51CrV4 Spring Steel Strip

51CrV4 is a spring steel that can be cold rolled and formed to make a wide variety of products, including compression and valve springs. It is also used in axles, crankshafts and connecting rods.

This grade contains vanadium to refine the steel’s grains, decrease overheating sensitivity and improve strength and toughness.

Chemical Composition

51CrV4 spring steel is a common alloy spring steel grade, with tensile strength up to 1000MPa. It is often used in components such as auto parts industry, clutch spring friction plate, etc. The main composition of this type of steel is medium high carbon, manganese and chromium and the addition of vanadium to improve its elasticity, intensity and wear resistance. Due to its hardness, it is also a suitable alloy steel for use in components subjected to stress, vibration and shock.

Like other carbon and alloy grades, 51CrV4 steel is available in the annealed and softened condition. However, the material can be easily heat treated to produce a range of mechanical properties. The AISI 6150 steel grade is similar to 5160 steel but it contains small amounts of vanadium which helps to make the crystalloid particles smaller, decrease overheating sensitivity and increase its strength and toughness.

The steel is easily butt-welded by argon arc welding but it has a low weldability coefficient. It can also be forged with ease. Tempering is recommended as soon as possible after quenching for optimum results. Ovako offers a variety of variants with tight chemical compositions, suitable for various applications and material thicknesses. For instance, SB4292 is a strong grade with good hardenability in the +HH band and a low content of non-metallic inclusions.

Mechanical Properties

1.8159 (51CrV4) is an oil quench and temper steel grade which has 51CrV4 spring steel strip good mechanical properties such as high proportional limit, high strength, good plasticity, and toughness. It also has excellent fatigue resistance and good tempering stability. Moreover, it has a higher proportional limit than other spring steel grades.

In the as-received state, 51CrV4 steel has a microstructure consisting of coarse lamellar pearlite and spheroidite. It has a small X-ray diffraction (XRD) pattern with no peaks and few spherical carbides. The tensile fracture of tempered 51CrV4 steel shows a dimple morphology. When the specimen is quenched at 80 degC oil-bath temperature, the fracture has a larger spherical surface than when it is quenched at 60 degC oil-bath temperature.

Engineering stress-strain diagrams of tempered 51CrV4 steel strip at different temperatures are shown in Figure 1.

The stress-strain curves of 51CrV4 show that it has a high elastic limit and high strength, but its cold deformation plasticity is poor. It can be improved by refinement of the microstructure, which includes reducing the size of the ferrite grains and spheroidite, and decreasing the intercarbidity space. This can be achieved through effective heat treatment, which involves soaking, quenching, and tempering. The resulting material has better stress-strain behaviour and is more suitable for forming applications. The machinability of 51CrV4 is good as well.

Heat Treatment

The 51CrV4 spring steel is used to make coil springs in freight car bogies. It has excellent mechanical properties and high fatigue strength. Its high tensile strength is Tinplate steel coils supplier mainly due to its medium-high carbon content and the addition of chromium, manganese, and vanadium. However, its low cold deformation plasticity makes it difficult to machine shape it. This has seriously influenced its practical use in the production of coil springs for high-speed railways.

Heat treatment is a crucial factor in determining the mechanical properties of 51CrV4 spring steel strip. It consists of soaking, quenching, and tempering. Soaking is performed in a liquid medium such as water, mechanical oil, or polyalkylene glycol (PAG) aqueous solution. Quenching is performed in mechanical oil or special quenching oil. The quenching medium influences the phase transformation temperature of the primitive austenite, the distribution of grain-boundary precipitates, and the microstructure of the as-quenched martensite and tempered troostite.

This study analyzed the effect of different quenching conditions on the microstructure and mechanical properties of 51CrV4 spring strip by examining its as-quenched, quenched, and tempered microstructures using scanning electron microscopy and X-ray diffraction (XRD). The results showed that an increase in the oil-bath temperature caused coarsening of the as-quenched martensite. The size of the carbide islands and their intercarbide spacings increased with an increase in the out-of-oil temperature. The tempered troostite displayed dimple and quasi-cleavage morphology, which enhanced its ductility.

Applications

1.8159 (51CrV4) is a Chromium Vanadium alloyed heat-treatable spring steel available in as-rolled and spheroidize annealed condition. It is suited for oil quenching and tempering which yields an excellent combination of spring characteristics with good wear and abrasion resistance. This material is commonly used in the automotive and manufacturing industries. It also possesses durability and shock resistance.

Unlike most carbon and alloy grades, 1.8159 has high hardness, low vulnerability to tempering, and a high resistance for variable and heavy loads. It is also able to operate at elevated temperatures for extended periods. This makes it suitable for a variety of applications where toughness is required, including crankshafts, steering knuckles, and gears.

The present work focuses on the effect of quenching conditions on the microstructure and mechanical properties of 51CrV4 spring steel. Various oil-bath and out-of-oil temperatures were explored to examine the effects on the morphological changes of both the martensite and tempered troostite, and the relationship between the quenching parameters and mechanical properties. Engineering stress-strain diagrams were obtained and compared to the results of prior studies on this steel grade. The results showed that a coarsening of the martensite and an increase in the size of bainite islands are observed with increasing oil-bath temperature. These changes significantly affect the tensile strength, elongation, and hardness of this grade.