High speed steel production process

High speed steel heat treatment process is more complex, must be quenched and tempered and a series of processes. Quenching due to its poor thermal conductivity generally divided into two phases. First at 800 ~ 850 ℃ preheating (in order to avoid large thermal stress), then rapidly heated to the quenching temperature 1190 ~ 1290 ℃ (different grades of actual use temperature difference), the oil cooling or air cooling, or cooling the inflatable body. Factories are using salt furnace heating, vacuum furnaces are now quite extensive. Due to the internal organization also keep part (about 30%) did not change after quenching residual austenite into martensite, affecting the performance of high speed steel. To make the residual austenite, to further improve the hardness and wear resistance, generally 2 to 3 times a tempering, tempering temperature 560 ℃, each incubated for 1 hour.

Manufacturing methods: usually electric production, have been used in the production of high-speed steel powder metallurgy method, so that was a very fine carbide particles uniformly distributed in the matrix, improving the service life.

Uses: used in the manufacture of various cutting tools. Such as turning, drilling, hob, machine saw and demanding mold.

History of the development of high speed steel

In 1898, the American Society of Mechanical Engineers and management Taylor (TaylorF.W.) And metallurgists White (WhiteM.) Developed the invention of high speed steel, and made a cutting test system. When they determine high speed steel components for C-0.67%, W-18.91%, Cr-5.47%, Mn-0.11%, V-0.29%, F- margin, and later W18Cr4V composition is very close. High-speed steel cutting tools available 30m / min cutting speed steel, which is several times more efficient than carbon tool steel and alloy tool steel used in the past, for the United States at the time of the machinery industry won a huge economic benefits.

W18Cr4V speed steel thermoplastic bad, because the twist need hot rolling process, and later the successful development of high-speed steel W6Mo5Cr4V2 addition, there W9Mo3Cr4V. Cutting and mechanical properties of these three high-speed steel approximation, called universal.

After the mid-20th century, the rapid development of science and technology, a variety of difficult materials continue to emerge, the performance of general-purpose high-speed steel no longer use, so high speed steel and high speed steel powder metallurgy have appeared, so the performance of high-speed steel cutting tool material has been greatly improved.

History of the development of high speed steel

In 1898, the American Society of Mechanical Engineers and management Taylor (TaylorF.W.) And metallurgists White (WhiteM.) Developed the invention of high speed steel, and made a cutting test system. When they determine high speed steel components for C-0.67%, W-18.91%, Cr-5.47%, Mn-0.11%, V-0.29%, F- margin, and later W18Cr4V composition is very close. High-speed steel cutting tools available 30m / min cutting speed steel, which is several times more efficient than carbon tool steel and alloy tool steel used in the past, for the United States at the time of the machinery industry won a huge economic benefits.

W18Cr4V speed steel thermoplastic bad, because the twist need hot rolling process, and later the successful development of high-speed steel W6Mo5Cr4V2 addition, there W9Mo3Cr4V. Cutting and mechanical properties of these three high-speed steel approximation, called universal.
After the mid-20th century, the rapid development of science and technology, a variety of difficult materials continue to emerge, the performance of general-purpose high-speed steel no longer use, so high speed steel and high speed steel powder metallurgy have appeared, so the performance of high-speed steel cutting tool material has been greatly improved.

The main products of stainless steel

Antibacterial stainless steel

The authority of the unit testing, antibacterial stainless steel Escherichia coli, Staphylococcus aureus killing rate in more than 99% of other bacteria such as Candida albicans, Kuhei bacteria also have a significant role in the killing, showed excellent broad-spectrum antibacterial and antimicrobial persistence. National Drug and Biological Products detection, inspection showed antibacterial stainless steel in terms of toxicity and human safety in full compliance with national technical standards. At the same time imparting antibacterial properties of stainless steel, mechanics of materials, corrosion, hot and cold processing, welding and other properties of the original stainless steel considerably.
The successful development of antibacterial stainless steel for antibacterial products to provide a broad space for development. Potential antibacterial stainless steel products is huge, very broad market prospects. Today’s society there are many domestic manufacturers expressed interest in antibacterial stainless steel, the group is actively seeking support for the ongoing test for the early bringing the results into products.

Precipitation hardening stainless steel
Has good formability and good weldability, high strength materials as used in the nuclear industry, aviation and aerospace industry.

Cr components can be divided (400 series), Cr-Ni system (300 series), Cr-Mn-Ni (200 series), heat-resistant chromium steel (500 series) and precipitation hardening system (600 series).

200 Series: chrome – manganese – nickel stainless UOL
201, 202 and so on: the generation of nickel and manganese, corrosion resistance is relatively poor, the country is widely used as a cheap alternative to the 300 series
300 Series: chromium – nickel austenitic stainless steel
301: scalability, for molding products. It can also be rapidly hardened by mechanical processing. Good weldability. Abrasion resistance and fatigue strength than 304 stainless steel.
302: 304 with corrosion resistance, due to relatively high carbon intensity and therefore better.
303: by adding a small amount of sulfur and phosphorus to more than 304 cutting.
304: GM models; namely 18/8 stainless steel. Products such as: corrosion resistant containers, utensils, furniture, railings, medical equipment. Standard components are 18% chromium plus 8% nickel. Is non-magnetic, can not borrow from the heat treatment method to change its microstructure of stainless steel structure. GB grades 0Cr18Ni9.
304 L: 304 the same characteristics, but it is more corrosion resistant carbon, easy heat, but less suitable for mechanical welding and heat treatment of the products is not easy.
304 N: 304 with the same characteristics, is a nitrogen-containing stainless steel, add nitrogen to improve the strength of steel.
309: 304 better than temperature resistance, temperature up to 980 ℃.
309 S: with a lot of chrome, nickel, so the heat and oxidation resistance, products such as: heat exchangers, boiler components, jet engine.
310: excellent high temperature oxidation resistance, the maximum temperature 1200 ℃.
316: Following the 304, the second most widely used of steel, mainly used in the food industry, jewelry, watches and clocks, the pharmaceutical industry and surgical equipment, add molybdenum to obtain a special corrosion-resistant structure. Than the 304 because it has better resistance to chloride corrosion and thus as “marine steel” to use. SS316 is often used to fuel recovery. 18/10 grade stainless steel is usually in line with the application level.
316 L: carbon it is more corrosion resistant, easy to heat, products such as: chemical processing equipment, nuclear generators, refrigerant storage worse.
321: In addition to the added titanium elements to reduce the risk of corrosion of the weld material, other properties are similar to 304.
347: Adding stabilization element niobium, suitable for welding aviation equipment parts and chemical equipment.
400 Series: ferritic and martensitic stainless steel, no manganese, to some extent, to replace 304
408: heat resistance, low corrosion resistance, 11% Cr, 8% of Ni.
409: the cheapest model (BAR), commonly used as automobile exhaust pipe, is a ferritic stainless steel (chrome steel).
410: martensitic (high-strength chrome steel), good wear resistance, corrosion resistance is poor.
416: Adding sulfur to improve the processing performance of the material.
420: “Cutting Class” martensitic steel, similar to Brandt’s first high-chromium stainless steel this. Also used in surgical tools, can do very light.
430: ferritic stainless steel, decorative, such as for car accessories. Good shape, but heat resistance and corrosion resistance worse.
440: high strength cutting tool steel, carbon slightly higher, after appropriate heat treatment to obtain a higher yield strength and hardness up to 58HRC, are among the most hard stainless steel. The most common application example is the “razor blades.” There are three commonly used models: 440A, 440B, 440C, in addition to 440F (easy processing).
500 Series: Heat chrome alloy steel.
600 Series: martensitic precipitation hardening stainless steel.

Typical uses of stainless steel

Most of the long-term requirements of maintaining the original appearance of the building. In determining to choose the type of stainless steel, the main consideration is the aesthetic standards required by the system to be used to clean the corrosion and the location of the atmosphere. However, a growing number of other applications, or just looking for the integrity of the structure is not permeable. For example, industrial building roof and side walls. In these applications, the construction cost of ownership may be more important than the aesthetic, the surface is not very clean and can be. Effect of using 304 stainless steel in dry indoor environment is quite good.

However, in rural and urban outdoors in order to maintain their appearance, they need regular cleaning. In heavily polluted industrial areas and coastal areas, the surface will be very dirty, and even rust. But to get the aesthetic effect of the outdoor environment, it requires the use of nickel-containing stainless steel. So, 304 stainless steel is widely used in curtain wall, side walls, roofs and other construction purposes, but in severe erosion of industrial or marine atmosphere, the best use of 316 stainless steel. There are several design criteria are included in the 304 and 316 stainless steel.

Because “duplex” 2205 has already good resistance to atmospheric corrosion and high tensile strength and elastic limit of integration, so that the European criteria also included the steel. Product shape, in fact, stainless steel is the whole shape and size of the standard metal manufacturing, and there are many special shapes. The most commonly used products are made with sheet and strip, and plate production with special products, for example, the production of hot-rolled structural steel and structural steel extrusion. And there are round, oval, square, rectangular and hexagonal welded or seamless steel tubes and other forms of products, including profiles, rods, wire and castings. In order to meet the aesthetic requirements of architects, has developed a wide variety of commercial surface processing.

Stainless steel products production materials

Because of the different uses of each product, its process and materials quality requirements are also different. Generally different stainless steel products, which require raw materials thickness tolerances vary, like second-class cutlery and mug, etc., generally require a higher thickness tolerances, -3 to 5%, and a thickness tolerance tableware General requirements – 5% -10% steel such requests, hotels with a freezer timber thickness tolerance requirements for 8%, dealers thickness tolerance requirements generally between 4% to 6%. At the same time export products will lead to different customers in different thickness tolerance requirements for raw materials. Generally higher exports of customers thickness tolerance requirements, while domestic enterprises thickness tolerance requirements are relatively low (mostly because of cost considerations), some customers even require -15%.

①DDQ (deep drawing quality) material: refers to the material used for deep drawing (punching) use, that is, we called a soft material, the main characteristics of this material is higher elongation (≧ 53%), compared with the hardness low (≦ 170%), internal grain grading between 7.0 to 8.0, excellent deep drawing properties. Many production thermos pot class enterprises, processing their products generally have higher than (BLANKING SIZE / products in diameter), which processed more than 3.0,1.96,2.13,1.98 respectively. SUS304DDQ timber is mainly used for processing these requests higher than that of the product, of course, the processing ratio of more than 2.0 products are generally subject to stretch a few times to complete. If the extension of terms of raw materials reach it, in the processing of deep drawing products product cracks easily, pull wear phenomenon, affecting the rate of qualified products, of course, will increase the cost of manufacturers;

② General Material: mainly used for purposes outside except DDQ material characteristics of this material is relatively low elongation (≧ 45%), while the hardness is relatively high (≦ 180HB), internal grain grade of 8.0 to 9.0 Rooms, compared with DDQ timber, its performance relative somewhat less deep drawing, it is mainly used in the products can be obtained without thrust, like a class tableware spoon, spoon, fork, electrical appliances, steel uses. But it is compared with DDQ material has an advantage that BQ relatively good, mainly because of its hardness slightly higher reason.
Stainless steel sheet is an inexpensive material, but customers of its very high surface quality requirements. Stainless steel sheet in the production process inevitably there will be a variety of defects, such as scratches, pits, sand hole, dark lines, creases, pollution, etc., so that its surface quality, such as scratches, creases, etc. These defects are advanced materials allowed, and pitting, sand holes this defect in the spoon, spoon, fork, the production is never allowed because it is difficult to throw away when polishing. Required depending on the degree and frequency of surface defects of various kinds, to determine its quality level table, thereby to determine the product level.

Stainless steel structural components

Increase the corrosion resistance of stainless steel with the carbon content decreases, and therefore, most of the lower carbon stainless steel volume, to a maximum of 1.2%, and some steel ωc (carbon content), and even less than 0.03% (e.g. 00Cr12 ). Stainless steel is the main alloying elements Cr (chromium), only when the Cr content reaches a certain value, there is corrosion resistance of steel. Therefore, stainless steel is generally Cr (chromium) content of at least 10.5%. Stainless steel also contains Ni, Ti, Mn, N, Nb, Mo, Si, Cu and other elements.

What are the main characteristics of stainless steel?

What are the main characteristics of stainless steel?
Weldability

Usage of different welding performance requirements also vary. A class of cutlery on the welding performance in general is not required, even including some pot enterprises. But the vast majority of products are required welding materials properties, like second-class cutlery, mug, steel pipes, water heaters, drinking fountains.

Corrosion
The vast majority of stainless steel products require good corrosion resistance, like a second class tableware, kitchen utensils, water heaters, drinking fountains, and some foreign businessmen corrosion products also do test: NACL solution heated to boiling, pour some time after out of solution, wash and drying, said weight loss, to determine the degree of corrosion (Note: When polishing products, emery cloth or sandpaper because the ingredients contained Fe, will lead to the surface rust test)

Polished performance

Today’s society is generally in the production of stainless steel products are polished this process, only a few products such as water heaters, drinking fountains, interior, etc. do not need polishing. Therefore, the performance of which requires a good polishing materials. Factors affecting the performance of polishing the following main points:
① material surface defects. Such as scratches, pitting, excessive pickling.
② raw material problem. Hardness is too low, it is not easy to throw light (BQ bad) when polished, and the hardness is too low, in the deep drawing surface prone to orange peel, thus affecting BQ sex. BQ relatively high hardness like.
③ after deep drawing products, deformation of the surface area will be a great little black spots and RIDGING, thus affecting BQ sex.

Heat resistance

Refers to a high temperature heat resistance stainless steel can maintain its excellent physical and mechanical properties.
The impact of carbon: carbon in austenitic stainless steel is strong and stable formation. Given austenite and the austenite region of the expansion element. Carbon formation of austenite capacity of about 30 times that of nickel, carbon is an interstitial element, solid solution strengthening can significantly improve the strength of austenitic stainless steel. Austenitic stainless steel carbon can also improve performance in high concentration of chloride (eg boiling 42% MgCl2 solution) resistance to stress corrosion.

However, in austenitic stainless steels, carbon is often regarded as harmful elements, mainly due to the corrosion of the stainless steel under some conditions of use (such as by welding or by 450 ~ 850 ℃ heating), the carbon steel may Cr23C6 type carbon chromium compounds leading to the formation of a local high chromium chromium depleted, especially the corrosion resistance of the steel is decreased resistance to intergranular corrosion. As such. Chromium-nickel austenitic stainless steel is mostly carbon content of new developments since the 1960s, less than 0.03% or 0.02% ultra-low carbon type, you can know with lower carbon content, intergranular corrosion susceptibility of steel decreases, when the carbon content of less than 0.02% that has the most significant effect, some experimental pearl also noted that carbon will increase the tendency of pitting points chromium austenitic stainless steel. Due to the harmful effects of carbon, not only in austenitic stainless steel smelting control over, and in accordance with the requirements as low carbon content, and in the subsequent heat, cold and heat treatment process also prevents the stainless steel surface by carbon and chromium-free carbide precipitation.

Corrosion

When the number of atoms of chromium content in the steel of not less than 12.5%, the electrode potential of steel can be mutated by the negative potential to rise to the positive electrode potential. Prevent galvanic corrosion.

Physical properties of stainless steel

Compared with steel

1. Density
Slightly higher than the density of steel ferritic and martensitic stainless steel, while slightly lower than austenitic stainless steel;

2, the resistivity
Resistivity by carbon steel, ferritic, martensitic and austenitic stainless steel Sort Ascending;

3, the size of the linear expansion coefficient of the sort similar, austenitic stainless steel and carbon steel up to minimum;

4, carbon steel, ferritic and martensitic stainless steel magnetic, non-magnetic austenitic stainless steel, but it will have to generate a magnetic work hardening, heat treatment method available martensitic transformation to eliminate this martensite organization and restore its non-magnetic.

Compared with austenitic stainless steel, has the following characteristics:
1) high resistivity, carbon steel is about 5 times.
2) a large linear expansion coefficient, 40% larger than that of carbon steel, and as the temperature rises, the value of the linear expansion coefficient is also increased accordingly.
3) low thermal conductivity, about 1/3 of carbon steel.

Austenitic stainless steel

More than 18% chromium, it also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Good overall performance, corrosion resistant variety of media. Common austenitic stainless steel grades are 1Cr18Ni9,0Cr19Ni9 like. Wc 0Cr19Ni9 steel <0.08%, steel labeled “0.” This kind of steel contains large amounts of Ni and Cr, the steel at room temperature was austenitic state. Such steel has good ductility, toughness, weldability, corrosion resistance and non-magnetic or weakly magnetic, corrosion resistance are good in oxidizing and reducing medium, used to produce acid and equipment, such as corrosion resistant containers and equipment linings, pipelines, nitric acid resistant parts and other equipment, and also can be used as the main material of stainless steel jewelry watches.

Austenitic stainless steels commonly used solution treatment, is about steel heated to 1050 ~ 1150 ℃, and then air-cooled or water-cooled, in order to obtain a single phase austenite.