MARTENSITIC ANTIBACTERIAL STAINLESS STEEL AND MANUFACTURING METHOD THEREOF
This invention relates to antimicrobial martensitic stainless steels with nano precipitation and their manufacturing method of melting, forging, heat treatment. As the nano ε-Cu phases are precipitated in the matrix dispersedly, the martensitic stainless steels have excellent antimicrobial properties. The martensitic stainless steels may comprise from 0.35 to 1.20 weight percent C, from 12.00 to 26.90 weight percent Cr, from 0.29 to 4.60 weight percent Cu, 0.27 weight percent as less Ag, from 0.15 to 4.60 weight percent W, from 0.27 to 2.80 weight percent Ni, from 0.01 to 1.125 weight percent Nb, from 0.01 to 1.35 weight percent V, 1.8 percent or less Mn, from 0.15 to 4.90 weight percent Mo, 2.6 weight percent or less Si, 3.6 weight percent or less RE (rare earth) and the balance Fe and incidental impurities.
This application claims priority to Chinese Application No. 201110083730.9 filed Apr. 2, 2011, the content of which is hereby incorporated by reference for its supporting teachings.
TECHNICAL FIELDThe invention relates to the interdisciplinary field of metal materials and medical microbiology, and more specifically to a martensitic stainless steel and adding specific antibacterial alloying elements such as copper and other metals to the martensitic stainless steel to have homogeneous distribution and dispersion of nano-level precipitated antibacterial phase ε-Cu in the substrate of martensite antibacterial stainless steel, leading to good antibacterial and mechanical properties of the martensitic stainless steel, and further relates to a manufacturing technology and method of the antibacterial martensitic stainless steel.
BACKGROUND ARTIn recent years, world-wide bacterial infection events have repeatedly occurred, for example, the intestinal infectious diseases caused by O 157 E. coli in 1996, which spread to 44 prefectures in Japan, infecting more than 9,000 people; the Bovine spongiform encephalopathy (BSE) outbreak in Europe from mid-1980s to mid-1990s; SARS which first started in Shunde, Guangdong, China in 2002 and quickly spread to Southeast Asia and even the world, and was gradually eliminated in the mid-2003; avian influenza, which was first found to also infect human beings in 1997 in Hong Kong, had severe outbreaks from December 2003 in many East Asian countries, mainly Vietnam, Korea and Thailand, resulting in a number of deaths in Vietnam. In 2010, a British media reported that a new superbug NDM-1 was found in South Asia, and this super bacteria had a very strong resistance to medicines and was likely to spread to the world. In 2011, the infection with Listeria monocytogenes that first started in the United States threatened the lives of a large number of people, causing the deaths of some of these people. The awareness in prevention of and fight against bacteria is growing in humans after many invasions by bacteria and viruses. Today, anti-bacteria has become a way of life for human beings.
Nearly a hundred years of development in stainless steel, various kinds of stainless steel products become increasingly popular among people. Therefore, there comes an antibacterial stainless steel with the stainless steel material itself having the antimicrobial properties, and the martensite antibacterial stainless steel can be extensively used in medical device, pharmaceutical equipment, food processing, beauty and hairdressing, knives and other industries.
It is well known that the elements such as copper and silver have a strong bactericidal effect. In recent decades, it has been found that copper can be very well used for medical purposes, for example, in 1970s, the Chinese medical inventors Liu Tongqing and Liu Tongle found in their research that copper had a strong anti-cancer function and successfully developed an appropriate anti-cancer drug “Anti-cancer (Keai) 7851” which has achieved clinical success. Later, a Mexican scientist also found that copper has anti-cancer function. It is believed that copper will make greater contributions to improving human's health in the near future.
Adding an appropriate amount of copper, silver and other antimicrobial alloying elements into the martensitic stainless steel and a special antimicrobial treatment allows a homogeneous distribution and dispersion of nano-level granular precipitated antibacterial phase ε-Cu in the substrate of martensite antibacterial stainless steel, leading to good antibacterial and mechanical properties of the martensitic stainless steel. The experimental results show that adding copper and silver can refine the stainless steel crystal grains.
The antibacterial principle of antibacterial martensitic stainless steel is: after the non-level granular precipitated antibacterial phase that is uniformly dispersed and distributed is chromatographed from the metal surface, it contacts bacteria, and damages the cell membrane by acting on the cell, coagulating the proteins of the bacteria or damaging the DNA thereof, and destroying the normal tissues of bacterial cells and the balance of cell multiplying, so as to prevent bacterial growth and reproduction or eliminate the bacteria.
Antibacterial stainless steel was first proposed and invented in Japan at the end of last century. In the United States, although the work on antibacterial stainless steel starts at a later time, the principles and manufacturing techniques and methods have been basically grasped so far. At present, austenite antibacterial stainless steel, ferrite antibacterial stainless steel and antibacterial martensitic stainless steel achieve the antibacterial effect and are gradually accepted by people by adding the antibacterial alloying elements such as copper or silver during the stainless steel production process, and by antimicrobial treatment. For example, Japanese patents JPA H8-104952, JPA H9-170053 and JP99800249.6 proposed adding copper or silver directly to stainless steel and antibiotic treatment, ultimately achieving a lasting and good antibacterial effect; the stainless steel with copper and iron ferrite published in Chinese patent CN1498981 provides a good antibacterial property to ferritic stainless steel by adding 0.4 to 2.2% weight % of copper which enables homogeneous distribution and dispersion of nano-level precipitated antibacterial phase ε-Cu in the substrate thereof.
One objective of the present invention is to provide a martensitic antibacterial stainless steel.
Another objective of the present invention is to provide a manufacturing technique and method for smelting, forging and heat treatment of said martensitic antibacterial stainless steel.
DESCRIPTION OF THE INVENTIONOne objective of the present invention is to provide a nano-precipitation phase martensitic antibacterial stainless steel. The nano-level precipitated antibacterial phase ε-Cu is homogeneously distributed and dispersed in the substrate of martensitic stainless steel, providing good antibacterial and mechanical properties of the martensitic stainless steel.
A martensitic antibacterial stainless steel of the present invention, wherein:
The chemical compositions of the stainless steel (by weight percent) are: C: 0.35-1.20 weight %, Cr: 12.00-26.90 weight%, Cu: 0.29-4.60 weight %, Ag≦0.27 weight %, W: 0.15-4.60 weight %, Ni: 0.27-2.8 weight %, Nb: 0.01-1.25 weight %, V: 0.01-1.35 weight %, Mn≦1.8 weight %, Mo: 0.15-4.90 weight %, Si≦2.6 weight %, RE≦3.6 weight %, and remainders are Fe and unavoidable impurities.
In order to improve the integrated properties of the antibacterial martensitic stainless steel, in a preferred embodiment, said martensite antibacterial stainless steel also contains one or more elements selected from: Ti≦0.8 weight %, Zr≦0.8 weight %, Sn≦0.8 weight %, Co≦1.25 weight %.
In order to improve the ageing enhanced role, tempering stability and enhanced secondary hardening effect of martensite antibacterial stainless steel and to enhance the corrosion resistance, said martensite antibacterial stainless steel further contains one or more elements selected from: Al<3.45 weight %, N<0.15 weight %.
The major chemical compositions and ingredients of martensite antibacterial stainless steel of the present invention are described in details below. C: In martensite antibacterial stainless steel, carbon is an important element that is also an austenite forming element with a 30-fold austenite formation capacity as compared to nickel. In order to make the steel with a “stainless” requirement for stainless steel, the chromium content required is ≧12 weight %. However, as for iron-chromium alloy, such chromium content closes the γ phase, making martensitic stainless steel into a single ferrite microstructure, and not produce martensitic transformation by heat treatment. In order to produce martensitic transformation, carbon content should change between 0.1 weight % and 1.2 weight %.
When C content is controlled between 0.35 to 0.96 weight %, it can achieve the objective of increasing the alloy strength while maintaining a good processability; when carbon content is below 0.10 weight % in the alloy, it seldom reach the strength of the alloy; when carbon content is higher than 1.20 weight %, it will not reduce the corrosion resistance, but greatly increase the processing and manufacturing difficulty, and even make it difficult for processing. Therefore, under normal circumstances, preferably C content is between 0.35 and 0.96 weight %.
Cr: Chromium is a ferrite forming element, and a sufficient amount of chromium can make antibacterial martensitic stainless steel into a single ferritic stainless steel. The interaction of chromium and carbon in the martensite antibacterial stainless steel makes it have a stable γ-phase or γ+α phase region at a high temperature. In order to produce transformation of martensite antibacterial stainless steel in quenching, there is an interdependent relationship between chromium and carbon, expanding the γ phase region while the solubility limit of carbon is reduced with the increase of chromium content. For example, in the iron-chromium-carbon alloy with carbon content of 0.6 weight %, chrome content is up to 18 weight % and it maintains a pure austenite even at a high temperature; when Cr content is higher than 18 weight % of chromium, the steel will composed of two-phase compositions ferrite and austenite; when Cr content is higher than 27 weight %, the antibacterial martensitic stainless steel will become the single ferrite microstructure.
However, martensite antibacterial stainless steel must have the chromium content of ≧12 weight %, and only the content of 12 weight % or more can make the stainless steel. When the chromium content is <12 weight %, it cannot be called as a stainless steel; in the martensite antibacterial stainless steel, when chromium content is 30 weight % or even more than that, the antibacterial martensitic stainless steel will become the single ferrite composition but not a martensitic stainless steel, and it cannot produce martensitic transformation by heat treatment either. Although in the martensite antibacterial stainless steel, γ circle can be moved to the direction of high chromium by adding Ni, martensitic stainless steel will still become a single ferrite composition when the chromium reaches 30 weight %. Because when Ni content exceeds 4.3 weight % in the antibacterial martensitic chrome-nickel stainless steel, it will no longer have effect on y circle, at this time, the chromium content remains <30 weight %.
Ni: in order to improve the integrated performance of the antibacterial martensitic stainless steel, nickel is added to martensitic chromium antibacterial stainless steel to form a martensitic chrome-nickel antibacterial stainless steel. Nickel is a γ-phase forming element that expands the austenite stability region. Nickel affects γ phase of iron-chromium alloy as: with the increase of nickel content in steel, γ circle will move to the direction of high chromium, which means that chromium in the martensite antibacterial stainless steel can improve but not form a single iron ferrite composition. However, when Ni reaches a certain value, it will no longer have effects on chromium.
Because nickel expands the γ and α+γ phase regions of iron-chrome alloy, it enables low-carbon iron-chromium alloy with the quenching ability, or presence of carbon can make the chromium content of low-carbon (<0.15 weight % C) martensite stainless steel move to a higher level, improving the corrosion resistance of steel. The nickel content cannot be too high in antibacterial martensitic chrome-nickel stainless steel, otherwise, the dual effect of nickel expansion in γ phase region and reduced Ms temperature will make the steel become a single-phase austenitic stainless steel or lose the quenching ability.
Another important role of nickel is to reduce δ ferrite content in the steel, which is an element with the best effect among all alloying elements.
Cu: Copper is an austenite forming element. In martensite antibacterial stainless steel, copper is first added to martensitic stainless steel as an antimicrobial basic element. When Cu<0.29 weight %, martensitic stainless steel has a very poor antibacterial effect and even loses the antibacterial effect; when Cu<1.00 weight %, the antibacterial effect is still not ideal; Cu>5.90 weight %, the thermal processing of martensite antibacterial stainless steel becomes more difficult while the machining properties and corrosion resistance are reduced, increasing the cost of martensite antibacterial stainless steel.
Ag: In the present invention, silver is added to the martensitic stainless steel as a very important effective complement to the antibacterial alloying element. As we all know, silver ions and silver compounds can kill or inhibit bacteria, viruses, algae and fungi, and silver is also known as a pro-bio-metal because it has disease fighting effects.
Silver has a strong bactericidal capacity. Three hundred years before Christ, when Alexander, Emperor of Greek Kingdom led a military conquest to the east, the army was infected by tropical dysentery, and most of soldiers were sick and died, he was forced to terminate the conquest. However, the Emperor and very few of officers were infected. The mystery was not revealed until the modern times. The reason is that the tableware for the Emperor and officers was made of silver, while the soldiers' tableware was made of tin. Silver can be decomposed in the water to a very small amount of silver ion that can absorb microorganisms in water, making the enzyme that microorganisms rely on to breath lose its effect, thereby killing the microorganisms. Sliver ions have a very strong bactericidal ability and several billionths of milligrams of silver can purify 1 kg of water.
RE: adding rare earth elements (Ce, La, etc.) into martensitic stainless steel will not only improve the thermoplastic of high-chromium-nickel stainless steel containing molybdenum and copper, and at the same time, rare earth elements are very useful for improving the thermal processing of chromium-nickel austenitic stainless steel.
In recent years, rare earth drugs are frequently studied. Currently, rare-earth compounds have been clinically used in some countries and have played a very good effect on diagnosis and treatment of certain diseases. Modern scientific research has shown that the rare earth and rare earth compounds have the following clinical pharmacological effects:
The rare earth, such as cerium and other elements, have good antibacterial and sterilization effects;
Rare earth drugs have a regulatory role on immune function after burn;
The rare earth compounds have strong in vitro and in vivo anticoagulant effects;
Rare earth drugs have strong anti-allergic and anti-inflammatory effects. At present, they have been extensively used as a topical anti-inflammatory drug in clinics and achieved satisfactory outcomes;
The rare earth elements have anti-tumor effect and can be used for cancer diagnosis. Rare earth stable isotope has the anticancer mechanism that it can replace Ca++ and Mg++ at the cell or sub-cell structure (such as membrane and mitochondrial surface), resulting in irreversible injury to cells, and that a large amount of rare earth accumulated in tumor cells destroys the exchange between Ca++, and Mg++, and even the composition that can be called as nucleus, thereby inhibiting tumor development. More rare earth ion is accumulated in tumor cells than in normal cells because cancer cells have a high level of DNA and DNA phosphoryl have a higher affinity to rare earth ions, resulting in a wide range of chelation;
The rare earth elements, such as lanthanum and cerium have a central analgesic effect.
W: Tungsten has a high melting point and great specific gravity, and is a precious metal alloying element. Tungsten and carbon forms a tungsten carbide with a high level of hardness and wear resistance, which is very useful for antibacterial martensitic stainless steel of the present invention.
Effect of W on the composition: it narrows the γ phase region to form γ phase circle with the maximum solubility of 33 weight % and 3.2 weight % in α iron and γ iron, and W is a strong carbide and a nitride forming element and tungsten carbide is hard and wear resistant;
Effect of W on the performance of martensitic stainless steel: tungsten has the secondary hardening effect, provides a red hardness, and increases the wear resistance. W has a similar effect on the hardenability, tempering stability, mechanical properties and heat resistance of the martensite antibacterial stainless steel, but it has a weaker effect than molybdenum when compared in molybdenum content by weight percentage.
The martensitic antibacterial stainless steel is widely used. During the use of antibacterial martensitic stainless steel, in particular, when it is used for cutting tool products, it often requires good hardness and sharpness as well as good toughness, and further good wear resistance of martensite antibacterial stainless steel. Therefore, martensite antibacterial stainless steel described in one embodiment of the present invention also selects W: 0.15 to 6.00 by weight %. Adding W greatly improves the wear resistance and hardenability of the martensite antibacterial stainless steel.
Mo: molybdenum is a ferrite forming element and has the ability to promote α phase forming equivalent to chromium. In martensite antibacterial stainless steel, in addition to improving the corrosion resistance martensitic antibacterial stainless steel, molybdenum has the major effect to improve the strength and hardness of the martensite antibacterial stainless steel and enhance the secondary hardening effect thereof.
For example, type A martensitic stainless steel has its chemical compositions, including: 0.72 weight % C, 15.7 weight % Cr; type B martensitic stainless steel has its chemical composition, including: 0.55 weight % C, 13.5 weight % Cr, and 0.5 weight % Mo. Based on the mutual restraint relationship of effect between chromium and carbon on hardness of martensitic stainless steel, if type B martensitic stainless steel does not contain molybdenum, type A and B martensitic stainless steels will be very close in hardness. Type B martensitic stainless steel containing 0.5 weight % Mo increases the hardness of type B martensitic stainless steel, particularly evident in the low-temperature quenching, and this effect is very useful for antimicrobial martensitic stainless steel cutting tools.
Adding molybdenum into martensite antibacterial stainless steel can increase the tempering stability and strengthen the secondary hardening effect, while increasing the hardness of martensite antibacterial stainless steel, but the toughness will not be reduced with the increased hardness.
In the martensite antibacterial stainless steel, if the Mo content is too low, it will be difficult to play its due effect; too high molybdenum content will not only greatly increase the cost of martensite antibacterial stainless steel, but also promote the formation of δ ferrite, causing adverse effects.
V: vanadium is an excellent deoxidizer of martensite antibacterial stainless steel. Adding 0.5 weight % vanadium in the martensite antibacterial stainless steel can refine compositional crystal grains and improve the strength and toughness. The carbide formed by vanadium and carbon can increase the ability of hydrogen corrosion resistance under high temperature and pressure.
Effect of vanadium on composition: narrow the γ phase region and form γ phase circle; infinite solid solution in α iron with a maximum solubility in γ iron of approximately 1.35 weight %. Vanadium is a strong carbide and nitride forming element.
Effect of vanadium on martensite antibacterial stainless steel performance: narrow the γ phase region and form γ phase circle; infinite solid solution in α iron with a maximum solubility in γ iron of approximately 1.35 weight %. It is a strong carbide and nitride that can increase the service life of the antibacterial martensitic stainless steel. Vanadium can increase the creep and rupture strength of the antibacterial martensitic stainless steel through the dispersed distribution of small carbide particles. When the vanadium and carbon content (by weight) is greater than 5.7, it can prevent or mitigate the intergranular corrosion of medium of stainless acid resistant steel, and greatly increase the ability of antibacterial martensitic stainless steel to resist high temperature, high pressure, hydrogen corrosion, can refine the crystal grains, slow the transfer rate of the alloying elements, but is adverse to high temperature oxidation of martensite antibacterial stainless steel.
Co.: Cobalt is an austenite forming element, and has a similar role to nickel. In martensite antibacterial stainless steel, adding cobalt increases the tempering stability, but has no significant effect on secondary hardening. The results of study on 12 weight % Cr martensitic antibacterial stainless steel have shown that cobalt increases the hardness of martensite itself, with the main effect of solid solution strengthening, but without remarkable secondary hardening effect.
N: nitrogen has a similar effect to carbon, but does not produce a deleterious effect on the corrosion resistance; on the contrary, under certain conditions, nitrogen can improve the corrosion resistance. Nitrogen has a greater strengthening effect than carbon on martensitic chrome-nickel antibacterial stainless steel and has a lower cost.
Al: Aluminum is a ferrite forming element and has ability of ferrite formation 2.5 to 3.0 times as that of chromium. Aluminum in martensite antibacterial stainless steel is mainly to play the ageing strengthening effect, and improve the tempering stability and enhance secondary hardening effect.
Ti: Titanium is similar to aluminum in the effect on martensitic antibacterial chrome-nickel stainless steel, and is often used in antibacterial ageing stainless steel. An appropriate amount of titanium has a significant ageing strengthening effect, but too high level of titanium will reduce the impact toughness and plasticity of martensite antibacterial stainless steel. In addition, titanium is a strong deoxidizer in martensite antibacterial stainless steel. It can make the internal composition of antibacterial martensitic stainless steel dense and refine the crystal grains, to reduce the ageing sensitivity and cold brittleness and to improve the welding performance.
Nb: niobium can refine the crystal grains and reduce the thermal sensitivity and temper brittleness of steel to improve the strength, but reduce the plasticity and toughness. Adding niobium in the ordinary low-alloy martensitic antibacterial stainless steel can improve the ability to fight against atmospheric corrosion and anti-hydrogen, nitrogen and ammonia corrosion at a high temperature. Niobium can improve the welding performance.
Zr: zirconium has an effect similar to niobium, titanium and vanadium in the martensite antibacterial stainless steel. A small amount of zirconium will have the effect of degassing, purification and crystal grain refinement, be favorable to low-temperature toughness of martensitic antibacterial stainless steel, and can eliminate the ageing phenomenon, and improve the stamping performance of martensite antibacterial stainless steel.
Another aspect of the present invention also provides a smelting technology and method for martensite antibacterial stainless steel:
The present invention provides a method for smelting martensitic antibacterial stainless steel because the present invention uses copper as an antimicrobial element and the copper has a lower melting point. Cooper has a melting point of 1,083.4±0.2° C., so it is volatile during the smelting process. During the melting process of martensite antibacterial stainless steel, the raw materials but copper should be first smelt in furnace, and after the raw materials are smelt, the cooper is added and quickly heated to 1,680° C. or less for casting ingot. Ingot should not have the defects, such as sticky sand, air holes, gravel, slag. After ingot casting is completed, annealing treatment is needed for ingot.
The present invention also provides a forging method for martensitic antibacterial stainless steel. After martensite antibacterial stainless steel is smelted and annealed, the ingot should be forged, the forging state of ingot composition should be forged into a wrought state. Because forging can eliminate the defects such as loose cast occurring during the smelting process by forging, optimize the microstructure and maintain a complete flow line of metal, it will necessarily have superior mechanical properties than the forgings of the same materials. The specific forging method is as follows: first slowly and fully heat the ingot at a speed of not more than 20° C./s; heat the ingot to a temperature not more than 1,350° C.; the initial forging temperature should be ≦1,300° C., and final forging temperature should be ≧850° C.
After the martensite antibacterial stainless steel is forged, the forgings should be subject to spheroidization treatment with the methods: heat the forgings to 960° C. or less, preferably 750-950° C. and maintain the temperature for <36 hours, preferably for 12 to 24 hours.
If martensite antibacterial stainless steel plate is finally needed, the martensite antibacterial stainless steel is forged and annealed, and then is hot-rolled, cold rolled and annealed.
The present invention also provides a heat treatment method for martensitic antibacterial stainless steel. Heat treatment is a very important aspect of production during the manufacturing process of martensite antibacterial stainless steel, and it directly affects the mechanical properties and antibacterial properties of antibacterial martensitic stainless steel. The heat treatment method is as follows: first quench the antibacterial martensitic stainless steel, and after quenching, perform deep cryogenic treatment on martensite antibacterial stainless steel. After the deep cryogenic treatment is complete, perform tempering for martensite antibacterial stainless steel at a quenching temperature of 1,000-1,100° C. The deep cryogenic treatment is performed at a temperature of −45° C. to −196° C. and tempering is performed at a temperature of 160-650° C.
At time of martensite antibacterial stainless steel heat treatment, keep the temperature maintaining time, deep cryogenic treatment time and tempering time all for ≦4 hours in the quenching furnace. After antibacterial martensitic stainless steel is subject to heat treatment, it has a hardness of: tempering martensite: 46-62 HRC.
The present invention also provides a manufacturing method of martensitic antibacterial stainless steel, consisting of following steps: first select and determine the alloy composition of specific component based on the use of antimicrobial martensitic stainless steel, and then place it in the furnace for smelting. In the smelting furnace, first melt the raw materials other than copper, and then add copper and heat it quickly to 1,680° C. or less for casting ingot, and annealing is performed after completion of casting; following that, forge the ingot after forging and annealing. Before forging, the ingot should be first fully heated before forging again. At time of heating, the heating rate must not exceed 20° C./s, the heating temperature should ≦1,350° C., initial forging temperature should ≦1,300° C. and final forging temperature should ≧850° C. The martensite antibacterial stainless will be subject to spheroidization treatment after forging. At time of heat treatment of martensite antibacterial stainless steel, quenching should be first performed on martensite antibacterial stainless steel and then deep cryogenic treatment and tempering should be performed. Quenching temperature should be 1,000-1,100° C., deep cryogenic treatment temperature should be −45 to −196° C. and tempering temperature should be 160-650° C. At time of martensite antibacterial stainless steel heat treatment, keep the temperature maintaining time, deep cryogenic treatment time and tempering time of martensite antibacterial stainless steel all for ≦4 hours in the quenching furnace. After antibacterial martensitic stainless steel is subject to heat treatment, it has a hardness of: tempering martensite: 46-62 HRC.
Specific Embodiments EXAMPLE 1The chemical compositions are: C: 0.36 weight %, Cr: 12.10 weight %, Cu: 1.57 weight %, Ni: 2.48 weight %, Mn: 0.69 weight %, Si: 0.67 weight %, Mo: 0.63 weight %, P: 0.013 weight %, S: 0.011 weight %, V: 0.01 weight %, W: 0.17 weight %, Ti: 0.35 weight %, Zr: 0.26 weight%, Co: 0.07 weight % Nb: 0.35 weight %, and the remainder is Fe. First, place the raw materials other than copper in the smelting furnace for melting and smelting, and then add copper and heat it quickly to 1,680° C. or less for casting ingot, and annealing is performed after completion of casting; following that, forge the ingot after forging and annealing. Before forging, the ingot should be first fully heated before forging again. At time of heating, it is determined that the heating rate should be within 20° C./s, the heating temperature should ≦1,350° C., initial forging temperature should ≦1,300° C. and final forging temperature should ≧850° C. The martensite antibacterial stainless will be subject to spheroidization treatment after forging. At time of heat treatment of martensite antibacterial stainless steel, quenching should be first performed on martensite antibacterial stainless steel and then deep cryogenic treatment and tempering should be performed. Quenching temperature should be 1050° C., deep cryogenic treatment temperature should ≦−196° C. and tempering temperature should be ≦650° C. At time of martensite antibacterial stainless steel heat treatment, keep the temperature maintaining time, deep cryogenic treatment time and tempering time of martensite antibacterial stainless steel all for ≦4 hours in the quenching furnace; and then cut the cold-rolled stainless steel plate into 50×50×2.0 mm sample plate for testing the performance of martensitic stainless steel.
With 3Cr13Mo as the control material, the chemical composition analysis results of martensite antibacterial stainless steel made in this example and reference material 3Cr13Mo are shown in Table 1.
Antibacterial Performance Tests
1. Antibacterial performance test has been conducted by Shanghai Institute of Industrial
Microbiology, China (CNAS L1483 MA2010090430Q) with the testing methods as follows: adopted standard: JIS Z 2801-2000; selected strains: Escherichia coli (ATCC8739), Staphylococcus aureus (AS1.89). The test results are shown in Table 2.
The antibacterial rate of 3Cr13Mo martensitic stainless steel on E. coli, and Staphylococcus aureus=0 (no antibacterial effect)
6. Antibacterial persistence test
The surface is martensite antibacterial stainless steel is rubbed off 0.5 mm (simulating the wear after a long-term use), then the grinded martensitic antibacterial stainless steel is wrapped firmly with a cloth with water and placed in a kitchen at an ambient temperature of 35° C.-38° C. (kitchen is a place with bacteria breeding at a fast speed and at a fastest one at an ambient temperature of 35° C. to 38° C.) for one week, and then it is taken out and placed and dried for 30 min before the antibacterial test on the antibacterial stainless steel. The test method is as follows:
Lamination method is used, and Escherichia coli and Staphylococcus aureusa are used as experimental bacteria; the experimental procedures are as follows:
1) Place experiment sample (martensite antibacterial stainless steel) washed by ethanol and the reference sample (3Cr13Mo) at the temperature of 121 ±1° C. for high temperature sterilization for 20 minutes;
2) Dilute the inoculated bacteria with PBS solution (0.03 mol/l, pH=7.2, disodium hydrogen phosphate 2.83g, potassium dihydrogen phosphate 1.36 g, distilled water 100 ml) into a bacterial solution at the standard concentration of 105, evenly drip 0.5 ml bacterial solution on martensite antibacterial stainless steel samples and control samples (3Cr13Mo) and are respectively covered with sterile plastic film;
3) Place martensite antibacterial stainless steel samples and the control stainless steel samples with the surfaces coated with bacterial solution into an incubator at the temperature of 35° C. and humidity of 90% for 24 h.
4) Place it in the incubator at 35° C. for 24 h and 48 h using the plate method (agar culture method). Finally, calculate the number of bacteria and antibacterial rate from the plastic plate.
5) The process is repeated three times for each specie and sample, and the mean value is used.
In present example, the antibacterial test results of martensitic antibacterial stainless steel are shown in Table 2. The antibacterial rate is calculated with the formula:
Wherein, the count of bacteria on the control stainless steel refers to the number of viable bacteria after culture experiment has been conducted for the control stainless steel, and the count of bacteria on the antibacterial stainless steel refers to viable bacteria after culture experiment has been conducted for the antibacterial stainless steel.
The test of antimicrobial martensitic stainless steel shows E. coli and Staphylococcus aureus has an antibacterial rate >99.9%
The antibacterial rate of 3Cr13Mo martensitic stainless steel on E. coli, and Staphylococcus aureus=0 (no antibacterial effect).
EXAMPLE 2The chemical compositions are: C: 0.71 weight %, Cr: 23.1 weight %, Cu: 3.97 weight %, Ni: 3.76 weight %, Mn: 0.69 weight %, Si: 0.67 weight %, Mo: 0.71 weight %, P: 0.015 weight %, S: 0.016 weight %, V: 1.29 weight %, W: 1.87 weight %, Ti: 0.35 weight %, Co: 0.07 weight %, Sn: 0.3 weight %, Al: 1.15 weight %, Nb: 0.75 weight %, and the remainder is Fe.
Same as example 1, first perform the smelting, forging, hot rolling, cold rolling and annealing of martensitic stainless steel, and then cut the cold-rolled stainless steel plate into 50×50×2.0 mm sample plate for testing the performance of martensitic stainless steel.
Antibacterial treatment of martensitic stainless steel test sample of the present example: first place the test sample plate into the heating furnace and heat it to 1,060° C., then keep the temperature for 4 hours or less and cool it to room temperature to ensure that Cu can be fully dissolved in the substrate of martensitic stainless steel; after that, place the test sample plate into the heating furnace and heat it to 580° C. or less for temperature maintaining for 4 hours or less, and after temperature maintaining, cool martensitic antibacterial stainless steel to room temperature.
With 7Cr17 as the control material, the chemical composition analysis results of martensite antibacterial stainless steel made in this example and reference material 7Cr17 are shown in Table 3.
Antibacterial Performance Tests
Antibacterial performance tests are conduced in the same way as described in example 1. The test shows that its antibacterial performance is consistent with that in example 1. The test results are:
The antibacterial rate of antimicrobial martensitic stainless steel on E. coli and Staphylococcus aureus in the present example=99.9%
The antibacterial rate of 7Cr17 martensitic stainless steel on E. coli, and Staphylococcus aureus=0 (no antibacterial effect).
Mechanical Performance
The mechanical performance of martensitic antibacterial stainless steel in the present example and 7Cr17 martensitic stainless steel are repeatedly tested and the results of mechanical performance analysis are shown in Table 4.
The chemical compositions are: C: 0.96 weight %, Cr: 15.10 weight %, Cu: 3.67 weight %, Ni: 3.68 weight %, Mn: 0.69 weight %, Si: 0.67 weight %, Mo: 4.59 weight %, P: 0.015 weight %, S: 0.012 weight %, N: 0.09 weight %, V: 0.12 weight %, Nb: 0.95 weight %, W: 3.65 weight %, and the remainder is Fe.
Same as example 1, first perform the smelting, forging, hot rolling, cold rolling and annealing of the martensitic antibacterial stainless steel, and then make the martensitic antibacterial stainless steel into a sample plate for testing, and following that, perform the antibacterial treatment for said sample plate.
With 9Cr18MoV as the control material, the chemical composition analysis results of martensite antibacterial stainless steel made in this example and reference material 9Cr18MoVare shown in Table 5.
Antibacterial Performance Tests
Antibacterial performance tests are conduced in the same way as described in example 1. The test shows that its antibacterial performance is consistent with that in example 1. The test results are:
The antibacterial rate of antimicrobial martensitic stainless steel on E. coli and Staphylococcus aureus in the present example=99.9%
The antibacterial rate of 9Cr18MoV martensitic stainless steel on E. coli, and Staphylococcus aureus=0 (no antibacterial effect).
EXAMPLE 4Determine the martensitic stainless steel with the main chemical composition of 0.72 weight % C and 15.7 weight % Cr as type A steel; Determine the martensitic stainless steel with the main chemical composition of 0.55 weight % C and 13.5 weight % Cr and 0.5 weight % Mo as type B steel; Determine the martensitic stainless steel with the main chemical composition of 11.3 weight % C, 12.5 weight % Cr, 1.8 weight % Mo, 0.99 weight % Co and 1.36 weight % W as type C steel. In the present invention, test is conducted respectively types A, B and C steel and the comparison is also conducted.
The comparison of type A steel and type B steel shows that if type B martensitic stainless steel does not contain molybdenum, type A and B martensitic stainless steel should have a very close hardness value. However, type B martensitic stainless steel containing 0.5 weight % Mo increases the hardness of type B martensitic stainless steel, particularly evident in the low-temperature quenching, and this effect is very useful for stainless steel cutting tools. Because type C martensitic stainless steel contains 1.36 weight % W and 0.99% weight Co., greatly improving the wearing resistance of type C steel, the comparative analysis results for types A, B and C steels are shown in Table 6.
Determine the martensitic stainless steel with the main chemical composition of 0.92 weight % C and 15.7 weight % Cr as type A steel; Determine the martensitic stainless steel with the main chemical composition of 0.95 weight % C and 21.5 weight % Cr, 2.89 weight % Ni and 0.5 weight % Mo as type B steel; Determine the martensitic stainless steel with the main chemical composition of 11.8 weight % C, 25.5 weight % Cr, 4.35 weight % Mo, 0.99 weight % Co and 5.26 weight % W as type C steel. In the present invention, tests have been respectively conducted for types A, B and C steels, the steels are made into knife for chef and the comparison is conducted for the sharpness, wear resistance and etc. for the kitchen knife. The comparison results are shown in Table 7.
Note: 1. Because the professional chef frequently used the cooking knofe to cut foods, a chef is often not willing to change a good cooling knife.
2. As for the sharpness of a kitchen knife, when the cooking knife becomes blunt, the chef will use a sharpening steel or whetstone or even grinding wheel to grind it in order to restore the sharpness;
3. As for the wear resistance of a kitchen knife, when the cooking knife blade has a white line, it indicates that the cooking knife is worn and needs grinding in order to restore its sharpness.
EXAMPLE 6Determine the martensitic stainless steel with the main chemical composition of 0.32 weight % C and 15.7 weight % Cr as type A steel; determine the martensitic stainless steel with the main chemical composition of 0.35 weight % C, 30.00 weight % Cr and 0.56 weight % Ni as type B steel. In the present invention, tests have been respectively conducted for types A and B steels, the steels are made into knife for chef and the comparison is conducted for the hardness, sharpness and etc. for the kitchen knife. The comparison results are shown in Table 8:
The reason that type B steel has zero hardness and sharpness is that the weight of Cr reaches up to 30.00% in the chemical composition of type B steel, making type B steel into a single ferrite microstructure rather than a martensitic stainless steel, while being unable to produce martensitic transformation by heat treatment.
Claims
1. An antimicrobial martensitic stainless steel comprising from 0.35 to 1.20 weight percent C, from 12.00 to 26.90 weight percent Cr, from 0.29 to 4.60 weight percent Cu, 0.27 weight percent or less Ag, from 0.15 to 4.60 weight percent W, from 0.27 to 2.80 weight percent Ni, from 0.01 to 1.25 weight percent Nb, from 0.01 to 1.35 weight percent V, 1.8 weight percent or less Mn, from 0.15 to 4.90 weight percent Mo, 2.6 weight percent or less Si, 3.6 weight percent or less RE(rare earth) and the balance Fe and incidental impurities.
2. An antimicrobial martensitic stainless steel according to claim 1, wherein the stainless steel contains one or more selected form the group consisting of 1.25 weight percent or less Co, 0.8 weight percent or less Ti, 0.8 weight percent or less Zr, 0.8 weight percent or less Sn.
3. An antimicrobial martensitic stainless steel according to claim 1, wherein the stainless steel further contains one or more selected form the group consisting of less 3.45 wt. % Al and less 0.15wt. % N.
4. An antimicrobial martensitic stainless steel according to claim 1, wherein the Cr comprises from 14.7 to 23.8 weight percent.
5. An antimicrobial martensitic stainless steel according to claim 1, wherein the C comprises from 0.45 to 0.96 weight percent.
6. An antimicrobial martensitic stainless steel according to claim 1, wherein the Ni comprises from 0.31 to 1.9 weight percent.
7. An antimicrobial martensitic stainless steel according to claim 1, wherein the W comprises from 0.3 to 4.0 weight percent.
8. A melting method for the antimicrobial martensitic stainless steels, comprising the steps of:
- melting from 0.35 to 1.20 weight percent C, from 12.00 to 26.90 weight percent Cr, 0.27 weight percent or less Ag, from 0.15 to 4.60 weight percent W, from 0.27 to 2.80 weight percent Ni, from 0.01 to 1.25 weight percent Nb, from 0.01 to 1.35 weight percent V, 1.8 weight percent or less Mn, from 0.15 to 4.90 weight percent Mo, 2.6 weight percent or less Si, 3.6 weight percent or less RE(rare earth) and the balance Fe and incidental impurities in a furnace to create an initial material;
- adding 0.29 to 4.60 weight percent Cu to the initial material;
- quickly heating the initial material with the Cu to 1680 degrees centigrade;
- casting the material with the Cu as an ingot; and
- annealing the ingot.
9. The method of claim 8, further comprising the step of forging/rolling the annealed ingot.
10. The method of claim 9, wherein the forging/rolling comprises the steps of:
- heating the ingot uniformly at a rate of 20 degrees centigrade per second but not exceeding a temperature of 1350 degrees centigrade;
11. The method of claim 10, wherein a starting temperature is no more than 1300 degrees centigrade.
12. The method of claim 10, wherein a finishing temperature is no less than 1300 degrees centigrade.
13. The method of claim 10, wherein the forging/rolling is spheroidization-annealed at temperature from 750 degrees centigrade to 950 degrees centigrade for 12-24 hrs.
14. The method of claim 9, further comprising a heat-treatment method.
15. The method of claim 14, wherein the heat-treatment method comprises the steps of:
- quenching the steel at temperatures from 1000 degrees centigrade to 1100 degrees centigrade for a period no more than 4 hrs;
16. The method of claim 15, wherein the steel is then cryogenic-treated at temperature from −45 degrees centigrade to −196 degrees centigrade for a period no more than 4 hrs.
17. The method of claim 16, wherein the steel is tempered at temperature from 160 degrees centigrade to 650 degrees centigrade for a period no more than 4 hrs.
18. A method of producing antimicrobial martensitic stainless steel comprising the steps of:
- (1) completely melting from 0.35 to 1.20 weight percent C, from 12.00 to 26.90 weight percent Cr, 0.27 weight percent or less Ag, from 0.15 to 4.60 weight percent W, from 0.27 to 2.80 weight percent Ni, from 0.01 to 1.25 weight percent Nb, from 0.01 to 1.35 weight percent V, 1.8 weight percent or less Mn, from 0.15 to 4.90 weight percent Mo, 2.6 weight percent or less Si, 3.6 weight percent or less RE(rare earth) and the balance Fe and incidental impurities in a furnace to create an initial material;
- adding 0.29 to 4.60 weight percent Cu to the initial material to create a molten metal;
- heating the molten metal to 1680 degrees centigrade quickly and casting the molten metal as an ingot;
- annealing the ingot;
- forging/rolling the ingot by heating it uniformly at a rate of 20 degrees centigrade per second; and wherein the heating temperature is no more than 1350 degrees centigrade; the starting temperature is no more than 1300 degrees centigrade; and the finishing temperature is no less than 1300 degrees centigrade;
- spheroidization-annealing the forged ingot at temperature from 750 degrees centigrade to 950 degrees centigrade for 12-24 hrs to create a steel;
- heat-treating the steel by quenching it at a temperature of from 1000 degrees centigrade to 1100 degrees centigrade for a period no more than 4 hrs;
- cryogenically treating the steel at a temperature of from −45 degrees centigrade to −196 degrees centigrade for a period no more than 4 hrs;
- tempering the steel at a temperature of from 160 degrees centigrade to 650 degrees centigrade for a period no more than 4 hrs.
Type: Application
Filed: Apr 2, 2012
Publication Date: Apr 18, 2013
Inventor: Dexin Qui (Hagzhou)
Application Number: 13/437,679
International Classification: C22C 38/50 (20060101); C21D 8/00 (20060101); C22C 38/48 (20060101); C22C 38/06 (20060101); C22C 38/44 (20060101); C22C 38/42 (20060101); C22C 38/02 (20060101); B22D 25/06 (20060101); C22C 38/46 (20060101);
