Surface treatment methods of commonly used plastic molds

Chlorination is divided into nitrogen seepage and nitrogen carbon co-osmosis. The biggest advantage of this process is that the heat treatment temperature is low (usually 500-600), the deformation after heat treatment is small, the nitride layer is very hard, so that the wear resistance of the mold

And anti-bite improved. The corrosion resistance, heat resistance and fatigue strength of the mold have been greatly improved.
1. Nitriding: Nitriding methods are divided into gas nitriding, liquid nitriding, solid nitriding, ion seepage chlorine and so on. At present, gas nitriding is commonly used, which is to pass nitrogen (NH3) into a furnace of about 550, and the nitrogen obtained by ammonia decomposition penetrates into the steel. The nitriding time is longer, generally about 0.015-0.02mm per hour for shallow layers, and about 0.0050.015mm per hour for deep nitriding. In high alloy steel, due to the high content of alloy elements, the diffusion rate of nitrogen is low, and the nitriding rate will be lower than the above data. The time of gas nitriding (the workpiece is less than 300 X300X50mm) is generally 8-9 hours, the depth of the seepage layer is between 0.1-0.2mm, the surface hardness after nitriding is between HV850-1200 mm (HRC65-72 mm), and the surface color is bright.
2. Nitrogen carbon co-osmosis: that is what we call soft nitride, also known as liquid nitrogen. The nitrogen carbon co-osmosis temperature is slightly higher than the nitrogen seepage temperature, which will not have a great impact on the hardness of the seepage layer. It will not increase the brittleness of the seepage layer, but it can increase the diffusion rate. Nitrogen carbon co-osmosis is generally about 570 as good, low-carbon steel can be more than 600 nitrogen carbon co-osmosis, in order to obtain a thicker compound layer. The depth of the seepage layer increases the fastest in the first 3 hours of nitrogen carbon co-osmosis, and after more than 6 hours, the increase in the depth of the seepage layer is not obvious, so the time of nitrogen carbon co-osmosis is generally not more than 6 hours. The depth of the nitride layer is generally
0.05-0.100mm, the surface hardness is HV1000(RC68 or above), the surface color is 3. Some requirements for nitriding materials: dark gray.

(1) At the nitriding temperature, any material that does not undergo annealing can be nitrided.
(2) Metals with relatively high chromium content (such as 420, S136, 2083, M300), etc. are not subject to gas and nitrogen (because the gas with too high chromium content is difficult to penetrate into the steel).
4. Some phenomena after nitriding
(1) There will be some "swelling" on the surface of the workpiece after nitriding, which is a very thin (0.02-0.03mm) white bright layer formed on the surface of the workpiece, and it is relatively soft,
This layer must be polished off after the workpiece can be restored to its original size, take off the hardness of this layer is also the hardest.
(2) For some thin walls, sharp corners and threads should be properly protected during nitriding to prevent cracking.
5. The relationship between nitriding and welding
(1) In the process of processing, if the workpiece has been burned and welded, it must be told to the heat treatment plant when sending nitriding, so as to facilitate its local tempering treatment, otherwise the hardness of the workpiece after nitriding is uneven, and it is easy to crack or collapse. (2) When the workpiece needs to be welded due to improper use or other reasons after nitriding, if it has a large area, it must be sent back to the heat treatment plant for nitrogen removal (heated to more than 800), then welded, and then nitrided after processing (note: the hardness of the entire workpiece may change). In the case of local welding, there is
There are two methods, one is to polish off the nitride layer and burn it, and the other is to burn it after the nitrogen is removed such as local heating and burning red.