The DLP method (direct lead patenting process) is a controlled cooling process in which the wire rod is treated with two salt baths after hot rolling, referred to as the two-salt bath method. It was developed by Japan’s Junjin Steel Works and New Nippon Steel Corporation. This method uses the waste heat after wire rod rolling to perform salt bath treatment to obtain the same structural properties as lead bath quenching treatment.
Compared with the wire rod processed by the Stellmore method, it has the characteristics of high strength, good toughness, small performance dispersion, and uniformity. It can completely replace the lead bath quenching treatment before the wire rod is reprocessed, saving man-hours, energy, and eliminating the need for Lead dust and lead smoke pollute the environment and harm the human body.
The process flow is shown in the figure. After the wire rod comes out of the finishing mill, it forms a loose coil through the coiler and enters the first salt bath. It is quickly cooled to about 500°C in the bath to prevent austenite from transforming into coarse pearlite in the high temperature zone; then it enters the second salt bath. The transformation from austenite to troostite is completed at ahigh temperature and special composite alloy machining ; after the wire comes out of the second salt bath, the residual salt remaining on its surface is washed away with warm water, and finally enters the hub to be collected into a disk. The salt bath contains nitrates.
Link to this article：DLP Law
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