CN116377316A - A kind of as-cast ultra-low temperature ductile iron and production method thereof - Google Patents

Abstract

The invention belongs to the field of casting technology, and mainly relates to an as-cast ultra-low temperature ductile iron and a production method thereof. The weight percentage content of each component in the as-cast ultra-low temperature ductile iron includes: 3.70% to 3.90% of C, 1.90% to 2.10% Si, ≤0.10% Mn, ≤0.030% P, ≤0.012% S, 0.45%-0.55% Ni, 0.035%-0.055% Mg, ≤0.006% Ce, ≤0.03% Cu, ≤ 0.004% Sn, ≤0.0015% Pb, ≤0.001% Bi, ≤0.002% Sb, ≤0.035% Cr, ≤0.002% As, the balance is Fe and impurity elements; the as-cast ultra-low temperature ductile iron Pearlite index Px<2.0. The as-cast ultra-low temperature ductile iron disclosed by the present invention does not need ferritic annealing, and can meet the material index requirements of QT350-22LT in the as-cast state, has good low-temperature impact toughness at -60°C, simplifies the production process, reduces production energy consumption, and has stable quality; Using silicon-magnesium alloy spheroidizing agent and rare earth spheroidizing agent for spheroidizing treatment, the spheroidizing reaction is stable, the spheroidizing rate is high, and it has the advantages of high roundness of graphite balls and small graphite balls.

Description

A kind of as-cast ultra-low temperature ductile iron and production method thereof

technical field

The invention belongs to the technical field of casting, and mainly relates to an as-cast ultra-low temperature ductile iron and a production method thereof.

Background technique

When the ductile iron is used in a low temperature environment, its toughness drops sharply, turning the ductile iron into a brittle material, unable to resist the impact of various use environments, which may lead to sudden brittle fracture of parts, resulting in major economic losses. The improvement of the batching, spheroidizing and inoculation treatment process of ductile iron can obtain low temperature and high toughness ductile iron. Low-temperature high-toughness ductile iron is mainly used for important equipment components in cold regions, such as wind power hubs, bases and other components, railway and subway accessories, petroleum and petrochemical accessories, etc.

With the gradual development of wind farms, areas with harsh environments but rich wind energy resources will also be developed into wind farms, which requires the development of ultra-low temperature ductile iron parts made of QT350-22LT. When the temperature drops to -60°C, the strain rate of the impact energy increases greatly with the temperature drop, so there is a higher requirement for the pearlite content in the matrix structure. As far as the existing production process is concerned, the control of the pearlite content in the matrix structure is unstable. In order to meet the impact performance requirements of the material at -60°C, it is generally necessary to perform ferrite annealing treatment on the casting to eliminate the pearlite in the matrix structure of the casting. This leads to increased costs, longer cycle times, and lower labor productivity.

Contents of the invention

In order to solve the above technical problems, the present invention provides an as-cast ultra-low temperature ductile iron and its production method, which can produce high-strength and high-toughness ultra-low temperature ductile iron without ferritizing annealing. The as-cast material has a high temperature at -60°C. impact power.

In order to achieve the above object, the technical scheme of the present invention is as follows:

A kind of as-cast ultra-low temperature ductile iron, the chemical composition is calculated by weight percentage, comprising:

3.70%~3.90% C, 1.90%~2.10% Si, ≤0.10% Mn, ≤0.030% P, ≤0.012% S, 0.45%~0.55% Ni, 0.035%~0.055% Mg, ≤0.006% Ce, ≤0.03% Cu, ≤0.004% Sn, ≤0.0015% Pb, ≤0.001% Bi, ≤0.002% Sb, ≤0.035% Cr, ≤0.002% As, the balance is Fe and impurity elements; the pearlite coefficient Px of the as-cast ultra-low temperature ductile iron <2.0; the calculation formula of the pearlite coefficient is:

Px=3.0Mn-2.65(Si-2.0)+7.75Cu+90Sn+357Pb+333Bi+20.1As+9.6Cr+71.7Sb.

Preferably, the pearlite coefficient Px of the as-cast ultra-low temperature ductile iron is <1.7.

Further, Rm≥330MPa, Rp _0.2≥210MPa , and A≥18% of the as-cast ultra-low temperature ductile iron; the single value of -60°C impact absorbed energy of the V-notch impact specimen is ≥9J, and the average value is ≥12J.

Further, the as-cast ultra-low temperature ductile iron has a spheroidization rate ≥ 90%, and the number of graphite ≥ 120/mm ² .

The production method of the as-cast ultra-low temperature ductile iron described in any of the above, comprising the following steps:

For smelting, weigh 60% to 70% of high-purity pig iron, 30% to 40% of low-manganese steel scrap, 0.80% to 1.00% of recarburizer, and 0.60% to 0.80% of ferrosilicon to melt in the melting furnace;

Pretreatment, adding 0.40% to 0.60% silicon carbide into the melting furnace;

Modification treatment, the silicon-magnesium alloy nodulizer of 0.40% to 0.50% of iron weight, the rare earth nodulizer of 0.50% to 0.60% of iron weight, the silicon barium inoculant of 0.40% to 0.60% of iron weight and the iron Silicon steel sheets with a weight of 0.60% to 0.80% are placed in the ladle in advance, the pretreated molten iron is poured into the ladle for deterioration treatment, and the slag is removed after the transformation treatment is completed;

For pouring, a compound inoculant with a pouring weight of 0.1% to 0.15% is placed in the inoculum of the ladle in advance, and the inoculum is opened during pouring, and the inoculant flows into the mold cavity together with the flow of molten iron after deterioration treatment.

Further, the silicon-magnesium alloy nodulizer includes 43%-48% Si, 6.5%-7.5% Mg and 0.5%-2.0% Ca.

Further, the rare earth nodulizer includes 44%-48% Si, 5.5%-6.2% Mg, 0.5%-1.5% RE and 0.8%-1.2% Ca.

Further, the silicon-barium inoculant includes 65%-75% Si, 2%-4% Ba and ≤1.5% Ca.

Further, the composite inoculant includes 65%-75% Si, 0.6%-1.2% Sr, ≤0.10% Ca and ≤0.50% Al.

Further, in the modification treatment step, the silicon-magnesium alloy spheroidizer and the rare earth spheroidizer are placed in the spheroidization reaction chamber at the bottom of the ladle, and the silicon-barium inoculant is placed in the two spheroidizers. On the inoculant, the silicon steel sheet is placed on the silicon barium inoculant.

Further, the particle size of the silicon-magnesium alloy spheroidizer is 10mm-30mm, the particle size of the rare earth spheroidizer is 10mm-30mm, the particle size of the silicon-barium inoculant is 1mm-6mm, and the silicon-magnesium alloy sphere The sizing agent, the rare earth spheroidizing agent, the silicon barium inoculant and the silicon steel sheet are all compacted. .

Further, the particle size of the composite inoculant is 0.20mm-0.80mm.

As can be seen from the foregoing technical solutions, the advantages and positive effects of the present invention are:

The as-cast ultra-low temperature ductile iron disclosed by the invention does not require ferritizing annealing, can meet the material index requirements of QT350-22LT in the as-cast state, has good low-temperature impact toughness at -60°C, simplifies the production process, reduces production energy consumption, and has stable quality.

The as-cast ultra-low temperature nodular cast iron disclosed by the present invention uses a silicon-magnesium alloy nodulizer and a rare earth nodulizer for nodularization treatment, the nodularization reaction is stable, the nodularization rate is high, and it has the advantages of high roundness of graphite balls and small graphite balls. ;Silicon carbide is used for pretreatment, and composite inoculants are used for instantaneous inoculation during pouring, which can effectively enhance the nucleation ability of molten iron, prolong the inoculation effect, refine grains, promote tissue ferritization, and effectively prevent the formation of pearlite structure .

Detailed ways

The following specific examples further illustrate the present invention, so that those skilled in the art can better understand the present invention and implement it, but the given examples are not intended to limit the present invention. According to common technical knowledge and customary means in this field, without departing from the above-mentioned basic technical idea of the present invention, other various forms of modification, replacement or change made to the above-mentioned structure of the present invention shall all fall within the protection scope of the present invention .

Percentages, %, and fractions in the examples refer to calculations by weight unless otherwise specified.

The embodiment of the present invention discloses an as-cast ultra-low temperature ductile iron, the weight percentage of the chemical components after the furnace includes:

3.70%~3.90% C, 1.90%~2.10% Si, ≤0.10% Mn, ≤0.030% P, ≤0.012% S, 0.45%~0.55% Ni, 0.035%~0.055% Mg, ≤0.006% Ce, ≤0.03% Cu, ≤0.004% Sn, ≤0.0015% Pb, ≤0.001% Bi, ≤0.002% Sb, ≤0.035% Cr, ≤0.002% As, the balance is Fe and impurity elements. In order to effectively reduce the pearlite content in the matrix structure, the pearlite number Px of the as-cast ultra-low temperature ductile iron should be <2.0, where the formula for calculating the pearlite number is:

Px=3.0Mn-2.65(Si-2.0)+7.75Cu+90Sn+357Pb+333Bi+20.1As+9.6Cr+71.7Sb.

For the as-cast ultra-low temperature ductile iron disclosed in the embodiments of the present invention, the raw material ratio includes 60% to 70% of high-purity pig iron, 30% to 40% of low manganese scrap steel, 0.8% to 1.0% of carburizer and 0.6% to 0.8% % ferrosilicon, high-purity pig iron and low-manganese scrap steel are used as raw materials to effectively control the pearlite coefficient Px<2.0, avoid the formation of pearlite structure, and achieve the -60°C low-temperature shock required by the material without ferritizing annealing Toughness; the mechanical properties of the material reach Rm≥330MPa, Rp _0.2 ≥210MPa, A≥18%; the individual value of the impact absorption energy of the V-notch impact specimen at -60°C is ≥9J, the average value is ≥12J, and the metallographic structure reaches the spheroidization rate ≥90%, the number of graphite ≥120/mm ² , and no pearlite structure appears in the matrix structure.

The as-cast ultra-low temperature ductile iron disclosed in the embodiment of the present invention is smelted using an induction furnace, and the smelting process includes:

Use an electronic scale to weigh 60% to 70% of high-purity pig iron, 30% to 40% of low-manganese steel scrap, 0.8% to 1.0% of recarburizer and 0.6% to 0.8% of ferrosilicon into an induction furnace for melting. The feeding sequence is scrap steel before high-purity pig iron, and the melting temperature is <1380°C; after melting, samples can be taken and spectrometers can be used to detect the composition before the furnace.

The as-cast ultra-low temperature nodular cast iron disclosed in the embodiment of the present invention is pre-furnace pretreated after melting, and the pretreatment process includes:

Adding 0.40% to 0.60% silicon carbide in the induction furnace, adding silicon carbide for pretreatment can increase the number of eutectic clusters, reduce the supercooling degree of molten iron, and silicon carbide also has a deoxidation effect, so that the deoxidized product can undergo a series of deoxidation in the molten iron. reaction, reduce the harmful effects of oxides in the rusted charge, and effectively purify molten iron. Preferably, the particle size of the silicon carbide is 1mm-4mm, and the SiC content is ≥98%.

The as-cast ultra-low temperature nodular cast iron disclosed in the embodiment of the present invention undergoes a metamorphic treatment after the pretreatment is completed, and the metamorphic treatment process includes:

S1. Put the silicon-magnesium alloy nodulizer and the rare earth nodulizer into the nodularization reaction chamber at the bottom of the ladle and compact them. The amount of the silicon-magnesium alloy nodulizer added is 0.40% to 0.50% %, the amount of rare earth spheroidizing agent added is 0.50% to 0.60% of the iron weight.

The silicon-magnesium alloy spheroidizer may include 43%-48% Si, 6.5%-7.5% Mg and 0.5%-2.0% Ca, and its particle size may be 10mm-30mm. The rare earth spheroidizer may include 44%-48% Si, 5.5%-6.2% Mg, 0.5%-1.5% RE and 0.8%-1.2% Ca, and its particle size may be 10mm-30mm.

S2. Place a silicon barium inoculant on the two nodulizers and compact it. The amount of the silicon barium inoculant is 0.40% to 0.60% of the iron weight.

The silicon-barium inoculant may include 65%-75% Si, 2%-4% Ba and ≤1.5% Ca, and its particle size may be 1mm-6mm.

S3. Cover the silicon-barium inoculant with a silicon steel sheet. The amount of silicon steel sheet added is 0.60% to 0.80% of the tapping weight. The silicon steel sheet is completely melted when the tapping is completed, effectively preventing the molten iron from contacting the inoculant and nodularizing agent in advance. Reaction, stabilize the spheroidization reaction process.

S4. Transport the ladle to the induction furnace, adjust the ladle to the front of the furnace mouth, tilt the furnace to tap iron into the ladle, start inoculation and spheroidization reaction after the iron tapping is completed, remove slag after the spheroidization reaction, and take samples to test the furnace post chemical composition.

S5. After the spheroidization reaction is completed, pouring is completed within 10 minutes to avoid spheroidization breeding and recession.

It should be noted that the composite inoculant needs to be put into the inoculation hopper of the ladle in advance before tapping the iron, and the inoculation hopper is opened during the pouring process so that the composite inoculant in the inoculation hopper flows evenly on the molten iron flow. The instantaneous inoculation of the composite inoculant can enhance the nucleation ability of molten iron, prolong the inoculation effect, refine the grains, promote ferriteization, avoid the formation of pearlite and reduce the low-temperature impact toughness of the material.

The added amount of the composite inoculant can be 0.1%-0.15% of the pouring weight, the particle size of the composite inoculant can be 0.20mm-0.80mm, and it can be a composite inoculant of strontium, calcium and barium. Specifically, the composite inoculant may include 65%˜75% Si, 0.6%˜1.2% Sr, ≤0.10% Ca, and ≤0.50% Al.

The as-cast ultra-low temperature ductile iron disclosed in the embodiments of the present invention can achieve high low temperature impact toughness while ensuring strength and plasticity without ferritizing annealing treatment, simplifies the treatment process, reduces production energy consumption, and has stable quality. The invention uses a silicon-magnesium alloy spheroidizing agent together with a rare earth spheroidizing agent for spheroidizing treatment, wherein the rare earth has a stable spheroidizing effect on the hypereutectic molten iron, can neutralize anti-spheroidizing elements, and has strong anti-interference ability , high density, high boiling point, melting point close to the temperature of molten iron, no boiling and flame smoke during spheroidizing treatment; rare earth spheroidizing agent is used in conjunction with silicon magnesium alloy spheroidizing agent to optimize the kinetic conditions of spheroidizing reaction, with spherical It has the advantages of stable reaction, high spheroidization rate, high roundness of graphite spheres, small graphite spheres and uniform distribution.

The as-cast ultra-low temperature nodular cast iron disclosed in the embodiment of the present invention was sampled to detect the chemical composition after the furnace, and the detection results are shown in Table 1. When pouring the casting, the attached casting test block of U40 was poured synchronously, and the mechanical properties and metallographic structure were tested. The test results are shown in Table 2.

Table 1 Chemical Composition Test Results (%)

C Si mn P S Cu Cr sn Pb Ce Mg Ni Bi As Sb Test block 1 3.71 1.95 0.09 0.014 0.009 0.030 0.028 0.001 0.001 0.003 0.048 0.46 0.0005 0.0014 0.0012 Test block 2 3.79 1.99 0.08 0.019 0.008 0.026 0.033 0.001 0.001 0.005 0.051 0.51 0.0009 0.0019 0.0005 Test block 3 3.81 2.01 0.09 0.021 0.009 0.022 0.026 0.001 0.001 0.005 0.054 0.49 0.0008 0.0018 0.0007 Test block 4 3.83 2.04 0.08 0.023 0.011 0.026 0.031 0.001 0.001 0.004 0.046 0.50 0.0009 0.0015 0.0005 Test block 5 3.77 2.00 0.08 0.016 0.011 0.029 0.030 0.001 0.001 0.004 0.049 0.54 0.0005 0.0012 0.0005

Table 2 mechanical properties and metallographic examination results

The above-mentioned embodiments only express the specific implementation manner of the present invention, and the description thereof is relatively specific and detailed, but should not be construed as limiting the patent scope of the invention. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (10)

1. A kind of as-cast ultra-low temperature ductile iron, is characterized in that, chemical composition comprises by weight percentage content: 3.70%~3.90% C, 1.90%~2.10% Si, ≤0.10% Mn, ≤0.030% P, ≤0.012% S, 0.45%~0.55% Ni, 0.035%~0.055% Mg, ≤0.006% Ce, ≤0.03% Cu, ≤0.004% Sn, ≤0.0015% Pb, ≤0.001% Bi, ≤0.002% Sb, ≤0.035% Cr, ≤0.002% As, the balance is Fe and impurity elements; The pearlite coefficient Px of the as-cast ultra-low temperature ductile iron is <2.0; The calculation formula of the pearlite number is: Px=3.0Mn-2.65(Si-2.0)+7.75Cu+90Sn+357Pb+333Bi+20.1As+9.6Cr+71.7Sb. 2. The as-cast ultra-low temperature ductile iron according to claim 1, characterized in that, Rm≥330MPa, Rp _0.2≥210MPa , A≥18% of the as-cast ultra-low temperature ductile iron; The single value of ℃ impact absorption energy is ≥9J, and the average value is ≥12J. 3. The as-cast ultra-low temperature nodular cast iron according to claim 1, characterized in that the as-cast ultra-low temperature nodular cast iron has a spheroidization rate ≥ 90%, and the number of graphite ≥ 120/mm ² . 4. a production method of as-cast ultra-low temperature ductile iron as claimed in claim 1, is characterized in that, comprises the following steps: For smelting, weigh 60% to 70% of high-purity pig iron, 30% to 40% of low-manganese steel scrap, 0.80% to 1.00% of recarburizer, and 0.60% to 0.80% of ferrosilicon to melt in the melting furnace; Pretreatment, adding 0.40% to 0.60% silicon carbide into the melting furnace; Modification treatment, the silicon-magnesium alloy nodulizer of 0.40% to 0.50% of iron weight, the rare earth nodulizer of 0.50% to 0.60% of iron weight, the silicon barium inoculant of 0.40% to 0.60% of iron weight and the iron Silicon steel sheets with a weight of 0.60% to 0.80% are placed in the ladle in advance, the pretreated molten iron is poured into the ladle for deterioration treatment, and the slag is removed after the transformation treatment is completed; For pouring, a compound inoculant with a pouring weight of 0.1% to 0.15% is placed in the inoculum of the ladle in advance, and the inoculum is opened during pouring, and the inoculant flows into the mold cavity together with the flow of molten iron after deterioration treatment. 5. The production method of as-cast ultra-low temperature ductile iron according to claim 4, characterized in that, the silicon-magnesium alloy nodularizer comprises 43% to 48% of Si, 6.5% to 7.5% of Mg and 0.5% to 2.0% Ca. 6. The production method of as-cast ultra-low temperature nodular cast iron according to claim 4, characterized in that the rare earth nodularizer comprises 44% to 48% of Si, 5.5% to 6.2% of Mg, 0.5% to 1.5% RE and 0.8% to 1.2% of Ca. 7. The production method of as-cast ultra-low temperature ductile iron according to claim 4, characterized in that the silicon-barium inoculant comprises 65%-75% Si, 2%-4% Ba and ≤1.5% Ca. 8. The production method of as-cast ultra-low temperature nodular cast iron according to claim 4, wherein the composite inoculant comprises 65% to 75% of Si, 0.6% to 1.2% of Sr, ≤0.10% of Ca and ≤ 0.50% Al. 9. The production method of the as-cast ultra-low temperature nodular cast iron according to any one of claims 4-8, characterized in that, in the modification step, the silicon-magnesium alloy nodulizer and the rare earth nodulizer are placed In the spheroidizing reaction chamber at the bottom of the ladle, the silicon-barium inoculant is placed on the two spheroidizing agents, and the silicon steel sheet is placed on the silicon-barium inoculant. 10. The production method of as-cast ultra-low temperature nodular cast iron according to claim 9, characterized in that, the particle size of the silicon-magnesium alloy nodulizer is 10 mm to 30 mm, the particle size of the rare earth nodulizer is 10 mm to 30 mm, The particle size of the silicon-barium inoculant is 1 mm to 6 mm, and the silicon-magnesium alloy nodulizer, the rare earth nodulizer, the silicon-barium inoculant and the silicon steel sheet are all compacted; the composite inoculant The particle size is 0.20mm～0.80mm.