风电法兰用钢S355NL探伤缺陷的分析和工艺改进

Analysis on Nondestructive Examination Defects of Steel S355NL for Wind Power Flange and Process Improvement

风电法兰用钢S355NL(/%:0.14~0.48C,0.15~0.40Si,1.30~1.60Mn,≤0.013P,≤0.005S,0.04~0.12V,0.03~0.05Nb,≤0.009Ti,≤0.30Cr,≤0.50Ni,≤0.20Cu,≤0.10Mo,>0.020Alt)的冶金流程为100 t UHP EAF—LF—VD—Φ650 mm,Φ800 mm坯CC工艺。该钢1~2 mm裂纹探伤不合格的分析结果表明,其主要原因为氧的铝类夹杂和铸坯疏松缺陷所致。通过在LF终点喂钙线0.45 kg/t,VD处理时间由原25 min增至27 min,降低钢中[N]至78×10^(-6)82×10^(-6),[H]为1.1×10^(-6)1.3×10^(-6),[O]为12×10^(-6)~15×10^(-6),软吹氩气流量由2×25L/min降至2×20 L/min,时间≥12 min,降低钢水过热度5℃等工艺措施,使铸坯锻造后的探伤合格率超过99%。

The metallurgical flowsheet for steel $355NL for wind power flange （/% ： 0. 14 -0. 48C, 0. 15 ~0.40Si, 1.30-1.60Mn,≤0. 013P, ≤0.005S, 0.04~0.12V, 0.03 ~0. 05Nb, ≤0.009Ti, ≤0.30Cr, ≤0.50Ni, ≤0.20Cu, ≤0.10Mo, ≥0. 020Ah） is 100 t UHP EAF-LF-VD-φ650 mm, 0800 mm bloom CC process. The results of analysis on unqualified steel by nondestructive examination due to 1 ~ 2 mm cracks show that cracks are mainly caused by alumina in- clusions and casting bloom porosity defects. By the process measures including feeding calcium wire 0. 45 kg/t at end LF, increasing VD treading time to 27 min from original 25 min, decreasing the [ N] in steel to 78 × 10^-6 -82 × 10^-6, the [ H] to 1.1 × 10^-6 ~ 1.3 × 10^-6 and the [ O] to 12 × 10^-6 - 15 × 10^-6, decreasing the soft argon blowing rate to 2 ~ 20 L/rain from 2 ×25 L/min, time ≥12 min and decreasing the liquid overheating extent by 5 ℃, the qualified ratio of steel forged from casting bloom is more than 99%.