KR100276311B1 - The manufacturing method of 100kg grade super high strength steel plate with continous casting method - Google Patents

Abstract

PURPOSE: A method for manufacturing superhigh tensile strength steel plates (tensile strength: 100kg) by continuous casting method for the application to bulletproof materials. CONSTITUTION: The superhigh tensile strength steel plate is manufactured by preparing a hot metal comprising C 0.10-0.19wt.%, Si 0.15-0.35wt.%, Mn 0.10-0.40wt.%, P 0.012wt.% or less, S 0.005wt.% or less, Ni 2.75wt.%-3.50wt.%, Cr 1.30-1.80wt.%, Mo 0.35-0.45wt.%, V 0.010-0.025wt.%, a balance of Fe and inevitable impurities; continuous casting the hot metal in such a manner that the amount of water spray in a cooling table ranges 0.32 to 0.40L/kg, and thereby obtaining slab; air cooling the slab at ambient condition; rolling process of slab; selective cooling processes where either the obtained plate is cooled very slowly at the rate of 5-14deg.C/hr in case the plate is over 50mm in thickness or the obtained plate is air-cooled in case the thickness of the plate is 50mm or less; quenching the cooled plate in the temperature range of 900 to 920deg.C; and then tempering it in the temperature range of 470 to 580deg.C.

Description

Manufacturing Method of 100kg Ultra High Tenacity Plate with Excellent Internal Quality by Continuous Casting Method

The present invention relates to a method for manufacturing a super high-strength thick plate used in structures requiring bulletproof properties such as electronic boards, self-propelled outer shell plate, more specifically 100kg excellent in hardness, low temperature toughness and internal quality while producing by the continuous casting method It relates to a method for producing a super high tensile steel plate.

In general, the hardness and toughness of steel are mutually opposite physical properties. If the hardness is high, the toughness is lowered. If the toughness is high, the hardness is lowered. It should have good characteristics in the breaking test, which is a measure of. However, thicker plates used in various antiballistic structures are more difficult to secure internal quality as the thickness thereof is thicker, and thus manufacturing conditions are more difficult.

Conventionally, the 100kg high-tension thick plate is manufactured by ingot processing by injecting the steel completed in the steelmaking process by injecting the steel, and rolling the steel ingot in the process of forming the slab to make slabs, and then heat-treating them. In order to secure the internal quality, this manufacturing method is extremely low-low cooling in an enclosed space during the ingot casting process to release the impurity gas, especially hydrogen gas, remaining in the slab to the outside to prevent deterioration of internal quality to obtain high internal quality. Could. However, the method has a problem that the slab error rate in the process of the slab decreases, and also due to the case of a number of manufacturing process decreases productivity and increases the manufacturing cost. In particular, due to the difficulty in mass production, it is required to develop a new manufacturing method that can replace the coalescence method in terms of economics.

Therefore, the present invention has been proposed based on the results of the research and experiment to apply the continuous casting (CONTINIOUS CASTING) method instead of the conventional ingot-disintegration process having the above problems, the present invention is a continuous casting In order to prevent the segregation of the core, by controlling the non-quantity during the second cooling of the performance, and by controlling the various components and manufacturing conditions with the maximum air cooling after rolling of the thick plate, it is produced by continuous casting, but the hardness, low temperature toughness and internal quality To provide a method for producing this excellent 100kg high-tension thick plate, the purpose is.

FIG. 1 is a photograph (65 mm thickness of a rolled plate) showing the results of a fracture test of the present invention, a conventional material, and a comparative material.

2 is a photograph showing the fracture test results of the present invention and the conventional material (thickness of the rolled plate 45mm).

The present invention for achieving the above object, in weight%, C: 0.10-0.19%, Si: 0.15-0.35%, Mn: 0.10-0.40%, P: 0.012% or less, S: 0.005% or less, Ni: 2.75 Preparing a molten steel consisting of -3.50%, Cr: 1.30-1.80%, Mo: 0.35-0.45%, V: 0.010-0.025%, balance Fe and other unavoidable impurities; Manufacturing a slab by continuously casting the molten steel under a condition in which the specific amount of the secondary cooling zone is in the range of 0.32 to 0.40 l / kg, and multi-stagely stacking the air to cool to room temperature; After the usual rolling to the slab, if the thickness of the thick plate is 50mm or more, ultra-cooling at a rate of 5 ~ 14 ℃ / hr, if it is 50mm or less, usually air-cooling; 100kg by the continuous casting method with excellent hardness and low temperature toughness and internal quality comprising the step of quenching the cooled thick plate in the temperature range of 900 ~ 920 ℃ after quenching in the temperature range of 900 ~ 920 ℃ It relates to a method for producing a super high-tension thick plate.

Hereinafter, the component composition and the production conditions of the present invention will be described in detail.

The carbon (C) increases the hardness and strength by increasing the hardenability during the heat treatment of the steel, if the content is more than 0.19% by weight (hereinafter referred to as '%') is harmful to toughness and weldability, and less than 0.10% If the amount is small, the quenchability is low, and thus hardness cannot be guaranteed. Therefore, it is preferably added in the range of 0.10-0.19%.

The silicon (Si) forms a carbide and is an element that is solid-solution in Fe to increase the elastic limit tensile strength, the content is less than 0.15%, the effect is insufficient, 0.35% or more, the ferrite structure is reduced and the formation of non-metallic inclusions (toughness) It is preferable to add in the range of 0.15-0.35% since it deteriorates.

The manganese (Mn) is an effective element capable of improving hardness when heat-treated as an element for improving hardenability, and its content deteriorates weldability when added in an amount of 0.40% or more and secures hardness due to a decrease in hardenability when a small amount of 0.10% or less is added. Since it is unstable, it is preferable to add in the range of 0.10-0.40%.

The phosphorus (P) is the largest impurity that inhibits the low-temperature impact toughness of the steel sheet, so the internal quality is degraded, and the content thereof is preferably limited to 0.012% or less.

The sulfur (S) is the same harmful element as the phosphorus (P) component, so it is preferable to limit the content to 0.005% or less since it causes the deterioration of low-temperature impact toughness and weldability in the thick plate product.

The nickel (Ni) is an alloying element that increases the low temperature toughness and improves the hardenability, but it is disadvantageous in terms of economics because it is expensive, and since the effect is small when a small amount is added, the content is added in the range of 2.75-3.50%. desirable.

The chromium (Cr) is an element effective for quenching and is widely used for increasing hardness and strength. Hence, chromium (Cr) is detrimental to weldability when a large amount is added, and it is disadvantageous to secure hardness when a small amount is added, so that the content is immersed in the range of 1.30-1.80%. It is preferable.

The molybdenum (Mo) contributes to the improvement of creep rupture strength of the austenite state in the steel structure, and improves the hardenability to increase the strength, but may lead to brittle brittleness when a large amount is added or harmful to the deterioration of the weld toughness The content is preferably added in the range of 0.35-0.45%.

The vanadium (V) is an alloying element that is effective for hardenability but impairs weldability, and therefore, the content of vanadium (V) is preferably added in the range of 0.010-0.025%.

The manufacturing method of the present invention based on the steel having the composition range as described above is applied to the continuous casting instead of the general ingot-disintegration process. In this case, the general playing method tends to collect impurities and other components in the center during refining operation after steelmaking, so that continuous cracks or components, impurities, and segregation in the center of the judgment surface during the judgment test for the internal quality inspection of the final steel. As a result of the combined bonding, it could not be applied to the thick plate over 50mm. Therefore, the present invention is characterized in controlling the specific amount of water in the secondary cooling zone during continuous casting to solve the segregation of the center of the cast during continuous casting. That is, after molten steel is injected into the mold from the tundish, the cast piece exiting the mold is intermediately cooled in the secondary cooling zone, which is a section which is quenched by a high speed water cooling spray device while passing through the end of the player, where the ratio It is preferable to make the amount of water into the range of about 0.32-0.40 l / kg. The reason is that when the water injection amount is 0.4ℓ / kg or more, the steel contains large amounts of Cr and Mo, which are effective alloys for quenching, so there is a fear that quenching may occur on the surface and inside of the slab due to quenching. In this case, impurities inside the slab may be segregated in the center, and defects may occur due to cracks at the fracture test in the final product.

After the slab is manufactured after continuous casting under the above conditions, the slabs are commonly used in the art, that is, the stacks are stacked and stacked in multiple stages for air cooling to prolong the period required for cooling to diffuse hydrogen, which is an impure gas remaining inside. Give the greatest possible opportunity. After the normal thick plate rolling, the thick plate material having a thickness of 50 mm or more is preferably slowly cooled at a rate of 4-14 ° C./hr so that hydrogen in the rolled material is sufficiently diffused and released to the outside. The reason for this is that the thickness of the rolled sheet is so thick that it is not sufficiently pressed during rolling, so that the inclusions remain inside the product in a state where the inclusions are elongated in the rolling direction. There is a possibility of spreading and causing cracks. Therefore, the cooling is delayed at the highest temperature so that the hydrogen can be sufficiently diffused and released to the outside, so that the hydrogen of the thick plate is slowly cooled at a rate of 4 to 14 ° C./hr to be released to the outside.

If the thickness is 50mm or more, the cooling treatment is performed under the same conditions as above, and if the thickness is less than 50mm, the internal impurities are compressed by sufficient thick plate rolling so that cracks due to hydrogen do not occur.

The thick plate material cooled as described above is then subjected to quenching and annealing heat treatment, and the heat treatment conditions at this time determine the application temperature in consideration of thickness and desired physical properties, ie hardness and low temperature toughness. Hardening is preferably carried out at, and it is preferable to carry out the light immediately in the range of 470-580 ° C.

Hereinafter, the present invention will be described in detail through examples.

Example 1

Five kinds of ingots were cast as shown in Table 1 below, and each of the obtained ingots was rolled to prepare a thick plate having a thickness of 65 mm. The prepared plate was cooled to 10 ° C / hr into slow cooling snow and unexecuted, and then cooled to collect the specimen from the plate, and then subjected to mechanical tests on the collected specimen and the results are shown in Table 2 below. It was. Meanwhile, in Table 2, the conventional material was prepared by an ingot-fragmentation process of an existing steel grade E. In addition, the evaluation of mechanical properties and internal quality was based on MIL-A-12560H and MIL-A-12560D presented in the US Navy standard. In the case of 65mm thick plates, the tensile strength is 90-110kg / mm2 and the hardness is 269-. It was evaluated that 311HB and low temperature toughness (-40 DEG C) had desirable properties when 3.9 Kg.m or more was satisfied. In addition, the internal quality was observed by the fracture surface after the bending test to determine the pass or fail as cracks.

TABLE 1

TABLE 2

As shown in Table 2, in the case of the invention material (1-4) using A to D steel satisfying the composition range of the present invention and subjected to the appropriate heat treatment as in the existing method, it has a satisfactory value corresponding to the above standard. In addition, it was evaluated to have an internal quality equivalent to that of the conventional ingot-flocculation material in the fracture test. On the other hand, although A to D steels satisfying the composition range of the present invention were used, the comparative material (1-4) meeting the manufacturing conditions of the present invention requires cracking inside the fracture surface during the fracture test, thereby requiring high internal quality. It turned out that it is not suitable as a bulletproof material.

On the other hand, the fracture surface photographs of the invention material 1, the comparative material 1, and the conventional material 1 are shown in Fig. 1, but the invention material 1 (Fig. 1 (a)) and the prior art material 1 (Fig. While the fracture surface of 1 (b) was excellent in internal quality without cracking, it was found that the crack was generated in the fracture surface photograph of the comparative material 1 (FIG. 1 (c)).

Example 2

The thickness of the plate was 45 mm and the heat treatment conditions were carried out in the same manner as in Example 1 except that the heat treatment conditions were as shown in Table 3 below. The specimens were collected from the heat-treated plate and mechanical tests were performed on the collected specimens. 3 is shown. In addition, the evaluation of the mechanical properties and internal quality was evaluated in the same manner as in Example 1.

TABLE 3

As shown in Table 3, when using the A to D steel satisfying the composition range of the present invention and subjected to the same heat treatment and thick plate cooling furnace process as the existing method (invention material (5-8), if not) All specimens of (9-12) had satisfactory values corresponding to the above standards, and also had an internal quality equivalent to that of conventional ingot-disintegrating materials in the fracture test. In the case of the 45 mm thick plate of the non-implemented material, it was found that the diffuser hydrogen remaining in the product was not pressed into the crack due to the crushing of the internal inclusions during rolling, so that the thick plate having a thickness of 45 mm or less was applied to the casting casting process. The condition alone was found to be suitable for bulletproof materials requiring high internal quality.

On the other hand, the fracture surface photograph of the invention material (5) and the invention material (4) conventional material (2) was shown in FIG. 2, but invention material (5) (FIG. 2 (a)), invention material (9) ( The internal quality of the whole part of FIG. 2 (b) and the prior art material 2 (FIG. 2 (c)) was excellent.

As described above, the present invention, by the continuous casting method and the method of delaying the cooling in the thick plate as much as possible to discharge hydrogen, which is impurity gas which worsens the internal quality to the outside, the internal quality is ingot-flocculation material in comparison with the conventional material It is possible to provide a manufacturing method that is equivalent to or more than, and can provide a 100kg high-tension thick plate excellent in hardness and low temperature toughness, and excellent in error rate and productivity, and can greatly reduce manufacturing cost. The manufactured thick plate is excellent in bulletproof properties and has a useful effect that can be widely used as a bulletproof structural material.

Claims (1)

(Correction) In weight%, C: 0.10-0.19%, Si: 0.15-0.35%, Mn: 0.10-0.40%, P: 0.012% or less, S: 0.005% or less, Ni: 2.75-3.50%, Cr: 1.30 Providing a molten steel consisting of -1.80%, Mo: 0.35-0.45%, V: 0.010-0.025%, balance Fe and other unavoidable impurities; Manufacturing a slab by continuously casting the molten steel under a condition in which the specific amount of the secondary cooling zone is in the range of 0.32 to 0.40 l / kg, and multi-stagely stacking the air to cool to room temperature; After the usual rolling to the slab, if the thickness of the thick plate is 50mm or more, ultra-cooling at a rate of 5 ~ 14 ℃ / hr, if it is 50mm or less, usually air-cooling; 100kg by the continuous casting method with excellent hardness and low temperature toughness and internal quality comprising the step of quenching the cooled plate as described above in the temperature range of 470 ~ 580 ℃ after quenching at a temperature range of 900 ~ 920 ℃ Method for manufacturing high-strength thick plates.