Metallurgical factors influencing the HIC and SSC behavior of low alloy C-Mn steel plates for pressure vessels are investigated. Numerous HIC and SSC tests have been performed on a great number of plates. From the results obtained it is shown that the behavior of steels can be improved by: 1) Use of very clean steels: The sulfur and phosphorus content must be kept as low as possible. It is shown that for very low sulfur content (< 0,001%), calcium treatment is not necessary since sulfides are already globular. Oxygen has also to be kept low (< 0,002%) to avoid oxide inclusions. 2) Avoiding segregation: It is shown that cracking occurs in hard segragated bands. HIC cracking has been found to be related to phosphorus segregation. C and Mn content must be kept as low as possible, improvement of mechanical properties can be obtained by alloying and microalloying additions.
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