JP2733423B2 - Plated sheet excellent in secondary workability and weldability and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to an original plate having excellent secondary workability, that is, an original plate suitable for tinplate and tin free and a method for producing the same.

[0002]

2. Description of the Related Art According to JIS G3303, a plating base plate for tinplate and tin-free is made of T-1 (HR 30T) according to Rockwell T hardness (HR 30T) which indicates surface hardness among material properties.
It is classified from ≒ 49 ± 3) to T-6 (HR 30T ≒ 70 ± 3). Of these, most of the hard plated bases of T-4 to T-6 grade are manufactured by the continuous annealing method, and T-4CA to T-6CA (HR 30T = 61 ± 3 to 70 ± 3) Is stipulated. In the case where such materials having different surface hardnesses are separately produced, usually, the material components, hot rolling conditions, annealing conditions, or the temper reduction ratio after annealing are appropriately adjusted.

[0003] That is, a soft plating base plate of T-1 to T-3 class is manufactured by annealing a low-carbon aluminum-killed steel by a box annealing method and applying a tempering reduction of several percent or less. On the other hand, T-4CA to T-6CA grade hard plating base plates are P or N for the purpose of increasing hardness.
It is manufactured by subjecting a low-carbon aluminum-killed steel to which an appropriate amount is added to continuous annealing and applying a tempering reduction of several percent or less. On the other hand, in recent years, C and N contents in steel were both reduced to 0 at the steelmaking stage.
Nb and the like are added to aluminum-killed ultra-low carbon steel reduced to 004 wt% or less, annealed by continuous annealing method, and further subjected to tempering reduction of several tens% or less to obtain T-1 to T-6 grades. A method for producing all plating original sheets has been developed.

[0004]

First, a method of producing a T-1 to T-3 grade soft-plated original sheet by box annealing low-carbon aluminum-killed steel is described as follows. It does not exist in a solid solution state in steel due to precipitation. For this reason, even if an alloying treatment (reflow treatment) or a heat treatment at the time of painting printing is performed, no strain aging occurs, no yield point elongation occurs, and a stretcher strain (fine streaks) during secondary processing is not generated. There is almost no occurrence of pattern. However, with this technique, it is difficult to obtain a texture advantageous for drawability, and a Rankford value r value indicating plastic anisotropy

(Equation 1) Has a value of about 1.0, which causes a problem of lowering the deep drawability and eventually lowering the secondary workability. In addition, there is a problem that productivity is low and box lead time is long because box annealing which requires a long holding time is indispensable.

On the other hand, P or N
And T-4CA to T-6 by continuous annealing.
About the method of manufacturing the hard plating original plate of CA class,
There is a problem that most of C and N in the steel remain in a solid solution state without being precipitated outside the iron matrix. C and N in the solid solution state are accumulated on dislocation lines by reflow treatment or heat treatment at the time of coating printing, and form a Cottrell atmosphere, thereby causing a strain age hardening phenomenon. For this reason, such an original plate for plating has a large yield point elongation amount and often causes stretcher strain during secondary processing, and thus has a problem of impairing the appearance.

[0006] Further, by continuously annealing an ultra-low carbon steel to which an appropriate amount of Nb or the like is added, and appropriately selecting a temper reduction ratio so as to obtain a predetermined surface hardness, all temper degrees ranging from T1 to T6 are obtained. For producing an original plating plate (JP-A-58-197224)
In Japanese Patent Application Laid-Open No. 59-129733), C and N in a solid solution state hardly remain, which is effective in suppressing the occurrence of stretcher strain, and has a high average r value and excellent secondary workability. There was a feature that an original plating plate was easily obtained. In addition, the conventional T-
That is, a soft plating base plate of 1 to T-3 class can be efficiently produced by a continuous annealing method.

However, in each of these prior arts,
By reducing elements such as C, Mn, and P, which are also strengthening elements of the iron base, the softest T-1 grade plating base plate can be manufactured, but a hard (T3 to T6 grade) plating base plate is obtained. For this purpose, it is necessary to apply a refining reduction significantly higher than that of the conventional method, and there is a problem that the secondary workability is reduced. This is because, in general, the iron base material undergoes work hardening when subjected to a high tempering pressure, significantly increasing the elastic limit and lowering the secondary workability. Further, there is a problem that productivity of the refining reduction step is significantly reduced.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, particularly, T1 which is excellent in secondary workability by only applying a small temper reduction with a continuous annealing material of extremely low carbon steel. An object of the present invention is to establish a technology for stably producing a T-6 grade plating original plate.

[0009]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned objects, ultra-low carbon steels were found to contain Mn and / or
Alternatively, the present invention was developed based on the finding that the iron base can be strengthened without significantly lowering P, and for example, all tin-free steel sheets ranging from T1 to T6 can be stably obtained. That is, the gist configuration of the present invention is as follows. (1) C: 0.004 wt% or less, Si: 0.04 wt% or less, Mn: more than 0.3 to 1.5 wt%, S: 0.04 wt% or less, provided that Mn / S: 8 or more, P: 0.02 wt% or less, Al : 0.02 to 0.20 wt%, N: 0.004 wt% or less, and Nb equivalent to 0.3 to 1.5 in Nb / C atomic ratio, with the balance being
A plated original sheet having excellent secondary workability and weldability, which are Fe and inevitable impurities (first invention). (2) C: 0.004 wt% or less, Si: 0.04 wt% or less, Mn: more than 0.3 to 1.5 wt%, S: 0.04 wt% or less, provided that Mn / S: 8 or more, P: more than 0.02 to 0.1 wt% , Al: 0.02 to 0.20 wt%, N: 0.004 wt% or less, and Nb equivalent to 0.3 to 1.5 in Nb / C atomic ratio, with the balance being
A plated original sheet having excellent secondary workability and weldability, which are Fe and inevitable impurities (second invention). (3) Then, each of the plating original sheets described in (1) or
When the steel having the composition described in (2) is continuously cast, and the continuous cast slab is subjected to hot rolling, the finish rolling temperature is set to 800 to 950 ° C and the rolled to 500 to 700 ° C. Temperature, then pickling and then cold rolling.
Continuous annealing at 50-850 ° C and rolling rate 0.2-5%
Is obtained by subjecting to temper rolling within the range. (3rd and 4th inventions).

[0010]

The reason why the composition of the original plate for plating of the present invention is limited as described above will be described below. C: 0.0040 wt% or less C is an element that affects the secondary workability of the plating base sheet. If this amount exceeds 0.004 wt%, the drawability is reduced, and the amount of C remaining in a solid solution state increases, so that tin plating alloying treatment (reflow treatment), heat treatment during painting printing, etc. Heating before and after causes a strain aging phenomenon. For this reason, the yield point elongation of the plating base sheet increases, and a stretcher strain is generated at the time of secondary processing to impair the appearance characteristics.

Si: not more than 0.04 wt% When Si exceeds 0.04 wt%, the tendency of hardening becomes remarkable,
The rolling load is increased, and a temper color is easily generated during annealing. Further, the plating property and the coating property are reduced, which causes a reduction in corrosion resistance.

Mn: more than 0.3 to 1.5 wt% If Mn is less than 0.3 wt%, there is no contribution to strengthening the iron base,
In order to obtain a surface hardness equivalent to that of a hard plating base plate of T3 class or higher, the tempering reduction rate after annealing must be increased.
For this reason, the elastic limit is increased, and the secondary workability such as drawability is reduced. In addition, the quenching property and the softening resistance due to heat are insufficient, so that when welding is performed, the welded portion and the influence of welding heat (HA)
The strength of the portion Z) significantly decreases, and welding defects such as HAZ cracks are likely to occur. Further, Mn has a function of lowering the Ar ₃ transformation temperature, but its effect is poor at a content of 0.3 wt% or less. For this reason, when the C% further decreases within the above-mentioned range of the C content, the Ar ₃ transformation temperature rises remarkably,
In the case of an original plate with a thin hot-rolled sheet, it becomes difficult to hot-roll in the γ (austenite) phase region, and transformation temperature cracking during rolling, a remarkable deterioration of the quality of the hot-rolled sheet, abrasion of the roll, etc. are likely to occur. . On the other hand, to avoid these, α
When hot rolling is performed in the (ferrite) phase region, there is also a problem that coarsening and accompanying orange peel (rough skin) are likely to occur. In addition, such an effect is expressed as Mn ≧
It becomes remarkable when it exceeds 0.4 wt%. On the other hand, if the Mn content exceeds 1.5 wt%, the hardening becomes remarkable, the rolling load increases remarkably, and the average r-value also remarkably decreases. Cause a decrease in
More than 0.3 to 1.5 wt%.

S: 0.04% by weight or less S is a component that induces red hot embrittlement, and if it exceeds 0.04% by weight or becomes 8 or less as Mn / S (weight ratio), cracks called hot cracks during hot rolling. Is more likely to occur. Therefore, S is set to 0.04 wt% or less and Mn / S is set to 8 or more.

P: 0.02% by weight or less or more than 0.02% to 0.1% by weight Since P significantly hardens the iron base even in a trace amount, it is usually set to 0.02% by weight or less. However, in order to produce a hard material equivalent to T4 class or higher under light tempering pressure of about several%,
It is better to add this P content with an upper limit of 0.1 wt%. However, this P segregates at the grain boundaries while strengthening the iron base material, embrittles the grain boundaries, and significantly lowers the secondary workability. Therefore, the addition of P over 0.1 wt% must be avoided.

Al: 0.02 to 0.20 wt% If Al is less than 0.02 wt%, it is difficult to fix solute N in steel as AlN and precipitate it out of the iron matrix. If this solute N remains in the iron matrix, as in the case of solute C, heating at around 200 ° C, such as reflow treatment or heat treatment during coating printing, causes a strain aging phenomenon, and the yield point elongation decreases. Enlarge and generate stretcher strain. Conversely, if this Al seems to be insufficient, it is necessary to increase the amount of Nb to be added, which causes a problem that the raw material cost increases, the recrystallization temperature increases, and the continuous annealing becomes difficult.
Therefore, it is necessary to contain Al at 0.02 wt% or more. On the other hand, if the Al content exceeds 0.20 wt%, the economy is impaired, so the content was limited to 0.02 to 0.20 wt%.

The Nb: Nb / C atomic ratio of 0.3 to 1.5 Nb is added to fix C and N in the steel. However, when N and Al are limited to the above range,
Nb is mainly used only for fixing C. Therefore,
This Nb content must be determined relative to the C content. That is, this Nb / C atomic ratio is
If it is less than 0.3, the effect of the addition of Nb is poor, causing the above-mentioned strain aging phenomenon, the accompanying increase in yield point elongation, and the occurrence of stretcher strain. On the other hand, if the Nb / C atomic ratio exceeds 1.5, economic efficiency is impaired. Therefore, in the present invention, Nb is Nb /
C is limited to 0.3 or more and 1.5 or less.

Next, the production method of the present invention will be described.
Continuous casting of steel consisting of the above chemical composition into a continuous cast slab,
The continuous cast slab is first hot-rolled. In this hot rolling, the hot finishing temperature (FDT) is set to 800 to 950 ° C. (A ₃
A transformation point -30 ° C. to A ₃ transformation point +100 ° C.), performing the coiling temperature (CT) under the condition of 500 to 700 ° C..

With regard to the hot rolling conditions, if the FDT is outside the upper limit of the above range, the cost required for heating increases and the economic efficiency remarkably decreases. On the other hand, when the value falls below the lower limit, hot working is performed in the α phase, so that the rolling load is increased, and the crystal grains are remarkably coarsened to deteriorate the secondary workability. Further, the reason why the CT must be controlled within the above range is that if the CT is outside the upper limit, the precipitation and growth of NbC becomes insufficient, so that solid solution C remains, and the secondary workability decreases. .

Next, the hot-rolled steel material thus obtained is pickled and descaled according to a conventional method, and is subjected to cold rolling and continuous annealing. This continuous annealing is important in the present invention, and is carried out within a temperature range of 650 to 850 ° C. The reason for limiting to this temperature range is that recrystallization annealing does not proceed sufficiently at temperatures below 650 ° C, and at 850 ° C or higher, a vertical streak called a heat buckle occurs in a thin steel sheet during annealing, such as a base plate. This is because continuous annealing becomes extremely difficult, for example, it is easy to occur.

Next, the above-described continuous annealed material is subjected to temper rolling. This temper rolling in the present invention has a rolling reduction of 0.2 to 5%.
It is. The reason for this limitation is that when the rolling reduction is increased, the elastic limit is increased, so that the secondary workability is reduced and the productivity of the temper rolling step is reduced. However, generation of a stretcher strain or the like is suppressed by appropriate refining pressure, and secondary workability is improved. This is because the range in which these are harmonized is the above range.

[0021]

EXAMPLE Steel having the composition shown in Table 1 was melted in a converter and decarburized by a vacuum decarburizer to obtain a continuous cast slab.
After that, among the continuous cast slabs, steel type A (first invention example),
With respect to I (second invention example), hot rolling was performed under the conditions shown in Table 2. After the pickling, continuous annealing was performed in a continuous annealing furnace by the heat cycle shown in FIG. 1 and temper rolling was performed at various rolling reductions. Table 2 also shows the results of the hot rollability of the test materials (A, I) corresponding to the respective hot rolling conditions and the results of the secondary workability of the obtained plated original sheet.
The results show that the best results are obtained when the finish rolling temperature is within the range of 860 to 920 ° C, and that the winding temperature is preferably within the range of 600 to 660 ° C. Was. Further, under the annealing conditions using the above steel types A and I as test materials, as shown in Table 3, the temperature was 700-80.
It has been found that annealing at a temperature of 0 ° C, more preferably 700-750 ° C, is more suitable.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

Next, for each steel type shown in Table 1, the above hot rolling conditions and annealing conditions were applied, and the results of investigations on secondary workability and other weldability are shown in Table 4. Hardness (HR30T),
Yield point elongation (YEl), Rankford value (average r value) 210 ° C after 2% and 5% tempering reduction
The value after aging treatment of × 20min is shown.

[0026]

[Table 4]

As is clear from the results shown in Table 4, according to the A to K test materials according to the present invention, it is possible to obtain a hardness equivalent to T-3 or more at a temper reduction of 5% or less. There is almost no yield point elongation even after the aging treatment, indicating that the possibility of occurrence of stretcher strain is extremely low. The Rankford value (average r
Values) are all greater than 1.0, the drawability is good, and it can be said that the original plate is extremely excellent in secondary workability. on the other hand,
It is apparent that the comparative materials L to T have problems in industrial production, have high yield point elongation or low average r values, and are inferior in secondary workability.

[0028]

As described above, according to the present invention, it is possible to stably produce a plating base plate having excellent secondary workability and suitable for soft to hard tinplate, tin-free, and the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing a continuous annealing heat cycle in an example.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-129733 (JP, A) JP-A-58-197224 (JP, A)

Claims (4)

(57) [Claims] 1. C: 0.004 wt% or less, Si: 0.04 wt% or less, Mn: more than 0.3 to 1.5 wt%, S: 0.04 wt% or less, provided that Mn / S: 8 or more, P: 0.02 wt% or less. , Al: 0.02 to 0.20 wt%, N: 0.004 wt% or less, and Nb equivalent to 0.3 to 1.5 in Nb / C atomic ratio, with the balance being
An original plate with excellent secondary workability and weldability, which are Fe and inevitable impurities. 2. C: 0.004 wt% or less, Si: 0.04 wt% or less, Mn: more than 0.3 to 1.5 wt%, S: 0.04 wt% or less, provided that Mn / S: 8 or more, and P: more than 0.02 to 0.1. wt%, Al: 0.02 to 0.20 wt%, N: 0.004 wt% or less, and Nb equivalent to 0.3 to 1.5 in Nb / C atomic ratio, with the balance being
An original plate with excellent secondary workability and weldability, which are Fe and inevitable impurities. 3. C: 0.004 wt% or less, Si: 0.04 wt% or less, Mn: more than 0.3 to 1.5 wt%, S: 0.04 wt% or less, provided that Mn / S: 8 or more and P: 0.02 wt% or less. , Al: 0.02 to 0.20 wt%, N: 0.004 wt% or less, and Nb equivalent to 0.3 to 1.5 in Nb / C atomic ratio, with the balance being
Continuous casting of steel consisting of Fe and unavoidable impurities, and hot rolling of the continuous cast slab, the finish rolling temperature is 800 ~ 950 ℃, winding at 500 ~ 700 ℃ winding temperature And then pickling and cold rolling are sequentially performed.
Subjected to continuous annealing at to 850 ° C., the secondary processability Contact, characterized by further performing temper rolling with rolling ratio 0.2 5% coverage
And a method for producing a base plate with excellent weldability . 4. C: 0.004 wt% or less, Si: 0.04 wt% or less, Mn: more than 0.3 to 1.5 wt%, S: 0.04 wt% or less, provided that Mn / S: 8 or more, and P: more than 0.02 to 0.1. wt%, Al: 0.02 to 0.20 wt%, N: 0.004 wt% or less, and Nb equivalent to 0.3 to 1.5 in Nb / C atomic ratio, with the balance being
Continuous casting of steel consisting of Fe and unavoidable impurities, and hot rolling of the continuous cast slab, the finish rolling temperature is 800 ~ 950 ℃, winding at 500 ~ 700 ℃ winding temperature And then pickling and cold rolling are sequentially performed.
Subjected to continuous annealing at to 850 ° C., the secondary processability Contact, characterized by further performing temper rolling with rolling ratio 0.2 5% coverage
And a method for producing a base plate with excellent weldability .