JPS63169331A - Production of chromium stainless steel strip of high strength double phase structure having excellent ductility - Google Patents

Abstract

PURPOSE:To obtain a stainless steel strip of double phase structure having high ductility and high strength by hot rolling a steel slab which consists essentially of Cr and is controlled in the relation with the essential component then subjecting the slab to one pass of cold rolling to a product sheet thickness, holding the steel in a specific temp. region in a continuous heat treatment furnace then subjecting the sheet to controlled cooling. CONSTITUTION:The slab of the steel consisting of <=0.15wt.% C, <=2.0% Si, <=4.0% Mn, <=0.040% P, <=0.030% S, <=0.60% Ni, >=10.0% and <=20.0% Cr, <=0.12% N, <=0.02% O, <=4.0% Cu, and the balance Fe and unavoidable impurities and satisfying the relations expressed by the formulas I, II is produced. Said slab is then subjected to hot rolling and one pass of cold rolling without including intermediate annealing to the product sheet thickness. The rolled sheet is passed through the continuous heat treatment furnace where the sheet is held at the two-phase region temp. of ferrite + austenite of Ac1 point or above and <=1,100 deg.C within 10min and is then cooled at 1-500 deg.C/sec average cooling rate from the max. heating temp. down to 100 deg.C. The chromium stainless steel strip of high-strength double phase structure having >=200 hardness HV and excellent ductility is obtd. by the above-mentioned finishing heat treatment.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a new industrial manufacturing method for a high-strength, multi-phase m-weave ROM stainless steel strip that has excellent ductility and small in-plane anisotropy of strength and ductility. The present invention provides a method for manufacturing a high-strength, high-ductility stainless steel strip that is required to have high strength and is used as a forming material that is subjected to processing such as press forming.

[Background of this field]

Chromium stainless steel containing chromium as a main alloy component includes martensitic stainless steel and ferritic stainless steel. Both are cheaper than austenitic stainless steels, which contain chromium and nickel as the main alloy components, and have physical properties that are not found in austenitic stainless steels, such as ferromagnetism and a small coefficient of thermal expansion. Therefore, there are many uses that are limited to chromium stainless steel not only for economic reasons but also for characteristics. Particularly in the fields of electronic equipment and precision mechanical parts in recent years, demand for chrome stainless steel sheets has increased, resulting in higher functionality, miniaturization, integration, higher precision, and simplification of processing processes for processed products in applications that use chrome stainless steel sheets. requirements are becoming increasingly strict. For this reason, in addition to the inherent corrosion resistance of stainless steel and the above-mentioned characteristics of chromium stainless steel, the material of the chrome stainless steel plate needs to have even greater strength, workability, and precision. Therefore, the emergence of chromium stainless steel sheet materials that have the contradictory properties of high strength and high ductility, excellent shape and thickness accuracy at the time of raw steel sheet, and excellent shape accuracy after processing. is awaited.

[Conventional technology]

When looking at conventional chrome stainless steel sheet materials from the viewpoint of two strengths, firstly, martensitic stainless steel is well known as a chrome stainless steel having high strength. For example, JIS G 4305 stipulates seven types of steel as martensitic stainless steel for cold rolled stainless steel sheets. These martensitic stainless steels have C content ranging from 0.08% or less (SUS410S) to 0.08% or less (SUS410S).
60 to 0.75% (SUS440A), compared to ferritic stainless steel at the same -Cr content level.
It contains high C and can be given high strength by hardening treatment or hardening and tempering treatment. For example, this J
In IS G 4305, 0.26-0.40%
In 5US420J2, which contains C and 12.00 to 14.00% Cr, hardness of HRC40 or higher can be obtained by quenching by rapid cooling from 980 to 1040°C and then tempering by air cooling at 150 to 400°C. and 0.60-0.75% C and 16.00-18
．． For 5US440A containing 00% Cr, 10
After quenching by rapid cooling from 10 to 1070℃, 150 to
It has been shown that the same hardness (HRC 40 or higher) can be obtained by air-cooling tempering at 400°C.

On the other hand, ferritic stainless steel sheets, which are chromium stainless steels, cannot be expected to be hardened very much by heat treatment, so two ways to increase their strength are to perform cold temper rolling after annealing to increase strength through work hardening. things are being done.

However, the reality is that ferritic stainless steels are not often used in applications that inherently require high strength.

[Problem that the invention seeks to solve]

In martensitic stainless steel sheets, the M weave after quenching or quenching and tempering is basically martensitic Mi weave, as its name suggests.

Although very high strength and hardness are obtained, elongation is very low. Therefore, if quenching or quenching and tempering treatment is performed, subsequent processing becomes difficult. In particular, processing such as press forming is not possible after quenching or quench-tempering. Therefore, when processing is performed, it is performed before quenching or quenching and tempering. In other words, the material manufacturer says that it is in an annealed state, that is, JIS G 4.
As shown in Table 16 of 305, it is usually shipped in a soft state with low strength and hardness, and after being processed into a shape almost similar to the final product at a processing manufacturer, it is quenched or quenched and tempered. be. The surface oxide film (scale) produced by this quenching or quenching and tempering treatment is often undesirable for stainless steel, where surface beauty is important, and as a countermeasure, heat treatment in a vacuum or inert gas atmosphere is recommended. This requires steps such as applying heat treatment and removing scale by polishing or the like after heat treatment. In any case, in order to obtain high strength with martensitic stainless steel sheets, a heat treatment process at the processing manufacturer is essential, which increases the burden on the processing manufacturer, and this increases the cost of the final product. The problem was that I couldn't do it.

On the other hand, ferritic stainless steel plate ffl! When the strength is increased by rolling, the elongation decreases significantly and the strength-ductility balance worsens.

This results in poor workability. The degree of increase in strength due to III-quality rolling is significantly higher in yield strength than in tensile strength. For this reason, when the rolling rate becomes high, the difference between proof stress and tensile strength becomes smaller, and the yield ratio (= proof stress / tensile strength) becomes close to 1, the plastic working area of the material becomes very narrow, and the yield strength becomes high. This increases the springback and deteriorates the shapeability after press working. Furthermore, the temper-rolled material has very large in-plane anisotropy in strength and elongation, and even light press processing results in poor shape after processing. Furthermore, since the processing strain due to rolling is larger closer to the surface of the plate, it is inevitable that the strain distribution in the thickness direction of the illi-quality rolled material becomes non-uniform. This results in non-uniform distribution of residual stress in the thickness direction of the plate, which may cause changes in shape such as warping of the plate after punching or photo-etching, especially in the case of ultra-TR'14 +H. This is a big problem in applications that require precision. In addition to the above-mentioned problems in terms of material properties, skin-pass rolled materials also have many problems in their manufacturability. First, regarding the control of strength, since temper rolling utilizes work hardening due to cold rolling, the rolling rate is the most important factor determining strength. therefore.

In order to achieve excellent plate thickness accuracy as a finished product and to achieve the target strength level accurately and stably, strict control of the rolling rate, specifically strict control of the initial plate thickness before temper rolling, is extremely important. In addition to this, it is necessary to control the strength level of the material before rolling. In addition, in terms of shape control, unlike so-called skin pass rolling and temper rolling, which have a light rolling ratio of at most 2 to 3% for the purpose of shape correction, temper rolling, which aims to increase strength, requires rolling. Since this is essentially cold rolling with a rolling rate of several tens of percent, it is difficult to obtain a copper strip with excellent shape properties as it is cold rolled. For this reason, material recovery and
It may be necessary to heat the material to a temperature range below the recrystallization temperature range at which it does not soften, and to perform stress relief treatment. As described above, temper-rolled materials have many problems in terms of manufacturability.

In addition to the problems caused by the above-mentioned temper rolling, ferritic stainless steel sheets also have the problem of ridging, which can be said to be an essential drawback. Rigging is normal.

It is a type of surface defect that occurs when a cold rolled annealed ferritic stainless steel plate is subjected to processing such as press forming.
Even after cold rolling, ridging, generally called cold rolling ridging, may occur.

This is still a big problem in applications where surface roughness is important.

[Means to solve problems]

To solve the above-mentioned problems, material manufacturers are trying to find a chromium stainless steel material that has moderately high strength, good ductility and workability that can be processed into the desired shape, has small anisotropy, and does not cause ridging. This could be solved if it could be provided in the form of a steel plate or copper strip. In order to solve this problem, the present inventors have continued extensive research on chromium stainless steel from both the chemical composition and manufacturing conditions. As a result, the steel composition is appropriately controlled, and the manufacturing conditions include hot rolling, hot rolling annealing as necessary, and cold rolling to achieve the product thickness. The cold-rolled steel strip is heated to the proper ferritic ten-austenite two-phase region, rather than the conventional finish annealing at a temperature in the ferrite single-phase region, that is, the annealing treatment applied to a steel plate or steel strip product. If a continuous finishing heat treatment is performed under specific conditions consisting of a subsequent rapid cooling treatment, it is possible to obtain a multi-phase structure in which a substantially soft ferrite phase and a hard martensitic phase are evenly mixed.
We have achieved great results in that virtually all of the problems mentioned above can be solved.

Thus, the present invention.

In weight%.

c: o, to% or less.

Si: 2.0% or less.

Mn: 4.0% or less.

p: o, o4o% or less.

S: 0.030% or less.

Ni: 4.0% or less.

Cr: 10.0% or more and 20.0% or less.

N: 0.12% or less.

o: o, o2% or less.

cu:4. o% or less.

and, in some cases, further contain 0.20% or less of A.
l, B of 0.0050% or less, M of 1.0% or less
o, REV of 0.109A or less, Y of 0.20% or less
0.01%≦C+N≦0.20% 0.5%≦Ni+ (Mn+Cu)/3≦5. A process of producing a steel slab that satisfies the 0% relationship and hot rolling it to produce a hot rolled steel strip.

A cold rolling process in which a cold-rolled steel strip is manufactured by cold-rolling to the product thickness by one-time cold rolling without intermediate annealing.

and.

The obtained cold-rolled steel strip is passed through a continuous heat treatment furnace and maintained at a temperature in the ferrite decaustenite two-phase region of 1 Ac+ point or more and 1100°C or less for less than 10 minutes, and then averagely cooled from the maximum heating temperature to 100°C. Speed 1℃/see or higher 500℃
Continuous finishing heat treatment process in which finishing heat treatment is performed by cooling at a speed of /sec or less.

The present invention provides a method for producing a high-strength multi-phase chromium stainless steel strip having a hardness of HV 200 or more and excellent ductility.

According to the method of the present invention, not only virtually all of the above-mentioned problems are solved, but also the strength can be freely and easily adjusted by controlling the steel composition or the heating temperature and cooling rate during finishing heat treatment. It provides an advantageous and new manufacturing technology for the industrial production of chromium stainless steel sheets or strip materials, and it can be applied to martensitic stainless steel sheets or strips and ferritic stainless steel sheets or strips that have been shipped to the market in the past. The purpose of the present invention is to provide the market with a new chromium stainless steel material that has both ductility and strength characteristics that are not available in other materials, and has less in-plane anisotropy in ductility and strength. According to the method of the present invention, the finished product that has undergone the final continuous finishing heat treatment process is industrially manufactured in the form of a coiled belt, and when it is shipped to the market, it remains as a coiled belt (coil). Or it will be shaped into a steel plate.

Conventionally, 8 For example, even in 5TLS430, which is a representative steel type of ferritic stainless steel, austenite is generated when heated to a temperature in the two-phase region, and this austenite is transformed into martensite by rapid cooling, resulting in a two-phase m weave of martensite in ferrite. It was known that it would happen. However, in the production of ferritic stainless steel strips that produce austenite at high temperatures, the heat treatment after cold rolling is only annealing at a temperature in the ferrite single phase region, and high-temperature heat treatment that produces martensite is not recommended. It is common sense to avoid this because it causes deterioration in material quality such as a decrease in ductility, and it has not been considered at all in the actual manufacturing of industrial steel strips.

Therefore, assuming continuous heat treatment as in the present invention after the cold rolling process of chrome stainless steel, and performing finishing heat treatment to heat to the ferrite + austenite dual phase region, the relationship between heating temperature, strength and ductility, and the relationship between ductility and strength. There are no examples of detailed research on anisotropy, etc. The present invention provides a completely new method of manufacturing high-strength chromium stainless steel strips that has not been previously considered as an industrial manufacturing method, and as a result, it provides a completely new method of manufacturing high-strength chromium stainless steel strips, and as a result, conventional chrome stainless steel strips or copper strips do not have The present invention provides a new ROM stainless steel sheet material with excellent properties.

[Details of the invention]

Below, the reasons for limiting the range of chemical component values of the classes regulated by the present invention and the content of each manufacturing process employed in the method of the present invention will be specifically explained in detail.

First, the reasons for limiting the content range (wt%) of the components of the chromium stainless steel to which the method of the present invention is applied are as follows.

This is because C and N are stronger and cheaper austenite-forming elements than Ni, Mn, Cu, etc., and are also elements with a greater ability to strengthen martensite.

It is an effective element for controlling strength and increasing strength after continuous finishing heat treatment. Therefore, after the continuous finishing heat treatment process, 10
Multi-phase structure containing % or more of martensite Hv200
To obtain sufficient strength, use Ni.

Even if austenite-forming elements such as Mn and Cu are added, the amount of (C+N) must be at least 0.01%.
or more is required. However, if the amounts of C and N are too high, a large amount of martensite 1 will be generated after the continuous finishing heat treatment process, and in some cases it will become 100% martensite, and the hardness of the martensite phase itself will become very high, so high strength will not be achieved. However, the ductility decreases. Therefore, the amount of (C+N) should be 0.20% or less, and 0.0
It is necessary to satisfy the relationship 1%≦C+N≦0.20%.

Furthermore, if a large amount of C is added, Cr carbides may precipitate at grain boundaries during cooling during continuous finishing heat treatment, resulting in a decrease in corrosion resistance. Therefore, the amount of C is set to 0.10% or less.

Further, it is difficult to add a large amount of N due to its solubility, and addition of a large amount causes an increase in surface defects, so the amount is set to 0.12% or less.

Si is a ferrite-forming element and has a strong solid solution strengthening ability for both ferrite and martensite phases. Therefore, it is an effective element for controlling the 41 (marten rhinoceros) and strength level. However, adding a large amount leads to a decrease in hot workability and cold workability, so
The upper limit is %.

M n + N r + Cu is an austenite-forming element.

It is an effective element for controlling the amount of martensite and strength after continuous finishing heat treatment. In addition, the amount of C added can be reduced by adding Mn, Ni+'Cu, which improves ductility as soft martensite and suppresses precipitation of Cr carbides at grain boundaries to prevent deterioration of corrosion resistance. I can do it.

Furthermore, the important effects of Mn, Ni, and Cu are shown in the test results (for example, the relationship shown in Figure 1) and examples below, but in the continuous finishing heat treatment process according to the present invention, the addition of Mn, Ni, and Cu improves A stable region with small hardness fluctuations can be obtained from the low temperature side over a wide temperature range.

This provides great benefits in actual operation, both in terms of high-temperature strength required for continuous finishing heat treatment and in terms of energy savings. Therefore, Mn, Ni, Cu
The addition of is not only contributing to the production of multi-phase Mi woven steel strips with stable strength properties, but also making it possible to perform heat treatment at low temperatures with higher high-temperature strength, thereby preventing coil breakage in the furnace due to continuous finishing heat treatment. It is possible to avoid problems caused by a decrease in high-temperature strength, and it also has a great effect from the perspective of energy conservation. To obtain such an effect, Mn, Ni, and Cu must be L'! at least 0.5
% or more, but Ni has the greatest influence on the increase in hardness of the multiphase structure material after continuous finishing heat treatment, and the process degree of Mn and Cu is approximately 3 times that of Ni. Therefore, when determining the amount of Mn+Ni+Cu added, N
It is regulated using the relational expression of i+ (Mn +Cu)/3, and Ni+ (Mn +Cu)/3 is at least 0.
．． Add 5% or more. However, if a large amount is added, the product becomes expensive, which affects the economic efficiency, which is one of the characteristics of the steel strip of the present invention. Therefore, each of Mn, Ni, and Cu alone should be 4.0% or less, and Ni+(Mn+Cu
)/3 to be 5.0% or less.

If S is too high, it will adversely affect corrosion resistance and hot workability, so it is preferably lower, and the upper limit is 0.030%.

Although P is an element with a large solid solution strengthening ability, addition of a large amount may lead to a decrease in toughness (9), so it should be kept at 0.040% or less, which is the normally allowed level.

At least 10.0% of Cr should be contained as the minimum necessary amount in order to maintain the corrosion resistance of stainless steel, but if the Cr content is too high.

The upper limit is set at 20.0% because the amount of austenite-forming elements required to generate martensitic phase and obtain high strength increases and the product becomes expensive.

O forms oxide-based nonmetallic inclusions! Since it lowers the cleanliness of II, it is preferable that it is lower, and it should be 0.02% or less.

A7! is an effective element for deoxidizing, and has the effect of significantly destroying A2-based inclusions that adversely affect press workability. However, if the content exceeds 0.20%, the effect not only becomes saturated, but also causes an increase in surface defects, resulting in negative effects such as (), so the upper limit is set at 0.20%.

B is an effective component for improving toughness, but its effect is brought about in a very small amount, and its effect is saturated when it exceeds 0.00%, so its upper limit is set at 0.0050%.

Mo is an element effective in improving corrosion resistance.

If added in large amounts, the product becomes expensive, so the upper limit is set at 1.0%.

REV and Y are elements effective in improving hot workability. It is also an effective element for improving oxidation resistance. The method of the present invention, which performs continuous finishing heat treatment at high temperatures, is effective in suppressing the generation of oxidized scale and obtaining a good surface texture after descaling. However, these effects
M saturates when it exceeds 0.10% and Y exceeds 0.20%, so the upper limit is 0.10% for REM and 0.10% for Y.
is 0.20%.

Next, the contents of each manufacturing process of the multi-phase steel strip according to the present invention will be explained.

In the method of the present invention, a slab of chromium stainless steel adjusted to one or more steel composition ranges is produced by conventional steel casting techniques, and this slab is produced by conventional hot rolling to produce a hot-rolled steel strip. After hot rolling, it is preferable to perform hot rolled sheet annealing and descaling. Although it is not necessary to carry out hot-rolled sheet annealing, this annealing softens the hot-rolled steel strip and improves its cold-rollability, and also removes the transformed phase remaining in the hot-rolled steel strip (austenitic phase at high temperatures). This is desirable for producing a steel strip with a uniform multi-phase structure after cold rolling and continuous finishing heat treatment. This hot rolled sheet annealing may be either continuous annealing or box annealing. Further, the descaling step may be carried out by ordinary pickling. The slab manufacturing process so far, hot rolling process,
For the hot-rolled sheet annealing process and the descaling process, conventional chrome stainless steel strip manufacturing techniques can be applied to the method of the present invention as they are.

Next, a dual-phase steel strip is manufactured through a cold rolling process and a continuous finishing heat treatment process, and these processes are characteristic of the method of the present invention and will be explained in detail.

"Cold rolling process" In the cold rolling process, hot rolled steel strip (hot rolled steel strip after hot rolled plate annealing) is cold rolled to product plate thickness by one cold rolling without intermediate annealing to produce cold rolled steel. Manufacture obi. Here, "single cold rolling without intermediate annealing" means that cold rolling is not performed two or more times with intermediate annealing in between. More specifically, by carrying out cold rolling by one-bath cold rolling or multi-bath cold rolling without intermediate sintering, it is possible to produce a cold rolled steel strip by cold rolling to the product thickness. Therefore, regardless of the number of passes through the rolling rolls, from the thickness of the hot-rolled steel strip to the product thickness of the cold-rolled steel strip, the reduction of sheet I is performed cold without intermediate annealing.

In the case of the method of the present invention, since the continuous finishing heat treatment step described below is performed after the cold rolling step, there are in-plane differences in strength and elongation resulting from the directional rolling structure that occurs in the cold rolled steel strip. It has been found that the orthotropic history is virtually eliminated in the dual-phase steel strip obtained by subsequent successive finishing heat treatments.

therefore.

The production of cold rolled steel strip according to the present invention does not require intermediate annealing (even if the thickness is reduced to the product thickness, the final multiphase structure will result in a steel strip with small in-plane anisotropy of strength and elongation). However, it has been found that the in-plane anisotropy, especially in elongation, of the multiphase steel strip becomes even smaller when intermediate annealing is performed and cold rolling is performed multiple times. An increase in manufacturing costs due to the increase in man-hours and thermal energy consumption due to carrying out annealing is therefore unavoidable.

According to the method of the present invention, which does not involve intermediate annealing, it is possible to economically advantageously produce a multi-phase &ll textured band. For these reasons, in the present invention, the hot-rolled steel strip is rolled down to the product thickness in one pass, or one-time cold rolling is adopted in which the hot-rolled steel strip is rolled down to the product thickness in multiple passes without intermediate annealing. Manufactures steel strips. The rolling reduction ratio at this time is preferably 30% or more and 95% or less.

Below, it will be explained based on typical test results that a multiphase steel strip with small in-plane anisotropy can be obtained even by cold rolling without intermediate annealing.

Steels A, B, and C having the chemical composition shown in Table 1 were melted and hot-rolled under normal conditions to a plate thickness of 3.611II.
A hot-rolled sheet having a diameter of 1.5 m was prepared, annealed by heating at 780° C. for 6 hours and cooling in a furnace, and then pickled. This hot-rolled sheet was cold rolled without intermediate annealing, and then a test was conducted by changing the final heat treatment conditions (the data in Figures 1 and 2 also show the results of this test; (The contents will be explained later).

Table 2 below uses the w4B hot rolled sheet (hot rolled sheet after hot rolling annealing and pickling) shown in Table 1.

(at, cold rolled without intermediate annealing to a thickness of 0.7 mm, cold rolling rate 80.6%), After soaking this cold rolled plate for 1 minute at 1000°C, from this temperature 1
A multi-phase structure material that has been finish heat treated to 00°C at an average cooling rate of 20°C/sec.

(b), a temper-rolled material that has been cold-rolled to a plate thickness of 0.7 mm and has the same strength as the fal multiphase structure material.

Tensile strength (kgf/mm”) and elongation (z) of each plate of
The value in the rolling direction (shi), the value in the 45° direction (D) with respect to the rolling direction, and the value in the 90° direction with respect to the rolling direction (T) are shown.

As is clear from Table 1, Table 2, and Table 2, the elongation of the multi-phase U woven material is the same as that of the same hardness and strength level! It can be seen that it is significantly superior to the rolled material of quality 11 and has an excellent balance of strength and elongation. Also, looking at in-plane anisotropy, in terms of tensile strength, the multi-phase &l woven material has a small difference in tensile strength depending on the direction, that is, in-plane anisotropy, whereas iI! The difference in tensile strength between the lowest tensile strength direction and the highest tensile strength T direction is 14
kgf/m+*", which means that the in-plane anisotropy is large. Also, regarding elongation, multi-phase structure materials with high elongation have relatively smaller in-plane anisotropy than temper-rolled materials with low elongation. Recognize.

That is, it is clear that even if cold rolling is performed without intermediate annealing, a high-strength chromium stainless steel sheet with excellent ductility and small in-plane anisotropy of strength and ductility can be obtained by forming a multi-phase structure.

"Continuous finishing heat treatment process" The cold-rolled steel strip with the product thickness obtained in the cold rolling process is then passed through a continuous heat treatment furnace to produce a two-phase region of Ac and ferrite decaustenite below 1100℃. After maintaining the temperature for 10 minutes or less, a continuous finishing heat treatment is performed in which the material is cooled from the maximum heating temperature to 100°C at an average cooling rate of 1°C/see or more and 500°C/sec or less.

This continuous finishing heat treatment step is the most characteristic step of the method of the present invention, and the conditions for this continuous finishing heat treatment have an important meaning in the present invention, as will be shown in Examples below. An overview of the reasons for regulating the heating conditions and cooling conditions in this continuous finishing heat treatment step is as follows.

It is an absolute condition that the heating temperature during the continuous finishing heat treatment is in the ferrite + austenite dual phase region temperature. When carrying out the method of the present invention, when the toning zone is heated from a low temperature during continuous finishing heat treatment, austenite 1-it fluctuates greatly with respect to temperature changes near the temperature at which austenite begins to form (that is, the temperature at the Ac+ point). Stable hardness may not be obtained after rapid cooling. However, in the steel composition range targeted by the present invention, it has been found that such fluctuations in hardness do not substantially stop when heated to a high temperature range of 100° C. or more above the Ac point. Therefore, the heating temperature during continuous finishing heat treatment is preferably set to Act point +100°C or higher, more specifically 850°C or higher, and even more preferably 900°C or higher.On the other hand, the upper limit of the heating temperature is If the temperature is too high, the increase in strength not only becomes saturated, but also decreases in some cases, and is also disadvantageous in terms of manufacturing costs, so it is preferable to set the upper limit to 1100°C.

The metallurgical significance of heating in the ferrite + austenite two-phase region during continuous finishing heat treatment in the method of the present invention is as follows: ■CrCr
Carbide-nitride solution, ■Generation of austenite phase, ■C and N into the generated austenite? ! There are three points that can be mentioned.

In the case of the chromium stainless steel strip targeted by the method of the present invention, all of these phenomena reach an almost equilibrium state within a short time. The heating time may be short, approximately 10 minutes or less. The fact that this short heating time is sufficient is very advantageous in terms of actual operation of the method of the present invention as well as in terms of production efficiency and manufacturing cost. Under the above heating conditions and holding time, it is possible to generate austenite necessary for the amount of martensite generated by subsequent cooling to be 10% by volume or more.

Regarding the cooling rate during finishing heat treatment, it is necessary to set the cooling rate to 1°C/sec or more in order to obtain a multi-phase &IIVa of martensitic phase and soft ferrite phase.
It is virtually difficult to obtain cooling rates in excess of 0°C/sec. Therefore, in the present invention, cooling from two-phase temperature range heating is performed at a cooling rate of 1 to b. This cooling rate is the average cooling rate from the maximum heating temperature to 100℃, but it is not necessary to use this cooling rate in the cooling process after austenite has transformed into martensite. The end point temperature is sufficient for the austenite produced at high temperature under the above-mentioned heating conditions to transform into martensite. As a cooling method, a forced cooling method in which a gas and/or liquid cooling medium is sprayed onto the steel strip, a roll cooling method using water-cooled rolls, etc. can be applied. Continuous heating and cooling under such conditions can be carried out using a continuous heat treatment furnace having a heating soaking zone and a quenching zone between the coil unwinding machine and the winding machine.

Figure 1 shows the thickness of hot rolled sheets (hot rolled sheets after hot rolled sheet annealing and pickling) manufactured by the method already explained for each steel in Table 1 above, by cold rolling without intermediate annealing. A cold rolled plate of 0.7 mm, cold rolling rate: 80.6%), and
This cold-rolled plate was heated at each temperature between 800 and 1100°C.
The amount of martensite (volume %
) and hardness IIV).

This is shown in terms of the heating temperature during finishing heat treatment (A, B, and C in the figure represent each steel in Table 1).

As is clear from Fig. 1, when the heating temperature reaches the ferrite + austenite dual phase region, martensite appears after the final heat treatment, and the amount of martensite increases as the heating temperature increases, but for EB and C, 850 ~ 9
When the temperature exceeds 00°C, the degree of increase decreases and the temperature tends to gradually become saturated. The behavior of hardness is also martensai 1-f.
A similar tendency is shown in response to changes in fi, and the more martensai) I, the higher the hardness; on the other hand, + M
Steel A, in which the amount of n + N i + Cu is less than the specification of the present invention, has a temperature range in which the amount of martensite and hardness saturate is on the high temperature side and is narrow. This has an important significance when performing on a continuous heat treatment line. In other words, a certain degree of temperature fluctuation is unavoidable in a continuous heat treatment line, and in particular fluctuations in the lengthwise direction of the steel strip8 and differences in heat treatment temperature due to differences in threading opportunities even if the target temperature is the same, will occur during actual line operation. Therefore, it is necessary to allow for fluctuations of about ±20°C with respect to the target temperature. Figure 1 is.

If the cooling rate is kept almost constant and a heat treatment temperature range with small hardness fluctuations is adopted, it is possible to produce copper strips with small fluctuations in hardness, that is, strength, even if there are slight temperature fluctuations in the continuous heat treatment line. It shows. In particular, by adding appropriate amounts of Mn, Ni, and Cu,
This is even more advantageous because a finishing heat treatment temperature range with small hardness fluctuations can be obtained on the low temperature side and over a wide range. By controlling the intensity level by controlling the components as described above, the target intensity can be stably obtained, and the intensity fluctuations are small over the entire length of the a-band.

Furthermore, a high-strength material with small strength differences between copper strips can be manufactured easily and inexpensively using an existing continuous heat treatment line.

Figure 2 shows the correlation between hardness and elongation (weighted average value in three directions) of several multiphase materials with different amounts of martensite made within the range of steel composition and manufacturing conditions regulated by the present invention. This is shown in comparison with the correlation of temper-rolled materials. Note that the production of the multi-phase structure material is the same as that explained in FIG. 1, and the heating temperature in the finishing heat treatment is 900° C. or higher. Further, the temper-rolled material is obtained by annealing after cold rolling, and then changing the hardness by changing the temper rolling rate indicated by the subscript in the figure.

As is clear from FIG. 2, the elongation of the temper-rolled material sharply decreases as the hardness increases as the temper rolling rate increases.

On the other hand, even if the hardness of the multi-phase Mi woven material increases, the elongation decreases slowly. especially,? The elongation of the 3I braided material is more pronounced than that of the temper-rolled material in the region of high hardness, specifically in the region of Hv 200 or higher. In other words, the increase in ductility achieved by forming a material with a multi-phase structure is even more pronounced in the region of Hν200 or higher, and for this purpose, as can be seen from the above-mentioned Figure 1, it is necessary to increase the martensite content by approximately 10% by volume or more. That's about it. In this way, the multi-phase structure material produced by the method of the present invention is characterized by the ability to achieve high ductility when the hardness is Hν200 or more, which cannot be achieved with temper-rolled material.
Because of this good strength-elongation balance, the dual-phase steel strip obtained by the method of the present invention has properties such as press formability and other workability that cannot be obtained by temper rolling.

FIG. 3 is a photograph of the metallographic structure of steel B in Table 1 produced by the method [al] in Table 2. The white (visible area) in the photo is ferrite, and the black or gray area is martensite.As can be seen from this photo, this material has a multi-phase Mi texture in which fine ferrite and martensite are evenly mixed. are doing.

As explained above, the high ductility and high strength steel strip material with low strength and ductility anisotropy was obtained by hot rolling.
After hot-rolled sheet annealing and cold rolling, finishing heat treatment involves heating to a two-phase region of ferrite + austenite and then rapidly cooling, resulting in a double phase in which fine ferrite and martensite, which is transformed from austenite by rapid cooling, are evenly mixed. This was achieved by working as an organization. In other words, the hard martensite provides strength (hardness) and the soft ferrite provides ductility, and by finely and uniformly mixing both phases, the in-plane anisotropy of strength and ductility is reduced. It could have been done. Note that trace amounts of retained austenite may be detected in X-ray examination of the U weave after finishing heat treatment.

Two examples in which the method of the present invention was implemented are listed below.

The characteristics of a multi-phase steel strip obtained by the method of the present invention will be specifically shown in comparison with a comparative example.

Example Slabs were manufactured by melting steel having the chemical components shown in Table 3. After hot rolling to a plate thickness of 3.6 mm,
The hot-rolled plate was annealed by heating and furnace cooling at 780°C for 6 hours, and after pickling, it was cold rolled without intermediate annealing to a plate thickness of 0.
7n+11 cold rolled steel strip with cold rolling rate 80.6%)2
Continuous finish heat treatment was carried out in a continuous VT heat treatment furnace under the finish heat treatment conditions shown in Table 4 (However, Comparative Example No. 4 was subjected to batch annealing treatment in a box furnace). The properties of the obtained steel strip material are also listed in Table 4.

As is clear from Table 4, by the two methods of the present invention, dual-phase steel strips having high tensile strength, hardness, and good elongation were obtained. Furthermore, it is clear that the steel strip manufactured by the method of the present invention has small anisotropy in 0.2% proof stress, tensile strength, and elongation, and no ridging is observed in the tensile test specimen after fracture.

On the other hand, in Comparative Example 11kl, the manufacturing conditions are within the range specified by the present invention, but the Mn, Nj, and Cu contents of one steel deviate from the requirement of Ni+(Mn+Cu)/3≧0.5% specified by the present invention. , 24%, which is the steel in Corner 8 of Table 3, so no martensite is generated after continuous finishing heat treatment and the hardness is low.

In Comparative Example No. 2, the manufacturing conditions were still within the scope of the present invention, but the C-shape and Nil of the steel were 0.4, higher than the 0, 10% or less, and 4.0% or less stipulated in the present invention, respectively.
Since the steel contains 0.5% and 5.07% of C and Ni, the amount of martensite after continuous finishing heat treatment is 100% and the strength is high, but the elongation is low.

In Comparative Examples 11 & 13, the heating temperature in continuous finishing heat treatment was 7.
At this heating temperature, which is as low as 50°C, the steel of steel No. 1 does not enter the ferrite + austenite dual phase region. Therefore, the metal Mi weave after finishing heat treatment is a ferrite single phase Mi weave without martensite, and the elongation is high. The strength and hardness of objects are low.

Comparative Example Floor 4 was subjected to finishing heat treatment in a box furnace.

Since the cooling is also by furnace cooling, the cooling rate is 0.03℃/se
Since the c was very low, no martensite was formed after the heat treatment, and like Comparative Example No. 3, the elongation was high, but the strength and hardness were low.

Comparative Example No. 5 is a temper-rolled material and has significantly lower elongation than the material of the present invention. Also 0.2% of tensile strength
It has a high yield strength ratio, that is, a high yield ratio, and has large anisotropy in 0.2% yield strength, tensile strength, and elongation. Therefore, it is clear that the workability and shape properties after working are inferior to the steel strip obtained by the method of the present invention.

Regarding the steel strips of Comparative Examples 1k1.3.4 and 5, the occurrence of ridging was observed in the tensile test specimens after fracture, whereas the occurrence of ridging was observed in the steel strips of the dual phase structure steel strip of Invention Example 1. It can be seen that processing such as press molding can be performed satisfactorily.

As described above, according to the method of the present invention, it has both high ductility and high strength, has a strength of 1 degree and small in-plane anisotropy of ductility, and has a low yield strength.
A dual phase steel strip with a low yield ratio is provided. In the field of chromium stainless steel sheets, there has never been an example of a high-strength material of LLV 200 or higher with such good workability being shipped to the market in the form of steel sheets or strips. Therefore, one aspect of the present invention is to provide a new material steel plate or strip for the conventional chrome stainless steel plate field. The material according to the present invention is particularly useful as a high-strength material that requires processability into electronic parts, precision mechanical parts, etc., and can achieve great results in this field.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between heating temperature, amount of martensite, and hardness in finishing heat treatment according to the present invention. FIG. 2 is a diagram showing the correlation between hardness and elongation for finish heat-treated materials and temper-rolled materials according to the present invention. FIG. 3 is a micrograph showing the metallographic structure of a chromium stainless steel strip subjected to continuous finishing heat treatment according to the present invention.

Claims (1)

[Claims] (1) In weight%, C: 0.10% or less, Si: 2.0% or less, Mn: 4.0% or less, P: 0.040% or less, S: 0.030. % or less, Ni: 4.0% or less, Cr: 10.0% or more and 20.0% or less, N: 0.12% or less, O: 0.02% or less, Cu: 4.0% or less, steel with the balance consisting of Fe and unavoidable impurities, and which satisfies the following relationships: 0.01%≦C+N≦0.20% 0.5%≦Ni+(Mn+Cu)/3≦5.0% The process of producing a steel slab and hot rolling it to produce a hot-rolled steel strip.The cold-rolling process involves producing a cold-rolled steel strip by cold-rolling it once to the product thickness without intermediate annealing. After the inter-rolling process, the obtained cold-rolled steel strip is passed through a continuous heat treatment furnace to obtain Ac_1
After maintaining the ferrite + austenite two-phase region temperature of 1100°C or higher for less than 10 minutes, the average cooling rate from the maximum heating temperature to 100°C is 1°C/sec or more and 500°C.
A method for producing a high-strength multi-phase chromium stainless steel strip having a hardness of HV200 or more and excellent ductility, comprising: a continuous finishing heat treatment step of performing a finishing heat treatment with cooling at a temperature of ℃/sec or less. (2) The heating temperature in the continuous finishing heat treatment process is Ac_1
The manufacturing method according to claim 1, wherein the temperature is +100°C or higher and 1100°C or lower. (3) The heating temperature in the continuous finishing heat treatment process is 850℃
The manufacturing method according to claim 1, wherein the temperature is above 1100°C. (4) The cold rolling rate in the cold rolling process is 30% or more and 95%.
The manufacturing method according to claim 1, 2, or 3 below. (5) In weight%, C: 0.10% or less, Si: 2.0% or less, Mn: 4.0% or less, P: 0.040% or less, S: 0.030% or less, Ni: 4 .0% or less, Cr: 10.0% or more and 20.0% or less, N: 0.12% or less, O: 0.02% or less, Cu: 4.0% or less, and 0.20% or less Al, 0.0050% or less B, 1.0% or less Mo, 0.10% or less REM, 0
．． Steel containing 20% or less of one or more types of Y, with the balance consisting of Fe and unavoidable impurities, and 0.01%≦C+N≦0.20% 0.5%≦Ni+(Mn+Cu) A process of manufacturing a steel slab that satisfies the relationship of /3≦5.0% and hot rolling it to produce a hot rolled steel strip, which is cooled to the product thickness by one cold rolling without intermediate annealing A cold rolling process in which a cold rolled steel strip is produced by inter-rolling, and the obtained cold rolled steel strip is passed through a continuous heat treatment furnace to produce Ac_1
After maintaining the ferrite + austenite two-phase region temperature of 1100°C or higher for less than 10 minutes, the average cooling rate from the maximum heating temperature to 100°C is 1°C/sec or more and 500°C.
A method for producing a high-strength multi-phase chromium stainless steel strip having a hardness of HV200 or more and excellent ductility, comprising: a continuous finishing heat treatment step of performing a finishing heat treatment with cooling at a temperature of ℃/sec or less. (6) The heating temperature in the continuous finishing heat treatment process is Ac_1
The manufacturing method according to claim 5, wherein the temperature is +100°C or higher and 1100°C or lower. (7) The heating temperature in the continuous finishing heat treatment process is 850℃
The manufacturing method according to claim 5, wherein the temperature is above 1100°C. (8) The cold rolling rate in the cold rolling process is 30% or more and 95%.
The manufacturing method according to claim 5, 6 or 7 as follows.