First, 304 stainless steel
1 Introduction:
304 stainless steel is a common material in stainless steel, with a density of 7.93 g/cm3. Also known as 18/8 stainless steel in the industry. High temperature resistance of 800 degrees, good processability and high toughness, widely used in industry, furniture decoration industry and food and medical industry.
Common marking methods in the market are 06Cr 19Ni 10 and SUS304, in which 06Cr 19Ni 10 generally represents national standard production, 304 generally represents ASTM standard production and SUS 304 represents Japanese standard production.
304 is a general-purpose stainless steel, which is widely used to manufacture equipment and parts that require good comprehensive performance (corrosion resistance and formability). In order to maintain the inherent corrosion resistance of stainless steel, steel must contain more than 18% chromium and more than 8% nickel. 304 stainless steel is a stainless steel brand produced according to American ASTM standard.
2 scope of application:
System description: 304 stainless steel is the most widely used chromium-nickel stainless steel [1]. As a widely used steel, it has good corrosion resistance, heat resistance, low temperature strength and mechanical properties. Good hot workability such as stamping and bending, and no heat treatment hardening phenomenon (service temperature-196℃ ~ 800℃). Corrosion resistance in the atmosphere, if it is industrial atmosphere or heavily polluted area, it needs to be cleaned in time to avoid corrosion. Suitable for food processing, storage and transportation. It has good machinability and welding performance. Plate heat exchangers, corrugated pipes, household articles (1 2 tableware, cabinets, indoor pipes, water heaters, boilers, bathtubs), auto parts (wipers, silencers, molded products), medical devices, building materials, chemistry, food industry, agriculture, ship parts, etc. 304 stainless steel is a nationally recognized food-grade stainless steel.
Most of the use requirements are to keep the original appearance of the building for a long time. When determining the type of stainless steel to be selected, the main considerations are the required aesthetic standards, the corrosiveness of the local atmosphere and the cleaning system to be adopted. However, more and more other applications only seek structural integrity or impermeability. Such as roofs and side walls of industrial buildings. In these applications, the owner's construction cost may be more important than beauty, and the surface is not very clean. The effect of using 304 stainless steel in dry indoor environment is quite good. However, in rural and urban areas, if you want to keep its appearance outdoors, you need to clean it frequently. In heavily polluted industrial areas and coastal areas, the surface will be very dirty and even rusty.
However, in order to obtain the beautiful effect in outdoor environment, nickel-containing stainless steel must be used. Therefore, 304 stainless steel is widely used in curtain walls, side walls, roofs and other building applications, but in the industrial or marine atmosphere with severe corrosiveness, it is best to use 3 16 stainless steel. Stainless steel sliding door, people have fully realized the advantages of using stainless steel in structural application. Some design standards include 304 and 3 16 stainless steel. Because "duplex" stainless steel 2205 combines good atmospheric corrosion resistance with high tensile strength and elastic ultimate strength, it is also included in European standards. Product shape In fact, stainless steel is made according to all standard metal shapes and sizes, and there are many special shapes. The most commonly used products are thin plate and strip steel, and special products are also medium plate, such as hot rolled structural steel and extruded structural steel. There are also round, oval, square, rectangular and hexagonal welded or seamless steel pipes and other forms of products, including profiles, bars, wires and castings.
Second, zinc alloy
1 Introduction:
Zinc alloy is an alloy based on zinc and added with other elements. The alloying elements usually added are low-temperature zinc alloys, such as aluminum, copper, magnesium, cadmium, lead and titanium. Zinc alloy has low melting point, good fluidity and easy fusion welding. Brazing and plastic processing, corrosion resistance in the atmosphere, and easy recovery and remelting of prohibited materials; But the creep strength is low and easy to occur? Natural aging leads to dimensional changes. Prepared by melting, die casting or press working. According to the manufacturing process, it can be divided into cast zinc alloy and deformed zinc alloy.
The main additive elements of zinc alloy are aluminum, copper and magnesium. Zinc alloy can be divided into deformed zinc alloy and cast zinc alloy according to processing technology. The cast zinc alloy has good fluidity and corrosion resistance, and is suitable for die-casting instruments, automobile parts shells and so on.
Two characteristics:
1) is more important.
2) The casting performance is good, precision parts with complex shapes and thin walls can be die-cast, and the casting surface is smooth.
3) Surface treatment: electroplating, spraying, painting, polishing, grinding, etc.
4) In the process of melting and die casting, no iron is absorbed, no corrosion is formed, and no mold is stuck.
5) It has good mechanical properties and wear resistance at room temperature.
6) Low melting point, melting at 385℃, easy for die casting.
3 Instructions for use:
1) has poor corrosion resistance.
When the impurity elements lead, cadmium and tin in the alloy composition exceed the standard, the casting will undergo aging deformation, which shows volume expansion, mechanical properties, especially plasticity, decrease significantly, and even break after a long time.
Lead, tin and cadmium have little solubility in zinc alloys, so they are enriched on grain boundaries to become cathodes, and aluminum-rich solid solutions become anodes, which promote intergranular electrochemical corrosion in the presence of water vapor (electrolyte). Die castings are aged due to intergranular corrosion.
2) Aging effect
The microstructure of zinc alloy is mainly composed of zinc-rich solid solution containing Al and Cu and Al-rich solid solution containing Zn, and their solubility decreases with the decrease of temperature. However, due to the extremely fast solidification speed of die casting, the solubility of solid solution is greatly saturated at room temperature. After a certain period of time, this supersaturated state will gradually ease, and the shape and size of the casting will change slightly.
3) Zinc alloy die castings should not be used at high temperature and low temperature (below 0℃). Zinc alloy has good mechanical properties at room temperature. However, the high-temperature tensile strength and low-temperature impact properties decreased significantly.
4) The zinc alloy die casting will have burrs on its surface due to the problems of insufficient clamping force, poor clamping, insufficient mold strength, too high melting temperature and so on. This phenomenon is called product burr, which is often a post-processing process that enterprises must face. According to the nature of the product, it is mainly solved by manual grinding, oxyhydrogen explosion and Zhaolin freezing shot blasting machine.