JPH0527481B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field This invention relates to a method for manufacturing pure nickel hot coils, which are often used for electrode plates, containers, heat exchangers, etc. in the caustic soda, food, and pharmaceutical industries. This invention relates to a method for manufacturing high-quality pure nickel hot coils with fewer edge cracks and surface flaws than manufacturing methods using nickel as a material. Conventional technology Conventional pure nickel hot coils are made by press-blowing a small ingot melted in a high-frequency furnace and making it into a slab.
A commonly used manufacturing method is hot rolling in a Steckel mill, planetary mill, four-stage lever mill, or the like. Recently, large ingots melted in an electric furnace/vacuum smelting furnace (VOD) are press-blunted or slab-rolled to produce slabs. FIG. 3 shows the manufacturing process for making a hot coil from the large ingot. In this manufacturing process, a large ingot of pure nickel melted in an electric furnace (VOD) is bloomed into a slab, the surface of which is treated, an antioxidant is applied, and continuous hot rolling is performed. The slab obtained by blooming a large ingot by the above method has a rolled texture, with finer grains and improved hot workability. A reduction in surface flaws can be expected by preventing cracking and reducing grain boundary oxidation by lowering the heating temperature. However, compared to methods using continuous cast slabs, blooming is required, and
The manufacturing cost increases due to a decrease in yield due to cutting off both the top and bottom ends of the ingot. Problems to be Solved by the Invention However, continuous casting slabs have unique columnar crystals, coarse grains, and poor hot workability. In addition, since pure nickel material has a single austenite phase structure, it has the disadvantage that low melting point impurities and precipitates are concentrated at grain boundaries during solidification, and edge cracks and surface flaws occur during hot rolling. Furthermore, pure nickel material has high Ni-Fe
Although there is less grain boundary oxidation during heating compared to alloys and high Ni-Cu alloys such as Monel metal, measures to prevent grain boundary oxidation are required to improve the coil surface quality.
For this reason, the technology for manufacturing hot coils from continuously cast slabs has not yet been established. In view of the above-mentioned current situation, this invention addresses the problems encountered when producing pure nickel hot coils from continuous casting slabs, namely, deterioration of hot workability, edge cracks and surface flaws due to concentration of impurities and precipitates, and coil surface defects. The present invention provides a method for manufacturing high-quality pure nickel hot coils with few edge cracks and surface defects by solving the grain boundary oxidation prevention measures necessary to improve properties. Means for Solving the Problems In order to achieve the above object, the present inventors have conducted various studies and found that the reduction of impurities such as P and S, appropriate control of the slab heating temperature, and the use of antioxidants of appropriate thickness. It was discovered that a pure nickel hot coil with fewer edge cracks and surface flaws could be produced by applying the above coating, and the present invention was completed. That is, in this invention, Ni≧99.0 in terms of weight ratio
%, Fe≦0.40%, C≦0.15%, Si≦0.35%, Mn≦
0.35%, Cu≦0.25%, P≦0.008%, S≦0.005%
Continuously cast slabs of pure nickel material, consisting of the remaining unavoidable impurities and the remaining unavoidable impurities, are made into metal by carefully cleaning the surface.
Antioxidant containing Cr powder as the main component to a thickness of 50~
After coating 300um, it is heated to a temperature range of 1080~1200℃ and continuously hot rolled. Function A slab obtained by continuous casting of pure nickel material melted in an electric furnace-VOD to reduce impurities and suppressed to an extremely low range of P≦0.008% and S≦0.005% is shown in Figure 1. After cleaning the surface and applying an antioxidant, it is heated and subjected to continuous hot rolling to obtain a high quality pure nickel hot coil with few edge cracks and surface flaws. The reason why the chemical components of the target material are limited in this invention will be explained. The Ni content of pure nickel conforms to the standard SAE HSJ1086,
Since ASTM DS56B stipulates the content to be 99.0% or more, this invention also sets the content to be 99.0% or more. In addition, the contents of impurities Si, Mn, and Cu are also determined by the above standards, and in this invention, Si, Mn, and
The Cu content corresponds to its upper limit,
In order to improve corrosion resistance, it is desirable to reduce the content of these impurities as much as possible. C, which is also contained as an impurity, precipitates at grain boundaries as graphite in the temperature range of 430 to 650°C and causes embrittlement, so it was set to 0.15% or less. If Fe exceeds 0.4%, it causes cracking during hot working, so it was set at 0.40%. Since P precipitates at grain boundaries and causes cracking during hot working, the content was set to 0.008% or less. Like P, S precipitates at grain boundaries and reduces hot deformability, causing cracking during hot working.
It was set to 0.005% or less. In this invention, the heating temperature of the slab during hot rolling is limited for the following reason. As shown in Figure 2, pure nickel, monel metal (70% Ni-Cu alloy), 42% Ni in air
- Oxidation progress rate per hour of Fe alloy (mm/
Compared to other alloys, pure Tsukeru's oxidation progress rate is lower than that of other alloys, and less oxide scale is generated during heating. However, oxide scale and surface flaws on the slab surface need to be removed by a surface polisher in a subsequent process. In order to reduce this oxide scale and surface flaws, the heating temperature was limited to a range of 1080 to 1200°C. That is, if the heating temperature is lower than 1080°C, rolling is difficult due to the performance limit of the continuous hot rolling mill, and even if low-temperature rolling is performed, edge cracks and surface defects occur, making efficient production impossible. On the other hand, when the temperature exceeds 1200℃, oxidation of the slab surface increases even if an antioxidant is applied, and surface cracks and oxide scales occur, which increases surface defects in subsequent processing steps.
The number of man-hours required to remove surface flaws increases, and the product yield also decreases. An antioxidant mainly composed of metallic Cr powder applied to the slab surface is effective in preventing grain boundary oxidation of the slab and improving hot workability. However, if the thickness of the coating is less than 50 μm, the coating effect will not be improved, and if it is thicker than 300 μm, it will be difficult to coat it uniformly, and even if it can be coated, it will cause surface defects such as indentation scratches that occur during hot rolling. It causes the occurrence. Moreover, the coating effect also becomes saturated. Therefore, it is desirable that the antioxidant forms a film with a thickness in the range of 50 to 300 um. As mentioned above, if an antioxidant film with a thickness of 50 to 300 μm is formed on the slab surface and continuous hot rolling is performed by heating it to a temperature range of 1080 to 1200°C, it will be possible to form an antioxidant film with a thickness of 50 to 300 μm. The synergistic effect with the heating temperature prevents grain boundary oxidation of the slab, and as a result, it is possible to manufacture high-quality pure nickel hot coils with fewer edge cracks and surface flaws. Example Pure nickel materials, test materials A and B according to the present invention whose chemical components are shown in Table 1, were heated in an electric furnace.
Made by VOD and continuous casting machine to a thickness of 150mm and width.
After casting a 1000mm continuous casting slab and cleaning the surface to remove surface flaws, about 60% of the metal Cr powder is removed.
The contained antioxidant was applied to form a film with a thickness of 150 μm, heated to 1180° C. in a continuous heating furnace and held for 6 hours, and then a hot coil with a thickness of 6.0 mm was manufactured using a continuous rolling mill. In addition, for comparison, pure nickel materials of sample materials C and D in Table 1 were melted using a conventional manufacturing method in an electric furnace-VOD, poured into a mold to form an ingot, and then bloomed. A blooming slab of the same size was obtained, and a hot coil was manufactured through the same steps as in the above-mentioned embodiments of the invention. Then, edge cracks, surface flaws, and oxidized layers were examined and evaluated in three stages: good (◯), somewhat good (△), and poor (×). The results are shown in Table 2. From Table 2, sample materials A and B according to the implementation of this invention
Sample material C obtained by the conventional method was evaluated to be good in all test items with few edge cracks, surface flaws, and oxidized layers.
Sample material D was defective in all test items, indicating that the hot coil produced by the method of the present invention had excellent properties.

【table】

[Table] ○: Good △: Slightly good ×: Bad Effects of the invention As mentioned above, this invention has been developed to prevent cracks caused by low melting point impurities that precipitate at grain boundaries when pure nickel material is continuously cast and then hot rolled. There are fewer cracks and surface flaws, and due to the synergistic effect of the antioxidant coating thickness and the appropriate heating temperature range during hot rolling, grain boundary oxidation of the slab is prevented, resulting in high quality with fewer edge cracks and surface flaws. It is possible to manufacture pure nickel hot coils with high yield, contributing to a significant reduction in manufacturing costs.

[Brief explanation of the drawing]

Figure 1 is a process diagram showing the manufacturing method of this invention, and Figure 2 is a diagram showing pure nickel, high Ni-Cu alloy, and high Ni
A graph showing the oxidation progress rate of -Fe alloy in air, and FIG. 3 is a process chart showing a conventional manufacturing method from an ingot.

Claims (1)

[Claims] 1 Weight ratio: Ni≧99.0%, Fe≦0.40%, C≦
0.15%, Si≦0.35%, Mn≦0.35%, Cu≦0.25%,
A continuously cast slab of pure nickel material, consisting of P≦0.008%, S≦0.005%, and the remainder being unavoidable impurities, was surface-treated and coated with an antioxidant mainly composed of metallic Cr powder to a thickness of 50 to 300 μm. After, 1080~1200
A method for producing a pure nickel hot coil characterized by continuous hot rolling by heating to a temperature range of °C.