JP4388501B2 - Steel material with excellent corrosion resistance against molten Zn alloy - Google Patents

Description

  The present invention relates to a steel material having excellent corrosion resistance against a molten Zn alloy. More specifically, the corrosion rate for a molten Zn alloy containing Mg, Al, etc., such as molten Zn-Mg plating and molten Zn-Mg-Al plating, It is smaller than steel for plating pots, and can be used for various plating equipment such as plating pots, transport pumps, synchros, stirring jigs, submerged heaters and heating tubes, and has excellent corrosion resistance to molten Zn alloys. This is related to steel materials.

  Conventionally, in the fields of power transmission towers, bridges, road materials, construction hardware, construction and civil engineering materials, hot-dip Zn-plated steel materials have been widely used from the viewpoints of economy and durability. Hot-dip Zn alloy-plated steel materials, such as hot-dip Zn-Mg alloy-plated steel materials and hot-dip Zn-Al alloy-plated steel materials, which have better corrosion resistance than plated steel materials, have been put into practical use.

  However, when these hot-dip Zn alloy plating is performed, if the low alloy steel that has been used as a steel material for Zn plating pots is used as it is as a pot material, the pot will be corroded and the life of the plating pot will be significantly shortened. Become. That is, in the hot-dip Zn plating bath, Fe of the steel for the kettle reacts with hot Zn to form an Fe—Zn alloy layer, and the steel melts, but when the plating bath contains Mg, Al, etc. Since the formation rate of the Fe—Zn alloy layer is remarkably increased, the steel for the kettle is consumed rapidly. As a result, the life of the kettle is drastically reduced, and the durability as in the case of the molten Zn plating bath cannot be obtained. In addition, the Zn alloy plating referred to here means that one or both of Mg in mass% of 0.5% to 20% or Al in mass% of 0.04% to 60%. In addition, although the remainder indicates a plating composed of Zn and inevitable impurities, other elements such as Si, Fe, Co, Ni, Pb, Cd, Bi, Cr, and Ti may be included.

For this reason, various steel materials for pots having excellent corrosion resistance have been studied. For example, for molten Al—Zn plating, C: 2.0 to 4.0%, Si: 2.0 to 5.0%, Mn: 0.1 to 3.0%, Ni: 5.0 %, And a steel material containing Cr: 3.0 to 25.0% is disclosed (Patent Document 1), but since it is a high-C, high-Si casting in the first place, the weldability when welded or welded It is not certain whether it is inferior in toughness and is effective for a plating bath containing Mg.
Moreover, C: 0.005-0.05%, Si: 0.005-0.25%, Mn: 0.1-1.1%, P: 0.01% or less, targeted at hot-dip Zn plating , S: 0.01% or less, Ni: 0.1-1.0%, Cr: 3.5-6.5%, Al: 0.005-0.1% steel materials are disclosed ( It is not certain whether Patent Document 2) is effective for a plating bath containing 0.5% or more of Mg, and there is also a problem in the toughness of the welded part and the strength at high temperature when used as a kettle. .

Furthermore, C: 0.5 to 2.5%, Si: 0.4 to 3.0%, Mn: 2% or less, Ni: 2.5% or less, Cr : 11.5 to 14.5%, Co: 0.05 to 0.15%, V: 0.05 to 0.15%, Nb: 0.05 to 0.15%, one or more (Patent Document 3) is a high C, high Cr casting, but is inferior in workability and high in manufacturing cost. C: 0.40% or less, Si: 1.50 to 3.50%, Mn: 2.0% or less, Ni: 5.0% or less, Cr: 3. A steel material containing 0 to 20.0% is disclosed (Patent Document 4), but since it is a high Si-based material, it is inferior in the toughness of the welded portion and the strength at high temperature when used as a kettle. Moreover, since it contains Cr, the manufacturing cost is high.
JP 2000-104139 A JP 2002-322534 A Japanese Patent Application Laid-Open No. 58-117859 JP-A-55-79857

As described above, various proposals have been made as materials for hot dipping plating pots, all of which are intended to improve the corrosion resistance against molten Zn by adding Cr, and molten Zn alloys, particularly molten Zn alloys containing Mg and Al. However, there are various problems in terms of workability, weld toughness, high-temperature strength, economy, and the like.
The present invention solves such various problems, and has high corrosion resistance, high workability, sufficient weldability, toughness, strength as a steel material for welding, and excellent corrosion resistance to molten Zn alloy. It is an object to provide an excellent steel material and a pot using the same.

  The present invention solves the above-mentioned problems, has sufficient corrosion resistance, workability, weldability, welded portion toughness, high-temperature strength as a steel material for a kettle, and is excellent in corrosion resistance against molten Zn alloy, which is also economical. A steel material and a kettle using the steel material are as follows.

(1) By mass%, C: 0.5% or less, Si: 1% or less, Mn: 2% or less, P: 0.2% or less, S: 0.05% or less, Ni: 1.2-20 In addition, Mg: 0.0001 to 0.01%, Ca: 0.0001 to 0.01%, rare earth elements: 0.0001 to 0.01%, or one or more of them A steel material excellent in corrosion resistance to a molten Zn alloy, wherein the balance is made of iron and inevitable impurities.

(2) By mass%, Mo: 0.01-2%, V: 0.001-0.5%, Ti: 0.001-0.5%, Nb: 0.001-0.5% The steel material excellent in corrosion resistance with respect to the molten Zn alloy as described in (1) characterized by including 1 type (s) or 2 or more types.

(3) The melting according to (1) or (2), further comprising one or two of Cr: 0.5 to 5% and Cu: 0.1 to 2% by mass%. Steel material with excellent corrosion resistance against Zn alloys.

(4) A hot-dip Zn alloy plating kettle comprising the steel material according to any one of (1) to (3) at least in a portion in contact with the molten Zn alloy.

According to the steel material of the present invention, the corrosion resistance to the molten Zn alloy is excellent, the welding is possible, and the economy is excellent. By using this steel material in various plating equipment such as plating pots, transport pumps, synchros, stirring jigs, immersion heater heating tubes, etc., these durability will be improved more than before, Industrial value is extremely high.
Moreover, the hot pot for hot dip Zn alloy plating of the present invention is less susceptible to erosion by hot dip Zn alloy and is excellent in durability, so that the frequency of replacement of the hot pot can be reduced, so that equipment stoppage can be avoided and productivity is improved.

The best form of the steel material excellent in the corrosion resistance with respect to the molten Zn alloy of this invention and the hot pot for molten Zn alloy plating using the same is demonstrated.
In addition, since this form is demonstrated in detail in order to make the meaning of an invention understand better, unless there is particular designation | designated, this invention is not limited.

Hereinafter, the present invention will be described in detail.
First, the molten Zn alloy which the steel material of this invention makes object is demonstrated. The molten Zn alloy is a molten metal mainly composed of Zn mainly for molten Zn alloy plating, and includes molten Zn-Al, molten Zn-Mg, molten Zn-Al-Mg, and other Mg and Al. It means Zn.

  Mg has the effect of greatly improving the corrosion resistance of hot-dip Zn plating, but if Mg is less than 0.5% by mass, the effect is insufficient. If it exceeds 20% by mass, oxidation of the plating bath becomes intense and dross is large. It is preferable that the content be 0.5% by mass or more and 20% by mass or less.

  Al has the effect of improving the corrosion resistance of the hot-dip Zn-plated steel material, and also has the effect of suppressing oxidation of the plating bath when Mg is added, but the effect is insufficient when Al is less than 0.04% by mass. If it exceeds 20% by mass, non-plating is likely to occur. Therefore, the content is preferably 0.04 to 60% by mass.

  In addition, the molten Zn alloy targeted by the steel material of the present invention includes one or more metals such as Ni, Cr, Sn, Si, Fe, Pb, Cd, Mn, Cu, Ti, Sb, Bi, and Ag. You can leave. Although the preferable range of these metals is not particularly specified, each is preferably 15% by mass or less.

Next, the component elements and their contents of the steel material of the present invention will be described.
Ni is an important element in the present invention. Ni has the effect of significantly reducing the corrosion rate of the steel material against the molten Zn alloy. The mechanism of action is not clear, but it reacts with Al and Mg in the molten Zn alloy, or Ni concentrates on the surface of the steel material to form a barrier film. It is conceivable to suppress the corrosion of steel. When Ni is less than 1.2% by mass, the effect is not remarkable, and when it exceeds 20% by mass, the effect tends to be saturated, and the workability, toughness of the welded portion, and economical efficiency are inferior. The content is 1.2 to 20% by mass. Preferably, they are 2 mass%-10 mass%, More preferably, they are 2.5 mass%-5 mass%.

  C has the effect of ensuring the strength at high temperatures and further improving the corrosion resistance against the molten Zn alloy. If C exceeds 0.5% by mass, the corrosion resistance is deteriorated, and the workability and the toughness of the welded part are inferior, so the C content is 0.5% by mass or less. Preferably, it is 0.05 mass% or more and 0.2 mass% or less.

  Si is necessary for deoxidation, but if it exceeds 1% by mass, it is inferior in corrosion resistance, workability, and toughness of the welded part, so the Si content is 1.0% by mass or less. Preferably, it is 0.5 mass% or less.

  Mn is necessary for deoxidation and securing strength, but if it exceeds 2% by mass, it tends to become brittle, and workability and toughness of welded parts are also inferior, so the Mn content is 2% by mass or less. . Preferably it is 1.5 mass% or less.

  Since both P and S have the effect of lowering the corrosion resistance to the molten Zn alloy and the toughness of the welded portion, it is desirable that the content thereof be smaller. For this reason, in consideration of economic efficiency, P is 0.2% by mass or less, and S is 0.05% by mass or less. Preferably, P is 0.1% by mass or less and S is 0.01% by mass or less.

  Mg, Ca, and a rare earth element (hereinafter referred to as REM) form a nonmetallic compound and have the effect of improving the toughness of the weld due to the pinning effect of these fine particles, and therefore are added as necessary. In any case, if the amount is less than 0.0001% by mass, a sufficient amount of the nonmetallic compound cannot be formed. If the amount exceeds 0.01% by mass, a coarse nonmetallic compound is formed and the toughness is lowered. For this reason, content is made into Mg: 0.0001-0.01 mass%, Ca: 0.0001-0.01 mass%, and REM: 0.0001-0.01 mass%, respectively. Preferred ranges are Mg: 0.001 to 0.005 mass%, Ca: 0.001 to 0.005 mass%, and REM: 0.001 to 0.005 mass%.

  Mo, V, Ti, and Nb have the effect of increasing the strength at high temperatures. If Mo is less than 0.01% by mass, the effect of increasing the high-temperature strength is not remarkable. Moreover, when it exceeds 2 mass%, it exists in the tendency for toughness to fall. Therefore, the range of Mo is set to 0.01 to 2% by mass. V is less than 0.001% by mass, and the effect of increasing the high temperature strength is not remarkable. Moreover, when it exceeds 0.5 mass%, it exists in the tendency for toughness to fall. Therefore, the range of V is set to 0.001 to 0.5 mass%. Ti is less than 0.001% by mass, and the effect of increasing the high temperature strength is not remarkable. Moreover, when it exceeds 0.5 mass%, it exists in the tendency for toughness to fall. Therefore, the range of Ti is set to 0.001 to 0.5 mass%. Nb is less than 0.001% by mass, and the effect of increasing the high temperature strength is not remarkable. Moreover, when it exceeds 0.5 mass%, it exists in the tendency for toughness to fall. Therefore, the range of Nb is set to 0.001 to 0.5 mass%.

  Since Cr can be expected to improve the corrosion resistance, it is desirable to contain 0.5% by mass or more as necessary. However, even if the content exceeds 5% by mass, the effect is saturated and the economy is inferior, so the content is 0.5 to 5% by mass.

  Since Cu can be expected to improve the corrosion resistance, it is desirable to contain Cu as necessary. Since the effect is saturated when it exceeds 2% by mass, the content is 0.1-2% by mass.

  The steel material of the present invention can be manufactured by adjusting a predetermined steel material component in the steel making process, manufacturing a steel slab by a continuous casting method or an ingot forming method, and performing a process such as heating, rolling, or forging. In addition, the steel material of the present invention is excellent in high temperature strength, workability, toughness, oxidation resistance, weldability, etc., plating pot, transport pump, synchro, stirring jig, immersion heater heating. It can be applied to various plating equipment such as tubes.

  Furthermore, when the steel material of the present invention is used in these various plating equipments, it is not always necessary to use the entire thickness of the equipment member as the steel material of the present invention. You may coat | cover and use with steel materials. In this case, the thickness of the steel material of the present invention is not particularly specified, but when used in a plating pot, for example, it is preferably about 10 to 30 mm. The steel material of the present invention is particularly excellent in corrosion resistance against a molten Zn alloy such as a molten Zn-Mg alloy or a molten Zn-Al alloy. In Zn-based plating, the life of various plating facilities such as a plating pot, a transport pump, a sync, a stirring jig, and a submerged heater heating tube can be extended.

  Next, a hot-dip Zn alloy plating pot using the steel material of the present invention will be described. Since the steel material of the present invention is excellent in weldability and workability, a pot for hot-dip Zn alloy plating can be manufactured using the steel material of the present invention. In the case of manufacturing a molten zinc alloy plating pot, the steel material of the present invention is formed into a predetermined pot shape by hot, cold, or welding. When manufacturing a plating pot by welding, it is necessary to weld using a welding material containing 1 mass% or more of Ni. By using a welding material containing 1 mass% or more of Ni, corrosion of the welded portion in the molten Zn alloy can be suppressed. The welding method is not particularly limited as long as the strength of the welded portion can be sufficiently ensured, such as arc welding or laser welding. The thickness of the steel material of the present invention is not particularly specified as long as sufficient strength, workability, and corrosion resistance are satisfied, and is preferably 10 to 90 mm.

  In addition, as described above, the hot-dip Zn alloy plating pot using the steel material of the present invention does not necessarily have the entire wall thickness of the steel material of the present invention, and the plating pot manufactured using other steel materials such as ordinary steel. The inner surface or the entire surface may be coated with the steel material of the present invention. Alternatively, it is preferable to coat the inner surface or the entire surface of the hot-dip Zn alloy plating pot using the steel material of the present invention with ceramic or a Ni-based high alloy because further improvement in corrosion resistance can be expected.

"Experiment 1"
Steels having the compositions shown in Table 1 were melted by a vacuum melting method and then hot-rolled to produce steel materials having a plate thickness of 5 mm and a plate thickness of 25 m. A steel material having a thickness of 5 mm was cut into a size of 25 mm × 50 mm × 3 mm, and a sample for evaluation of the corrosion amount with respect to the molten zinc alloy was produced. The produced test piece was immersed in a Zn-0.05% Al-0.5% Mg plating bath maintained at 460 ° C. and taken out after 48 hours. Thereafter, the adhered zinc alloy was dissolved with 15% hydrochloric acid containing an inhibitor, and the average corrosion of the steel in a molten Zn-0.05% Al-0.5% Mg bath based on the mass change of the test piece before and after the test. The speed was determined.

In addition, a 100 mm × 10 mm × 3 mm bending test piece was prepared, and the workability was evaluated by performing a 90 ° bending process with a bending radius of 5 mm using a press. As a result of visual evaluation, it was evaluated as defective when cracks were observed in the fractures and the bent portions, and was evaluated as good otherwise. In addition, in order to evaluate the toughness of the welded portion, two pieces were cut into a size of 100 mm × 50 mm × 20 mm from a steel material with a plate thickness of 25 m, the surfaces with a length of 100 mm were butted, welded, and a joint specimen was produced. HAZ toughness was evaluated. Note that a welding material containing 3% of Ni was used as the welding material. Furthermore, a creep test was performed to measure the high temperature strength. A stress of 150 MPa was applied in a state where a 100 × 30 × 15 mm test piece was held at 500 ° C., and the time until the fracture time was measured.
Table 1 shows the average corrosion rate and workability of steel materials in a molten Zn-0.05% Al-0.5% Mg bath, evaluation results of HAZ toughness, and creep test results.

Inventive Examples A1 to A40 each have an average corrosion rate of 300 to 700 g / m ² / day, good workability, a HAZ Charpy impact value of 100 J or more, a creep rupture time of 4000 hours or more, and good performance. Have. If it sees in detail, A1-A6 will be the steel materials which changed Ni content rate, and as Ni content rate becomes large, an average corrosion rate tends to become small, and it is excellent in corrosion resistance. On the other hand, the HAZ Charpy impact value tends to decrease and the toughness decreases. A3 and A4 having a Ni content in the range of 2.5% by mass to 5% by mass, which is a more preferable range in the steel material of the present invention, are desirable because they are balanced.

  A7 and A8 are steel materials with different C contents. A8 has a higher C content than A7 and is excellent in corrosion resistance, but the toughness of the welded portion is slightly lowered. A9 and A10 are steel materials with different Si contents. A9 is desirable because it has a lower Si content than A10 and is excellent in both corrosion resistance and toughness of the weld. A11 and A12 are steel materials with different Mn contents. A11 is desirable because it has a lower Mn content than A12 and is excellent in both corrosion resistance and weld toughness. A13 and A14 are steel materials in which the P content and the S content are higher than those of A4, respectively. In either case, the corrosion resistance and the toughness of the welded portion are slightly lower than those of A4, but at a level with no problem. A16 and A17 are steel materials including Ca, and A18 and A19 are steel materials including REM. All have good performances in terms of corrosion resistance, workability, weld toughness, and high-temperature strength.

  A20 to A24 are steel materials to which Mg, Ca, and REM are added in combination. All are excellent in the toughness of a welded part compared with the case where it adds independently (A1-A19). A25 to A32 are steel materials containing Mo, V, Nb, and Ti. In all cases, the creep rupture time is long and the high-temperature strength is excellent as compared with the case of no addition (A1 to A24). A33 to A37 are steel materials to which Mo, V, Nb, and Ti are added in combination. In any case, the high temperature strength is superior to the case of single addition (A25 to A32). A38 to A40 are steel materials containing Cr or Cr and Cu. In any case, the average corrosion rate is small and the corrosion resistance is excellent as compared with the case of no addition (A1 to A37).

On the other hand, looking at Comparative Examples B1 to B12, B1 is inferior in corrosion resistance because the Ni content is 0.8 mass%, which is below the range of the present invention, and the average corrosion rate is 8210 g / m ² / day. Since B2 has a Ni content of 30% by mass and exceeds the range of the present invention, it is inferior in workability, has a small HAZ Charpy impact value, and is inferior in toughness. B3 has a C content of 0.6% by mass and B4 has an Si content of 1.5% by mass, both of which exceed the scope of the present invention, and therefore are inferior in corrosion resistance, workability, and weld toughness. Since B5 has a Mn content of 2.5 mass% and exceeds the range of the present invention, it is inferior in workability and toughness of a welded portion.

  B6 has a P content of 0.5% by mass and B7 has an S content of 0.1% by mass, both of which exceed the scope of the present invention, and therefore are inferior in corrosion resistance and toughness of the weld. Since B8 does not contain Mg and is outside the scope of the present invention, it is inferior in the toughness of the weld. B9, B10, and B11 each have an Mg content of 0.03% by mass, a Ca content of 0.03% by mass, and a REM content of 0.03% by mass, which are outside the scope of the present invention. Inferior toughness of part. B12 has a Ni content of 0.8% by mass, does not contain Mg, and is out of the scope of the present invention, so it is inferior in corrosion resistance and weld toughness.

"Experimental example 2"
The corrosion resistance of the components shown in Table 2 in a hot-dip Zn alloy plating bath was examined for steels A4 and B12 having the compositions shown in Table 1. The test method is the same as in Example 1, the test material size is 25 mm × 50 mm × 3 mm, and the immersion time in the molten Zn alloy plating bath is 48 hours. The results are shown in Table 2.

A4, which is a steel material of the present invention, has an average corrosion rate of 650 g / m ² / day or less with respect to any hot-dip Zn alloy plating bath, and has good corrosion resistance. On the other hand, B12, which is a steel material outside the scope of the present invention, has an average corrosion rate of 8000 g / m ² / day or more and is inferior in corrosion resistance.

"Experiment 3"
In order to confirm the effect of improving the corrosion resistance in the molten Zn alloy bath of the steel material of the present invention, the toughness of the welded portion, and the high temperature strength, using steel A35 and B12 having the composition shown in Table 1, the width is 2 m, the length is 8 m, A steel plate with a depth of 2 m (plate thickness of 50 mm) was manufactured and welded for 3 years as a molten Zn-0.05% Al-0.5% Mg plating kettle. The presence or absence of cracks in the part and the amount of deformation in the width direction were measured.

  As a result, A35, which is the steel material of the present invention, had a steel material average thickness reduction of 12 mm, no cracks in the welded portion, and a deformation amount in the width direction of 5 to 12 mm, whereas the steel material outside the scope of the present invention. B12, which has a steel material average thickness reduction of 38 mm, cracks in the welded portion, and a deformation amount in the width direction of 30 to 35 mm, and the plating pot using the steel material of the present invention had good performance.

Claims (4)

In mass%, C: 0.5% or less, Si: 1% or less, Mn: 2% or less, P: 0.2% or less, S: 0.05% or less, Ni: 1.2 to 20% And
In addition, Mg: 0.0001-0.01%, Ca: 0.0001-0.01%, rare earth elements: 0.0001-0.01% of one or more kinds,
A steel material excellent in corrosion resistance against a molten Zn alloy, wherein the balance is made of iron and inevitable impurities.   1% by mass, Mo: 0.01-2%, V: 0.001-0.5%, Ti: 0.001-0.5%, Nb: 0.001-0.5% The steel material excellent in corrosion resistance with respect to the molten Zn alloy of Claim 1 characterized by including 2 or more types.   It is excellent in the corrosion resistance with respect to the molten Zn alloy of Claim 1 or 2 characterized by including 1 type or 2 types of Cr: 0.5-5% and Cu: 0.1-2% by mass% further Steel material. A hot-dip Zn alloy plating pot comprising the steel material according to any one of claims 1 to 3 at least in a portion in contact with the molten Zn alloy.