In this column, I will propose a simple control plan for oil-based quenchants and corrective actions.
Oil quenchants have been used extensively to harden steel for more than 100-plus years. There is a wide variety of commercially available quenchants on the market from nearly as many different producers. In this column, a control plan for oil quenchants will be presented.
Many types of oils have been used for quenching, including vegetable, fish and animal oils, and particular sperm whale oil have been used for quenching operations. The first petroleum-based quenching oils were developed around 1880 by E.F. Houghton in Philadelphia. Since that time, many advancements have been made in the development of quenching oils to provide highly specialized products for specific applications.
A wide range of quenching characteristics can be obtained through careful formulation and manufacturing. High quality quenching oils are formulated from refined base stocks of high thermal stability. Selected wetting agents, antioxidants, and accelerators are added to achieve specific quenching characteristics. The additions of these complex antioxidant packages are included to maintain performance for long periods of continued use — particularly at elevated temperatures. Emulsifiers may be added to enable easy cleaning after quenching.
Petroleum-based quench oils can be divided into several categories such as quenching speed, operating temperatures, and ease of removal. The simplest category is operational temperature: cold oils for operation below 90°C, and martempering oils used for temperatures above 90°C.
As part of good practice and required by many auditing agencies such as NADCAP and CQI-9, quarterly or semi-annual testing of the used oil characteristics is required. Typical testing required, and the test method associated with the testing, is shown in Table 1. A corrective action plan is required for out-of-specification testing.
All quenching oils should be checked periodically for their chemical and physical characteristics. If the user does not have in-house capability, the oil supplier or a qualified independent laboratory facility should be used. The results of the laboratory tests should show the quality of the used oil, along with an indication of the type of contamination present. The supplier should also have the expertise to help the user eliminate further degradation. Table 2 shows a typical oil quenchant control plan.
Water is the most common and dangerous contaminant and should be avoided. Water in quench oil causes foaming and even explosions in certain systems. The tendency to initiate fires is greatly enhanced by this foam. Water also increases the tendency toward distortion and cracking of the quenched material. Entire heat-treating facilities have been destroyed by a fire resulting from a quench cycle into an oil containing small amounts of water. If water is detected, then settling, centrifuging, filtration, or heating methods can remove water. Care should be taken that additives are replaced if removed with the water. If heat separation is used, the temperature and time must be controlled to minimize possible oxidation of the oil.
Solvents and other low flash material should be kept away from quenching oils. Reclaimed quench oils from washers, centrifuges, etc., can be returned to the quench tank. However, care must be taken to segregate the quench oil from other products and check its condition prior to adding it to the system.
It is important that the user and supplier of quench oil work together to establish appropriate limits for the user’s process. Many of the latest revisions of specifications, such as AMS 2759  and auditing agencies such as NADCAP , require the heat-treating quenchant supplier to specify in the report whether the oil is “good” or “bad.” It is not possible for the quenchant supplier to know whether an oil or other quenchant provides satisfactory performance, as the supplier does not completely know the parts processed or the processes used. The quenchant supplier can only determine if the used oil satisfies the manufacturing limits for new oil. Working with the customer, these limits can be modified for each application.
As always, should you have any comments or questions regarding this article, please contact the editor or me.
- SAE International, Heat Treatment of Steel Parts, General Requirements, Warrendale, PA: SAE International, 2014.
- SAE International, National Aerospace and Defense Contractors Accreditation Program (NADCAP) Requirements for Heat Treating, Warrendale, PA: SAE International, 2008.