The Different Processes of Tempering Tools Made from Metals and Alloys

Tempering is a type of heat treatment used for metals and alloys. With metals and alloys, tempering ensures that a balance between brittleness and ductility is obtained. Steel objects, for instance, tempering is applied to transform martensite into ferrite or bainite. There are different ways to temper metals and alloys and all of them have their own sets of pros and cons.

The Different Processes of Tempering Tools Made from Metals and Alloys

Precipitation Hardening – This technique is mainly used to strengthen or harden extremely malleable materials. There are mostly alloys without or lacking iron content and including even titanium and aluminum.

Tempering by the Color Method – Sometimes, the level of temper is gauged by its color. Firstly, the object is placed on a gas-heated plate or a heated similar structure. Afterwards, the surface of the metal object brightens; it will gradually show more colors as its temperature rises. The first color you’ll see is a hint of yellow on its surface. Later on, it will blend into brown, purple, blue and a lot more colors in between. You can find tables on the Internet to determine the range of temperature ascribed to each color change.

Tempering in Oil – Another way of tempering metals and alloys is by using oil baths. The object being tempered is plunged into an oil bath in this process. A thermometer is used to determine temperature levels of the object. Not all types of metals and alloys however can be tempered in oil baths. Cold steel, for instance, cannot be immersed in oil baths because they can be in danger of cracking. They should be pre-heated at first and reach approximate 300 degrees Fahrenheit before being immersed.

Oil baths can produce a temperature range from 650 to 700 degrees Fahrenheit. Lead baths can go higher. Tempering in oil baths can be achieved with a fire test and an oil bath made from a mixture of saponifiable and mineral oil. Besides requiring specific percentage compositions for both substances, the oil bath must also ascribe to certain flash point and specific gravity figures. Tempering in oil baths can have improved performance if you constantly add in new mineral oil.

Tempering in Lead – As previously mentioned, tempering may be done in lead baths if you desire higher temperature levels. In some cases, they serve as a preparatory step prior to tempering in oil bath and as such is in the case of preheating steel. When you wish to lower the temperature level in lead baths, you’ll just have to change the percentage composition of tin and led.

One of the difficulties with tempering in lead is preventing lead from clinging to steel. To solve this, you can mix wood alcohol with common whiting then applying it to the part or side of the object that’s going to be tempered. If you wish to substitute common whiting with water, that’s possible but it does require you to wait for the paint to completely dry first before tempering it in a lead bath.

Another method of preventing lead from sticking to steel is by creating thick paste made up of 2 pounds of table salt, one to one and a half pound of fine wheat flour, and lastly, one pound of charred leather. After applying the mixture to the metal tool, heat the tool, letting the paste dry and harden.

A third method is heat the metal tool until it shows off a bluish shade, typical when the temperature level reaches 600 degrees Fahrenheit. When it reaches that level, dip it in a potent salt water solution prior to immersion in a lead bath.

Be careful when choosing pots to hold your lead bath for tempering. The best ones are made from seamless drawn steel. Cast steel, iron, and other metals are also adequate but only if they are of excellent quality. In any case, the latter is still less durable, lasting only a couple of days when the former can last up to half a year.

Tempering in Sand – Tools can also be tempered in a sand bath. In this technique, tools may be tempered in varying degrees because of a sand bath’s design and the positioning of the tool. First, sand is deposited on a heated iron plate. With this design, temperatures tend to be higher on the bottom end.

Tools that are tempered in sand must first be subjected to polishing since leaving them unpolished makes them difficult to gauge by color.

Using a Toolmakers Microscope to Evaluate Tools
Once you’re done tempering and the tools have sufficiently cooled off, you can place them on the stage of your toolmakers microscope and observe your end product. Check for flaws in design and functionality.

If you don’t have a toolmakers microscope yet, make sure you buy one that’s equipped with digital camera features, USB connection, and excellent magnification range. Check if it also offers the special type of illumination required for studying the shiny surfaces of metals and alloys.

For more information, please visit http://www.toolmakers-microscope.com.