Common defects of the hottest ion nitriding

Common defects of ion nitriding

first, the hardness is low

in production practice, the surface hardness of the workpiece after nitriding sometimes does not meet the requirements of the process regulations. The light one can be reworked, and the heavy one will cause scrap. There are many reasons for low hardness: there are equipment reasons, such as oxidation caused by system leakage; There are reasons for material selection, such as improper material selection; There are reasons for early heat treatment, such as low basic hardness, surface decarburization, etc; There are technological reasons, such as too high or too low nitriding temperature, short time or insufficient nitrogen potential, resulting in too thin nitriding layer, and so on. Only by finding out the causes according to the specific situation can the problem be solved

II. Uneven hardness and infiltration layer

improper charging method, improper air pressure adjustment (such as excessive air supply), uneven temperature, unshielded small holes and narrow seams, resulting in overheating, will cause uneven hardness and infiltration layer

III. deformation out of tolerance

deformation is difficult. The biggest advantage of this experimental machine is that it can measure the wear depth of the sample. For deformable parts, the following measures are taken to reduce deformation. Before nitriding, stabilization treatment (treatment times can be several) shall be carried out until the deformation before nitriding is controlled within a small range (generally not more than 50% of the allowable deformation after nitriding); The speed of temperature rise and drop during nitriding should be slow; In the insulation stage, try to make the temperature of all parts of the workpiece uniform and consistent. For the workpiece with strict deformation requirements, if the process permits, the nitriding temperature should be as low as possible

IV. poor apparent quality

the appearance quality of nitrided parts shall be checked with the naked eye first after coming out of the furnace. The surface of steel parts after nitriding treatment is usually silver gray or dark gray (the surface color of workpieces of different materials is slightly different after ion nitriding), and the surface of titanium and titanium alloy parts shall be golden yellow. After plasma nitriding, the workpiece surface should not have obvious defects such as arc burn and peeling, which can be achieved under normal conditions. Abnormal nitriding color has the following conditions:

1. Surface arc burn: it is mainly caused by strong arc discharge caused by oil-containing impurities on the surface of the workpiece, in the small holes on the workpiece, or in the cavity of the weldment and the joint surface of the assembly

2. Surface peeling and peeling: peeling occurs. For example, the mechanism of sh/t0202 ⑼ 2 ring stiffness testing machine, which is usually applicable to the heightening of equipment, is not very clear, but in production practice, peeling sometimes occurs due to unclean surface cleaning of workpiece, decarburization or excessive oxygen content in gas, high nitriding temperature, etc

3. The surface is bluish or purplish blue

this is caused by oxidation. If the oxidation is generated during the shutdown process after nitriding, it will only affect the appearance quality, but not the hardness and depth of the nitriding layer. If oxidation is produced in the nitriding process, it will not only affect the appearance of the product, but also directly affect the hardness and depth of the nitriding layer

the reasons for the bluish surface may be: the furnace system leaks air, and the atmosphere contains too much water and oxygen; In addition, the parts with low temperature are green due to weak nitriding; When cooling, the cooling speed of various parts of the workpiece is inconsistent, and the parts that are cooled slowly may be blue

4. The surface is blackened

this will affect the appearance of parts with nitriding as the last process, but generally does not affect the hardness and depth of the nitriding layer. The reasons for this phenomenon may be: the furnace system leaks air, and the water content and oxygen content in the atmosphere are too high; The temperature is too high; The oil stain and oxide skin on the workpiece are not removed

v. vein nitride

vein nitride is also commonly known as vein tissue, which refers to the nitride in the diffusion layer with a white wavy trend parallel to the surface. Its formation mechanism is still unknown. It is generally believed that it is related to the grain boundary segregation of alloy elements and the diffusion of nitrogen atoms. Therefore, the measures to control the segregation of alloy elements are conducive to reducing the formation of vein nitrides. In terms of process parameters, the higher the nitriding temperature is, the longer the holding time is, the easier it is to promote the formation of vein structure. For example, at the edges and corners of the workpiece, because the nitriding temperature is relatively high, the vein structure is much more serious than other parts. (end)