"became rusty" is a grammatically correct and commonly used phrase in written English.
It can be used to describe an object, skill, or knowledge that has deteriorated or lost its effectiveness due to neglect or lack of use. Example: After years of disuse, the old bike in the garage became rusty and was no longer rideable.
After the withdrawal, the American tools to understand the complexity of relationships in Central and South Asia became rusty.
The technology was too expensive to implement, and bike-share organizers found that the bicycles, when stored outdoors for extended periods, became rusty.
In those years (which immediately follow the close of his autobiography 'A Sort of Life'), his writing became rusty with misuse and disuse.
The tower was closed in 1914 following the outbreak of the First World War, for the duration of which the steel structure was not maintained and consequently became rusty.
Nails had become rusty, planks had to be smashed to open the cases.
Once learned, they are not forgotten, even if the language one studied in elementary school and high school becomes rusty.
Surmounting the structure at intervals of about three feet are Y-shaped pieces of metal, on which are strung strands of barbed wire that have become rusty.
It is very strong, it has hardly any friction on the surface, it doesn't want to react with anything, [it] cannot oxidize and become rusty".
Long-term joblessness causes people's skills to become rusty, which makes it harder for them to find work even when the labour market recovers.In this section Output, prices and jobs The Economist commodity-price index Long term unemployment Trade, exchange rates, budget balances and interest rates Markets Foreign direct investment Reprints.
And when it comes to conveying intangibles, skills tend to become rusty with disuse.
(She's become rusty on basic questions over the years).
