1.the definition of stainless steel
In the air or chemically corrosive media to resist corrosion of a high-alloy steel, stainless steel is a beautiful surface and good corrosion resistance, without the need for color plating and other surface treatment, and the play of stainless steel inherent surface properties, the use of a variety of steel, commonly known as stainless steel. The representative performance of 13 chromium steel, 18-chromium-nickel steel and other high-alloy steel.
From the metallographic point of view, because stainless steel contains chromium and the surface of the formation of a very thin chromium film, this film separates the invasion of oxygen with the steel to play a role in corrosion resistance. In order to maintain the inherent corrosion resistance of stainless steel, the steel must contain more than 12% chromium.
2.the types of stainless steel
Stainless steel can be broadly classified by use, chemical composition and metallographic organization.
Austenitic system of steel by 18% chromium – 8% nickel as the basic composition, the addition of the elements vary, and the development of various uses of steel.
- Classified by chemical composition.
①CR series: ferritic series, martensitic series
②CR-NI series: austenite series, abnormal series, precipitation hardening series.
- Classification by metallographic organization.
①Austenitic stainless steel
②Ferrite stainless steel
③Martensitic stainless steel
④Duplex stainless steel
⑤ precipitation hardening stainless steel
3. the surface category of stainless steel
Now the development of stainless steel, has made the corrosion resistance, appearance, processability, strength and other characteristics of stainless steel far more than other materials, and, many surface treatment method of stainless steel, you can obtain a colorful color and shape, which makes a great contribution to the development of stainless steel.
Stainless steel manufacturing process surface treatment method and mechanical grinding surface treatment method (surface characteristics manufacturing method outline uses):
NO.1 Silvery white, non-glossy A rough, non-glossy surface that is hot-rolled to a specified thickness and then annealed and descaled.
NO.2D Silvery white, cold rolled, heat treated, pickled, and sometimes lightly rolled in a final pass on a rough roll. 2D products are used for applications where surface finish is not required, general purpose materials, and deep-drawn materials.
NO.2B The luster is stronger than NO.2D. After NO.2D treatment, the final light cold rolling is done by polishing rolls to obtain the proper luster. This is the most common surface treatment, and it can be used as the first step in polishing. General materials used
BA Bright as a mirror No standard, but usually a bright annealed surface finish with high surface reflectivity. Construction materials, kitchen utensils
NO.3 Rough grinding The NO.2D and NO.2B materials are ground with a 100~200 grit grinding belt. Building materials and kitchen utensils
NO.4 Intermediate grinding The polished surface obtained by grinding NO.2D and NO.2B with 150~180 grindings is a general-purpose, mirror-reflective, bright surface with visible ‘grains’.
NO.240 Fine polishing: Grind the NO.2D and NO.2B materials with a 240 grain abrasive belt.
NO.320 Extremely fine grinding grinding of NO.2D and NO.2B with a 320 grit abrasive belt Ditto
NO.400 Brightness close to BA Grind NO.2B with 400 polishing wheel General use, construction use, kitchen utensils
HL Hairline polishing Abrasive material with appropriate particle size for hairline polishing (150~240) with a lot of particles for building and construction materials.
NO.7 Near mirror grinding Grinding with 600# rotary polishing wheel for art and decoration
NO.8 Mirror grinding Mirror grinding with polishing wheel Reflective mirror, decorative use
4. classification of steel
Classified by chemical composition.
Alloy steel: low alloy steel: alloy elements ≤ 5% High alloy steel: alloy elements ≥ 10% Medium alloy steel: alloy elements
5%-10% Note: Stainless steel is high-alloy steel.
Classification by quality.
High quality steel
High quality (A)
Extra high quality steel (E)
Classified by smelting method.
Flat Furnace Steel
Electric furnace steel
Classified by application.
C plain structural steel
Alloy structural steel e.g. 40Cr
C plain tool steel e.g. T8
Alloy tool steel e.g. 3Cr2W8V
Spring steel e.g. 60Si2Mn
Bearing steel such as:GCr15
Stainless steel heat-resistant steel
High-speed steel such as: W18Cr4V
Classified by metallographic organization.
By annealing state:
By annealing state: Stainless steel as an example
Austenitic: 0Cr18Ni9 (304) aka: 18-8
Martensitic: 1Cr13 2 2Cr13 3Cr13 also known as: Cr13 type
Ferritic: 1Cr17 Cr25Ti
Duplex stainless steel (ferritic, austenitic duplex): e.g.: 3RE60
Sink pad solid solution hardening stainless steel: 0Cr17Ni7A1 for the missile nuclear industry
5.the characteristics of stainless steel
- General characteristics
Beautiful surface and the possibility of diversification of use
Good corrosion resistance, long-lasting than ordinary steel
Good corrosion resistance
High strength, so the possibility of using thin plates
High temperature oxidation resistance and high strength, so it can resist fire
Normal temperature processing, i.e., easy plastic processing
Easy and simple maintenance because surface treatment is not necessary
High cleanliness and finish
Good welding performance
2-1 Quality characteristics of stainless steel
Item Basic organization
Representative steel grade STS304 STS430 STS410
Heat treatment solid melt heat treatment annealing annealing and rapid cooling
Hardness Process hardening Slight hardening Small amount of hardening
Main applications Interior and exterior decoration of buildings, kitchen utensils, chemical scales, aerospace equipment, construction materials, automotive parts, appliance, kitchen utensils, lunch boxes, etc. Brazier and knife parts, hospital utensils, surgical utensils
Corrosion resistance High High Medium
Strength High Medium High
Workability High Medium High
Magnetism Non-magnetic Upper magnetic Upper magnetic
Weldability High Medium Low
2-2 Stainless steel quality characteristics required Application Object product Processing process Required quality characteristics
Surface quality BQ material shape thickness tolerance weldability corrosion resistance
Shallow processing knives, forks, etc. Drop → cross extension → cutting head → forming → polishing → cleaning → packaging high requirements shall not have defects such as pitting good general material general -5% not required good
Deep processing class Two types of tableware, insulation cups, etc. Material → oiling → forming → (sometimes several times) cutting edge → rolled edge → cleaning → re-bottom → polishing → welding handle → packaging High requirements shall not have scratches and creases and other defects Good DDQ high requirements -3 ~ -5% Good Good
PIPE decorative tubes and other narrow strips → extrusion into pressure forming → butt welding → polishing welding seam → pipe cutting → grinding mouth → polishing → packaging high requirements shall not have creases and other defects general general material good -8% good general
The outer wall of the kitchen cold cabinet etc. is dropped→folded→electric welding→polishing high requirements shall not have creases and other defects general general material general-8% good general
Vessel water heater drinking fountain liner narrow strip → roll → welding → pipe cutting → welding bottom → polishing weld → packaging general general general material general -10% good general
※The quality requirements of processing and raw materials are different for each product due to the different uses.
2-3 Quality requirements characteristics microfine items
① DDQ (deep drawing quality) material: refers to the material used for deep drawing (punching) purposes, which is what we call soft material, the main feature of this material is a high elongation (≧ 53%), low hardness (≦ 170%), internal grain grade between 7.0 ~ 8.0, deep punching performance is excellent. At present, many production of thermos bottles, pots and pans, the processing ratio of its products (BLANKING SIZE / product diameter) are generally higher, their processing ratio of 3.0, 1.96, 2.13, 1.98. SUS304 DDQ with material is mainly used for these requirements of higher processing ratio of products, of course, processing ratio of more than 2.0 products are generally required after several times of Stretching to complete. If the extension of raw materials can not reach, in the processing of deep-drawn products, the product is very easy to produce cracks, pull through the phenomenon, affecting the finished product qualification rate, of course, also increases the cost of manufacturers.
②general material is mainly used in addition to DDQ use of materials, this material is characterized by relatively low elongation (≧ 45%), and relatively high hardness (≦ 180), internal grain size grade between 8.0 ~ 9.0, and DDQ with the material, its deep punching performance is relatively slightly worse, it is mainly used for products that can be obtained without stretching, such as a class of tableware spoons, spoons, forks, electrical appliances, steel pipes Use, etc. But it has an advantage compared with DDQ material, that is, BQ sex is relatively good, which is mainly due to its slightly higher hardness.
(2) Surface quality.
Stainless steel sheet is a very high priced material, and customers have very high requirements for its surface quality. But stainless steel sheet in the production process will inevitably appear a variety of defects, such as scratches, pockmarks, creases, pollution, etc., and thus its surface quality, such as scratches, creases, etc. These defects are not allowed to appear whether it is a senior material or low-grade, and pockmarks such defects in the spoon, spoon, fork, production is never allowed, because polishing is difficult to throw it off. We determine the surface quality grade according to the degree and frequency of various defects on the surface, so as to determine the product grade.
(3) Thickness tolerance.
Generally speaking, the different stainless steel products, the requirements of the thickness tolerance of raw materials vary, such as the second class tableware and insulation cups, etc., the thickness tolerance is generally required higher, -3 ~ 5%, while a class of tableware thickness tolerance is generally required -5%, steel pipe class requirements -10%, the hotel with the thickness tolerance of cold cabinet material requirements for -8%, the dealer requirements for thickness tolerance is generally between -4% to 6%. At the same time, the difference between domestic and foreign sales of products will also lead to different requirements of customers on the thickness tolerance of raw materials. General export products customer thickness tolerance requirements are higher, while the domestic sales enterprises on the thickness tolerance requirements are relatively low (mostly for cost considerations), some customers even require -15%.
Product use of different welding performance requirements are also different. A class of tableware on the welding performance is generally not required, even including some pot enterprises. But the vast majority of products need raw materials welding performance is good, like the second class tableware, insulation cups, steel pipes, water heaters, water dispensers, etc..
(5) Corrosion resistance.
The vast majority of stainless steel products require good corrosion resistance, such as one or two types of tableware, kitchenware, water heaters, drinking fountains, etc. Some foreign businessmen on the product also do corrosion resistance test: NACL aqueous solution heated to boiling, pour off the solution after a period of time, wash and dry, weigh the loss, to determine the degree of corrosion (Note: the product polishing, because of the composition of the sand cloth or sandpaper containing Fe, will lead to test (when the surface rust spots)
Polishing performance (BQ sex).
At present, stainless steel products are generally polished in the production of this process, only a few products such as water heaters, water dispenser lining, etc. do not need to polish. Therefore, this requires a good polishing performance of raw materials. The main factors affecting the polishing performance are the following.
① raw material surface defects. Such as scratches, pockmarks, over acid washing, etc..
② raw material material problems. Hardness is too low, polishing is not easy to polish bright (BQ sex is not good), and hardness is too low, the surface is prone to orange peel phenomenon when deep drawing, thus affecting the BQ sex. High hardness of BQ sex is relatively good.
③ After deep drawing of the product, the surface of the area of great deformation will also be small black spots and RIDGING, which affects the BQ sex.
- Characteristics and uses of various stainless steels
Steel number characteristics and uses
17Cr-7Ni – low carbon
Compared with 304 steel, Cr, Ni content is less, cold processing tensile strength and hardness increased, non-magnetic, but magnetic after cold processing. Trains, aircraft, conveyor belts, vehicles, bolts, nuts, springs, screens
17Cr-7Ni-0.1N-low carbon is based on 301 steel, reduce the C content, improve the weld resistance to grain boundary corrosion; by adding N elements to compensate for the lack of strength caused by the reduction in C content, to ensure the strength of the steel. Railway vehicle frame and exterior decorative materials
18Cr-8Ni as a widely used steel, has good corrosion resistance, heat resistance, low temperature strength and mechanical properties; good hot workability such as stamping and bending, no heat treatment hardening phenomenon (non-magnetic, use temperature -196 ℃ ~ 800 ℃). Household goods (1 or 2 types of tableware, cabinets, indoor piping, water heaters, boilers, bathtubs), auto parts (windshield wipers, mufflers, molded products), medical appliances, building materials, chemicals, food industry, agriculture, ship parts
18Cr-8Ni-low carbon as low C 304 steel, in the general state, its corrosion resistance and 304 just similar, but after welding or stress relief, its excellent resistance to grain boundary corrosion; in the absence of heat treatment, can also maintain good corrosion resistance, the use of temperature -196 ℃ ~ 800 ℃. Used in chemical, coal and petroleum industries with high requirements for resistance to grain boundary corrosion, open-air machines in the field, heat-resistant parts for building materials and parts with heat treatment difficulties
13Cr-7.7Ni-2Cu because of the addition of Cu its formability, especially drawing and aging crack resistance is good, so it can be complex shape of the product forming; its corrosion resistance is the same as 304. Insulated bottles, kitchen sinks, pots and pans, insulated lunch boxes, door handles, textile processing machines.
18Cr-8Ni-N is based on 304 steel with reduced S and Mn content and added N element to prevent plasticity reduction, improve strength and reduce steel thickness. Structural parts, street lights, water storage tanks, water pipes
18Cr-8Ni-N is a high-strength steel for structural parts with the addition of N and Nb compared to 304. Components, street lights, water storage tanks
18Cr-12Ni-2.5Mo is particularly good in corrosion resistance, atmospheric corrosion resistance and high-temperature strength because of the addition of Mo, and can be used under harsh conditions; excellent work hardening (non-magnetic). Equipment for use in seawater, chemical, dye, paper, oxalic acid, fertilizer and other production equipment; photography, food industry, coastal area facilities, ropes, CD rods, bolts, nuts
18Cr-12Ni-2.5Mo low carbon as the low C series of 316 steel grade, in addition to having the same characteristics as 316 steel, its resistance to grain boundary corrosion is superior. 316 steel is used for products that have special requirements for anti-grain boundary corrosion.
18Cr-9Ni-Ti adds Ti element to 304 steel to prevent grain boundary corrosion; suitable for use at 430℃-900℃ temperature. Aircraft, exhaust pipe, boiler ladle
11.3Cr-0.17Ti-low C, N because of the addition of Ti elements, so its high-temperature corrosion resistance and high-temperature strength is better. Automobile exhaust pipes, heat exchangers, containers and other products that are not heat treated after welding.
13Cr-Low C is based on 410 steel, and the C content is reduced, so its processability, resistance to welding deformation, and high-temperature oxidation resistance are excellent. Mechanical construction parts, engine exhaust, boiler combustion chamber, burner.
16Cr is the representative steel of ferritic steel, and it has excellent thermal expansion resistance, formability and oxidation resistance. Heat-resistant appliances, burners, home appliances, class 2 tableware, kitchen sinks, exterior decorative materials, bolts, nuts, CD rods, screens
18-Cr0.5Cu-Nb-low C.N In 430 steel, Cu and Nb are added; its corrosion resistance, formability, weldability and high temperature oxidation resistance are good. Building exterior decorative materials, automotive parts, hot and cold water supply equipment.
18Cr-1Mo-Ti, Nb, Zr low C, N good heat resistance, wear and corrosion resistance, because it contains Nb, Zr elements, so its processability, excellent weldability. Washing machine, car exhaust pipe, electronic products, 3-layer bottom of the pot.
Martensitic steel 410
13Cr-low carbon as a representative steel of martensitic steel, although high strength, but not suitable for harsh corrosive environment; its processability is good, depending on the heat treatment face hardening (magnetic). Knife blades, mechanical parts, oil refining devices, bolts, nuts, pump rods, Class 1 cutlery (knives and forks).
13Cr-0.2C high hardness after quenching, good corrosion resistance (magnetic) Cutlery (knives), turbine blades.
13Cr-0.3C hardened, higher hardness than 420J1 steel (magnetic) Knife blades, pipe nozzles, valves, plate rulers, cutlery (scissors, knives).
Today’s article is about the introduction of stainless steel. If you have any question, please don’t hesitate to contact us.