Engineering terms usually help out by subtly suggesting their meanings. If someone talks about a quenching operation, then the process becomes self-evident. But that’s not always the case, certainly not when we talk about the normalizing process. It’s a generic term, after all, one that has a dozen different meanings. In heat treatment terminology, however, there’s only one possible meaning. Let’s talk about stress relief.
What is The Normalizing Process?
Steel is generally normalized by inserting a workpiece into an extremely hot furnace. That controlled thermal envelope heats the steel component until it reaches the material’s stated critical transformation range. Hovering just above this transformation point, the grain of the steel alters. It acquires a more uniform structure. After a predetermined hold period, a length of time that maintains the thermal load, the component is allowed to cool in the open air.
What Does Normalizing Mean?
What’s it all about, this normalizing operation? The process has been briefly described, but we’re still left to wonder over the reasoning behind the process. Well, the clues are held in the resulting uniform carbide size and even grain distribution. Cold worked steel has a form of memory. Those ‘memory cells’ form inside the alloy part’s microcrystalline structure. Stress is the hardest memory to eliminate. The normalizing procedure wipes out that memory. It relieves material stress, restores ductility, and generally strengthens that steely backbone.
The Technical Side
As the soaking temperature is maintained, somewhere between 810°C and 930°C, the grain refinement phase is triggered. The normal air cooling stage further enhances the smaller metal grains and distributes the newly transformed cementite structure. Like a magnet wiping the patterns on an old reel-to-reel tape deck, the normalizing process erases work stress until the structural base of the part is ductile but still hard. Used to improve component workability, this technique is inexpensive, especially when compared with the annealing method that carries out a similar role inside a heat treatment facility.
Loaded with pearlite, with a refined grain type that’s rich in ferrite and cementite, the ferrous part is freed of mechanical irregularities, of work hardened stress, and made ductile. Cooled in the open air or in a nitrogen atmosphere, the consistent metal grain is transformed until it reaches a state of refined uniformity. Listen for other descriptive labels when this work is undertaken, like the heat and hold process. And, just as a by-the-way, do remember that the ferrous composition and thickness of the subject workpiece will affect the results of a normalizing treatment.
Despite appearances, heat treatment work relies on a scientifically accurate process. Sure, the coarse industrial outlines operating here may suggest otherwise, but don’t be fooled, this is engineering fidelity labouring at the highest level. Just how are those optimised results achieved? The answer is simple. Every step in the process has to be governable. There’s no room for an unpredictable control element here, so where does this controllability factor originate?
Optimally Maintaining the Furnace Atmospheres
In practically every other industrial process, we ignore the atmosphere. Granted, some of these factories filter the air, or they even opt for a clean room environment, but they don’t control every property in that atmosphere. If heat treatment techniques are to be properly optimized, that atmospheric envelope must be entirely controllable. To that end, the air is sometimes delivered by powerful fans, all the better to ensure uniform heat distribution. Conversely, the air is replaced by an inert gas, such as argon or nitrogen. Sometimes, and this is where the processing methods really take flight, the atmosphere is entirely removed. That’s a principle that’s responsible for the development of vacuum heat treating furnaces.
Intelligently Analyzing Current Operations
If the processing chain is operating, the facility is spitting out heat treated workpieces. Only, much to the distress of all concerned, there’s a higher than average reject rate. The equipment is functioning, but something is going wrong. Fortunately, a process analyzing stratagem can optimize the hardware and the interconnecting linkages that bridge the hardware stations. For example, a process audit not only calibrates the furnace, it also calibrates the instrumentation that records those thermal envelopes. Residual gases are monitored, identified, and addressed. Leakage models are generated and tested. In short, in-house system audits optimize the heat treatment process.
Employing Applied Detective Services
In-house engineering departments can track down heat treatment problems, obviously. Alternatively, there are special services whose duty it is to scrutinize the results of an operational heat treatment facility. Those auditing agents focus on atmospheric integrity and heat distribution uniformity. If there’s an unsatisfactory mechanical and material finish, the specialized operative addresses the issue. Metallurgically proficient, the engineers who carry out this auditing service are trained to identify and refine every processing defect.
Finally, when that auditing procedure is concluded, there comes a time when the management team must decide whether an elevated maintenance program will improve the heat treatment results. If not, this is an opportunity to upgrade the equipment, to incorporate a system that vacuum-seals or otherwise controls all of the conflicting process elements impacting the heat treatment cycle.