Mechanism for Development of Faults Originating from Compound Inclusions in the Forging Process of 30Cr2Ni4MoV Heavy Ingots

Abstract

Non-metallic inclusions are considered undesired, yet unavoidable components of all steels and are prone to act as sources of stress that play a predominant role in crack initiation. Experiments conducted during the forging process of 30Cr2Ni4MoV steel revealed that cracks mainly originate from compound inclusions, especially intensive plastic inclusions or sliced brittle inclusions containing particles in their interior. The deformation behavior of these two types of compound inclusions was then simulated. It has been shown that the intensive plastic inclusions parallel to the applied stress result in two effects that cause additional stress and produce strain concentration, which are key factors of the union of inclusions and the origins of cracks. Tensile stress that can also lead to cracking certainly exists among intensive plastic inclusions distributed perpendicular to the applied stress. In a compound brittle inclusion, as the amount of deformation increases, areas of strain concentration first develop and then conical cracks are initiated on both sides of the interior particle. When multiple particles are distributed within a small distance, the adjacent conical cracks tend to be connected under the maximum shear stress and finally sever the sliced brittle inclusion at an angle of 45°.

Formation mechanism of inspection defects in hundred-ton class 55NiCrMoV7 die steel forging

“…Zhao et al 18 explored the mechanisms of defect formation and propagation during the forging process of 30Cr2Ni4MoV steel ingots. They noted that cracking during the forging process is primarily caused by complex inclusions.…”

Analysis and Research on the Cause of the “White Stripe” of 30Cr1Mo1V Side HAZ

“…The traditional rotor structure often adopts the whole forging rotor structure due to the load bearing requirements in its operation process, which requires high forging performance and processing technology of materials. 1,2) If there are defects, the whole structure will be scrapped, which make massive material consumption. 1) Welding rotor structure can avoid difficult machining, and select materials according to requirements.…”

Staggered Anvil and Rotation Processes for Refining and Homogenizing Centimeter-Scale Grains during FM Forging of Superheavy Ingots

“…© 2015 The Japan Institute of Metals and Materials from being generated. 1,6,8) All the hot-deformed specimens were immediately quenched in water to retain the grain boundaries of the austenitized grains. Next, they were etched with a C 6 H 3 N 3 O 7 -H 2 O solution for metallographic observations after being cut along the longitudinal direction and polished mechanically.…”

“…6,12) The boundary conditions were simplified and took into account only the heat transferred and the interfacial friction. For example, the environmental temperature was set as 20°C, while the coefficients of heat convection and transfer between the ingot, the environment, and the anvil were set as 0.02 W/(m 2 ·K) and 11 W/(m 2 ·K), respectively.…”

“…For example, our previous study had confirmed the grain structure of superheavy 30Cr2Ni4MoV steel ingots weighing more than 300 tons by dissection and metallographic analysis, which was found to comprise centimeterscale columnar grains, equiaxed grains, and dendrites. 1,2) This material is commonly used to fabricate low-pressure rotors for 1000 and 1400 MW advanced passive pressurized water reactors in China. Given that the mechanical properties of heavy forgings are directly attributable to their microstructure, they can only be deemed suitable for use if the coarse grain structure of the steel can be suitably refined during forging.…”