Large cross-section stability and properties of ductile iron research

Title: Large cross-section stability and properties of ductile iron research Author: Roger Degree-granting units: South China University of Technology Keywords: cross-section ductile iron;; Chunky graphite;; trace elements;; bred with the flow Summary:

As a large cross-section ductile iron solidification cooling is slow, making the casting center often appear Chunky graphite graphite distortion phenomenon, greatly reducing the heart of the casting department of mechanical properties. In the past 40 years,Magnetic lifter  researchers at home and abroad for large cross-section ductile iron casting in graphite distortion problem a lot of research, but also made great progress. However, the current for the formation mechanism of Chunky graphite is still not very clear, for the study of the problem has also been continued.

This article first production site in the industrial casting of Φ590 × 800mm ductile iron casting large cross-section analysis of the different cross-section at the solidification process, the morphology and mechanical properties of the casting of the broken graphite block causes. Then, the paper developed a modular multi-resistance furnace 1500 ℃, and the use of the device control the simulation of casting solidification, to achieve a large section of the physical simulation of solidification process. On this basis, we further study the trace elements Sb, Bi, and with the birth dose of the simulation flow and properties of castings, studied with the flow by adding nano-SiC particles on the ductile properties of the organization. The main conclusions are as follows:

(1) Φ590 × 800mm large section nodular cast slow cooling solidification, solidification in the casting center of the longest, reaching 372 minutes. Shortest edge in the casting solidification time, 232 minutes; casting wall thickness at the different microstructures and mechanical properties of special circumstances. 170mm away from the center of the casting office, http://www.999magnet.com/products/131-magnetic-lifter serious deterioration of graphite morphology, Chunky graphite up, the worst mechanical properties, casting tensile strength, hardness, elongation were 362MPa, 195HBW, 1.67%. 255mm away from the center of the casting office, the best form of graphite, the best mechanical properties, tensile strength and hardness of castings were 494MPa and 225HBW. 85mm from the center of the circle casting range, there is a certain amount of spherical graphite and graphite Chunky, good mechanical properties of castings.

(2) Φ590 × 800mm large section castings, magnesium and rare earth elements along the radial direction there was a certain macro-segregation. 170mm away from the center of the casting office, magnesium and rare earth elements enrichment, its contents were cast away from the center than 255mm high at 26% and 20%.

(3) 1500 ℃ modular multi-resistance furnace structure is simple, easy to use. Use of the resistance furnace can better control the simulation of casting cooling, casting simulation to achieve a large section of the Ministry of casting solidification simulation of the heart. Simulation with a large cross-section castings casting solidification cooling curves of the actual error is less than 1.7%.

(4) trace elements Sb, Bi can improve the simulation of casting distortion in the form of graphite. When the added amount was 0.01wt.% Time, Sb elements to improve the effect is stronger than Bi elements. When the added amount of Sb alloy 0.03wt.%, The simulation of casting away Chunky graphite morphology, nodular form is best. At this point, casting tensile strength, yield strength and elongation, respectively, the highest value 707MPa, 610MPa and 2.96%, compared with simulations without trace of the mechanical properties of cast high-74.4%, respectively, 81.9% and 22.9%.

(5) flow through the birth of the way with the ball of molten iron after the birth process to continue adding 0.1wt.% And 0.2wt.% Of the inoculant to promote the increase in the number of graphite castings, but also contributed to the distortion of graphite and ferrite matrix increase, reducing the casting of tensile strength and hardness.

(6) through breeding with the flow in the normal way to add casting 0.2wt.% Nano-SiC particles can be better to increase the number of spheroidal graphite in cast, improve the graphite morphology, improve the mechanical properties of castings. With the flow in the simulation in castings by adding 0.2wt.% Nano-SiC particles for graphite precipitation, reducing the tensile strength and hardness of the casting. Degree Year: 2010