Can someone please explain?

Question

This tool is called a McLeod rake, a tool commonly used in fighting forest fires or wild fires. It is used to clear vegetation in order to make firebreaks, and also to cut off stray branches. The metallic head part of the rake is often made out of steel with low-to-moderate carbon content of around 0.5 wt% carbon, making it a reasonably ductile material.
You and your friend decided to take a break to get some water. However, as you returned with cold drinking water, you were alarmed to find a sudden change in wind direction has brought some rogue embers right in front of you. Your friend rushes to grab his McLeod rake that he had left on the ground, but as he picked it up, he found a large burning ball of grass attached to the “teeth” of the rake. Almost by reflex, he dumps his drinking water onto the metal head to put out the fire. The water sizzled as it touched the hot metal and steam rose into the foggy air.

As your friend p
lowed through the dry grass, he accidentally hit the head of the rake on a large rock. To his dismay, several teeth of the rake broke off.

You knew why your friend’s normally ductile rake suddenly fractured in a brittle fashion. What do you think happened?