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Corrosion resistant alloy cast iron
Casting parts resistant to seawater corrosion and marine atmospheric corrosion. The representative material is STNi2CrCuRe. They are mainly used in coastal water conservancy projects, Haihe sluices, coastal power generation projects, sewage treatment projects and other castings that need to be resistant to seawater and marine atmospheric corrosion and urban sewage treatment. , Used to replace expensive stainless steel. Compared with stainless steel structural parts or stainless steel composite structural parts, seawater corrosion-resistant castings have the advantages of flexible structural design and low cost. In recent years, they have been successfully applied in coastal projects.
Introduction to the performance of STNi2CrCuRe seawater corrosion resistant castings
For seawater hydraulic engineering, the amount of corrosion-resistant metal materials is large, and the amount of one project may reach tens of thousands of tons. The use of high-grade alloys is unrealistic and a waste of resources. The use of ordinary carbon steel and cast iron is difficult to meet the requirements of actual use and design; the use of stainless steel welded steel structure matrix composite materials, due to the different electronic potential differences of different materials, often due to the accelerated corrosion of the welded parts, the composite material embedded parts are premature After failure, after comprehensively considering various material selection principles and balancing various factors, low-alloy seawater corrosion-resistant cast iron is the best choice. The low-alloy cast iron currently developed and in use is a low-alloy corrosion-resistant cast iron formed by adding elements such as Ni, Cr, Si, Cu, RE to the cast iron. The addition of Ni, Cr, Si and other elements reduces the anode phase in the cast iron, which is the matrix. The activity moves toward the positive potential, thereby reducing the corrosion rate of the material; adding Cr, Si, etc. to form a protective film on the surface of the cast iron, which is equivalent to increasing the corrosion resistance of the microbattery, reducing the current and reducing the corrosion; adding rare earth elements to make cast iron Degassing, removing impurities, improving the structure, especially the impurities on the grain boundary, thereby improving the corrosion resistance of cast iron, especially the intergranular corrosion resistance. In recent years, corrosion-resistant cast iron represented by STNi2CrCuRE has gradually formed, the corrosion rate is about 0.05-0.2mm/a, and the corrosion resistance level is 4-6. It is currently the most widely used corrosion-resistant cast iron material. In recent years, a large number of applications have been obtained in seawater hydraulic engineering, with good results. STNi2Cr alloy cast iron material has been praised by users for its excellent cost performance. In recent years, it has been increasingly used in offshore engineering and coastal water conservancy projects. In more than forty project applications, no corrosion phenomenon exceeding the design requirements was found after tracking.
The STNi2Cr alloy cast iron material has the following problems:
1. When alloy cast iron materials without surface corrosion are exposed to the air for a long time, a layer of floating rust will be formed, but it will not affect the seawater corrosion resistance of the alloy cast iron materials.
2. The material is a brittle material of the gray cast iron matrix. Improper operation will cause the embedded parts to break during the lifting and transportation process.

表1   常用耐海水腐蚀铸件的化学成分

牌号

C

Si

Mn

P≤

S≤

Ni

Cr

Cu

RE

耐腐蚀性能

STNi2CrCuRE

2.8~3.6

1.8~2.8

0.6~1.0

0.12

0.06

2.0~2.8

0.8~1.5

0.50~1.00

≤0.15

 

 

 

 

 

 

 

 

 

STNi2Cr

2.8~3.6

1.8~2.8

0.6~1.0

0.12

0.06

2.0~2.8

0.8~1.5

 

 

STNi2Cr

2.8~3.6

1.8~2.8

0.6~1.0

0.12

0.06

1.5~2.0

0.8~1.5

 

 

STNi2Cr

2.8~3.6

1.8~2.8

0.6~1.0

0.12

0.06

0.8~1.2

0.8~1.5

 

 



 

 

 

 

 

 

 

 

 

 

 

 

For the above-mentioned commonly used seawater corrosion-resistant cast iron materials, the design unit can select material components with different alloy contents according to the application environment's seawater salt content, seawater flow rate, seawater (or sewage) pollution degree, and the importance of the project. Table 1 grades from top to bottom as the alloy content decreases, the corrosion resistance and cost are gradually reduced.
   When designing the material of alloy cast iron, the design unit should avoid using AS (arsenic) and Sb (antimony) alloy elements. Although AS, Sb and other elements reduce the activity of the cathode phase in cast iron, move the cathode phase toward the negative potential, reduce the potential difference between the different phases of the corrosion-resistant cast iron, and reduce the corrosion rate of the material, but the casting has a great tendency to crack Reduce the mechanical properties of alloy cast iron. Increasing the Cr content not only improves the corrosion resistance of the alloy cast iron, but also greatly increases the hardness of the alloy cast iron. However, when the Cr content is greater than 1.2% and the hardness is greater than 350HB, it will be difficult to process. If the working surface of the embedded part needs high hardness, in order to reduce the manufacturing cost, the alloy composition content of different embedded parts should be distinguished according to the use function of the embedded parts, such as: door lintel (top sill), bottom sill can choose Cr: 0.8-1.2%, hardness HB≧220; Cr: 1.2-1.8% can be selected for main rail, anti-rail, main anti-rail, hardness HB≧300
In order to meet the design life of alloy cast iron, when selecting materials for seawater engineering embedded parts, the first thing to do is to select the applicable metallurgical product varieties and grades. The products of this grade should have corrosion resistance, comprehensive mechanical properties and suitable heat treatment conditions that meet the design requirements; After determining the type and brand to be used, the metallurgical quality of the castings must be strictly required, including the accuracy and uniformity of the chemical composition; secondly, the metallurgical process for the production of seawater engineering embedded parts must be considered, because the advanced smelting process produces high-quality products It is difficult to guarantee the accuracy and uniformity of the composition in the cupola. Only the low-frequency induction electric furnace and other smelting furnaces can smelt high-quality molten iron to ensure that the design requirements are met. Furthermore, it depends on the casting process of the product. Only advanced casting technology can cast high-quality castings that not only have high appearance quality, but also have good internal quality. These aspects should be paid special attention to when selecting materials.

表2  典型海水工程埋件用腐蚀铸铁的性能

牌号

抗拉强度(Mpa)

抗弯强度(Mpa)

硬度(HB)

腐蚀率(mm/y)

STNi2CrCuRE

≥240

480

≥240

  0.05~0.20

 

 

 

Note: For the main rail, anti-rail, main anti-rail and other embedded parts that need to be in contact with the wheel, the Cr content can be adjusted to 1.2% or more. If the user has no special requirements, the Cr content is not adjusted for the convenience of machining.

Introduction to GSTNi2CrCuRe
In order to solve the problem of insufficient toughness of STNi2CrCuRe, after long-term research, our company has developed a new type of alloy cast iron material GSTNi2CrCuRe with high strength and certain toughness, and has been registered by the International Intellectual Property Office to form our company’s proprietary technology. Its chemical composition and main The performance is as follows:

          表3   GSTNi2CrCuRe耐海水腐蚀铸件的化学成分

牌号

C

Si

Mn

P≤

S≤

Ni

Cr

Cu

RE

GSTNi2CrCuRE

2.8~3.6

2.0~3.5

0.5~1.0

0.12

0.06

2.0~2.8

0.6~1.5

0.50~1.00

≤0.15

 

 

 

表4  GSTNi2CrCuRe腐蚀铸铁的性能 

牌号

抗拉强度(Mpa)

延伸率(δ5)

硬度(HB)

腐蚀率(mm/y)

GSTNi2CrCuRE

≥420

≥ 3%

≥270

 

 

 

 

 

 

Compared with STNi2CrCuRe, GSTNi2CrCuRe has significant advantages of its material: when the strength is nearly doubled, the matrix also has a certain degree of toughness (its toughness index is equivalent to the bucket teeth of an excavator), and the seawater corrosion resistance is greatly improved. ...
Typical structure of seawater corrosion resistant alloy cast iron embedded parts

底坎典型结构

 门楣典型结构

主轨典型结构

主反轨典型结构

Structural technology of door slot embedded parts
   At present, there are two types of embedded parts for door grooves in water conservancy projects: structural parts and casting parts. Because of the difference in manufacturing process, the structure of these two kinds of workpieces is quite different. The rationality of the structure determines the quality of the manufacturing process, which affects the difficulty and accuracy of the embedded parts manufacturing, and further affects the cost of the investor.
   Reasonable casting wall thickness and connection
Reasonable casting wall thickness and transition can obtain ideal casting physical properties, without white mouth tendency, and obtain reasonable graphite shape

Structural craftsmanship of embedded parts of cast door groove
   Design of ribs and plates for castings: The distance between ribs and plates should not exceed 500mm. For main and anti-rail castings, it is necessary to consider setting grouting holes on the ribs.
  The cross-sectional shape of the embedded part: a reasonable cross-sectional shape should be 1) The width of the plane should not exceed 500mm; 2) The structure of the embedded part is generally symmetrical; 3) The wall thickness should not be too large
   Unreasonable cross-sectional shape will cause pouring collapse box, shrinkage deformation after casting, shrinkage holes and shrinkage defects at the hot junction of the casting.
  The length of embedded parts: 2.5-3m of embedded parts is reasonable. Too short embedded parts increase the difficulty of installation and reduce installation accuracy. If embedded parts are too long, it will cause increased deformation and processing difficulties.

Reasonable thickness of coating on alloy cast iron processing surface
   Corrosion-resistant alloy cast iron relies on the properties of the material itself for anti-corrosion. When designing the anti-corrosion design, it is recommended that the thickness of the processed surface paint film should not exceed 100um. Because the working surface of the embedded parts is smooth and clean after mechanical processing, the paint film adhesion is very poor compared with the steel structure after shot blasting or sand blasting. If the paint film design is too thick (such as more than 150um), the paint film coating is drying It will become very brittle after being touched by an external force and will easily fall off and lose its anti-corrosion significance. Therefore, it is recommended that the paint film thickness of the corrosion-resistant alloy cast iron processing surface should not exceed 100um.

耐腐蚀合金铸铁埋件实物图片

各种结构形状的主反轨图片

 

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