Method for obtaining high-pearlite high-tenacity nodular cast iron crankshaft

Abstract

The invention relates to a method for obtaining a high-pearlite high-tenacity nodular cast iron crankshaft by improving the pearlite content of nodular cast iron and improving the mechanical properties. For a nodular cast iron crankshaft casting containing less than 0.82% of Mn, after treatment of the casting by a double normalizing process of residual heat normalizing and general normalizing, the pearlite content of the nodular cast iron crankshaft casting is greater than or equal to 95%, the elongation is greater than or equal to 5%, and HB is greater than or equal to 260. The invention dispenses with the cost of adding Cu and the cost of normalizing liquid and consumption thereof, and enables the pearlite content of the nodular cast iron crankshaft casting to be greater than or equal to 95% and the nodular cast iron crankshaft casting to have favorable mechanical properties.

Description

technical field [0001] The present invention relates to heat treatment, in particular to a method for high pearlite content and improved mechanical properties of nodular cast iron. Background technique [0002] The role of pearlite in ductile iron is very obvious. It can increase the tensile strength and hardness of ductile iron and improve its mechanical properties. At present, there are three ways to increase the content and methods of pearlite in ductile iron: [0003] The first one is "Research on new cast high-strength pearlite ductile iron" published by Zhu Xianyong and Liu Yaohui from the School of Materials Science and Engineering of Jilin University in "Journal of Materials Heat Treatment" 2007 02 and in February 2007 in agricultural machinery The "Microstructure and Properties of As-Cast Pearlite Ductile Iron" published in the second issue of Volume 38 of the Journal of the Chinese Academy of Sciences proposed the same method for obtaining a pearlite content great...

AI Technical Summary

Problems solved by technology

The pearlite content of the cast iron is greater than (equal to) 95%, cementite ≤ 5%, and the tensile strength can reach 700-850N / mm 2 , hardness 280-350HB, elongation 3%-5%, its disadvantages are: 1 low tensile strength, only 700N / mm 2 , cannot be used on crankshaft products above QT800-2. 2. The hardness is as high as 350HB and the machinability is poor, which brings inconvenience to machining. 3. The lower limit of elongation is 3%, the upper limit is 5%, and the plastic reserve is insufficient.

[0004] The second is the "Trial Production of Cast Pearlitic Ductile Iron 276Q Crankshaft" published by Chen Lianta of Liuzhou Machinery Factory in Guangxi, which proposed the use of rare earth magnesium nodularizers to produce as-cast pearlitic ductile iron by the flushing method. The pearlite content up to 90-95%, the shortcoming of this technology is that the pearlite content can not reach more than 95% stably

[0005] The third is the method of using normalizing liquid to obtain pearlite ≥ 95% proposed by Industrial Furnace Information Network in "Application of Ideal Normalizing Liquid": heating the as-cast crankshaft to 940°C for 2 hours and then adding to the normalizing liquid Medium cooling, then heating to 550°C for 1.5 hours, tempering and water cooling, so as to obtain a pearlite ≥ 95% metallographic structure and a tensile strength of 855N / mm 2 , the elongation rate is 3.6%, and the mechanical properties of hardness HB are 277. The defects of this technology are: 1 normalizing liquid is 20,000 yuan / ton, the price is expensive, and the normalizing liquid consumes a lot during normalizing cooling, and the normalizing cost is relatively high. High, 2. The above properties can only be obtained by tempering at 550°C for 2 hours, and the production cost is higher. 3. The elongation rate is 3.6% and the plastic reserve is insufficient

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