Slab corner crack inspection method

Abstract

The invention discloses a slab corner crack inspection method, which comprises the following steps of: 1) cutting the corner of a casting blank along the length direction by using a cutting knife to obtain a sample, the length of the sample is not less than 100mm, the width of the sample is not less than 20mm, and sampling other corners of the casting blank by using the same method; 2) heating hydrochloric acid with a certain concentration to more than 50 DEG C, putting the taken horn sample into the heated hydrochloric acid, boiling for more than 10 minutes, and properly prolonging the pickling time along with the reduction of the concentration of the acid in the later period; (3) after the color of the horn sample is off-white and surface impurities and hydrochloric acid are subjected to chemical reaction to be removed, taking out the sample and putting the sample into clear water to be washed; 4) placing the pickled sample in a place with good light to check whether the surface has cracks; and 5) timely notifying a team leader to adjust after cracks are found, and if the adjustment is invalid, performing shutdown treatment to prevent quality accidents from being expanded.

Description

Technical Field

[0001] The invention relates to a method for inspecting cracks at corners of slabs, and belongs to the field of steel smelting and material processing. Background Art

[0002] During the continuous casting process, molten steel begins to solidify from the crystallizer, first forming a shell of a certain thickness, then solidifying from the shell from the outside to the inside, and finally completely solidifying into a cast billet. During the solidification of molten steel into a cast billet, corner cracks are easily generated due to uneven cooling, bending straightening force and other stresses. The cracks are often small and covered with casting slag and iron oxide scale. It is difficult to directly inspect and find the cracks. The defects will be magnified in the subsequent rolling process, seriously affecting product quality.

[0003] Literature search: (1) The 2007 issue of the Proceedings of the 8th National Continuous Casting Academic Conference on “Continuous Casting Billet Quality Inspection and Control” used ultrasonic electromagnetic induction to detect billet cracks at 900-1000°C. The minimum crack length can be detected to be 20 mm. Cracks smaller than that cannot be detected. In addition, ultrasonic electromagnetic induction equipment is expensive and difficult to maintain. (2) The patent “A tool for inspecting the quality of the lower surface of a billet” discloses a tool for inspecting the quality of the lower surface of a billet. The device has a handle, a connector, and a clamp. The handle is provided on the upper part of the connector, and the clamp is provided on the lower part of the connector. A visualization device is mounted on the clamp. The tool can only inspect cracks visible to the naked eye on the billet surface, and cannot detect capillary cracks under the iron oxide scale. Summary of the invention

[0004] The purpose of the present invention is to provide a method for inspecting cracks at corners of slabs, which can timely discover defects in the slabs and make adjustments to prevent quality accidents from expanding.

[0005] The implementation method of the present invention is: a method for inspecting cracks at the corners of a slab, 1) cutting a sample from the corner of the ingot along the length direction with a cutter, the sample length is not less than 100 mm, the width is not less than 20 mm, and the other corners of the ingot are sampled in the same way; 2) heating hydrochloric acid of a certain concentration to above 50°C, and then putting the taken corner sample into the heated hydrochloric acid and boiling for more than 10 minutes, with the concentration of the acid decreasing in the later stage, the pickling time should be appropriately extended; 3) after the color of the corner sample appears grayish white, and the surface impurities react with the hydrochloric acid to be removed, take out the sample and rinse it in clean water; 4) putting the pickled sample in a place with good light to check whether there are cracks on the surface; 5) notifying the team leader in time to make adjustments after cracks are found, and shutting down the machine if the adjustments are ineffective to prevent the expansion of quality accidents.

[0006] The method of the present invention is characterized in that the impurities such as iron oxide scale on the surface of the ingot are first cleaned, the defects are clearly exposed, and the cracks at the corners of the ingot can be accurately and truly checked by naked eyes. It has high accuracy, strong applicability and operability, and reduces the probability of sending cracked ingots to the next process and the expansion of quality accidents. The method is used to check the quality of ingots, and no quality accidents have occurred, mass production has been achieved, the surface crack rate of medium and thick plates has been greatly reduced, and the first-time fulfillment rate of contracts has been improved. Implementation

[0007] A method for inspecting cracks at the corner of a slab comprises the following steps: 1) cutting a sample from the corner of the ingot along the length direction with a cutter, wherein the sample has a length of 150 mm and a width of 30 mm, and sampling is performed on other corners of the ingot in the same manner; 2) heating hydrochloric acid with a concentration of 5% to 20% to above 50°C, and then placing the sample in the heated hydrochloric acid and boiling for more than 10 minutes. As the concentration of the acid decreases in the later stage, the pickling time is extended to 30 minutes; 3) when the color of the sample turns grayish white and surface impurities are removed by chemical reaction with the hydrochloric acid, the sample is taken out and rinsed in clean water; 4) placing the sample after pickling in a place with good light to check whether there are cracks on the surface; 5) notifying the team leader in a timely manner to make adjustments after cracks are found, and shutting down the machine if the adjustments are ineffective, so as to prevent the expansion of quality accidents.

Claims

1. A method for inspecting cracks at slab corners, characterized in that: 1) Cut a sample from the corner of the ingot along the length direction with a cutter. The length of the sample should not be less than 100mm and the width should not be less than 20mm. Use the same method to sample the other corners of the ingot; 2) Heat a certain concentration of hydrochloric acid to above 50℃, and then put the corner sample into the heated hydrochloric acid and boil for more than 10 minutes. As the concentration of the acid decreases in the later stage, the pickling time should be appropriately extended; 3) When the color of the corner sample appears grayish white and the surface impurities react chemically with the hydrochloric acid to remove them, take out the sample and rinse it in clean water; 4) Put the pickled sample in a place with good light to check whether there are cracks on the surface; 5) If cracks are found, notify the team leader in time to make adjustments. If the adjustments are ineffective, shut down the machine to prevent the expansion of quality accidents.