How to Use Quenching Medium Correctly

Today, the popularity of water-soluble quenching media in domestic fastener enterprises is increasing. Besides low-carbon and medium-carbon steels, products such as alloy steels, martensitic stainless steels, and hot-forming mold steels are also attempting to use water-soluble quenching media, and the experience in process control is becoming increasingly mature. However, there are often deviations in the control of the concentration of water-soluble quenching media, which leads to various heat treatment quality problems.

Currently, the heat treatment quenching media used by domestic fastener enterprises mainly include rapid quenching oil and water-soluble quenching media. They come into direct contact with high-temperature workpieces during use, and inevitable changes in physical and chemical properties occur. Therefore, during use, the cooling performance will change to a certain extent, and effective monitoring is required. One is to improve the stability of the quenching medium to ensure that the performance and deformation of the quenched workpiece are within the controllable range; the second is to provide an effective cooling performance monitoring method and "tailor" an optimized quenching medium scheme according to the working conditions to ensure the long-term stable use of the quenching medium.

From the production practice of most fastener enterprises, rapid quenching oil is mainly used for alloy structural steel grades and thin-walled bolts, nuts, and special-shaped parts; water is mainly used for carbon structural steel and simple-shaped fasteners; PAG polymer quenching medium lies between water and oil, and under certain conditions, it can replace water or oil, and has a wide range of cooling intensity.

Polymer quenching medium can eliminate the smoke from quenching oil. It reduces carbon emissions and is a global trend to promote the use of polymer quenching medium. Polymer quenching medium can fully meet safety production requirements and can be confirmed as an important process material for the clean production of fastener heat treatment in China.

Currently, polymer quenching medium is used more and more widely due to its unique advantages in terms of environmental protection, technology, and cost. In recent years, various new environmentally friendly and carbon-reducing quenching media have been developed in China to reduce heat treatment smoke emissions. Currently, the use of polymer quenching medium accounts for approximately 30% to 40% of the total quenching media (oil + polymer quenching medium). In production practice, to improve the effect of the use of polymer quenching medium, the reproducibility of the test results is mainly determined by the reproducibility of the stirring, which is actually turbulence. The use temperature, concentration, and stirring of polymer quenching medium are the key factors to ensure the quenching quality.

Because bacteria in PAG polymer quenching medium use organic matter as raw materials and catalyze their changes, they accelerate the aging of polymer quenching medium, shorten its service life, and increase the cooling rate in the convective stage, increasing the tendency of bolts and nuts to deform and crack during quenching, making it difficult to ensure the quenching quality of fasteners. Only adjusting the concentration to slow down the cooling rate can be achieved, but the effect is not obvious. Using the stable biological polymer quenching medium AQ245 and the excellent rapid cooling agent with excellent environmental performance can better solve the problems of deformation and cracking.

First, configure different concentrations of quenching liquid with new liquid, and test the 300°C cooling rate of the quenching liquid under different concentrations using a cooling characteristic tester, thereby establishing a standard table or graph of different concentrations and cooling rates. Using a cooling characteristic tester is a relatively ideal method. Secondly, for rapid quenching oil, it is best to replace the new oil once a year; water-soluble quenching media are different from quenching oil, and the temperature, concentration, and stirring intensity have a significant impact on their cooling performance. It is recommended to use a helical impeller for strong stirring to ensure the uniformity of cooling, thereby achieving uniformity in microstructure and hardness.