JPS6126724A - Manufacturing method for ultra-soft surface treatment original plate by continuous annealing - Google Patents

Abstract

PURPOSE:To obtain the titled dead soft base sheet for surface treatment without adding any special elements by hot-rolling, descaling, and cold-rolling a low-C aluminum-killed steel of specified composition under appropriate conditions, and then annealing continuously under specified conditions. CONSTITUTION:A billet, contg. 0.01-0.04%, by weight, C, 0.05-0.60% Mn, <=0.02% P, 0.005-0.10% acid-soluble Al, <=0.01% N, and the remainder of Fe and incorporated, in necessary, with B in 0.5-1.0 ratio of B/N, is heated at 1,000-1,240 deg.C. The billet is hot-rolled, wound at 620-700 deg.C, descaled, and cold- rolled. In continuous annealing, the obtained sheet is firstly recrystallization-annealed at Ac1-800 deg.C, and slowly cooled from the soaking temp. to 650-730 deg.C. Then the sheet is cooled at 30 deg.C/sec velocity to the cooling end temp. which is 100-250 deg.C and <=(100XlogV-30 deg.C. Then the sheet is reheated at 250-450 deg.C, overaged for >=30sec, and refined by rolled at 0.2-6.0% draft. A base steel sheet suitable for Sn plating and chromate treatment can be obtained by this method.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing an extremely soft surface-treated base plate with a temper of 2 or less, which is subjected to surface treatments such as tin plating and chromic acid treatment, and Decarburization by vacuum degassing in
, Nb, and other additive elements, and relates to a method of manufacturing an original plate for extremely soft surface treatment by continuous annealing.

(Conventional technology) Tin-plated furiki can be selected according to the degree of material required, depending on the degree of tempering (tempering once).
is stipulated. Tempering is indicated by Rockwell surface hardness (HR30T or HR15T), from softest to T-146 to 52, T-250 to 56, and T-35.
4-60, T-458-64, T-562-68, T-
667-73.

These tin plates are generally manufactured by hot-rolling a hot-rolled coil made from a billet of low carbon steel to a specified thickness, annealing it, and then applying tin plating to a tin plate that is temper-rolled. ing. Among these manufacturing processes, two methods are used for annealing: batch annealing method and continuous annealing method, but T-1 to T-3 blanks for plating are conventionally annealed by batch annealing method, which is also classified by JIS. There is.

Since continuous annealing is an annealing cycle consisting of rapid heating, short-time soaking, and rapid cooling, it has conventionally been applied to the production of hard plastics of T-4 or higher. However, continuous annealing has advantages such as high productivity, uniform quality, energy saving, labor saving, and short delivery time. For this reason, in recent years, various studies have been conducted on methods of manufacturing soft plastic original sheets of T-3 or less by applying continuous annealing at .degree.

In general, in order to manufacture soft steel sheets, including cold-rolled steel sheets, by continuous annealing, the following steps are required: (1) coarsening of crystal grains, (2) reduction of solid solution C remaining after annealing, and (3) solid solution remaining after annealing. It is well known that reducing N is important.

However, in the production of soft tin plate blanks, in addition to these metallurgical effects and causes, it is necessary to pay attention to the amount of hardening in the processes after temper rolling. In other words, with cold-rolled steel sheets, the final step that determines the product material is temper rolling, but with buttsuki, there is an additional process of tin plating and melting of the tin layer to make the surface glossy. After strain age hardening, it becomes a product material.

Therefore, when producing soft tin plate blanks by continuous annealing, not only do the annealed plates become softer by avoiding fine grain hardening and solid solution hardening of C and N, but also the strain caused by the tin layer melting process. In order to prevent age hardening, it is important to sufficiently reduce solid solution C and solid solution N remaining in the annealed plate.

By the way, (1) In order to prevent crystal grain refinement, there is a method in which the finishing temperature is set to a low temperature of 700° C. to Ar3 transformation point in hot rolling (for example, Japanese Patent Publication No. 55-48574),
A method has been proposed in which the continuous annealing temperature is set to a high temperature of 680° C. or higher (for example, Japanese Patent Laid-Open No. 58-27932).

(2) In order to reduce solid solution C after continuous annealing, over-aging treatment is carried out at 300 to 500°C in the cooling process after soaking (the above-mentioned Japanese Patent Publication No. 55-48574, Japanese Patent Application Laid-open No. 58 -27932 publications). (3) In order to reduce solid solution N, the following methods are used: ) Addition of Al (Japanese Patent Publication No. 55-48574 and Japanese Patent Application Laid-open No. 58-27932) or further addition of Nb (for example, 1978
-197224). For these reasons, recently, continuous annealing has been applied to some parts of producing soft tin blanks of about T-3.

However, in order to stably manufacture ultra-soft tin blanks of T-2 or less by continuous annealing, there is a limit to softening with the combination of the above techniques, so decarburization is performed by vacuum degassing during steel manufacturing, and teeth etc. solid solution C and solid solution N
must be completely fixed. The cost associated with these decarburization treatments and additive alloys is lower than that of the batch annealing method.
Continuous annealing of extremely soft tin plate of T-2 or less is not necessarily advantageous.

(Problems to be Solved by the Invention) The inventors of the present invention have developed an ultra-soft surface treatment of T-2 or below, and continuously annealed the original plate without decarburizing it by vacuum degassing or using additional elements such as Ti and Nb. In order to manufacture the steel by applying this method, we investigated the entire manufacturing process, including the steel components.

As mentioned above, after skin pass rolling, the surface treatment original plate is subjected to a treatment that induces strain aging such as a tin layer melting process to become a product. The present invention provides a method for manufacturing an original plate for extremely soft surface treatment with a small number of steps.

(Means for Solving the Problems) The present invention is an Al-killed steel with a low carbon content of C: 0.01% to less than 0.04wt (hereinafter omitted) and a P:O content of 15% or less. Depending on the weight ratio of B to N, B/N is 05~
A steel piece of Al-killed steel containing 1.0%
Heated at low temperature of 240℃, hot rolled, 620-700℃
In continuous annealing after rolling and cold rolling, Ac+~800
Soak at a temperature of ℃, and from this soaking temperature 650 to 730℃
from this temperature to 100-250℃ at 30℃/
Cooling is performed at a cooling rate i (V °C/sec) equal to or higher than S and at a cooling rate related to the temperature at the cooling end point, and then 25
After heating to a temperature of 0 to 450°C and overaging, both solid solute C and solid solute N are significantly reduced, and even after the tin layer melting process, the hardness does not increase due to the formation of strong carbonitrides such as Ti and Nb. This is a method for producing an extremely soft original plate for surface treatment, which is equivalent to or less than the case where elements are added, and whose tempering temperature is 'f'-2 or less.

First, let's talk about the steel components.

There is a method for C to be made into an extremely low carbon of less than O and OOS by vacuum degassing treatment at the molten steel stage, but this increases the cost, and in the present invention, it becomes soft when combined with a continuous annealing cycle. The lower limit is 0.01%. On the other hand, if this amount increases, the growth of crystal grains will be inhibited and the annealed plate will already become hard due to dispersion strengthening of cementite, so the upper limit is set to less than 0.04 inch.

Mn is required to be 0.05% or more in order to prevent thermal embrittlement caused by S. On the other hand, if this amount is large, hardening occurs due to solid solution strengthening, so the upper limit is set to 0.60%.

P has a large effect on the hardness of the annealed plate, and must be adjusted to 0.02% or less in order to make the tempering of the product plate T-2 or less.

Since Al fixes solid solution N in the form of AlN, acid-soluble Al
0.005% or more is required. On the other hand, if this amount increases, A-/-20s inclusions will increase, causing cracks in the flange, etc., and will also increase costs, so the upper limit is set at 0.10%.

N causes hardening of the product plate through solid solution hardening in the process before annealing the plate and strain age hardening in the process after temper rolling, so it needs to be kept at 0.01% or less.

Further, when B is further contained, BN precipitates during hot rolling, and solid solution N can be fixed more effectively than kA. In order to achieve this effect, it is necessary not only to contain B, but also to have a weight ratio of B/B to the N content in the steel.
It is necessary to contain N at 0.5 to 1.0.

Next, the manufacturing process conditions will be described.

The slab manufacturing method may be an agglomeration/blowing method or a continuous casting method. The slab (steel billet) is heated prior to hot rolling, which prevents ktN precipitated during the slab manufacturing process from remelting, and
In order to precipitate AlN in a relatively large form so as not to inhibit crystal grain growth during the hot rolling process or subsequent processes, heating is performed to a temperature of 1240° C. or lower. The slab heating temperature is preferably a low temperature within a range that does not deteriorate the workability of hot rolling, but its lower limit is 1000°C.

In hot rolling, the finishing temperature does not need to be particularly specified, but after hot rolling, it is rolled up at a temperature of 620 to 700°C.

In order to sufficiently precipitate ktN in the hot-rolled sheet, the winding temperature must be 620° C. or higher.

Further, if the winding temperature exceeds 700°C, the pickling properties will be significantly deteriorated and the corrosion resistance will be impaired due to coarsening of the carbide, so the upper limit of the winding temperature is set at 700°C.

The hot-rolled steel strip is pickled using a conventional method, cold-rolled, and finished to a predetermined thickness. Thereafter, continuous annealing is performed under the following conditions.

First, it is heated to a temperature of Act~800°C and soaked to sufficiently perform recrystallization and solid solution of carbides precipitated in the hot-rolled plate.

For recrystallization, it is sufficient to soak at a temperature above the recrystallization temperature, but carbides precipitated during the hot-rolled sheet stage are redissolved in a short period of time during continuous annealing to increase solid solution C before the start of subsequent cooling. Therefore, in order to ensure supersaturated solid solution C to promote the overaging treatment effect, a soaking temperature of Ac1 or higher is required.

On the other hand, the upper limit of the soaking temperature is set at 800° C., because if the soaking temperature is set to a high value, the strength of the copper strip during threading will decrease, causing work failures and shape defects.

Next, it is slowly cooled from the soaking temperature to a temperature of 650 to 730°C. This makes the solid solution C in the ferrite phase the most abundant state,
This is to efficiently reduce solid solution C through subsequent cooling and over-aging treatment, and to prevent hardness from increasing due to aging during surface treatment. When slowly cooled to a temperature below 650°C or above 730°C, solid solution C in the ferrite phase decreases, and the effects of subsequent cooling and overaging treatment are reduced.

After that, the temperature lower than the overaging treatment temperature (cooling end point temperature T
) to 100-250°C. It is important to set the cooling rate at this time to 30°C/S or more, and to maintain the relationship T≦100 250-450℃
reheat to 30 seconds or more and perform an overaging treatment for 30 seconds or more. The processing conditions for darning were determined based on experiments and will be described with reference to FIGS. 1, 2, and 3.

The sample material had C: 0.018-0.034%, Mn: 0.
18-0.35%, P: 0.006-0.015%
, 5otAl: steel with base component of 0.031-9.083%, slab heating temperature 1050-1200°C
and a normal temperature of 1260-1300°C, followed by hot rolling at a finishing temperature of 800-860°C and a winding temperature:
The process is carried out at 640 to 700°C, and then cold rolled to a plate with a thickness of 0.
．． 35111111, continuous annealing is performed at a soaking temperature of near 50
~ 800°C, and after slow cooling to 680°C, rapid cooling was performed by varying the cooling rate V and cooling end point temperature T, and then at 400°C for 1
Over-aging treatment was performed for 1 minute.

Next, it was temper-rolled at a reduction rate of 1.5 to 5.5%, and then rolled at a temperature of 250°C, which corresponds to the tin layer melting process (reflow treatment).
Aging treatment was performed for seconds. Thereafter, the hardness HR30T was measured, and the influence of the cooling rate V after soaking in continuous annealing and the cooling end point temperature T on the hardness was investigated. The results are shown in FIG. Further, FIG. 2 shows the influence of the cooling end point temperature T on hardness when the cooling rate is 20° C./sec, and FIG. 3 shows the influence when the cooling rate is 100° C./sec.

As can be seen from these figures, the cooling end point temperature T is
If the temperature is lower than 100°C or higher than 250°C, and the cooling rate V is lower than 30°C/sec, the increase in hardness during surface treatment aging will be large (
, it becomes difficult to make the material softer than T-2.

In addition, the cooling end point temperature T is in the range of 100 to 250°C,
In addition, even if the cooling rate (■) is 30°C/sec or more, if the cooling rate (V) is slow and the cooling end point temperature is relatively high as shown in Figure 1, a temperature of T-2 or less cannot be obtained once. was found through testing.

This means that when the cooling rate V is slow and the cooling end point temperature T is relatively high, the supersaturation degree of C at the end of cooling is relatively small, and the grains become the core of rapid precipitation of C during overaging treatment. This is thought to be because the inner cementite is overaged and not formed before the start of treatment.

Therefore, based on experimental data, the above-mentioned relational expression was determined between the cooling rate V and the cooling end point temperature T.

Furthermore, as is clear from FIG. 3, even if the cooling rate V and the cooling end point temperature T are within the range of the present invention, if the slab heating temperature is high and outside the range of the present invention, HR30T: exceeds 56, and T- 2.It does not become extremely soft.

Next, it is reheated to a temperature of 250 to 450°C and subjected to an overaging treatment. If the temperature is lower than 250°C, the overaging treatment will take a long time and solid solution C cannot be reduced.

Further, if the temperature exceeds 450°C, the equilibrium solid solution amount of C at the overaging treatment temperature becomes large, so that it becomes difficult to reduce the solid solution C below that temperature. - The force holding time is required to be 30 seconds or more in order to completely precipitate supersaturated C.

After the overaging treatment, it is cooled to a temperature that allows skin pass rolling and is subjected to skin pass rolling. Temper rolling controls the degree of temper and adjusts the shape, but in order to adjust the shape and achieve the degree of temper for extremely soft materials, such as T-1, a rolling reduction of 0.2% or more is required. .

On the other hand, if the rolling reduction rate becomes high, the steel will harden and the object of the present invention cannot be achieved, so the upper limit is set at 6.0%. Next, surface treatments such as tin plating and chromic acid treatment are performed.

(Example) The samples shown in Table 1 were treated under the conditions shown in the same table to obtain original plates for surface treatment. Next, the equivalent temperature of reflow treatment; 2
Artificial aging treatment was performed at 50°C for 9 seconds. Thereafter, the hardness was measured and the results are shown in the same table.

With the steel of the present invention, an extremely soft steel plate for surface treatment with a temperature of T-2 or less can be obtained. - Comparative steels outside the scope of the strength-grip invention are:
Once tempered, the hardness exceeds the standard upper limit of T-2 (HR30T hardness 56) and becomes hard.

[Brief explanation of drawings]

Figure 1 is a chart showing the cooling rate and cooling end point temperature range at which the hardness becomes T-2 or less once tempered after the tin layer melting process of the steel plate, and Figure 2 is the cooling end point temperature of the steel plate and the tin layer melting process. (Reflow treatment) Figure 3 is a chart showing the relationship between the equivalent diameter hardness of the steel plate and the cooling end point temperature of the steel plate and the equivalent diameter hardness of the tin layer melting process. /θ /θθ 10θθ)

Claims (1)

[Claims] 1% by weight: C: 0.01 to less than 0.04%, Mn: 0
．． 05-0.60%, P: 0.02% or less, acid-soluble Al
: 0.005 to 0.10%, N: 0.01% or less, and the balance is iron and inevitable impurity elements.
Heating to a temperature of ~1240℃ and hot rolling to 620℃~
In performing rolling at a temperature of 700°C, then descaling, cold rolling, and then continuous annealing, recrystallization annealing is performed at a temperature of Ac_1 transformation point or higher and 800°C or lower, followed by 6
After slow cooling to a temperature of 50 to 730°C, the temperature is reduced to 30°C.
100 to 2 at a cooling rate of 1/sec or more (V°C/sec)
Rapid cooling to a cooling end point temperature of 50°C and [100×kgV-30]°C or less, then reheating to an overaging treatment temperature, overaging treatment at 250 to 450°C for 30 seconds or more, and 0.2~ A method for producing an extremely soft surface treatment original plate by continuous annealing, characterized by skin pass rolling at a rolling reduction of 6.0%. 2% by weight: C: 0.01 to less than 0.04%, Mn: 0
．． 05-0.60%, P: 0.02% or less, acid-soluble Al
: 0.005 to 0.10%, N: 0.01% or less, B containing 0.5 to 1.0 in B/N ratio, and the balance consisting of iron and inevitable impurity elements. ~1240℃
Ac_1 transformation point or higher, 800°C when heating to a temperature of , hot rolling, rolling at a temperature of 620°C to 700°C, then descaling, cold rolling, and then continuous annealing.
Recrystallization annealing is performed at the following temperature, followed by 650-730
After slow cooling to a temperature of 100 to 250 °C and [
100×kgV-30]℃ or less, rapidly cooled to the cooling end point temperature, then reheated to the overaging treatment temperature, 250~
Over-aging treatment at 450℃ for 30 seconds or more, 0.2-6
．． A method for producing an extremely soft surface treatment original plate by continuous annealing, characterized by skin pass rolling at a rolling reduction of 0%.