A4-70 Stainless Steel Bolt
A4-70 stainless steel bolts are corrosion-resistant fasteners designed for applications where reliable fastening and resistance to more demanding environments are required. As an A4 stainless steel fastener grade, A4-70 contains molybdenum (Mo), which provides better resistance to corrosion than A2 stainless steel, particularly in environments exposed to moisture, chlorides and other corrosive conditions. With a minimum nominal tensile strength of 700 MPa, A4-70 bolts combine good mechanical strength with the corrosion resistance required for long-term fastening performance.
A4-70 bolts are commonly associated with 316 stainless steel and can be produced from 316 or 316L material depending on the required specification. They are suitable for a wide range of industrial, marine, construction and equipment applications where A2 stainless steel may not provide sufficient corrosion resistance. Different bolt types, diameters, lengths and thread specifications can be selected according to the requirements of the application.
Type of A4-70 Bolt:
We supply a wide range of A4-70 stainless steel bolts for different fastening requirements, including hex bolts, flange bolts, carriage bolts, anchor bolts, T-bolts and U-bolts. Different diameters, lengths and thread specifications are available to meet standard and custom requirements. For A4-70 bolts, we pay close attention to material selection and production control, with raw materials checked before production and key manufacturing processes monitored to ensure consistent dimensions, thread quality and mechanical performance. Material certificates and inspection documents can also be provided according to customer requirements.
Material Chemical Composition of A4-70 Bolt:
A4-70 stainless steel bolts are made from austenitic stainless steel in the A4 material group, which is characterized by the addition of molybdenum (Mo) for improved corrosion resistance. A4-70 bolts are commonly manufactured from 316 or 316L stainless steel, although the specific material grade should be selected according to the applicable standard and customer requirements. The chromium, nickel and molybdenum content of A4 stainless steel provides good resistance to moisture, chlorides and other corrosive environments, making A4-70 suitable for applications where higher corrosion resistance is required. For more information about 316 stainless steel fasteners, see our SS316 bolts page.
The chemical composition of A4-70 bolts is controlled according to the applicable ISO3506-1 stainless steel fastener standard. Key elements include carbon, silicon, manganese, phosphorus, sulfur, chromium, nickel, molybdenum and, where applicable, copper. The chemical composition helps determine the corrosion resistance and material characteristics of the finished fasteners. The table below shows the typical chemical composition requirements for A4 stainless steel used in A4-70 bolts.
| Property Class | Tension Strength(min)MPA | Stress at 0.2% non-proprotional elongation(min)MPA | Elongation after fracture(min)mm |
| A4-70 | 700 | 450 | 0.4d |
Mechanical Property of A4-70 Bolt:
The mechanical properties of A4-70 stainless steel bolts are specified according to ISO 3506-1. The “70” in the A4-70 designation indicates a minimum nominal tensile strength of 700 MPa. A4-70 bolts also require a minimum stress at 0.2% non-proportional elongation of 450 MPa and a minimum elongation after fracture of 0.4d. These requirements provide a combination of strength and ductility suitable for a wide range of stainless steel fastening applications. The main mechanical property requirements for A4-70 bolts are shown in the table below.The table below shows the chemical composition requirements for A2 stainless steel used in A2-70 bolts according to ISO 3506-1.
| Property Class | Chemical Compistion(max) | ||||||||||
| C | Si | Mn | P | S | Cr | Mo | Ni | Cu | N | Other Element | |
| A4-70 | 0.08 | 1 | 2 | 0.045 | 0.03 | 16.0~18.5 | 2.00~3.00 | 10.0~15.0 | 4 | / | h,i |
Application of A4-70 Bolt:
Marine & Coastal Applications
A4-70 stainless steel bolts are well suited for marine and coastal applications where fasteners are exposed to moisture, salt spray and chloride-containing environments. They can be used in marine equipment, boats, docks, coastal structures, outdoor fixtures and other assemblies where good corrosion resistance is important. The molybdenum-containing A4 stainless steel provides better resistance to chloride-related corrosion than A2 stainless steel, while the 700 MPa minimum tensile strength provides reliable mechanical performance.
Industrial & Chemical Equipment
A4-70 bolts are commonly used in industrial equipment, processing systems, pumps, tanks, pipelines and other machinery exposed to moisture or corrosive media. Their combination of corrosion resistance and mechanical strength makes them suitable for equipment operating in demanding industrial environments. A4-70 can be considered where A2 stainless steel fasteners may not provide sufficient corrosion resistance for the working conditions.
Food Processing & Water Treatment
A4-70 stainless steel bolts can also be used in food processing equipment, water treatment systems, commercial kitchens and other applications where fasteners may be exposed to water, cleaning processes and humid conditions. Their stainless steel construction provides durable corrosion resistance and helps maintain the service life of the fastening connection. The appropriate stainless steel grade should be selected based on the specific chemicals, temperatures and environmental conditions involved.