high heat input ≥ 45kj/cm, and the excessively high nitrogen content also needs to be limited. Therefore, in addition to controlling the nitrogen content at 0.010-0.025%, the content (wt%) of Ti, V, B and N in the steel also needs to meet Ti+V+10B≥4.525N-0.002.

10. Boron is also a key microalloying element in the steel. Trace amounts of boron segregate at the austenite grain boundaries in the form of solid solution boron in the steel, which can delay the transformation of austenite to ferrite. Inhibits the formation of coarse grain boundary ferrite and promotes bainite transformation. Boron has a similar effect in the near-seam region of the high heat input weld of the steel. But too low boron is not conducive to exerting the above-mentioned effects, therefore, its content should not be lower than 0.0005%. However, too high boron content will promote the formation of coarse granular bainite in the high heat input welding zone near the seam of ≥45kj/cm, which will increase the local embrittlement tendency caused by M-A islands, and its content should not exceed 0.0025%. Therefore, the appropriate boron content should be controlled at 0.0005-0.0025%. On the other hand, the amount of boron added must be compatible with the level of nitrogen increase, that is, a reasonable ratio of boron content to nitrogen content must be controlled in order to maximize strengths and avoid weaknesses, so that boron can play the above-mentioned beneficial effects. The reason is that in the near seam area of high heat input welding, when the ratio of boron to nitrogen is low, the inhibition effect of boron on the formation of coarse grain boundary ferrite is weak, while the promotion effect of nitrogen on the formation of coarse grain boundary ferrite is relatively weak. When the ratio of boron to nitrogen is too high, the promotion effect of boron on the formation of coarse granular bainite is too strong, while nitrogen is limited by the induction of intragranular ferrite by VN particles. The growth effect of bainitic ferrite is weak, and a large amount of coarse granular bainite will still be produced, but the local embrittlement phenomenon caused by M-A islands cannot be suppressed. Therefore, in addition to controlling the boron content and nitrogen content in the nitrogen-increased steel that can be welded with high heat input within the above range, the proportion of boron content and nitrogen content must also be controlled within 0.010≤2N-15B≤0.018 within range.

The present invention has the following advantages:

1. For the boron-nitrogen composite microalloy steel that can be welded with high heat input according to the present invention, after welding under the conditions that the heat input is 45-80Kj/cm and the corresponding t _8/5 is 30-100s, the near seam area The microstructure is mainly composed of intragranular ferrite, granular bainite and MA islands of grain boundary ferrite, in which the percentage of intragranular ferrite is ≥30%; ≥47J.

2. The boron-nitrogen composite microalloy steel that can be welded with high heat input according to the present invention has a microstructure containing quasi-polygonal ferrite and bainite, wherein the volume fraction of bainite is ≥ 40%; yield strength ≥ 550MPa, Tensile strength≥670MPa, elongation≥18%, Charpy impact energy at -40℃≥100J.

3. The manufacturing method of the boron-nitrogen composite micro-alloy steel that can be welded with high heat input according to the present invention has a simple production process, and is especially suitable for the production of medium-thick steel plates requiring high heat input welding.

Description of drawings

Fig. 1 shows that the metallographic structure of the boron-nitrogen composite microalloy steel that can be welded with high heat input according to the present invention is a mixed structure composed of quasi-polygonal ferrite and bainite.

Fig. 2 is that when the boron-nitrogen composite microalloy steel that can be welded by high heat input according to the present invention is 30Kj/cm (corresponding t _8/5 is 15s) when the welding heat input, the near seam area is formed by intragranular ferrite ( Acicular or massive), mixed structure composed of grain boundary ferrite and granular bainite.

Figure 3 shows that when the high heat input weldable boron-nitrogen composite microalloy steel increases the welding heat input from 30Kj/cm to 45Kj/cm (the corresponding t _8/5 is 30s), the microstructure of the near seam area is almost different Intragranular ferrite still accounts for the majority, and the number of grain boundary ferrite and granular bainite increases slightly.

Fig. 4 shows the microstructure in the near seam region when the welding heat input of the boron-nitrogen composite microalloy steel that can be welded with high heat input is further increased from 45Kj/cm to 60Kj/cm (corresponding t _8/5 is 60s) according to the present invention The composition remains unchanged, the number and size of grain boundary ferrite and granular bainite increase, but intragranular ferrite still occupies a considerable proportion.

Figure 5 shows that when the welding heat input of comparative steel 1 (increased nitrogen alone, no boron added) is 60Kj/cm, the near seam area is composed of a large amount of coarse grain boundary ferrite, a small amount of granular bainite and intragranular ferrite mixed organization.

Figure 6 shows that when the welding heat input of comparative steel 2 (boron added alone, no nitrogen added) is 60Kj/cm, a mixed structure consisting of a large amount of coarse granular bainite and a small amount of intragranular ferrite is formed in the near seam area.

Figure 7 shows the nitrogen-increased steel that can be welded with high heat input according to the present invention (Figure 7a), comparative steel 1 (Figure 7b, nitrogen-increased alone, without boron) and comparative steel 2 (Figure 7c, boron added alone, without nitrogen-increased ) When the welding heat input is 60Kj/cm, the M-A island morphology shown by coloring and corrosion is adopted in the near-seam area, which shows that the present invention adds boron and nitrogen to the steel in combination. Compared with adding boron alone, it can make high-heat input welding near the seam The number and density of M-A islands in zone M-A are reduced; compared with nitrogen addition alone, it can reduce the number, size and distribution of M-A islands near the seam in high heat input welding.

Fig. 8 shows the change trend of Charpy impact energy with heat input at -40°C near the seam zone of the boron-nitrogen composite microalloy steel weldable with high heat input and the comparative steel, which shows that the welded near seam zone of the steel of the present invention has relatively more Excellent low-temperature toughness, even when the welding heat input increases to 80Kj/cm, the impact energy at -40°C in the near-seam area is still higher than 47J, while when the welding heat input of comparative steel is ≥ 45Kj/cm, the impact energy at -40°C in the near-seam area is still higher than 47J The work is lower than 47J.

Detailed ways

A boron-nitrogen composite microalloy steel capable of welding with high heat input and its manufacturing method according to the present invention will be further described in detail below in conjunction with specific examples.

According to a boron-nitrogen composite microalloy steel capable of welding with high heat input and its manufacturing method described in the present invention, three kinds of test steels with different boron content and nitrogen content were trial-produced as examples. The test steel was smelted in a 150-ton converter. Smelting and continuous casting trial production follow the following process points:

1. During the tapping process of the converter, add a compound deoxidizer to the ladle and blow argon at the bottom for pre-deoxidation;

2. At the CAS station, first add aluminum into the ladle from the dipping hood for deep deoxidation, and control the acid-soluble aluminum content in the molten steel to ≤0.015%, and then add vanadium-nitrogen alloy to make the vanadium and nitrogen content in the water close to the target value , and argon blowing treatment at the same time to improve the deoxidation effect and composition uniformity;

3. At the LF station, white slag is produced first, deep desulfurization and target composition adjustment are carried out, and then calcium wire, titanium wire and boron wire are fed in sequence, and argon is blown at the same time to make the composition uniform. After the element composition reaches the target value, the steel is tapped and then sent to the continuous casting stand;

4. The continuous casting process adopts the whole process of protective pouring.

The thickness specification of the continuous casting slab is 220mm, and each test slab is further rolled into plates with two thickness specifications of 20mm and 30mm on a 3.5m rolling mill. Follow the following process points when rolling:

1. The billet heating temperature is 1180±20°C, and the heating time is 5 hours;

2. The starting rolling temperature is 1100-1150°C, the finishing rolling temperature is 850-900°C, and the total reduction rates of the test steel plates of three different thickness specifications are 90%, 86% and 82% respectively;

3. For the steel plate after final rolling, the start-cooling temperature in the ACC section is 770-820°C, the cooling rate is 15°C/s, and the reheating temperature is 480-550°C;

4. After the steel plate leaves the ACC, it stays for 30 seconds before hot straightening.

After rolling, the steel plate is subjected to a tempering treatment, the tempering temperature is 560±10°C, and the tempering time of the steel plates with three different thickness specifications is 50, 60 and 70 minutes respectively.

The chemical compositions of the three test steels are shown in Table 1. Another two commercial hot-rolled sheets were selected for comparison, and their chemical compositions are also listed in Table 1.

Table 1: Chemical Composition of Steel (wt%)

It can be seen from Table 1 that the chemical composition of the three test steels prepared according to the present invention all meet the requirements of the present invention. The levels of the boron content are high, medium and low respectively, and the ratio of the boron content to the nitrogen content also meets the limitation requirements of the present invention. Comparative steel 1 is a low-carbon vanadium-nitrogen micro-alloyed high-strength steel that does not add boron but has other chemical components equivalent to those of Example 3. Comparative steel 2 is an ordinary low-carbon bainitic steel without nitrogen addition.

Sampling of each embodiment test steel plate and comparative steel, according to GB/T 13239-2006 standard, adopts MTS NEW810 type tensile testing machine, stretches with 3mm/min constant chuck moving speed, tests longitudinal tensile performance, sampling The part is 1/2 of the plate thickness, and the test result is the average value of 2 samples. According to the GB/T 229-2007 standard, the NCS series 500J instrumented pendulum impact testing machine is used to test the Charpy impact energy at -40°C. The sampling location is 1/2 of the plate thickness, and the test results are taken from 3 samples. average value. The test results of the mechanical properties of the steel plate are shown in Table 2.

Table 2: Mechanical properties of steel

It can be seen that the yield strength of the test steel prepared according to the present invention reaches Q550-Q620 grade, and the Charpy impact energy at -40°C is above 200J. The mechanical properties are equivalent to those of comparative steel.

The test steel and comparative steel were further processed into test pieces with a size of 10×10×80 (mm). First, the Gleeble3500 testing machine was used to simulate the structure of the weld near the seam. The corresponding thermal cycle parameters included: no preheating before welding, the highest heating The temperature is 1350°C, the welding heat input (Kj/cm) is 20, 25, 30, 45, 60, 80 respectively, the corresponding t _8/5 are 6s, 10s, 15s, 30s, 60s, 100s, and the cooling stop temperature is 100 ℃. Then, in accordance with the GB/T 229-2007 standard, the NCS series 500J instrumented pendulum impact testing machine was used to test the Charpy impact energy at ℃ near the simulated seam area. The results are shown in Table 3.

Table 3: Low temperature notch toughness of welding near seam zone

It can be seen from Table 3 that the impact energy at -40 °C in the near-seam area of the five steels shows a downward trend as the heat input increases. However, for the three test steels prepared according to the present invention, under the same heat input conditions in the welding near-seam area, the impact energy at -40°C is higher than the corresponding value of the comparison steel, and when the heat input ≥ 45Kj/cm, the invention steel and The difference in low-temperature toughness of the welded near seam zone of the comparative steels is more significant. Among them, compared with Comparative Steel 1, because the former contains a small amount of B, under the welding conditions of higher heat input (≥45Kj/cm), the formation of coarse grain boundary ferrite in the near seam area is inhibited, so the low temperature The impact energy is 2 to 3 times that of the latter. Compared with Comparative Steel 2, Example 2 has no nitrogen increase, and the ratio of boron content to nitrogen content is relatively high. Under the welding conditions of high heat input (≥45Kj/cm), the granular Bainian steel in the near seam area The body is severely coarsened, so the low temperature toughness is much lower than the former.

Claims (2)

1. the boron nitrogen composite micro-alloyed steel that can adopt high heat input welding is characterized in that chemical component weight percentage ratio is: C:0.04～0.09, Mn:1.00～1.80; Si:0.10～0.50, S :≤0.010, P :≤0.015, Mo:0.10～0.30; V:0.03～0.10, Ti:0.005～0.030, N:0.010～0.015; B:0.0005～0.0011, Al :≤0.015, surplus is Fe and unavoidable impurities; Proportioning between boron content and the nitrogen content meets the requirement of 0.010≤2N-15B≤0.018 and Ti+V+10B>=4.525N-0.002 simultaneously.

2. the method for manufacture of the described boron nitrogen of claim 1 composite micro-alloyed steel is characterized in that, the following technical parameter of control in technology:

The smelting of steel and continuous cast method: in the converter tapping process, in ladle, add composite deoxidant and argon bottom-blowing carries out preliminary dexidation; At the CAS station, carry out deep deoxidation by in ladle, adding aluminium in the impregnating cover earlier, and acid-soluble aluminum content is≤0.015% in the control molten steel; Add VN alloy again; Make content of vanadium and nitrogen content in the water near target value, and Argon is handled simultaneously, to improve deoxidation effect and homogeneity of ingredients; At the LF station, make white slag earlier, carry out the adjustment of dark desulfurization and target component, after feed calcium line, titanium wire and boron line successively, and simultaneously Argon is handled, and makes composition even, confirms through sampling analysis that each elemental composition reaches target value in the molten steel and requires the back to tap, and send the continuous casting platform again; Casting process is taked the whole process protection cast;

Steel rolling: the Heating temperature of steel billet in soaking pit is 1150～1200 ℃, and be 4～8 hours heat-up time; Start rolling temperature is 1100～1150 ℃, and finishing temperature is 850～900 ℃, and total draft is 70%～90%; Steel plate after finish to gauge is that 770～820 ℃, speed of cooling are 10～30 ℃/s, to return hot temperature be 480～550 ℃ in the cold temperature of opening of ACC section; It is strong that steel plate goes out to stop behind the ACC to carry out behind the 30s heat;

Carry out temper one to rolling the attitude steel plate, tempering temperature is 550～600 ℃, and tempering time is 1min/mm * thickness of slab mm+30min;

The chemical component weight percentage ratio of described boron nitrogen composite micro-alloyed steel is: C:0.04～0.09, Mn:1.00～1.80, Si:0.10～0.50; S :≤0.010, P :≤0.015, Mo:0.10～0.30; V:0.03～0.10, Ti:0.005～0.030, N:0.010～0.015; B:0.0005～0.0011, Al :≤0.015, surplus is Fe and unavoidable impurities; Proportioning between boron content and the nitrogen content meets the requirement of 0.010≤2N-15B≤0.018 and Ti+V+10B>=4.525N-0.002 simultaneously.

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