Michael Pasko explores the advantages of employing 420 chrome stainless steel coiled spring pins across diverse applications.
Spirol invented the Coiled Spring Pin in 1948 and are used in companies developing automotive, medical, heavy equipment, military, aerospace, and consumer products. In applications requiring a combination of high strength, superior fatigue life, and corrosion resistance, 420 martensitic chrome stainless steel offer a host of technical benefits and provides an overall robust cost-effective solution.
High strength
Spirol’s 420 stainless steel Coiled Spring Pins are hardened to values approximating their high carbon steel equivalents and share the same minimum rated shear strength. This process also develops desired spring properties and fatigue resistance.
Chrome stainless steel Coiled Pins also offer good corrosion protection against most common atmospheric and environmental conditions without the risk of rapid work hardening associated with 302/304 austenitic stainless steel. In most cases, companies may use 420 chrome stainless steel Coiled Spring Pins as drop-in replacements for high carbon steel pins assuming galvanic potential has been considered relative to the host material.
Corrosion resistance
When companies require corrosion resistant Spring Pins, there are two common options: carbon steel with a sacrificial protective plating or coating or stainless steel alloys which are inherently corrosion resistant.
Platings and coatings provide excellent performance though they are consumed over time, whereas stainless steel provides a lifetime of protection providing free oxygen is available in the environment (free oxygen allows the fastener’s protective chromium oxide layer to reform if damaged). For plated and coated parts, once the plating or coating is depleted, the carbon steel is left unprotected and rapidly corrodes.
420 martensitic chrome stainless steel also provides good corrosion resistance in environments, including, but not limited to, normal atmosphere and humidity, steam, fresh water, alcohol, ammonia, alkalis, mild acids (e.g., carbonic), petroleum products such as gasoline, oil, crude, and mild detergents and sterilising solutions.
While 302/304 austenitic stainless steel Coiled Pins provide excellent corrosion protection, this material is not an appropriate solution when the pin will be subject to dynamic loads, or where strength and fatigue resistance must equal or exceed that of high carbon steel. Alternatively, 420 martensitic chrome stainless steel provides an exceptional combination of strength and fatigue resistance – in addition to its inherent corrosion resistance.
Fatigue life
420 chrome stainless steel also provides enhanced fatigue life, an important consideration given that Coiled Spring Pins often function as dynamic elements within many applications. A unique characteristic of Coiled Spring Pins is that their flexibility after installation protects host holes and assemblies by dampening vibration and shock loading.
For comparison, Coiled Pins of the same duty (i.e. material thickness) produced from material of equal dimensions, were tested in the three standard materials: MBK – a standard duty, high carbon steel, plain finish; MCK – a standard duty, 420 chrome stainless steel, plain finish; and MDK – a standard duty, 300 series austenitic stainless steel, plain finish.
Resultant trend lines demonstrate 420 chrome stainless steels superiority in fatigue when tested at increasing percentages of assigned minimum double shear strength.
Summary
Coiled Spring Pins manufactured from 420 chrome stainless steel are an excellent material choice where high strength, moderate corrosion protection, and superior fatigue life are critical. Additional benefits to consider include cost/benefit relationship in performance applications, high-wear resistance, good tensile and creep strength at moderately elevated temperatures, oxidation and erosion resistance, improved component cleanliness as compared to high carbon steel, and reduced potential for mixed product & debris compared to plated and coated carbon steel product.
Michael Pasko is Applications Engineer at Spirol International.
