KR100570892B1 - method for manufacturing the ferritic stainless steel sheet with a good elongation and execllent anti-ridging - Google Patents

Abstract

The present invention relates to weight percent C; 0.01% or less, Si: 1.0% or less, Mn: 1% or less, P: 0.035 or less, S: 0.03 or less, Cr: 10-12%, Mo: 0.1% or less, N: 0.01% or less, Cu: 0.1% or less , Al: 0.1% or less, Ni: 0.2% or less, Ti: 0.3% or less, consisting of remaining Fe and inevitable impurities added, C + N: 0.015% or less, 10≤Ti / (C + N) ≤15 Hot-rolling the steel having a satisfactory composition such that the slab manufactured to have an equiaxed crystal rate of 70% or more in the playing slab is heated to 1200 ° C. or less and the finish rolling temperature is 800 ° C. or less to omit hot rolling annealing; In addition, after cold rolling with a cold rolling reduction rate of 85% or more, the temperature increase rate of 400 ℃ / sec. Performing rapid cold annealing for 5 seconds or more to 15 seconds or less within this temperature range by rapid heating; Provides a method for producing a ferritic STS409L stainless steel having a high elongation, and excellent dropping properties.

Elongation

Description

Method for manufacturing the ferritic stainless steel sheet with a good elongation and execllent anti-ridging}

1 is a graph showing the change in elongation and leasing height according to the temperature increase rate during STS409L cold annealing.

Figure 2 is a chart showing the chemical composition and hot rolling and annealing conditions and elongation and leasing height measurement results of each specimen.

The present invention relates to a method for manufacturing ferritic stainless steel having excellent elongation and degumming ability, and more particularly, to control the chemical composition within a certain range in STS409L steel, and to manufacture a slab having a constant equiaxed crystal, eliminating hot-rolling annealing, The present invention relates to a method of manufacturing STS409L steel hot rolled annealing having low manufacturing cost and good moldability by increasing the annealing temperature and the temperature rising rate during cold rolling and cold rolling annealing to improve elongation and ridging properties.

In general, STS409L steel is the cheapest steel type because of its low Cr content in stainless steel, and is widely used for automobile exhaust system parts. Therefore, in order to reduce manufacturing cost and improve productivity, when hot-rolled annealing and pickling, cold rolling and cold-rolling annealing are inferior in elongation and downsetting, there is a problem that breakage occurs frequently during molding.

Conventional technology to solve this problem is hot-rolled annealing STS409L steel at 950 ~ 960 ℃ and pickled by cold rolling annealing at 920 ℃ after 50 ~ 80% cold reduction rate 10 ~ 15 ℃ / sec. In the case of heat treatment for 20 seconds, the elongation is 38%, the ridging height is 20mm level. On the contrary, when the hot-rolled annealing is omitted, the elongation is 36% and the ridging height is very high at the level of 40mm.

The present invention has been made to solve the above problems, the present inventors conducted the experiment to improve the problems of the above-described hot-rolled annealing material of STS409L steel, and proposed the present invention on the basis of the results, the present invention is STS409L If steel is controlled within a certain range, a slab with a constant isotropic rate is manufactured to omit hot-rolled annealing, and it is cheaper to manufacture by improving elongation and ridging property by increasing the annealing temperature and temperature increase rate during constant cold rolling rate and cold-rolled annealing At the same time, the object of the present invention is to provide a method for producing STS409L steel hot rolled annealing having good moldability.

Hereinafter, the present invention will be described.

The present invention provides a method for producing STS409L ferritic stainless steel,

By weight% C: 0.01% or less, Si: 1.0% or less, Mn: 1% or less, P: 0.035 or less, S: 0.03 or less, Cr: 10-12%, Mo: 0.1% or less, N: 0.01% or less, Cu: 0.1% or less, Al: 0.1% or less, Ni: 0.2% or less, Ti: 0.3% or less Composition with remaining Fe and inevitable impurities added, C + N: 0.015% or less, 10 ≦ Ti / (C + In a composition satisfying N) ≤15, the slab equiaxed crystallization rate is manufactured to have 70% or more of the slab, and the hot rolling is carried out by hot rolling at the slab heating temperature of 1200 ° C. or lower and the finishing rolling temperature of 800 ° C. or lower. Cold rolling after cold rolling to the rate of 85% or more within the range of 1000 ~ 1100 ℃ based on the plate temperature, the temperature rising rate of 400 ℃ / sec. The cold rolling annealing time is maintained at a temperature of 1000 ° C. or higher and 1100 ° C. or lower for 5 seconds to 15 seconds or less. It is a method for manufacturing a non-hot-rolled annealing STS409L ferritic stainless steel.

Hereinafter, the present invention will be described in more detail.

In order to achieve the above object, in the present invention, it is preferable to form the steel as described above. Hereinafter, the reason for limiting the composition range of the inventive steel will be described.

The C and N are Ti-nitride bonded with Ti to form Ti carbonitride. When the C and N contents are increased, the unbound solid solution C and N contents are increased, the strength is high, and the elongation is lowered. 0.01% or less, N satisfies 0.01% or less, and the C + N content is limited to 0.015% or less because the elongation is lowered when the C + N content exceeds 0.015%.

Si is a ferrite forming element, which increases the stability of ferrite phase and improves oxidation resistance, but when added in excess of 1.0%, Si increases hardness, yield strength, tensile strength and lowers elongation. do.

Mn is limited to 1.0% or less because the content of Mn elutes MnS and lowers pitting resistance.

Since P and S form inclusions such as MnS to inhibit corrosion resistance and hot workability, P and S should be kept as low as possible, so they are limited to P: 0.035% or less and S: 0.03% or less.

If Cr is too low, the content is less than 10%, the corrosion resistance is lowered. If the content is too high, the corrosion resistance is improved, but if it is more than 12%, the strength is increased and the moldability is reduced due to the decrease in elongation. It is limited to 12%.

Mo significantly improves the corrosion resistance, but increases the strength, resulting in poor moldability. Therefore, the Mo content is limited to 0.1% or less in consideration of corrosion resistance and moldability.

Al is limited to 0.1% or less because a large amount of element is added as a deoxidizer, and causes surface defects.

When Cu is added as a gamma-phase generating element, Cu increases in manufacturing cost due to an increase in the input amount of ferroalloy, and decreases hot workability, causing surface defects during hot rolling. Therefore, Cu is limited to 0.1% or less.

Ti is a stabilizing element. If the Ti content is too high, the elongation and formability are deteriorated, so that the ratio is 10≤Ti / (C + N) ≤ It is limited to 15.

Hereinafter, the manufacturing conditions of the present invention will be described.

First, if the equiaxed crystallinity in the slab is lowered to 70% or less, the equiaxed crystallinity is limited to 70% or more because the columnar structure in the slab remains unchanged after hot rolling and cold annealing.

When the slab heating temperature is more than 1200 ℃ and the finishing rolling temperature is more than 800 ℃, the internal strain accumulation energy is low during hot rolling, so if cold rolling and cold annealing are followed by cold rolling and cold annealing, there are many bad band structures in the ridging property. In order to perform low-temperature rolling for the purpose of increasing internal strain accumulation energy during rolling, the slab heating temperature is limited to hot rolling at 1200 ° C. or lower and the finish rolling temperature at 800 ° C. or lower.

After hot rolling, hot rolling annealing is omitted, and when cold rolling is lowered at the time of pickling and cold rolling, columnar tissue destruction in the 1 / 4t thickness direction is less likely to occur, thereby promoting internal columnar tissue destruction and recrystallization during cold rolling. Cold rolling reduction is limited to 85% or more.

Cold rolling annealing condition is to improve elongation and ridging by rapid heating at high temperature for a short time. If the cold rolling annealing temperature is below 1000 ℃, the recrystallization is insufficient. The annealing temperature is limited to 1000 ° C to 1100 ° C because of rupture of plate due to tension.

The temperature increase rate is 400 ℃ / sec. If it is below, since the recrystallization aggregate which improves ridging property and elongation will not develop, a temperature increase rate will be 400 degreeC / sec. It is limited to the above.

If the cold annealing time is too short, the recrystallized aggregate structure does not develop, and if the time is too long, the grains are coarsened as in the case of 1100 ° C or higher when the annealing temperature is high. Cold rolling annealing time is limited to 1000 seconds or more and 1100 degrees C or less from 5 seconds to 15 seconds or less based on the plate temperature.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

2, a ferritic stainless steel prepared as shown in FIG. 2 was dissolved in a 30Kg vacuum induction furnace to prepare an ingot having a length of 110 (mm), and the prepared ingot was heated at 1250 ° C and 1180 ° C for 150 minutes, and was heated at 900 ° C and After hot rolling at 790 ° C, hot rolled plates having thicknesses of 4mm, 8.6mm and 12mm were prepared, and specimens subjected to hot-rolling annealing at 950 ° C and specimens which were omitted were subjected to cold rolling reduction rates of 70%, 86%, after pickling. Cold rolling was performed at 90% to make the final cold roll thickness constant at 1.2 mm. The cold rolling annealing treatment is performed at annealing temperatures of 900, 920, 1050, 1200 ℃, temperature rising speed of 13, 100, 300, 400, 500 (℃ / sec.) And annealing time of 10, 20, 25 seconds. Pickled by cold rolling annealing by direct electric resistance heating method. Tensile test was carried out by processing tensile specimens in the direction parallel to the rolling direction in accordance with JIS 5 specimen standard after pickling, and the maximum ridging height was measured by surface roughness after 15% tensioning.

The chemical composition, hot rolling and annealing conditions, elongation, and leasing height of each specimen are shown in FIG. 2.

In addition, using a hot-rolled annealing material is cold rolled at a cold rolling rate of 86%, the second drawing shows the elongation and leasing height according to the temperature increase rate at a cold rolling annealing temperature of 1050 ℃. When the temperature increase rate is 400 ℃ or more, it was confirmed that the elongation is 39% or more, the leasing height is 20mm or less and excellent in elongation and lowering property.

1 and 2, the C + N content is 0.015% or less, 10≤Ti / (C + N) ≤ 15, the chemical composition is satisfied, and the equiaxed crystal in the slab is 86%, 90% Using slab that satisfies 70% or more, the slab heating temperature is 1180 ℃, the finish rolling temperature is 790 ℃, hot rolled, and the cold rolling rate is 86% and 90%, and the cold rolling annealing temperature is 1050 ℃. Inventive materials (A, B, C) subjected to cold rolling annealing for 400 ° C, 500 ° C and annealing time for 10 seconds have developed recrystallized aggregates, which are beneficial for improving elongation and ridging, with elongation of 39% or more and leasing height of 20mm or less As compared to the comparative material does not satisfy the above manufacturing conditions it shows a good characteristic. Moreover, it turns out that the characteristic is improved compared with the hot-rolled annealing material (sample Q) which is normal manufacturing conditions. Therefore, by omitting hot annealing, it was possible to manufacture STS409L steel with low manufacturing cost and excellent elongation and quenchability.

As described above, according to the present invention, a recrystallized aggregate that is beneficial for improving elongation and ridging develops and exhibits a favorable effect compared to the comparative material which does not satisfy the above manufacturing conditions with elongation of 39% or more and leasing height of 20 mm or less. .

In addition, it is possible to obtain an effect of improved characteristics over the hot-rolled annealing material which is a normal manufacturing condition.

In addition, by omitting the hot-rolled annealing according to the production method of the present invention, it was possible to produce STS409L steel with low manufacturing cost and excellent elongation and degumming.

Claims (1)

C by weight; 0.01% or less, Si: 1.0% or less, Mn: 1% or less, P: 0.035 or less, S: 0.03 or less, Cr: 10-12%, Mo: 0.1% or less, N: 0.01% or less, Cu: 0.1% or less , Al: 0.1% or less, Ni: 0.2% or less, Ti: 0.3% or less, consisting of remaining Fe and inevitable impurities added, C + N: 0.015% or less, 10≤Ti / (C + N) ≤15 The river of the composition to satisfy, Hot-rolling the slab manufactured to have an equiaxed crystallinity of 70% or more in the playing slab to a heating temperature of 1200 ° C. or lower and a finishing rolling temperature of 800 ° C. or lower so as to omit hot rolling annealing; In addition, after cold rolling with a cold rolling reduction rate of 85% or more, the temperature increase rate of 400 ℃ / sec. Performing rapid cold annealing for 5 seconds or more to 15 seconds or less within this temperature range by rapid heating; A method of manufacturing a ferritic STS409L stainless steel having a high elongation, and excellent driftability, characterized in that consisting of.

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