WO2016011759A1

WO2016011759A1 - Forging method for ultra-high temperature soft core of steel ingot

Info

Publication number: WO2016011759A1
Application number: PCT/CN2014/092623
Authority: WO
Inventors: 李殿中; 孙明月; 栾义坤; 刘宏伟; 傅排先; 徐斌; 李依依
Original assignee: 中国科学院金属研究所
Priority date: 2014-07-21
Filing date: 2014-11-29
Publication date: 2016-01-28
Also published as: CN105268884B; CN105268884A

Abstract

Provided is a forging method for ultra-high temperature soft core of a steel ingot, comprising firstly subjecting a cast steel ingot with a liquid core to ultra-high temperature demoulding; then placing same in a temperature-holding car to a uniform temperature and conveying to a forging press, subjecting the steel ingot with the liquid core to high-temperature and pressure-maintaining forging to fully crush dendrites at the solidification end, which forms a large amount of equiaxial crystal structures, eliminates the shrinkage porosity and looseness, and alleviates the dendritic crystal segregation; finally, performing a conventional forging to fully refine the crystalline grains and structures. The above-mentioned method breaks through conventional methods for forging mould cast steel ingots only after full solidification. The ultra-high temperature demoulding of a steel ingot with a liquid core, creates semi-solid state structure with excellent fluidity in the core of the steel ingot and a large temperature difference between the surface and the core, and after combination with a subsequent heavy pressurization and pressure-maintaining method, a forced feeding and pressure solidification can be achieved, which not only solves problems of shrinkage porosities, looseness, segregation etc., in the centre of the steel ingot to improve the metallurgical quality, but also reduces the riser weight and the heating number for forging, and prolongs the mould service life.

Description

Steel ingot ultra-high temperature soft core forging method

Technical field

The present invention relates to the field of forging of steel, and more particularly to an ultra-high temperature soft core forging method for a die cast steel ingot.

Background technique

As a core component of large-scale complete sets of equipment in metallurgical machinery, petrochemical industry, transportation, energy and power, large forgings play an extremely important role in national economic construction, national defense equipment and major scientific installations. Their production capacity and quality level are An important indicator of a country's autonomy and strength. Therefore, it is of great significance to improve the intrinsic quality of large forgings and ensure the safety and reliability during their operation.

Large forgings are typically forged from large steel ingots. Inside the ingot, a large number of microscopic shrinkage holes and loose defects are inevitably generated due to solidification shrinkage of the metal. These hole-shaped defects are dispersed in the core of the ingot, which destroys the continuity of the material and affects the mechanical properties of the forging. At the same time, due to the redistribution of solute during solidification, the solidification end is not only high in alloy concentration, but also enriches low-melting substances and impurity elements to form dendrite segregation. This segregation can only be partially improved in the subsequent forging process and cannot be completely eliminated. Destruction of the homogeneity of the material affects the structure and properties of the forging.

In order to improve the compactness and homogeneity of forgings, a large number of researchers have long been committed to the development of "central compaction" processes to eliminate microscopic holes in the core of steel ingots and to improve microsegregation. Currently, industrial processes have been obtained, such as: WHF method. (wide anvil strong pressure method), FM method (heart tension reduction method), JTS method (hard shell forging method), and the like. These techniques improve the stress and strain state of the forging core and promote the healing of the hole-like defects. The as-cast structure is broken by recrystallization, and the forgings are served in a defect-free or micro-defective state, which improves the operational safety of major equipment. However, due to the diversity and complexity of material composition and ingot specifications, the size and distribution of central defects are difficult to quantify by uniform standards. Different ingot types are used for the same forging process, and some can pass the inspection. Some can't. For example, the 42CrMo and H13 steel ingots are produced using a 15 ton ingot with a height to diameter ratio of 2, and the forging is also applied by the WHF method. The forged piece of 42CrMo material can pass the flaw detection, but the H13 cannot pass, mainly because the H13 solidification interval is wide and the shrinkage hole is small. Loose defects are more serious. This status quo indicates that the current center compaction process is not sufficient to eliminate some of the more serious defects in the steel ingot center. Therefore, it is imperative to develop a more powerful and effective forging method and completely eliminate the defects in the center of the steel ingot.

At present, almost all forgings are forged by cold (warm) ingot reheating. 1) Method 1: For some steel ingots with lower weight, the steel ingot is first poured, the ingot is cooled to 300-500 ° C in the ingot mold, and then to avoid cracking when it is cooled to room temperature, long-term stress relief annealing is required, and then Long-term gradient reheating in the furnace, the temperature inside and outside the steel ingot is evenly above 1200 °C, and finally forging, the processing cycle is very long; 2) Method 2: For some heavy steel ingots, the steel ingot is first poured, and the steel ingot is placed The ingot mold is cooled until the riser is completely solidified, and then the mold is released. The temperature of the ingot is generally 700-900 ° C. The warm steel ingot is placed in a heat preservation tank and sent to a heating furnace for heating, so that the temperature inside and outside the steel ingot is uniformly above 1200 ° C, and finally forging is performed. To some extent, it saves heating energy and shortens the processing flow; 3) However, for some steel grades, AlN precipitates along the as-cast coarse austenite grain boundary at 850-950 °C, weakening the grain boundary, and immediately red Sending heat, austenite decomposition and austenitization two phase transitions occur in a short time, which is easy to cause surface cracks. The steel ingot has to be cooled to 200-300 ° C, and then heated, and the residual temperature of the steel ingot is lost. Causes great waste.

In recent years, a soft reduction technique has been developed in the field of continuous casting blanks, which compensates for the solidification shrinkage of the slab by applying a certain amount of reduction in the vicinity of the end of the continuous casting/slab wick. . On the one hand, it can eliminate or reduce the internal void formed by the shrinkage of the slab, prevent the molten steel with intergranular enrichment of solute elements from flowing to the center of the slab; on the other hand, the extrusion caused by the light pressing can also promote the center of the sap The enriched solute element molten steel flows in the opposite direction of the casting direction, so that the solute elements are redistributed in the molten steel, so that the solidification structure of the casting blank is more uniform and dense, and the center segregation and the center looseness are improved. The soft pressing technique is very important for the selection of the pressing position. If the pressing is too early, the center metal has not yet solidified, and the loose defect will form after the pressing; if the pressing is too late, the metal is in the two-phase region with a higher solid fraction. The fluidity is poor, and dense cracks are likely to occur under small deformation. It is generally believed that when the center solid fraction reaches 0.3 to 0.7, the press will play a good role. At the same time, the choice of reduction is also important. According to the equipment capacity, the general reduction rate is 1 to 3%. The soft reduction technology of continuous casting billet can improve the central quality of ordinary carbon steel and low alloy steel billet to a certain extent, but it can't do anything for alloy steel which must be produced by die casting. In fact, the solidification interval of alloy steel tends to be wider, and the defects such as looseness of center shrinkage and dendrite segregation are more serious. It is necessary to combine the solidification and deformation means to eliminate or reduce the central defects of the billet.

Summary of the invention

In view of the central defects and intrinsic quality problems of steel ingots currently produced in the industry, the object of the present invention is to provide a steel ingot ultra-high temperature soft core forging method, which can eliminate the metallurgical defects such as shrinkage porosity of the steel ingot, reduce dendrite segregation, and refine the structure. Improve the metallurgical quality and mechanical properties of forgings, shorten the processing cycle, save energy, save materials, improve the service life of the mold, and reduce the purpose of forging.

The technical solution of the present invention is:

The invention discloses a steel ingot ultra-high temperature soft core forging method, which firstly demolishes the poured steel ingot with a liquid core at a high temperature; then, it is placed in a heat preservation vehicle and is transported to a forging press, and the steel ingot is subjected to high temperature pressure forging, so that the steel ingot is subjected to high temperature pressure forging. The solidified terminal dendrites are fully broken, forming a large number of equiaxed crystal structures, eliminating shrinkage porosity and loosening dendrite segregation; finally, conventional forging is performed to fully refine grains and structures.

The steel ingot ultra-high temperature soft core forging method, the specific steps are as follows:

The first step is to remove the mold at a high temperature; the surface temperature of the ingot after demolding is not lower than 1100 ° C, and the center is 1300 ~ 1450 °C;

The second step is to close the top of the riser; use a spray or air blower to continuously act on the riser of the steel ingot to completely solidify the top of the riser;

The third step is to transfer and equalize the temperature; place the steel ingot in the heat preservation car, transport it to the forging press, and the average temperature is 0.5 to 2 hours, ready for forging;

The fourth step is to widen the large anvil; place the ingot on the table of the forging press, and use a wide flat anvil to deform 10 to 50% in the thickness direction;

The fifth step is to maintain the pressure at high temperature; after the steel ingot is deformed to the specified size, the wide flat anvil is used to maintain the pressure and continue to act on the steel ingot, the action time is not less than 5 minutes, and the deformation amount is not more than 5%;

In the sixth step, the steel ingot is forged to the final forging size. For the forging with complicated shape, if the temperature is lower than the final forging temperature, the temperature is returned to the high temperature furnace, and the next forging fire is performed.

The steel ingot ultra-high temperature soft core forging method, in the first step, the steel ingot demoulding time is determined by computer simulation, the steel ingot mold is designed in two ways, one is reverse taper, that is, “upper down and large” mode, demoulding When the riser box and the body are removed at the same time; the other is a positive taper, that is, the "upper and lower" mode. After pouring, the boom is inserted at the edge of the riser, and after the edge of the riser is solidified, the riser box is removed and passed. The lifting rod removes the steel ingot and the ingot mold.

The steel ingot ultra-high temperature soft core forging method, in the second step, when the top of the riser is completely solidified, the surface temperature of the riser is lower than 1200 °C.

The steel ingot ultra-high temperature soft core forging method, in the third step, before the opening and forging, the lowest surface temperature of the steel ingot is not lower than 1000 °C.

The steel ingot ultra-high temperature soft core forging method, in the fourth step, during the main deformation process, the anvil width deformed by the wide flat anvil should cover the total length of the steel ingot, and once deformed into position, the shrinkage hole looseness defect is closed.

The steel ingot ultra-high temperature soft core forging method, in the fifth step, after the main deformation is finished, the wide flat anvil is used for holding and micro-deformation, so that the closed defects are sufficiently welded.

The steel ingot ultra-high temperature soft core forging method, in the sixth step, after the center compaction, the steel ingot is forged to the final forging size, and if the forging fire cannot be formed, the forging fire is formed.

The physical metallurgy and mechanical analysis of the present invention are as follows:

During the solidification phase transformation of the molten metal, the volume will change greatly. Taking steel materials as an example, the density in liquid state is about 7300 kg/m ³ , and the density in solid state is about 7800 kg/m ³ . Such a large density difference will cause different degrees of shrinkage and loose defects in the as-cast microstructure after solidification. In general, the wider the solid-liquid two-phase zone, the more severe the tendency to loosen. In order to supplement this volumetric shrinkage, the conventional method is to place a riser on the top of the ingot, and through good riser insulation conditions, the metal which maintains the liquid in the riser can replenish the volume shrinkage of the ingot under the action of gravity, thereby reducing the shrinkage cavity, Loose defects. Generally, the larger the riser, the better the insulation effect, and the better the shrinkage effect on the ingot.

However, increasing the riser is at the expense of the material utilization of the steel ingot. In order to avoid shrinkage defects in the center of the steel ingot, some risers account for more than 30% of the weight of the ingot, which is very uneconomical. Ideally, steel ingots with high material utilization should have a shape with a high diameter and a small riser. However, because the feeding distance is too long, the liquid metal in the riser portion cannot be replenished to the center of the ingot, causing a serious second time. Shrinkage defects. Such shrinkage defects can be alleviated by subsequent forging, but for particularly severe shrinkage defects, especially when the purity of the molten steel is poor, the defect surface is enriched with low melting point materials, and these void defects are more difficult to heal by conventional forging. A very large forging ratio is required to break and disperse the inclusions at the healing interface, resulting in extremely high production costs and unstable product quality.

Some classical solidification theory and experimental studies at home and abroad have shown that the formation of shrinkage porosity defects in steel ingots is a process of nucleation and growth. The earliest micro-looseness often originated from inclusions or bubbles. During the subsequent cooling and shrinking process, these micro-looseness grows sharply under the action of tensile stress, forming loose or even shrinkage and shrinkage defects. If it can heal in the early stage of loose formation and create a three-way compressive stress environment in the subsequent volumetric shrinkage process, it is expected to completely suppress the formation and expansion of loose defects.

In the early stage of the invention, through the experimental research of the system, the process method of steel ingot ultra-high temperature liquid core release is proposed. This method realizes the design of steel ingot by using ingenious mold design and anti-traditional thinking. Ultra-high temperature with liquid core demoulding, steel ingot surface temperature of 1100 ~ 1250 ° C, the center still contains part of the liquid core, the temperature reaches 1300 ~ 1450 ° C. At this time, the loose defect in the center has just been formed and has not yet grown up. If heavy pressure is applied and heat preservation and pressure preservation are performed, the small loose defects can be completely welded; at the same time, the semi-solid metal at the solidified end acts under pressure and deformation. Under the local remelting, the overlapping dendrites are completely broken, and the concentrated molten steel and broken crystal grains between the dendrites will be discharged to other lower concentrations, mixed with the remelted molten steel, reducing The concentration of solute at the solidified end increases the proportion of equiaxed crystals, thereby reducing dendrite segregation and promoting homogenization of the material.

In summary, the invention is based on the law of solidification and microstructure evolution of metal under pressure and deformation, and proposes to first demould the steel ingot with a liquid core at a high temperature, the surface temperature is not lower than 1100 ° C, the center is 1300 ~ 1450 ° C; Hold the forging and keep the pressure on the ingot. The invention breaks through the method of completely forging and then forging the cast steel ingot, and fully combines the two original separation processes of the ingot and the forging, and creates the steel core with excellent fluidity through the ultra-high temperature liquid core release. The semi-solid structure and the huge temperature difference between the surface and the core, combined with the subsequent heavy pressure and pressure holding process, can achieve forced feeding and pressure solidification, which not only solves the problem of shrinkage, looseness, segregation, and coarse structure in the center of the steel ingot. The metallurgical quality is improved, the weight of the riser is reduced, the heating heat of the forging is reduced, the service life of the mold is prolonged, the processing flow is shortened, and the heat processing cost of the forging is greatly reduced.

The present invention has the following advantages and benefits:

1. The internal quality of the material has been greatly improved. Due to the ultra-high temperature deformation of the center of the ingot, the shrinkage porosity is completely eliminated, the dendrite segregation defects are alleviated, and the uniformity of the structure is improved. The central mechanical properties of the large-section forging blank can be close to or even reach the performance level of the surface.

2. The surface quality of steel ingots has been greatly improved. Since there is no need to worry about the problem of looseness of the center shrinkage hole, the pouring temperature and the pouring speed can be increased, and the surface quality of the alloy steel ingot can be greatly improved.

3. Reduce processing costs and achieve energy saving and emission reduction. Due to the ultra-high temperature liquid core release, the steel ingot has a large heat capacity, which can save the main fire heating, and the forging operation time can be extended by one time compared with the conventional heating method, which greatly reduces the heating and forging costs.

4. Significantly shorten the processing flow and cycle. High-temperature demoulding can shorten the cooling time by 30 to 50%, and use the waste heat forging to reduce the heating time by 30 to 40%, which greatly improves the production efficiency. At the same time, the life of the ingot mold can be increased by 1 to 2 times due to the shortened demolding time.

5. Material utilization has increased significantly. Because it does not rely on the gravity feeding, the weight of the riser can be reduced by 30-50%, and the ingot is designed to have a shape with a height to diameter ratio of 5 or more. Compared with the traditional high-diameter ratio of 1~2, the utilization rate of the ingot-type lifting material is more than 15%. .

6. Reduce the requirements for forging equipment capabilities. Since the steel ingot is in an ultra-high temperature two-phase zone state, the deformation resistance in the central region is less than 1/10 of that of the solid state, thus greatly reducing the capacity requirement of the forging process for the press equipment, and it is possible to realize "making large forgings with small equipment".

DRAWINGS

1 is a schematic view of a forging process of a steel ingot ultra-high temperature soft core according to the present invention; wherein (a) is a steel ingot poured into a ladle, (b) is spray cooled after removing the riser box, and (c) is sent to the ingot in a heat preservation vehicle. And the average temperature, (d) is deformation along the diameter/thickness direction of the ingot, (e) is the pressure after deformation, and (f) is forged to the finished product.

Figure 2 is a schematic diagram of the healing process of shrinkage porosity defects during ultra-high temperature deformation; (a) is a loose defect that has just sprouted, (b) is loose under large deformation, and (c) is closed. Under the action of pressure retention, it is decomposed into microscopic pores, and (d) the microscopic pores gradually diffuse and disappear under high temperature and high pressure.

Fig. 3 is a schematic view showing the process of breaking and homogenizing dendrites when deformed at an ultrahigh temperature; wherein (a) is a solidified terminal dendrite and a residual liquid, and (b) is a dendrite broken and remelted under a large deformation. Decomposed into a multi-stage discrete structure, which becomes the nucleus of the subsequent solidification of the melt, (c) is an equiaxed crystal structure formed by the near-solidification of the center of the ingot under pressure, and (d) is an equiaxed crystal structure. The temperature below the solidus line is greatly deformed, and a finer equiaxed crystal structure formed after recrystallization occurs.

4 is a photograph of the metallographic structure of the H13 forging obtained by the ultra-high temperature soft core forging method in the embodiment of the present invention.

Figure 5 is a photograph of the metallographic structure of the H13 forging obtained by a conventional forging process in a comparative example of the present invention.

detailed description

Hereinafter, the present invention will be described in further detail by way of examples and the accompanying drawings.

As shown in Fig. 1, the forging process of the ultra-high temperature soft core of the steel ingot of the present invention is as follows: (a) ladle pouring steel ingot → (b) spray cooling after removing the riser box → (c) placing the steel ingot into the heat preservation car and sending both Temperature → (d) deformation along the diameter/thickness direction of the ingot → (e) holding pressure after deformation → (f) forging to the finished product. The method of the invention is applicable to carbon manganese steel, low alloy steel, medium and high alloy steel, especially for ultra high temperature soft core forging of steel ingot with wide solidification interval and particularly developed as-cast structure.

In a specific embodiment, the steel ingot ultra-high temperature soft core forging method of the present invention firstly demolds the poured ingot with a liquid core at a high temperature; then, it is placed in a heat preservation vehicle and is transported to a forging press, and the steel ingot is carried out with a liquid core. High-temperature pressure forging, the solidification end dendrites are fully broken, forming a large number of equiaxed crystal structures, eliminating shrinkage porosity and loosening dendritic segregation; finally, conventional forging such as upsetting and lengthening, and fully refining grains and microstructure; Specific steps are as follows:

1) The first step is to demould the steel ingot with a liquid core at a high temperature, the surface temperature of the ingot is not lower than 1100 ° C (preferably 1150 ° C ~ 1250 ° C), and the center temperature is maintained at 1300 ~ 1450 ° C;

As shown in Fig. 2, during the ultra-high temperature deformation, the healing process of the shrinkage porosity defect is as follows: (a) the loose defect just emerging → (b) the looseness is closed under the large deformation → (c) the closed looseness is in the continuous holding pressure Under the action of the decomposition into microscopic holes → (d) microscopic pores gradually diffuse and disappear under high temperature and high pressure. It can be seen from Fig. 2 that the large deformation at the solidification end of the steel ingot can accelerate the high-temperature diffusion of the closed interface of the hole, and the defect of the loose-hole defect is efficiently healed, thereby increasing the density of the material.

As shown in Fig. 3, when deformed at ultra-high temperature, the process of dendrite and homogenization is as follows: (a) solidification terminal dendrites and residual liquid → (b) dendrites are broken, remelted and decomposed under large deformation For a multi-segment discrete structure, it becomes the nucleus of the subsequent melt to solidify → (c) the center of the ingot under pressure, in the form of approximately simultaneous solidification, the equiaxed crystal structure is formed → (d) equiaxed crystal structure in the solidus line The following temperature is greatly deformed, and a finer equiaxed crystal structure formed after recrystallization occurs. It can be seen from Fig. 3 that, compared with the deformation in the complete solid state, the large deformation at the solidification end of the ingot can more fully break the dendrites, form a larger number of smaller equiaxed grains, and further refine the material structure. Reduce dendrite segregation and promote uniform composition.

2) The second step is to use a spray or air blower to continuously act on the riser of the steel ingot to completely solidify the top of the riser;

3) In the third step, the steel ingot is placed in the heat preservation car and transported to the forging press at an average temperature of 0.5 to 2 hours;

4) In the fourth step, the steel ingot is placed on the table of the forging press, and the wide flat anvil is deformed by 10 to 50% along the diameter (thickness) direction;

5) In the fifth step, after the steel ingot is deformed to the specified size, the wide flat anvil is used to maintain the pressure and continue to act on the steel ingot, the action time is not less than 5 minutes, and the deformation amount is not more than 5%;

6) In the sixth step, the steel ingot is forged to the final forging size. For the forging with complicated shape, if the temperature is lower than the final forging temperature, the temperature is returned to the high temperature furnace, and the next forging fire is performed.

In the first step, the demolding time of the ingot is determined by computer simulation. The ingot mold is designed in two ways, one is the reverse taper, that is, the “upper and lower” mode, and the riser box and the ingot are simultaneously removed during demolding; The other type is a positive taper, that is, a "upper and lower" mode. After pouring, a boom is inserted at the edge of the riser. After the edge of the riser is solidified, the riser box is removed, and the steel ingot and the ingot mold are removed by the lifting rod.

In the second step, a spray or air blower is used to continuously act on the riser of the steel ingot to completely solidify the top of the riser, and the surface temperature is lower than 1200 ° C (preferably 1100 ° C ~ 1180 ° C).

In the third step, the steel ingot is placed in the heat preservation car for 0.5 to 2 hours, and is transported to the forging press. The lowest surface temperature of the ingot before the forging is not less than 1000 ° C (preferably 1100 ° C to 1250 ° C).

In the fourth step, during the main deformation process, a wide flat anvil should be used. The width of the anvil should cover the total length of the ingot, and the deformation rate is 10 to 50% (preferably 20 to 50%). Once the deformation is in place, the shrinkage porosity is closed. ;

In the fifth step, after the main deformation is finished, the wide flat anvil is used for holding pressure and slow micro-deformation, the pressure action time is not less than 5 minutes (preferably 5 to 10 minutes), and the deformation amount is not more than 5% (preferably 1 to 5). %), so that the closed defects are sufficiently welded.

In the sixth step, after the center is compacted, the steel ingot is forged to the final forging size. If the fire cannot be formed, the fire forming may be increased.

Example 1

The smelting and pouring ingot has a weight of 9 tons, a rectangular cross section, and a size of 720×1080×1450mm. The material is H13 steel. The measured components are shown in Table 1.

Table 1 Chemical composition of H13 steel in Example 1 (% by weight, %)

Ultra-high temperature soft core forging of 9 tons of H13 steel ingots, the specific steps are as follows:

The first step is to remove the mold at an extremely high temperature. After the ingot is poured for 3.5 hours, the riser protection slag is blown off, so that the steel ingot is released from the liquid core at a high temperature, the surface temperature of the ingot is 1230 ° C, and the center temperature of the ingot is maintained above 1350 ° C.

The second step is to close the top of the riser. The sprinkler is used to continuously act on the riser of the steel ingot for 10 min, so that the top of the riser is completely solidified, and the surface temperature is 1180 °C.

The third step is transshipment and temperature equalization. The steel ingot is placed in the heat preservation car, and transported to the forging press in 30 minutes. After the average temperature is 30 minutes, the minimum temperature of the steel ingot surface is 1100 ° C, and the maximum temperature of the steel ingot surface is 1250 ° C. At this time, the steel car is separated from the heat preservation car and ready for forging.

The fourth step is the wide anvil deformation. The steel ingot was placed on the table of the forging press, and the wide flat anvil was deformed by 240 mm in the thickness direction to be deformed once.

The fifth step is to keep the pressure at high temperature. After the steel ingot is deformed to the specified size, the wide flat anvil is used to maintain the pressure and continue to act on the steel ingot. The action time is 10 min, and the deformation amount is 3%, so that the closed defects are sufficiently welded.

In the sixth step, the section of the ingot is drawn to 800×800 mm, and the chamfered to the height is 1200 mm, and the length is Φ450 mm.

Comparative example 1

In Comparative Example 1, the weight of the steel ingot, the chemical composition of the material, and the subsequent processing and final forging dimensions were all the same as in Example 1. Comparative Example 1 uses a conventional steel ingot after complete solidification, demolding, annealing and reheating and forging processes, the specific steps are as follows:

The first step is to release the mold at medium temperature. After the ingot was poured for 8 hours, the ingot and the riser were completely solidified, and the ingot was demolded, and the surface temperature of the ingot was 700 °C.

The second step is high temperature annealing. The steel ingot was placed in a heating furnace at 850 ° C, and after 15 hours of heat preservation, it was slowly cooled to a surface temperature of 300 ° C.

The third step is transshipment. The ingot was placed in a heat preservation car, transported to a forging press in 30 minutes, then slowly heated to 850 ° C, and after 5 hours of heat preservation, slowly heated to 1230 ° C, ready for forging.

The fourth step is the first fire forging. The ingot is upset 50% in the height direction, and then elongated to a section size of 800×800 mm, chamfered and then heated into the furnace.

The fifth step, the second fire forging. The ingot is upset 50% in the height direction, and then elongated to a section size of 800×800 mm, chamfered and then heated into the furnace.

The sixth step, the third fire forging. Pull the steel ingot to Φ450mm.

The H13 forgings in Example 1 and Comparative Example 1 were subjected to isothermal spheroidization treatment, respectively, incubated at 850 ° C and 750 ° C for 5 h, and slowly cooled to room temperature. The center sample of the forging was taken, and the microstructure of the sample was measured by a metallographic microscope. Analysis, the specific metallographic organization is shown in Figure 4 and Figure 5. As can be seen from the figure, the structure in the examples was sufficiently refined, and the average grain size was only 10 μm, while the large crystal grains of 100 μm were still present in the comparative example. At the same time, the carbide distribution in the examples was very uniform, and there was no liquid carbonization, and the carbides in the comparative examples were segregated, unevenly distributed, and a small amount of liquid carbides. The microstructure state of the post-forging heat treatment fully demonstrates that the conventional forging process is difficult to completely eliminate the liquid precipitation carbide, and the structure is coarse and the secondary carbide distribution is not uniform, and the ultra-high temperature soft core forging method of the present invention can effectively eliminate the liquid precipitation carbide. The uniform fine crystal grains and the finely dispersed secondary carbides are obtained, so that the service life of the mold steel can be greatly improved.

Claims

The invention discloses a steel ingot ultra-high temperature soft core forging method, which is characterized in that firstly, the poured steel ingot is stripped with a liquid core at a high temperature; then placed in a heat preservation vehicle and transported to a forging press, and the steel ingot is subjected to a high temperature protection with a liquid core. Press forging, the solidification end dendrites are fully broken, forming a large number of equiaxed crystal structures, eliminating shrinkage porosity and loosening dendritic segregation; finally, conventional forging is performed to fully refine grains and structures.
The steel ingot ultra-high temperature soft core forging method according to claim 1, wherein the specific steps are as follows:

The first step is to remove the mold at a high temperature; the surface temperature of the ingot after demolding is not lower than 1100 ° C, and the center is 1300 to 1450 ° C;

The second step is to close the top of the riser; use a spray or air blower to continuously act on the riser of the steel ingot to completely solidify the top of the riser;

The third step is to transfer and equalize the temperature; place the steel ingot in the heat preservation car, transport it to the forging press, and the average temperature is 0.5 to 2 hours, ready for forging;

The fourth step is to widen the large anvil; place the ingot on the table of the forging press, and use a wide flat anvil to deform 10 to 50% in the thickness direction;

The fifth step is to maintain the pressure at high temperature; after the steel ingot is deformed to the specified size, the wide flat anvil is used to maintain the pressure and continue to act on the steel ingot, the action time is not less than 5 minutes, and the deformation amount is not more than 5%;

In the sixth step, the steel ingot is forged to the final forging size. For the forging with complicated shape, if the temperature is lower than the final forging temperature, the temperature is returned to the high temperature furnace, and the next forging fire is performed.
The steel ingot ultra-high temperature soft core forging method according to claim 1, wherein in the first step, the stripping time of the ingot is determined by computer simulation, and the ingot mold is designed in two ways, one is reverse taper, that is, “on” In the small undersize mode, the riser box and the ingot are simultaneously removed during demolding; the other is a positive taper, that is, the “upper and lower” mode, after the pouring, the boom is inserted at the edge of the riser, and the riser edge is solidified. Remove the riser box and remove the steel ingot and the ingot mold by lifting the rod.
The steel ingot ultra-high temperature soft core forging method according to claim 1, wherein in the second step, when the top of the riser is completely solidified, the surface temperature of the riser is lower than 1200 °C.
The steel ingot ultra-high temperature soft core forging method according to claim 1, wherein in the third step, before the forging, the lowest surface temperature of the steel ingot is not lower than 1000 °C.
The steel ingot ultra-high temperature soft core forging method according to claim 1, wherein in the fourth step, during the main deformation process, the anvil width deformed by the wide flat anvil is to cover the total length of the steel ingot, and the deformation is in place once to make the shrinkage hole. Loose defects are closed.
The steel ingot ultra-high temperature soft core forging method according to claim 1, wherein in the fifth step, after the main deformation is finished, the wide flat anvil is used for holding and micro-deformation, so that the closed defects are sufficiently welded.
The ingot ultra-high temperature soft core forging method according to claim 1, wherein in the sixth step, after the center is compacted, the steel ingot is forged to the final forging size, and if the forging fire cannot be formed, the forging fire is increased. Forming.