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  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/001—Austenite
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  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/008—Martensite

Definitions

• the present invention relates to a metal material and processing method therefor, in particular to a martensitic stainless steel and manufacturing process therefor.
• Martensitic stainless steel is a chromium-based stainless steel that is widely used in fields such as cutters, gauges, turbine blades, etc. where toughness and corrosion resistance are required.
• the low-carbon martensitic stainless steel having both a relatively high hardness (30 ⁇ 40 HRC) and good toughness (Charpy V-notch impact energy is more than 30 J) are usually required by the users.
• the strength and hardness after heat treatment are mainly increased by adding carbon element. However, increasing the carbon content lowers the toughness, so high strength and high toughness are always two properties that martensitic steel cannot have simultaneously.
• the Chinese patent CN101906587A provides a low-carbon martensitic stainless steel for a brake disc, wherein the stainless steel having a high strength and toughness by using a low carbon content (0.03 ⁇ 0.1 wt %) and a high manganese content (1 ⁇ 2.5 wt %).
• the patent controls silicon as less than 0.5% by weight of an impurity element, thereby the high temperature oxidation resistance of the invention is relatively poor.
• Chinese patent CN103255340B proposes a high-strength hot-formed steel plate and a preparation method thereof to overcome the problem of high strength and insufficient toughness after the formation of the high-strength automobile steel, wherein the steel plate is heated to an austenitizing temperature at a heating speed of 20-100° C./s.
• the steel plate was kept at the austenitizing temperature for a period of time and subjected to a hot-rolling, and thereby the austenite grains were refined; and then the plate quenched to 50-370° C. at a speed of 50-120° C./s to obtain partially supersaturated martensite and untransformed residual austenite; and then the plate was maintained a tempering temperature of 200-500° C. for 5-600 s, to partition the carbon is from martensite to residual austenite to stabilize austenite; finally the plate was quenched to room temperature to obtain a complex phase structure of refined martensite and residual austenite.
• high strength and high toughness steel can be obtained.
• Such method of quenching and partitioning to arrive at a complex phase structure and a combination of high strength and high toughness has been widely used in carbon steels.
• a formulation of steel is proposed in CN103160680A, wherein a complex phase structure of refined martensite and residual austenite was obtained using a combinative quenching technique.
• the steel had a strength-ductility product index of more than 30 GP wt %;
• CN103243275B proposes a low-alloy high-strength steel, wherein a complex phase structure of bainite, martensite and austenite was obtained through the partitioning and tempering treatment, having a good combination of strength and ductility;
• CN103045950B also proposes a low-alloying low-cost steel, wherein the strength of the steel was increased and strength was maintained through rapid quenching and carbon repartitioning. Quenching and partitioning method is not often used in stainless steel.
• CN103614649B proposes a martensitic stainless steel comprising a carbon content of 0.15-0.4 wt %, a nitrogen content of 0-0.12 wt % and a chromium content of 13.0-17.0 wt %, a Ni content of 0-5%, a molybdenum content of 0-2.0 wt %, wherein the stainless steel was made as follows: a hot-rolled slab made from conventional materials was heated to 950-1100° C. and insulated for 0.5-2 h, and then air-cooled to 25-200° C., then heated to 350-500° C. and insulated for 10-60 min, air-cooled to room temperature. In the process, through quenching and partitioning method was used to disperse the residual austenite into the microstructure, and thereby significantly increased the strength and ductility of the martensitic stainless.
• the first object of the present invention is to provide a martensitic stainless steel having a specific composition.
• the martensitic stainless steel has a high hardness and high toughness and has excellent high-temperature oxidation resistance.
• the present invention provides a martensitic stainless steel
• the mass ratio of chemical elements is C: 0.01 ⁇ 0.18 wt %, Si: 0.4 ⁇ 1.5 wt %, Mn: 0.4 ⁇ 3.0 wt %
• P ⁇ 0.04 wt %
• S 0.002 ⁇ 0.01 wt %
• Cr 11.0 ⁇ 15.0 wt %
• N 0.01 ⁇ 0.15 wt %
• Nb 0.001 ⁇ 0.01 wt %
• V 0.05 ⁇ 0.25 wt %
• Mo 0.01 ⁇ 1.50 wt %
• B 0.0005 ⁇ 0.001 wt %
• balance Fe and other unavoidable impurities.
• the mass ratio of chemical elements is C: 0.03 ⁇ 0.15 wt %, Si: 0.53 ⁇ 1.25 wt %, Mn: 0.45 ⁇ 2.45 wt %, Cr: 11.2 ⁇ 14.5 wt %, N: 0.01 ⁇ 0.08 wt %, Nb: 0.001 ⁇ 0.007 wt %, V: 0.05 ⁇ 0.23 wt %, Ti: 0.002 ⁇ 0.008 wt %, Mo: 0.01 ⁇ 1.10 wt %, B: 0.0005 ⁇ 0.0009 wt %, and balance being Fe and other unavoidable impurities.
• the mass ratio of chemical elements satisfies a relationship: 0.02 wt % ⁇ C+N ⁇ 0.20 wt %.
• the mass ratio of chemical elements satisfies a relationship: V+Ti+Nb ⁇ 0.25 wt %.
• the microstructure of the martensitic stainless steel is a complex phase structure of martensite and residual austenite.
• the phase ratio of the martensite is 55 ⁇ 65%, and the phase ratio of the residual austenite is 35 ⁇ 45%.
• the martensitic stainless steel is prepared by the following steps:
• the present invention provides a martensitic stainless steel, being an alloy system of C—Si—Mn—Cr—N—Nb—V—Ti—Mo—B.
• the chemical composition of the stainless steel makes the stainless steel have a high hardness, high toughness and excellent oxidation resistance.
• the rationale for the specific chemical composition is as follows:
• C it is an important austenitizing element. Certain carbon content ensures that a complete austenite structure can be obtained at high temperature. It is also an important element for ensuring the hardness after heat treatment. Carbon is an important solid solution strengthening element and precipitation strengthening element. It can exist in a form of interstitial atoms in the steel. During the reheating process after quenching, repartitioning of carbon can be accomplished by interphase diffusion to stabilize the residual austenite structure.
• the carbon in the present invention is used in combination with nitrogen element and having a content of 0.01 ⁇ 0.18 wt %, and preferably 0.03 ⁇ 0.15 wt %.
• N Similarly with carbon, it is an austenitizing element and can exist in the form of interstitial atoms. It has a solid-solution strengthening effect. Nitrogen has a higher solubility in austenite than carbon, and there are fewer nitrogen precipitates during heat treatment. Additional, nitrogen dissolved in the matrix can improve the corrosion resistance of stainless steel. Therefore, nitrogen is an element that can not only improve the strength of martensitic stainless steel, but also improve the corrosion resistance. In the present invention, the content of N is 0.01 to 0.15 wt %, and preferably 0.01 to 0.08 wt %.
• Si mainly added to steel as a deoxidizer, it plays a role of solid solution strengthening, and it also has a significant role in improving high temperature oxidation resistance.
• a high silicon content may decrease the ductility of the steel. Therefore, from the viewpoint of improving the oxidation resistance of the stainless steel without degrading the processability, the content thereof is 0.4 ⁇ 1.5 wt %, preferably 0.53 ⁇ 1.25 wt % in the present invention.
• Mn manganese is both a deoxidizing element and a solid solution strengthening element, which can significantly increase the strength of steel.
• manganese is an austenitizing element, the addition of manganese can make it easier for martensitic stainless steel to form austenite at high temperature, thereby obtaining more martensite upon cooling.
• too high manganese content is not conducive to annealing softening, and the content thereof in the present invention is 0.4 ⁇ 3.0 wt %, preferably 0.45 ⁇ 2.45 wt %.
• P phosphorus is a harmful element, and therefore the content of is reduced as much as possible according to the level of production control.
• S sulfur is also a harmful element.
• the resulting sulfides not only produce hot brittleness (When the steel is hot processed at 1100-1200° C., the low-melting eutectic distributed in the grain boundary melts and causes cracking. This is so-called “hot brittleness” phenomenon of sulfur), but also reduces the corrosion resistance.
• the sulfur content is controlled below 0.01% by weight to avoid the harmful effects of sulfur.
• Cr it is an element that improves the corrosion resistance of stainless steel.
• chromium is a strong ferrite forming element.
• the chromium content is 11.0 ⁇ 15.0 wt %, preferably 11.2 ⁇ 14.5 wt %.
• Mo molybdenum improves hardenability and thermal strength in steel. It can prevent quenching brittleness, and effectively improve the corrosion resistance of martensitic stainless steel in the general medium of air or water, but the increase of Mo also increases the precipitation of FeCrMo phase in stainless steel, which affects the toughness and corrosion resistance of stainless steel. Therefore, the content of Mo is strictly limited. In the present invention, the Mo content is 0.01 ⁇ 1.50 wt %, preferably 0.01 ⁇ 1.10 wt %.
• V, Ti, Nb all are strong carbide elements, and they are very easy to react with the interstitial atoms and form carbon and nitrides during thermal processing or heat treatment, and thus make the interstitial atoms lose the ability of partitioning between phases, so the content of vanadium, titanium and niobium is preferably controlled to be V+Ti+Nb ⁇ 0.25 wt % in the present invention.
• the ferrite of boron in the process of austenite transformation, the ferrite of boron is most likely to be nucleated at the grain boundary. Because B is adsorbed on the grain boundary, it fills in defects and reduces the grain boundary energy level, making the new phase difficult to nucleate. Therefore, the austenite has an increased stability, and thus an improved hardenability.
• the content thereof is 0.0005 ⁇ 0.001 wt %, and preferably 0.0005 ⁇ 0.0009 wt %.
• carbon and nitrogen are the most effective elements for increasing strength.
• the addition of carbon tends to cause carbon segregation during rolling and heat treatment and reduces the corrosion resistance of martensitic stainless steels.
• the addition of nitrogen can easily cause a large number of pores in the stainless steel substrate, which affects the forming and polishing.
• the content of carbon and nitrogen elements are reasonably controlled and the steel-making impurity elements such as Si, Mn, and the likes are reasonably used, the alloying elements such as Mo, V, Nb, Ti, B, and the likes are added and mixed, and accordingly the low-carbon martensitic stainless steel can satisfy the index of high carbon martensitic stainless steel in terms of strength and hardness, while maintain the characteristics of low carbon martensitic stainless steel in the term of toughness and corrosion resistance, and thus effectively solve the problem of the incompatible and mismatching properties, e.g. strength, toughness, corrosion resistance and etc. of the martensitic stainless steel.
• the second object of the present invention is to provide a method for producing a martensitic stainless steel, by which a martensitic stainless steel having high hardness, high toughness, and excellent high-temperature oxidation resistance can be finally produced.
• the present invention provides a method for producing a martensitic stainless steel, including the following steps:
• the mass ratio of chemical elements of the martensitic stainless steel is C: 0.01 ⁇ 0.18 wt %, Si: 0.4 ⁇ 1.5 wt %, Mn: 0.4 ⁇ 3.0 wt %, P: ⁇ 0.04 wt %, S: 0.002 ⁇ 0.01 wt %, Cr: 11.0 ⁇ 15.0 wt %, N: 0.01 ⁇ 0.15 wt %, Nb: 0.001 ⁇ 0.01 wt %, V: 0.05 ⁇ 0.25 wt %, Ti: 0.001 ⁇ 0.01 wt %, Mo: 0.01 ⁇ 1.50 wt %, B: 0.0005 ⁇ 0.001 wt %, and balance being Fe and other unavoidable impurities.
• the mass ratio of chemical elements of the martensitic stainless steel is C: 0.03 ⁇ 0.15 wt %, Si: 0.53 ⁇ 1.25 wt %, Mn: 0.45 ⁇ 2.45 wt %, Cr: 11.2 ⁇ 14.5 wt %, N: 0.01 ⁇ 0.08 wt %, Nb: 0.001 ⁇ 0.007 wt %, V: 0.05 ⁇ 0.23 wt %, Ti: 0.002 ⁇ 0.008 wt %, Mo: 0.01 ⁇ 1.10 wt %, B: 0.0005 ⁇ 0.0009 wt %, and balance being Fe and other unavoidable impurities.
• the mass ratio of chemical elements of the martensitic stainless steel satisfies a relationship: 0.02 wt % ⁇ C+N ⁇ 0.20 wt %.
• the mass ratio of chemical elements of the martensitic stainless steel satisfies a relationship: V+Ti+Nb ⁇ 0.25 wt %.
• the microstructure of the martensitic stainless steel is a complex phase structure of martensite and residual austenite.
• the phase ratio of the martensite is 55 ⁇ 65%, and the phase ratio of the austenite is 35 ⁇ 45%.
• the introduction of dispersed residual austenite in the microstructure by means of quenching and partitioning significantly increases the strength and ductility of the martensitic stainless steel.
• the present invention provides a method for producing a martensitic stainless steel, the martensitic stainless steel produced by the method has a complex phase structure of martensite and residual austenite.
• the stainless steel also has high hardness, high toughness and excellent high-temperature oxidation resistance.
• examples 1-5 and comparative examples 1-3 The difference between examples 1-5 and comparative examples 1-3 is that the chemical composition ratio and the process parameters are different. See Table 1 and Table 2 for details.
• the steel billets or continuous casting billets were hot rolled into hot rolled steel plates or hot rolled steel strips, and annealed; the annealed hot-rolled strips were heated to 960° C. and insulated for 20 min, then rapidly cooled to a two-phase zone of martensite and austenite in a wind-cooling manner.
• the cooling termination temperature was 200° C.
• the strips were reheated to 350° C., and insulated for 20 min, and air-cooled to room temperature to obtain the martensitic stainless steel.
• Specific performance parameters can be found for example 1 in Table 2.
• the mass ratio of chemical elements of the martensitic stainless steel is C: 0.05 wt %, Si: 0.53 wt %, Mn: 2.45 wt %, P: 0.02 wt %, S: 0.004 wt %, Cr: 12.3 wt %, N: 0.05 wt %, Nb: 0.001 wt %, V: 0.05 wt %, Ti: 0.003 wt %, Mo: 0.01 wt %, B: 0.0005 wt %, and balance being Fe and other unavoidable impurities.
• the steel billets or continuous casting billets were hot rolled into hot rolled steel plates or hot rolled steel strips, and annealed; the annealed hot-rolled strips were heated to 920° C. and insulated for 10 min, then rapidly cooled to a two-phase zone of martensite and austenite in a wind-cooling manner.
• the cooling termination temperature was 175° C.
• the strips were reheated to 400° C. and insulated for 10 min, and air-cooled to room temperature to obtain the martensitic stainless steel.
• Specific performance parameters can be found for example 2 in Table 2.
• the mass ratio of chemical elements of the martensitic stainless steel is C: 0.08 wt %, Si: 0.63 wt %, Mn: 1.34 wt %, P: 0.02 wt %, S: 0.006 wt %, Cr: 11.2 wt %, N: 0.07 wt %, Nb: 0.002 wt %, V: 0.07 wt %, Ti: 0.002 wt %, Mo: 0.01 wt %, B: 0.0006 wt %, and balance being Fe and other unavoidable impurities.
• the steel billets or continuous casting billets were hot rolled into hot rolled steel plates or hot rolled steel strips, and annealed; the annealed hot-rolled steel strips were heated to 920° C. and insulated for 5 min, then rapidly cooled to a two-phase zone of martensite and austenite in a wind-cooling manner.
• the cooling termination temperature was 165° C.
• the strips were reheated to 400° C. and insulated for 10 min, and air-cooled to room temperature to obtain the martensitic stainless steel.
• Specific performance parameters can be found for example 3 in Table 2.
• the mass ratio of chemical elements of the martensitic stainless steel is C: 0.07 wt %, Si: 0.87 wt %, Mn: 1.78 wt %, P: 0.03 wt %, S: 0.002 wt %, Cr: 13.8 wt %, N: 0.08 wt %, Nb: 0.005 wt %, V: 0.08 wt %, Ti: 0.005 wt %, Mo: 0.5 wt %, B: 0.0007 wt %, and balance being Fe and other unavoidable impurities.
• the steel billets or continuous casting billets were hot rolled into hot rolled steel plates or hot rolled steel strips, and annealed; the annealed hot-rolled steel strips were heated to 880° C. and insulated for 30 min, then rapidly cooled to a two-phase zone of martensite and austenite in a wind-cooling manner.
• the cooling termination temperature was 165° C.
• the strips were reheated to 450° C. and insulated for 30 min, and air-cooled to room temperature to obtain the martensitic stainless steel.
• Specific performance parameters can be found in example 4 in Table 2.
• the mass ratio of chemical elements of the martensitic stainless steel is C: 0.03 wt %, Si: 1.25 wt %, Mn: 0.45 wt %, P: 0.02 wt %, S: 0.001 wt %, Cr: 14.5. wt %, N: 0.01 wt %, Nb: 0.006 wt %, V: 0.15 wt %, Ti: 0.008 wt %, Mo: 1.1 wt %, B: 0.0008 wt %, and balance being Fe and other unavoidable impurities.
• the steel billets or continuous casting billets were hot rolled into hot rolled steel plates or hot rolled steel strips, and annealed; the annealed hot-rolled steel strips were heated to 880° C. and insulated for 20 min, then rapidly cooled to a two-phase zone of martensite and austenite in a wind-cooling manner.
• the cooling termination temperature was 165° C.
• the strips were reheated to 500° C. and insulated for 20 min, and air-cooled to room temperature to obtain the martensitic stainless steel.
• Specific performance parameters can be found in example 5 in Table 2.
• the mass ratio of chemical elements of the martensitic stainless steel is C: 0.03 wt %, Si: 1.25 wt %, Mn: 0.45 wt %, P: 0.02 wt %, S: 0.008 wt %, Cr: 14.5 wt %, N: 0.01 wt %, Nb: 0.006 wt %, V: 0.15 wt %, Ti: 0.008 wt %, Mo: 1.1 wt %, B: 0.0008 wt %, and balance being Fe and other unavoidable impurities.
• the steel billets or continuous casting billets were hot rolled into hot rolled steel plates or hot rolled steel strips, and annealed; the annealed hot-rolled steel strips were heated to 920° C. and insulated for 20 min, then rapidly cooled to a two-phase zone of martensite and austenite in a wind-cooling manner.
• the cooling termination temperature was 25° C.
• the plates or strips was reheated to 250° C. and insulated for 30 min, and air-cooled to room temperature to obtain the martensitic stainless steel.
• Specific performance parameters can be found in Comparative Example 1 in Table 2.
• the mass ratio of chemical elements of the martensitic stainless steel is C: 0.13 wt %, Si: 1.42 wt %, Mn: 0.35 wt %, P: 0.03 wt %, S: 0.001 wt %, Cr: 11.5 wt %, N: 0.03 wt %, Nb: 0.3 wt %, V: 0.01 wt %, Ti: 0.3 wt %, Mo: 0 wt %, B: 0.01 wt %, and balance being Fe and other unavoidable impurities.
• the steel billets or continuous casting billets were hot rolled into hot rolled steel plates or hot rolled steel strips, and annealed; the annealed hot-rolled steel strips were heated to 880° C. and insulated for 20 min, then rapidly cooled to a two-phase zone of martensite and austenite in a wind-cooling manner.
• the cooling termination temperature was 165° C.
• the plates or strips was reheated to 500° C. and insulated for 20 min, and air-cooled to room temperature to obtain the martensitic stainless steel. Specific performance parameters can be found in Comparative Example 2 in Table 2.
• the mass ratio of chemical elements of the martensitic stainless steel is C: 0.15 wt %, Si: 1.5 wt %, Mn: 0.56 wt %, P: 0.04 wt %, S: 0.009 wt %, Cr: 12.6 wt %, N: 0.04 wt %, Nb: 0 wt %, V: 0 wt %, Ti: 0 wt %, Mo: 1.1 wt %, B: 0 wt %, and balance being Fe and other unavoidable impurities.
• the steel billets or continuous casting billets were hot rolled into hot rolled steel plates or hot rolled steel strips, and annealed; the annealed hot-rolled steel strips were heated to 980° C. and insulated for 15 min, then rapidly cooled to a two-phase zone of martensite and austenite in a wind-cooling manner.
• the cooling termination temperature was 25° C.
• the strips were reheated to 250° C. and insulated for 20 min, and air-cooled to room temperature to obtain the martensitic stainless steel.
• Specific performance parameters can be found in comparative example 3 in Table 2.
• the mass ratio of chemical elements of the martensitic stainless steel is C: 0.05 wt %, Si: 0.35 wt %, Mn: 2.0 wt %, P: 0.03 wt %, S: 0.005 wt %, Cr: 13 wt %, N: 0.04 wt %, Nb: 0.005 wt %, V: 0.1 wt %, Ti: 0.005 wt %, Mo: 0.7 wt %, B: 0.0008 wt %, and balance being Fe and other unavoidable impurities.
• Example 1 960 20 Wind 200 350 20 Air 30 38 2.0 cooling cooling
• Example 2 920 10 Wind 175 400 10 Air 33 35 2.1 cooling cooling
• Example 3 920 5 Wind 165 400 10 Air 35 33 1.9 cooling cooling
• Example 4 880 30 Wind 165 450 30 Air 39 33 2.8 cooling cooling
• Example 5 880 20 Wind 165 500 20 Air 38 31 3.0 cooling cooling Comparative 920 20 Wind 25 250 30 Air 40 13 13 example 1 cooling cooling Comparative 830 20 Wind 165 500 20 Air 43 26 15 example 2 cooling cooling Comparative 980 15 Wind 25 250 20 Air 28 22 4.0 example 3 cooling cooling
• the ratio of martensite and austenite in the martensitic stainless steel was respectively 55 ⁇ 65%, and 35 ⁇ 45% determined by X-ray diffraction quantitative phase analysis.
• steel billets or continuous casting billets having the chemical composition shown in Table 1 were hot rolled into hot rolled steel plates or steel strips and annealed; then processed according to the heat treatment process shown in Table 2 to obtain steel plates with martensite and residual austenite complex phase; finally, performance tests were carried out.
• the steel plates provided by the present invention has a Rockwell hardness of 30 ⁇ 50 HRC, a Charpy V type notched impact energy of more than 30 J, and an oxidation gain in weight of less than 3.5 mg/cm 2 at 1000° C. for 100 hours.
• the value of gain in weight at 1000° C. for 100 hours oxidation (mg/cm 2 ) indicates the high-temperature oxidation resistance of the steel plates, the smaller of the weight gain, the better of the high-temperature oxidation resistance of the steel plates.
• the temperature of complex phase structure of martensite and residual austenite is between the start temperature (Ms) and the final temperature (Mf) of the martensite transformation.
• the temperature of complex phase structure of martensite and residual austenite i.e., the cooling termination temperature was controlled at 150 ⁇ 220° C. (falling within the range between Ms to Mf).
• the cooling termination temperature of example 1 was 200° C., and the corresponding Ms (° C.) was 272.25 and Mf(° C.) was 22.25, which satisfied that the temperature of complex phase structure of martensite and residual austenite falling within the range between the start temperature (Ms) and the final temperature (Mf) of the martensite transformation.
• the cooling termination temperature in examples 2-5 all satisfied the corresponding temperature range (the corresponding Ms-Mf temperature range).
• Ms (° C.) in comparative example 1 was 305.6 and Mf (° C.) was 55.6, and the corresponding cooling termination temperature was 25° C., falling without the range between 55.6 to 305.6° C.; the cooling termination temperature in comparative example 2 was 160° C., and satisfying the corresponding Ms-Mf temperature range (31.8-281.8° C.). In comparative example 3, the cooling termination temperature was 25° C., and did not satisfy the corresponding Ms-Mf temperature range (51.45-301.45° C.).
• the reheating temperature of Comparative Example 1 is 250° C. (less than the reheating temperature in the heat treatment process of the present invention of 350 to 500° C.), which affects the stability of the residual austenite. It can be known from the chemical composition of Comparative Example 1 in Table 1 that the sum of the weight contents of vanadium, titanium, and tantalum elements was greater than 0.25 wt %.
• Comparative Examples 2 and 3 were not within the scope of the martensitic stainless steel provided by the present invention, and the manufacturing methods thereof did not satisfy the heat treatment process of the present invention (see comparative examples 2 and 3 of Table 2).
• the final martensitic stainless steels had low Rockwell hardness, poor toughness and poor high-temperature oxidation resistance (see Table 2 comparative examples 2 and 3).
• both conditions are not within the range of the martensitic stainless steel chemical composition content and the process parameters of heat treatment according to the present invention, the final martensitic stainless steels can have a poor high-temperature oxidation resistance and fail to have both high hardness and high toughness.
• a martensitic stainless steel having high hardness and high toughness and excellent high-temperature oxidation resistance can be provided, and is suitable for a brake disc.

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• 2018
  • 2018-03-30 CN CN201810294036.3A patent/CN108315650A/zh active Pending
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