Analysis of several typical defect forms of stainless steel medium and thick plates

As an important industrial material,stainless steel plates are widely used in the fields of construction,machinery manufacturing,chemical industry,shipbuilding,etc.However,during the production and use process,stainless steel plates often have various defects,which not only affect the appearance quality of the product,but also reduce its mechanical properties and processing performance,and even lead to product scrapping.This article will analyze in detail several typical defect forms of stainless steel plates,and explore their causes and preventive measures.

1.Small longitudinal fissure

Small longitudinal cracks are a common defect on the surface of stainless steel plates.They are small cracks with a length of less than 200 mm,a width of less than 3 mm,and a depth of less than 0.3 mm.These cracks are usually distributed along the rolling direction,which has a certain impact on the surface quality and performance of the steel plate.

Cause Analysis:

The formation of small longitudinal cracks is mainly due to the mixing of fine impurities into the crystallization.During the smelting and casting process of stainless steel,if impurities are mixed into the crystallization,these impurities will form hard spots in the molten steel,thus causing stress concentration during the rolling process,leading to the formation of cracks.

Precautions:

Check the crystallization regularly,especially the water sample,to ensure that no small impurities are mixed in and cause changes in water quality.

Strengthen quality control during smelting and casting processes to ensure the purity of molten steel.

Optimize the rolling process and reduce stress concentration during rolling.

2.Peak crack

Peak cracks are another common defect in stainless steel medium and thick plates.Their characteristic is that a"peak"-shaped crack perpendicular to the rolling direction is formed on the lower surface of the steel plate 5-60 mm away from the edge.

Cause Analysis:

The peak-shaped cracks are mainly caused by transverse cracks under the outer arc skin of the ingot.During the continuous casting process of stainless steel,if transverse cracks appear under the outer arc skin of the ingot,these cracks will expand along the rolling direction during the rolling process to form peak-shaped cracks.

Precautions:

Strictly control the process parameters during continuous casting to ensure the quality of the ingot.

Carry out strict inspection on the ingots to promptly detect and deal with defects such as transverse cracks.

Optimize the rolling process,reduce stress concentration during rolling,and avoid crack expansion.

3.Edge cracks

Edge cracks mainly occur in stainless steel plates 20-80mm from the edge,and are in the form of multiple parallel longitudinal cracks of varying sizes.This defect is more serious when the steel plate is thicker and wider.

Cause Analysis:

The formation of edge cracks is mainly due to the rollover of the edges of the ingot to the surface during the rolling process.During the rolling process,if the edges of the ingot are not effectively controlled,these edges will roll over to the surface under the action of the rolling force,forming edge cracks.

Precautions:

Optimize the rolling process to ensure the stability of the ingot during the rolling process.

Use wide end face ingots to produce wide width steel plates as much as possible to reduce the widening amount during rolling,thereby reducing the degree of uneven deformation at the edges.

Strengthen quality control during the rolling process,and promptly detect and deal with defects such as edge cracks.

4.Inclusions and scarring

Inclusions and scars are another common defect on the surface of medium and thick stainless steel plates.They are distributed regularly and become obvious after finishing operations such as edge flame peeling crack inspection or flame cleaning of ingot scratches.

Cause Analysis:

The formation of inclusions and scars is mainly due to the failure to clean up the surface oxide slag during finishing.During the smelting and casting process of stainless steel,a layer of oxide slag will form on the surface of the molten steel.If this layer of oxide slag is not thoroughly cleaned during the finishing process,defects such as inclusions and scars will form on the surface of the steel plate.

Precautions:

Improve the finishing ability of the ingot and ensure that the slag is thoroughly cleaned.

Strengthen quality control during the finishing process,and promptly detect and deal with defects such as inclusions and scars.

Optimize smelting and casting processes to reduce the formation of slag.

5.Decarburization layer and overheating

Decarburization layer and overheating are common defects of stainless steel plates during heating.If the billet stays in the high temperature section of the heating furnace for too long or the heating temperature is too high,the billet surface will be over-oxidized and a decarburization layer of a certain depth will be formed.This not only makes the surface of the steel plate seriously rough and the internal grains grow excessively,but also seriously reduces the mechanical properties and processing properties of the steel plate.

Cause Analysis:

The formation of decarburization layer and overheating is mainly due to the excessive oxidation in the heating furnace or the excessive heating temperature.During the heating process,if the oxidation of the furnace atmosphere is too strong or the heating temperature is too high,it will cause excessive oxidation on the surface of the steel billet and form a decarburization layer.At the same time,high temperature will also cause the grains inside the steel billet to grow excessively,reducing the mechanical properties and processing properties of the steel plate.

Precautions:

Establish a reasonable heating system,control the heating temperature,heating speed and heating time,and prevent the steel billet from overheating.

Control the atmosphere in the furnace,minimize the amount of excess air while ensuring complete combustion of the fuel,adopt micro-positive pressure control,reduce the opening time of the furnace door,and prevent the inhalation of cold air.

Optimize the structure and process parameters of the heating furnace to improve heating efficiency and quality.

6.Iron oxide sheet pressing

Iron oxide scale indentation is one of the common defects in the rolling process of stainless steel medium and thick plates.Before rolling,if the iron oxide scale on the surface of the steel billet is not thoroughly cleaned or cleaned incompletely,it will be pressed into the steel plate body during the rolling process,forming an iron oxide scale indentation defect.

Cause Analysis:

The formation of scale indentation is mainly due to the excessive thickness of scale on the surface of the billet before rolling or incomplete cleaning.During the rolling process,if the scale on the surface of the billet is too thick or incompletely cleaned,it will be pressed into the steel plate body under the action of the rolling force,forming scale indentation defects.

Precautions:

Strengthen the surface cleaning of the steel billet before rolling to ensure that the iron oxide scale is thoroughly cleaned.

Optimize rolling process parameters to reduce stress concentration and uneven deformation during rolling.

Strengthen quality control and inspection during the rolling process,and promptly detect and deal with defects such as iron oxide scale intrusion.

7.Metallic inclusions and non-metallic inclusions

Metallic inclusions and non-metallic inclusions are one of the common internal defects in stainless steel plates.They are formed when foreign substances(such as metal fragments,non-metallic oxides,etc.)are embedded in the steel plate body during the smelting and casting process.

Cause Analysis:

The formation of metallic inclusions and non-metallic inclusions is mainly due to lax quality control during smelting and casting.During the smelting process,if the deodorizing compounds formed after the addition of deodorizers do not have time to float out and be removed and remain in the billet,they will be exposed on the surface of the steel plate after rolling to form non-metallic inclusions.At the same time,if the protective slag is involved in the molten steel or the refractory material breaks and falls on the surface of the billet during continuous casting,metallic inclusions or non-metallic inclusions will also be formed after rolling.

Precautions:

Strengthen quality control and inspection during the smelting and casting processes to ensure the purity of the molten steel and the quality of the ingots.

Optimize smelting and casting process parameters to reduce the chance of embedding of foreign matter.

Strengthen quality control and inspection during the rolling process,and promptly detect and deal with defects such as metal inclusions and non-metallic inclusions.

Conclusion

As an important industrial material,the quality of stainless steel plates is directly related to the performance and safety of the products.Therefore,during the production and use process,the generation and development of various defects must be strictly controlled.By strengthening quality control and testing,optimizing production process parameters,and improving equipment maintenance,the defect rate of stainless steel plates can be effectively reduced,and product quality and performance can be improved.At the same time,the defects that have occurred must be handled and repaired in a timely manner to ensure the safety and reliability of the product.