CA2056362C - Heat resisting ferritic stainless steel excellent in low temperature toughness, weldability and heat resistance - Google Patents
Heat resisting ferritic stainless steel excellent in low temperature toughness, weldability and heat resistance Download PDFInfo
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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Abstract
A heat resisting ferritic stainless steel which com-prises, by weight, up to 0.03 % of C, from 0.1 to 0.8 %
of Si, from 0.6 to 2.0 % of Mn, up to 0.006 % of S, up to 4 % of Ni, from 17.0 to 25.0 % of Cr, from 0.2 to 0.8 %
of Nb, from 1.0 to 4.5 % of Mo, from 0.1 to 2.5 % of Cu, and up to 0.03 % of N, and optionally one or more of appropriate amounts of Al, Ti, V, Zr, W, B and REM, the balance being Fe and unavoidable impurities, wherein the alloying elements are further adjusted so that the ratio of Mn%/S% is not less than 200, [Nb] defined by the equa-tion: [Nb] - Nb% - 8 (C% + N%) is not less than 0.2, and (Ni% + Cu%) is not more than 4. The stainless steel ac-cording to the invention is suitable for use in con-strutting an exhaust gas path-way of an automobile, par-ticularly, a path-way from an engine to a converter, which is exposed to high temperatures, and which requires an improved low temperature toughness and a high resis-tance to weld cracking due to high temperatures.
of Si, from 0.6 to 2.0 % of Mn, up to 0.006 % of S, up to 4 % of Ni, from 17.0 to 25.0 % of Cr, from 0.2 to 0.8 %
of Nb, from 1.0 to 4.5 % of Mo, from 0.1 to 2.5 % of Cu, and up to 0.03 % of N, and optionally one or more of appropriate amounts of Al, Ti, V, Zr, W, B and REM, the balance being Fe and unavoidable impurities, wherein the alloying elements are further adjusted so that the ratio of Mn%/S% is not less than 200, [Nb] defined by the equa-tion: [Nb] - Nb% - 8 (C% + N%) is not less than 0.2, and (Ni% + Cu%) is not more than 4. The stainless steel ac-cording to the invention is suitable for use in con-strutting an exhaust gas path-way of an automobile, par-ticularly, a path-way from an engine to a converter, which is exposed to high temperatures, and which requires an improved low temperature toughness and a high resis-tance to weld cracking due to high temperatures.
Description
~~5636~
HEAT RESISTING FERRITIC STAINLESS STEEL EXCELLENT IN LOW
TEMPERATURE TOUGHNESS, WELDABILITY AND HEAT RESISTANCE
Field of the Invention The present invention relates to a heat resisting ferritic stainless steel excellent in low temperature toughness, weldability and heat resistance. The stain-less steel according to the invention is suitable for use in composing a part of an exhaust gas path-way of an au-tomobile, especially, a path-way from an engine to a con-verter, which is exposed to high temperatures.
Background of the Invention and Prior Art In recent years, air pollution caused by an automo-bile exhaust gas has become a serious problem and NOx, HC, C0, etc. of the exhaust gas have been restricted in quantities from a view point of preventing environmental pollution. The restriction is now getting more and more severe in consideration of acidic rain and others.
Therefore, it is necessary to further improve an effi-2 0 ciency of the exhaust gas purification.
On the other hand, a recent increasing demand for a more powerful and capable engine tends to rise up the ex-haust gas temperature. Under the circumstances, parts of 2 5 an exhaust gas system are exposed to higher temperatures 2~~636~
while driving the engine. Particularly, parts between the engine and a converter of exhaust gas purifying in-struments, for example, an exhaust manifold, dual tube and the like, cannot help being exposed to still higher temperatures. In addition, these parts undergo not only changes in mechanical stress due to oscillation caused by driving the engine and running of the automobile, but also changes in temperature due to heating and cooling cycles depending upon patterns of driving and, in some 1~ cases, to freezing in cold areas. Thus, the parts are exposed to mechanically and thermally severe conditions.
As long as a heat resisting steel, for example, a stainless steel is applied as a material for the produc-tion of these parts, heat resistivity, of course, is ex-cellent. However, because of weld-joints (the pipe used for these parts is usually made by weld and is often jointed to other parts by weld), the material must be ex-cellent in weldability and in mechanical workability.
2 0 Therefore, it is important that the material used for this purpose must be not only corrosion resistant which is the fundamental property of a stainless steel but also heat resistant, tough at low temperature, weldable and workable.
zo~~~~2 SUS304, a typical austinitic stainless steel, has been considered as a favorable material for use for the above-mentioned purpose because of its excellent worka-bility and favorable weldability. However, since an aus-tinitic stainless steel has a large thermal expansion co-efficient, fears are entertained for a thermal fatigue cracking caused by a thermal stress which comes about in the repeated heating and cooling. In addition, because of a large difference in thermal expansion between an austinitic stainless steel and its surface oxide, the ox-ide layer tends to splinter off from the surface of the steel. For these reasons, a nickel base alloy repre-sented by Inconel 600 is used in some parts as the path-way material for an exhaust gas of an automobile. This alloy is promising for the reasons that its thermal ex-pansion coefficient is small whereby the oxide layer is tight adhesive to the surface and, in consequence, it is excellent in high temperature oxidation resistance as well as high temperature strength. However, this alloy 2 0 is very expensive so that it is not extensively used.
On the other hand, when compared with the austinitic stainless steel, a ferritic stainless steel is cheap and, in addition, excellent in thermal fatigue properties be-t 5 cause of its small thermal expansion coefficient, so that it is considered suitable for use in parts which are 20~~~0~
HEAT RESISTING FERRITIC STAINLESS STEEL EXCELLENT IN LOW
TEMPERATURE TOUGHNESS, WELDABILITY AND HEAT RESISTANCE
Field of the Invention The present invention relates to a heat resisting ferritic stainless steel excellent in low temperature toughness, weldability and heat resistance. The stain-less steel according to the invention is suitable for use in composing a part of an exhaust gas path-way of an au-tomobile, especially, a path-way from an engine to a con-verter, which is exposed to high temperatures.
Background of the Invention and Prior Art In recent years, air pollution caused by an automo-bile exhaust gas has become a serious problem and NOx, HC, C0, etc. of the exhaust gas have been restricted in quantities from a view point of preventing environmental pollution. The restriction is now getting more and more severe in consideration of acidic rain and others.
Therefore, it is necessary to further improve an effi-2 0 ciency of the exhaust gas purification.
On the other hand, a recent increasing demand for a more powerful and capable engine tends to rise up the ex-haust gas temperature. Under the circumstances, parts of 2 5 an exhaust gas system are exposed to higher temperatures 2~~636~
while driving the engine. Particularly, parts between the engine and a converter of exhaust gas purifying in-struments, for example, an exhaust manifold, dual tube and the like, cannot help being exposed to still higher temperatures. In addition, these parts undergo not only changes in mechanical stress due to oscillation caused by driving the engine and running of the automobile, but also changes in temperature due to heating and cooling cycles depending upon patterns of driving and, in some 1~ cases, to freezing in cold areas. Thus, the parts are exposed to mechanically and thermally severe conditions.
As long as a heat resisting steel, for example, a stainless steel is applied as a material for the produc-tion of these parts, heat resistivity, of course, is ex-cellent. However, because of weld-joints (the pipe used for these parts is usually made by weld and is often jointed to other parts by weld), the material must be ex-cellent in weldability and in mechanical workability.
2 0 Therefore, it is important that the material used for this purpose must be not only corrosion resistant which is the fundamental property of a stainless steel but also heat resistant, tough at low temperature, weldable and workable.
zo~~~~2 SUS304, a typical austinitic stainless steel, has been considered as a favorable material for use for the above-mentioned purpose because of its excellent worka-bility and favorable weldability. However, since an aus-tinitic stainless steel has a large thermal expansion co-efficient, fears are entertained for a thermal fatigue cracking caused by a thermal stress which comes about in the repeated heating and cooling. In addition, because of a large difference in thermal expansion between an austinitic stainless steel and its surface oxide, the ox-ide layer tends to splinter off from the surface of the steel. For these reasons, a nickel base alloy repre-sented by Inconel 600 is used in some parts as the path-way material for an exhaust gas of an automobile. This alloy is promising for the reasons that its thermal ex-pansion coefficient is small whereby the oxide layer is tight adhesive to the surface and, in consequence, it is excellent in high temperature oxidation resistance as well as high temperature strength. However, this alloy 2 0 is very expensive so that it is not extensively used.
On the other hand, when compared with the austinitic stainless steel, a ferritic stainless steel is cheap and, in addition, excellent in thermal fatigue properties be-t 5 cause of its small thermal expansion coefficient, so that it is considered suitable for use in parts which are 20~~~0~
subjected to cyclic variation of temperature such as heating and cooling. Type 409 or SUS430, a representa-tive of the ferritic stainless steel, is going on to use in part of an automobile exhaust gas path-way . However, these materials have a property that the strength goes sharply down as the temperature 900 °C. and higher, and in consequence, give rise to problems of which one is fa-tigue cracking due to insufficient strength and the other is abnormal oxidation when conditions go beyond the limit 1~ of oxidation resistivity. A counter action to these problems may be possible by means of addition of various alloying elements, which improve high temperature strength, or by means of increasing a chromium content to improve oxidation resistance. However, such means of ad-dition of alloying elements or increase of chromium con-tent make, in general, not only impact toughness of the steel weaken steeply but also weldability and workability get worse remarkably.
2 0 Any stainless steel that is in conformity with the above-mentioned conditions becoming more and more severe according to the demands for a more powerful and capable engine and for the progress of a purification efficiency of an exhaust gas is not come out yet. In other words, a 2 S material which is economical and satisfies simultaneously various demands for properties such as high temperature s strength, oxidation resistance, heat resistance, tough-ness, weldability and workability is not yet obtainable from austinitic or the ferritic stainless steels nowa-days. If a ferritic stainless steel retaining the previ-ously stated desirable properties inherent to the fer-ritic stainless steel, and having improved heat resistiv-ity and high temperature strength and, in addition, being excellent in productivity, workability, weldability and low temperature toughness comes to be obtainable, it may be said that such a material is very promising for the particular use mentioned above.
JP A 64-8254 discloses a ferritic stainless steel for the like use, but is completely silent with respect to low temperature toughness. JP B 59-52226 and 61-44121 disclose to improve a ferritic stainless steel in its rust development due to chlorine ion and its acid resis-tivity by adding copper and nickel while extremely lower-ing S, but teach nothing about high temperature strength, 2 0 heat resistance, weldability and low temperature tough-ness.
Object of the Invention Accordingly, an object of the invention is to pro-vide a ferritic stainless steel having properties which 2 S simultaneously meet the above-mentioned many severe con-ditions required for a material of an automobile exhaust _ 246362 gas path-way, particularly, of a part between an engine and a converter where the material is exposed to high temperatures. Another object of the invention is to im-prove low temperature toughness, which is an inherent de-fect of ferritic stainless steels. A further object of the invention is the provision of a heat resistive fer-ritic stainless steel which does not suffer from a prob-lem of high temperature cracking of weld heat-affected zone.
Summary of the Invention The invention provides a heat resisting ferritic stainless steel excellent in low temperature toughness, weldability, and heat resistance which comprises, by 1 S weight, up to 0.03 0 of C, from 0.1 to 0.8 % of Si, from 0.6 to 2.0 % of Mn, up to 0.006 0 of S, 2 ~ up to 4 0 of Ni, from 17.0 to 25.0 0 of Cr, from 0.2 to 0.8 °s of Nb, from 1.0 to 4.5 0 of Mo, from 0.1 to 2.5 0 of Cu, and 2 S up to 0 . 03 0 of N, 20~6~6~
the balance being Fe and unavoidable impurities, wherein the alloying elements are further adjusted so that the ratio of Mno/So is not less than 200, [Nb] defined by the equation:
[Nb] - Nbo - 8 (Co + No) is not less than 0.2, and (Nio + Cuo) is not more than 4.
The invention further provides a heat resisting fer-ritic stainless steel excellent in low temperature tough-ness, weldability and heat resistance which comprises, in addition to the elements of the above-mentioned steel, one or more of:
up to 0.5 0 Al, of up to 0.6 0 Ti, of 1 $ up to 0.5 % V, of up to 1.0 0 Zr, of up to 1.5 0 W, of up to 0.01% B, and of up to 0.1 % REM.
of Brief Description of the Drawings Fig. 1 shows a relationship between molybdenum con-tent and tensile strength at the indicated elevated tem-~~~~3~
s peratures obtained by the elevated temperature tensile test noted below;
Fig. 2 shows a relationship between manganese con-s tent and amount of scale which has splintered off after the elevated temperature oxidation test noted below;
Fig. 3 shows a relationship between Mn/S and criti-cal strain obtained by the weld high temperature cracking test noted below; and Fig. 4 shows a relationship between copper content and Charpy impact strength obtained by the Charpy impact test at the indicated temperatures. The invention is 1S based on the results shown in these figures.
Detailed Description of the Invention After many experimental researches to achieve the object mentioned before, the inventors have been able to 2 0 obtain the following information.
Fig. 1 shows results of the tensile tests at the indicated elevated temperatures carried out on materials having a basic composition of Fe-18 o Cr-0.45 ~-Nb with 2 5 various Mo and Cu contents to examine effects of Mo and Cu on high temperature tensile strength. As seen from the figure, high temperature strength is improved by the addition of molybdenum in an amount of 1 0 or more.
Furthermore, the conjoint addition of molybdenum and cop-per is more effective than the addition of molybdenum alone to improve high temperature strength.
Fig. 2 shows results of the oxidation tests at the indicated elevated temperatures carried out on materials having a basic composition of Fe-18 % Cr-0.45 o-Nb with l~ various Mn contents. The oxidation was continued in air for 100 hrs at 900 °C. or 1000 °C., and at the end of the period an amount of scale which had splintered off was measured. As seen from the figure, the scale splintering was suppressed, irrespective of the oxidation temperature tested, by the addition of at least about 0.6 % of man-ganese. Thus, it can be understood that, as for the fer-ritic stainless steel, manganese makes the limit of oxi-dation resistivity to rise up.
2 0 Fig. 3 shows results of the weld high temperature affected cracking test on materials having a basic compo-sition of Fe-18 o Cr-0.45 %-Nb with appropriate Mo and Cu contents whose effects are recognized as shown in Fig. 1 (3 o Mo and 0.5 o Cu) and with varied Mn and S contents 2 5 to examine effects of the ratio, Mn/S, on weld high tem-perature affected cracking. The test was carried out as 20~63~
to follows. The cold rolled and annealed plate of 1.2 mm in thickness was cut into test pieces of 40 mm x 200 m. The test pieces were TIG welded under various tensile stresses imposed longitudinally. The minimum strain at which cracking began to occur was determined, which is referred to herein as the critical strain and is a mea-sure of the susceptibility to the weld high temperature affected cracking. It is revealed from Fig. 3 that if the ratio, Mn/S, is 200 or higher, ferritic stainless steels having conjointly incorporated with Mo and Cu have an increased critical strain, and, in consequence, an im-proved weldability. Thus, in order to overcome the weld high temperature affected cracking it is effective to add a proper amount of Mn rendering the ratio, Mn/S, not less than 200.
Fig. 4 shows results of the Charpy impact test car-ried out on materials having a basic composition of Fe-18 o Cr-0.45 o-Nb with varied Mo and Cu contents for examin-2 0 ing effects of molybdenum and copper on toughness. The impact value is lowered by the addition of molybdenum, as is known in the art. However, Fig. 4 provides new infor-mation that the reduction in the impact value due to Mo may be compensated to some extent by conjoint addition of 2 5 Cu. Particularly, even with such a material as a steel containing 4 ~ of molybdenum whose impact toughness is 20~63G j remarkably low, the conjoint addition of copper improves the impact value well enough. Furthermore, the conjoint addition of nickel and molybdenum can also improve low temperature impact toughness, as will be manifested in Examples described later. The information of these facts is of great importance, particularly for a material which constitutes parts exposed to low temperature circumstance in winter, for example, a manifold or dual tube which suffer from mechanical vibration in addition to low tem-perature when the engine starts, whereupon the material will become usable even under further more severe condi-tions expected in the future.
Based on the information noted above, the invention provides a ferritic stainless steel having well-balanced excellent properties as a whole, including high tempera-ture strength, thermal fatigue resistance, oxidation re-sistance and low temperature toughness.
2 0 The reasons for the restriction of each chemical component in the steel according to the invention will now be outlined.
C and N: C and N are, in general, important ele-2 5 ments because of promoting high temperature strength, but excessive amounts of them demote oxidation resistance, ~o~s~~~
workability and toughness. Besides above, C and N react and form compounds with Nb, thereby lowering the effec-tive Nb in the ferritic phase. Accordingly, it is favor-able that C and N are small in quantities, so that they should be controlled not more than 0.03 0, respectively.
Si: Si is an effective element to improve oxidation resistance, but an excessive amount of Si renders the steel hard, and, in consequence, adversely affects worka-bility and toughness. Therefore, Si is controlled within the range from 0.1 o to 0.8 0.
Mn: Mn reacts with S, which is harmful for weld high temperature affected cracking, and fixes S in the form of MnS, whereby S is removed or reduced in welded metal . It has been found that if the relation, Mn/S > 200, is sat-isfied, the effect is the same as that of S reduction.
On the other hand, the addition of at least 0.6 0 of Mn improves adhesion of scale Therefore, Mn is controlled 2 0 in the range from 0.6 o to 2.0 0, while satisfying the relation: Mn/S > 200.
S: As previously stated, since S is harmful to the weld high temperature affected cracking, it is desirable 2 S that S is as small as possible in quantity. However, the smaller S is, the more the cost is needed for the produc-205636 ~
tion. Even if S remains up to 0.006 0, enough durability to the weld high temperature affected cracking is held on the steel of this invention due to the effect of Mn, so that the upper limit of S is now set as 0.006 0.
Ni: As illustrated in Examples, Ni brings about a favorable result of improving toughness like copper does.
However, an excessive of Ni gives rise to deposition of an austenite phase at elevated temperatures, and follows the increase of thermal expansion coefficient as well as anxiety about the deterioration of thermal fatigue.
Therefore, in the case of the conjoint addition of Ni and Cu according to the invention, the Cu being also an austenite former, it has been found that (Ni + Cu) should be not more than 4 %.
Cr: Cr is an indispensable element to improve cor-rosion resistivity and oxidation resistivity. The reason of limiting Cr as not less than 17 o is that the addition 2 0 of at least 17 0 of Cr is required to keep a desired level of oxidation resistance at a temperature of at least higher 900 °C. In this view, the more Cr is, the better, but the addition of an excessive amount of Cr renders the steel brittle, and deteriorates workability 2 5 due to increase in hardness. Accordingly, the upper limit of Cr is now set as 25 0.
2o~s362 Nb: Nb is a necessary element to maintain high tem-perature strength. Furthermore, Nb improves workability and oxidation resistivity, and still brings about a fa-vorable influence in the manufacture of pipe by a high frequency welding method. The results of the tensile test at elevated temperatures, shown in Table 2 later on, reveal that at least 0.2 0 of Nb must be added to improve high temperature strength. However, Nb reacts and forms compounds with C and N, so that the Nb dissolved in the steel decreases and its effect on high temperature strength decreases also as far as the lower limit of Nb is merely set as 0.2%. Therefore, Nb must meet the con-dition that [Nb] expressed in the equation, 1 5 [Nb] - Nb a - 8 (C + N) o, is at least 0.20. On the other hand, when Nb is added in excess, welded parts become susceptible to high tempera-ture affected cracking. The upper limit of Nb is now set as 0.8 o so that sufficient high temperature strength may 2 0 be held and susceptibility to weld high temperature af-fected cracking may not be influenced so much.
Mo: As already stated, the more addition of Mo make high temperature strength to increase. Besides, Mo is 2 5 effective to improve high temperature oxidation resis-20~63~ ~?
is tance and corrosion resistivity. However, an excessive addition of it makes low temperature toughness as well as productivity and workability to decrease remarkably.
Therefore, Mo is restricted within the range from 1.0 0 s to 4.5 0, preferably from 2.0 o to 4.5 0, still more preferably within the range of more than 2.5 o and up to 4.5 a.
Cu: As mentioned previously, Cu is an important element of the steel according to the invention because of its remarkable effectiveness on toughness. As shown in Fig. 4, Cu is needed at least 0.1 o to achieve an ap-preciable improvement to toughness, so that the lower limit of Cu is now set as 0.1 0. On the contrary, the is addition of an excessive amount of Cu renders the steel hard and deteriorates its workability, in particular its hot workability, so that the upper limit of Cu is now set as 2.5 0.
2 0 A1: Al improves oxidation resistivity at elevated temperatures, but the addition of an excessive amount of A1 poses problems on productivity as well as weldability.
For this reason the upper limit of A1 is now set as 0.5 o.
2s 20563G~
Ti: Ti increases high temperature strength and im-proves workability. Like aluminum, the addition of an excessive amount of Ti, causes problems on productivity and weldability, so that the upper limit of Ti is now set as 0.5 V: Like Ti, V increases high temperature strength and improves workability, but the addition of an exces-sive amount of V invites reduction in strength.
Therefore, the upper limit of V is now set as 0.5 0.
Zr: Zr increases high temperature strength and im-proves oxidation resistance at elevated temperatures.
However, the addition of an excessive amount of Zr in-1$ vites reduction in strength. Therefore, the upper limit of Zr is now set as 1.0 0.
W: Similar to Ti and V, W increases high tempera-ture strength and improves workability, but the addition 2 0 of an excessive amount of W invites reduction in strength, so that the upper limit of W is now set as 1.5 o.
B: B improves hot workability, high temperature 2 5 strength and even workability. However, the addition of an excessive amount of B, adversely affects hot workabil-~~9~63G, ity, on the contrary, therefore the upper limit of B is now set as 0.01 0.
REM: Even in small quantity the addition of rare-earth metal improves hot-workability, oxidation resis-tance, particularly, adhesion of scale. However, the ad-dition of an excessive amount of REM adversely affects hot workability on the contrary. Therefore, the upper limit of REM is now set as 0.1 0.
Examples Table 1 shows chemical components, in % by weight, of the tested steels. Steels M1 to M21 are those in ac cordance with the invention, while Steels M22 to M30 are control steels. Each steel was made into a 30 kg ingot and forged to a rod having a diameter of 25 mm, or to a slab having a thickness of 25 mm. The rod was annealed at a temperature of from 950 °C. to 1100 °C., and test pieces for the high temperature tensile test in accor-2 0 dance with JIS were prepared from the annealed rod. The slab was cut into pieces, which were heated in a furnace, took out from the furnace at a temperature of 1200 °C., hot rolled to plates having a thickness of 5 mm and an-nealed at a temperature of from 950 °C. to 1100 °C.
2 5 Some of the annealed plates were as such worked to Charpy impact test pieces having a thickness of 4.5 mm, while 2o~s~s 1~
the others were made to cold plates having a thickness of 2 mm of 1.2 mm by repeating cold rolling and annealing.
The 2 mm plates were subjected to the high temperature oxidation test, while the 1.2 mm plates were subjected to the high temperature affected weld cracking test.
Table 2 shows tensile strength at elevated tempera-tures determined by the tensile test in accordance with JIS, amount of scale which splinters off by the oxidation test continued for 100 hours at 900 °C. and at 1000 °C., critical strain of weldment caused by the high tempera-ture affected cracking test which is previously de-scribed, and results of the Charpy impact test carried out on V-notched Charpy impact testing pieces of a thick-ness of 4.5 mm.
From the results of the tensile test shown in Table 2, it is understood that the addition of Nb, Mo and Ni increases high temperature strength and the conjoint ad-2 0 dition of Mo and Cu further improves high temperature strength. The results of the continuous high temperature oxidation tests carried out at 900° C. and at 1000 °C., indicate that resistivity of scale splintering off in-creases remarkably when Mn content exceeds 0.6 0. The 2 S critical strain caused by the test of high temperature affected weld cracking is highly improved when the ratio, zo~s~s Mn/S, is 200 or higher. The results of the Charpy impact test reveal that while impact toughness decreases by the addition of Mo, it is improved by the addition of Cu, and the same is true with the addition of Ni.
2~~~~~~
Zo Table 1 Chemical Components (wt.%) of Tested Steels Steel C Si Mn P S Ni Cr Nb Mo Cu N Other Mn/sNi+Cu[Nb]
M1 0.01120.950.810.0250.00310.3018.1.90.421.200.970.0128- 2791.130.23 M2 0.01180.400.700.0220.00290.2218.280.451.990.240.0113- 2910.960.27 M3 0.01900.250.630.0200.00300.2218.950.912.050.480.0107- 2100.700.21 M4 0.01210.251.920.0200.00350.2018.370.932.010.460.0113- 9060.660.29 M5 0.01060.900.790.0230.00330.2018.550.952. 0.490.0111- 2390. 0.28 M6 0.01060.370.780.0230.00280.2918.390.973.010.930.0113- 2791.170.29 M7 0.00970.430.790.0210.00270.2718.990.452.971.980.0103- 2932.250.29 M$ 0.01020.920.850.0200.00270.2218.420.962.952.990.010- 3152.660.29 M9 0.01360.980.690.0190.00261.4918.440.933.090.180.013- 2651.490.21 M100.01260.990.680.0170.00292.9818.570.933.020.190.011- 2832.980.29 A Mll0.01100.910.760.0230.00280.2718.310.963.920.520.010- 2710.790.28 M120.01080.920.760.0290.00290.2718.400.963.990.930.0109- 2621.200.29 M130.01140.380.730.0230.00270.2318.220.969.021.880.0112- 2702.110.28 M140.01050.920.790.0220.00280.2118.370.459.920.950.0109- 2821.160.28 M150.01070.390.920.0230.00390.2418.970.462.980.99O.O110A1:0.452360.730.29 M160.01160.420.790.0200.00280.2618.290.973.120.510.010Ti:0.172820.770.29 M170.01120.410.820.0220.00310.2218.360.993.060.500.0121V :0.262650.720.25 M180.01100.410.820.0220.00280.2618.370.963.060.96O.OlO12r:0.732930.720.29 M190.01020.380.850.0210.00330.2518.510.953.010.510.010W :0.892580.760.28 M200.00980.400.710.0210.00320.2018.900.982.990.990.0103B :0.0092220.690.32 M210.01250.410.760.0200.00280.2318.380.433.020.510.0105REM:0.052710.740.25 M220.01260.990.830.0260.00390.2017.950.460.180.130.0099- 2440.330.28 M230.00590.920.830.0210.00250.1918.370.900.220.990.0103- 3320.630.27 M240.01030.490.790.0220.00270.2917.230.910.250.890.0191- 2741.130.29 M250.00910.390.800.0190.00180.2318.370.99- - 0.0105- 9440.230.33 B M260.01200.250.390.0210.00230.2118.250.912.09- 0.0110- 1700.210.23 M270.01190.370.260.0230.00320.2218.350.932.090.920.010- 81 0.690.29 M280.01280. 0. 0.0290.00360.2018.990.052.060.350.0117- 1360.55-0.
M290.01320.980.900.0210.00280.2318.930. 3.02- 0.0107- 1430. 0 M300.01260.500.980.0220.00350.251.8.760.979.01- 0.0108- 2800.250.28 Note: [Nb] = Nb~ - $(Ca + N~) A: According to the invention B: Control 20~6J~~
Table 2 Properties of Tested Steels Amount Critical Steel Tensile of Strain Charpy strength scale upon impact at splin- Weldingstrength elevated tering (kg-m/cm2) tem- after peratures oxida-tion (k test /mm2) (mg/cmz) 700C 900C 900C 1000C( o) -25C 0C 25C
M1 21.7 4.2 0.07 0.12 4.7 18.9 20.2 24.2 M2 22.0 4.3 0.05 0.09 4.5 13.9 17.2 23.3 M3 22.2 4.4 0.04 0.08 4.0 19.0 21.7 27.6 M4 22.2 4.5 0.02 0.04 5.1 19.0 21.7 27.6 M5 22.4 4.6 0.01 0.03 3.9 10.3 11.0 18.9 M6 22.8 4.7 0.02 0.03 4.1 10.7 17.5 18.3 M7 23.1 4.8 0.01 0.04 4.4 6.4 13.6 16.9 M8 23.2 4.7 0.01 0.03 4.5 4.0 6.8 9.7 M9 22.5 4.8 0.01 0.04 4.1 5.9 13.9 17.8 M10 22.7 4.8 0.02 0.03 4.1 6.8 14.7 17.4 A M11 23.0 4.9 0.01 0.02 3.5 5.2 8.6 16.7 M12 23.3 5.0 0.01 0.02 3.7 7.1 14.9 16.3 M13 23.6 5.2 0.02 0.04 3.6 5.2 8.0 9.8 M14 23.4 5.1 0.01 0.03 3.7 6.2 9.7 12.3 M15 22.9 4.9 0.01 0.02 3.5 8.5 9.0 16.1 M16 21.9 4.7 0.02 0.03 4.3 9.2 10.7 17.2 M17 21.7 4.7 0.02 0.03 3.9 10.4 11.8 19.2 M18 21.9 4.8 0.01 0.03 4.3 10.2 13.1 19.7 M19 21.9 4.8 0.01 0.02 4.5 9.7 11.7 20.3 M20 21.8 4.7 0.01 0.02 3.7 10.1 10.9 19.1 M21 21.7 4.7 0.01 0.01 3.9 8.9 10.2 17.1 M22 19.4 3.1 0.10 0.22 3.9 15.6 21.1 25.5 M23 19.6 3.1 0.11 0.25 4.2 25.0 21.4 29.9 M24 20.0 3.2 0.11 0.28 4.4 18.1 19.3 23.2 M25 19.4 3.0 0.10 0.24 5.0 6.4 9.2 12.9 s M26 20.9 3.5 0.20 0.96 2.8 2.0 8.1 22.3 M27 19.1 2.9 0.32 1.32 2.0 17.9 20.5 22.3 M28 19.3 2.9 0.14 0.76 2.5 2.0 8.1 22.3 M29 22.3 4.6 0.16 0.66 1.9 1.9 6.0 6.7 M30 22.9 4.7 0.07 0.09 3.4 1.0 1.1 1.3 Note: A: According to the invention B: Control 20~6~6~
Having so described, the invention has provided a heat resistive ferritic stainless steel which achieves the above-mentioned object $ and which has excellent high temperature strength, resis-Lance to high temperature oxidation, resistance to high temperature affected weld cracking, improved low tempera-ture toughness, which is serious drawback of the ferritic stainless steel. Accordingly, the novel and useful mate-rial responsible to the progressive increase of power and capability of the engine has now been offered for an au-tomobile exhaust gas system, particularly, for a pipe be-tween an engine and a converter, which pipe is prepared by welding or jointed to other parts by welding.
2 0 Any stainless steel that is in conformity with the above-mentioned conditions becoming more and more severe according to the demands for a more powerful and capable engine and for the progress of a purification efficiency of an exhaust gas is not come out yet. In other words, a 2 S material which is economical and satisfies simultaneously various demands for properties such as high temperature s strength, oxidation resistance, heat resistance, tough-ness, weldability and workability is not yet obtainable from austinitic or the ferritic stainless steels nowa-days. If a ferritic stainless steel retaining the previ-ously stated desirable properties inherent to the fer-ritic stainless steel, and having improved heat resistiv-ity and high temperature strength and, in addition, being excellent in productivity, workability, weldability and low temperature toughness comes to be obtainable, it may be said that such a material is very promising for the particular use mentioned above.
JP A 64-8254 discloses a ferritic stainless steel for the like use, but is completely silent with respect to low temperature toughness. JP B 59-52226 and 61-44121 disclose to improve a ferritic stainless steel in its rust development due to chlorine ion and its acid resis-tivity by adding copper and nickel while extremely lower-ing S, but teach nothing about high temperature strength, 2 0 heat resistance, weldability and low temperature tough-ness.
Object of the Invention Accordingly, an object of the invention is to pro-vide a ferritic stainless steel having properties which 2 S simultaneously meet the above-mentioned many severe con-ditions required for a material of an automobile exhaust _ 246362 gas path-way, particularly, of a part between an engine and a converter where the material is exposed to high temperatures. Another object of the invention is to im-prove low temperature toughness, which is an inherent de-fect of ferritic stainless steels. A further object of the invention is the provision of a heat resistive fer-ritic stainless steel which does not suffer from a prob-lem of high temperature cracking of weld heat-affected zone.
Summary of the Invention The invention provides a heat resisting ferritic stainless steel excellent in low temperature toughness, weldability, and heat resistance which comprises, by 1 S weight, up to 0.03 0 of C, from 0.1 to 0.8 % of Si, from 0.6 to 2.0 % of Mn, up to 0.006 0 of S, 2 ~ up to 4 0 of Ni, from 17.0 to 25.0 0 of Cr, from 0.2 to 0.8 °s of Nb, from 1.0 to 4.5 0 of Mo, from 0.1 to 2.5 0 of Cu, and 2 S up to 0 . 03 0 of N, 20~6~6~
the balance being Fe and unavoidable impurities, wherein the alloying elements are further adjusted so that the ratio of Mno/So is not less than 200, [Nb] defined by the equation:
[Nb] - Nbo - 8 (Co + No) is not less than 0.2, and (Nio + Cuo) is not more than 4.
The invention further provides a heat resisting fer-ritic stainless steel excellent in low temperature tough-ness, weldability and heat resistance which comprises, in addition to the elements of the above-mentioned steel, one or more of:
up to 0.5 0 Al, of up to 0.6 0 Ti, of 1 $ up to 0.5 % V, of up to 1.0 0 Zr, of up to 1.5 0 W, of up to 0.01% B, and of up to 0.1 % REM.
of Brief Description of the Drawings Fig. 1 shows a relationship between molybdenum con-tent and tensile strength at the indicated elevated tem-~~~~3~
s peratures obtained by the elevated temperature tensile test noted below;
Fig. 2 shows a relationship between manganese con-s tent and amount of scale which has splintered off after the elevated temperature oxidation test noted below;
Fig. 3 shows a relationship between Mn/S and criti-cal strain obtained by the weld high temperature cracking test noted below; and Fig. 4 shows a relationship between copper content and Charpy impact strength obtained by the Charpy impact test at the indicated temperatures. The invention is 1S based on the results shown in these figures.
Detailed Description of the Invention After many experimental researches to achieve the object mentioned before, the inventors have been able to 2 0 obtain the following information.
Fig. 1 shows results of the tensile tests at the indicated elevated temperatures carried out on materials having a basic composition of Fe-18 o Cr-0.45 ~-Nb with 2 5 various Mo and Cu contents to examine effects of Mo and Cu on high temperature tensile strength. As seen from the figure, high temperature strength is improved by the addition of molybdenum in an amount of 1 0 or more.
Furthermore, the conjoint addition of molybdenum and cop-per is more effective than the addition of molybdenum alone to improve high temperature strength.
Fig. 2 shows results of the oxidation tests at the indicated elevated temperatures carried out on materials having a basic composition of Fe-18 % Cr-0.45 o-Nb with l~ various Mn contents. The oxidation was continued in air for 100 hrs at 900 °C. or 1000 °C., and at the end of the period an amount of scale which had splintered off was measured. As seen from the figure, the scale splintering was suppressed, irrespective of the oxidation temperature tested, by the addition of at least about 0.6 % of man-ganese. Thus, it can be understood that, as for the fer-ritic stainless steel, manganese makes the limit of oxi-dation resistivity to rise up.
2 0 Fig. 3 shows results of the weld high temperature affected cracking test on materials having a basic compo-sition of Fe-18 o Cr-0.45 %-Nb with appropriate Mo and Cu contents whose effects are recognized as shown in Fig. 1 (3 o Mo and 0.5 o Cu) and with varied Mn and S contents 2 5 to examine effects of the ratio, Mn/S, on weld high tem-perature affected cracking. The test was carried out as 20~63~
to follows. The cold rolled and annealed plate of 1.2 mm in thickness was cut into test pieces of 40 mm x 200 m. The test pieces were TIG welded under various tensile stresses imposed longitudinally. The minimum strain at which cracking began to occur was determined, which is referred to herein as the critical strain and is a mea-sure of the susceptibility to the weld high temperature affected cracking. It is revealed from Fig. 3 that if the ratio, Mn/S, is 200 or higher, ferritic stainless steels having conjointly incorporated with Mo and Cu have an increased critical strain, and, in consequence, an im-proved weldability. Thus, in order to overcome the weld high temperature affected cracking it is effective to add a proper amount of Mn rendering the ratio, Mn/S, not less than 200.
Fig. 4 shows results of the Charpy impact test car-ried out on materials having a basic composition of Fe-18 o Cr-0.45 o-Nb with varied Mo and Cu contents for examin-2 0 ing effects of molybdenum and copper on toughness. The impact value is lowered by the addition of molybdenum, as is known in the art. However, Fig. 4 provides new infor-mation that the reduction in the impact value due to Mo may be compensated to some extent by conjoint addition of 2 5 Cu. Particularly, even with such a material as a steel containing 4 ~ of molybdenum whose impact toughness is 20~63G j remarkably low, the conjoint addition of copper improves the impact value well enough. Furthermore, the conjoint addition of nickel and molybdenum can also improve low temperature impact toughness, as will be manifested in Examples described later. The information of these facts is of great importance, particularly for a material which constitutes parts exposed to low temperature circumstance in winter, for example, a manifold or dual tube which suffer from mechanical vibration in addition to low tem-perature when the engine starts, whereupon the material will become usable even under further more severe condi-tions expected in the future.
Based on the information noted above, the invention provides a ferritic stainless steel having well-balanced excellent properties as a whole, including high tempera-ture strength, thermal fatigue resistance, oxidation re-sistance and low temperature toughness.
2 0 The reasons for the restriction of each chemical component in the steel according to the invention will now be outlined.
C and N: C and N are, in general, important ele-2 5 ments because of promoting high temperature strength, but excessive amounts of them demote oxidation resistance, ~o~s~~~
workability and toughness. Besides above, C and N react and form compounds with Nb, thereby lowering the effec-tive Nb in the ferritic phase. Accordingly, it is favor-able that C and N are small in quantities, so that they should be controlled not more than 0.03 0, respectively.
Si: Si is an effective element to improve oxidation resistance, but an excessive amount of Si renders the steel hard, and, in consequence, adversely affects worka-bility and toughness. Therefore, Si is controlled within the range from 0.1 o to 0.8 0.
Mn: Mn reacts with S, which is harmful for weld high temperature affected cracking, and fixes S in the form of MnS, whereby S is removed or reduced in welded metal . It has been found that if the relation, Mn/S > 200, is sat-isfied, the effect is the same as that of S reduction.
On the other hand, the addition of at least 0.6 0 of Mn improves adhesion of scale Therefore, Mn is controlled 2 0 in the range from 0.6 o to 2.0 0, while satisfying the relation: Mn/S > 200.
S: As previously stated, since S is harmful to the weld high temperature affected cracking, it is desirable 2 S that S is as small as possible in quantity. However, the smaller S is, the more the cost is needed for the produc-205636 ~
tion. Even if S remains up to 0.006 0, enough durability to the weld high temperature affected cracking is held on the steel of this invention due to the effect of Mn, so that the upper limit of S is now set as 0.006 0.
Ni: As illustrated in Examples, Ni brings about a favorable result of improving toughness like copper does.
However, an excessive of Ni gives rise to deposition of an austenite phase at elevated temperatures, and follows the increase of thermal expansion coefficient as well as anxiety about the deterioration of thermal fatigue.
Therefore, in the case of the conjoint addition of Ni and Cu according to the invention, the Cu being also an austenite former, it has been found that (Ni + Cu) should be not more than 4 %.
Cr: Cr is an indispensable element to improve cor-rosion resistivity and oxidation resistivity. The reason of limiting Cr as not less than 17 o is that the addition 2 0 of at least 17 0 of Cr is required to keep a desired level of oxidation resistance at a temperature of at least higher 900 °C. In this view, the more Cr is, the better, but the addition of an excessive amount of Cr renders the steel brittle, and deteriorates workability 2 5 due to increase in hardness. Accordingly, the upper limit of Cr is now set as 25 0.
2o~s362 Nb: Nb is a necessary element to maintain high tem-perature strength. Furthermore, Nb improves workability and oxidation resistivity, and still brings about a fa-vorable influence in the manufacture of pipe by a high frequency welding method. The results of the tensile test at elevated temperatures, shown in Table 2 later on, reveal that at least 0.2 0 of Nb must be added to improve high temperature strength. However, Nb reacts and forms compounds with C and N, so that the Nb dissolved in the steel decreases and its effect on high temperature strength decreases also as far as the lower limit of Nb is merely set as 0.2%. Therefore, Nb must meet the con-dition that [Nb] expressed in the equation, 1 5 [Nb] - Nb a - 8 (C + N) o, is at least 0.20. On the other hand, when Nb is added in excess, welded parts become susceptible to high tempera-ture affected cracking. The upper limit of Nb is now set as 0.8 o so that sufficient high temperature strength may 2 0 be held and susceptibility to weld high temperature af-fected cracking may not be influenced so much.
Mo: As already stated, the more addition of Mo make high temperature strength to increase. Besides, Mo is 2 5 effective to improve high temperature oxidation resis-20~63~ ~?
is tance and corrosion resistivity. However, an excessive addition of it makes low temperature toughness as well as productivity and workability to decrease remarkably.
Therefore, Mo is restricted within the range from 1.0 0 s to 4.5 0, preferably from 2.0 o to 4.5 0, still more preferably within the range of more than 2.5 o and up to 4.5 a.
Cu: As mentioned previously, Cu is an important element of the steel according to the invention because of its remarkable effectiveness on toughness. As shown in Fig. 4, Cu is needed at least 0.1 o to achieve an ap-preciable improvement to toughness, so that the lower limit of Cu is now set as 0.1 0. On the contrary, the is addition of an excessive amount of Cu renders the steel hard and deteriorates its workability, in particular its hot workability, so that the upper limit of Cu is now set as 2.5 0.
2 0 A1: Al improves oxidation resistivity at elevated temperatures, but the addition of an excessive amount of A1 poses problems on productivity as well as weldability.
For this reason the upper limit of A1 is now set as 0.5 o.
2s 20563G~
Ti: Ti increases high temperature strength and im-proves workability. Like aluminum, the addition of an excessive amount of Ti, causes problems on productivity and weldability, so that the upper limit of Ti is now set as 0.5 V: Like Ti, V increases high temperature strength and improves workability, but the addition of an exces-sive amount of V invites reduction in strength.
Therefore, the upper limit of V is now set as 0.5 0.
Zr: Zr increases high temperature strength and im-proves oxidation resistance at elevated temperatures.
However, the addition of an excessive amount of Zr in-1$ vites reduction in strength. Therefore, the upper limit of Zr is now set as 1.0 0.
W: Similar to Ti and V, W increases high tempera-ture strength and improves workability, but the addition 2 0 of an excessive amount of W invites reduction in strength, so that the upper limit of W is now set as 1.5 o.
B: B improves hot workability, high temperature 2 5 strength and even workability. However, the addition of an excessive amount of B, adversely affects hot workabil-~~9~63G, ity, on the contrary, therefore the upper limit of B is now set as 0.01 0.
REM: Even in small quantity the addition of rare-earth metal improves hot-workability, oxidation resis-tance, particularly, adhesion of scale. However, the ad-dition of an excessive amount of REM adversely affects hot workability on the contrary. Therefore, the upper limit of REM is now set as 0.1 0.
Examples Table 1 shows chemical components, in % by weight, of the tested steels. Steels M1 to M21 are those in ac cordance with the invention, while Steels M22 to M30 are control steels. Each steel was made into a 30 kg ingot and forged to a rod having a diameter of 25 mm, or to a slab having a thickness of 25 mm. The rod was annealed at a temperature of from 950 °C. to 1100 °C., and test pieces for the high temperature tensile test in accor-2 0 dance with JIS were prepared from the annealed rod. The slab was cut into pieces, which were heated in a furnace, took out from the furnace at a temperature of 1200 °C., hot rolled to plates having a thickness of 5 mm and an-nealed at a temperature of from 950 °C. to 1100 °C.
2 5 Some of the annealed plates were as such worked to Charpy impact test pieces having a thickness of 4.5 mm, while 2o~s~s 1~
the others were made to cold plates having a thickness of 2 mm of 1.2 mm by repeating cold rolling and annealing.
The 2 mm plates were subjected to the high temperature oxidation test, while the 1.2 mm plates were subjected to the high temperature affected weld cracking test.
Table 2 shows tensile strength at elevated tempera-tures determined by the tensile test in accordance with JIS, amount of scale which splinters off by the oxidation test continued for 100 hours at 900 °C. and at 1000 °C., critical strain of weldment caused by the high tempera-ture affected cracking test which is previously de-scribed, and results of the Charpy impact test carried out on V-notched Charpy impact testing pieces of a thick-ness of 4.5 mm.
From the results of the tensile test shown in Table 2, it is understood that the addition of Nb, Mo and Ni increases high temperature strength and the conjoint ad-2 0 dition of Mo and Cu further improves high temperature strength. The results of the continuous high temperature oxidation tests carried out at 900° C. and at 1000 °C., indicate that resistivity of scale splintering off in-creases remarkably when Mn content exceeds 0.6 0. The 2 S critical strain caused by the test of high temperature affected weld cracking is highly improved when the ratio, zo~s~s Mn/S, is 200 or higher. The results of the Charpy impact test reveal that while impact toughness decreases by the addition of Mo, it is improved by the addition of Cu, and the same is true with the addition of Ni.
2~~~~~~
Zo Table 1 Chemical Components (wt.%) of Tested Steels Steel C Si Mn P S Ni Cr Nb Mo Cu N Other Mn/sNi+Cu[Nb]
M1 0.01120.950.810.0250.00310.3018.1.90.421.200.970.0128- 2791.130.23 M2 0.01180.400.700.0220.00290.2218.280.451.990.240.0113- 2910.960.27 M3 0.01900.250.630.0200.00300.2218.950.912.050.480.0107- 2100.700.21 M4 0.01210.251.920.0200.00350.2018.370.932.010.460.0113- 9060.660.29 M5 0.01060.900.790.0230.00330.2018.550.952. 0.490.0111- 2390. 0.28 M6 0.01060.370.780.0230.00280.2918.390.973.010.930.0113- 2791.170.29 M7 0.00970.430.790.0210.00270.2718.990.452.971.980.0103- 2932.250.29 M$ 0.01020.920.850.0200.00270.2218.420.962.952.990.010- 3152.660.29 M9 0.01360.980.690.0190.00261.4918.440.933.090.180.013- 2651.490.21 M100.01260.990.680.0170.00292.9818.570.933.020.190.011- 2832.980.29 A Mll0.01100.910.760.0230.00280.2718.310.963.920.520.010- 2710.790.28 M120.01080.920.760.0290.00290.2718.400.963.990.930.0109- 2621.200.29 M130.01140.380.730.0230.00270.2318.220.969.021.880.0112- 2702.110.28 M140.01050.920.790.0220.00280.2118.370.459.920.950.0109- 2821.160.28 M150.01070.390.920.0230.00390.2418.970.462.980.99O.O110A1:0.452360.730.29 M160.01160.420.790.0200.00280.2618.290.973.120.510.010Ti:0.172820.770.29 M170.01120.410.820.0220.00310.2218.360.993.060.500.0121V :0.262650.720.25 M180.01100.410.820.0220.00280.2618.370.963.060.96O.OlO12r:0.732930.720.29 M190.01020.380.850.0210.00330.2518.510.953.010.510.010W :0.892580.760.28 M200.00980.400.710.0210.00320.2018.900.982.990.990.0103B :0.0092220.690.32 M210.01250.410.760.0200.00280.2318.380.433.020.510.0105REM:0.052710.740.25 M220.01260.990.830.0260.00390.2017.950.460.180.130.0099- 2440.330.28 M230.00590.920.830.0210.00250.1918.370.900.220.990.0103- 3320.630.27 M240.01030.490.790.0220.00270.2917.230.910.250.890.0191- 2741.130.29 M250.00910.390.800.0190.00180.2318.370.99- - 0.0105- 9440.230.33 B M260.01200.250.390.0210.00230.2118.250.912.09- 0.0110- 1700.210.23 M270.01190.370.260.0230.00320.2218.350.932.090.920.010- 81 0.690.29 M280.01280. 0. 0.0290.00360.2018.990.052.060.350.0117- 1360.55-0.
M290.01320.980.900.0210.00280.2318.930. 3.02- 0.0107- 1430. 0 M300.01260.500.980.0220.00350.251.8.760.979.01- 0.0108- 2800.250.28 Note: [Nb] = Nb~ - $(Ca + N~) A: According to the invention B: Control 20~6J~~
Table 2 Properties of Tested Steels Amount Critical Steel Tensile of Strain Charpy strength scale upon impact at splin- Weldingstrength elevated tering (kg-m/cm2) tem- after peratures oxida-tion (k test /mm2) (mg/cmz) 700C 900C 900C 1000C( o) -25C 0C 25C
M1 21.7 4.2 0.07 0.12 4.7 18.9 20.2 24.2 M2 22.0 4.3 0.05 0.09 4.5 13.9 17.2 23.3 M3 22.2 4.4 0.04 0.08 4.0 19.0 21.7 27.6 M4 22.2 4.5 0.02 0.04 5.1 19.0 21.7 27.6 M5 22.4 4.6 0.01 0.03 3.9 10.3 11.0 18.9 M6 22.8 4.7 0.02 0.03 4.1 10.7 17.5 18.3 M7 23.1 4.8 0.01 0.04 4.4 6.4 13.6 16.9 M8 23.2 4.7 0.01 0.03 4.5 4.0 6.8 9.7 M9 22.5 4.8 0.01 0.04 4.1 5.9 13.9 17.8 M10 22.7 4.8 0.02 0.03 4.1 6.8 14.7 17.4 A M11 23.0 4.9 0.01 0.02 3.5 5.2 8.6 16.7 M12 23.3 5.0 0.01 0.02 3.7 7.1 14.9 16.3 M13 23.6 5.2 0.02 0.04 3.6 5.2 8.0 9.8 M14 23.4 5.1 0.01 0.03 3.7 6.2 9.7 12.3 M15 22.9 4.9 0.01 0.02 3.5 8.5 9.0 16.1 M16 21.9 4.7 0.02 0.03 4.3 9.2 10.7 17.2 M17 21.7 4.7 0.02 0.03 3.9 10.4 11.8 19.2 M18 21.9 4.8 0.01 0.03 4.3 10.2 13.1 19.7 M19 21.9 4.8 0.01 0.02 4.5 9.7 11.7 20.3 M20 21.8 4.7 0.01 0.02 3.7 10.1 10.9 19.1 M21 21.7 4.7 0.01 0.01 3.9 8.9 10.2 17.1 M22 19.4 3.1 0.10 0.22 3.9 15.6 21.1 25.5 M23 19.6 3.1 0.11 0.25 4.2 25.0 21.4 29.9 M24 20.0 3.2 0.11 0.28 4.4 18.1 19.3 23.2 M25 19.4 3.0 0.10 0.24 5.0 6.4 9.2 12.9 s M26 20.9 3.5 0.20 0.96 2.8 2.0 8.1 22.3 M27 19.1 2.9 0.32 1.32 2.0 17.9 20.5 22.3 M28 19.3 2.9 0.14 0.76 2.5 2.0 8.1 22.3 M29 22.3 4.6 0.16 0.66 1.9 1.9 6.0 6.7 M30 22.9 4.7 0.07 0.09 3.4 1.0 1.1 1.3 Note: A: According to the invention B: Control 20~6~6~
Having so described, the invention has provided a heat resistive ferritic stainless steel which achieves the above-mentioned object $ and which has excellent high temperature strength, resis-Lance to high temperature oxidation, resistance to high temperature affected weld cracking, improved low tempera-ture toughness, which is serious drawback of the ferritic stainless steel. Accordingly, the novel and useful mate-rial responsible to the progressive increase of power and capability of the engine has now been offered for an au-tomobile exhaust gas system, particularly, for a pipe be-tween an engine and a converter, which pipe is prepared by welding or jointed to other parts by welding.
Claims (5)
1. A heat resisting ferritic stainless steel excellent in low temperature toughness, weldability, and heat resistance which comprises, by weight, 0 to 0.03% of C, from 0.1 to 0.8% of Si, from 0.6 to 2.0% of Mn, 0 to 0.006% of S, 0 to 4% of Ni, from 17.0 to 25.0% of Cr, from 0.2 to 0.8 % of Nb, from 1.0 to 4.5% of Mo, from 0.1 to 2.5% of Cu, and 0 to 0.03% of N, the balance being Fe and unavoidable impurities, wherein the alloying elements are further adjusted so that the ratio of Mn%/S% is not less than 200, [Nb] defined by the equation:
[Nb] = Nb% - 8 (C% + N%) is not less than 0.2, and (Ni% + Cu%) is not more than 4.
[Nb] = Nb% - 8 (C% + N%) is not less than 0.2, and (Ni% + Cu%) is not more than 4.
2. The heat resisting ferritic stainless steel in accordance with claim 1 which contains molybdenum in an amount of more than 2.5%.
3. A heat resisting ferritic stainless steel excellent in low temperature toughness, weldability and heat resistance which comprises, by weight, 0 to 0.03% of C, from 0.1 to 0.8% of Si, from 0.6 to 2.0% of Mn, 0 to 0.006% of S, 0 to 4% of Ni, from 17.0 to 25.0% of Cr, from 0.2 to 0.8% of Nb, from 1.0 to 4.5% of Mo, from 0.1 to 2.5% of Cu, 0 to 0.03% of N, 0 to 0.5% of Al, 0 to 0.6% of Ti, 0 to 0.5% of V, 0 to 1.0% of Zr, 0 to 1.5% of W, 0 to 0.01% of B, and 0 to 0.1% of REM, the balance being Fe and unavoidable impurities, wherein the alloying elements are further adjusted so that the ratio of Mn%/S% is not less than 200, [Nb] defined by the equation:
[Nb] = Nb% - 8 (C% + N%) is not less than 0.2, and (Ni% + Cu%) is not more than 4.
[Nb] = Nb% - 8 (C% + N%) is not less than 0.2, and (Ni% + Cu%) is not more than 4.
4. The heat resisting ferritic stainless steel in accordance with claim 3 which contains molybdenum in an amount of more than 2.5%.
5. The heat resisting ferritic stainless steel in accordance with any one of claims 1 to 4 for use in constructing an exhaust gas pipe from an engine to an exhaust gas purifying instrument.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP74785/1990 | 1990-03-24 | ||
| JP2074785A JP2696584B2 (en) | 1990-03-24 | 1990-03-24 | Ferrite heat-resistant stainless steel with excellent low-temperature toughness, weldability and heat resistance |
| PCT/JP1991/000344 WO1991014796A1 (en) | 1990-03-24 | 1991-03-13 | Heat-resistant ferritic stainless steel excellent in low-temperature toughness, weldability and heat resistance |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2056362A1 CA2056362A1 (en) | 1991-09-25 |
| CA2056362C true CA2056362C (en) | 2001-08-28 |
Family
ID=13557292
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002056362A Expired - Lifetime CA2056362C (en) | 1990-03-24 | 1991-03-13 | Heat resisting ferritic stainless steel excellent in low temperature toughness, weldability and heat resistance |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0478790B1 (en) |
| JP (1) | JP2696584B2 (en) |
| KR (1) | KR0180206B1 (en) |
| CA (1) | CA2056362C (en) |
| DE (1) | DE69110816T2 (en) |
| WO (1) | WO1991014796A1 (en) |
Families Citing this family (32)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2085790C (en) * | 1991-12-19 | 2000-03-28 | Masao Koike | Steel for use in exhaust manifolds of automobiles |
| EP0593776B1 (en) * | 1992-04-09 | 2001-08-16 | Nippon Steel Corporation | Ferritic stainless steel with excellent high-temperature salt injury resistance and high-temperature strength |
| MY118759A (en) * | 1995-12-15 | 2005-01-31 | Nisshin Steel Co Ltd | Use of a stainless steel as an anti-microbial member in a sanitary environment |
| FR2746114B1 (en) * | 1996-03-15 | 1998-04-24 | PROCESS FOR PRODUCING FERRITIC STAINLESS STEEL HAVING IMPROVED CORROSION RESISTANCE, IN PARTICULAR INTERGRANULAR AND PITCH CORROSION RESISTANCE | |
| KR20000034395A (en) * | 1998-11-30 | 2000-06-26 | 이구택 | Ferrite type stainless steel excellent in toughness in welding unit |
| KR100605678B1 (en) * | 1999-11-08 | 2006-07-31 | 주식회사 포스코 | A heat resistant stainless steel having good heat resistant strength |
| DE60100880T2 (en) | 2000-07-25 | 2004-09-02 | Kawasaki Steel Corp., Kobe | Ferritic stainless steel with good ductility at room temperature and with good mechanical properties at higher temperatures, and methods of manufacturing the same |
| EP1413640B1 (en) * | 2001-07-05 | 2005-05-25 | Nisshin Steel Co., Ltd. | Ferritic stainless steel for member of exhaust gas flow passage |
| CN1308477C (en) * | 2003-10-31 | 2007-04-04 | 烨联钢铁股份有限公司 | Rich granule iron series stainless steel with good hot work ability and antibacterial effect |
| EP1818421A1 (en) * | 2006-02-08 | 2007-08-15 | UGINE & ALZ FRANCE | Ferritic, niobium-stabilised 19% chromium stainless steel |
| JP4948998B2 (en) * | 2006-12-07 | 2012-06-06 | 日新製鋼株式会社 | Ferritic stainless steel and welded steel pipe for automotive exhaust gas flow path members |
| CN100485077C (en) * | 2007-06-13 | 2009-05-06 | 陈卫东 | Ultrathin alloy material hose and producing method thereof |
| JP5178157B2 (en) | 2007-11-13 | 2013-04-10 | 日新製鋼株式会社 | Ferritic stainless steel material for automobile exhaust gas path members |
| JP5428396B2 (en) * | 2008-03-07 | 2014-02-26 | Ｊｆｅスチール株式会社 | Ferritic stainless steel with excellent heat resistance and weldability |
| US20110110812A1 (en) * | 2008-07-23 | 2011-05-12 | Nobulhiko Hiraide | Ferrite stainless steel for use in producing urea water tank |
| JP5462583B2 (en) * | 2008-10-24 | 2014-04-02 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel sheet for EGR cooler |
| EP2460899A4 (en) * | 2009-07-27 | 2014-07-09 | Nisshin Steel Co Ltd | Ferritic stainless steel for egr cooler and egr cooler |
| KR20120099152A (en) | 2010-03-11 | 2012-09-06 | 닛폰 스틸 앤드 스미킨 스테인레스 스틸 코포레이션 | Highly oxidation-resistant ferrite stainless steel plate, highly heat-resistant ferrite stainless steel plate, and manufacturing method therefor |
| JP5609571B2 (en) * | 2010-11-11 | 2014-10-22 | Ｊｆｅスチール株式会社 | Ferritic stainless steel with excellent oxidation resistance |
| US9399809B2 (en) | 2011-02-08 | 2016-07-26 | Nippon Steel & Sumikin Stainless Steel Corporation | Hot rolled ferritic stainless steel sheet, method for producing same, and method for producing ferritic stainless steel sheet |
| JP5703075B2 (en) * | 2011-03-17 | 2015-04-15 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel plate with excellent heat resistance |
| KR20140117476A (en) * | 2012-01-30 | 2014-10-07 | 제이에프이 스틸 가부시키가이샤 | Ferritic stainless steel foil |
| JP6037882B2 (en) | 2012-02-15 | 2016-12-07 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel sheet with excellent scale peel resistance and method for producing the same |
| JP6071608B2 (en) * | 2012-03-09 | 2017-02-01 | 新日鐵住金ステンレス株式会社 | Ferritic stainless steel plate with excellent oxidation resistance |
| JP5793459B2 (en) | 2012-03-30 | 2015-10-14 | 新日鐵住金ステンレス株式会社 | Heat-resistant ferritic stainless steel cold-rolled steel sheet excellent in workability, ferritic stainless hot-rolled steel sheet for cold-rolled material, and production method thereof |
| FI125855B (en) | 2012-06-26 | 2016-03-15 | Outokumpu Oy | Ferritic stainless steel |
| KR101692660B1 (en) | 2013-03-06 | 2017-01-03 | 닛폰 스틸 앤드 스미킨 스테인레스 스틸 코포레이션 | Ferritic stainless steel sheet having excellent heat resistance |
| CN105051234B (en) * | 2013-03-27 | 2017-05-10 | 新日铁住金不锈钢株式会社 | Hot-rolled ferritic stainless-steel plate, process for producing same, and steel strip |
| KR102206415B1 (en) | 2016-09-02 | 2021-01-22 | 제이에프이 스틸 가부시키가이샤 | Ferritic stainless steel |
| WO2018216236A1 (en) | 2017-05-26 | 2018-11-29 | Ｊｆｅスチール株式会社 | Ferritic stainless steel |
| EP3670692B1 (en) | 2018-12-21 | 2022-08-10 | Outokumpu Oyj | Ferritic stainless steel |
| CN112458379A (en) * | 2020-10-30 | 2021-03-09 | 萍乡德博科技股份有限公司 | Material suitable for variable-section nozzle ring disc parts of gasoline engine |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2701329C2 (en) * | 1977-01-14 | 1983-03-24 | Thyssen Edelstahlwerke AG, 4000 Düsseldorf | Corrosion-resistant ferritic chrome-molybdenum-nickel steel |
| JPS53118218A (en) * | 1977-03-25 | 1978-10-16 | Nippon Steel Corp | Stainless steel use in apparatus for purifying automotive exhaust gas |
| US4286986A (en) * | 1979-08-01 | 1981-09-01 | Allegheny Ludlum Steel Corporation | Ferritic stainless steel and processing therefor |
| CA1184402A (en) * | 1980-04-11 | 1985-03-26 | Sumitomo Metal Industries, Ltd. | Ferritic stainless steel having good corrosion resistance |
| US4391635A (en) * | 1980-09-22 | 1983-07-05 | Kubota, Ltd. | High Cr low Ni two-phased cast stainless steel |
| US4331474A (en) * | 1980-09-24 | 1982-05-25 | Armco Inc. | Ferritic stainless steel having toughness and weldability |
| FR2589482B1 (en) * | 1985-11-05 | 1987-11-27 | Ugine Gueugnon Sa | STAINLESS STEEL FERRITIC STEEL SHEET OR STRIP, ESPECIALLY FOR EXHAUST SYSTEMS |
| JP2514367B2 (en) * | 1987-06-27 | 1996-07-10 | 日新製鋼株式会社 | Automotive engine manifold steel |
| US4834808A (en) * | 1987-09-08 | 1989-05-30 | Allegheny Ludlum Corporation | Producing a weldable, ferritic stainless steel strip |
| JPH02145752A (en) * | 1988-11-28 | 1990-06-05 | Toshiba Corp | Ferritic stainless steel |
-
1990
- 1990-03-24 JP JP2074785A patent/JP2696584B2/en not_active Expired - Lifetime
-
1991
- 1991-03-13 DE DE69110816T patent/DE69110816T2/en not_active Expired - Fee Related
- 1991-03-13 CA CA002056362A patent/CA2056362C/en not_active Expired - Lifetime
- 1991-03-13 EP EP91906263A patent/EP0478790B1/en not_active Expired - Lifetime
- 1991-03-13 WO PCT/JP1991/000344 patent/WO1991014796A1/en active IP Right Grant
- 1991-03-13 KR KR1019910701642A patent/KR0180206B1/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| DE69110816T2 (en) | 1995-11-30 |
| KR920702434A (en) | 1992-09-04 |
| EP0478790A1 (en) | 1992-04-08 |
| KR0180206B1 (en) | 1999-02-18 |
| CA2056362A1 (en) | 1991-09-25 |
| EP0478790B1 (en) | 1995-06-28 |
| EP0478790A4 (en) | 1992-08-12 |
| WO1991014796A1 (en) | 1991-10-03 |
| DE69110816D1 (en) | 1995-08-03 |
| JP2696584B2 (en) | 1998-01-14 |
| JPH03274245A (en) | 1991-12-05 |
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