JP3940301B2 - Blasting weathering high-strength steel plate with excellent bending resistance and method for producing the same - Google Patents

Description

【表２】

【００２７】
【発明の効果】
本発明による鋼材は、高強度でありながら曲げ加工性および耐候性を同時に具備している。この鋼材を用いることにより、コンテナ等耐候性を有する鋼材の軽量化を図ることが出来、また、耐候性を具備しているので寿命が長い。従って、軽量化による環境への配慮、長寿命による経済性の効果を享受できる。
【図面の簡単な説明】
【図１】 腐食減量に及ぼすＮｉ量およびＰ量の効果を示した図である。
【図２】 プレス曲げ試験の概略を示した図である。
【図３】 腐食減量および曲げＲに及ぼすＰの影響を示した図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel material for a railway vehicle, land transportation, and marine transportation that requires strength, workability after blasting, and weather resistance, and a manufacturing method thereof.
[0002]
[Prior art]
In the past, containers have been required to be lightweight, long-life and weather resistant, and materials using aluminum have been the mainstream. However, because of its high price and low strength, a steel material having high strength and weather resistance is desired. As a conventional weather resistant steel material, there is a high weather resistant rolled steel material having a tensile strength of 50 kgf / mm ² (490 MPa) class shown in JIS G3125. As a steel material having higher strength than this, JP-A-3-2321 discloses a method for producing a weather-resistant hot-rolled steel sheet having a tensile strength of 60 kgf / mm ² or more and good cold workability.
[0003]
In addition, as the use of marine containers has increased, the usage environment has become even harsher, and even in painted containers, local corrosion has progressed and the situation that cannot withstand long-term use has increased. On the other hand, in JP-A-63-72853, Nb, Ti, V. It is disclosed that a long life can be obtained by adding B.
[0004]
[Problems to be solved by the invention]
However, in recent years, the demand for a high-strength and light-weight container has been further increased, and an ultra-high-strength weathering steel material having a yield strength of 700 MPa or more and good bending workability is required. In addition, the bending process is performed after blasting with the aim of applying the paint at the time of painting, fatigue characteristics, and surface hardenability, so that both the strength and workability required for the steel material are extremely severe. The reason why the required strength is not the tensile strength but the yield strength is that it is necessary to ensure the rigidity even if the plate thickness is thin in order to reduce the weight with a super high strength. Therefore, the components and the manufacturing method disclosed in JP-A-3-2321 cannot satisfy the specifications.
[0005]
In addition, in the component system presented in Japanese Patent Laid-Open No. 63-72853 aiming for a long life, even though the weather resistance life can be secured, cracks are generated in the blast-bending process leading to the container production. I was not satisfied.
The present invention solves these problems, and provides a steel material having a yield strength of 700 MPa or higher and withstanding weathering after bending, and a manufacturing method thereof. Is an issue.
[0006]
[Means for Solving the Problems]
The means of the present invention for achieving the above object is as follows: Ni: 0.2 to 2.0%, Cu: 0.2 to 0.5%, Cr: 0.2 to 1.0%, C : 0.05 to 0.15%, Si: 0.5% or less, Mn: 0.5 to 2.0%, P: 0.02% or less, S: 0.005% or less, Ti: 0.052 One or more of Nb: 0.01-0.07%, V: 0.01-0.07%, B: 0.0005-0.0050% Is a weatherable high-strength steel sheet for blasting that is excellent in bending resistance, characterized in that the balance is made of Fe and inevitable impurities.
[0007]
Moreover, the manufacturing method is as follows: Ni: 0.2-2.0%, Cu: 0.2-0.5%, Cr: 0.2-1.0%, C: 0.05- 0.1%, Si: 0.5% or less, Mn: 0.5-2.0%, P: 0.02% or less, S: 0.005% or less, Ti: 0.052-0.2% And Nb: 0.01 to 0.07%, V: 0.01 to 0.07%, B: 0.0005 to 0.0050%, or one or more, and the balance Is excellent in bending resistance, characterized in that after the steel material comprising Fe and inevitable impurities is heated at 1200 ° C. or higher, the rolling is finished in a temperature range of 850 ° C. to 950 ° C. and scraped off at 500 ° C. to 650 ° C. It is a manufacturing method of the weathering high strength steel plate for blasting.
Below, the reason for limitation of the steel plate and manufacturing method of this invention is described in detail.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In order to solve the above-mentioned problems, the present inventors have conducted investigations and investigations on a method for producing steel sheets of multiple steel types, and have been able to arrive at the present invention. The present invention is described in detail below.
Generally, a weather-resistant steel material does not change from ordinary steel during the initial period when it is exposed to the atmosphere, and the same rust is generated. However, after that, a part of the rust of the weather-resistant steel material becomes dense and is closely adhered to the base material, and this rust serves as a protective film to prevent the progress of rust due to the environment. In order to make such rust, it is considered effective to include Cu—Cr—P.
[0009]
In the case where the material has a tensile strength of 50 to 60 kgf / mm 2 (490 MPa to 590 MPa) as in the conventional case, it is possible to apply a weathering steel material for containers by this component system.
In recent years, coupled with global environmental problems, the weight reduction of automobiles for the purpose of improving fuel efficiency has been screamed, and there is a strong demand for weight reduction of containers used for land transportation and sea transportation. For the purpose of reducing the weight more than before, the target thickness of the steel material has been reduced, and a yield strength of 700 MPa or more has been required to ensure rigidity.
In addition, in the manufacture of containers, in order to improve desketing and painting, shot balls, sand, grids, etc. are projected on the steel plate, and the steel surface is made uneven by blasting. Since the surface is hardened by this process, bending cracks are likely to occur in subsequent bending molding. In particular, cracking susceptibility is significant in materials exceeding the yield strength of 700 MPa, and the influence of the selection of additive elements is increased.
[0010]
In order to produce a weathering steel material that can withstand bending with a blast material in a steel material whose yield strength exceeds 700 MPa as described above,
(1) Improvement of steel material strength (2) Ensuring bending characteristics (3) Ensuring weatherability must be satisfied at the same time.
When P is frequently used for the production of such a high-strength steel material having weather resistance, various problems occur.
First, when casting a slab of 200 mm to 300 mm in the manufacturing process, P tends to cause center segregation and is concentrated in the central portion of the plate thickness that is the final solidified portion. The portion where P is concentrated tends to cause embrittlement cracking. Furthermore, since the high-strength steel material itself has high cracking susceptibility, the P-added weathering-resistant high-strength steel sheet frequently undergoes slab cracking, resulting in a very low yield.
[0011]
Moreover, even if a steel plate can be formed, workability is poor because the material characteristics are brittle due to the addition of P. In general, since the elongation becomes lower as the strength of the steel becomes higher, the workability of the P-added material is further lowered, and the subject of this time is subjected to bending after shot blasting, so that bending cracking is likely to occur.
Furthermore, when a container is assembled by welding, it is easy to cause a weld crack.
As a result of detailed investigation of the characteristics of Cu—Cr—P, which has been used as a weathering element in conventional steel, it has been found that P has a strong adverse effect on the above-mentioned (2) and cannot be used in high strength steel materials. In the 90 ° press bending test shown in FIG. 2, the present inventors investigated the amount of P and bending crack generation conditions by changing R at the tip of the punch. At the same time, the relationship between P addition and corrosion weight loss was investigated and shown in FIG. As P increases, the corrosion weight loss decreases and the weather resistance improves, but it is clear that the increase in P increases the bending R that is the limit of bending cracking, and the bending workability of the steel sheet becomes severe.
Therefore, in order to ensure bending workability, it is necessary to examine a method for ensuring weather resistance without using P. Regarding Cu and Cr, the adverse effect on bending workability is small, but it is difficult to ensure the weather resistance even if only these amounts are increased. Also, it cannot withstand bending after blasting.
[0012]
Therefore, as a result of repeating various experiments,
It is possible to secure weather resistance instead of P by using Ni. Ensuring bending characteristics improves workability by lowering C, reduces the addition of P as much as possible, and adversely affects bending characteristics. In order to reduce the production of MnS, it is possible to achieve the objective by reducing S as much as possible and adjusting the strength by utilizing the precipitation effect of one or more combinations of Ti, Nb, V, and B. I found it.
FIG. 1 shows the effect of Ni on corrosion weight loss compared with the effect of P amount. It has been found that the corrosion weight loss decreases with an increase in Ni, and the same effect as in the case of adding P can be obtained.
[0013]
Further, unlike P, Ni does not segregate during slab casting, and there is no fear of slab cracking and the yield is good. In addition, since there is no problem in workability and weldability, there is no worry about bending after shot blasting or weld cracking, and it is very suitable for the production of high-strength steel sheets for weathering steel with excellent bending resistance. Element. With regard to weather resistance, the effect is exhibited by the combined use with Cu and Cr.
The inventors of the present invention repeated the experiment based on these conditions, and reached the present invention.
The reasons for limiting the additive elements of the present invention will be described in detail below.
[0014]
C:
C is utilized as an element for increasing the strength. In addition to solid solution strengthening, Ti and Nb and carbides can be made and used as precipitation strengthening. However, if it is frequently used, the workability is lowered. Since the workability decreases as the steel material strength increases, the C content is preferably low. The lower limit is set to 0.05% because if it is lower than this, it is difficult to ensure a yield strength of 700 MPa or more. The reason why the content is 0.15% or less is to prevent cracking due to bending.
Si:
Si is an element that easily becomes firelite (2FeO · SiO ₂ ) on the surface of the steel sheet, leaving fine Fe ₂ O ₃ on the outermost surface and generating red scale. When the red scale is formed on the surface of the steel plate, it becomes a mottled pattern and is avoided by users. In order to prevent this, the upper limit of the Si content is 0.5%.
[0015]
Mn:
Mn is an element necessary for increasing the strength of steel. If it is less than 0.5%, it is difficult to produce a high-strength steel material. Further, if adding over 2.0%, it becomes difficult to maintain the workability, so the range was made 0.5 to 2.0%.
P:
P is an element effective for increasing strength and beneficial for improving weather resistance, and has been used for weather-resistant steel materials. However, in the production of an ultra-high strength steel material whose yield strength exceeds 700 MPa, slab embrittlement occurs during the production of the steel material, and the weldability also deteriorates. Moreover, since bending workability also worsens, it is better not to add as much as possible, and the upper limit was made 0.02%.
[0016]
S:
S forms Mn and sulfide MnS. This sulfide is easily deformed, is stretched by rolling, and exists in the steel material. MnS degrades the bendability and workability of steel materials. Particularly in high-strength steel materials, it is better to reduce as much as possible in order to increase crack sensitivity, and the upper limit is set to 0.005% as a commercially achievable limit.
Ni:
Ni is an element that increases strength and weather resistance and is effective in preventing embrittlement. It is especially effective for weather resistance in an environment where the salinity is large. As described above, high-strength steel cannot be used because P effective for weather resistance has a significant adverse effect on workability. Ni can be used as an alternative element, and unlike P, it does not degrade slab cracking or workability of steel materials. In order to effectively use the characteristics of weather resistance, addition of 0.2% or more is necessary. On the other hand, Ni is an expensive metal, and even if it exceeds 2.0%, the effect does not change, so the upper limit was made 2.0%.
Containers are used for both sea and land transportation, and are affected by the salt content of seawater in the sea and salt by snow-melted salt that is swollen in cold regions on land, so Ni is an important element for weather resistance.
In the environment other than salt, the following Cu and Cr elements exhibit the effect, so that the combined use is effective for weather resistance.
[0017]
Cu:
Cu is an element that is important for improving weather resistance and is effective for forming stable rust. As an effect on the corrosive environment, 0.2% or more is necessary. However, if it exceeds 0.5%, surface flaws are liable to occur.
Cr:
Cr is also an element effective in improving weather resistance and effective in forming stable rust. As an effect on the corrosive environment, 0.2% or more is required. However, even if it exceeds 1.0%, the effect does not change, so 0.2 to 1.0% was set.
In order to produce a steel material with a yield strength exceeding 700 MPa, it is effective to use the precipitation strength. About the 4 elements which can utilize the following precipitation effect, the intensity | strength deficit is supplemented and the objective can be achieved by 1 type, or 2 or more types of utilization.
[0018]
Ti:
Ti forms carbides and nitrides with C and N, and improves the strength of the steel material. The effect is manifested when 0.03% or more is added, and the effect remains unchanged even when 0.2% or more is added.
Nb:
Nb also forms carbides and nitrides with C and N, and improves the strength of the steel material. The effect is manifested by addition of 0.01% or more, and the effect remains unchanged even if 0.07% or more is added.
[0019]
V:
V also forms carbides and nitrides with C and N, and improves the strength of the steel material. The effect is manifested by addition of 0.01% or more, and the effect remains unchanged even if 0.07% or more is added.
B:
B is an element that forms carbides and nitrides, is effective in improving hardenability, and is effective in improving strength. Addition of 0.0005 or more produces an effect, and even if 0.0050% or more is added, the effect does not change.
[0020]
Next, the reasons for limiting the manufacturing conditions will be described.
The heating temperature was set to 1200 ° C. or higher to make use of the precipitation effect of Ti, Nb, V, and B, so that carbides and nitrides were dissolved in the slab stage to produce fine precipitates during steel plate production. This is so that the precipitation effect can be fully utilized.
The rolling finishing temperature needs to be 850 ° C. or higher in order to make the precipitate finer, but if it exceeds 950 ° C., there are problems such as the tendency of coarsening of crystal grains and scale wrinkles to occur. The range was 850 ° C to 950 ° C.
[0021]
The scraping temperature affects the size of the precipitate, and the degree of the precipitation effect varies. When scraped at a high temperature, precipitates grow and become too large, reducing the strength effect. On the other hand, if it is too low, the formation of precipitates is insufficient and an increase in strength cannot be expected. For this reason, the moderate temperature control range which can expect an intensity | strength raise was 500 to 650 degreeC.
In production, there is no problem with the use of high-pressure deske and bar heaters, and continuous use of hot rolling to roll bar joints after rough rolling, while using these facilities, while improving the temperature process capability, Scale wrinkles can be prevented and yield can be improved.
[0022]
【Example】
After steel numbers 1 to 12 having various components shown in Table 1 were produced, steel materials were produced under the rolling conditions shown in Table 2, samples were taken, and after the surface was shot blasted, the characteristics were evaluated. .
For the evaluation, the yield strength, tensile strength, and total elongation were measured by a tensile test.
Further, bending was performed using a punch having a bending angle of 90 ° and the tip R of 3 mm, and the presence or absence of cracks in the bent portion was examined.
[0023]
Weldability was judged based on the presence or absence of weld cracks after arc welding.
The weather resistance was determined by performing a corrosion spray test after repeating salt spray treatment, measuring the sample weight before the test and the sample weight after removing the rust after the test, and obtaining the corrosion weight loss. For comparison, the case where the corrosion weight loss was larger than this was evaluated as x, and the case where the corrosion weight was equal or less was evaluated as ◯, based on the data of commercially available 490 MPa class colten.
[0024]
The surface condition was evaluated by observing the surface of the steel material after rolling.
The rolling conditions of test numbers 1 to 12 were all carried out within the conditions of the present invention. Test No. 7 had a small amount of Ni and poor weather resistance. No. 8 has good weather resistance, but because of the large amount of P, cracks occurred in weldability and bending. No. 9 had a lot of Si, and No. 10 had too much Cu. Therefore, the surface was bad because the shavings and patterns were formed on the surface. In No. 11, since C and Mn were too high, bending workability and weldability were poor. No. 12 had a high amount of S, so cracking occurred in the bending test.
[0025]
In Test Nos. 13 to 17, rolling conditions were changed using Steel No. 2 which is the scope of the present invention. In No. 13, since the heating temperature was too low, precipitation strengthening could not be used, and the target yield strength of 700 MPa could not be exceeded. No. 14 had a poor surface condition due to the high rolling temperature. In No. 15, the rolling temperature was low, so that the strengthening due to the refinement of precipitates did not occur, and the desired strength was not obtained. In No. 16, the scraping temperature was high, so that the steel material was softened and the desired strength was not obtained. In No. 17, since the scraping temperature was too low, the strength increased, but the hardened layer increased and cracking occurred after bending.
[0026]
No. 1 to No. 6 satisfying the component range and rolling conditions of the present invention satisfied all the characteristics, and gave good evaluation results.
Furthermore, the present invention Nos. 18 to 20 utilize hot rolling continuation in which the rough bar is subjected to surface scale descaling by high-pressure deske after rough rolling, hot bar heating by a bar heater, and rough bar joining after hot rolling. This is an example. All satisfy the material characteristic values according to the present invention, and further have effects by utilizing each process. For No. 18, a bar heater was used, but the temperature of the rough bar before finish rolling became high and uniform, so precipitation control occurred uniformly, and the material variation in the material decreased, which is usually about 6% in this class. The variation in elongation decreased to 3.8%. In addition, No. 19 is an example utilizing high pressure deske and hot rolling continuation. Due to the high-pressure deske, the surface condition of the steel material has been greatly improved. Moreover, the shape of the coil end portion was improved by continuous hot rolling, and the material yield, which is usually about 95%, was improved to 97%. Furthermore, No. 20 is an example using a bar heater and continuous hot rolling. The variation in elongation was reduced to 3.2%, and the material yield was improved to 98%.
[Table 1]

[Table 2]

[0027]
【The invention's effect】
The steel material according to the present invention is simultaneously provided with bending workability and weather resistance while having high strength. By using this steel material, the weight of the steel material having weather resistance such as a container can be reduced, and the life is long because it has weather resistance. Therefore, environmental considerations due to weight reduction and economic effects due to long life can be enjoyed.
[Brief description of the drawings]
FIG. 1 is a graph showing the effects of Ni amount and P amount on corrosion weight loss.
FIG. 2 is a diagram showing an outline of a press bending test.
FIG. 3 is a diagram showing the influence of P on corrosion weight loss and bending R.

Claims (2)

As mass%
C: 0.05 to 0.15%,
Si: 0.5% or less,
Mn: 0.5 to 2.0%
P: 0.02% or less,
S: 0.005% or less,
Ni: 0.2 to 2.0%,
Cu: 0.2 to 0.5%,
Cr: 0.2 to 1.0%
Ti: 0.052 to 0.2% , and
Nb: 0.01 to 0.07%,
V: 0.01 to 0.07%,
B: A weathering high-strength steel sheet for blasting that is excellent in bending resistance, characterized by containing one or more of 0.0005 to 0.0050%, with the balance being Fe and inevitable impurities. As mass%
C: 0.05 to 0.15%,
Si: 0.5% or less,
Mn: 0.5 to 2.0%
P: 0.02% or less,
S: 0.005% or less,
Ni: 0.2 to 2.0%,
Cu: 0.2 to 0.5%,
Cr: 0.2 to 1.0%
Ti: 0.052 to 0.2% , and
Nb: 0.01 to 0.07%,
V: 0.01 to 0.07%,
B: A steel material containing one or more of 0.0005 to 0.0050%, the balance being Fe and inevitable impurities is heated at 1200 ° C or higher, and then rolled at a temperature range of 850 ° C to 950 ° C. The method for producing a weatherable high-strength steel sheet for blasting that is excellent in bending resistance, characterized by being scraped off at 500 ° C. to 650 ° C.

Images