70Cr3Mo钢支承辊超探不合格原因分析及改进措施

Analysis on disqualification reason and improvement measures of steel 70Cr3Mo back-up roll by ultrasonic inspection

制造44800和19500 kg的两根70Cr3Mo钢支承辊大锻件。钢锭采用EAF+LF+VD+VC冶炼浇注,1锭锻制2件,锻后球化退火,出炉冷却后,毛坯进行超声波探伤检查。结果发现:小辊超探合格踩线,大辊在冒口端辊颈部分存在超标缺陷。为了探究锻造工艺合理性,切掉大辊两端辊颈部分,利用辊身合格的坯料改锻成小辊。改锻后的小辊经超声波探伤发现,除辊身外两端辊颈部分均存在超标密集缺陷。通过一系列试验,对孔洞缺陷和夹杂物进行了分析,确定了导致支承辊超探不合格的原因:铸锭缺陷中广泛分布的非金属夹杂物分割了钢基体的连续性,恶化了钢的性能,导致超探不合格。此外,分析了夹杂物的来源及其危害性,并提出了相应的工艺改进措施。

Two back-up roll forgings of steel 70Cr3Mo with the weight of 44800 kg and 19500 kg were respectively made.The ingot was melted and poured by the EAF＋LF＋VD＋VC method,and one ingot was forged into two pieces.After spheroidizing annealing and cooling,the blanks were checked through ultrasonic inspection.The result shows that the light roll is up to standard,but there are excessive defects in the roll neck of the heavy one.In order to explore the technological rationality of forging,two ends of the heavy roll neck part were cut to forge a new light back-up roll based on the qualified body.Nevertheless,there are still overproof defects in the roll neck of the new one except the roll barrel.Thus,the hole defects and inclusions were analyzed by a series of experiments,and the reasons for the disqualification of the back-up roll were determined after ultrasonic inspection.Furthermore,the non-metallic inclusions in the ingot widely distributing on the defect split the continuity of the steel matrix and deteriorate the steel performance,which result in the disqualification of ultrasonic inspection.In addition,the source and harmfulness of non-metallic inclusions were analyzed and the corresponding improvement measures were put forward to prevent such defects.