JPS629183B2 - - Google Patents

Description

[Detailed description of the invention]

Technical field The technical contents described in this specification regarding corrosion-resistant alloy roll steel for soda-based salt baths include the annealing process performed after cold rolling of stainless steel strip and the pickling process to remove scale generated during the annealing process. Corrosion and wear resistance of the immersion rolls or squeeze rolls used to guide the steel strip in the salt bath process that modifies scale to water-soluble as a pretreatment for the pickling process in the continuous annealing and pickling line that is carried out simultaneously. It is located in the field of cold-rolled stainless steel production equipment, including continuous annealing and pickling lines for stainless steel strips, in relation to the alloy design of the above-mentioned roll steel aimed at improving. Technical background An example of the above line is shown in Fig. 1, in which 1 is a payoff reel, 2 is a welding machine, 3 is an entry side looper,
4 is an annealing furnace, 5 is a cooling zone, 6 is a salt bath, 7 is a pickling tank, 8 is a scrubber brush, 9 is an outlet looper, 10 is a shear, 11 is a tension reel, and Figure 2 shows an outline of the salt bath 6.
12 is a soda salt bath, 13 is a dipping roll, and 14 is a squeezing roll. In such continuous lines, a pickling solution is usually used with a composition of sulfuric acid and nitric-fluoric acid, and to ensure that the pickling removes scale, it is usually 75%
A pretreatment is applied in which the steel plate to be treated is passed through a soda-based salt bath 12 having a composition of NaOH-25% NaNO ₃ . Conventionally, rolls for conveying steel strips such as the dipping roll 13 and the squeezing roll 14 in the soda-based salt bath 12 have been made of common steel SS41 or SUS304,
Austenitic stainless steel such as SUS316 was used. However, such conventional steel cannot be used in a soda-based salt bath12.
During use, the rolls 13 and 14 are subjected to corrosion by the salt bath and contact abrasion by the steel strip, resulting in unevenness on the roll surface, which causes the steel to deteriorate. There remained a problem in that the scratches were transferred to the surface of the band. Development Subject Based on the results of investigating the corrosion and wear characteristics of various alloy roll component compositions that should exhibit excellent corrosion and wear resistance in a soda-based salt bath, we investigated the above properties in a soda-based salt bath. We have discovered a steel for alloy rolls that has excellent properties, and have made it suitable for continuous annealing and pickling lines for stainless steel. Basics of the idea and its development Corrosion-resistant alloy rolls used in soda-based salt baths generally need to be heat resistant and oxidation resistant, as well as corrosion and wear resistant. , from a structural standpoint, first of all, for single-phase ferrite and two-phase ferrite-austenite, 400 to 500
There is a problem of embrittlement (475℃ brittleness) in the temperature range of ℃, and in martensitic structures, Cr is usually
% or less, there are problems in terms of oxidation resistance and strength. In order to avoid the above-mentioned embrittlement, adding austenite-forming elements such as C, Mn, and Ni to increase austenite stability may be considered as a countermeasure, but if the C content is too high, intergranular corrosion due to carbide precipitation may occur. Also, if Mn is too high, corrosion resistance will decrease. On the other hand, Si and Cr are added to impart oxidation resistance and strength, but if too much of these are added, austenite stability decreases. Based on this idea, C, Si, Cr, Mn
A 4-week immersion test was conducted in a soda-based salt bath while changing the content of each element of Ni and Ni, and the weight loss rate and maximum surface roughness (Rmax) were investigated. The results are shown in Table 1.

【table】

[Table] Experimental results From Table 1, sample material symbols G, H, I, J, K, L,
It can be concluded that M is superior, and the amount of weight loss is
Stays below 0.18%, maximum surface roughness is 3.0μm
The component range that meets the following requirements is C: 1.0% by weight
(hereinafter simply referred to as %) or less, Si: 2.0% or less,
Mn: 7.0-19.0%, Cr: 5-17%, Ni: 0.5-12.0
%, %Si+%Cr is 5.0 to 17.0% and %C+%
It can be seen that Mn+%Ni is compatible at 14.0 to 19.0%. If the weight loss exceeds 0.18% and the maximum surface roughness exceeds 3.0 μm, the resulting unevenness formed on the roll surface will cause scratches on the surface of the stainless steel strip to the extent that it cannot be put to practical use. . The materials used in conventional soda-based salt baths are
While common steels such as SS41 or austenitic stainless steels such as SUS304 and 316 have been commonly used, this invention has a stainless steel with lower Ni and Cr content and higher Mn content than these stainless steels. It is characterized by the presence of When using a high Mn system as described above, Mn reacts with the oxygen atoms (O) of Na ₂ O, which are present in large amounts in the soda salt bath, to form MnO. Since this exists as a protective coating on the roll surface, corrosion resistance and abrasion resistance are improved. If the amount of Mn added is too low, for example, Fe-Cr
-In the case of Ni alloys, Cr ₂ O ₃ , NiO, Fe ₃ O ₄
Even if a metal oxide such as Na 2 O is formed as a protective film, since Na ₂ O is more stable, the metal oxide will quickly dissociate oxygen atoms into Na, making it difficult to form a protective film. It is from. Furthermore, in Table 1, the effects on the above-mentioned compatibility are compared for the ferrite-forming elements of %Si + %Cr and the austenite-forming elements of %C + %Mn + %Ni, and the results are good (〇) and bad (× ), as shown in Figure 3, %Si + %Cr is
5.0~17.0%, %C+%Mn+%Ni 14.0~19.0%
Fits between. When %Si + %Cr is lower than 5.0%, oxidation resistance and strength are poor, and when it is higher than 17.0%, austenite stability is decreased. When %C + %Mn + %Ni is lower than 14.0%, austenite stability decreases, and when it is higher than 19.0%, there are problems such as occurrence of intergranular corrosion and decrease in corrosion resistance. Therefore, as above, %Si + %Cr, %C + %Mn
A compliance range is also set for +%Ni. The reasons for limiting the numerical values of each contained element are described below. C: 1.0% Although some amount of C remains after decarburization in the steelmaking process, it easily combines with alloying elements, especially Cr, and tends to form carbides. Since this phenomenon tends to occur at grain boundaries, the Cr removal phenomenon occurs at grain boundaries, causing intergranular corrosion. Therefore, it is necessary to keep it below 1.0%. Si: 2.0% Si is added as a deoxidizing element during the steelmaking process, but too much Si impairs austenite stability, so it must be kept at 2.0% or less. Mn: 7.0 to 19.0% Mn is required to be at least 7.0% to provide heat resistance, but if the amount added exceeds 19.0%, corrosion resistance and hot workability will be impaired, so this range is optimal. Become. Cr: 5-17% Cr is 5% to add oxidation resistance and strength.
It is necessary to add more than %. However, the presence of more than 17% is undesirable because it impairs austenite stability. Ni: 0.5-12.0% Ni improves the adhesion between MnO, which serves as a protective film, and the base metal, and also improves the toughness of the roll itself.
It is necessary to add 0.5% or more, but if the amount added increases, it becomes soft and wear resistance decreases, so it is necessary to keep it at 12.0% or less. %Si + %Cr: 5.0 to 17.0% If %Si + %Cr is less than 5.0%, oxidation resistance and strength will be poor. Furthermore, if it exceeds 17.0%, the austenite stability will decrease, so it is set within this range. %C+%Mn+%Ni: 14.0 to 19.0% When %C+%Mn+%Ni is less than 14.0%, austenite stability decreases. Moreover, if it exceeds 19.0%, there will be problems such as occurrence of intergranular corrosion and reduction in corrosion resistance and wear resistance, so it is set within this range. Example An immersion roll made by centrifugal casting of an alloy composition consisting of the test material (H) in Table 1 was 75%
After using NaOH-25% NaNO ₃ in a salt bath at 420°C for 6 months, the surface condition was investigated. In addition, as a comparative material, sample material (A) (SS-41) in Table 1 was investigated under the same conditions. Figures 4a and 4b show the surface roughness of sample material (H) (invention steel) and sample material (A) (comparative steel), respectively.
Table 2 shows the number of pitting corrosion per unit area.

[Table] Effects of the Invention The steel for alloy rolls according to the present invention has excellent corrosion resistance and wear resistance in a soda-based salt bath, and can be used as a pickling pretreatment in a continuous annealing and pickling line for stainless steel. In the past, there were often problems with salt baths.
The cause of productivity inhibition of stainless steel strips can be eliminated.

[Brief explanation of the drawing]

Figure 1 is a process diagram of a continuous annealing pickling line, Figure 2 is a skeleton diagram of a salt bath, and Figure 3 shows the compatible range of %Si + %Cr and %C + %Mn + %Ni according to the present invention. FIG. 4a,
b is a graph showing a comparison of the roll surface roughness of sample material H and sample material A, respectively.

Claims (1)

[Claims] 1 C: 1.0% by weight or less, Si: 2.0% by weight or less, Mn: 7.0 to 19.0% by weight, Cr: 5 to 17% by weight, Ni: 0.5 to 12.0% by weight, %Si+%Cr is 5.0 to 5.0%. Corrosion-resistant alloy roll steel for soda-based salt baths, characterized in that it is 17.0% by weight and contains %C + %Mn + %Ni in an amount of 14.0 to 19.0% by weight, with the remainder containing Fe and industrially unavoidable impurity elements. .