Salt bath dominated by cyanide

Soft nitriding salt bath contains a high proportion of toxic substances-cyanide of potassium and sodium. They are oxidized by ventilation. In this process, almost half of them are converted into cyanate. Cyanate immersed in oxygen is an active compound, which reacts with steel surface in salt bath nitration at 570℃ to form nitride. This compound is not as brittle as iron nitride [1], and its structure is effectively used to improve the durability and resistance of the system. Nitrogen also diffuses into the lower chemicals, which helps to improve their fatigue strength. This dual role of nitrogen began in1960s. [2]

However, the process of salt bath has another disadvantage, that is, the chemical composition in salt bath is difficult to control. In addition, the neutralized waste salt and the treated rinse water are harmful to the environment. The ecological problems caused by the use of toxic compounds have hindered its development. In many cases, this process has been replaced by gas nitriding.

Salt bath with cyanate as the main component.

The demand for new compounds that provide the same nitriding ability has led to successful solutions. That is to say, there is no cyanide in the salt bath of cyanate-based products [3,4]. With the help of developing more organisms, the new compounds keep the reaction to a minimum and simplify the control process, thus reducing the problem of salt collection. Compared with the cyanide salt bath in the past, the nitriding method adopted in the new salt bath reduces the treatment cost by 30%.

However, the chemical reactivity of salt bath dominated by cyanate is more difficult to control. To this end, for some time,

Later, the new salt bath technology based on cyanate was used in many heat treatment plants. 1973 Pakaraseiko Co., Ltd. of Japan established a low temperature treatment device for hot deformation extrusion nitriding die below 480℃. [5] The temperature of 480 C can prevent the hardness from decreasing during treatment. Under the condition that the hardness does not decrease, the low temperature nitriding of extrusion die appears repeatedly. The further study of this set of tools makes it possible to reduce the temperature to 430-440°C, which broadens the application of active salt bath nitriding method.