Material classification of stainless steel screws

Stainless steel screws are classified into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and precipitation hardening 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 these five aspects, the grades, varieties, specifications and material standards of stainless steel screws are finally determined

Martensitic stainless steel

Type 410 and 416 can be strengthened by heat treatment, with a hardness of 35～45HRC, good machining performance, heat-resistant and corrosion-resistant stainless steel screws for general purposes. Type 416 has a slightly higher sulfur content and is free-cutting stainless steel.

420 type, sulfur content? R0.15%, improved mechanical properties, can be strengthened by heat treatment, maximum hardness value 53～58HRC, used for stainless steel screws requiring higher strength.

Precipitation hardening stainless steel (Guide: Introduction to the materials used in fasteners)

17-4PH, PH15-7Mo, they can get higher strength than the usual 18-8 type stainless steel, so they are used for high-strength, corrosion-resistant stainless steel screws.

A-286, a non-standard stainless steel, has higher corrosion resistance than the commonly used 18-8 stainless steel, and still has good mechanical properties when the temperature increases. Used as high-strength, heat-resistant, and corrosion-resistant stainless steel screws, which can be used at 650-700°C.

Austenitic stainless steel

The commonly used grades are 302, 303, 304, and 305, which are the four so-called 18-8 austenitic stainless steel grades. Both the corrosion resistance and the mechanical properties are similar. The starting point for selection is the production process of stainless steel screws, and the method depends on the size and shape of the stainless steel screws, as well as the quantity of production.

Type 302 is used for mechanically processed screws and self-tapping bolts.

In order to improve the machining performance of Type 303, a small amount of sulfur is added to Type 303 stainless steel, which is used to machine nuts from bar stock.

Type 304 is suitable for processing stainless steel screws by hot heading, such as longer bolts and large diameter bolts, which may be beyond the scope of cold heading.

Model 305 is suitable for processing stainless steel screws by cold heading process, such as cold-formed nuts and hexagonal bolts.

Type 309 and Type 310, their Cr content and Ni content are higher than 18-8 type stainless steel, suitable for stainless steel screws working at high temperatures.

Type 316 and 317, they both contain alloying element Mo, so their high temperature strength and corrosion resistance are higher than 18-8 type stainless steel.

Type 321 and Type 347, Type 321 contains relatively stable alloying element Ti, Type 347 contains Nb, thereby improving the material's resistance to intergranular corrosion. It is suitable for stainless steel standard parts that are not annealed after welding or are in service at 420～1013℃.

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