JPH03271321A - Production of steel sheet for porcelain enameling - Google Patents

Abstract

PURPOSE:To combine high workability with fishscale resistance by subjecting a steel sheet for porcelain enameling having a composition in which respective contents of C, Si, Mn, P, S, Ti, and Cu and relationship among them are specified to pickling and then to nitriding annealing in a nitriding annealing atmosphere having a composition consisting of H2 and the balance N2. CONSTITUTION:A steel which has a composition consisting of, by weight, <=0.01% C, <=0.1% Si, <=0.5% Mn, <=0.1% P, <=0.03% S, 0.01-0.1% Ti, 0.01-0.1% Cu, and the balance Fe with inevitable impurities and satisfying Ti/2>=48X(C /12+N/14+S/32) is refined. After hot rolling, pickling and descaling are performed. Subsequently, nitriding annealing is carried out in a nitriding annealing atmosphere having a composition consisting of 3-80vol.% H2 and the balance N2 at 500-850 deg.C for 1min-20hr. If necessary, 0.0003-0.0020% B is incorporated to the above steel. Further, reduction annealing can be exerted instead of pickling. By this method, the characteristics of a Ti added steel sheet can be brought out while securing fishscale resistance.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing a steel plate for enameling, and in particular, a method for manufacturing a steel plate for enameling, which achieves both workability and nail-flying resistance, which have been considered difficult in the past. This relates to a manufacturing method.

(Conventional technology) "Haurou" is the process of coating a metal surface with a glassy glaze at high temperature (
Enamel products with such a glassy layer have features such as a beautiful surface, heat resistance, abrasion resistance, and strength, and are suitable for chemical equipment,
It has been used not only for kitchen equipment and sanitary equipment, but also for the interior and exterior of buildings.

By the way, the manufacturing method of the above-mentioned enamel products includes the "two-coat method" of applying an undercoat with good adhesion to the raw steel plate and then applying a top coat to give it a beautiful appearance, and the other method that involves pre-treatment of the raw steel plate. "1" is a process in which the glaze, which is rich in beauty and adhesion, is baked directly after thorough acid washing, Ni flash, etc.
There is a saying, ``The time is the law.'' Note that when multiplying twice, simple preprocessing is often performed even in the method.

In addition, since press working is usually performed before gluing, there is a demand for steel sheets with good workability. In this regard, it is disclosed in Japanese Patent Publication No. 44-18066 that by adding Ti to ultra-low carbon steel, a steel plate with excellent deep drawing properties can be obtained. Various studies have been conducted on the use of steel plates for enameling.

On the other hand, "nail flying" is a phenomenon in which h enters the inside of the steel plate during firing, etc., and the cooled steel base diffuses at the enamel layer interface, becomes gaseous, and flies off the enamel layer. Therefore,
Steel sheets for crawlers have a large amount of inclusions that occlude H2 inside the steel sheet.For example, the conventionally used Cambutte steel sheet has oxygen-based inclusions, and the Ti-added steel sheet has S (*opening 51- 98619), N (Unexamined Japanese Patent Publication No. 6
No. 1-104051] etc. are added to form a large amount of Ti compound, thereby improving the nail-flying resistance.

(Problem to be solved by the invention) However, in order to improve press formability, it is better to have fewer inclusions inside the steel sheet, and as mentioned above, S, N, etc. are added to improve the nail fly resistance. The Tr-added steel sheet for enameling has a problem of poor press formability.

An object of the present invention is to provide a method for manufacturing a steel plate for enameling that achieves both high press workability and high resistance to nail flying.

(Means for Solving the Problems) In order to reconcile these contradictory properties, the present inventors have
As a result of various studies, it has been found that in order to ensure the resistance to nail chipping in a Ti-added steel sheet, it is necessary to form a Ti compound. Therefore, we have discovered that by performing nitriding treatment on hot-rolled steel sheets to form a TiN layer on the surface layer, and at the same time coarsening carbides and sulfides, it is possible to achieve both nail chipping resistance and press formability. This heading led to the present invention.

Here, the gist of the present invention is as follows: C: 0.01% or less, Si: 0.1% or less, M
n: 0.5% or less, P: 0.1% or less, S: 0.
03% or less, Ti: 0.01 to 0.1% and Ti
/2≧48X (C/12+N/14+5/32),
Cu: 0.01~0.1%, balance Fe and unavoidable impurities. After hot rolling and pickling for descaling, Hz-residue of 3~80% by volume is produced. A method for producing a steel plate for enameling with excellent workability and nail chipping resistance, characterized by performing nitriding annealing in a N2 nitriding atmosphere at a temperature of 500 to 850°C for 1 minute or more and 20 hours or less. be.

The steel targeted by the present invention further includes B:o, ooo3
It may contain up to 0.0020%.

According to a modification of the present invention, the surface of the steel plate may be activated by performing reduction annealing instead of the above-mentioned pickling for descaling, thereby increasing the efficiency of the subsequent nitriding annealing. .

Moreover, such reduction annealing may be performed continuously with the subsequent nitriding treatment.

The steel plate for enameling produced according to the present invention may be used as a hot-rolled steel plate or as a cold-rolled steel plate.

When used as a hot-rolled steel sheet, it may be used as is after being nitrided, or after being temper rolled to a level of 3% or less; when used as a cold-rolled steel sheet, it may be used after nitriding annealing, cold rolling, It may also be used as a cold-rolled steel sheet for enameling by performing recrystallization annealing.

<Function> Next, the reason why the steel composition and processing conditions are limited as described above in the present invention will be explained.

First, the reason for limiting the ingredients will be explained.

C: It is better to have as little C as possible, and if the amount of carbon in the steel is too large, not only will the required amount of Ti increase, but also the press formability will be impaired, so the upper limit was set at 0.01%.

Si, Mn: These are elements that can increase the strength of steel plates at low cost, and are used when the strength of steel plates is required in products, or when
It can be used when the strength of the steel plate decreases due to exposure to high temperatures of 0°C or higher. However, if too much is added, the pickling performance will be impaired due to descaling in the case of Si, and the r value (Lankford value) will decrease in the case of Mn, so the upper limit was set at 0.1% and 0.5%, respectively. .

P: Like Si and Mn, it is an element that can be used to increase strength, but if the content is too high, grain boundary cracking is likely to occur, so the upper limit was set at 0.1%.

S: Forms a compound with Ti and impairs press moldability, so the upper limit was set at 0.03%.

Ti: An element that forms compounds with carbon, nitrogen, sulfur, etc. in steel and cleans the steel plate. If it is less than 0.01%, the effect will be small, and if it exceeds 0.1%, the effect will not only be saturated but also cause an increase in cost, so 0.01 to 0.1%.
And so.

Also, Ti/2≧48X (12xC+14xN+32
xS) The lower limit of the amount of Ti added is defined by the formula of C
, N, and S in an amount necessary to completely fix them, and to facilitate nitriding annealing in the subsequent process, the amount was set to be at least twice the equivalent amount.

Cu: is an element necessary to ensure the adhesion of wax, and 0
．． If it is less than 0.01%, good adhesion cannot be obtained, and if it is too much, not only will the cost increase, but the pickling properties during pickling for descaling will deteriorate, so 0.01 to 0.1%.
And so.

B: B is an element added as necessary to prevent vertical cracking. If it is less than 0.0003%, there is no effect,
On the other hand, if the amount is more than 0.0020%, not only the effect will be saturated, but also the recrystallization temperature will become high, leading to an increase in cost.

Next, the reasons for limiting the manufacturing conditions will be explained.

Descaling by pickling performed after hot rolling is usually sulfuric acid pickling, and complete descaling is desirable, but it is sufficient to remove at least as much scale as will not peel off during handling. Note that any conventional pickling is sufficient as the pickling itself.

In addition, when performing reduction annealing in place of the descaling process, the conditions for the reduction annealing are preferably to use 3% by volume or more of N2 as the atmosphere, and to perform reduction annealing in place of the 600-b scale process. There is no change in nail flying resistance. However, if reduction annealing is performed, a reduced Fe layer is formed on the surface of the steel sheet, which has the secondary effect of reducing the occurrence of pinholes during waxing.

Next, when performing nitriding after descaling a hot rolled steel sheet, if the N2 concentration in the nitriding atmosphere is lower than 3% by volume, the steel sheet will be oxidized and the nitriding reaction will be difficult to occur. Moreover, if it exceeds 80% by volume, the N2 concentration becomes low and this reaction becomes difficult to occur. Further, this nitriding atmosphere may contain a trace amount of NH3 of about 2 to 3% by volume, which promotes the nitriding reaction depending on the case.

If the heating temperature at this time is lower than 500°C, it will take time for the reaction to take place, and if it is higher than 850°C, abnormal grain growth will easily occur, and roughening of the surface will become a problem especially when used as a hot-rolled sheet. When used in , the r value becomes low.

If the annealing time is less than 1 minute, nitriding will not be sufficient and nails will fly. Moreover, if it exceeds 20 hours, not only the effect will be saturated, but also a large amount of TiN will be formed and the press moldability will deteriorate.

In general, such reduction annealing and nitriding annealing are advantageous because they can be performed by simply adjusting the atmosphere in an OCA annealing furnace intended for decarburization annealing.

When reduction annealing is performed instead of descaling by pickling (when reductive annealing is performed without descaling), the amount of oxidized scale is preferably limited to 30 g/m 2 or less (in terms of Fe). If the temperature exceeds this range, scale exfoliation is likely to occur.

When the hot-rolled steel sheet is used as a hot-rolled steel sheet for enameling, it may be further temper-rolled by 3% or less if desired. In that case, formability can be improved.

In the case of cold-rolled steel sheets, cold rolling and recrystallization annealing are subsequently performed, but in the present invention, there are no particular restrictions on these steps, and they may be performed in a conventional manner, and continuous annealing or box annealing may be used. In addition, temper rolling may be performed as necessary.

Next, the present invention will be explained in more detail with reference to examples thereof.

Example 1 A steel having the composition shown in Steel A in Table 1 was melted, hot rolled to 3.2 vs., and washed with sulfur M# for descaling to completely remove scale. . Thereafter, nitriding annealing was performed at 740°C for 10 hours in a HzNz nitriding atmosphere with varying hydrogen concentrations, and then cold rolled to 0.8 mil.
A cold rolled steel plate was obtained by continuous annealing at 830°C for 160 seconds,
We investigated the crawling characteristics. After pre-treatment of degreasing and sulfuric acid pickling, 1-diffraction glass manufactured by Nippon Ferro ■ is coated with N glaze.
(Product name 1553c), firing conditions 830℃ x 3
minutes in the atmosphere.

The results are shown in Figure 1, where the hydrogen concentration in the nitriding atmosphere was 3.
If it is less than % by volume, the steel plate will oxidize and cold rolling will not be possible.
Moreover, when it exceeds 80 volume %, the nitrogen concentration becomes low and the nail chipping resistance deteriorates rapidly.

Example 2 A steel having the composition of steel A was used in the same manner as in Example 1, and after pickling for descaling, it was treated at 740°C in a nitriding atmosphere of 20% by volume hydrogen-residual nitrogen. changed time. Thereafter, recrystallization annealing was performed in the same manner as in Example 1, and the mechanical properties of the obtained cold rolled steel sheet were investigated.

The results are shown in FIG. 2. If the nitriding annealing time is less than 1 minute, the elongation and r value will be less than 48% and 1.8, respectively, but if it is longer than this, they will be good values. Moreover, if the time exceeds 20 hours, a large amount of TiN is formed and the mechanical properties deteriorate.

A similar tendency was observed when the mechanical properties of hot-rolled steel sheets were evaluated in the same manner.

Example 3 Steels A to E having the respective compositions shown in Table 1 were produced, hot rolled to a thickness of 3.2-1, and nitrided in the same manner as in Example 1.

In Experiment 2.5 in Table 2, reduction and nitriding annealing were performed without descaling. Other steels were pickled for descaling and then nitrided.

The reduction annealing conditions were 700° C. for 5 hours in a 20% Hz atmosphere.

The amount of scale at this time is 25g/- in terms of Pa.
It was 2.

The nitriding conditions were 740° C. for 10 hours using a nitriding atmosphere of 20% by volume H2-residue N2.

After that, in the examples from experiments 11114 to 13, 0.8 +
It was cold rolled to u++ and continuously annealed at 830° C. for 60 seconds, and its floating properties were investigated. The waxing was carried out in accordance with Example 1.

The results are also summarized in Table 2.

It can be seen that the steel sheets manufactured according to the present invention have a low YS of less than 13 kgf/-m'', both hot-rolled steel sheets and cold-rolled steel sheets, and have good elongation and r-value. Instead, the steel plate of Jikken Hiro 2.5 was subjected to reduction annealing.
Pinhole characteristics are even better. Also, experiment N
[111] produced a large amount of bubbles and could not be tested for adhesion and nail-flying resistance.

Note that the adhesion was calculated from the peeled area ratio using a PEI tester. Nail fly resistance was evaluated by the presence or absence of occurrence after one week of firing. Pinhole characteristics were determined visually.

(The following is a blank space) (Effects of the Invention) According to the present invention, it can be seen that the characteristics of the Ti-added steel sheet can be fully brought out while ensuring the resistance to nail chipping.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the hydrogen concentration in the nitriding treatment atmosphere and the nail chipping resistance; and FIG. 2 is a graph showing the relationship between the nitriding treatment time, elongation, and r value.

Claims (3)

[Claims] (1) C: 0.01% or less, Si: 0.1% or less, Mn: 0.
5% or less, P: 0.1% or less, S: 0.03% or less, Ti: 0.01 to 0.1% and T
i/2≧48×(C/12+N/14+S/32), C
u: 0.01~0.1%, balance Fe and unavoidable impurities. After hot rolling and pickling for descaling, 3~80% by volume of H_2-residue. N_2
A method for producing a steel plate for enameling having excellent workability and nail chipping resistance, the method comprising performing nitriding annealing at 500 to 850°C in a nitriding atmosphere for 1 minute or more and 20 hours or less. (2) Furthermore, B: 0.0003 to 0.0020% by weight
The method for manufacturing a steel plate for enameling according to claim 1, which comprises: (3) The method for manufacturing a steel plate for enameling according to claim 1 or 2, characterized in that reduction annealing is performed in place of pickling for descaling.