KR102246704B1 - Temperature-treatment method of temperature-treated steel intermediate products and manganese steel intermediate products in a corresponding manner - Google Patents

Abstract

In the temperature-treatment method of the manganese steel intermediate product, its alloy is:
-Manganese content (Mn) with a manganese range (MnB) of 3% by weight ≤ Mn ≤ 12% by weight;
-Silicon (Si), aluminum (Al), nickel (Ni), chromium (Cr), molybdenum (Mo), phosphorus (P), sulfur (S), nitrogen (N), copper (Cu), boron (B) , Tungsten (W), and the content of one or more alloy components selected from the group consisting of cobalt (Co);
-An optional carbon content (C) of less than 1% by weight;
-Optional content of one or more microalloy components, wherein the total content of microalloy components is less than 0.45% by weight; And
-Contains iron content (Fe) and inevitable impurities as the remainder,
Wherein the temperature-treatment of the steel intermediate product includes a first temperature treatment process and a continuous second temperature treatment process,
The first temperature treatment process is a high-temperature process in which the steel intermediate product is subjected to a first annealing temperature above the _{critical temperature limit point (T KG ) during the first holding period, and this is T KG} = (856-S _k * manganese content ) Is defined as the temperature in degrees Celsius, where S _K is the slope value,
The second temperature treatment is an annealing process in which the steel intermediate product is subjected to a second annealing temperature lower than the first annealing temperature.

Description

Temperature-treatment method of temperature-treated steel intermediate products and manganese steel intermediate products in a corresponding manner

The present invention relates to a method for temperature treating an intermediate product of manganese steel. It also relates to specific alloys of manganese steel intermediate products, which are temperature-treated by a special process to obtain significantly reduced Luders strain. This application claims priority to European patent application EP 16 162 073.7, filed on March 23, 2016.

In addition to heat treatment in the manufacturing process, both the composition and the alloy each have a significant effect on the properties of the steel product.

In the course of heat treatment, warming-up, holding and cooling are known to affect the final structure of the steel product. Moreover, as already mentioned, the alloy composition of the steel product also plays a major role. In alloyed steels, the thermodynamic and material-technical relationships are very complex and depend on many parameters.

It appears that the combination of different phases in the microstructure of the steel product can affect the mechanical properties and deformability.

Depending on the specific requirements profile, different steels are used.

An important component of today's new steel alloys is manganese (Mn). This is called the so-called medium-manganese steels. The manganese content in weight percent (wt.%) is usually in the range between 3 and 12. Because of its microstructure, medium-manganese steel has a high combination of tensile strength and elongation. Typical applications in the automotive industry are complex safety-related deep-drawn components.

Figure 1 shows a classic, large schematic diagram, where the elongation A ₈₀ (also known as total elongation) is expressed as a percentage of the tensile strength in MPa. Tensile strength is abbreviated as _{R m in this specification.} The diagram in FIG. 1 schematically illustrates the strength classification of steel materials commonly used in the automotive industry. In general, the following applies: the _{higher the tensile strength R m} of the steel alloy, the The total stretch A ₈₀ becomes lower. In short, the total elongation A ₈₀ decreases with increasing tensile strength R _m, and vice versa. Therefore, it is necessary to find an optimal compromise between the full elongation A ₈₀ and the tensile strength R _{m for each application.}

In the automotive sector, each of which works with a full range of different steel alloys is specifically optimized for a specific application area of the vehicle. For interior and exterior panels, structural parts and bumpers, alloys with good energy absorption are used. The steel panels for the surface of the vehicle are relatively "soft", for example a tensile strength R _m of approximately 300 MPa and a good total elongation A ₈₀ > 30%. _{Steel alloys of safety-related components have a tensile strength R m} in the range between, for example, 600 and 1000 MPa. For example, TRIP (transformation-induced plasticity) steel (reference number 1 in Fig. 1) is very suitable for this purpose.

For steel barriers that must prevent the entry of vehicle parts in the event of an accident (eg for side impact protection), steel alloys with a _{high tensile strength R m above 1000 MPa are usually used.} In this case, for example, a new generation of high-strength AHSS (Advanced High-Strength Steels) steel is suitable (reference number 2 in Fig. 1). This category includes TBF (Trip Bainitic Ferrite) steel and Q&P (Quenching & Partitioning) steel. The high-strength AHSS steel has, for example, a manganese content ranging between 1.2 and 3 wt.% and 0.05 and 0.25 wt.%. It has a carbon content C between.

In the area designated by reference number 3 in Fig. 1, the already mentioned heavy-manganese steel is schematically summarized. The area designated by reference number 3 includes medium-manganese steel with a Mn content of between 3 and 12 wt.% and a carbon content of ≤ 1 wt.%.

ders strain) (A_L)로 불리운다. 그러한 분명한 항복강도를 가진 강 제품은 자동차 산업의 성분들의 표면에 바람직하지 않은 뤼더스 밴드(신장-변형 마크(stretcher-strainer marks))를 형성할 수 있다. 따라서, 분명한 항복강도는 전형적으로 재-압연 공정(re-rolling process)에 의해 감소될 필요가 있다. 상응하는 재-압연 공장에서 (보통 조질압연기(skin-pass mill)와 함께) 후처리는 또한 조질 압연(skin-pass rolling)이라 불리운다.Because of their ultra-fine grain (typically ≤ 1 μm), today's medium manganese has a definite yield strength, which is clearly visible in tensile tests. An exemplary tensile curve 4 (also called a stress-strain curve) is shown in FIG. 2. In Fig. 2, the tension σ (in MPa) is denoted by the elongation ε (in %). Tensile curve 4 represents a median maximum of 5, then plateau 6, called the _{upper yield strength (R eH ).} In the region of the lower yield strength (R _eL ), the plateau 6 changes to an increasing curved region. As shown in Fig. 2, the "length" of the stationary phase 6 is the Ludus strain (L

ders strain) (A _L ). Steel products with such an apparent yield strength can form undesirable ludus bands (stretcher-strainer marks) on the surface of the components of the automotive industry. Thus, the apparent yield strength typically needs to be reduced by a re-rolling process. The post-treatment (usually with a skin-pass mill) in the corresponding re-rolling plant is also called skin-pass rolling.

The energetic and technical effort for temper rolling is sometimes very high. In addition, the process leads to a reduction in the usable elongation.

Accordingly, it is an object of the present invention to develop a method for the production of manganese steel intermediate products in which the Ludus strain is less pronounced. Preferably, the manganese steel intermediate product should not have a (measurable) Ludus strain.

Studies of the numerous alloy compositions of medium-manganese steels have shown that there is a correlation between the original austenite grain size and Ludus strain of these steels. This means that the original austenite grain size influences the mechanical properties of these steels. In general, it can be assumed that the Ludus strain behaves in inverse proportion to the original austenite grain size.

Accordingly, some objects of the present invention are to find a process for temperature treatment and an alloy composition in order to increase the original austenite particle size and to exhibit the increased austenite particle size in the structure of the medium-manganese steel. Unlike the prior art (e.g., W0 2014095082 A1) which discloses the supply of ultrafine structures (with ultrafine grains with an average particle size of about 1 μm), the present invention has an object in different directions. have. Further, in the exemplary patent application W0 2014095082 A1, a dual annealing process is used, which works with different temperatures and process procedures. The steel product produced by the method of WO 2014095082 A1 has a definite yield strength.

According to the present invention, an optimized process for temperature-treating manganese steel intermediate products and a particularly suitable manganese steel alloy is provided.

The manganese steel alloy of the present invention is:

-Manganese content (Mn) with a manganese range (MnB) of 3% by weight ≤ Mn ≤ 12% by weight;

-Silicon (Si), aluminum (Al), nickel (Ni), chromium (Cr), molybdenum (Mo), phosphorus (P), sulfur (S), nitrogen (N), copper (Cu), boron (B) , Tungsten (W), and the content of one or more alloy components selected from the group consisting of cobalt (Co);

-An optional carbon content (C) of less than 1% by weight;

-Optional content of one or more microalloy components, wherein the total content of microalloy components is less than 0.45% by weight; And

-Includes iron content (Fe) and unavoidable impurities as the remainder.

The manganese steel intermediate product produced from the melt of the manganese steel alloy is subjected to a first temperature treatment step and a second temperature treatment step after the temperature treatment within the scope of the temperature treatment of the present invention.

The first temperature treatment process is a high-temperature process in which the steel intermediate product is subjected to a first annealing temperature above the critical temperature limit point (referred to as _{T KG ) during the first holding period, and the critical temperature limit point (T KG} ) is It is defined as: T _KG ≥ (856-S _K * manganese content) in degrees Celsius, and S _K is the slope value.

Serve as a definition of the expression is the critical temperature threshold (T _KG), and the critical temperature threshold (T _KG) are reduced to the mentioned noted with increasing manganese content of the manganese range.

The slope value is preferably as in the following formula in all embodiments: S _K = 7.83 ±10%, more preferably S _K = 7.83.

The second temperature treatment process is an annealing process in which the steel intermediate product is subjected to the second annealing temperature T2, where T2 is lower than the first annealing temperature T1 in each case.

Preferably, the first annealing temperature T1 exhibits a dependence on the manganese range of the alloy, which in all embodiments is defined as follows: T1 ≥ T _KG .

A particularly preferred embodiment of the invention is at a critical temperature T _K ≥ (866-S _K * manganese content) degrees Celsius, where the following equation applies: S _K = 7.83 ±10%.

Preferably, the first holding period is at least 10 seconds in all embodiments. Particularly preferably, the first holding period is between 10 seconds and 7000 minutes in all embodiments.

Preferably, the second annealing temperature T2 is in a range between the _{temperatures A 1} and A _{3 in all embodiments.}

Advantageous results are obtained when the second temperature treatment process comprising heating of the steel intermediate product, maintenance of the second annealing temperature, and cooling of the steel intermediate product takes less than 6000 minutes. Preferably, the total time is even less than 5000 minutes.

The invention is particularly preferably applicable to alloys in which at least one part of the alloying component lies in the following ranges:

-Silicon (Si) ≤ 3% by weight, preferably ≤ 2% by weight,

-Aluminum (Al) ≤ 8% by weight, preferably ≤ 6% by weight,

-Nickel (Ni) ≤ 2% by weight, preferably ≤ 1% by weight,

-Chromium (Cr) ≤ 2% by weight, preferably ≤ 0.5% by weight,

-Molybdenum (Mo) ≤ 0.5% by weight, preferably ≤ 0.25% by weight,

-Phosphorus (P) ≤ 0.05% by weight, preferably ≤ 0.025% by weight,

-Sulfur (S) ≤ 0.03% by weight, preferably ≤ 0.01% by weight,

-Nitrogen (N) ≤ 0.05% by weight, preferably ≤ 0.025% by weight,

-Copper (Cu) ≤ 1% by weight, preferably ≤ 0.5% by weight,

-Boron (B) ≤ 0.005% by weight, preferably ≤ 0.0035% by weight,

-Tungsten (W) ≤ 1% by weight, preferably ≤ 0.5% by weight,

-Cobalt (Co) ≤ 2% by weight, preferably ≤ 1% by weight.

Excellent results are shown in all embodiments with the following groups of elements used as microalloy elements: titanium (Ti), niobium (Nb), and vanadium (V).

For the first time, the present invention can provide a steel intermediate product with a _{Ludus strain A L} of less than 3%, preferably less than 1%.

At the same time, the inventive steel intermediate product preferably has a major average austenite particle size of greater than 3 μm in all embodiments.

The alloy of the inventive steel intermediate product preferably has an average manganese content according to the invention, which means that the manganese content is in the range of 3% by weight ≤ Mn ≤ 12% by weight. Preferably, in all embodiments the manganese content is in the range of 3.5% by weight <Mn <8.5% by weight.

The carbon content of the steel products of the present invention is generally quite low. Also, the carbon content is optional in all embodiments. That is, the carbon content is in the range of C ≤ 1% by weight in the present invention. Particularly preferred are embodiments in which the carbon content is within one of the following ranges.

a) 0.01 ≤ C ≤ 0.8% by weight, or

b) 0.05 ≤ C ≤ 0.3% by weight.

In a preferred method of the present invention, the first temperature treatment process is carried out in a continuous strip plant (annealing plant). This process is also known as continuous annealing. In addition, discontinuous heat treatment (hood-type annealing) of steel intermediate products is also possible.

When the temperature treatment of the hot strip is concerned, the first temperature treatment of the present invention can also be carried out by special temperature conditions during hot rolling. Along with special temperature control, care should be taken to ensure that the rolling end temperature of the hot strip during hot rolling is _{within the range above the critical temperature limit point T KG.}

In a preferred method of the invention, the second temperature treatment process is carried out in a plant operating discontinuously, wherein the steel intermediate product is subjected to an annealing process in the plant in a protective gas atmosphere. The process is preferably carried out in a hood-type annealing plant. However, the second temperature treatment process can also be carried out in a continuous strip plant (annealing plant) or a hot-dip galvanizing plant in all embodiments.

The steel intermediate products of all embodiments can optionally be subjected to a temper rolling process, which primarily affects the surface of the steel intermediate products. Since the steel intermediate product of the present invention has a low Ludus strain, more intensive temper rolling is not required.

Thus, with the present invention, the degree of temper rolling can be reduced or can be completely avoided.

It is an advantage of the invention that steel intermediate products can be produced with a Ludus strain of less than 3%, preferably less than 1%.

It is an advantage of the present invention that a steel intermediate product can be produced with a _{tensile strength R m} (also called minimum strength) greater than 490 MPa.

It is an advantage of the invention that a steel intermediate product with a _{(minimum) total elongation (A 80} ) of more than 10% can be produced as a result of the reduced Ludus strain.

It is an advantage of the present invention that the steel intermediate product has a technically useful increased elongation because of the reduced Ludus strain.

The invention can be used, for example, to provide a cold rolled steel product in the form of a cold rolled flat product (eg, a coil). In addition, the invention can be used, for example, to produce thin sheets or wire and wire products.

The invention can also be used to provide hot strip steel products.

Furthermore, the superior embodiments of the invention form the subject matter of the dependent claims.

Embodiments of the present invention will be described in more detail with reference to the following drawings.
1 shows a plot of the elevation (minimum) total elongation (A ₈₀ ) expressed as percentage versus tensile strength (R _{m) (MPa) for various steels in the automotive industry.}
Figure 2 shows a schematic stress-strain diagram of a steel product with a pronounced yield strength (Luders strain A _L).
3 shows a schematic diagram showing two temperature treatment processes.
4 shows the development of the critical temperature T _K and the corresponding critical temperature limit point T _KG in the form of a schematic diagram.
Figure 5 shows a schematic diagram showing the _{Ludus strain A L} in percent as a function of the first annealing temperature T1 on the one hand and the original average austenite particle size (D _{UAK M) on the other hand.} Corresponding curves of four different samples are shown.
Figure 6 shows a schematic diagram showing the tension σ (MPa) as a function of elongation ε (%) (similar to Figure 2), where four identical alloys were subject to four different temperature treatment processes in this case.

According to the invention, it relates to a steel product or steel intermediate product characterized by a special microstructure constellation and properties.

In the following, in a multi-stage production process, the term "intermediate steel products" is sometimes used to emphasize that the finished steel product is not relevant, but instead a preliminary or intermediate product is involved. The starting point for these manufacturing processes is usually the melt. In the following, an alloy composition of the melt is provided, since it can relatively accurately affect the alloy composition in one aspect of the manufacturing process (eg, by adding components such as an alloy component and an optional microalloy component). Usually the alloy composition of the steel intermediate product differs only slightly from the alloy composition of the melt.

Unless otherwise stated herein, amount or content information is provided in weight percent (wt.% for short). The composition of the alloy, or in addition to the exact listed substances or components, if information is provided respectively for the steel product, the composition is iron (Fe) as the base substance and always occurs in the melting bath and is also found in the resulting steel intermediate product. It contains so-called inevitable impurities. In the present specification, weight percent should always be added up to 100 weight percent, and all volume percent should always be added up to 100 percent of the total volume.

In addition to the special combination of alloying components, a process specially optimized for the temperature treatment is used. The corresponding diagram is in FIG. 3 and will be described in more detail below.

The temperature treatment of the steel intermediate product includes a first temperature treatment step S.1 and a subsequent second temperature treatment step S.2. The two temperature treatment processes S.1 and S.2 are represented by two temperature-time diagrams shown next to each other in FIG. 3.

The first temperature treatment step S.1 is a high-temperature process in which the steel intermediate product is subjected to the first annealing temperature T1 during the first holding period Δ1 (the step is also referred to as holding H1). Annealing temperature T1 is placed over the critical temperature limits while maintaining T _KG H1.

The process of the critical temperature limit point T _KG depends on the manganese content Mn of the alloy of the manganese steel intermediate product, among others, as determined by various investigations. In FIG. 4, the process of the critical temperature T _K (indicated by straight line 7) and the corresponding critical temperature limit point T _KG (indicated by straight line 8) is shown.

On the horizontal axis, the manganese range MnB is expressed in weight percent. As already mentioned, the present invention provides excellent results, particularly having a manganese content in the manganese range MnB: 3% by weight ≤ Mn ≤ 12% by weight. The manganese range MnB is represented in FIG. 4 by two vertical borders of Mn = 3% by weight and Mn = 12% by weight.

4 shows, as an example, measurement results of four samples based on a small circular symbol. Details of these four exemplary samples and additional samples of the invention are shown in Tables 1 and 2.

Table 1 alloy C Mn Al Nb S.1 S.2 Type 1 0.096 5.08 Cont. annealing Hood Type 2 0.097 5.13 0.09 Continued annealing Hood Type 3 0,100 6.38 Continued annealing Hood Type 4 0.106 3.53 Continued annealing Hood Type 5 0,110 3.56 0,095 Continued annealing Hood Type 6 0.148 7.73 2.09 Continued annealing Continued annealing Type 7 0.098 9.95 Continued annealing Hood

Table 2 number alloy T1, ℃ T2, ℃ R _p0.2 or R _eL MPa R _m , MPa A ₈₀ ,% RA, vol.% A _L ,% D _{UAK M} ,μm One Type 1 830 660 550 850 27.1 20.9 2.1 5 2 Type 1 875 660 551 878 28.7 20.1 0 13.7 3 Type 1 900 660 561 890 28.3 21.3 0 15.5 4 Type 1 920 660 561 898 28.5 21.1 0 18 5 Type 1 935 660 559 894 30.2 19.8 0 20 6 Type 1 950 660 522 820 30.7 21.4 0 22 7 Type 1 1100 660 560 852 27.9 21.2 0 45.7 8 Type 2 980 660 632 928 23.4 21.4 2.8 8.5 9 Type 2 1000 660 640 928 23.7 21.9 2.6 9.5 10 Type 2 1025 660 646 931 22.9 22.7 2.2 11.1 11 Type 2 1050 660 643 929 23.4 19.2 2 12 12 Type 2 1075 660 673 962 24.3 19.9 0 13.5 13 Type 2 1100 660 642 898 22.9 22.5 0 14.7 14 Type 3 810 640 635 901 33.3 32.1 2.6 6.4 15 Type 3 850 640 615 903 35.8 32.6 1.8 9.4 16 Type 3 900 640 595 898 36.1 32.2 0 13.8 17 Type 3 950 640 552 893 37 31.8 0 18.9 18 Type 4 840 660 413 559 18.5 6.4 2.2 6 19 Type 4 950 660 391 641 18.5 6.5 1.5 15 20 Type 5 950 630 352 543 19.2 2.7 1.2 7 21 Type 5 1025 630 432 631 17.1 4.9 0 11 22 Type 5 1100 630 623 710 11.8 4.1 0 15 23 Type 6 900 675 829 1083 19.8 20.3 2.3 4.86 24 Type 7 790 630 601 1145 25.2 39.1 2.2 4.8 25 Type 7 900 630 588 1130 28.1 37.2 0 8.8 26 Type 7 950 630 582 1122 29.3 34.6 0 12.9

Each type of alloy composition is shown in Table 1, where only the main alloy components are mentioned. For each type, there are numerous embodiments tested. Corresponding examples are numbered 1 to 26 in the left column of Table 2.

In Figure 4, the following four samples are indicated by the mentioned circular symbols: Type 4, 18; Types 1, 1; Types 3, 14 and Types 7, 24 (designated types 4, 18 represent, for example, type 4 alloy compositions, Example No. 18).

When the circular symbol of FIG. 4 or the measurement result is inserted by a straight line, respectively, the straight line 7 represents the result of constantly descending as shown in FIG. 4. The straight line 7 can be limited by the following equation (1), where T _K is given in degrees Celsius:

T _K = (866-S _K * manganese content) (1)

In degrees Celsius, the absolute value 866 defines the intersection with the vertical axis, and the value S _K defines the slope. Therefore, S _k is also called the slope value.

The investigations show that the slope value S _K is preferably 7.83 ± 10% in all embodiments.

In addition, it can be shown that _{the critical temperature T K} for the alloy composition according to the present invention is always above the lower critical temperature limit point T _KG. The lower critical temperature limit point T _KG is shown in FIG. 4 as shown in line 8.

Line 8 can be limited by the following equation (2), where T _KG is given in degrees Celsius:

T _KG = (856-S _K * manganese content) (2)

Line 8 lies parallel to line 7.

The following conditions can be assumed: for a steel alloy of a manganese steel intermediate product, as already defined, _{in order to obtain a manganese steel intermediate product with a Ludus strain A L} of less than 3%, the first annealing temperature T1 is always the lower critical temperature It must be above the threshold T _KG.

In addition, it can be seen that the second temperature treatment process S.2 affects the Ludus strain. In order to maintain the grain size of the austenite particles in the structure, the second annealing temperature T2 must in any case be lower than the first annealing temperature T1. Since the first annealing temperature T1 is always above the lower critical temperature limit point T _KG , it can be concluded that the second annealing temperature T2 should preferably be below the lower critical temperature limit point T _KG.

From the schematic embodiment of FIG. 3, it can be seen that the first annealing temperature T1 is _{above the temperature limit point T KG} and the second annealing temperature T2 is in a range between _{A 1} and A _3. The second temperature treatment S.2 is also referred to as intercritical annealing in this case.

The first holding period Δ1 is preferably at least 10 seconds in all embodiments, preferably between 10 seconds and 6000 minutes.

The second holding period Δ2 is at least 10 seconds in all embodiments. In Fig. 3, two holding periods Δ1 and Δ2 are only shown in the form of an embodiment. The interval between the second temperature treatment step S.1 and the second temperature treatment step S.2 may be selected as necessary. Typically, the second temperature treatment step S.2 is performed immediately after the first temperature treatment step S.1.

Preferred embodiments are those in which the first temperature treatment process S.1 comprising heating E1 of the steel intermediate product, maintenance H1 of the first annealing temperature T1 and cooling Ab1 of the steel intermediate product takes less than 7000 minutes.

Preferred embodiments are that the second temperature treatment process S.2 comprising heating E2 of the intermediate steel product, maintenance H2 of the second annealing temperature T2 and cooling Ab2 of the steel intermediate product is less than 6000 minutes, preferably less than 5000 minutes. These are the embodiments taken.

Furthermore, the first temperature treatment process S.1 and/or the second temperature treatment process S.2 may be a continuous strip plant (e.g. a continuous plant) or a discontinuous plant (e.g. a hood-type annealer). It can be seen that the fact of whether or not it is carried out in) and the significant reduction of the _{Ludus strain A L are independent.}

The present invention can be applied to both cold strip intermediate products and hot strip intermediate products. In both cases, a significant reduction in the _{Ludus strain A L can be seen.}

The first annealing temperature T1, which increases above the critical temperature limit point T _KG, clearly leads to an increase in the original mean austenite grain size and a significant decrease in the _{Ludus strain A L.}

5 shows the reduction (%) of the _{Ludus strain A L} and the original average austenite with increasing annealing temperature T1 for two exemplary samples of type 1 and type 2 (see also Table 1) as follows. All of the dependence (μm) of the particle size (D _{UAK M) are shown.}

Chemical composition of alloy samples of type 1 without microalloy:

Mn = 5.08% by weight,

C = 0.096% by weight,

The rest is iron Fe and unavoidable impurities.

Chemical composition of alloy samples of type 2 without microalloy:

Mn = 5.13% by weight,

C = 0.097% by weight,

Nb = 0.90% by weight,

The rest is iron Fe and unavoidable impurities.

It can be seen from FIG. 5 that the _{critical temperature limit point T KG} is ˜820° C. if desired to obtain a Ludus strain for the type 1 alloy composition that is less than 3% in the type 1 tested alloy composition (indicated by curve 9). Curve 10 shows the associated process of the original mean austenite particle size D _{UAK M 1 as a function of temperature T1.} For example type 1, the particle size for the above is obtained as> 3 μm.

It can be seen from FIG. 5 that the _{critical temperature limit point T KG2} is ~970° C. if it is desired to obtain a Ludus strain for this alloy composition of type 2 which is less than 3% in the tested alloy composition of type 2 (indicated by curve 11). Curve 12 shows the corresponding curve of the original mean austenite particle size (D _{UAK M) as a function of temperature T1.} For Example Type 2, the particle size for the result is> 8 μm. The microalloy element niobium (Nb) has a recognizable effect, which is expressed as the change to a higher critical temperature of _{T KG2} ( _{compared to T KG1 ) for A L} <3%.

Curves 10 and 12 in FIG. 5 show that the original austenite particle size increases with increasing temperature T1.

Based on the above equation (2), for the alloy composition of type 1, the lower temperature limit point T _KG1 can be determined as follows:

T _KG1 = (856-7.83 * 5) = ~817 ℃ (2.1)

In Fig. 5, the corresponding lower temperature limit point T _KG1 is indicated by a vertical line in a dash symbol. It can be seen that the type 1 alloy composition has an _{average particle size from an annealing temperature T1> T KG1> 3 μm.} The lower temperature limit point T _KG1 is indicated in FIG. 4 by a small black triangle.

Based on equation (2), for an alloy composition of type 2, the lower critical temperature limit T _KG2 can be determined as follows:

T _KG2 = (856-7.83 * 5) = ~817 ℃ = T _KG1 (2.2)

For alloy compositions with Nb content, the microalloy leads to an increase in the _{critical temperature limit T KG.} In FIG. 5, using the type 2 example, _{it can be seen that the critical temperature limit T KG2} is approximately 150° C. higher than that for the type 1 alloy composition. In Fig. 5, the corresponding effective lower critical temperature threshold T* _KG2 is indicated by a vertical line in dashes. For type 2 alloy composition, the annealing temperature should be T1> T* _KG2 = T _KG2 + 150 °C. The resulting original average austenite particle size is ≥ 8 μm in this case.

6 shows a schematic diagram showing the tension σ (MPa) as a function of elongation ε (%). The display of Fig. 6, which represents only a small part, is compared to the display of Fig. 2.

Specifically, four identical samples (type 3 alloys in Table 1) were compared here. Type 3 alloys also meet the requirements of the present invention. All four samples were subjected to the first temperature treatment step S.1 and the successive second temperature treatment step S.2, respectively. All process parameters were the same except for the first temperature treatment process S.1, and the first annealing temperature T1 was varied as follows (see column 2 of Table 3 below):

Table 3 alloy T1 [℃] T2 [℃] curve Type 3 810 640 13.1 Type 3 850 640 13.2 Type 3 900 640 13.3 Type 3 950 640 13.4

Alloys of type 3 have the following main composition in the above experiment:

Mn = 6.38% by weight,

C = 0.1% by weight,

The rest is iron Fe and unavoidable impurities.

The solid curve 13.1 in FIG. 6 (types 3 and 14 in Table 2) shows the yield strength clearly visible with a Ludus strain of ~2.6% _{A L.} Here the temperature T1 was 810 °C, this is for the type 3 alloy and the slope value S _K = 7.83 is just above the lower critical temperature limit T _KG.

Curve 13.2 represents another exemplary sample (types 3 and 15 in Table 2), where the yield strength is still slightly pronounced.

The other same sample (curve 13.3 of the dashed-dot symbol in FIG. 6 _{) was temperature-treated at a higher temperature T1 = 900°C (ie, T1> T kg} ), and the apparent yield strength could no longer be visually confirmed. This relates to types 3 and 16 in Table 2.

Curve 13.4 represents an additional exemplary sample of type 3, and in this case also no apparent yield strength could be visually confirmed any more. This relates to types 3 and 17 in Table 2.

When considering the manganese steel intermediate product of the present invention with respect to FIG. 1, the corresponding measurements (e.g., for the alloy compositions of type 1, type 2 and type 3) are total elongation A in the range of about 20 to 40%. _{Together with 80} lies in the range of about 700 to 1000 MPa.

TRIP steel One Q&P and TBF steel 2 Middle-manganese steel 3 Tensile curve 4 Middle max 5 Plateau 6 Straight 7 Straight 8 curve 9 curve 10 curve 11 curve 12 curve 13.1, 13.2, 13.3, 13.4 Starting temperature of austenite A ₁ Starting temperature of total austenite A ₃ Full stretch A ₈₀ Ludus strain A _L 1st cooling Ab1 2nd cooling Ab2 Original average austenite grain boundary D _{uak m} 1st maintenance period △1 2nd maintenance period △2 First heating E1 2nd heating E2 kidney ε Keep 1 H1 2nd maintenance H2 Manganese range MnB Residual austenite content RA Upper yield strength R _eH Lower yield strength R _eL The tensile strength R _m 0.2% yield strength R _p0.2 1st temperature treatment process S.1 2nd temperature treatment process S.2 tension σ Slope value S _K First annealing temperature T1 2nd annealing temperature T2 Critical temperature limit point T _KG Critical temperature limit point T _KG1 Critical temperature limit point T _KG2 Effective critical temperature limit point T* _KG2

Claims (33)

In the temperature-treatment method of the intermediate product of manganese steel, the alloy of the product is
-Manganese content (Mn) with a manganese range (MnB) of 3% by weight ≤ Mn ≤ 12% by weight;
-A carbon content (C) of 0% by weight <C ≤ 1% by weight; and
-Contains iron content (Fe) and inevitable impurities as the remainder,
Here, the temperature-treatment of the steel intermediate product includes a first temperature treatment process (S.1) and a continuous second temperature treatment process (S. 2),
The first temperature treatment process (S.1) is a high-temperature process in which the steel intermediate product is subjected to a first annealing temperature (T1) above the _{critical temperature limit point (T KG) during the first holding period (Δ1),} The critical temperature threshold (T _KG ) is defined as T _KG = (856-S _k * manganese content) degrees Celsius, where S _K is the slope value, the slope value S _k = 7.83 ±10%,
-The second temperature treatment process (S.2) is a temperature-treatment of an intermediate manganese steel product, which is an annealing process in which a steel intermediate product is subjected to a second annealing temperature (T2) lower than the first annealing temperature (T1). Way.
The method of claim 1, wherein S _k = 7.83.
The temperature of the manganese steel intermediate product according to claim 1, wherein the first annealing temperature (T1) in the manganese range (MnB) has a dependence defined as a temperature in degrees Celsius _{-T 1} = (866-S _{K * manganese content)} Processing method.
The method of claim 1, wherein the first holding period (Δ1) is at least 10 seconds.
The method according to claim 4, wherein the first holding period (Δ1) is between 10 seconds and 6000 minutes.
The method of claim 1, wherein the second annealing temperature (T2) is in the range between _{temperatures A 1} and A _{3 , where A 1} is the starting temperature of austenitization and A ₃ is full austenite. The temperature-treatment method of the intermediate product of manganese steel, which is the starting temperature of fire.
The method according to claim 1, wherein the second annealing temperature (T2) is in the range of 630°C to 675°C.
The temperature of the manganese steel intermediate product according to claim 1, wherein within the range of the second temperature treatment step (S.2), the second annealing temperature (T2) is maintained for a second holding period (Δ2) of at least 10 seconds. -Treatment method.
The second temperature treatment process according to claim 1, comprising a heating process (E2) of a steel intermediate product, a holding process (H2) of a second annealing temperature (T2), and a cooling process (A2) of the steel intermediate product (S. 2) The temperature-treatment method of the intermediate product of manganese steel, which takes less than 6000 minutes.
10. The method of claim 9, wherein the second temperature treatment step (S.2) takes less than 5000 minutes.
delete delete delete delete delete delete delete delete delete delete delete delete delete The method of claim 1, wherein the alloy comprises at least one microalloy component, the total content of the microalloy component is less than 0.45% by weight, and the microalloy component is titanium (Ti), niobium (Nb), and vanadium (V ) Is a component selected from the group consisting of,
The alloy contains niobium (Nb), T1> T _KG + 150 °C, and T _KG = (856-S _k * manganese content) in degrees Celsius, a temperature-treatment method for a manganese steel intermediate product.
delete The method according to claim 1, wherein the first temperature treatment process (S.1) relates to a process carried out in a discontinuously operating plant or in a continuous strip plant.
The steel intermediate product according to claim 1, wherein the second temperature treatment process (S.2) is a process performed in a discontinuously operated plant or a continuous strip plant, and in the discontinuously operated plant or a continuous strip plant. A method for temperature-treating manganese steel intermediate products, wherein silver is exposed to a protective gas atmosphere in an annealing process.
28. The method of claim 27, wherein the hood-type annealing apparatus is used in a discontinuously operating plant.
The method of claim 1, wherein the steel intermediate product is a target of a temper rolling process in a step downstream of the second temperature treatment process (S.2), and the temper rolling process affects the surface of the steel intermediate product. A method for temperature-treating manganese steel intermediate products.
The method of claim 1, wherein the first temperature treatment process (S.1) is performed during a hot rolling process, and the hot rolling process is performed at a rolling end temperature within a range of a _{critical temperature limit point (T KG) or more.} Temperature-treatment method of phosphorus, manganese steel intermediate products.
A steel intermediate product heat-treated according to any one of claims 1 to 10, 24 and 26 to 30, having a _{Ludus strain (A L) of less than 3%,} Steel intermediate products.
The steel intermediate product according to claim 31, having a Ludus strain (A _{L) of less than 1%.}
32. The steel intermediate product according to claim 31, wherein less than 3% Ludus strain (A _L ) can be measured in the steel intermediate product before the steel intermediate product is subjected to the next temper rolling process.

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