Quenching: Still Many Unknowns
We have previously mentioned the IFHTSE Liquid Quenchants Database project.
Quenching has certainly been around for some time, and its origins are a wonderful example of empiricism. Since swords were first plunged into water, specifications and parameters have expanded somewhat, to put it mildly – there are large and small components of different chemical composition, simple and complex geometries, process varieties, quenchant types, etc.
In the many years since the process has been looked at in an analytical and experimental way, “what actually happens when you quench a metal component” has been increasingly well understood. The use of that understanding for improved process control has, however, brought with it a whole range of other questions, both general and detailed, and asks for a truly multidisciplinary approach to their resolution. Metallurgists are certainly needed, but the development and spread of understanding also requires mechanical engineers, design engineers, chemists, physicists and mathematicians.
Ideally, users of furnaces, quenching equipment and quenchants should have a look-it-up table of all the optimum or recommended parameters for the engineering component they are manufacturing. Such a facility would, of course, still only be a guideline. It would not by any means exclude practical adjustment and modification for individual quality advantage and competitive edge.
Thus, two slightly different but complementary needs can be distinguished:
• More scientific and technological understanding of the process and its control possibilities for specific products, leading to better prediction.
• Establishment of some fundamental practical guidelines for process and quenchant selection. There is no universally recognized technique for measuring, recording and comparing quenchant cooling intensities.
These needs have been addressed most recently by significant developments in modeling techniques. There are commercial software packages, and many academic institutions and some companies have developed their own software. There is no shortage of mathematical capability. The subject is regularly addressed in conferences, especially, for example, in the series Quenching and Distortion Control. Quenching is also a major feature of the series Thermal Process Modelling and Computer Simulation in Heat Treatment and Surface Engineering.
Additionally, the German government put serious funding into a project run by IFHTSE member IWT Bremen, which among other things yielded the term “distortion engineering” and the series of three conferences with that title. There are indications that the German effort will continue. The conference approach to spreading knowledge has, unsurprisingly, produced many hundreds of papers.
The second, very practical need lends itself most usefully to collaborative action. The IFHTSE Liquid Quenchants Database project involves comparative determination of cooling curves to try to nail down the cooling capacities of some common quenchants.
A great deal has been achieved, but holes remain and there is still a long way to go.
• The heavily mathematical approach to the modeling procedures cannot be easily understood by everyone. Feedback from the latest conference in the quenching and distortion series (Chicago, September 2012) revealed a serious gap between the modeling fraternity and the rather larger population who also need to know and understand what is being achieved. There is a real need for explanatory workshops in this area.
• The continuously improving models are of doubtful value without continuously improving real input data.
• Phase 1 of the Liquid Quenchants Database project has meant extensive collaboration among eight participants in eight countries evaluating three types of oil, using three different temperatures for each coolant and with three repetitions. Naturally, as in real industrial life, there were some variations in equipment and calculation method. When the results of this exercise were presented at the 2nd Mediterranean Conference on heat treatment and surface engineering in Croatia in June 2013, however, the scatter in the results presented was surprisingly large (certainly larger than expected). So even this (relatively simple) work needs tighter specification.
Work on the Liquid Quenchants Database and planning for future events in relevant conference series, therefore, will continue. IH