Method for distinguishing corrosion pits and oxide skin indentation on surface of hot-rolled steel plate
Through metallographic microscope, the cross-section of the corrosion points on the steel plate surface is observed, and the corrosion pits and the scale pressure pits are distinguished, which solves the problem of difficulty in qualitative evaluation of the causes of rust in the existing technology, and achieves rapid and accurate steel plate quality control and reduces costs.
Patent Information
- Application Number
- CN202411254895.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-09
- Publication Date
- 2025-01-10
AI Technical Summary
At this stage, it is difficult to quickly distinguish the surface corrosion pits of hot-rolled steel plates from scale pressure pits, which leads to difficulty in qualitative evaluation of the causes of rust and affects the quality control and cost management of steel plates.
The cross-section of the corrosion points on the surface of the steel plate was observed by using a metallographic microscope. By comparing the metallographic diagrams of the standard oxide scale, standard corrosion products and pits to be tested, the corrosion pits and the scale pressure pits were distinguished to ensure the rapid identification of the root cause of the rust point.
It has achieved rapid and accurate distinction between corrosion pits and scale pits, which has reduced the incidence of surface quality defects, reduced quality costs, and improved the economic benefits of the steel and metallurgy industry.
Smart Images
Figure CN119290889A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of hot-rolled steel plates, and in particular to a method for distinguishing rust pits and oxide scale pressure pits on the surface of hot-rolled steel plates. Background Art
[0002] The surface of the hot-rolled steel plate is covered with a layer of oxide scale. When the hot-rolled steel plate produces surface defects due to the intrusion of oxide scale during the production process, the dot-like pits on the surface of the steel substrate are often not observed due to the oxide scale.
[0003] During the process of open-air storage and transportation, hot-rolled steel plates will inevitably encounter rainy and snowy weather. Steel is prone to rust in such an environment. The rust of hot-rolled steel plates in a humid environment is a spontaneous phenomenon in nature. The oxide scale on the hot-rolled steel plate is often not uniform. Under the same corrosive environment, the relatively loose positions of the oxide scale will first rust. When the rust is severe, rust pits will be formed. The corrosion products in the pits accumulate and protrude from the surface of the steel plate, forming observable rust spots.
[0004] There are scale indentation defects on hot-rolled steel plates. The scale is thick, loose, and prone to scale cracks. Water or other corrosive media are easily accumulated at this location and some rust occurs. The steel matrix at the bottom of the scale pressure pit rusts, and the corrosion products produced by the rust lift up the scale. People often observe rust spots on the raised steel plate surface.
[0005] Hot-rolled steel plates are mostly delivered in a hot-rolled state. After the storage and logistics stages, the surface of the steel plates often has slight or severe rust. When the steel plate user finds multiple discrete rust spots or large-scale rust spots on the surface of the steel plate before use, whether it is the rust spots where the oxide scale is pressed into the steel plate or the rust spots formed by severe corrosion of the steel plate, they all look the same and are difficult to distinguish with the naked eye. When the hot-rolled steel plate is in this state, it is very important to distinguish the cause of this type of rust. The root cause of rust pits lies in the control of warehousing and logistics links, while the root cause of oxide scale pressure pits lies in production quality control. It is of great significance to distinguish between rust pits and oxide scale pressure pits.
[0006] At present, it is a technical difficulty to quickly distinguish rust pits from scale pits. The usual idea is to sample the rust products in the rust pits and scale pits, and use XRD phase analysis to identify whether they are rust products or scales. However, the amount of rust on the steel plate is generally small, and it is difficult to obtain enough samples for XRD analysis.
[0007] Therefore, it is necessary to develop a new method for rapid identification of rust pits and scale pits to qualitatively evaluate the root causes of rust pits on hot-rolled steel plates. Summary of the invention
[0008] Purpose of the invention: In view of the shortcomings and defects of the prior art, the present invention provides a method for distinguishing rust pits and oxide scale pressure pits on the surface of hot-rolled steel plates, quickly identifying rust pits and oxide scale pressure pits, and qualitatively evaluating the root causes of rust spots on hot-rolled steel plates.
[0009] Technical solution: A method for distinguishing rust pits and oxide scale pressure pits on the surface of a hot-rolled steel plate according to the present invention is characterized by comprising:
[0010] 1) Sampling: Take a sample with oxide scale on the steel plate without rust as a comparison sample; take a sample with the oxide scale of the steel plate peeled off, the surface of the steel plate is evenly rusted and there is no rust pit; take a sample with rust pit or rusted oxide scale pressure pit;
[0011] 2) Observe the oxide scale / steel matrix interface using a metallographic microscope to obtain a standard oxide scale metallographic image; observe the uniform rust layer / steel matrix interface using a metallographic microscope to obtain a standard rust product metallographic image; observe the cross section of the pit to be tested using a metallographic microscope to obtain a metallographic image of the pit to be tested;
[0012] 3) Compare the obtained standard oxide scale metallographic image, standard rust product metallographic image and the metallographic image of the pit to be tested. Figure 1 If the oxide scale and rust products appear on the metallographic diagram of the pit to be tested at the same time, it is determined that the initial state of the pit to be tested is an oxide scale pressure pit, and then rust occurs, and the rust makes the original oxide scale pressure pit further enlarged; if no oxide scale appears on the metallographic diagram of the pit to be tested, it is determined that the pit to be tested is a rust pit.
[0013] Wherein, when taking samples of rust pits or rusted oxide scale pressure pits in the step 1), the rust point position is coated with epoxy A / B glue before sampling. After the glue is cured, the rust point position sample of the hot-rolled steel plate is completely removed by sawing to ensure that the original state of the rust point position is not damaged during the sampling process, and a conventional metallographic structure observation sample is prepared.
[0014] Wherein, during the sawing, the pit rust points are cut along the cutting line on the surface of the steel plate to ensure that the state of the oxide scale in the pit can be observed on the cross section of the sample.
[0015] Wherein, the standard oxide scale metallographic diagram includes the oxide scale and steel matrix morphology.
[0016] Wherein, the standard corrosion product metallographic diagram includes the morphology of the corrosion product and the steel matrix.
[0017] Wherein, the metallographic image of the pit to be tested includes the pit to be tested and the morphology of the oxide scale of the steel matrix.
[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the present invention can be applied to evaluate the types of surface defects on steel plates, identify the root causes of pits on the surface of steel plates, and promote the improvement of the surface quality of hot-rolled steel plates. It is highly practical in the iron and steel metallurgical industry. It can reduce the incidence of surface quality defects, reduce quality costs, and have significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 It is a schematic diagram of sampling the location of pit rust points of the present invention;
[0020] Figure 2 It is a standard oxide scale metallographic diagram of an embodiment of the present invention;
[0021] Figure 3 It is a metallographic diagram of a standard corrosion product of an embodiment of the present invention;
[0022] Figure 4 A metallographic image of a pit to be tested according to an embodiment of the present invention;
[0023] In the figure, 1 is the surface of the steel plate; 2 is the pit rust point; and 3 is the cutting line. DETAILED DESCRIPTION
[0024] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific implementation methods.
[0025] In order to quickly identify whether the rust spots on the surface of hot-rolled steel plates with oxide scale are rust pits or oxide scale pressure pits, the present invention provides a method for quickly detecting the position of rust spots using a metallographic microscope to distinguish between rust pits and oxide scale pressure pits. The equipment operation method used in this method needs to be simple, preferably in line with the commonly used test methods in the industry, so that test personnel can quickly get started. However, the application of the idea of this method should be novel, the first application in this field, innovative, and able to substantially solve the problems existing at this stage. Employers are generally equipped with metallographic microscopes, and this method does not require additional equipment; the experimental operation steps are simple, and it is very easy for operators to operate.
[0026] The method of distinguishing rust pits and oxide scale pressure pits on the surface of hot-rolled steel plates of the present invention is divided into the following steps:
[0027] 1. Sampling.
[0028] (1) Take a comparison sample. Take a sample with oxide scale on the steel plate without rust. At the same time, take a sample with the oxide scale of the steel plate completely shed, and it is obvious that the steel plate is evenly rusted and has no rust pits.
[0029] (2) Take samples of rust pits or rusted oxide scale pressure pits. Before sampling, epoxy A / B glue can be used to coat the rust spot. After the glue is cured, the rust spot samples of the hot-rolled steel plate are completely removed by sawing to ensure that the original state of the rust spot is not damaged during the sampling process, and to prepare conventional metallographic structure observation samples. Figure 1 The schematic diagram shown is to cut the specimen to ensure that the state of the oxide scale inside the pit can be observed on the cross section of the specimen.
[0030] 2. Observe using a metallographic microscope.
[0031] (1) The oxide scale / steel matrix interface was observed using a metallographic microscope to obtain a standard oxide scale metallographic image.
[0032] (2) Use a metallographic microscope to observe the uniform rust layer / steel matrix interface and obtain a standard rust product metallographic image.
[0033] (3) Use a metallographic microscope to observe the cross section of the pit to be tested and obtain a metallographic image of the pit to be tested.
[0034] 3. Analysis.
[0035] The obtained standard oxide scale metallographic image, standard rust product metallographic image and the metallographic image of the pit to be tested are compared. Figure 1 If the pit to be tested has oxide scale, it is determined that there is oxide scale in the pit to be tested. If oxide scale and rust products appear on the metallographic image of the pit to be tested at the same time, it is determined that the initial state of the pit to be tested is an oxide scale pressure pit, and then rust occurs, and the rust makes the original oxide scale pressure pit further enlarged. If no oxide scale appears on the metallographic image of the pit to be tested, it is determined that the pit to be tested is a rust pit.
[0036] Example:
[0037] This example is a rust spot on the surface of a Q345R hot-rolled steel plate, and the thickness of the steel plate is 36 mm.
[0038] 1. Sampling.
[0039] 2. Observe using a metallographic microscope.
[0040] like Figure 2 The oxide scale / steel matrix interface was observed using a metallographic microscope to obtain a standard oxide scale metallographic diagram.
[0041] like Figure 3 The uniform rust layer / steel matrix interface was observed using a metallographic microscope to obtain a standard metallographic image of the rust product.
[0042] like Figure 4 , a metallographic microscope is used to observe the cross section of the pit to be tested and a metallographic image of the pit to be tested is obtained.
[0043] 3. Analysis.
[0044] The metallographic image of the pit to be tested in this embodiment has oxide scale but no rust products.
[0045] The present invention can be applied to evaluate the types of surface defects on steel plates, identify the root causes of pits on the steel plate surface, and promote the improvement of the surface quality of hot-rolled steel plates. It has strong practicality in the iron and steel metallurgical industry, can reduce the incidence of surface quality defects, reduce quality costs, and has significant economic benefits.
Claims
1. A method for distinguishing rust pits and oxide scale pressure pits on the surface of hot-rolled steel plates, characterized in that: include: 1) Take samples, and take a sample with oxide scale on the steel plate without rust as a comparison sample; Take samples of steel plates with rusted scales that have fallen off and uniformly corroded surfaces without rust pits; take samples of rust pits or rusted scale pressure pits; 2) Observe the oxide scale / steel matrix interface using a metallographic microscope to obtain a standard oxide scale metallographic image; observe the uniform rust layer / steel matrix interface using a metallographic microscope to obtain a standard rust product metallographic image; observe the cross section of the pit to be tested using a metallographic microscope to obtain a metallographic image of the pit to be tested; 3) Compare the obtained standard oxide scale metallographic image, standard rust product metallographic image and the metallographic image of the pit to be tested. When a part consistent with the standard oxide scale metallographic image appears on the internal metallographic image of the pit to be tested, it is determined that there is oxide scale in the pit to be tested; if oxide scale and rust products appear on the metallographic image of the pit to be tested at the same time, it is determined that the initial state of the pit to be tested is an oxide scale pressure pit, and then rust occurs, and the rust makes the original oxide scale pressure pit further enlarged; if no oxide scale appears on the metallographic image of the pit to be tested, it is determined that the pit to be tested is a rust pit.
2. The method for distinguishing rust pits and oxide scale pressure pits on the surface of hot-rolled steel plates according to claim 1, characterized in that: When taking samples of rust pits or rusted oxide scale pressure pits in the step 1), the rust point position is coated with epoxy A / B glue before sampling. After the glue is cured, the rust point position sample of the hot-rolled steel plate is completely removed by sawing to ensure that the original state of the rust point position is not damaged during the sampling process, and a conventional metallographic structure observation sample is prepared.
3. The method for distinguishing rust pits and scale pressure pits on the surface of hot-rolled steel plates according to claim 2, characterized in that: During the sawing, the pitted rust spots (2) are cut along the cutting line (3) on the surface (1) of the steel plate, ensuring that the state of the oxide scale in the pit can be observed on the cross section of the sample.
4. The method for distinguishing rust pits and scale pressure pits on the surface of hot-rolled steel plates according to claim 1, characterized in that: The standard oxide scale metallographic diagram includes the oxide scale and steel matrix morphology.
5. The method for distinguishing rust pits and scale pressure pits on the surface of hot-rolled steel plates according to claim 1, characterized in that: The standard corrosion product metallographic diagram includes the morphology of the corrosion product and the steel matrix.
6. The method for distinguishing rust pits and scale pressure pits on the surface of hot-rolled steel plates according to claim 1, characterized in that: The metallographic image of the pit to be tested includes the pit to be tested of the steel matrix and the morphology of the oxide scale.