The paper presents results of modeling and testing of a heavy weight part
made of Cr-Mo, which was V-modified ultra-high strength steel grade AISI
4140, processed through a novel open-die forging schedule and two
alternative routes of two-stage heat treatment cycles designed to meet
requirements of high-duty components for energy sector. Taking advantage of
unconventional forging conditions based on assumption of large feed and
reduction ratios and the modification of chemical composition better control
of austenite grain was achieved to minimize abnormal grain growth and/or
strain uniformity problems. With aid of Finite Element Modeling of
multi-stage sequence of upsetting and cogging strain distribution was
optimized so as to minimize strain fluctuations on the length to range
2.2?2.7,and correlated with microstructure produced at every major stage on
the large cross-sections of the shaft. Designed with aid of finite element
method processing cycles was verified in full-scale physical modeling with
use of 16 ton forging ingot, including two alternative quenching strategies:
oil vs. water spray and air. Examination of material in as-forged,
normalized and heat-treated condition was carried out to observe response of
hot-worked material and the effect of cooling conditions on microstructure
during final heat treatment. As observed, employing large feed ratios on
cogging and varied cooling allowed suppress detrimental effect of inevitable
abnormal grain growth which resulted in 1-2 ASTM grain in as-forged
conditions to reach 6 ASTM in normalized and 8/9 ASTM after quenching in oil
and water spray, respectively, which allows producing after tempering,
correspondingly, 44?48 and 85?122 J/cm2 V-notch impact strength in the
critical area of the forged shaft.