It can be said that the pendulum clock is made up of invar because invar's coefficient of thermal expansion is small. So, the length of the pendulum remains unaffected during changes in temperature. Invar is derived from the word invariable. It is an alloy which is made from nickel and iron. It has a low coefficient of thermal expansion. So, there will not be linear expansion of the pendulum due to the rise in temperature. And the time shown in the clock will be accurate. Thus, invar is used in the pendulum of the clock. Invar, also known as Nickel Alloy 36, is a nickel-iron alloy noted for its uniquely low coefficient of thermal expansion. 

Austenitic grades of stainless steels tend to be the most weldable, but they are especially susceptible to distortion due to their high coefficient of thermal expansion. Some alloys of this type are prone to cracking and reduced corrosion resistance as well. Hot cracking is possible if the amount of ferrite in the weld is not controlled—to alleviate the problem, an electrode is used that deposits a weld metal containing a small amount of ferrite. Other types of stainless steels, such as ferritic and martensitic stainless steels, are not as easily welded, and must often be preheated and welded with special electrodes.