What are the grades of stainless steel bolt materials?

(HY-marketing department)

Stainless steel screws are classified into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and precipitation hardened stainless steel. The selection of stainless steel screws is also principled. From what aspect, let you choose the stainless steel screws you need. After comprehensive and comprehensive consideration of the following five aspects, the grades, varieties, specifications and material standards of stainless steel screws are finally determined.

  1. ferritic stainless steel:Type 430 ordinary chrome steel, its corrosion resistance and heat resistance are better than 410 type, it is magnetic, but it can not be heat-treated and strengthened. It is suitable for stainless steel stainless steel with high strength and corrosion resistance. Screw.

  2. martensitic stainless steel:Types 410 and 416 can be heat-treated and reinforced with a hardness of 35 to 45 HRC. They have good machinability and are used for general purpose heat-resistant and corrosion-resistant stainless steel screws. The Type 416 has a slightly higher sulfur content and is a free-cutting stainless steel. Type 420, sulfur content R0.15%, improved mechanical properties, heat treatment strengthening, maximum hardness value 53~58HRC, used for stainless steel screws requiring higher strength.

  3. Precipitation hardening stainless steel:17-4PH, PH15-7Mo, they can be used with higher strength than the usual 18-8 type stainless steel, and are therefore used for high strength, corrosion resistant stainless steel stainless steel screws.A-286, a non-standard stainless steel, has higher corrosion resistance than the commonly used 18-8 stainless steel and good mechanical properties at elevated temperatures. Used as a high-strength, heat-resistant and corrosion-resistant stainless steel screw, it can be used up to 650~700 °C.

  4. Austenitic stainless steel:Commonly used grades are four grades of 302, 303, 304, and 305, the so-called “18-8” type austenitic stainless steel. Both corrosion resistance and mechanical properties are similar. The starting point for the selection is the production process of stainless steel screws, which in turn depends on the size and shape of the stainless steel screws, and also on the quantity produced.

  • Type 302 is used for machined screws and self-tapping bolts.

  • Type 303 In order to improve the cutting performance, a small amount of sulfur is added to the Type 303 stainless steel for the processing of nuts with bar stock.

  • Type 304 is suitable for machining stainless steel screws with a hot boring process, such as longer gauge bolts and larger diameter bolts, which may exceed the range of the cold heading process.

  • Type 305 is suitable for machining stainless steel screws with cold heading, such as cold formed nuts and hexagon bolts.

  • Types 309 and 310, which have higher Cr content and Ni content than 18-8 stainless steel, are suitable for stainless steel screws working at high temperatures.

  • Types 316 and 317, both of which contain the alloying element Mo, are therefore superior in their high temperature strength and corrosion resistance to 18-8 stainless steel.

  • Types 321 and 347, Type 321 contains a relatively stable alloying element Ti, and Type 347 contains Nb, which improves the intergranular corrosion resistance of the material. Suitable for stainless steel standard parts that are not annealed after welding or serviced at 420~1013°C

The grades of stainless steel bolts are divided into 45, 50, 60, 70, 80 materials mainly divided into austenite A1, A2, A4, martensite and ferrite C1, C2, C4, which are represented by methods such as A2-70, “- – “The bolt material and strength level are indicated before and after respectively.

The grades of carbon steel bolts are divided into more than 10 grades of 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc. The numbers before and after the decimal point respectively indicate the nominal tensile strength and yield ratio of the bolt material, for example: The mark 8.8 bolt indicates that the tensile strength of the material reaches 800 MPa, and the yield ratio is 0.8, that is, the yield strength reaches 800×0.8=640 MPa.

  • Ordinary bolt materials Q215, Q235, 25 and 45 steel. For important or special purpose threaded couplings, alloy steels with high mechanical properties such as 15Cr, 20Cr, 40Cr, 15MnVB and 30CrMrSi can be used.

  • SUS304 (0Cr18Ni9 – also known as A2, mainly used for the manufacture of ordinary stainless steel bolts, screws, washers, nuts, the strength level of the general bolt is 70;

  • SUS 316 (0Cr18Ni12Mo2), SUS 316L (00Cr17Ni14Mo2) – also known as A4 is mainly used for the manufacture of high corrosion-resistant stainless steel bolts, screws, washers, nuts, the strength of the general bolt is 70, can also achieve high strength Level 80.

  • A for austenite, 2 for the second material (actually 2 means 304), -70 means the strength grade is 700MPa. Common materials are A2 and A4, respectively, 304 and 316 materials.

  • Stainless steel bolts A4-70 and A4-80 are no different in the material itself. 70 and 80 behind A4-70 and A4-80 represent 1/10 of the minimum tensile strength of the fastener. A4-70 and A4-80 are no different in the material itself. Because it is austenitic stainless steel, it cannot be heat treated. The method improves the tensile strength, and the tensile strength is improved by the dislocation barrier after the deformation (commonly known as cold work hardening), and the A4-70 bolts on the market are more circulated.

  • A1, A2, A4 represent 302, 304, 316; 45, 50, 60, 70, 80 represents 1/10 of the minimum tensile strength of the fastener.

  • The four groups are austenitic stainless steels, which were developed for boiling sulfuric acid. Therefore, they are named acid-resistant steels, which are metastable acid-resistant steels, typically SUS316.

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