JPS6142775B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a roll for hot dip galvanizing, and particularly to a roll with improved corrosion resistance. Hot-dip galvanizing equipment is equipped with rolls such as sink rolls and support rolls (also known as exit rolls and coating rolls) that are used by being immersed in or in contact with molten zinc. The materials for these rolls must satisfy the following conditions for use. B. The roll must have strength and hardness that can withstand use at high temperatures of 450 to 500°C. In particular, it must have the strength to withstand the thermal shock that occurs when immersed in molten zinc. (b) The roll surface has good plating wettability, and the zinc alloy metal does not peel or fall off. (c) Excellent corrosion resistance against molten zinc. (d) It has excellent wear resistance. (e) It must be economically efficient. Conventionally, rolls for hot-dip galvanizing have been made of pure iron, low silicon carbon steel, or high chromium high nickel steel, taking into account various conditions such as high temperature strength, thermal shock resistance, peeling resistance of the alloy layer, and corrosion resistance. material was used. However, these roll materials have recently become unsatisfactory due to technical problems such as increased speed of plating lines, improved quality of galvanized sheet surfaces, and extension of the service life of rolls for hot-dip plating. In other words, pure iron and low-silicon carbon steel have poor corrosion resistance and wear resistance against molten zinc, tend to cause surface roughness on galvanized plates, and have a short service life.On the other hand, high-chromium, high-nickel steel has excellent corrosion resistance, but roll Due to the poor plating wettability of the surface, there is a problem in that floating iron-zinc compounds, ie, dross, adhere to the roll surface, making the galvanized plate prone to scratches. The present invention aims to provide a roll for hot-dip galvanizing that simultaneously has corrosion resistance and plating wettability, which are mutually contradictory properties that are problematic in conventional roll materials for hot-dip galvanizing. Conventional roll materials have a matrix structure of ferrite, ferrite + pearlite, or austenite, giving them the properties required for hot-dip galvanizing rolls, whereas the roll material of the present invention has tempered martensite and austenite. Chromium-iron eutectic carbide is crystallized inside,
It is characterized by a mixed structure of eutectic carbide, tempered martensite, and austenite that satisfies various properties required of rolls for hot-dip galvanizing. In other words, in the roll material of the present invention, the eutectic carbides uniformly crystallized in a network form are resistant to alloying reactions with molten zinc and impart corrosion resistance, while the base tempered martensite and austenite react with molten zinc. It forms an alloy layer and provides plating wettability. Furthermore, the roll material of the present invention has network-like eutectic carbides that act as a wedge for the alloy layer formed on the base surface, causing the alloy layer to peel off, as shown in the micrograph in Figure 1 and in Figure 2, which is a schematic diagram thereof. It prevents falling off and has excellent corrosion and wear resistance against sliding action between the roll and the galvanized plate. As mentioned above, the present inventors focused on the property that chromium-iron eutectic carbide hardly reacts with molten zinc, and conducted research to find a roll material with excellent corrosion resistance, abrasion resistance, and plating wettability against molten zinc. As a result of pushing forward, C0.5~2.5%, Si0.3~5.0%,
Contains 0.3~3.0% Mn, 15~30% Cr, and the balance is Fe.
and an alloy consisting of impurities, or the above components.
0.5-5.0% for Ni alone, 0.3-3.0% for Co alone,
It has been found that a roll material containing 0.5 to 5.0% of Ni and Co in total is optimal. The reason for limiting the content of each component in the roll material of the present invention will be explained below. C: C is an important element for the formation of Cr--Fe eutectic carbide necessary for improving corrosion resistance, and 0.5% or more is required to crystallize a suitable amount of eutectic carbide.
The upper limit was set at 2.5% because a hypereutectic composition would not provide enough strength to withstand thermal shock. The preferred range is 1.0 to 2.3%. Si: Si is an important element for maintaining castability as well as being a deoxidizing element, and 0.3% or more is required. The reason why Si is set to 1.5% or less is to suppress a decrease in corrosion resistance. Mn: 0.3 because Mn is a deoxidizing element like Si
% or more, and if it is contained in a large amount, the corrosion resistance and strength of the material will decrease at the same time, so the upper limit was set at 3.0%. Preferably, it is in the range of 0.5 to 1.5%. Cr: Cr forms a carbide, and a part of it is dissolved in the matrix to improve corrosion resistance and also has the effect of improving wear resistance. If Cr is less than 15%, the corrosion resistance and wear resistance of the base will be insufficient;
In the above, if the C content is low, the hardness of the base will decrease, while if the C content is high, the thermal shock resistance will deteriorate, and it will also be economically disadvantageous, so the lower and upper limits are set at 15% and 30%, respectively. did. Ni, Co: Ni and Co are effective elements to dissolve in the matrix and improve corrosion resistance, so 0.5% and 0.3% or more are required, respectively.If they are contained in large amounts, retained austenite will increase and wear resistance will increase. , so the upper limit is set to 5.%, respectively.
It was set at 3.0%. In case of combined addition of Ni and Co,
In order to improve corrosion resistance, 0.5% or more is effective, and if it is contained in a large amount, retained austenite increases and wear resistance decreases, so the upper limit was set at 5.0%. The roll of the present invention is a cast roll containing the above-mentioned chemical components, and is completely annealed at 850 to 950°C.
Aging treatment at 550-700℃ improves shore hardness.
It is adjusted to Hs50-60. This heat treatment reduces retained austenite in the matrix structure, improves wear resistance, and at the same time improves machinability.
The purpose is to improve thermal shock resistance. Next, the experimental results regarding the roll material of the present invention and the actual use of the roll will be explained. An immersion test was conducted on the roll material of the present invention, a conventional roll material, and a comparative material. The chemical composition of the test roll material is shown in Table 1. Table 2 shows the results of a corrosion test in which each of these materials was immersed in molten zinc for 10 days. From this table, the corrosion loss of conventional roll materials No. 17 to 19 is 3.42 to 12.51%, and that of comparative material No. 17 to 19.
In contrast to 5.21 to 6.45% for roll materials No. 20 to 23, it was 1.24 to 2.34% for roll materials No. 1 to 16 of the present invention, confirming that they have particularly excellent corrosion resistance against molten zinc. Table 3 shows the results of using rolls made of the conventional roll material and the roll material of the present invention as support rolls in actual hot-dip galvanizing equipment. The roll made of the roll material of the present invention can be used for a single use period approximately 5 times longer than that of a roll made of a low-silicon carbon material, and approximately 3 times longer than that of a roll made of a high-chromium, high-nickel steel material. The groundbreaking result was that the amount of carbon dioxide was lower than that of both materials.
Further, in the roll made of the roll material of the present invention, the thickness of the alloy layer is sufficient, the product has no occurrence of board defects, and the surface of the roll has a good texture. As described above, the present invention has extremely high corrosion resistance against molten zinc and wear resistance against galvanized plates by crystallizing chromium-iron eutectic carbide in the base of conventional roll materials, and the roll An alloy layer of an appropriate thickness is formed on the surface. Therefore, when the roll of the present invention is used in locations where corrosion resistance to molten zinc and wear resistance are required, the effect is even more significant. Although the present invention was made for hot-dip galvanizing rolls, it is equally applicable to other roll bearing parts such as sleeves, metals, and bushings that require corrosion resistance and wear resistance against molten zinc. Please note that it is a thing.

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[Table] Grinding of each material roll
Reduction amount/use period

[Brief explanation of the drawing]

FIG. 1 is a metallographic micrograph of the structure near the surface of the roll material of the present invention after immersing it in molten zinc, and FIG. 2 schematically shows the structure. a: Base of base material, b: Eutectic carbide, c: Fe-
Zn alloy layer, d: deposited Zn.

Claims (1)

[Claims] 1 C0.5-2.5%, Si0.3-1.5%, Mn0.3-3.0%,
A roll for hot-dip galvanizing, characterized in that it contains 15 to 30% Cr by weight, with the remainder consisting of Fe and impurities. 2 C0.5~2.5%, Si0.3~1.5%, Mn0.3~3.0%,
Cr15-30% and Ni alone 0.5-5.0%, Co alone 0.3-3.0%, total Ni and Co 0.5-5.0%
A roll for hot-dip galvanizing, characterized in that it contains 5.0% by weight, with the remainder consisting of Fe and impurities.