Inhibit alloy gray cast iron to produce white mouth; cut the effect of RE''s nodulizer on graphite spheroidization; cut the effect of RE''s nodulizer on graphite spheroidization; xinyuanzhu group combined with Ce, La on the effect of thin-walled ductile iron graphite ball number to make the following summary.
1、Inhibit alloy gray cast iron to produce white mouth
In gray cast iron containing 0.1% S, add 0.2% RE, observe and analyze the amount of each alloying element (V, Cr, Cu) added with the depth of white mouth and tensile strength
In gray cast iron (0.1% S), 0.2% RE was added to substantially suppress the tendency of white mouth due to the addition of alloying elements (V, Cr).
If no RE is added, with the addition of alloying elements, the tensile strength increases only a little; when V and Cr are added to 0.6% each, 30 test bars with full white mouth add 0.2% RE, when 1% Cr or V is added, the tensile strength can reach 349MPa and 405MPa respectively.
2、The effect of spheroidizing agent of cutting RE on graphite spheroidization
xinyuanzhu group by using six different RE content of spheroidizing agent to treat the spheroidization effect of ductile iron. Using 100kg medium frequency furnace melting, (original molten iron composition: C3.7%, Si2.8%, Mn0.40%, P0.020%, S0.010%), treatment temperature 1500 ℃, each treatment 45Kg of iron, spheroidizer 1.3%, inoculant 0.3% (Ba system 75% Si) inoculation, covering agent 0.6%, punching method treatment.
Compare the spheroidization effect of Y-type specimen with and without secondary inoculant (Ba system 75% Si, 0.2%), thermal analysis specimen and final cast specimen (after casting 8 samples) just after treatment. The test results show that.
With secondary incubation, the graphite spheroidization rates were all high values, which did not depend much on the RE content in the spheroidizing agent; however, the final specimens without secondary incubation had the lowest spheroidization rates with RE content of 0% and 1.5%.
The number of graphite spheres tended to increase with increasing RE content in the spheroidizing agent, but the number of graphite spheres decreased when RE increased too much (1.5%). This may be caused by insufficient amount of other elements forming RE compounds such as sulfur corresponding to the RE in the spheroidizer containing 1.5% RE added and excess RE, which prevents graphite precipitation.
There was no significant tendency between the tensile strength and the RE content in the spheroidizing agent, but the strength of the final cast specimen increased with the increase in the amount of RE when there was no secondary incubation. Similarly, there was no significant tendency between elongation and the RE content in the spheroidizer, and the final cast specimens with secondary incubation all had high elongation.
According to the specimen profile and thermal analysis to determine the spheroidizing agent in the RE content of low produce a large tendency to shrinkage (with the amount of graphite precipitation and changes in the mode of solidification of ferrofluid)
Comprehensive view: under the aforementioned conditions, in order to produce no shrinkage sound ductile iron, spheroidizing agent RE content in 0.5% to 1.0% or so is good; such as the use of secondary breeding RE content and then reduce the point, it is possible to produce the same level of ductile iron.
3、Ce, La on thin-walled ductile iron graphite ball number effect
RE added to the production of ductile iron for a long time is composed of about 50% Ce, 30% La, 10% Nd, Pr, Sm and other La-system elements, that is, mixed rare earth alloys (mischmetal). In recent years, with the development of new materials, the demand for Nd, Pr, and Sm tends to increase. In order to reduce the cost of applying RE in cast iron, it is important to explore how to produce ductile iron from RE-Si alloy after separating Nd, Pr, and Sm, and to produce ductile iron using RE-Si alloy with 100% Ce and 100% La as RE source. The effect of adding RE with different Ce/La ratios (addition of Ce + La 0.05%) on the spheroidization treatment was investigated using RE-Si alloys with close to 100% Ce and 100% La. The tests were conducted with Fe-Si-Mg (Mg6.7%) spheroidizing agent, 0.4% Fe-Si alloy breeding, and RE alloy added simultaneously with the spheroidizing agent. The experimental results showed that
RE with different Ce/La ratios added versus spheroid number (3mm wall thickness, CO2 casting), Ce added 100%, graphite spheroid number up to 910/mm2; La added 100%, 790/mm2; Ce and La added 50:50, 630/mm2, significantly less graphite spheroid number than Ce and La added alone.
Ce/La addition ratio versus sphere diameter (wall thickness 3mm) , the graphite sphere diameter becomes larger near Ce/La ratio 50:50 in RE.
For 30 mm specimens (shell type), there was no major difference in tensile strength and elongation for different Ce/La ratio additions, which were about 540 MPa tensile strength and 14% elongation for each specimen. Previous relevant studies have similar situation, 30 specimens of the cooling rate is smaller, the formation of RE sulfide coalescence upward, reducing the graphite precipitation core, and thus the difference is not obvious.
4、xinyuanzhu group production of ductile iron process is: spheroidizing agent (Fe-45%Si-4.5%Mg-1.8/1.6% RE system), add 1.1% to 1.2%; cover material (0.7% ~ 1.0%), inoculant ( ~ 0.4%), punching method spheroidization treatment, 15 minutes after pouring. In order to confirm the applicability of reducing RE spheroidizing agent, on the basis of the current process, in the laboratory and production line combined with the actual castings for a large number of tests, the results show that.
Spheroidizer without RE, add Ba alloy secondary breeding, inhibit the decline, material performance can meet the requirements (FCD600), but the solidification form has changed, the casting quality deterioration (internal defects, white mouth), especially the wall thickness difference in the casting (such as differential shell, etc.) more likely to occur.
Reduce the RE content in the spheroidizer, from the current 1.6% to 0.8%: the solidification pattern is similar to the current one. After secondary conception, internal defects and white mouth problems are substantially improved and meeting the quality requirements of the castings is possible. For this reason, xinyuanzhu Group has implemented a reduction in the amount of RE in the current spheroidizer by approximately 30% since June 2018.
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