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The impact of defects in billets on rolling
deformation mold steel
Commonly used heat deformation mold steel

Spring steel quenching common defects and preventive measures

Common defects when Spring steel quenching

Spring steel quenching defects appear in the following four main:

  1. Decarburisation (reduced service life)
  2. Quenched hardness is not enough, the number of non-martensite, ferrite in the heart (generated and residual deformation, reducing service life)
  3. Overheating (increased brittleness)
  4. Cracking (increased brittleness, seriously reduce service life)
Spring steel

Measures to improve the quality of spring steel

  1.  Deformation heat treatment

    The steel deformation strengthening and heat treatment strengthening of the two combined to further improve the strength and toughness of steel. Deformation heat treatment has high, medium and low temperature. High-temperature deformation heat treatment is in the austenitic state of the deformation immediately after quenching, can also be combined with forging or hot rolling, that is, hot forming immediately after quenching. Deformation heat treatment has been applied to the production of automotive springs.

  2. isothermal quenching of the spring

    For a small diameter or permeability enough spring can be used isothermal quenching, it can not only reduce deformation, but also improve the toughness, isothermal quenching is best after a tempering, can improve the elastic limit, tempering temperature and isothermal quenching temperature the same.

  3.  spring relaxation treatment

    Spring work for a long time under the action of external forces, as a result of stress relaxation will produce a small amount of permanent (plastic) deformation, especially the high temperature work of the spring, stress relaxation phenomenon is more serious at high temperatures, so that the accuracy of the spring is reduced, which is not allowed for the general precision spring. Therefore, this type of spring in the quenching, tempering should be relaxed after processing – the spring preload, so that the deformation of the spring may exceed the amount of deformation generated when working. Then heated under conditions higher than the working temperature of 20C, holding 8-24h.

  4.  low-temperature carbonitriding

    The combination of tempering and low-temperature carbonitriding (nitrocarburizing) process can significantly improve the fatigue life of the spring and corrosion resistance, this process is mostly used for coil springs.

  5. shot peening treatment

    Scratches, folding, oxidation decarburization and other surface defects will often become the spring work where the stress is concentrated and fatigue fracture sources. If the spring surface with fine steel shot at high speed, not only improve the surface quality of the spring, improve the surface strength, and make the surface in a state of compressive stress, thereby improving the spring fatigue strength and service life.

Spring steel quenching

Operating considerations for Spring steel quenching

  1. Check the surface for defects such as decarburization and cracks before the spring steel quenching and heat treating . These surface defects will seriously reduce the fatigue limit of the spring.
  2.  spring steel quenching and heating should pay special attention to prevent overheating and decarburization, good salt bath deoxidation, control the furnace gas atmosphere, strict control of the heating temperature and time.
  3. to reduce deformation, spring steel quenching in the heating of the furnace, fixture form and cooling quenching into the cooling method.
  4. spring steel quenching and tempering as soon as possible, heating to try to even spoon. Tempering after fast cooling can prevent tempering brittleness and cause surface compressive stress, improve fatigue strength.
Spring steel quenching