Spring steel

Spring steel is an alloy steel, intended for components that should be characterized by very good elastic properties, and these are, in particular, springs, springs and torsion shafts, spring washers, but also other vehicle suspension components, clock components, industrial machinery, medical equipment, etc.

The mechanical properties of these steels should exhibit:

high elastic limit Rsp
high tensile strength Rm
high ratio of elastic limit Rsp to yield strength Rp
high fatigue strength
good ductility.

These steels usually contain 0.4÷0.7% carbon, which affects the value of elastic limit and strength. In addition, about 2.5% silicon is introduced into the steel, increasing the elastic limit, yield strength and toughness. However, due to low hardenability, silicon spring steels are used for springs with small cross sections.To improve hardenability, increased manganese and chromium content is introduced into the steel.

In addition, carbide-forming elements such as molybdenum and vanadium are introduced, which reduce the steel's susceptibility to decarburization and provide a fine-grained structure that is beneficial for increasing strength properties. Silicon-chromium-molybdenum and silicon-chromium-vanadium spring ste els are particularly used for springs of large cross-sections subjected to heavy loads.

Spring alloy steels are supplied as:

hot-rolled products (according to PN-EN 10089:2005)
wires (according to PN-EN 10270-2:2011)
narrow strips with a thickness of 0.3 ÷ 6 mm (according to PN-EN 10132-4:2004).

Heat treatment consists of heating to 800÷870℃ and quenching in water or oil and medium tempering at 380÷520℃. The process is carried out in a protective atmosphere or salt bath to protect the springs from decarburization, thereby increasing fatigue strength.

Spring steels produced in wire form are characterized by the highest strength properties, due to oil quenching and tempering their tensile strength can reach Rm = 2100 MPa.

Steel designation	Yield strength, Rp [MPa]	Tensile strength, Rm [MPa]	Application
45S	⋝980	⋝1180	lightly loaded springs, springs, springs for agricultural machinery
50HF/51CRV4 50HS	⋝1080 ⋝1190	⋝1280 ⋝1320	springs and springs for heavy duty motor vehicles, shock absorber springs, choke springs, compression springs
55S2 60S2	⋝1180	⋝1320	medium duty motor vehicle springs, disc springs, flat springs, coil springs, valve springs, check springs
C55E C55R	⋝550	⋝980	lightly loaded springs
65G	⋝780	⋝980	lightly loaded springs
65S2WA	⋝1670	⋝1860	loaded springs with larger dimensions and torsion shafts
X29CrS13 X30Cr13	⋝650	⋝850	flat and spiral springs made of bars and sections
54SiCr7 60SiCr7	1130	1320	high-load springs and spring parts, valve springs, torsion shafts, disc springs
55Cr3 50CrV4 51CrMoV3	1180	1370	high-load springs and spring parts, valve springs, torsion shafts, disc springs

You can find50CRV4, 51CRV4 and 50HS spring steel among hot-rolled round bar steel grades.

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