JPS63169330A - 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 C+N, 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, <=1.0% Mn, <=0.040% P, <=0.030% S, <=0.60% Ni, >=10.0% and <=20.0% Cr, <=0.12% N, <=0.02% O, and the balance Fe and inevitable impurities and satisfying the relations expressed by the formula 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 the 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 Mi-woven chromium stainless steel strip with excellent ductility and low 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.

[Prior Art] Looking at conventional chromium stainless steel sheet materials from the viewpoint of two strengths, firstly, martensitic stainless steel is well known as a chromium stainless steel with high strength.For example, cold rolled stainless steel according to JIS G 4305 Seven types of martensitic stainless steel are specified for steel plates. These martensitic stainless steels have a 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%
5US420J2 containing 12.00% to 14.00% Cr, it is possible to obtain a hardness of IRC40 or higher (after quenching by quenching from 980 to 1040°C and then tempering by air cooling at 150 to 400°C). , and 0.60-0.75% C and 16.00-1
For 5US440A containing 8.00% Cr, 1
After quenching by rapid cooling from 010 to 1070℃, 150℃
It has been shown that the same hardness <HRC40 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 a way to increase the strength is to perform further cold tIIX rolling after annealing to increase the strength through work hardening. is being carried out.

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 Mi weave that is hardened or tempered after hardening is basically a martensitic structure, as its name suggests.

Although it has very high strength and hardness, it has very low elongation, so it is difficult to process it after quenching or quenching and tempering. 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, when the strength of a ferritic stainless steel sheet is increased by temper rolling, the elongation decreases significantly and the strength-ductility balance deteriorates.

This results in poor workability. The degree of increase in strength due to temper 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. As a result, the spring bank becomes larger and the shape after pressing etc. becomes worse. 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. In addition, since processing distortion due to rolling is larger closer to the surface of the plate,
It is unavoidable that the strain distribution in the thickness direction of the i-quality positive 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 ultra-thin a-plates. This becomes a big problem in applications where this is required. In addition to the above-mentioned problems in terms of material properties, the #A'l rolled material also has many problems in its manufacturability. First, let's look at intensity control! Since quality rolling utilizes work hardening caused by 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 obtain the target strength level accurately and stably, strict control of the rolling rate, specifically strict control of the initial #J4 plate thickness before temper rolling, is required. In addition to being very important, control of the strength level of the material for pressure abrasion is required. In addition, in terms of shape control, unlike so-called skin pass rolling and temper rolling, which have a light rolling rate of at most 2 to 3% and have a light rolling ratio of 11 quality, temper rolling aims to improve strength. Since this is essentially cold rolling with a rolling rate of several tens of percent, it is difficult to obtain a belt with excellent shape properties as 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 steel plates or strips. 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, we have been able to properly control the steel composition, and furthermore, as manufacturing conditions, after hot rolling,
Furthermore, if necessary, after hot-rolled sheet annealing, cold rolling is performed to produce a cold-rolled steel strip of product thickness, and this cold-rolled steel strip is finished at a conventional ferrite single-phase region temperature. Rather than annealing, which is applied to steel sheets or steel strip products, if continuous finishing heat treatment is applied under specific conditions consisting of heating to the appropriate ferrite + austenite dual phase region and subsequent rapid cooling treatment, it is practically possible to We were able to obtain a multi-phase structure in which a soft ferrite phase and a hard martensitic phase were uniformly mixed, and were able to obtain an excellent result in which virtually all of the above-mentioned problems could be solved. Thus, the present invention.

In weight%.

C: 0.15% or less.

Si: 2.0% or less.

Mn: 1.0% or less.

P: 0.040% or less.

S: 0.030% or less.

Ni: Q, 5Q% or less.

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

N: 0.12% or less.

0: 0.02% or less.

and, in some cases, further contain 0.20% or less of A.
j! , B of 0.0050% or less, M of 1.0% or less
Steel containing one or more of o, 0, 10% or less of RE M, and 0.20% or less of Y, with the balance consisting of Fe and inevitable impurities, and 0.02%≦C+N≦ A process of producing a steel slab that satisfies the 0.20% 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.

After maintaining the temperature in the two-phase region of austenite in ferrite of Ac+ point or higher and 1100°C or lower for less than 10 minutes, finishing heat treatment involves cooling from the maximum heating temperature to 100°C at an average cooling rate of 1°C/sec to 500°C/sec. Continuous finishing heat treatment process.

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 toning materials, and it can be applied to martensitic stainless steel sheets or copper strips or ferritic stainless steel sheets or copper strips that have been conventionally shipped on the market. 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 product that has undergone the final continuous finishing heat treatment process is industrially manufactured in the form of a steel strip, and when it is shipped to the market, it is left as a copper strip (coil). Or it will be shaped into a steel plate.

Conventionally, for example, even in 5US430, 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 structure of ferrite + martensite. That itself was known. 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 properties such as a decrease in ductility, and it has not been given any consideration in the actual manufacturing of industrial belts.

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 have been no detailed studies on anisotropy, etc. The present invention provides a completely new manufacturing method that has not been considered as an industrial manufacturing method for high-strength chromium stainless steel strips. As a result, a new chrome stainless steel sheet material with excellent properties not possessed by conventional chrome stainless steel sheets or belts is provided.

[Detailed description of the invention]

Below, the reason for limiting the range of chemical composition values of steel regulated by the present invention and the contents of each manufacturing process adopted by 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.

Since C and N are two strong austenite-forming elements and have a large ability to strengthen martensite, they are effective elements for controlling and increasing the strength after continuous finishing heat treatment. Therefore, after continuous finishing heat treatment process, 10%
In order to obtain a multi-phase structure containing the above martensite and sufficient strength of Hv200 or more, the amount of (C+N) must be small (
Both require 0.02% or more. However, C and N! If the is too high, the amount of martensite generated after the continuous finishing heat treatment process will increase, and in some cases it will become 100% martensite, and the hardness of the martensite phase itself will become very high, so although high strength can be obtained, ductility will decrease. . Therefore, it is necessary to set (C+N)it to 0.20% or less and satisfy the relationship 0.02%≦C+N≦0.20%, and cl to be 0.15%.
% 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 martensite l and controlling the strength level. However, adding a large amount leads to a decrease in hot workability and cold workability, so 2.0%
is the upper limit.

Mn and Ni are austenite forming elements.

martensai after continuous finishing heat treatment)! It is also an effective element for controlling strength. However, if added in large amounts, the product becomes expensive, which affects the economic efficiency, which is one of the characteristics of the steel strip of the present invention. Therefore, 2 the normally allowed limit of Mn
; 1.0% or less; Ni; 0.6%, respectively.

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.

Although at least 10.0% of Cr should be contained as the minimum necessary amount in order to maintain the corrosion resistance of stainless steel, 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.

◯ forms oxide-based nonmetallic inclusions and reduces the cleanliness of the steel, so a lower value is desirable, and the content should be 0.02% or less.

^p 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 brings about adverse effects such as an increase in surface defects, so the upper limit is set at 0.20%.

B is a component that is effective in improving toughness, but its effect is brought about by a very small amount, and if it exceeds 0.0050%, its effect is saturated, so its upper limit is set to o, ooso%.

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%.

REM 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
V saturates when it exceeds 0.10%, and Y exceeds 0.20%, so the upper limit is 0.10% for REV and 0.10% for Y.
is 0.20%.

Next, the contents of each manufacturing process of the multi-phase & II woven 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 have a steel composition range of two or more is produced by ordinary steel casting techniques, and this slab is produced into a hot rolled steel strip by ordinary hot rolling. 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 hot-rolled sheet annealing is preferable for producing a steel strip with a uniform multi-phase structure after cold rolling and continuous finishing heat treatment because it can transform and decompose the ferrite and carbide into ferrite + carbide. Either of these is fine. 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 sheet annealing) is cold rolled to the product thickness by one cold rolling without intermediate annealing to produce cold rolled steel. Manufacture obi. Here, "single cold rolling without intermediate annealing" means not cold rolling two or more times with intermediate annealing in between, and more specifically, cold rolling is one-pass cold rolling or intermediate It means manufacturing cold-rolled steel strip by cold-rolling to the product thickness by performing multi-pass cold rolling without annealing. Regardless of the number of times the sheet is passed through the rolling rolls until the sheet thickness is reached, the sheet W-reduction is performed 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, the in-plane strength and elongation derived from the directional rolled Mi weave occurring in the cold rolled steel strip are It has been found that the anisotropic history is virtually eliminated in the dual-phase Mi woven steel strip obtained by subsequent continuous finishing heat treatment. therefore.

In the production of cold-rolled steel strip according to the present invention, even if the thickness is reduced to the product thickness without performing intermediate annealing, the final multi-phase m weave will result in a steel strip with small in-plane anisotropy of strength and elongation. can do. However, it has been found that the in-plane anisotropy of the multi-phase U-woven steel strip, especially in elongation, becomes even smaller when intermediate annealing is performed and cold rolling is performed multiple times. This inevitably increases manufacturing costs due to increased man-hours and thermal energy consumption. Therefore, according to the method of the present invention that does not involve intermediate annealing, a steel strip with a multiphase structure can be economically advantageously produced. For these reasons, in the present invention, the hot-rolled steel strip is rolled down to the product thickness in one bath, or
A cold-rolled steel strip is manufactured by employing a single cold rolling process in which the steel strip is rolled down to the product thickness in multiple passes without performing intermediate annealing. 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 to a thickness of 3.6 m under normal conditions.
An m0 hot rolled sheet 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 hot rolled sheet of Steel B in Table 1 (hot rolled sheet after hot rolling annealing and pickling).

(al, cold rolled to 0.7 mmJ!J- without intermediate annealing, cold rolling rate 80.6%), After soaking this cold rolled plate at 970°C for 1 minute, from this temperature to 100°C. A multi-phase &lI woven material that has been heat treated for finishing at an average cooling rate of 20°C/sec.

lb), a temper-rolled material with a strength equivalent to that of the multi-phase structure material of fa), which is cold-rolled to a plate thickness of 0.7+mm.

The tensile strength (kgf/+wt) and elongation (χ
) is the value in the rolling direction (shi), the value in the 45° direction to the rolling direction (D), and the value in the 90° direction to the rolling direction (T)
This is what is shown.

As is clear from Table 1 and Table 2, the elongation of the multi-phase m-woven material is significantly superior to that of the iJi'ff rolled material with the same hardness and strength level, and the strength-elongation balance is It turns out that it is excellent. Regarding the in-plane anisotropy, the multi-phase structure material has a small difference in tensile strength depending on the direction, that is, the in-plane anisotropy, whereas the i-rolled material has the highest tensile strength. The difference in tensile strength between the lowest direction and the highest T direction is 17k.
gf/mm" and has large in-plane anisotropy. Also, regarding elongation, multiphase materials with high elongation have low elongation iI
! It can be seen that both the quality rolled material and the in-plane anisotropy are relatively small.

In other words, even if cold rolling is performed without intermediate annealing, the multiphase Mi
It is clear that by weaving, a high-strength chromium stainless steel sheet with excellent ductility and small in-plane anisotropy of strength and ductility can be obtained.

"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 +Acr=1100
1 for the two-phase region temperature of austenite in ferrite below ℃
After holding for less than 0 minutes, 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/sec to 2500°C/sec.

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 continuous finishing heat treatment is the temperature in the ferrite + austenite two-phase region.8 In carrying out the method of the present invention, the temperature at which austenite begins to form when the toning zone is heated from a low temperature in a continuous heat treatment furnace. (That is, A
In the vicinity of point c), the amount of austenite fluctuates greatly with respect to temperature changes, and 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 Ac+ point +100°C or higher, more specifically 900°C or higher, and even more preferably 950°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
Three points can be mentioned: carbide-nitride dissolution, (1) generation of austenite phase, and (2) concentration of C and N in the generated austenite.

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. This short heating time is very advantageous in terms of production efficiency and manufacturing cost in the actual operation of the method of the present invention. Depending on the 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.

The cooling rate during finishing heat treatment is set at 1°C/1°C in order to obtain a multi-phase structure of martensitic phase and soft ferrite phase.
It is necessary to set the cooling rate to sec or more, but the cooling rate is 500℃/
It is virtually difficult to obtain cooling rates in excess of sec.

Therefore, in the present invention, cooling from two-phase temperature range heating is carried out at a cooling rate in the range of 1 to 500" C/see. This cooling rate is the average cooling rate from the highest heating temperature to 100 ° C. It is not necessary to use this cooling rate in the cooling process after the austenite has transformed into martensite. This cooling rate and cooling end point temperature are the same as the austenite formed at high temperature under the heating conditions described above transforms into martensite. It is sufficient.

As a cooling method, a forced cooling method in which a gas and/or liquid cooling medium is sprayed onto the belt, 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. 0.7 mm cold rolled plate and cold rolling rate -80.6%), and
This cold-rolled plate was heated at each temperature between 800 and 1100°C.
Martensite is a finished heat-treated material obtained by soaking for a minute and then performing a finish heat treatment of cooling from that temperature to 100°C at an average cooling rate of 20°C/sec! (capacity%
) and hardness HV).

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 Figure 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 rises, but when the heating temperature exceeds 900-950°C, The degree of increase tends to become smaller and gradually become saturated. The behavior of hardness also shows a similar tendency in response to changes in the amount of martensite, and the larger the amount of martensite, the higher the hardness.

The results shown in FIG. 1 have important significance when performing finishing heat treatment on a continuous heat treatment line. Namely.

In a continuous heat treatment line, some degree of temperature fluctuation is unavoidable.1 In particular, fluctuations in the length direction of the strip, and differences in heat treatment temperature due to differences in threading opportunities even if the target temperature is the same, cannot be avoided in actual line operation. It is necessary to allow for fluctuations of about ±20°C with respect to the target temperature. Figure 1 shows the case where the cooling rate is kept almost constant and a heat treatment temperature range with small hardness fluctuations is adopted.

This shows that even if there are some temperature fluctuations in the continuous heat treatment line, it is possible to produce steel strips with small fluctuations in hardness, that is, strength. If one intensity level is controlled by component control as described above, the target intensity can be stably obtained.

A high-strength material with small strength fluctuations over the entire length of the steel strip and small strength differences between steel strips can be easily and inexpensively produced using an existing continuous heat treatment line.

Figure 2 shows the correlation between hardness and elongation (average value with weight in three directions) of several multi-phase M-woven materials with different amounts of martensite within the range of steel composition and manufacturing conditions regulated by the present invention. The results were investigated and compared with the correlation of temper-rolled materials. Incidentally, the manufacturing of the dephasing combination m+o is the same as that explained in FIG. 1, and the heating temperature in the finishing heat treatment is 900° C. or higher. Furthermore, the hardness of the temper-rolled material is changed by changing the temper rolling rate indicated by the subscript in the figure after annealing.

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 multiphase structure material increases, the elongation decreases slowly. In particular, the elongation of multi-phase um material is 1J1ff
It is superior to rolled materials in the area of high hardness, specifically H.
It becomes noticeable in the region of v 200 or higher. In other words, the high ductility achieved by forming a multi-phase structure material is even more pronounced in the Hv 200 or higher region, and for this purpose, as can be seen from the above-mentioned Figure 1, approximately 10% by volume is required. The above is the amount of martensite. 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 Hv200 or more, which cannot be achieved with temper-rolled materials. The obtained double-phase M steel strip has properties such as press formability and other workability that cannot be obtained by UR quality rolling.

FIG. 3 is a photograph of metal weave when steel B in Table 1 is manufactured by the method +a+ in Table 2. The white 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 structure in which fine ferrite and martensite are evenly mixed.

As explained above, the high ductility and high strength belt 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. m
This was achieved through the use of textiles. In other words, the hard martensite provides strength (hardness) and the soft ferrite provides ductility.By finely and uniformly mixing both phases, the in-plane anisotropy of strength and ductility is reduced. It could have been done. The Mi weave after finishing heat treatment is
Trace amounts of retained austenite may be detected in linear surveys.

Below are nine examples in which the method of the present invention was implemented.

The characteristics of the multi-phase U-woven net belt 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,
Hot-rolled plate annealed by heating and furnace cooling at 780°C for 6 hours, and after pickling, cold rolling was performed without intermediate annealing to obtain a plate with a thickness of 0.
, 7mm cold rolled steel strip (cold rolling ratio 80.6%),
Continuous finish heat treatment was performed in a continuous heat treatment furnace under the finish heat treatment conditions shown in Table 4 (However, Comparative Example Kan 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 produced 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 Case 1-, the manufacturing conditions are within the range specified by the present invention, but the C and N contents of the steel are lower than the conditions for the present invention steel (C+N)≧0.02%, (C++N )
-0,012% steel (steel No. 8 in Table 3), no martensite is generated after continuous finishing heat treatment, and the hardness is low.

In Comparative Example No. 2, the manufacturing conditions are still within the scope of the present invention, but the C content of the steel is lower than the cl (C50,15
%) higher than C = 0.155% steel (Nci in Table 3)
9, j14), and the amount of (C+N) also exceeds 0.20% specified in the present invention, so the amount of martensite after continuous finishing heat treatment is 100%.

Although the strength is high, the elongation is very low.

In comparative example No. 3, the heating temperature in continuous finishing heat treatment was 750°C.
At this heating temperature, the steel of Steel No. 1 does not enter the ferrite + austenite dual phase region. Therefore, after finishing heat treatment, the metal &IIm has a ferrite single phase structure without martensite, and although the elongation is high, the strength and hardness are low. is low.

In Comparative Examples 1 and 14, the final heat treatment was performed 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 No. 1 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.

In addition, regarding the steel strips of Comparative Examples 1.3.4 and 5,
While the occurrence of ridging was observed in all of the tensile test pieces after fracture, the occurrence of ridging was not observed in the multi-phase steel strip of Example 1 of the present invention, indicating that processing such as press forming can be performed satisfactorily.

As described above, according to the two methods of the present invention, a multiphase steel strip having both high ductility and high strength, small in-plane anisotropy of strength and ductility, low yield strength, and low yield ratio is provided. In the field of chrome stainless steel sheets, there has never been an example of such a high strength material with Hv 200 or more combined with good workability being shipped to the market in the form of a steel plate or steel strip. Therefore, the present invention provides a new material steel plate or steel strip in the field of conventional chrome stainless steel plates. 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 the heating temperature of the finishing heat treatment, the amount of martensite, and the hardness 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 (8)

[Claims] (1) In weight%, C: 0.15% or less, Si: 2.0% or less, Mn: 1.0% or less, P: 0.040% or less, S: 0.030% or less, Ni: 0 .60% or less, Cr: 10.0% or more and 20.0% or less, N: 0.12% or less, O: 0.02% or less, and the balance is Fe and inevitable impurities. A process of manufacturing a steel slab that satisfies the relationship of 0.02%≦C+N≦0.20%, and hot rolling it to produce a hot rolled steel strip, one-time cooling without intermediate annealing. A cold rolling process in which a cold rolled steel strip is produced by cold rolling to a product thickness, 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. (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 900℃
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: 0.15% or less, Si: 2.0% or less, Mn: 1.0% or less, P: 0.040% or less, S: 0.030% or less, Ni: 0 .60% or less, Cr: 10.0% or more and 20.0% or less, N: 0.12% or less, O: 0.02% or less, and Al of 0.20% or less, 0.0050% or less B, 1.0% or less Mo, 0.10% or less REM, 0
．． A steel slab containing 20% or less of one or more types of Y, with the remainder consisting of Fe and unavoidable impurities, and which satisfies the relationship 0.02%≦C+N≦0.20%. A cold rolling process of producing a cold rolled steel strip by cold rolling it to a product thickness by one cold rolling without intermediate annealing, and producing a cold rolled steel strip by hot rolling it. Then, the obtained cold rolled steel strip was 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. (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 900℃
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.