Corrosion of materials and protection methods
Corrosion of materials
1. Chemical corrosion 65Mn is oxidized at high temperatures and is affected by carbon dioxide, sulfur dioxide, oxygen, hydrogen and other gases in a dry environment at room temperature, and causes chemical effects in non-electrolyte liquids (such as gasoline and lubricating oil). This is the chemistry of 65Mn corrosion.
2. Electrochemical corrosion 65Mn often comes into contact with other materials during work, or dust, dirt, etc. are often scattered on the work piece. The two different state parts or the parts where the two substances are in contact will cause a potential difference. If you contact the electrolyte or Absorbing sulfur dioxide, carbon dioxide, and moisture, etc., will cause micro-batteries to form an electric current and dissolve the metal that is the negative electrode. In the industrial atmosphere, all kinds of dust (including acid, alkali, salt) and dirt are often dropped, and the materials will corrode quickly.
Anti-corrosion measures for materials
1. Anti-corrosion To prevent 65Mn from rusting, it should be coated with preservatives or chemically treated to form a protective film before leaving the factory, or plated or packaged, and then transported to the warehouse. (The oiled material when entering and exiting, if found to be stained Or if the oil bottom is rusted or volatile and dry, it should be decontaminated and descaled, and repainted with oil.) During acceptance, the box should be folded according to the regulations, and the packaging should be restored immediately after acceptance. When storing, put a desiccant in the warehouse to reduce moisture and humidity.
2. Spraying anti-corrosion 65Mn is generally used in the open air. Spraying anti-corrosion coating on the surface of the material can isolate the material from air, rain and other corrosive media, and eliminate the chance of electrochemical corrosion of the material during storage. Especially the 73418 anti-rust oil, it can form a continuous film on the surface of the steel, after natural drying, firmly adhere to the surface of the steel, can prevent the steel from rusting for a year, and has low cost and easy use.
Welding of 65Mn steel wire:
The welding experiment of 65Mn steel wire with φ0.7 mm was carried out by the method of argon tungsten arc welding. Studies have shown that: when the welding current is 10 A, a perfect cylindrical welded joint can be obtained, but the joint is very brittle and hard. The use of a heating temperature of 280°C and a post-heating process of 10 minutes of heat preservation can greatly reduce the brittleness and hardness of the joint. The tensile strength of the welded joint after treatment is up to 1 370 MPa, and it has excellent fatigue strength. Therefore, if the welded ring-shaped steel wire is plated with diamond abrasive, it may become an efficient cutting tool.
Composition and performance of 65Mn steel wire
The steel wire used in this study is a 65Mn cold drawn steel wire with a diameter of 0.7 mm. The original structure is sorbite and a small amount of ferrite, which are distributed in fibrous form. The carbon content of 65Mn is 0.62% to 0.70%, and the content of Si and Mn are 0.17% to 0.37% and 0.9% to 1.2%, respectively. Mn moves the S and E points in the iron-carbon phase diagram to the lower left and lowers the A3 and A1 lines. Therefore, manganese steel has a tendency to overheat. 65Mn steel is a high-carbon steel, and the combined effect of Mn and Si makes its carbon equivalent more than 0.8%. This makes 65Mn steel have a great tendency to harden, and the weldability is extremely poor.
Argon arc welding butt welding process of 65Mn steel wire
In order to reduce the consumption of the electrode, the DC positive connection is selected for the butt welding test of the wire, that is, the DC power supply is selected, the wire is connected to the positive electrode of the power source, and the tungsten electrode is connected to the negative electrode of the power source.
The tungsten electrode containing 1% or 2% thorium oxide has high electron emission efficiency, good current carrying capacity, good anti-pollution performance, easy arc ignition and relatively stable arc. In order to facilitate the operation, a finer thorium tungsten electrode with a diameter of 2 mm was selected, and the tip of the electrode was sharpened.
Since the lower arc voltage characteristics of argon are particularly beneficial for manual arc welding of thin plates and wires, argon is selected as the shielding gas.
A DC manual argon arc welding machine was used for the test. Before welding, both ends of the steel wire were carefully polished flat. In order to prevent pores in the solder joints, the end oil was cleaned with acetone. Place the flat wire on both ends on a flat and clean alignment plate, align the ends without leaving a gap at the joint, and press the two sides of the joint with a weight. Connect the wire to the positive electrode of the welding machine and the tungsten electrode to the negative electrode, and adjust the current to 20 A, 15 A, 10 A, and 8 A for welding. When welding, ignite the ignition arc next to the joint and make it stable. Move the arc to the joint to melt the joint metal and quickly extinguish the arc. At the same time, apply a slight upsetting force to complete the welding process after cooling. Use filler wire.
The test found that when the welding current is 20 A, the arc burns violently, the metal spatter at the joint is serious, and the welding joint collapses seriously. When the current is adjusted to 15 A, the arc burns more smoothly and the molten pool splashes less, but the weld still collapses. But when the current drops to 10 A, the arc is easy to start, the arc burns stably, and there is no collapse in the weld. Figure 2 shows the shape of the welded joint taken with a digital camera under a Leica MZ6 stereo microscope when the welding current is 10 A. It can be seen that the cylindricity of the joint is good, and it can meet the requirements of a wire saw after grinding. When the current is adjusted below 8 A, it is difficult to start the arc and the arc is unstable, making it difficult to complete the welding process.