Pearlitic stage
Pearlite stage is a lamellar structure of ferrite and cementite, formed during slow isothermal transformation of undercooled austenite. It has higher hardness than austenitic steel but less toughness.
Physical-Chemical Mechanism of Action
During the slow isothermal transformation of austenite into pearlite, ferrite and cementite form through a diffusion-controlled phase transition. The ferrite lamellae are fine and have low hardness, while the cementite lamellae are thinner and harder.
Metallurgical Relevance & Welding Risks
Pearlitic structures can lead to crack-sensitive microstructures if cooling is too fast. Rapid cooling can prevent austenite from having enough time to transform into pearlite, instead forming glass-hard martensite. This increases hardness and raises the risk of hot cracking.
Workshop Practice & Action Guidelines
To achieve a stable pearlitic structure, it's important to keep the cooling of the weld to a minimum. This can be done by choosing a suitable shielding gas or using cooling water. The optimal cooling rate depends on the specific steel and the desired properties, but as a rule, cooling should be slower than rapid cooling.