Abstract: For the development of direct charging on low alloy steel, Q345B steel was chosen for direct charging study, three regions were divided according to the temperature on the slab surface , found that surface crack less when direct charging in low and high temperature zone, more found in moderate zone, the thin ferrite layers around austenite grain boundary is the prime reason; analysis of cold bending crack on the direct charging plate in the low temperature zone, the results show that band structure and MnS inclusion are the main reason; analysis the effect of microstructure, inclusions, precipitates to the quality of direct charging plate, concludes that direct charging process must avoid the twophase region (austenite and ferrite), avoid the formation of thin ferrite layers, reduce the sulfur content or adding a certain amount of RE for modifying the shape of MnS inclusions, adjust the content of microalloying elements in order to guarantee the strengthening effect.

Key words: direct charging of low alloy steel, direct charging crack, metallurgical structure, inclusions, precipitates