Manufacturing method for nodular cast iron

Abstract

A technology for producing nodular graphite cast iron QT800-6 features that it contains Ca (0.001-0.05 wt.%) and Ba (0.006-0.1) beside conventional components, and its heat treatment includes normalizing at 860+ / -40 deg.C for 1.5+ / -1.0 hr and tempering at 600+ / -50 deg.C for 2.0+ / -1.0 hr. Its casting features high tension strength, elongation, impact toughness and hardness, and low cost.

Description

technical field [0001] The invention belongs to the field of production methods of nodular cast iron. Background technique [0002] In the national standard of ductile iron in my country, only QT800-2 and QT900-2 have a tensile strength greater than 800Mpa, and their elongation is about 2%. The ultimate fatigue bending moment of these cast irons is generally only about 750Nm. However, in the ductile iron produced by my country, some non-standard materials of QT800-3 and QT900-3 have been produced. For example, Jiangling Automobile Factory has used this material to manufacture crankshafts, and its elongation is about 3%. Abroad then has the technology of QT880-5 nodular cast iron production crankshaft, for example Italy Fiat company produces 4 cylinder small crankshafts with this nodular cast iron, and its elongation is about 5%. These materials can only still be brittle materials because their toughness and plasticity are not high enough. ...

AI Technical Summary

Problems solved by technology

[0003] At present, in foreign advanced casting technology, the QT800-6 nodular cast iron material with an elongation rate of 6% can reach or exceed 6%. The metallographic structure of the steel is Aube ductile iron, which can reach the index of tensile strength of 800Mpa and elongation of 6%. Using this process to produce ductile iron parts, although the elongation has been improved by one level, it has the following comparative advantages: Obvious shortcomings: the isothermal quenching process requires high control precision of equipment, especially the quenching furnace, and there is no professional manufacturer of this kind of quenching furnace in my country; the isothermal quenching process is not mature enough, and there are still hardenability and quenching deformation Large and other problems, so that the workpiece to be processed can only be small parts; at the same time, there is a problem of work hardening, which puts forward higher requirements for machining; the cost of quenching is also very high; therefore, the method of austempering is used to produce QT800-6 nodular cast iron parts The technology has been difficult to be promoted in our country

[0004] In order to improve the toughness and plasticity of ductile iron, expand the scope of application of ductile iron, and in order to make ductile iron castings can be used in more important places, there have been many technical schemes for alloying ductile iron, but most of these schemes use relatively expensive Expensive metals, such as nickel, vanadium, titanium, molybdenum, cobalt, etc., although the ductile iron with these elements have the effect of improving toughness, it is difficult to greatly improve the toughness, and it is difficult to make the elongation of ductile iron reach More than 6%, it cannot reach the toughness material, and the production cost cannot be reduced