Stainless Steel Fasteners

Industry-Grade Selection Guide of Stainless Steel Fasteners

Stainless Steel vs Other Materials

Carbon Steel vs Stainless Steel

In a comparison between stainless steel (SS) and carbon steel, the most distinguishable characteristic is the corrosion resistance- stainless steel is better than carbon steel, thus it is applicable in the outdoors, corrosive, and hygienic environment. Carbon steel, in its turn, is able to be heat-treated to get higher strength and, as a rule, is cheaper. Stainless steel has better finishing, and it does not rust aesthetically. Look into High Tensile Fasteners in case of high strength and durability.

Galvanized Steel vs Stainless Steel

Galvanized steel is carbon steel that has been covered using zinc to combat corrosion. Although it is inexpensive at first, its durability and looks are minimal; scratches interfere with protection. Stainless steel forms a passive chromium oxide layer, which keeps its shine and heals itself and provides durability in the long run. Stainless steel is used where aesthetics and low maintenance are needed in the project.

304 vs 316 Stainless Steel

316 stainless steel contains 2-3 percent molybdenum, which gives the material high resistance to chlorides and salt, and is suitable in marine, chemical and coastal applications as well as in the general corrosion applications. 304 stainless steel is good for indoor and general corrosion. Note that 316 costs 20-30 % higher than 304 because it has a higher corrosion resistance.

Austenitic (300) vs Ferritic (400) vs Martensitic

The most commonly used stainless steel is called austenitic (300 series) and is non-magnetic, extremely corrosion-resistant, and non-ferromagnetic. Ferritic (400 series) is magnetic, cheaper and moderately corrosion resistant. The Martensitic stainless steel is magnetic and has a heat treatment and the greatest strength, but has low corrosion resistance. The balance between the strength, corrosion resistance, and application environment is what determines the choice of the correct grade.

Common Challenges with Stainless Steel Fasteners

The most common challenges of stainless steel fasteners are given below. 

Galling (Seizing)

Galling, or cold welding, is a phenomenon that takes place when stainless steel fasteners are clamped under large friction, or when material of the same type is joined together resulting in thread seizing. The methods to avoid this are to use anti-seize compounds, coat with PTFE or Xylan, install gradually, use different materials (e.g., SS bolt with brass nut) and to be sure that they are well lubricated when assembled.

Thread Stripping

Stainless steel is more prone to thread stripping compared to carbon steel, as it is softer. The preventive measures are coarse threading, sufficient thread engagement (at least 1.5× the diameter) and not over-torque in installation.

Stress Corrosion Cracking (SCC)

SCC happens under tensile stress in chloride-rich environments and some grades of stainless steel are vulnerable to it but 304 stainless steel is more vulnerable; 316 or duplex are better resistant. The risk can also be reduced through a reduction in tensile loads.

Crevice Corrosion

Crevice corrosion forms in narrow spaces between stagnant liquids, which undermines the fasteners in the long run. This can be prevented by use of 316 or duplex stainless steel in constructing assemblies in a manner that eliminates crevices.

Galvanic Corrosion

Galvanic corrosion occurs as a result of contact between stainless steel with dissimilar metals, such as aluminum or zinc. SS is a cathode, which leads to corrosion of the other metal. Some of the preventive measures are the use of insulating washers or fasteners that are constructed in the same metal as the other component.

Manufacturing Process of Stainless Steel Fasteners

The manufacturing process of the stainless steel fasteners, followed by use, is given below. 

Raw Material Sourcing: 

Before the production starts, stainless steel is obtained as certified mills in the form of wire rods or bars, and it is guaranteed of adequate grade, chemical composition, and complete heat traceability. 

Wire/Bar Drawing: 

A raw material is made by the accuracy of diameters to provide homogeneous mechanical characteristics and dimensional precision. 

Cold Heading / Hot Forging: 

The head and body are forged, either by cold beating or by hot beating, depending on the size and design of the fastener; this furnishes the head and body with a due flow of grain and strength. 

Thread Rolling vs Cutting: 

The threads are rolled to achieve more strength and fatigue resistance or cut when the design factors need it. 

Heat Treatment: 

Martensitic-like SS 410 are heat treated, whereas austenitic ones are annealed in solution in order to re-establish corrosion resistance. 

Passivation:

Passivation of all stainless steel screws is done in order to strengthen the chromium oxide coating and eliminate free iron. 

Inspection & Packing: 

To achieve uniform quality and secure delivery throughout the world, each batch is grade-marked, examined at every pass, recorded, and loaded in export-quality packaging.

Quality Assurance & TestingMaterial Verification (PMI)

All our products come from the Positive Material Identification test that is used to verify the proper Monel grade and chemical makeup, thus removing chances of material confusion.

Chemical Analysis: 

Elemental composition is confirmed using the Optical Emission Spectrometry (OES), which is in accordance with prescribed standards.

Dimensional Inspection: 

Calibrated equipment like calipers, micrometers and optical comparators are used to measure dimensions like diameter, length, and tolerances.

Thread Gauging: 

GO / NO-GO gauges are used to check the threads according to ISO and ASME standards to check their proper pitch, class, and engagement.

Mechanical Testing: 

The tests are carried out using tensile strength, proof load, and hardness tests in respect of relevant ASTM requirements.

Salt Spray Testing: 

In necessary cases, corrosion resistance can be tested by ASTM B117 salt spray testing.

Passivation Verification: 

Passivated fasteners are examined to ensure that they are free of free iron and corrosion protection is improved.

Certification: 

On the full basis of documentation and compliance information, Mill Test Certificates (EN 10204 3.1 / 3.2) are issued.

Lot Traceability: 

All manufacturing and supply is tracked by complete heat number and batch traceability.

Third-Party Inspection: 

That can be independently checked by certified agencies like SGS, Bureau Veritas, or other similar ones, at a request.

Size Range & Availability of Stainless Steel Fasteners

Why Choose Unifit Fastener for Stainless Steel?

Unifit Fastener is a reliable supplier of stainless steel fasteners because it has a broad range of grades, such as 304,316, 316L, 310, 410, and 430 fasteners produced in accordance with ISO 3506 and ASTM requirements. We supply various industrial requirements precisely with high-pressure ASTM A193 B8/ B8M bolts, as well as with custom-made fasteners based on drawings. The passivation is done in-house, PMI testing is done on each batch, and full certification of MTC 3.1 ensures that quality and grades are consistent. Unifit Fastener has an easy stock of common sizes, competitive bulk prices, fast delivery within and outside India, and high-quality technical support that ensures it is a reliable supplier of stainless steel fasteners in a variety of food, pharma, marine, and chemical industries in Mumbai and India.