Introduction to Nickel-Based Alloy Fasteners

In recent years, nickel-based corrosion-resistant alloys have been increasingly used in fasteners and equipment. Due to the alloy's unique high-temperature mechanical properties and corrosion resistance, it has been widely used in many fields such as chemistry, petroleum, alloys, aerospace, marine development, and atomic energy. It can solve engineering corrosion problems that cannot be solved by general stainless steel and other metal and non-metal materials. In order to facilitate the application of nickel and nickel alloys, the relevant material information is now sorted out for reference.

1. Classification of Nickel and Nickel-Based Alloys

1) Classification by chemical composition

In my country, nickel materials with a sum of nickel and cobalt contents greater than or equal to 99% and a cobalt content less than or equal to 1.5% are customarily called industrial pure nickel, and materials with a nickel content greater than or equal to 50% are called nickel-based alloys. Alloys with a nickel content of 30% to 50% and a nickel content and iron content greater than or equal to 60% are called iron-nickel-based alloys. The difference between them and stainless steel is that the iron content in stainless steel should be greater than or equal to 50%, and the nickel content should be less than 30%.

In ASME, nickel and nickel alloys are collectively referred to as high-nickel alloys, including pure nickel, nickel-based alloys and iron-nickel-based alloys (including cobalt alloys and chromium alloys with high nickel content). The definition of iron-nickel-based alloys is different from that in my country. The main difference lies in the classification of iron-nickel-based alloys and chromium-nickel stainless steels, such as the commonly used Swedish 2RK65 and my country's corresponding grades 03Cr20Ni25Mo5Cu (904L). The United States classifies it as a nickel-based alloy, N08904, while my country classifies it as stainless steel

2) According to performance

my country's nickel alloys include corrosion-resistant alloys, which are denoted by NS*** (GB/T15007), and high-temperature alloys, which are denoted by GH*** according to GB/T14992. my country's nickel alloys for fasteners only consider the grades of corrosion-resistant alloys, and corrosion-resistant alloys do not consider pure nickel and nickel-copper alloys, while fastener nickel and nickel-based alloys include pure nickel and nickel-copper alloys.

3) According to the strengthening effect of alloy elements

There are two types of nickel-based alloys: solid solution strengthened and precipitation strengthened (or precipitation hardened). The fastener standards of various countries basically use solid solution strengthened nickel alloys, and rarely use precipitation strengthened nickel alloys. The bars and tubes used in fasteners in my country are all made of solid solution strengthened nickel-based materials.

4) According to the main alloy system of nickel and nickel alloys

In my country, nickel is usually classified into: industrial pure nickel, nickel-copper alloy, nickel-chromium alloy, nickel-molybdenum alloy, nickel-chromium-molybdenum alloy, nickel-chromium-molybdenum-copper alloy. In the United States, it is classified into: industrial pure nickel, nickel-copper alloy, nickel-chromium alloy, nickel-iron-chromium alloy, nickel-molybdenum alloy, nickel-cobalt alloy, etc. according to UNS grade classification.

2. Nickel and nickel-based alloy brand identification

Since nickel and nickel alloys are highly internationalized commodities, in addition to adopting their own brands, countries also often use the UNS brands and trade names and codes in the United States ASTM. Most of my country's iron-based materials are imported, and the imported ones are also commonly imported with American standard brands. In addition, in recent years, more and more ISO standard material brands have been adopted. Therefore, in addition to understanding the brands of nickel and nickel-based alloys in China, you should also be familiar with the brand representations of ASTM, ISO, etc.

1) Brand marking in China

(1) Industrial pure nickel and nickel-copper alloy are non-ferrous metals. The grades of their pressure-processing materials are indicated in accordance with the provisions of GB/T340. Industrial pure nickel is indicated by N plus a serial number, such as N5, N6, N7. Nickel-copper alloy is indicated by NCu. The components other than the matrix component nickel are indicated by numbers, such as NCu30, NCu28-2.5-1.5, etc.

(2) Nickel alloy pressure processing materials other than nickel-copper alloys shall be indicated by NS××× in accordance with GB/T15007.

The first digit is the iron-nickel type

NS1 ×× ——Iron-nickel based alloy, solid solution strengthened

NS2××——Fe-Ni alloy, aging-strengthened type (rarely used)

NS3××——Nickel alloy, solid solution-strengthened type

NS4××——Nickel-based alloy, aging-strengthened type (rarely used)

The second digit is the alloy system

NS×1×——Nickel-chromium series

NS×2×——Nickel-Molybdenum Series

NS×3×——Nickel-chromium-molybdenum series

NS×4×——Nickel-chromium-molybdenum-copper system

The third digit indicates the order of different alloy grades

In addition to the above representation methods, corrosion-resistant alloys may also use unified digital codes in accordance with GB/T17616 "Uniform digital code system for steel and alloy grades".

Comparison table of corrosion resistant alloy processing material Table 1.

Table 1