Alloys with specified elastic properties: types and properties

Alloys with specified elastic properties (spring steels) have high resistance to minor plastic deformations under both short-term and long-term loads, heat resistance, and corrosion resistance when used in adverse atmospheric conditions and in a number of aggressive environments. The composition contains nickel (Ni), chromium (Cr), cobalt (Co), niobium (Nb), molybdenum (Mo), rhenium (Re). They are available both in the form of cold-rolled strip, strip or sheets, and in the form of wire, rods and pipes.

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Features of alloys with specified elastic properties

The requirements for spring steels, their physical properties and chemical composition are regulated by GOST 10994-74. According to this document, alloys must not only have high elastic properties, but also:

• low magnetic permeability;
• increased strength;
• high weldability;
• electrical conductivity;
• malleability;
• plasticity;
• small elastic hysteresis.

At high pressure, the presented alloys must remain deformed, and in the event of the opposite effect, they must quickly return to their original form.

Due to their characteristics, steels of this class of precision alloys are widely used in the manufacture of:

• elastic-sensitive elements of instrumentation and automation;
• watch springs and other high-precision mechanisms;
• different membranes and resonators.

Due to their chemical neutrality and the absence of rejection by living tissues, such alloys have also become popular in medicine.

Steel grades 36NHTYU, 40KHNM and 40K27XNM are used for the production of medical instruments, including injection needles, and materials implanted into the human body. One of the domestic enterprises that has independently mastered the full production cycle of the 40KHNM alloy and is successfully manufacturing it is located in the northern capital: the St. Petersburg Precision Alloy Plant.

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Grading

Alloys with specified elastic properties differ in physical and mechanical properties and chemical composition and, accordingly, have their own technological features during production. In total, 3 groups of spring alloys can be distinguished:

1. Disperse-hardening products have high plasticity and are easy to process by pressure. The required physical and chemical properties are achieved by cold plastic deformation or hardening. The composition contains Ni-Cr compounds with the possible addition of Fe and Mn, Nb-Ti and Co-Ni.
2. Elinvars — at temperatures below the Curie point, they are non-magnetic (provided there is no magnetic field). They are based on a Mo-Re compound with the addition of Cr or Co.
3. Deformation-hardening ones have lower strength relative to the first group, have high hardness and corrosion resistance, and are non-magnetic. Production requires cold deformation followed by hardening. They are made from Cr-Ni with Fe or Co, as well as from Mo-Re.

The second group also includes all tuning fork bimaterials that are used for the production of stabilizers and filters.

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Scope of application

In total, there are 12 main steel grades that are precision alloys with specified elastic properties. Each of them has found its own application.

42NHTU steel is used in the manufacture of elastic-sensitive parts and equipment whose operating temperature does not exceed 100°C, 44NHTU — for similar elements with an operating temperature of up to 200°C, 17HNGT and 36NHTU — up to 250°C (36NHTU is also used to make injection needles), 43NKTYU and 97NL — up to 300°C, 36NHTY5M — up to 350°C, 36NHTY8M — up to 400°C, 68NXVKTYU — from 196°C to 500°C.

40KNHMVTYU and 42NHTUA steels are used in the manufacture of clockwork and various spring elements; 40KHNM is also used in surgery for stitching blood vessels, fastening bones, and installing joint prostheses.