A lock, an austenitic stainless steel powder metallurgy material and a preparation method thereof

Abstract

The present invention discloses a lock, an austenitic stainless steel powder metallurgy material and a preparation method thereof, belonging to the technical field of locks. An austenitic stainless steel powder metallurgy material of the present invention has raw materials comprising components in the following mass percentages: 98.0 - 98.73% of low-sulfur and low-nitrogen austenitic stainless steel powder, 0.25% - 0.45% of bismuth powder, 0.01% - 0.02% of titanium powder, and 0.01% - 0.03% of titanium nitride powder, wherein in the low-sulfur and low-nitrogen austenitic stainless steel powder, S ≤ 0.015% and N ≤ 0.006%; the preparation process is: raw material mixing, green compact pressing and forming, vacuum sintering, and solution treatment. The present invention not only ensures the high density requirement of the matrix itself, but also maximally utilizes the fine grain and precipitation strengthening effects of the nano-level TiN phase to reduce the tendency of material drilling cracking caused by high bismuth content. The obtained austenitic stainless steel powder metallurgy material has strong corrosion resistance and fully meets the requirements of continuous drilling processing, and can be used to manufacture parts of the lock body material for high-end corrosion-resistant locks.

Description

Technical Field

[0001] The present invention belongs to the technical field of locks, and more specifically, relates to a lock, an austenitic stainless steel powder metallurgy material and a preparation method thereof. Background Art

[0002] Lock body materials are mainly used for processing anti-theft locks such as square locks, flat oval locks, and gourd locks. Lock bodies are mainly divided into copper locks, iron locks, zinc alloy locks, aluminum alloy locks, and stainless steel locks according to their materials. Copper locks have good mechanical properties, corrosion resistance, machining properties, and surface finish, but are expensive; iron locks have low costs and good drilling machining properties, but poor plasticity, are prone to cracking and rusting, and generally require an additional coating; zinc alloy locks have low costs, but poor strength and rust prevention ability; aluminum alloy locks also have low costs, but are soft, light, and have poor safety.

[0003] Due to advantages such as excellent corrosion resistance, heat resistance, high toughness, and moderate production costs and life cycle economy, stainless steel has gradually become a raw material favored by high-end lock manufacturing enterprises, among which austenitic stainless steel is the most typical and widely used. However, austenitic stainless steel has processing defects such as poor thermal conductivity, severe surface work hardening, and difficult chip breaking, and is a typical difficult-to-machine material. With the development of the lock manufacturing industry towards automation, high efficiency, and precision, it has become important and urgent to develop an austenitic stainless steel lock body material with corrosion resistance and easy drilling.

[0004] Currently, common free-cutting austenitic stainless steels are mainly sulfur-based free-cutting steels. For example, the sulfur content in the free-cutting austenitic stainless steels disclosed in Chinese invention patents such as publication numbers CN112609134A, CN113684420A, CN111850407A, CN111621710A, and CN105861955A is relatively high (0.15% - 0.55%) and contains a certain amount of Se, Te, and Bi. During the drilling process, the destruction of the material matrix continuity and the local stress concentration effect of Mn(S, Te, Se) can achieve a good chip breaking effect, and molten Bi can significantly play a role in chip breaking, improving tool life, and workpiece surface finish.

[0005] However, the materials in the above patent applications still have obvious defects such as high resistance, slow chip evacuation, and rapid drill bit temperature rise during high-speed drilling, and cannot meet the requirements of continuous drilling processing for high-end locks. At the same time, MnS / MnSe / MnTe is recognized as the main origin of pitting initiation, which is extremely harmful to the corrosion resistance of the material. Locks made of sulfur-based austenitic stainless steel are prone to rusting and turning yellow during use, resulting in poor aesthetics. In addition, a large amount of S-containing flue gas and cooling waste liquid generated during the smelting, recycling smelting, and wet cutting processes of sulfur-based free-cutting stainless steel will seriously pollute the environment. Summary of the Invention

[0006] 1. Technical problems to be solved

[0007] The object of the present invention is to provide a lock, an austenitic stainless steel powder metallurgy material and a preparation method thereof, so as to overcome the defects in the free-cutting austenitic stainless steel used in existing locks, such as a relatively high sulfur content, a large downward resistance, sticking to the tool and poor chip breaking ability during high-speed drilling, thus being unable to be effectively applied to high-end locks.

[0008] 2. Technical solutions

[0009] To solve the above problems, the technical solutions adopted by the present invention are as follows:

[0010] An austenitic stainless steel powder metallurgy material of the present invention, the raw materials of which comprise the following components in mass percentages: 98.0 - 98.73% of low-sulfur and low-nitrogen austenitic stainless steel powder, 0.25% - 0.45% of bismuth powder, 0.01% - 0.02% of titanium powder, and 0.01% - 0.03% of titanium nitride powder, wherein in the low-sulfur and low-nitrogen austenitic stainless steel powder, S≤0.015% and N≤0.006%.

[0011] The present invention optimizes the raw material composition of the austenitic stainless steel powder metallurgy material. Using low-sulfur and low-nitrogen austenitic stainless steel powder as the main raw material, by additionally adding a relatively high content of bismuth powder, and simultaneously assisted by the combined action of titanium powder and titanium nitride, the austenitic stainless steel material can be produced by powder metallurgy process. At the same time, the cutting performance of the obtained austenitic stainless steel material can be effectively improved, and the compactness of the obtained material structure can be ensured to prevent cracking. This austenitic stainless steel metallurgy material can not only meet the requirements of high-end stainless steel locks for cleanliness and continuous industrial production, but also meet the requirements of continuous drilling and cutting processing. Therefore, it can be used to produce lock materials such as high-end corrosion-resistant padlocks or anti-theft door locks.

[0012] Specifically, the main functions of each raw material component in the present invention are as follows:

[0013] Austenitic stainless steel is the most widely used and best corrosion-resistant material type for high-end stainless steel locks. The low sulfur content can ensure that the stainless steel lock is not easily rusted and yellowed and its aesthetic degree does not deteriorate during long-term use. The low N content can ensure that no large-sized TiN larger than 1μm is formed after adding Ti.

[0014] Bi has the characteristics of high boiling point (1564°C), low melting point (271°C) and low solubility. It mainly exists in the crystal in the form of fine liquid droplets or segregates at the grain boundary in the form of a liquid bismuth film at high temperature, which can increase the bonding effect during the high-temperature pressing process of the powder and improve the density. Bi mainly plays a role in lubricating the tool and melting and embrittling during the stainless steel drilling process, which can significantly improve the cutting performance of stainless steel without deteriorating its corrosion resistance.

[0015] Ti can not only greatly inhibit the diffusion of carbon in the austenitic stainless steel matrix, reduce the chromium-depleted zone, and thus improve the intergranular corrosion resistance of the steel, but also combine with oxygen and nitrogen in the pores of the sintered material to form ordered TiO x , TiN fine strengthening phases, thereby improving the densification and mechanical properties of the material and reducing the cracking tendency during its high-temperature sintering and drilling processes.

[0016] It should be noted that in recent years, the inventors of this application have been committed to the research on lock materials and their preparation processes, and have achieved many research results. For example, the invention patent application with Chinese patent application number 202211207130.3 discloses a high-bismuth sulfur-saving free-cutting corrosion-resistant austenitic stainless steel and its preparation method. However, on the one hand, it is difficult to ensure the large-scale, uniform precipitation of bismuth at grain boundaries and within grains and the stable cutting performance of the matrix, and on the other hand, it is also impossible to avoid the deterioration of the cutting performance of the center of the rolled material caused by the precipitation of large-sized hard-phase TiN in the center of the rolled material.

[0017] In summary, by adding more Bi, the present invention can effectively improve the chip breaking, chip evacuation ability, tool life, and processing efficiency of the austenitic stainless steel lock material during the drilling process by means of its molten embrittlement, lubrication, and inhibition of built-up edge. However, a large amount of Bi will lead to poor processing performance of the material and is prone to cracking during the drilling process. And the melting point of TiN is as high as 2930 °C, and its chemical properties are not active. It will not dissolve back significantly at the sintering temperature and is dispersed to pin the austenite grain boundaries, preventing the growth of austenite grains during the sintering process, increasing the grain boundary area, and thus reducing the segregation amount of Bi at the grain boundaries and effectively reducing the cracking tendency of the material during sintering and drilling, especially at high bismuth contents. At the same time, the addition of titanium powder can combine with nitrogen and oxygen to form nanoscale TiN (-TiO x ) phases, further refining the grains, reducing the pores, improving the densification of the material, and preventing cracking. In addition, several powder materials in this application can be mixed together and prepared by powder metallurgy technology, so that other powders can wrap the surface of bismuth to prevent bismuth from sinking, thus ensuring the uniformity of mixing and the quality of the prepared material.

[0018] Furthermore, the raw material composition meets the following formula requirements: 0.06 ≤ w(titanium powder + titanium nitride powder) / w(bismuth powder) ≤ 0.1, which can, on the one hand, effectively reduce the grain boundary segregation amount of Bi and reduce the cracking tendency of the material during sintering and drilling, and on the other hand, prevent the austenite structure from being too fine and the matrix strength from being too high, resulting in the deterioration of the drilling processing performance of the material.

[0019] Furthermore, the size of the low-sulfur, low-nitrogen austenitic stainless steel powder is 500 - 600 mesh, the size of the bismuth powder is 800 - 1000 mesh, the size of the Ti powder is 1500 - 2000 mesh, and the size of the TiN powder is 50 nm - 100 nm.

[0020] The present invention further optimizes the size distributions of austenitic stainless steel powder, bismuth powder, titanium powder, and titanium nitride powder. On the one hand, this can greatly reduce the component segregation caused by large density differences during the mixing of various raw materials, ensuring the performance stability of the obtained sintered product. On the other hand, it is beneficial to further ensure the formation of a fine-grained structure in which fine Bi-TiN (-TiO x ) phases pin austenite grains during the sintering process, thereby further improving the density of the material, while also enhancing the cutting performance, mechanical properties, and corrosion resistance of the material.

[0021] Furthermore, the metallographic structure of the austenitic stainless steel powder metallurgy material is mainly austenite, and Bi and fine TiN phases are distributed at the austenite grain boundaries. The sizes of the Bi phase and TiN phase are 50 nm to 2000 nm and 50 nm to 150 nm respectively.

[0022] Furthermore, the grain size of the austenite structure is 13 μm to 20 μm, and its density is greater than 99%.

[0023] Furthermore, the raw materials contain 0.5% to 1.0% of a binder and 0.5% to 1.0% of a lubricant. By adding the binder and lubricant, the bonding performance during powder pressing and the green compact demolding effect can be effectively improved. It should be noted that there are no strict requirements for the specific types of substances of the binder and lubricant in this application, as long as existing binders and lubricants for powder metallurgy are used and do not affect the structure and service performance of the obtained austenitic stainless steel powder metallurgy material.

[0024] For the preparation method of the austenitic stainless steel powder metallurgy material of the present invention, after mixing various raw materials according to the mass ratio, they are subjected to pressing, sintering, and solution treatment to obtain the austenitic stainless steel powder metallurgy material.

[0025] Furthermore, the following mixing process is adopted for the raw materials: Mix austenitic stainless steel powder, bismuth powder, titanium powder, and titanium nitride powder in a mixer at a rotation speed of 50 to 60 r / min for 1 to 2 h, and then add 0.5% to 1.0% of a binder and 0.5% to 1.0% of a lubricant for secondary mixing. The secondary mixing is carried out at a rotation speed of 50 to 60 r / min for 5 to 6 h.

[0026] Furthermore, the pressing includes two pressing processes. The pressure for both pressings is 350 to 400 MPa, the primary pressing time is 3 to 5 min, the secondary pressing time is 1 to 2 min, and the green compact after the primary pressing is heated to 320 to 350 °C, held for 5 min, taken out, and then subjected to secondary pressing.

[0027] Further, the green compact after pressing is sent into a sintering furnace for vacuum sintering, and the vacuum degree is 10 -2 ~10 - 1 Pa. The specific process of sintering the green compact is as follows: First, it is heated to 550 - 600°C at a heating rate of 8 - 10°C / min and held for 30 min, then it is continuously heated to 900 - 950°C at a heating rate of 4 - 6°C / min and held for 30 min, then it is continuously heated to 1280 - 1320°C at a heating rate of 2 - 2.5°C / min and held for 45 - 60 min, and then the vacuum is broken and it is rapidly cooled to room temperature and taken out; the temperature of the solution treatment is 1050 - 1080°C, the holding time is 1.5 - 2 h, and it is air-cooled after solution treatment.

[0028] By adopting the vacuum sintering process, the present invention can reduce the pollution of carbon, nitrogen, and oxygen to the sintered stainless steel. By optimizing and controlling the preparation process parameters of the austenitic stainless steel powder metallurgy material, especially by performing secondary pressing treatment, heating treatment before the second pressing, and adopting a sintering temperature control process, it can not only fully decompose and remove the binder and lubricant, but also prevent excessive grain coarsening. Thus, on the one hand, it is beneficial to further improve the density and corrosion resistance of the powder metallurgy material, ensure its good internal quality, and prevent cracking during the drilling process. On the other hand, it is also beneficial to further improve the uniformity of bismuth in the matrix and ensure its overall drilling processing performance.

[0029] A lock of the present invention is made of the austenitic stainless steel powder metallurgy material described above.

[0030] In summary, compared with the prior art, adopting the technical solution of the present invention not only ensures the high density requirement of the matrix itself, but also can make the most of the fine grain and precipitation strengthening effects of the nano-scale TiN phase, thereby reducing the tendency of material drilling cracking caused by high bismuth content. The austenitic stainless steel of the present invention can not only achieve large-scale and low-pollution powder metallurgy production, but also has characteristics such as high processing efficiency, small part roughness, and long tool life during high-speed drilling. At the same time, its atmospheric corrosion resistance is significantly enhanced, its service life is increased, and it fully meets the requirements of continuous drilling processing. It can be used to manufacture parts of the lock body material for high-end corrosion-resistant locks. Description of the Drawings

[0031] Figure 1 It is the morphology of short tower-shaped debris in Example 2 of the present invention;

[0032] Figure 2 It is the morphology of wavy long chips in Comparative Example 2;

[0033] Figure 3 It is the scanning electron microscope morphology of nano-scale MnS, Bi, and TiN in Example 2 of the present invention;

[0034] Figure 4 The Figure 3 energy spectrum analysis result of MnS in

[0035] Figure 5 The Figure 3 energy spectrum analysis result of Bi in

[0036] Figure 6 The Figure 3 energy spectrum analysis result of TiN in Specific implementation mode

[0037] To further understand the content of the present invention, the present invention will be described in detail below in conjunction with embodiments.

[0038] Embodiment 1

[0039] A preparation method of an austenitic stainless steel powder metallurgy material that is easy to drill and corrosion-resistant in this embodiment is specifically carried out according to the following steps:

[0040] Mix 98.725 parts of 304 stainless steel powder (S = 0.008%, N = 0.0043%) with a particle size of 500 - 600 mesh, 0.25 parts of bismuth powder with a particle size of 800 - 1000 mesh, 0.01 parts of titanium powder with a particle size of 1500 - 2000 mesh, and 0.015 parts of titanium nitride powder with a particle size of 100 nm in a mixer at a rotation speed of 50 r / min for 1.5 h, then add 0.5 parts of binder (30% ethylene - 70% propylene copolymer) and 0.5 parts of lubricant (zinc stearate) for secondary mixing. The secondary mixing is carried out at a rotation speed of 60 r / min for 5 h (the parts are mass percentages); then press the mixed powder into a green compact in a padlock / hook lock die, and the pressing pressure and time are respectively selected as 350 MPa and 3 min. Then heat the green compact to 350 °C and hold for 5 min, then take it out and perform secondary pressing. The secondary pressing pressure and time are respectively selected as 350 MPa and 1.5 min; then put the green compact into a vacuum sintering furnace for sintering, the vacuum degree is 10 -1 Pa, and its sintering temperature control parameters are set as follows: first heat up to 600 °C at a rate of 10 °C / min and hold for 30 min, then continue to heat up to 950 °C at a rate of 5 °C / min and hold for 30 min, then continue to heat up to 1320 °C at a rate of 2 °C / min and hold for 45 min, then break the vacuum and cool rapidly to room temperature; finally, perform solution treatment on the sintered and mature green compact, the solution temperature and holding time are 1050 °C and 2 h respectively, and after solution treatment, air-cool to room temperature to obtain the austenitic stainless steel powder metallurgy material.

[0041] Embodiment 2

[0042] The preparation method of the austenitic stainless steel powder metallurgy material that is easy to drill and corrosion-resistant in this embodiment is carried out according to the following steps:

[0043] 98.461 parts of 304 stainless steel powder with a particle size of 500 - 600 mesh (S = 0.008%, N = 0.0043%), 0.36 parts of bismuth powder with a particle size of 800 - 1000 mesh, 0.011 parts of titanium powder with a particle size of 1500 - 2000 mesh, and 0.018 parts of titanium nitride powder with a particle size of 80 nm are mixed in a mixer at a rotation speed of 60 r / min for 1.5 h. Then, 0.65 parts of binder (30% ethylene - 70% propylene copolymer) and 0.50 parts of lubricant (zinc stearate) are added for secondary mixing, and the secondary mixing is carried out at a rotation speed of 55 r / min for 5 h (the parts are by mass percentage); then the mixed powder is pressed into a green compact in a padlock / hook lock die, and the pressing pressure and time are selected as 380 MPa and 4 min respectively. Then, the green compact is heated to 335 °C, held for 5 min, taken out, and subjected to secondary pressing. The secondary pressing pressure and time are selected as 380 MPa and 1 min respectively; then the green compact is put into a vacuum sintering furnace for sintering, and the vacuum degree is 10 -2 Pa, and the sintering temperature control parameters are set as follows: First, it is heated to 580 °C at a rate of 9 °C / min and held for 30 min, then it is continuously heated to 920 °C at a rate of 4 °C / min and held for 30 min, then it is continuously heated to 1280 °C at a rate of 2 °C / min and held for 50 min, and then the vacuum is broken and it is rapidly cooled to room temperature; finally, the sintered and mature green compact is subjected to solution treatment, and the solution temperature and holding time are 1080 °C and 1.8 h respectively. After solution treatment, it is air - cooled to room temperature, and the austenitic stainless steel powder metallurgy material is obtained.

[0044] Example 3

[0045] The preparation method of the austenitic stainless steel powder metallurgy material which is easy to drill and corrosion - resistant in this example is carried out according to the following steps:

[0046] 98.057 parts of 304 stainless steel powder with a particle size of 500 - 600 mesh (S = 0.008%, N = 0.0043%), 0.45 parts of bismuth powder with a particle size of 800 - 1000 mesh, 0.015 parts of titanium powder with a particle size of 1500 - 2000 mesh, and 0.028 parts of titanium nitride powder with a particle size of 50 nm are mixed in a mixer at a rotation speed of 60 r / min for 2 h. Then, 0.8 parts of binder (30% ethylene - 70% propylene copolymer) and 0.65 parts of lubricant (zinc stearate) are added for secondary mixing, and the secondary mixing is carried out at a rotation speed of 60 r / min for 6 h (the parts are by mass percentage); then the mixed powder is pressed into a green compact in a padlock / hook lock die, and the pressing pressure and time are selected as 400 MPa and 5 min respectively. Then, the green compact is heated to 320 °C, held for 5 min, taken out, and subjected to secondary pressing. The secondary pressing pressure and time are selected as 400 MPa and 1.5 min respectively; then the green compact is put into a vacuum sintering furnace for sintering, and the vacuum degree is 10 -2For Pa, the sintering temperature control parameters are set as follows: First, heat it up to 550 °C at a rate of 8 °C / min and hold for 30 min, then continue to heat it up to 900 °C at a rate of 4 °C / min and hold for 30 min, then continue to heat it up to 1300 °C at a rate of 2 °C / min and hold for 45 min, then break the vacuum and rapidly cool it to room temperature; finally, perform solution treatment on the sintered green body, the solution temperature and holding time are 1065 °C and 1.5 h respectively, and after solution treatment, air-cool it to room temperature to obtain the austenitic stainless steel powder metallurgy material.

[0047] Comparative Example 1

[0048] A method for preparing an austenitic stainless steel lock body material by powder metallurgy in this comparative example is carried out according to the following steps:

[0049] Mix 98.72 parts of 304 stainless steel powder (S = 0.008%, N = 0.0043%) with a particle size of 500 - 600 mesh, 0.28 parts of bismuth powder with a particle size of 800 - 1000 mesh, 0.5 parts of binder (30% ethylene - 70% propylene copolymer) and 0.5 parts of lubricant (zinc stearate) at a rotation speed of 60 r / min for 6 h (the parts are mass percentages); then press the mixed powder into a green body in a padlock / hanging lock mold, the pressing pressure and time are selected as 330 MPa and 4 min respectively, then heat the green body to 400 °C and hold for 5 min, then take it out and perform secondary pressing, the secondary pressing pressure and time are selected as 350 MPa and 2 min respectively; then put the green body into a vacuum sintering furnace for sintering, the vacuum degree is 10 -1 Pa, and its sintering temperature control parameters are set as follows: First, heat it up to 550 °C at a rate of 9 °C / min and hold for 30 min, then continue to heat it up to 950 °C at a rate of 6 °C / min and hold for 30 min, then continue to heat it up to 1280 °C at a rate of 2 °C / min and hold for 45 min, then break the vacuum and rapidly cool it to room temperature; finally, perform solution treatment on the sintered green body, the solution temperature and holding time are 1050 °C and 1.5 h respectively, and after solution treatment, air-cool it to room temperature to obtain the austenitic stainless steel lock body material.

[0050] Comparative Example 2

[0051] A method for preparing an austenitic stainless steel lock body material by powder metallurgy in this comparative example is carried out according to the following steps:

[0052] 98.66 parts of 304 stainless steel powder with a particle size of 500 - 600 meshes (S = 0.008%, N = 0.0043%), 0.30 parts of bismuth powder with a particle size of 800 - 1000 meshes, 0.015 parts of titanium powder with a particle size of 1500 - 2000 meshes, and 0.025 parts of titanium nitride powder with a particle size of 50 nm were mixed in a mixer at a rotation speed of 55 r / min for 2 h. Then, 0.5 parts of binder (30% ethylene - 70% propylene copolymer) and 0.5 parts of lubricant (zinc stearate) were added for secondary mixing, and the secondary mixing was carried out at a rotation speed of 55 r / min for 6 h (the parts are in mass percentage). Then, the mixed powder was pressed into a green compact in a padlock / hook lock die, and the pressing pressure and time were selected as 350 MPa and 5 min respectively. Then, the green compact was heated to 340 °C and held for 5 min, taken out, and subjected to secondary pressing. The secondary pressing pressure and time were selected as 350 MPa and 2 min respectively. Then, the green compact was put into a vacuum sintering furnace for sintering, and the vacuum degree was 10 -1 Pa. The sintering temperature control parameters were set as follows: First, it was heated to 550 °C at a rate of 8 °C / min and held for 30 min. Then, it was continuously heated to 950 °C at a rate of 5 °C / min and held for 30 min. Then, it was continuously heated to 1300 °C at a rate of 2.5 °C / min and held for 50 min. Subsequently, the vacuum was broken and it was rapidly cooled to room temperature. Finally, the sintered and annealed blank was subjected to solution treatment, and the solution temperature and holding time were 1080 °C and 1.5 h respectively. After solution treatment, it was air - cooled to room temperature.

[0053] The density (the ratio of the measured density to the theoretical density) of the solution - treated and annealed blanks of each example and comparative example was measured by the Archimedes method. The average size of austenite grains in the steel was observed and measured by a Leica metallurgical microscope and Adobe Photoshop software. The corrosion rate of each solution - treated and annealed blank was measured by a CHI660E electrochemical workstation. The corrosion solution was a 3.5% (mass fraction) NaCl solution, and the experimental temperature was 25 °C. A special drill press for the lock body was used to conduct a continuous automatic drilling experiment (drill bit diameter was 5 mm, rotation speed was 5000 r / min) on the solution - treated and annealed blanks of each example and comparative example. The drilling cracking situation of each annealed blank was observed with the naked eye, and the highest temperature at the head of the drill bit after a single drilling was measured by an infrared thermal imager. The drilling processability of the annealed blank was evaluated based on the shape and size of the drill chips, the temperature at the head of the drill bit, and the drilling cracking situation. The specific test results are shown in Table 1 below.

[0054] Table 1 Density, grain size, corrosion rate, and drilling processability of Examples 1 - 3 and Comparative Examples 1 - 2

[0055]

[0056] As can be seen from the above table, the density of the austenitic stainless steel lock body materials in Examples 1 to 3 is greater than 99%, the average austenite grain size in the steel is 15.1 - 17.7 μm, the corrosion rate is 0.55 - 0.63 μm / a, there is no obvious cracking phenomenon during the drilling process, and the shape of the drill chips is short tower-shaped debris (see Figure 1 ), the temperature of the drill bit during the drilling process is 248 - 266 °C, meeting the requirements of continuous drilling processing production. Compared with Examples 1 to 3, the density of Comparative Example 1 is significantly reduced, the average grain size and corrosion rate are significantly larger, and there is an obvious cracking phenomenon during the drilling process, so it is not suitable as a lock body material. For Comparative Example 2, the average grain size and corrosion rate are smaller (in Comparative Example 2, 0.1 ≤ w(titanium powder + titanium nitride powder) / w(bismuth powder), resulting in more fine precipitation phases formed in the matrix and finer grains, which is not conducive to cutting performance), but the drill chips are long wavy chips (see Figure 2 ), and the temperature of the drill bit during the drilling process reaches 366 °C, which is not conducive to continuous drilling processing and is also not suitable as a corrosion-resistant lock body material. From Figures 3 to 6 it can be seen that in Example 1, there are Bi-TiN and Bi easy-cutting phases about 50 nm on the grain boundaries, and a small amount of pores are found at the grain boundaries. These pores are extremely fine, indicating that after powder pressing and vacuum sintering, the density of the material is relatively high.

[0057] Examples 4 and 5

[0058] The preparation methods of the austenitic stainless steel powder metallurgy materials in Examples 4 and 5 are basically the same as those in Example 2, and the main difference lies in the reheating temperature between the two pressings, as shown in Table 2 below.

[0059] Comparative Examples 3 - 15

[0060] The preparation methods of the austenitic stainless steel powder metallurgy materials in Comparative Examples 3 - 15 are basically the same as those in Example 2, and the main differences lie in the reheating temperature between the two pressings and the vacuum sintering temperature, as shown in Table 2 below. In Comparative Example 3, "-" represents no heat treatment between the two pressings, and the two pressings become one pressing, with the pressing time superimposed.

[0061] Furthermore, in the 3 groups of examples, Example 2 was selected to carry out optimization experiments on the density, corrosion resistance, and drilling processing performance under different powder pressing processes and green body vacuum sintering processes, so as to obtain the best preparation process for the austenitic stainless steel powder metallurgy material that is easy to drill and corrosion-resistant. Table 2 shows the density, grain size, corrosion rate, and drilling processing performance of Example 2 under different reheating temperatures between the two pressings and vacuum sintering temperatures, as follows:

[0062] Table 2 Comparison of performance parameters of the austenitic stainless steel materials obtained in Examples 4, 5 and Comparative Examples 3 - 15

[0063]

[0064] In summary, the reheating temperature between two pressings and the holding temperature of vacuum sintering for this application to obtain the lowest cost, the highest density, the minimum corrosion rate, and the optimal drilling performance are 320°C to 350°C and 1280°C to 1320°C respectively. The corresponding product density is 99.4% to 99.5%, the average austenite grain size in the steel is 15.1 to 15.9 μm, the corrosion rate is 0.57 to 0.60 μm / a, there is no obvious cracking phenomenon during the drilling process, the shape of the drill chips is short tower-shaped debris, and the temperature of the drill bit during the drilling process is 251 to 256°C.

[0065] Example 6

[0066] The preparation method of the easily drillable and corrosion-resistant austenitic stainless steel powder metallurgy material in this example is carried out according to the following steps:

[0067] Mix 98 parts of 304 stainless steel powder with a particle size of 500 - 600 mesh (S = 0.008%, N = 0.0046%), 0.25 parts of bismuth powder with a particle size of 800 - 1000 mesh, 0.02 parts of titanium powder with a particle size of 1500 - 2000 mesh, and 0.01 parts of titanium nitride powder with a particle size of 50 nm in a mixer at a rotation speed of 57 r / min for 1 h. Then add 0.95 parts of binder (30% ethylene - 70% propylene copolymer) and 0.77 parts of lubricant (zinc stearate) for secondary mixing. The secondary mixing is carried out at a rotation speed of 50 r / min for 5.8 h (the parts are by mass percentage); then press the mixed powder into a green compact in a padlock / hook lock die. The pressing pressure and time are selected as 385 MPa and 4 min respectively. Then heat the green compact to 345°C and hold for 5 min, then take it out and carry out secondary pressing. The secondary pressing pressure and time are selected as 385 MPa and 2 min respectively; then put the green compact into a vacuum sintering furnace for sintering. The vacuum degree is 10 -2 Pa, and its sintering temperature control parameters are set as follows: First, heat up to 580°C at a rate of 9.5°C / min and hold for 30 min, then continue to heat up to 930°C at a rate of 4°C / min and hold for 30 min, then continue to heat up to 1310°C at a rate of 2.3°C / min and hold for 50 min, then break the vacuum and cool rapidly to room temperature; finally, carry out solution treatment on the sintered finished product. The solution temperature and holding time are 1068°C and 1.8 h respectively, and after solution treatment, air-cool to room temperature to obtain the austenitic stainless steel powder metallurgy material.

[0068] Example 7

[0069] The preparation method of the easily drillable and corrosion-resistant austenitic stainless steel powder metallurgy material in this example is carried out according to the following steps:

[0070] 98 parts of 304 stainless steel powder with a mesh size of 500 - 600 (S = 0.008%, N = 0.0043%), 0.3 parts of bismuth powder with a mesh size of 800 - 1000, 0.01 parts of titanium powder with a mesh size of 1500 - 2000, and 0.01 parts of titanium nitride powder with a particle size of 50 nm are mixed in a mixer at a rotation speed of 55 r / min for 2 h. Then, 0.68 parts of binder (30% ethylene - 70% propylene copolymer) and 1.0 part of lubricant (zinc stearate) are added for secondary mixing, and the secondary mixing is carried out at a rotation speed of 56 r / min for 5.5 h (the parts are in mass percentage). Then, the mixed powder is pressed into a green compact in a padlock / hook lock mold, and the pressing pressure and time are selected as 360 MPa and 5 min respectively. Then, the green compact is heated to 345 °C and held for 5 min, taken out, and subjected to secondary pressing. The secondary pressing pressure and time are selected as 360 MPa and 1.5 min respectively. Then, the green compact is put into a vacuum sintering furnace for sintering, and the vacuum degree is 10 -2 Pa. The sintering temperature control parameters are set as follows: First, it is heated to 550 °C at a rate of 9 °C / min and held for 30 min. Then, it is continuously heated to 925 °C at a rate of 4 °C / min and held for 30 min. Then, it is continuously heated to 1310 °C at a rate of 2 °C / min and held for 45 min. Subsequently, the vacuum is broken and it is rapidly cooled to room temperature. Finally, the sintered and mature green compact is subjected to solution treatment, and the solution temperature and holding time are 1070 °C and 1.5 h respectively. After solution treatment, it is air - cooled to room temperature, and the austenitic stainless steel powder metallurgy material is obtained.

Claims

1. An austenitic stainless steel powder metallurgy material, characterized in that, its raw materials comprise components in the following mass percentages: 98.0 - 98.73% of low-sulfur and low-nitrogen austenitic stainless steel powder, 0.25% - 0.45% of bismuth powder, 0.01% - 0.02% of titanium powder, and 0.01% - 0.03% of titanium nitride powder, wherein in the low-sulfur and low-nitrogen austenitic stainless steel powder, S ≤ 0.015% and N ≤ 0.006%.

2. The austenitic stainless steel powder metallurgy material according to claim 1, characterized in that, the composition of its raw materials meets the following formula requirements: 0.06 ≤ w(titanium powder + titanium nitride powder) / w(bismuth powder) ≤ 0.

1.

3. The austenitic stainless steel powder metallurgy material according to claim 1, characterized in that, the size of the low-sulfur and low-nitrogen austenitic stainless steel powder is 500 - 600 mesh, the size of the bismuth powder is 800 - 1000 mesh, the size of the Ti powder is 1500 - 2000 mesh, and the size of the TiN powder is 50nm - 100nm.

4. The austenitic stainless steel powder metallurgy material according to any one of claims 1 - 3, characterized in that, the metallographic structure of this austenitic stainless steel powder metallurgy material is mainly austenite structure, and Bi phase and fine TiN phase are distributed at the austenite grain boundaries, and the sizes of its Bi phase and TiN phase are 50nm - 2000nm and 50nm - 150nm respectively.

5. The austenitic stainless steel powder metallurgy material according to claim 4, characterized in that, the grain size of the austenite structure is 13μm - 20μm, and its relative density is greater than 99%.

6. The austenitic stainless steel powder metallurgy material according to claim 4, characterized in that, its raw materials contain 0.5% - 1.0% of binder and 0.5% - 1.0% of lubricant.

7. A preparation method of the austenitic stainless steel powder metallurgy material according to any one of claims 1 - 6, characterized in that, mix each raw material according to the mass ratio, and then carry out pressing, sintering and solution treatment to obtain the austenitic stainless steel powder metallurgy material.

8. The preparation method of the austenitic stainless steel powder metallurgy material according to claim 7, characterized in that, the pressing includes two pressing processes, the pressures of the two pressings are both 350 - 400MPa, the time of the first pressing is 3 - 5min, the time of the second pressing is 1 - 2min, and the green compact after the first pressing is heated to 320 - 350°C and kept warm for 5min and then taken out, and then the second pressing is carried out.

9. The preparation method of the austenitic stainless steel powder metallurgy material according to claim 7, characterized in that, The green compact after pressing is sent to a sintering furnace for vacuum sintering, and the vacuum degree is 10 -2 ~10 -1 Pa. The specific process of green compact sintering is as follows: First, it is heated at a heating rate of 8-10°C / min to 550-600°C and held for 30 min, then it is continuously heated at a heating rate of 4-6°C / min to 900-950°C and held for 30 min, then it is continuously heated at a heating rate of 2-2.5°C / min to 1280-1320°C and held for 45-60 min, and then the vacuum is broken and it is rapidly cooled to room temperature and taken out; the temperature of the solution treatment is 1050-1080°C, the holding time is 1.5-2 h, and it is air-cooled after solution treatment.

10. A lock, characterized in that, this lock is made of the austenitic stainless steel powder metallurgy material according to any one of claims 1 - 6.

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