WO2008004506A1

WO2008004506A1 - Cr-CONTAINING STEEL EXCELLENT IN THERMAL FATIGUE CHARACTERISTICS

Info

Publication number: WO2008004506A1
Application number: PCT/JP2007/063185
Authority: WO
Inventors: Junichi Hamada; Haruhiko Kajimura; Nobuhiko Hiraide; Toshio Kojima; Daiharu Doi
Original assignee: Nippon Steel & Sumikin Stainless Steel Corporation
Priority date: 2006-07-04
Filing date: 2007-06-25
Publication date: 2008-01-10
Also published as: KR20080038218A; US20100218856A1; JP2008144263A; CN101346487B; EP2036994A1; CN101346487A; EP2036994A4; EP2036994B1; JP5208450B2

Abstract

A Cr-containing steel excellent in thermal fatigue characteristics which contains by mass C: 0.01% or below, N: 0.015% or below, Si: 0.8 to 1.0%, Mn: 0.2 to 1.5%, P: 0.03% or below, S: 0.01% or below, Ni: 0.2% or below, Cu: 0.2% or below, Cr: 13 to 15%, Mo: 0.1% or below, Nb: 0.3 to 0.5%, Ti: 0.05 to 0.2%, V: 0.01 to 0.2%, Al: 0.015 to 1.0%, and B: 0.0002 to 0.0010% in such a way as to satisfy the relationship: (Nb + 1.9 x Ti)/(C + N) ≤ 50 with the balance consisting of Fe and unavoidable impurities, characterized by exhibiting a 0.2% proof stress of 20MPa or above at 800°C after the aging at 800°C for at least 10 hours, a reduction of area of 35% or above at 200°C, and a total content of solid-dissolved Nb and solid-dissolved Ti of 0.08% or above after the aging at 800°C for at least 100 hours.

Description

Cr-containing steel with excellent thermal fatigue properties

Technical field

The present invention relates to a Cr-containing steel having excellent thermal fatigue characteristics that is optimal for use in exhaust system members that particularly require high-temperature strength and oxidation resistance.

Background art

Exhaust system components such as automobile exhaust manifolds, CFC top pipes, and center pipes pass high-temperature exhaust gas discharged from the engine, so the materials that make up the exhaust members include oxidation resistance, high-temperature strength, heat Various characteristics such as fatigue characteristics are required.

Conventionally, pig iron has generally been used for automobile exhaust members, but stainless steel exhaust manifolds have been used from the viewpoints of stricter exhaust gas regulations, improved engine performance, and lighter vehicle bodies. It has come to be used. In recent years, the exhaust gas temperature has increased to about 800 to 900 ° C., and there is a demand for a material having oxidation resistance, high temperature strength and thermal fatigue characteristics in an environment where the exhaust gas is used at a high temperature for a long time.

Among stainless steels, austenitic stainless steel is excellent in heat resistance and workability, but because of its large thermal expansion coefficient, when applied to a member that repeatedly receives heating and cooling, such as an exhaust manifold. Thermal fatigue destruction is likely to occur.

On the other hand, ferritic stainless steel has a lower thermal expansion coefficient than austenitic stainless steel, and therefore has excellent thermal fatigue characteristics. In order to increase the high-temperature strength according to the exhaust gas temperature, steel with adjusted alloy additions such as Cr, Mo, Nb is used. Exhaust gas high temperature Although the amount of these alloys added has increased with the progress of the process, the thermal fatigue life, which is the most important characteristic, has not necessarily increased. In addition, excessive increase in the amount of alloy added leads to an increase in cost, and may have disadvantages that are not economical.

Japanese Laid-Open Patent Publication No. 7-145453 discloses ferrite stainless steel excellent in oxidation resistance, high temperature strength, and thermal fatigue characteristics for automobile exhaust manifolds. The Cr content is 11-14%, which is a relatively low Cr content. By adding Si, this technology improves oxidation resistance, high temperature strength, and thermal fatigue characteristics at 900 ° C or higher. Among them, thermal fatigue properties are achieved under the condition of 50% restraint at 200-900 ° C. The invention steel has a long thermal fatigue life, but the restraint rate is low, or the temperature is about 800 ° C. Therefore, sufficient characteristics could not be obtained under the condition that the applied cycle was long. This is thought to be due to the lack of high-temperature strength and high-temperature ductility when the material was subjected to aging treatment, that is, when exposed to a long-term use environment. In addition, in the above Japanese Patent Laid-Open No. 7-145453, there is an example of combined addition of Ti and Nb. In this case, however, a phenomenon (secondary processing cracking) occurs in which cracking occurs during the processing of an actual molded part. In some cases, the material could not be molded or the thermal fatigue characteristics deteriorated significantly due to micro cracks.

Japanese Patent Application Laid-Open No. 9-279316 discloses an invention in which Si / Mn is controlled to improve the high temperature characteristics by increasing the resistance to 900 MPa at 15 MPa or more. In this case as well, it was not enough in a long-term use environment to specify the tensile strength of the product plate at 900 ° C. In addition, since Mn was added in an amount of 0.7 to 3%, the ductility was low, and there was a problem that the formability when processing into a member and the thermal fatigue life decreased due to the decrease in high hot ductility.

Japanese Patent Laid-Open No. 2002-105605 discloses that the 0.2% resistance to 18 MPa or more after holding at 900 ° C. for 1 hour by adjusting the components. Here, it is possible to maintain a strong environment in the environment by holding it for 1 hour at a high temperature. The technical idea is to improve the temperature, but when subjected to a thermal cycle, the thermal fatigue life may not be improved only by improving the high-temperature strength.

In JP-A-9-279312, JP-A-2000-169943 and JP-A-10-204590, steel containing B is disclosed as a ferrite stainless steel having excellent high temperature characteristics. It has been added to improve workability, and its influence on high-temperature properties has not been clear from conventional knowledge. The role of B in improving workability is to improve the grain boundary strength due to grain boundary segregation and improve secondary workability. In the present invention, the addition of B refines the precipitate, It is intended to improve high temperature strength. In addition, V was added to the above three patents, but in some cases it was added from the viewpoint of improving the corrosion resistance of the weld and improving the workability by fixing C and N. Disclosure of the invention

The present invention provides excellent oxidation resistance, high temperature strength, and thermal fatigue characteristics especially in an environment where the exhaust temperature is near 800 ° C, which is used for a long time at high temperatures, or repeatedly subjected to heating and cooling. And providing relatively inexpensive Cr-containing steel.

In order to solve the above-mentioned problems, the present inventors investigated the relationship between the components and the high temperature deformation characteristics regarding the oxidation resistance, high temperature strength, and thermal fatigue characteristics of the Cr-containing steel. In particular, considering the environment subject to thermal cycling, we carefully investigated how the deformation characteristics in the low temperature range in addition to the deformation characteristics in the high temperature range affect the thermal fatigue life. As a result of various studies to achieve this purpose, the following findings were obtained. This feature is mainly due to the addition of Cr and Si from the viewpoint of oxidation resistance, the addition of Nb-Ti composite from the viewpoint of improving high-temperature characteristics, and the adjustment of each component in the new ingredients added with V and B. Therefore, it ensures the strength and ductility during long-term use and greatly improves the thermal fatigue characteristics. The gist of the present invention is as follows.

(1) In mass%, C: 0.01% or less, N: 0.015% or less, Si: 0.8-1.0%, Mn: 0.2-1.5%, P: 0.03% or less, S: 0.01% or less, Ni: 0.2 % Or less, Cu: 0.2% or less, Cr: 13 to 15%, Mo: 0.1% or less, Nb: 0.3 to 0.55%, Ti: 0.05 to 0.2%, V: 0.0 to 0.2%, A1: 0.015 to 1.0 %, B: 0.0002 to 0.0010%, and (Nb + 1.9XTi) / person C + N) ≤40, with the balance being Fe and inevitable impurities, with excellent thermal fatigue properties Cr-containing steel.

(2) It is characterized by 0.2% Kaka resistance at 800 ° C after aging treatment at 800 ° C for 100 hours or more and OMPa resistance at 200 ° C and a drawing value at 35 ° C at 35% or more. Cr-containing steel with excellent thermal fatigue properties.

(3) Thermal fatigue as described in (1) or (2), characterized in that the amount of solid solution Nb + solid solution Ti after aging treatment at 800 ° C for 100 hours or more is 0.08% or more Cr-containing steel with excellent properties.

(4) The Cr-containing steel excellent in thermal fatigue properties according to any one of (1) to (3), characterized by satisfying Mn / Ti≥3. Brief Description of Drawings

Figure 1 shows the relationship between (Nb + 1.9Ti) / (C + N) and the elongation at break at room temperature.

Figure 2 shows the effect of Ti addition on the thermal fatigue life.

Figure 3 shows the resistance to 800 ° C after aging at 800 ° C.

Figure 4 shows the aperture value at 200 ° C after aging at 800 ° C.

Figure 5 shows the aperture at 200 ° C after aging at 800 ° C. FIG. 6 is a graph showing the relationship between MnZTi and Cr ₂₀ ₃ thickness when subjected to a continuous oxidation test at 900 ° C. for 200 hours. BEST MODE FOR CARRYING OUT THE INVENTION

The reason for limitation of the present invention will be described below.

C degrades the formability and corrosion resistance and lowers the high-temperature strength. Therefore, the lower the content, the better. Therefore, C was made 0.015% or less. However, excessive reduction leads to an increase in fine cost, so 0.001 to 0.005% is more desirable.

N, like C, deteriorates formability and corrosion resistance and lowers the high-temperature strength. The lower the content, the better. Therefore, N was set to 0.015% or less. However, excessive reduction leads to an increase in fine cost, so 0.00 to 0.010% is also desirable.

Si is an important element for improving oxidation resistance and high temperature characteristics in the present invention. Oxidation resistance and high-temperature strength improve with increasing Si content, and the effect is manifested at 0.8% or more. In addition, Si promotes precipitation of intermetallic compounds mainly composed of Fe and Nb called Laves phase at high temperatures. If the Laves phase precipitates excessively, the amount of dissolved Nb necessary to ensure high temperature strength is reduced. If Si is added excessively, the room temperature workability deteriorates and the ductility during long-time use is reduced, leading to a reduction in thermal fatigue life. From these viewpoints, the upper limit was set to 1.0%. Further, it is preferably 0.8 to 0.9%.

Mn is an element that is added as a deoxidizer and improves the high-temperature strength, and the effect is manifested from 0.2% or more. In addition, it was found that the addition of Mir suppresses the oxidation of Ti during continuous oxidation and improves the oxidation resistance of the steel with a composite addition with Ti. On the other hand, addition over 1.5% reduces ductility In addition, it forms MnS and reduces corrosion resistance. Excessive addition also causes deterioration of oxidation resistance. Therefore, it was set to 0.2 to 1.5%. Furthermore, considering high temperature ductility and scale adhesion, 0.3 to 1.0% is desirable.

Since P is a solid solution strengthening element like Mn and Si, the lower the content, the better. Therefore, the upper limit is preferably 0.03%. However, since excessive reduction leads to an increase in the cost of refinement, the lower limit is preferably 0.01%. In addition, considering the milling cost and corrosion resistance, 0.012 to 0.025% is desirable.

S is an element that degrades corrosion resistance and oxidation resistance, but since the effect of improving workability by combining with Ti and C is manifested from 0.0001%, the lower limit was set to 0.0001%. On the other hand, the upper limit is set to 0.01% because the high-temperature strength decreases because it combines with Ti and C by appropriate addition to reduce the amount of solid solution Ti and cause coarsening of precipitates. Furthermore, if considering the sickle cost and high temperature oxidation characteristics, 0.0010 to 0.0090% is desirable.

Cr is an essential element for ensuring oxidation resistance in the present invention. If it is less than 13%, the effect is not manifested, and if it exceeds 15%, the workability is deteriorated or the toughness is deteriorated. Furthermore, considering high temperature ductility and manufacturing cost, 13.2 to 14.5% is desirable.

Ni is effective in improving toughness and resistance to high temperature salt damage and corrosion. However, it is an austenite-forming element, has an adverse effect on oxidation resistance, and is expensive.

Cu is effective for improving high-temperature strength, but it lowers the ductility and adversely affects oxidation resistance.

Mo is effective for improving corrosion resistance, suppressing high-temperature oxidation, and improving high-temperature strength by strengthening solid solution. However, it is not more than 0.2% because it causes high hot ductility and is expensive. More desirably, it is 0.1% or less.

Nb improves the high-temperature strength by strengthening solid solution and refining precipitates. It is an element necessary for the purpose. It also has the role of fixing C and N as carbonitrides and contributing to the development of recrystallization textures that affect the corrosion resistance and r-value of product plates. These effects appear from 0.3% or more. On the other hand, if it is precipitated as a LaFez phase depending on the temperature in the environment of use, the effect will be saturated even if it is added excessively because it loses its solid solution strengthening ability. Moreover, excessive addition reduces ductility at low temperatures and shortens the thermal fatigue life. In the present invention, the amount of solute Nb is ensured by the combined addition with Ti. In this case, the action is saturated at 0.55%, so it was set to 0.3 to 0.55%. Furthermore, if considering moldability, intergranular corrosion and manufacturing cost, 0.32 to 0.45% is desirable.

Ti is an element that combines with C, N, and S to improve corrosion resistance, intergranular corrosion resistance, and deep drawability. In addition, in the combined addition with Nb, the addition of an appropriate amount brings about the improvement of high-temperature strength and high-temperature ductility after exposure at high temperature for a long time, and improves thermal fatigue properties. These effects are manifested from 0.05% or more, but addition of more than 0.2% increases the amount of solid solution Ti and degrades formability, as well as surface toughness, toughness, and oxidation resistance. Therefore, the content is set to 0.05 to 0.2%. Furthermore, considering the manufacturability, 0.05 to 0.15% is desirable.

When V is added in an amount of 0.01% or more, fine carbonitrides are formed and a precipitation strengthening action is generated, contributing to the improvement of high temperature strength. On the other hand, addition of over 0.2% lowers the low temperature ductility and conversely reduces the thermal fatigue life, so the upper limit was made 0.2%. Furthermore, considering the manufacturing cost and manufacturability, 0.08 to 0.15% is desirable.

In addition to being added as a deoxidizing element, A1 is an element that improves high-temperature strength through oxidation resistance and solid solution strengthening, and is an essential element in the present invention. The effect starts from 0.015%, but addition of more than 1.0% hardens, deteriorates surface flaws and weldability, so 0.015 to 1.0% . In addition, 0.03 to 0.7% is desirable considering the cost of fertility.

B is an element that improves secondary workability during product press working. In particular, Ti-added steel is an essential element in the present invention because secondary work cracks are likely to occur. In addition, it has been found that the component system to which Nb and Ti are added and Si is added as in the present invention contributes to the improvement of the high temperature strength. In general, B is considered to form (Fe, Cr) 23 (C, 6) 6 and Cr 2 で at high temperatures and segregate at grain boundaries, but in the component system to which Si is added, These precipitates did not precipitate, and it was found that they had the effect of precipitating Laves as described above. The Laves phase reduces the amount of dissolved Nb and usually coarsens, so there is almost no high-temperature strengthening ability after long-term aging, but it has precipitation strengthening ability because it precipitates finely by adding B. It will contribute to the improvement of strength. The reason why B precipitates the Laves phase finely is presumed that the interfacial energy decreases due to grain boundary segregation, making it difficult for grain boundaries to precipitate.

These effects are manifested at 0.0002% or more. However, excessive addition deteriorates the hardness and intergranular corrosion, and also causes weld cracks. Therefore, the content was set to 0.0002 to 0.0010%. Furthermore, if considering moldability and manufacturing cost, 0.0003 to 0.0007% is desirable. In the case of the combined addition of Ti and Nb, it has been found that if both are added excessively, solid solution Ti and solid solution Nb increase and the cold ductility is remarkably reduced.

In the present invention, as shown in FIG. 1, by setting (Nb + 1.9XTi) / (C + N) ≤50, the elongation at break at room temperature can be secured at 32% or more. Here, with regard to Ti, Nb, C, and 14% Cr steel with different amounts of steel and a sheet thickness of 2 mm, JIS No. 13 B specimens were taken in the rolling direction, subjected to a tensile test, and the elongation at break was measured. If the elongation at break is 32% or more, cracking and constriction will not occur even if the pipe material is bent after press working from the plate material to the exhaust member or after bending into a pipe shape. We also found that ductility is important in addition to high-temperature strength after aging for improving thermal fatigue life. Here, the thermal fatigue test will be described. The product plate was pipe-formed (outside diameter 38. lmm) by electro-welding and subjected to a thermal fatigue test.

The thermal fatigue test was conducted with a computer-controlled electrohydraulic control fatigue tester. The temperature cycle to be applied was such that the temperature was raised from 200 to 800 ° C in 120 seconds, held at 800 ° C for 30 seconds, then cooled to 300 ° C in 120 seconds, and further cooled to 200 ° C in 90 seconds. Heating was performed with a high-frequency induction heating coil, and cooling was performed by supplying air into the test tube. The restraint rate was set so that compressive strain was applied so as to be a constant ratio with respect to the amount of free expansion. That is, for example, in the case of 50% restraint, compression strain was mechanically applied so that the expansion amount was half of the free expansion.

The chemical composition of the test material is shown in Table 1. Steel A is a compatible steel of the present invention and Steel B is a comparative steel. Here, Steel B is a heat-resistant stainless steel plate used for general purposes.

01

S8l £ 90 / .00idf / 13d 90S 丽 800Z ΟΛ \ From Fig. 2, the steel of the present invention has a longer life than the comparative example at any constraint. This is because the high ductility is maintained in the low temperature region of the thermal cycle, in addition to the fact that there is almost no decrease in strength even when high temperature strength is aged, that is, a long time thermal cycle is applied. During a thermal cycle, a compressive load is applied to the material at a high temperature, and creep deformation or stress relaxation occurs at 800 ° C. Therefore, an increase in 0.2% proof stress at 800 ° C It is considered effective for extending the fatigue life. On the other hand, during the cooling process from 800 ° C to 200 ° C, the material is given tensile stress. This tensile stress is much larger than the compressive stress in the high temperature range, and when damage (defect) occurs in the thermal cycle, the plastic deformation at this site is remarkable. Therefore, an increase in the ductility (drawing) of the material at 200 ° C is considered to have the effect of suppressing damage progression during the cooling process.

Figures 3 and 4 show the tensile strength and drawing at high temperatures after aging at 800 ° C. The steel of the present invention has high strength at a high temperature strength of 20 MPa or more and a drawing value of 35% or more at 200 ° C, even when subjected to long-term aging treatment at 800 ° C for 10 hours or more. This means that even when subjected to a long thermal cycle process during thermal fatigue, the strength at the highest temperature is high and the ductility at the lowest temperature is high. As a result, as shown in Fig. 2, it is considered that the thermal fatigue life is improved at any constraint rate. In the conventional invention, the technical idea was only to improve the strength at the maximum temperature when subjected to the thermal cycle, but in the present invention, the thermal fatigue life is remarkably improved by improving the ductility at the minimum temperature. I found out.

The improvement of the drawing value at 200 ° C is considered to be due to the above-mentioned securing of the elongation at break at room temperature and the suppression of aging deterioration. In other words, the present invention has revealed that the addition balance of Ti and Nb is important. . On the other hand, the improvement in high-temperature strength at 800 is affected by the amount of solute Nb and the amount of solute Ti. Figure 5 shows the relationship between the amount of solute Nb + solute Ti after aging at 800 ° C and the high temperature strength at 800 ° C. When the solid solution Nb + solid solution Ti content is 0.08% or more, the high-temperature strength at 800 ° C is 20MPa or more. In order to obtain a high-temperature strength of 20 MPa or more and to improve the thermal fatigue life, the solid solution Nb amount + the solid solution Ti amount was set to 0.08% or more.

In the present invention, by adding a proper amount of Ti and Nb in combination, thermal fatigue properties are improved by improving high-temperature strength and high-temperature ductility after long-term aging. There is a deterioration effect. When the steel containing Si, Cr, Mn, Ti shown in the present invention is continuously oxidized in the atmosphere, the scale is composed of spinel oxide mainly containing Ti0 ₂ , Cr, Mn in the outer layer, and Cr _{2 in} the inner layer. 0 ₃ is formed. As the Ti content increases, the inner Cr ₂ O ₃ film becomes thicker and the oxidation resistance deteriorates. The present inventors have studied the effects of Mn, an increase in the Mn, Ti0 ₂ content of the outer layer is reduced, the growth of the inner layer of Cr ₂ 0 ₃ film is suppressed, thereby oxidation resistance It was found that Figure 6 shows the inner layer of Cr ₂ 0 ₃ film thickness after 200 h continuous oxidation with Ti / Mn and 900 ° C. If the thickness of the Cr ₂₀ ₃ inner scale exceeds 5 / m, scale peeling will occur and oxidation resistance will be inferior. However, if Mn / Ti≥ 3, the thickness of the Cr ₂₀ ₃ inner scale will be thin. Excellent in oxidation resistance. Ti diffuses outward through the inner layer of Cr ₂ 0 _3, but the result of outward diffusion of Ti is inhibited by Mn, and considered Erareru growth of the inner layer of Cr ₂ 0 ₃ film is suppressed. For good oxidation resistance, it is important to suppress the growth of the inner layer of Cr ₂ 0 ₃ coating, Cr ₂ 0 ₃ to be generated when 200 h, was continuously oxidation in air at 900 ° C In order to make the inner scale thickness 5 xm or less, MnZTi≥3. Example Steels with the composition shown in Table 2 were melted and formed into slabs, and the slabs were hot-rolled to form hot rolled coils with a thickness of 5M. Thereafter, the hot rolled coil was annealed and pickled, cold-rolled to a thickness of 2 mm, and annealed and pickled to obtain a product plate. The annealing temperature of the cold rolled sheet was set to 980 to 1050 ° C in order to make the grain size number about 6 to 8. From the product plate thus obtained, high-temperature tensile test pieces were collected and subjected to tensile tests at 200 ° C and 800 ° C. In addition, after aging treatment at 800 ° C. for 100 hours, a high temperature tensile test was conducted in the same manner as described above. In addition, the product plate was pipe-formed (outer diameter 38.1 mm) by electro-welding and subjected to a thermal fatigue test. The temperature cycle to be applied is a pattern in which the temperature is raised from 200 to 800 ° C in 120 seconds, held at 800 ° C for 30 seconds, then cooled to 300 ° C at 120sec and further cooled to 200 ° C in 90 seconds. The rate was 50%. For evaluation of oxidation resistance, a 20 mm wide and 25 mm long test piece was cut from the product plate, polished to # 600 with emery paper, and then continuously oxidized in the atmosphere at 900 ° C for 200 h. A test was conducted. The thickness of the Cr ₂₀ ₃ inner layer scale was determined by observing a cross section with a SEM (scanning electron microscope).

As is apparent from Table 2, when steel having the composition defined in the present invention is produced by the conventional method as described above, the normal temperature elongation is higher than that of the comparative example and the workability is excellent. I understand. Also, the high temperature strength satisfies the above range and 'excellent thermal fatigue properties. In the comparative example, Steel Nos. 12 and 13 have high C and N, so the elongation at break at room temperature is low and the drawing value at high temperature is also low. Also, high temperature strength is low due to carbonitride formation. Steel No. 14 is low in Si, so its high temperature strength after aging is low. Steel Nos. 15, 17, 18, 19, and 20 have high Mn, S, Ni, Cu, and Cr, respectively, so they have poor normal temperature workability and a low drawing value after aging. In Steel No. 16, S is outside the upper limit, the amount of solid solution Ti + Nb after aging is low, and the high temperature strength after aging is low. Steels Nos. 21, 22, 23, 24, 25, and 26 have Mo, Nb, Ti, V, Al, and B outside the upper limit. It is. Although these contribute to high-temperature strength, they have poor room-temperature processability and a low thermal fatigue life due to low drawing at 200 ° C.

In terms of oxidation resistance, the thickness of the inner layer of the steel of the present invention is good at 5 m or less. In the comparative example, Si deviates from the scope of the present invention, and steels Nos. 14, 17, 23, 24, and 26 with small MnZTi have an inner layer scale thickness exceeding 5 m, and are inferior in oxidation resistance.

The manufacturing method of the steel sheet is not particularly specified, but hot rolling conditions, hot rolled sheet thickness, hot and cold rolled sheet annealing temperatures, atmosphere, etc. may be selected as appropriate. Further, temper rolling or tension leveler may be applied after cold rolling / annealing. Furthermore, the product thickness may be selected according to the required member thickness.

Table 2

: Deviated from the present invention

Industrial applicability

According to the present invention, it is possible to provide a Cr-containing steel having excellent thermal fatigue characteristics without adding an expensive alloy element, and in particular, by applying it to exhaust system members such as automobiles, A great effect can be obtained.

Claims

The scope of the claims

1. By mass%

C: 0.01% or less,

N: 0.015% or less,

Si: 0.8-1.0%

Mn: 0.2 ~ 1 · 5%,

P: 0.03% or less,

S: 0.01% or less,

Ni: 0.2% or less,

Cu: 0.2% or less,

Cr: 13-15%

Mo: 0.1% or less,

Nb: 0.3-0.55%,

Ti: 0.05-0.1%

V: 0.01-0.2%

A1: 0.015-1.0%,

B: Contains 0.0002 to 0.0010%,

And (Nb + 1.9XTi) Z (C + N) ≤50, a Cr-containing steel with excellent thermal fatigue characteristics characterized by the balance being Fe and inevitable impurities.

2. The 0.2% proof stress at 800 ° C after aging treatment at 800 ° C for 100 hours or more is 20MPa or more, and the aperture value at 200 ° C is 35% or more. Cr-containing steel with excellent thermal fatigue properties.

3. Excellent thermal fatigue properties according to claim 1 or 2, characterized in that the amount of solid solution Nb + solid solution Ti after aging treatment at 800 ° C for 100 hours or more is 0.08% or more. Cr-containing steel.

4. The Cr-containing steel having excellent thermal fatigue properties according to any one of claims 1 to 3, wherein MnZTi≥3 is satisfied.