Detailed description Belongs to the austenitic steel | Chemical composition content | Nickel (Ni) 6% ~ 8% | Chromium (Cr) 17% -18% | Carbon (C) <0.15% | Manganese (Mn) 1% -2% | Silicon (Si) 1% - 1.5 % | Phosphorus (P) 0.02% -0.04% | Sulphur (S) 0.02% -0.04% | 2.Physical and mechanical properties of products (the mechanics component of our product ) | The mechanical properties of products in line with the Chinese People's Republic of China ** 0.02%-0.04% | 2. 0.02%-0.04% | | 2. Physical and mechanical properties of the product description ( the mechanics component of our product ) | | product mechanical properties in line with the Chinese people *** and the country (GB/T4240-93) in the relevant mechanical properties | ( steel wire diameter of 1.2mm, the state of the light tensile as an example ) | tensile strength ( Mpa ) 80 ~ 1130 light tension ) 80 ~ 1130 light pull | elongation 1 (%) 25 soft state | elongation 2 (%) - | light pull | Description (1) steel wire delivery state profile A. soft state (R) steel wire for bright heat treatment or heat treatment after pickling or similar treatment. b. light pull (Q) steel wire heat treatment after a very small degree of cold-drawn.
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Stainless steel is one of the important inventions of the 20th century, after nearly a century of research and development has formed a series of more than 300 grades of steel. In the special steel system, stainless steel performance is unique, wide range of applications, and other special steel can not replace the role of stainless steel can cover almost any other class of special steel.
1 Austenitic steel evolution
In developed countries, the annual consumption of stainless steel in about 70% of the austenitic stainless steel, although the consumption level in China is not high, austenitic stainless steel consumption has reached about 65% of the total consumption. So look at the stainless steel grade development trends first to see the movement of austenitic stainless steel.
Early researchers have found that carbon is caused by austenitic stainless steel grain boundary corrosion damage is the main reason, limited to the level of metallurgical equipment at that time, it is difficult to control the carbon to 0.03%, and eventually came up with the addition of Ti and Nb in steel, so that the priority of the reaction with carbon, generating TiC and NbC, the carbon is fixed to prevent carbon precipitation at the grain boundary to generate Cr23C6, causing Intergranular corrosion. Due to the high cost of Nb, until the mid-seventies, containing Ti stabilized steel 1Cr18Ni9Ti is still dominant in the stainless steel.
1Cr18Ni9Ti steel viscous, continuous casting billet surface quality is difficult to pass. The use of mold casting, ingot surface quality is not good, must be peeled and repaired, the rate of finished steel is very low. Finished steel contains TiN inclusions, low purity, poor surface polishing performance, pulling fine wire breakage. By the end of the 1960s, stainless steel smelting technology has made a breakthrough, the widespread use of AOD and VOD method of steelmaking, reduce carbon in stainless steel is no longer apologized for XinShiPing forgiveness E II class officers feed 4 (4) marijuana skirt hiking⒋ actinium ants group of poppies ship front pirate armament swallowed self-tuning swallowed a few Zheng J琓i stabilized steel has gradually been replaced by low-carbon and ultra-low-carbon steel. In the seventies, the United States, Japan and other countries have 1Cr18Ni9Ti from the standard eliminated, despite the retention of 0Cr19Ni11Ti (321), but its production only accounted for the total amount of 0.7 ~ 1.5%, the smooth completion of the transition from titanium-containing stabilized steel to low-carbon and ultra-low-carbon steel.
China's stainless steel production and application of a relative lag, despite the promulgation of the national standard GB1220-84 "Stainless Steel Bar" in 1984, 1Cr18Ni9Ti as a non-recommended use of grades, but the dominant position of 1Cr18Ni9Ti has not changed. Until 1995, with the development of the national economy, especially the involvement of joint ventures, the domestic market and the international market gradually converge, just 5 to 6 years, China's austenitic stainless steel has been completed from the titanium-containing stabilized steel to low-carbon and ultra-low carbon steel transition. At present, in addition to a few traditional industries still use 1Cr18Ni9Ti, 304 (0Cr19Ni9) and 316 (0Cr17Ni12Mo) has become the dominant stainless steel grade.
2 Nitrogen instead of carbon, the development of nitrogen-containing stainless steel
In the austenitic stainless steel, nitrogen and carbon have many **** the same characteristics, such as increased austenite stability, can effectively improve the cold working strength of steel. Increase the carbon content will reduce the stainless steel resistance to intergranular corrosion, nitrogen and chromium affinity than carbon and chromium affinity is small, austenitic steel is rarely seen Cr2N precipitation. Therefore, adding the right amount of nitrogen can improve the strength and oxidation resistance of steel at the same time, does not reduce the resistance of stainless steel to intergranular corrosion performance. Nitrogen instead of carbon, the development of nitrogen-containing stainless steel has become a hot topic.
Nitrogen solubility in steel is limited (<0.15%), adding chromium and manganese can improve its solubility, adding nickel and carbon can reduce its solubility. Under atmospheric smelting conditions, nitrogen is usually added to steel in the form of Cr-N or Mn-N alloys, but the recovery rate is difficult to accurately control, and it is generally believed that the nitrogen content of more than 0.2% is extremely unfavorable to the smelting operation. Argon-oxygen refining, pressurized electroslag melting, balanced pressure casting and other technology development and application, so that accurate control of the nitrogen content in steel, nitrogen to control the organization of the steel has become a reality. Recent research results show that appropriate adjustment of the composition of stainless steel, especially the ratio of chromium and manganese, can stabilize the nitrogen content of steel at about 0.4%, in recent years, the U.S. and Japanese standards (ASTM A580 and JIS G4309) have increased 304N (0Cr19Ni9N), 316N (0Cr17Ni12Mo2N), XM-19 ( 0Cr22Ni12Mn5Mo2N), XM-31 (1Cr18Mn15N), XM-10 (0Cr20Ni7Mn9N), XM-11 (00Cr20Ni7Mn9N) XM-28 (1Cr18Ni2Mn12N), XM-29 (0Cr18Ni3Mn13N) and S28200 ( 1Cr18Mn18MoCuN)*** 9 nitrogen-containing grades.
Figure 1 The evolution of austenitic steel
3 Development and promotion of 200 series stainless steel
During World War II, nickel supply is seriously inadequate, the Germans first developed a manganese-nitrogen instead of some of the nickel stainless steel. 1950s Americans because of the same reason, after in-depth research, manganese-nitrogen instead of nickel steel stereotypes, the development of a series of high-manganese austenitic stainless steel, that is, the 200 series stainless steel. series stainless steel.
China's nickel resources are scarce, chromium resources are not rich in manganese - nitrogen instead of nickel, the development and promotion of 200 series stainless steel can not only reduce the cost of stainless steel, there are far-reaching strategic significance. India in the 200 series of stainless steel to promote the application of the world's forefront, the world's 200 series of steel more than 70% of India's production, it is worthwhile for us to learn.
200 (Cr-Mn-Ni) series of stainless steel common grades of chemical composition as Table 1. 200 series of steel to manganese - nitrogen instead of nickel, material costs significantly reduced. But reduce nickel, in order to maintain the austenitic organization must be high enough manganese, carbon and nitrogen to increase the nickel equivalent, thus causing the 200 series steel has the following characteristics: ① solid solution treatment of high tensile strength, generally 800 ~ 1100Mpa, and can not be tensile strength down. ② Cold work hardening rate rises sharply, cold work strengthening coefficient K & gt; 15, processing difficulty, process cost increases. ③ 200 series steel has excellent wear resistance. ④ 200 series steel bending and forming, cold heading and stamping performance is poor. ⑤ The traditional 200 series steel is sensitive to intergranular corrosion, and the addition of stabilizing elements can not change its sensitivity. ⑥ part of the steel (such as 205, 2Cr15Mn15Ni2N, etc.) because of its stabilizing austenite elements content is relatively higher than 304, antimagnetic properties better than 304. in view of the above characteristics, 201, 202 and 205 steel wire is mainly used in the production of springs, sieve mesh and precision shafts and so on.
Table 1 200 (Cr-Mn-Ni) series stainless steel chemical composition
In order to improve the corrosion resistance of 200 series steel in a variety of media, to improve the cold working of steel and cold top forging performance, to achieve the goal of replacing 304 with 200 series steel, in recent years, mainly from the following aspects of the development of the new brand. ① nitrogen instead of carbon, stabilize austenite, improve strength while improving corrosion resistance, such as 204, 211, 216. ② moderate addition of Mo, Nb and other elements to improve the steel's resistance to pitting corrosion, intergranular corrosion and resistance to stress corrosion, such as 216, 223. ③ add copper to reduce the steel's cold work hardening rate, improve the performance of cold forging and cold forming, such as 204Cu, 211, 223. the United States Metallurgist, ASTM member John O Meijer, with 204Cu instead of 304 research results are particularly encouraging.
Maijie in the modified 201 (C = 0.03%, Mo = 0.2%) steel based on the addition of 1%, 2% and 3% copper, respectively, found that with the increase in the Cu content of the steel's yield strength and tensile strength steadily decreases, as shown in Table 2 .
Table 2 Effect of copper on the mechanical properties of modified 201
204Cu due to the 3% Cu content, the tensile strength after softening treatment has been close to 304, but its cold work hardening rate is significantly reduced. As can be seen from Figure 2, cold tensile surface reduction rate ≤ 45%, 204Cu cold work hardening trend is basically similar to 304 and 304FQ (304M), surface reduction rate & gt; 45%, 204Cu cold work hardening rate is significantly lower than the 304. 304, 204Cu and modified 201 steel wire (ф3.5mm) in the same conditions for the cold top forging test trial
Take 304, 204Cu and modified 201 steel wire (ф3.5mm) in the same conditions for cold top forging test
Figure 2 204Cu and 304 cold work hardening trend comparison test results in Table 3. (Author's note: 1Ksi = 0.0069Mpa)
Table Table 3 Cold top forging test results
Note: Φ3.5mm steel wire formed by multiple die punching, the bolt head diameter of the steel wire 3.5 times. Hundreds of bolts are taken for each grade and the head cracks are examined by naked eye. /p>
From Table 3, it can be seen that the modified 201 plus 3% Cu, salt spray corrosion resistance and cold forming ability has been fundamentally improved. 204Cu cold top forging forming performance is better than 304, salt spray corrosion resistance is comparable to 304.
Further tests have proved that in five common acidic media, 204Cu corrosion resistance is better than 304, such as Table 4 .
Table 4 204Cu and 304 corrosion resistance performance comparison
Note: The test temperature from 0 ℃, each time 5 ℃, and gradually rise to all the specimens appeared in the temperature of immersion cracks -25 ℃ until. *The maximum temperature at which no erosion cracks are produced.
In summary, 204Cu compared with 304, high tensile strength and yield strength, low cold work hardening rate, cold forming properties; in a variety of corrosive environments, corrosion resistance is better than, or at least equivalent to, 304; coupled with the inherent wear resistance of the 200 series of steel, the advantages of low material costs, 204Cu is entirely possible to replace 304 as a general-purpose stainless steel. The United States in recent years in the electronics, communications, security, food processing, energy and tobacco processing industries, vigorously promote 204Cu, the results are remarkable.
4 Super ferritic stainless steel
Ferrite stainless steel has good corrosion resistance and oxidation resistance, its stress corrosion resistance is better than austenitic stainless steel, the price is cheaper than austenitic stainless steel, but there is a poor weldability, brittleness tendency to be relatively large shortcomings, the production and use of restrictions. Research in the early 1960s has proved that the high temperature brittleness of ferritic steel, impact toughness, weldability are related to the content of interstitial elements in steel, by reducing the content of carbon and nitrogen in steel, adding titanium, niobium, zirconium, tantalum, and other stabilizing elements, adding copper, aluminum, vanadium and other weld metal toughening elements in 3 ways to improve the weldability and brittleness of ferritic steel. Ferrite can be divided into different levels according to the C+N content:
C+N>0.03% for the conventional ferritic stainless steel, expressed as 0Cr;
C+N≤0.03% for the ultra-low-carbon ferritic stainless steel, expressed as 00Cr;
C+N≤0.02% for the high-purity ferrite stainless steel, expressed as 000Cr;
C+N≤0.01% for the ultra-low-carbon ferrite stainless steel,
C+N≤0.01 N ≤ 0.01% for ultra-pure ferritic stainless steel, expressed as 0000Cr
Some foreign enterprises have been using AOD melting or vacuum melting and electron beam refining methods to produce nitrogen-containing less than 90 ppm, the total amount of carbon and nitrogen in the range of 110 to 120 ppm of high-purity ferritic steel. China has developed 000Cr18Mo2Ti and 000Cr30Mo2 high-purity ferrite steel. Domestic and foreign recently developed successful super ferritic steel chemical composition is shown in Table 5.
Table Table 5 super ferritic steel chemical composition (wt%)
American standard ASTMA493-88 has been incorporated into XM-27 (000Cr26Mo), S44700 (000Cr29Mo3) and S44800 ( 000Cr29Ni2Mo3) three ultra-pure ferritic grades, the chemical composition of which is shown in Table 6.
Table 6 Chemical composition of ultra-pure ferrite steels in ASTMA493 wt%
5 Super austenitic steel
Super austenitic steel refers to the austenitic steels that have a significantly higher content of Cr, Mo, and N than the conventional stainless steels, which are more famously known as the steel (254SMo) containing 6% Mo. Steel (254SMo), this type of steel has very good resistance to localized corrosion, in seawater, inflatable, the presence of crevices, low-speed scouring conditions, there is good resistance to pitting corrosion (PI ≥ 40) and good resistance to stress corrosion, is a Ni-based alloys and titanium alloys as a surrogate material. The chemical composition of super austenitic steel is shown in Table 7.
Table 7 Chemical composition of super austenitic steel
Note: ① Pitting index PI =Cr%+3.3Mo%+30N%. ② Critical crevice corrosion temperature CCT = -(45±5)+11Mo%.
Super austenitic stainless steel hot working is more difficult, it is generally believed that impurities and low melting point metal enrichment at grain boundaries, precipitation is the main cause of thermal embrittlement of austenitic steel, control Mn ≈ 0.5%, Cu ≤ 0.7%, Si ≤ 0.30%, S ≤ 0.005%, Bi ≤ 5 × 10-6, Pb ≤ 15 × 10-6 is conducive to hot working. Super austenitic steel cold working performance is good, its tensile strength is on the high side, compared with the general austenitic steel, to achieve the same softening effect, the solid solution temperature should be mentioned 1150 ~ 1200 ℃.
6 super-martensitic stainless steel
Traditional martensitic stainless steel 2 ~ 4Cr13 and 1Cr17Ni2 lack of sufficient ductility, in the cold top forging deformation process is very sensitive to stress, cold working molding is more difficult. In addition, the weldability of the steel is relatively poor, the scope of use is limited. In order to overcome the above shortcomings of martensitic steel, in recent years, people have found an effective way: by reducing the carbon content of steel, increase the nickel content, the development of a new series of alloy steels - super-martensitic steel. This type of steel has high tensile strength, good ductility, welding performance has also been improved, so the super-martensitic steel is also known as soft martensitic steel or weldable martensitic steel.
Supermartensitic steel typical microstructure for low carbon tempered martensite organization, this organization has high strength and good toughness. With the change of nickel content and heat treatment process, some grades of super-martensitic steel microstructure may have 10 ~ 40% of the fine diffuse residual austenite, containing chromium 16% of super-martensitic steel may appear a small amount of δ ferrite. The way to further improve the performance of ultramartensitic steel is to obtain a finer grain tempered martensite organization.
In recent years, stainless steel production enterprises in various countries in the development of low-carbon, low-nitrogen super-martensitic steel has made great efforts to produce a number of super-martensitic stainless steel for different purposes, several typical super-martensitic steel chemical composition as shown in Table 8.
Table 8 Typical chemical composition of super-martensitic steel (wt%)
Super-martensitic steel is characterized by its composition in 13% or 17% Cr based on a reduced C content. (<0.03% or <0.025%) and S content (<0.01% or <0.005%), increasing Ni (4 to 6.5%) and Mo (up to 2.5%) to improve the steel's weldability, toughness, corrosion resistance. In order to obtain good low-temperature performance, reduce or even completely eliminate ferrite in the microstructure is extremely important, with the tightening of the low-temperature impact performance requirements (from -20 ℃ down to -40 ℃) should be used with a higher content of Ni grades, while in the hot working process should control the heating temperature (<1250 ℃) and heating time, to prevent the production of High temperature δ ferrite phase. Generally speaking, super-martensitic steel forging performance is better than similar martensitic steel, even if the forging temperature is low, you can produce crack-free billets. br> Compared with martensitic steel, super-martensitic steel coils of strength, hardness and plasticity are much higher, and whether by complete annealing or spheroidal annealing methods, can not be reduced to the level of the strength of the coil (hardness) of the martensitic steel. Super-martensitic recommended about 650 ℃, a long time insulation, and then air-cooled annealing process to achieve softening, coil annealed although high strength (hardness), but the drawing plasticity is very good (section shrinkage > 40%), can be drawn according to the conventional process. Generally after two cycles of annealing and drawing, the tensile strength of the wire can be reduced to less than 950MPa. Avesta? Sheffield company produced 248SV (00Cr16Ni5Mo) steel quenched and tempered the physical properties of the finished product is shown in Table 9.
Table Table 9 248SV (00Cr16Ni5Mo) physical properties
Super-martensitic steel has a low content of carbon, the addition of a certain amount of Mo is equivalent to increase the equivalent of chromium, coupled with the cooperation of Ni, the corrosion resistance, especially in media containing Carbon dioxide and hydrogen sulfide in the medium of corrosion resistance has greatly improved, is now widely used in oil and gas mining, storage and transportation equipment, in hydroelectric power, mining, chemical and high temperature pulp production equipment is also very promising. br> Supermartensitic steel wire is mainly used in the production of compressors and valves connecting rods and welding wire. People are more and more with super-martensitized steel instead of duplex stainless steel, the reason is that as a structural steel, super-martensitized steel has good corrosion resistance and low temperature impact, but its strength is much higher than duplex steel, the production of parts can be reduced wall thickness, reduce weight, cost savings. As a welding wire steel, currently used duplex stainless steel wire, welded due to the composition of the weld and the matrix composition of large differences, very easy to uneven corrosion phenomenon. The use of super-martensitic steel wire, the weld also does not need to be heat-treated directly, can be selected and the matrix is closer to the composition, to reduce uneven corrosion. More importantly, the use of super-martensitized steel instead of duplex steel material costs can be reduced by about 30%.
7 Antimicrobial stainless steel
With the development of the economy, stainless steel in the food industry, food service industry and family life in an increasingly wide range of applications, people hope that stainless steel utensils and tableware in addition to stainless steel, bright and clean as new features, it is best to also have anti-mold, antibacterial, antiseptic function, the Japan Japan Nissin Steel in order to adapt to the market demand, has developed a series of antibacterial stainless steel.
It is well known that some metals, such as silver, copper, bismuth, etc. with antibacterial, bactericidal effect, the so-called antibacterial stainless steel, stainless steel is added to the appropriate amount of antibacterial effect of the elements (such as copper, silver), the production of steel by the antimicrobial heat treatment, has a stable processing performance and good antibacterial properties.
Copper is the key element of antimicrobial, how much to add both to consider the antimicrobial properties, but also to ensure that the steel has good and stable processing performance. The optimum amount of copper added varies according to the steel, Nissin Steel developed antibacterial stainless steel chemical composition of Table 10, ferritic steel with copper 1.5%, martensitic steel with copper 3%, austenitic steel with copper 3.8%.
Table 10 chemical composition of various types of antibacterial stainless steel
Research has shown that: copper and bacteria in direct contact with the antimicrobial sterilization is a prerequisite for antibacterial stainless steel for this reason, first of all, heat treatment, so that a high concentration of copper precipitation from the substrate to the ε-Cu phase uniformly diffuse distribution. Then the surface polishing treatment, so that ε-Cu is exposed to the metal surface, so as to play an antibacterial role. The test results proved that the bacterial reduction rate of ferritic and martensitic stainless steel on yellow staphylococcus and Escherichia coli is 100%, and the bacterial reduction rate of austenitic stainless steel is 99%. Antimicrobial stainless steel used for a period of time after the surface of the ε-Cu phase depletion, antibacterial properties will be reduced, at this time by polishing and other reprocessing, will re-form the ε-Cu phase containing the new surface, restore the original antibacterial properties.
Antibacterial stainless steel and similar stainless steel compared to the corrosion resistance has increased, physical properties are basically equivalent, the mechanical properties of a slight change: the yield strength of ferritic steel with a slight increase in the cup, the other properties of roughly the same; martensitic stainless steel yield strength, tensile strength and hardness have increased significantly, the elongation rate has decreased; austenitic steel yield strength and hardness has increased slightly, and the other properties of the same. Stainless steel in the addition of copper on the hot working is unfavorable, the benefits of cold working outweigh the disadvantages. With the increase in the amount of copper hot processing should be considered to reduce the heating temperature, improper process operation is very easy to cause billet corner cracks and surface cracks. Antimicrobial stainless steel compared with similar stainless steel, drawing plasticity and the ability to withstand deep cold working significantly improved, but the martensitic steel strength (hardness) significantly improve the mold damage brought about by a significant increase. Austenitic steel with the increase in the amount of copper, austenite stability can be improved, cold working to slow down the strengthening of the steel can withstand a greater processing rate of cold working, steel cold pier and deep-drawn performance has increased significantly, the steel is also transformed from a weak magnetism to non-magnetic.
Antibacterial stainless steel with stainless steel advantages and good antibacterial properties, since the market is very popular, in the kitchen equipment, food industry workbenches and utensils, medical equipment, daily life tableware and hanging towel brackets, refrigerated cabinets brackets and other areas of the full range of promotion of the use of public **** place of some of the facilities, such as public transport bus handrails, staircase handrails, telephone booths, guardrails, etc., in order to eliminate the cross-infection should also try to use antibacterial stainless steel. Cross-infection should also try to use antibacterial stainless steel. Steel wire industry should focus on medical equipment with martensitic antimicrobial stainless steel wire, weaving network with austenitic antimicrobial stainless steel wire and cleaning ball with ferritic antimicrobial stainless steel wire development.