Stainless Steel and Nickel Alloy Fastener Selection Guide

Core Material Selection Principle: Performance and Environmental Matching

When selecting fastener materials, strength should not be the only consideration; the service environment must be comprehensively evaluated.

Core considerations include:

• Define the Usage Environment: Determine the temperature range (e.g., -40°C to 300°C) and the type of corrosive media (e.g., dry air, fresh water, seawater, chlorides).

• Determine Performance Priority: Rank requirements as "Corrosion Resistance > Temperature Tolerance > Strength > Non-magnetic/Galling Resistance" to clarify core needs.

• Match Material Category: Based on environmental and performance requirements, filter corresponding groups from categories like Austenitic, Duplex, Martensitic, etc.

• Cost Effectiveness: Select the most economical material that meets the usage requirements.

I. Material Selection by Stainless Steel Microstructure Type

1. Austenitic Stainless Steel (Class A: A1-A5, A8)

Core Characteristics: Non-magnetic (cold working may produce weak residual magnetism, removable by heat treatment), cannot be hardened by quenching, relies on work hardening for improved performance. Generally good corrosion resistance, some groups (e.g., A8) can withstand marine and high chloride environments.

2. Martensitic Stainless Steel (Class C: C1, C2, C3)

Core Characteristics: Can be strengthened by quenching and tempering, high strength but corrosion resistance weaker than Austenitic stainless steel, strongly magnetic. Poor low-temperature toughness, use cautiously below 0°C.

3. Ferritic Stainless Steel (Class F: F1)

Core Characteristics: Slightly strengthened by cold working, magnetic, lower cost than Austenitic stainless steel. Corrosion resistance weaker than A2, A3, poor low-temperature toughness (not suitable below -20°C).

F1 Applicable Scenarios: Low cost, low corrosion, non-cryogenic scenarios (e.g., indoor simple brackets, non-load-bearing decorative fasteners).

4. Duplex (Austenitic + Ferritic) Stainless Steel (Class D: D2, D4, D6, D8)

Core Characteristics: Higher strength than Austenitic stainless steel, significantly better stress corrosion cracking resistance than A1-A5. Higher number indicates better corrosion resistance; D8 (Super Duplex) corrosion resistance is comparable to A8.

5. High-Temperature Stainless Steels and Nickel Alloys (CH0~CH2, V/VH/VW, SD, SB, 718)

Core Characteristics: Temperature range (High temp: 300°C~550°C; Very high temp: >550°C), must have sufficient oxidation resistance, high-temperature corrosion resistance, and creep resistance.

II. Material Selection for Special Performance Needs

1. Stress Corrosion Cracking (SCC) Risk Scenarios: Chloride-containing environments (e.g., swimming pools, marine), high temperature and humid environments. Recommended materials: D6/D8 Duplex steel, A8 Austenitic steel; Avoid: A1-A5 Austenitic steels.

2. Pitting/Crevice Corrosion Resistance: Pitting Resistance Equivalent Number (PREN) = %Cr + 3.3 * %Mo + 16 * %N; For Duplex steels containing Tungsten (W): PREN = %Cr + 3.3 * (%Mo + 0.5 * %W) + 16 * %N. Recommended materials: Groups with high PREN values (e.g., A8, D8, D6), suitable for chemical media containing chlorine, seawater environments.

3. Intergranular Corrosion Resistance: High-risk conditions: Carbon content > 0.03% + temperature range 550°C - 925°C (e.g., after welding, high temperature use). Recommended materials: Low-carbon groups: A2L, A4L (C ≤ 0.03%); Stabilized groups: A3, A5 (contain Ti/Nb, combines with carbon to prevent intergranular corrosion); Duplex steels: All groups D2-D8.

4. Low/Non-Magnetic Requirements: Core materials: Austenitically stable grades, such as A2L (4311-304-53-I), A4L (4406-316-53-I), QN1803 (Nitrogen-alloyed Austenitic steel). Note: Cold working can produce weak residual magnetism; subsequent heat treatment can remove it if non-magnetic is required, or confirm permeability with supplier in advance (require relative permeability close to 1.0).

5. High Strength + Anti-Galling: Recommended materials: Sorbitic high-strength stainless structural steel (S1 group): Suitable for large diameter, high load fasteners (e.g., large structural steel bolts), stable torque coefficient; QN1803 (A2 group nitrogen steel): High strength and weakly magnetic, low risk of galling during installation, suitable for frequent assembly/disassembly scenarios.

III. Common Stainless Steel Grades for Fasteners

Table 1: Cold Heading Fastener Stainless Steel Grades - Austenitic

Table 2: Cold Heading Fastener Stainless Steel Grades - Ferritic / Martensitic / Duplex