Abstract: Hot-tearing cracks usually form near the solidus temperature． It is caused by a combination of tensile stress and metallurgical embrittle-ment． In order to quantify embrittlement and to incorporate it in the thermal-stress analysis，many different criteria have been developed． Among them，the submerged split-chill tensile ( SSCT) test is an efficient one． This paper tries to use SSCT to estimate the critical strain of hot tearing for some steels．
1 Introduction
In recent years，internal cracks have become the main quality problem for many domestic steelmaking plants．Such defects can cause discontinuity of mechanical properties，or even rejection of hot-rolled sheets，which greatly reduces the economic benefits． Hot-tearing crack is a typical type of internal cracks．Crack formation is generated by a combination of tensile stress and metallurgical embrittlement． Although various mechanisms at different temperature ranges determine how solidifying metal is subject to embrittlement，hot-tearing cracks form near the solidus
temperature． Embrittlement is so severe near this temperature that hot-tearing cracks form at strains on the order of only one percent，making it obvious that there exists a critical strain responsible for most of the cracks observed in cast products．
During continuous casting，the solidifying strand shell bears both mechanical and thermal loads resulting from :contraction and phase transformation; temperature gradients along the surface or across the shell; friction between strand and mold; bending and straightening; bulging; soft reduction etc． These loads act on the steel shell and generate strain． So if the total strain exceeds the critical strain value of this kind of material，cracks will occur．In order to determine this hot-tearing critical strain，a variety of criteria and approaches，including Thermalanalysis-based Criteria，Mechanical-analysis-based Criteria and Micro-scale model-based Criteria ［1］，have been developed，for different approaches are required for different microstructures and metals，according to the most important phenomena which govern crack formation．
Regardless of the model formulation，developing an accurate criterion function to predict hot tears relies on measurements，such as the submerged split-chill tensile test． This experiment applies and measures a tensile load on the solidifying shell，perpendicular to the growth direction ，so it matches the conditions present in hot tearing between columnar grains． The focus of this paper is to study the critical strains for different steel grades in this way．
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