2013•Journal of Central South University(Science and Technology)Requires access
Continuous cooling transformation of undercooling austenite about 28CrMnMoV steel
Su Yang
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Abstract
The dilatometric curves of 28CrMnMoV steel during continuous cooling process at different cooling rates were measured on Gleeble 3500 thermal mechanical simulator.According to DSC analysis and microstructure observation combined with hardness test,the critical temperatures and phase transformation temperatures were determined from the dilatometric curves,which were used to determine the continuous cooling transformation(CCT) diagram of 28CrMnMoV steel.The results show that ferrite(or pearlite) can be formed in supercooled austenite of tested steel during higher temperature interval,and bainite transformation and martensite transformation can occur during intermedium temperature and low temperature zones respectively.The transformation product consists of polygonal ferrite,pearlite and a small amount of bainite at the cooling rates of 0.05 0.5 ℃/s.When the cooling rate is ranging from 1 to 5 ℃/s,the product is mainly composed of bainite.When the cooling rate is higher than 5 ℃/s,martensite is the main transformation product.Because the alloy elements of Cr,Mo and V can inhibit the decomposition of austenite,pro-eutectoid ferrite and pearlite can be formed only at the condition of cooling rate below 1 ℃/s.Higher manganese content can greatly accelerate the bainite transformation,and therefore bainite can be easily formed during the continuous cooling process for a large range of cooling rate.It is an effective way of decreasing the quenching stress of steel tubes to use the obtained CCT diagram to guide the multiple controlled cooling process,which indicates that the CCT diagram can provide guarantee for excellent touthness of V150 tubing and casing.