KR20030049812A - method for manufacturing the ferritic stainless steel sheet with a good elongation and execllent anti-ridging - Google Patents

Abstract

PURPOSE: A method for manufacturing ferritic stainless steel sheet with good elongation and excellent anti-ridging by using STS 409L steel is provided. CONSTITUTION: The method includes the steps of hot rolling a steel slab (isometric rate thereof is greater than 70 %) comprising 0.01 wt.% or less of C, 1.0 wt.% or less of Si, 1 wt.% or less of Mn, 0.035 wt.% or less of P, 0.03 wt.% or less of S, Cr 10 to 12 wt.%, 0.1 wt.% or less of Mo, 0.01 wt.% or less of N, 0.1 wt.% or less of Cu, 0.1 wt.% or less of Al, 0.2 wt.% or less of Ni, 0.3 wt.% or less of Ti, a balance of Fe and incidental impurities at less than 1200 deg.C so that hot annealing is excluded, wherein C+N is less than 0.015 wt.%, 10<=Ti/(C+N)<=15, finish hot rolling temperature is less than 800 deg.C; cold rolling the hot rolled steel sheet at a reduction ratio of higher than 85 %; rapid heating the cold rolled steel sheet to the temperature range of 1000 to 1100°C at temperature elevation rate of greater than 400 °C/sec; and cold annealing the heated steel sheet for 5 to 15 sec within the temperature range of 1000 to 1100 deg.C.

Description

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

The present invention relates to a method for manufacturing ferritic stainless steel with excellent elongation and slidability, and more particularly, to control the chemical composition within a certain range in TS409L steel, 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 increase rate during cold rolling and cold rolling annealing to improve elongation and refrigerability.

In general, STS409L steel is the most inexpensive steel grade due to low Cr content in stainless steel, and is widely used for automobile exhaust system parts. Therefore, in order to reduce manufacturing costs and improve productivity, pickling after hot rolling annealing and cold rolling annealing with ZM cold rolling have inferior elongation and slidability, which causes problems in forming 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 squirrel height is 20mm level. On the other hand, when the hot anneal is omitted, the elongation is 36% and the squirrel height is 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, the slab with constant equiaxed rate is manufactured to omit hot-rolled annealing, and it is cheaper to manufacture by improving the elongation rate and rimability by increasing the annealing temperature and the temperature increase rate during constant cold rolling rate 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.

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

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

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 the N) ratio ≤ 15, it is manufactured so that the performance slab equiaxed crystal ratio is 70% or more. Cold rolling after cold rolling to the reduction ratio 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 1000 ° C or above and 1100 ° C or below for 5 seconds or more and 15 seconds or less at the plate temperature. 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 if the C + N content is 0.015% or more.

Si is a ferrite forming element which increases the stability of ferrite phase and improves the oxidation resistance. However, if it is added more than 1.0%, Si is disadvantageous for improving elongation because it increases hardness, yield strength, tensile strength and lowers elongation. .

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 (10% or less), the corrosion resistance is lowered. If the content is too high, the corrosion resistance is improved, but if it is 12% or more, 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) ratio. It is limited to ≤ 15.

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

First, if the equiaxed crystallinity in slab is lowered to 70% or less, the equiaxed crystallinity is limited to 70% or more since the columnar crystals in the slab remain unchanged even 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 during hot rolling is low, so there are many bad band structures due to cold rolling and cold annealing after hot rolling annealing. In order to perform low-temperature rolling for the purpose of increasing the internal strain accumulation energy during rolling, the slab heating temperature is limited to hot rolling at 1200 ° C or lower and the finishing 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 rhythm through short time rapid heating at high temperature. In case of cold rolling annealing temperature is below 1000 ℃, recrystallization is insufficient. Annealing temperature is limited to 1000 ° C. to 1100 ° C., because of rupture of the plate.

The temperature increase rate is 400 ℃ / sec. The temperature increase rate is 400 ° C / 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 grain size becomes coarse, such as when the annealing temperature is higher than 1100 ° C. 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 JIS No. 5 after pickling, and the maximum regrinding height was measured by surface roughness after 15% tensioning.

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

In addition, using a hot-rolled annealing material is cold rolled to a cold reduction rate of 86%, the second drawing shows the elongation and drift height according to the temperature increase rate at the 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 ridge height is 20mm or less, excellent in elongation and slidability.

1 and 2, the C + N content is 0.015% or less, 10≤Ti / (C + N) ratio ≤ 15, the chemical composition is satisfied, and the equiaxed crystal in the slab is 86%, 90% Using slabs that satisfy more than 70% of the slab, the slab heating temperature is 1180 ℃, the finish rolling temperature is 790 ℃, and the hot rolled annealing specimens are 86% and 90% cold-rolled, and 1050 ℃ Inventive materials (A, B, C) subjected to cold annealing for 400 ° C, 500 ° C, and annealing time for 10 seconds at RH have developed a recrystallized texture which is beneficial for improvement of elongation and rhythm. It exhibits better characteristics than the comparative material that does not satisfy the above manufacturing conditions. 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 deformability.

As described above, according to the present invention, the recrystallized aggregates, which are beneficial for the improvement of elongation and rhythm, are developed, which shows a good effect compared to the comparative material which does not satisfy the above manufacturing conditions with elongation of 39% or more and ridgeal 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 manufacture STS409L steel with low manufacturing cost and excellent elongation and deformability.

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, composed of remaining Fe and inevitable impurities, C + N: 0.015% or less, 10≤Ti / (C + N) ratio≤15 Steel 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 at 85% or more of cold rolling reduction rate, it is rapidly heated to 400 (℃ / sec.) Or higher at a heating rate of 1000 ℃ ~ 1100 ℃ based on the cold rolling plate temperature, and then 5 seconds or more and 15 seconds or less within this temperature range. Performing cold rolling annealing; A high elongation, characterized in that made of a ferritic stainless steel manufacturing method excellent.