Cause Analysis and Improvement of Surface Warping of Inconel625 Alloy Hot Rolled Sheet

(HY-industry technical centre)

Inconel 625 is a Ni-Cr-Mo based solid solution reinforced deformation superalloy with high strength, high toughness, excellent fatigue resistance and resistance to chloride ion stress corrosion from room temperature to high temperature. It is widely used in nuclear industry and aerospace. In the fields of petrochemicals, the main product types are plates, strips, bars, pipes and forgings. The Inconel625 hot-rolled sheet produced by Baosteel has been found to have local warping defects on the surface of the alloy sheet after solid solution pickling. Since the existence of this defect will seriously affect the subsequent use and cannot be accepted by the user, it is necessary to form the mechanism. the study.

At present, there are many researches on the surface defects of hot-rolled steel sheets. However, the hot-rolled hot-rolled sheets are different from the continuous casting slabs in the processing of raw material-slabs, and the formation mechanism of surface defects and the formation mechanism of surface defects of hot-rolled steel sheets are endless. the same. In order to support Baosteel’s production of plates that meet military standards, researchers at Shanghai HY Industry Co., Ltd analyzed the characteristics of the inconspicuous defects of Inconel625 alloy hot-rolled sheets in order to find out the main causes and formation mechanisms that lead to the defects. Take corresponding improvement measures.

The basic production process of Inconel 625 hot-rolled sheet is: vacuum induction melting → protective atmosphere electroslag remelting → slab forging → blank surface grinding → hot rolling → solution treatment → pickling, the specification is 20mm thick × 1420mm wide.
The test results show that the warpage defects on the surface of hot-rolled Inconel 625 plate are mainly divided into two types, namely crack-like warp and knotted warp. Among them, the crack-like warpage defect portion has overheating phenomenon during heating, and the knotted warp-like defect portion has no overheating phenomenon. The main cause of crack-like warping defects is the presence of subcutaneous air bubbles in the slab, which extends in the subsequent rolling process as the matrix expands, thereby forming crack-like warping defects. The main cause of the knotted warp defect is the pit on the surface of the slab with an acute angle between the side and the bottom or an acute angle between the sides. During the rolling process, the metal is oxidized in the pit when flowing through the pit. The layer is entangled, causing the pits not to be rolled, eventually forming a knotted warp defect.
According to the production process of hot rolled Inconel 625 board and the mechanism of warping, the following measures are taken:

  • When vacuum induction furnace is smelting, the vacuum degree is appropriately increased, the appropriate pouring temperature is controlled and the casting speed is lowered to reduce the possibility of entrapment of gas; the freezing process is increased, and the gas is reduced with solubility during solidification. Small and released, reducing the possibility of ingots in the ingot.

  • Before the slab is forged, the surface quality of the electroslag ingot is inspected, and defects such as slag ditch and split eye should be repaired and removed.

  • Strengthening the surface finishing of the slab before rolling, not only grinding the surface cracks, hair lines and side burrs, but also strictly cleaning the surface pits, cleaning the width not less than 6 times of its depth, length Not less than 10 times its depth to ensure a smooth rounded corner.

  • Strengthen the cleaning of the surface of the roll to ensure that the surface of the roll is smooth and clean.

    By adopting the above control measures, the hot-rolled Inconel 625 plate warp defects produced by Baosteel have been greatly improved, and the incidence of warping has been reduced from 3.6% to 1%, with remarkable results.

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