中碳亚包晶成分钢连铸坯角横裂的防止对策

宝钢生产的中碳亚包晶成分钢连铸坯角横裂属于沿晶界的开裂,主要发生在850℃t以下温度,对3个钢种连铸坯试样的高温力学性能的测定表明,在$dot varepsilon $=4×10^-3/s应变速率下,所测钢种在熔点~700℃范围存在两个脆性温度区域,即熔点~1350℃的第I脆性温度区域和850~725℃的第Ⅲ脆性温度区域,在第Ⅲ脆性温度区域,γ单相域AlN等氮化物在γ晶界的析出和在γ+α两相区先共析α相呈网膜状,在γ晶界的析出是造成钢脆化的主要原因。通过控制钢中氮、铝含量,采用较温和的二冷方式,使铸坯在矫直处的边角部温度避开第Ⅲ脆性温度区,铸坯的角横裂缺陷有了大幅度的降低。

Countermeasures Against Transverse Corner Crackes of Medium Carbon Hypo-Peritectic Steel CC Slabs

It is found that the transverse corner cracks occurring on the medium cabon hypo-peritectic steel CC slabs produced by BAOSHAN STEEL are type of inter-γ granular fractures occurring mainly at temperature below 850℃. Hot ductility measurement of three medium carbon steels indicates that, under the strain rate of 4×10^-3/s, there exist two fow ductility temperature regions for the tested steels within the temperture range from steel melting points to 700℃, i.e. Region I from the melting points to 1350℃ and Region Ⅲ from 850℃ to 750℃. In Reginn Ⅲ, the ductility loss is mainly resulted from the precipitations of nitrudes of Al, Nb, etc. at the austenite boundaries in single γ phase tempeniture range and the formation of the film-like proeutectoid ferrites along the γgrain boundaries in γ+α two-phase temperature range. By taking measures of precisely controlling steel N, Al concentrations and adopting mild secondary cooling pattem to raise the slab unbending temperature out off the low ductility Region Ⅲ, the occurrence of the transverse corner cracks on medium carbon hypoperiteetic steel CC slabs has been significantly reduced.