Effects Of Different Processes On The Microstructure And Properties Of -40℃ Low Temperature Ductile Iron

Regarding-40℃ low-temperature ductile iron material, we did three different melting processes.Keeping charge ratio and melting process same, 0, 0.3~0.4% and 0.5~0.6% nickel alloy was added respectively, resulting in 15-30% pearlite in its microstructure. With the increasing of Ni content, pearlite increases too. And the tensile strength is more than or equal to 400 MPa, the yield strength is more than or equal to 240 MPa, elongation is more than or equal to 15% and-40℃low-temperature impact energy is more than or equal to 7.3J. The result is not qualified. The high pearlite content accounts for the failure of elongation and-40℃ low temperature impact test.Based on the result of melting process one, the HT processes of 600℃, 720℃ and 700℃ were conducted to reduce pearlite content. With 700℃ holding time, part of pearlite is decomposed into ferrite and graphite. With 0.5-0.6% of Ni content and 700 HT process, tensile strength is more than or equal to 400 MPa, the yield strength is more than or equal to 240 MPa, elongation is more than or equal to 18% and-40℃low-temperature impact energy is more than or equal to 12 J. The result is not qualified.With regard to heredity of structure and composition of pig iron, considering test cost and lead time, and with reference to composition and properties of samples, we adjusted charge ratio, reduced pig iron, increased returns and introduced into pretreatment method to test cast microstructure and properties without adding Ni. Higher graphite count and nodularity are obtained as a result. When pearlite is lower than 10%, tensile strength of the cast is more than or equal to 400 MPa, the yield strength is more than or equal to 240 MPa, elongation is more than or equal to 18% and-40℃low-temperature impact energy is more than or equal to 7.3J. The result is not qualified. We repeated this test, and 85% tests were qualified.-40℃ low temperature impact ductile iron material is successfully developed.Compared with the prior heat treatment technology, with the introduction of new melting processes, the cost is reduced by more than 10%, and the efficiency is increased by more than 5%, which has laid the foundation for producing-40℃ low temperature impact ductile iron castings.