SPA – H is a kind of low carbon low alloy structural steel, widely used in the production of container plate. SPA – H container plate is one of the most common defects in the process of manufacturing cold bending crack, cold bending performance will directly affect the product quality and economic benefit.
Analysis of the reasons:
Distribution of a large number of spherical aluminum oxide inclusion steel plate surface is the main cause of cold bending crack, these inclusions from the surface of metal, gradually formed around the micro hole, the hole with the deformation process of growing, joins, eventually forming the large crack or separation between metal and metal forming layered, deterioration in cold bending performance, until the craze.
Control measures are as follows:
1, speed up the cooling speed of liquid steel during solidification, the degree of partial poly slow element, reduce the concentration difference of partial poly, particularly fast cooling time may achieve unbiased state.
2, rolling heating, as far as possible according to the actual production with higher soaking temperature and longer soaking time, this is beneficial to the diffusion of solute elements, make components tend to be uniform, fundamentally prevent the generation of banded structure.
3, rolling steel plate, adopting high temperature hot rolled to solute elements of the large deformation of partial poly belt get squashed into a long strip, the solute enrichment region and solute depleted the spacing decreases, and prompted the composition homogenization of austenite area, make the rich area and poor solute area of the solute concentration difference between the reduced and not easy to form bands.
4, control in the austenite processing or the cooling speed after heat treatment, in the case of solute concentration still exists zonal distribution, increase the cooling speed to solute enrichment region completed before the formation of pearlite austenitic, ferritic phase transformation, avoid generating ferrite/pearlite banded structure, reduce the banded structure of the steel sheets.
5, SPA – H steel is more sensitive to the oxygen content in steel, aluminum deoxidation, SPA – H most in alumina oxide inclusions in steel. So by controlling the total oxygen content in molten steel, reduce the aluminum oxide inclusions in the steel substrate.