JPS649393B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to rolls such as support rolls used in hot-dip galvanizing, and particularly to the materials thereof. As is well known, hot-dip galvanizing equipment is provided with various rolls, such as support rolls (exit rolls, coding rolls), sink rolls, deflector rolls, etc., depending on the plating method. These rolls support and guide the board to be plated,
Alternatively, it has the function of attaching plating bath to the plate material. Recently, a small amount of Al has been added to the plating bath to facilitate gas wiping immediately after plating and removal of dross from the plating bath. By the way, the materials for rolls for hot-dip galvanizing are: (1) The amount of corrosion caused by the plating bath is small. (2) There should be less rough skin around the roll body. (3) Must be resistant to thermal shock due to bath temperature. (4) The roll surface should have good leakage against zinc. It must have the following properties. Conventionally, in consideration of these properties, low carbon-low silicon steel or low carbon-high nickel-high chromium steel has been used as rolls for hot dip galvanizing. However, as the requirements for the surface texture of galvanized sheets have recently become stricter, rolls with even less rough surface are required, and roll materials with a long life are also required from the viewpoint of maintenance and economic efficiency of plating equipment. We have started
Roll materials made of these materials have become unsatisfactory. That is, low carbon-low silicon steel is severely corroded by the Al in the plating bath, which tends to cause surface roughness and poor plating in the product, and the roll must be discarded early. In addition, with low carbon-high nickel-high chromium steel, the wear amount of the roll is small, but it is difficult to form an Al, Zn, and Fe alloy layer with relatively low hardness on the roll surface. Therefore, there is a problem in that the plate material comes into direct contact with the base material of the roll, which has high hardness, and the product is likely to have plate defects. This problem is particularly serious in the case of supporting rolls in which the traveling speed of the plating plate material and the roll circumferential speed are different. This invention was made to solve the above-mentioned problems with conventional hot-dip galvanizing rolls, and provides a hot-dip galvanizing roll that has excellent wear resistance and corrosion resistance and does not cause sheet defects. This is what I am trying to do. This invention will be explained in detail below. In this invention, the roll material has C0.3~1.0% and Si0.8%.
%, Mn 0.1-1.0%, Cr 0.5-6.0%, and the balance Fe. In addition, the above ingredients
Another feature is that it contains one or both of Ni 1.0% or less and Mo 0.5% or less. The reason for limiting the content of each component will be explained below. C: The reason why C is set at 0.3% or more is because if it is less than this, the wear resistance decreases, and the reason why C is set at 1.0% or less is to suppress the amount of corrosion. Si: Si is mainly dissolved in the matrix, has the effect of increasing tempering resistance, and is also a deoxidizing agent, so a certain amount is unavoidably contained in the material. The reason for setting Si to 0.8% or less is to suppress the amount of corrosion, similar to C. Mn: Like Si, Mn is a deoxidizing element, so it is always included in materials, but it is not very effective in terms of corrosion resistance. If Mn exceeds 1.0%, crack resistance decreases, so the content was set to 0.1 to 1.0%. Cr: An important element in this invention, and in order to improve corrosion resistance, it is necessary to contain 0.5% or more of Cr. Moreover, when Cr exceeds 6.0%, corrosion resistance decreases and the alloy layer formed on the roll surface becomes thin. Ni: Addition of Ni causes a significant decrease in corrosion resistance.
Under normal test conditions, TP melts and is difficult to compare. Therefore, it is meaningless unless it is added in combination with an element such as Cr that improves corrosion resistance. For this reason, the content was set at 1.0% or less so that the corrosion resistance would not deteriorate significantly. Mo: The addition of Mo is not intended to improve corrosion resistance itself, but is added to ensure hardness and hardening depth. For this reason,
Adding more than necessary will result in too high hardness, excessive quenching depth, and decreased toughness.
It was set to 0.5% or less. Next, experimental results and roll usage records that support the reason for limiting the above-mentioned component content will be explained. Immersion tests were conducted on comparative materials and roll materials of various compositions of the present invention. The composition of the test roll material is shown in Table 1. In addition, the experimental bath was a molten zinc bath with Al
was added to match the composition of the in-situ bath.

【table】

[Table] First, all steel types were immersed in a test bath, and steel types with good test results were immersed in an on-site bath again. Through these tests, they found a steel type with a low amount of corrosion. The results of the above tests are shown in FIGS. 1 to 5. Figures 1A and 2A are diagrams showing the relationship between the steel type and the amount of corrosion. Figure 1A shows the results for the test bath, and Figure 2A shows the results for the on-site bath. As is clear from this figure, the amount of corrosion of the steel of the present invention is significantly lower than that of the comparative steel. Comparative steel TP7 has a small amount of corrosion comparable to the steel of the present invention, but it has a low C content of 0.16% and a high content of Cr and Ni, resulting in extremely high manufacturing costs (e.g., compared to the steel of the present invention). 2-3
double) become something. Note that TP8 had a large surface unevenness and it was impossible to measure the amount of erosion. Figures 1B and 2B are diagrams showing the relationship between the steel type and the thickness of the alloy layer. Figure 1B shows the results for the test bath, and Figure 2B shows the results for the in-situ bath. This drawing and the first
Comparing the figures, it can be seen that steel types with a small amount of corrosion generally tend to have thinner alloy layers. In the steel of the present invention, the thickness of the alloy layer is approximately 50 μm or more, but according to actual use in hot-dip galvanizing equipment, it has been found that if the thickness of the alloy layer is within this range, no sheet defects will occur. In addition, in TP6, the alloy layer was damaged by melting and had a thickness of 0. Figure 3 is a graph showing the relationship between Cr, the amount of corrosion, and the thickness of the alloy layer, showing that the amount of corrosion is small at around 3.0% Cr and over 13.0%, and the alloy layer becomes significantly thinner at 12% Cr or higher. . Also, according to this graph, the range of Cr content in which the amount of corrosion is small and the alloy layer is thick is in the range of 0.5 to 6.0%, especially 1.0 to 5.0%.
A range of is preferred. FIG. 4 is a graph showing the relationship between the amount of Ni, the amount of corrosion, and the thickness of the alloy layer. The amount of corrosion increases rapidly as the amount of Ni increases, and the thickness of the alloy layer reaches its maximum when the amount of Ni is 1.0%, and becomes thinner when the amount of Ni exceeds 1.0%.
Based on the above trends in the amount of corrosion and the thickness of the alloy layer, Ni
The appropriate amount is 1.0% or less. FIG. 5 shows the relationship between the amount of C, the amount of corrosion, and the thickness of the alloy layer. When the amount of C is in the range of 0.3 to 0.8%, the amount of corrosion and the thickness of the alloy layer do not change significantly. but,
It has been found from the use of other rolls that when the C content is less than ~0.3%, the alloy layer becomes thinner and the wear resistance decreases, and when it exceeds 1.0%, the amount of corrosion increases. Table 2 shows the results of using rolls made of conventional and inventive materials as supporting rolls in actual hot-dip galvanizing equipment.

[Table] In Table 2, the amount of grinding represents the difference between the roll diameter before use and the roll diameter after use (ground to correct unevenness on the roll surface). This shows the decrease in roll diameter due to As shown in Table 2, conventional rolls made of low-carbon and low-silicon steel are considerably corroded after being used for about 3 days, and there are A sharp step appeared. Conventional rolls made of low carbon-high nickel-high chromium steel have significantly improved erosion corrosion, but the alloy layer has become very thin. On the other hand, in the roll made of the steel of the present invention, the amount of corrosion was approximately half that of the conventional low carbon-high nickel-high chromium steel. Furthermore, the thickness of the alloy layer was sufficient, and no board defects occurred on the product. Furthermore, the skin of the roll surface was also good. In addition, in the case where the thickness of the alloy layer is required to be larger in this invention, as in the second invention,
It is desirable to choose a material containing Ni and Mo. As explained in detail above, the roll for hot-dip galvanizing of the present invention has little corrosion and an alloy layer of an appropriate thickness is formed on the roll surface, so the roll can withstand long-term use, and the product does not have any scratches. will never occur. In particular, the second invention is even more effective for rolls where a relative speed occurs between the roll surface and the plate material, such as a support roll provided on the plating bath outlet side.

[Brief explanation of drawings]

Figures 1A and 2B are diagrams showing the relationship between steel type, corrosion amount, and alloy layer thickness for the first invention together with comparative examples, and Figures 2A and 2B are diagrams showing the relationship between steel type, corrosion amount, and alloy layer thickness for the second invention. Figure 3 is a graph showing the relationship between the amount of Cr, the amount of corrosion, and the thickness of the alloy layer, and Figure 4 is the graph showing the relationship between the amount of Ni and the amount of corrosion, along with comparative examples.
A graph showing the relationship between the thickness of the alloy layer and FIG. 5 is a graph showing the relationship between the amount of C, the amount of corrosion, and the thickness of the alloy layer.

Claims (1)

[Claims] 1. A roll for hot-dip galvanizing comprising 0.3 to 1.0% of C, 0.8% or less of Si, 0.1 to 1.0% of Mn, 0.5 to 6.0% of Cr, and the balance Fe. 2 It is characterized by consisting of one or two of the following: 0.3 to 1.0% C, 0.8% or less Si, 0.1 to 1.0% Mn, 0.5 to 6.0% Cr, 1.0% or less Ni, and 0.5% or less Mo, and the balance Fe. Roll for hot-dip galvanizing.