The term 'becomes inflexible' can be summarized by the crossword solution 'STEELS, ' which is a six-letter word. Steel is an alloy of iron and carbon, and is known for its strength and durability. It is often used in construction and manufacturing due to its ability to withstand high temperatures and pressures. When steel is exposed to extreme temperatures or pressure, it can become inflexible and brittle, making it less useful for certain applications.