CN101279362B - Method for manufacturing low-segregation large-sized steel ingot by quickening cooling of bottom and lateral wall - Google Patents

Abstract

The invention is a manufacturing method for obtaining low-segregation large-scale steel ingots by accelerating the cooling of the bottom and side walls, which involves the manufacturing process of various grades of large-scale steel ingots, is suitable for the segregation control of various components of carbon steel and alloy steel ingots, and can be used for vacuum pouring And the casting process of non-vacuum pouring steel ingot, control macro segregation and reduce micro segregation. The specific steps of the present invention are: 1) the steel ingot mold material is gray cast iron; 2) the riser adopts a thermal insulation riser, and its taper is 8 to 16%; 3) the height-diameter ratio of the steel ingot is 1:1 to 3:1; 4 ) The steel ingot is made of carbon steel or alloy steel; 5) Pre-cast the air duct in the lower part of the ingot mold and the chassis of the ingot mold; 6) After the ingot is poured, the chassis can start to pass compressed air. Only through compressed air. The invention designs a cooling system through which compressed air passes through the chassis of the large steel ingot and the side wall of the ingot mold, which greatly improves the cooling speed of the large steel ingot and effectively suppresses various segregation of the large steel ingot.

Description

Method for manufacturing large steel ingot with low segregation by accelerating bottom and side wall cooling

technical field

The invention is a manufacturing method for obtaining low-segregation large-scale steel ingots by accelerating the cooling of the bottom and side walls, which involves the manufacturing process of various grades of large-scale steel ingots, is suitable for the segregation control of various components of carbon steel and alloy steel ingots, and can be used for vacuum pouring And the casting process of non-vacuum pouring steel ingot, control macro segregation and reduce micro segregation.

Background technique

In recent years, as electric power, metallurgy, petrochemical, aerospace, shipbuilding and other industrial equipment continue to develop towards integration and large-scale, the demand for large forgings is increasing, so the grade requirements for large steel ingots are also getting higher and higher. The solidification process of large steel ingots is very long, ranging from tens of hours to hundreds of hours. The solute redistribution is sufficient, which makes the chemical composition of different regions of the steel ingot uneven, forming macro-segregation and micro-segregation. Composition segregation seriously affects the quality of steel ingots, and even leads to the scrapping of steel ingots. The problem of steel ingot segregation has become the key to the quality of large forgings.

The segregation of large steel ingots has attracted much attention from researchers and business circles. Although some progress has been made in the formation mechanism of segregation, the progress in segregation control measures is slow, and there is almost no effective measure to suppress macro-segregation. Heavy-duty enterprises have used the method of multi-package casting to suppress segregation, but due to the rapid mixing of molten steel in the ingot mold, the effect of suppressing segregation is very limited.

Contents of the invention

The purpose of the present invention is to provide a manufacturing method for obtaining large steel ingots with low segregation by accelerating the cooling of the bottom and side walls, so as to solve the current problems of serious segregation and low production efficiency of large steel ingots; The time and flow rate of wall ventilation ensure that the segregation of large steel ingots is suppressed and no other defects occur.

Technical scheme of the present invention is:

The present invention develops a manufacturing method for obtaining a large steel ingot with low segregation by accelerating the cooling of the bottom and side walls, including the following steps:

1) The material of the ingot mold is gray cast iron;

2) The riser adopts thermal insulation riser, and the taper of the riser is 8-16%;

3) The height-to-diameter ratio of the steel ingot (the ratio of the height of the steel ingot to the average diameter) is 1:1 to 3:1;

4) The steel ingot is made of carbon steel or alloy steel;

5) Pre-cast ventilation pipes in the lower part of the ingot mold and the chassis of the ingot mold;

6) After the steel ingot pouring, the chassis can start to pass the compressed air, and the side wall of the steel ingot mold can pass the compressed air after 1 to 6 hours.

In the chemical composition of the material used in the present invention, by weight percentage, C: 0.01-0.75%, S, P: ≤0.030%.

The riser of the present invention adopts thermal insulation riser, and the taper of the riser is 8-16%. Aluminum insulation materials, etc., there is a layer of asbestos insulation board outside the refractory material.

The invention is applicable to steel ingots with all height-to-diameter ratios, and can obtain obvious benefits when used on large-scale steel ingots, whose height-to-diameter ratio is generally 1:1-3:1.

The invention adopts a riser to add a heating agent and a thermal insulation covering agent; the preheating temperature of the steel ingot mold is 50-200 DEG C.

In the present invention, pipes are arranged in the middle and lower part of the side wall of the steel ingot mold and in the chassis, and the inner diameter ranges from 30 to 200 mm.

In the present invention, when the thickness of the solidified layer at the bottom of the steel ingot reaches more than 150mm, the side wall starts to pass compressed air.

In the present invention, the ventilation volume of the compressed air should be small at the beginning, and then gradually increase the flow rate, the flow rate of the compressed air changes in the range of 3-10 kg/s, and the pressure of the compressed air is 5-8 atmospheres.

In the present invention, a large steel ingot refers to a steel ingot of 100 to 600 tons.

In the present invention, the software used for computer simulation is ProCast.

The present invention has following beneficial effect:

1. The process design of the present invention is reasonable. By changing the external heat exchange conditions of large steel ingots, the method of passing compressed air through the chassis and side walls of large steel ingots is adopted, which greatly improves the cooling speed of large steel ingots, and can significantly shorten the solidification time of steel ingots. Reduce the demoulding time, improve the production efficiency of steel ingots, thereby increasing the output of large castings and forgings.

2. The ventilation system of the present invention is reasonably designed, the compressed air can be cooled through the steel ingot chassis and the side wall of the steel ingot mold, the system is simple, the safety is high, the operability is strong, and the enterprise is easy to realize.

3. By adopting the present invention, the solidification time of steel ingots is greatly shortened, and various macroscopic segregation of large steel ingots, especially "A" type segregation which seriously affects the quality of steel ingots, can be significantly inhibited.

4. The present invention is applicable to the manufacture of large steel ingots of various materials. The large steel ingot produced by the invention has the characteristics of low segregation, dense structure, low cost and short cycle, and is easily recognized by numerous research institutions and factories. Once widely used, it can greatly improve the production efficiency of large steel ingots and improve the quality of steel ingots. Bring tens to tens of billions of benefits.

5. Through the design of key process parameters, the present invention ensures that the production rate of large-scale steel ingots is increased and the segregation of steel ingots is suppressed while no other casting defects occur.

Description of drawings

Figure 1 Schematic diagram of large steel ingot mold assembly; in the figure:

1 steel ingot mold; 2 steel ingot; 3 thermal insulation riser; 4 thermal insulation board; 5 riser sleeve; 6 heating agent; 7 thermal insulation covering agent; 8 chassis;

Fig. 2 The temperature field when the steel ingot riser is completely solidified;

Fig. 3 The simulation results of the solid phase fraction when the chassis is ventilated for 1.5 hours after the large steel ingot is poured;

Figure 4 The temperature field when the riser of a 130t steel ingot is completely solidified under the condition of chassis and side wall ventilation;

Figure 5 segregation prediction results of 130t steel ingot "A" under natural cooling conditions;

Figure 6 segregation prediction results of 130t steel ingot "A" under the condition of chassis and side wall ventilation;

Fig. 7 Prediction results of axis porosity of 130t steel ingot under natural cooling condition;

Fig. 8 Prediction results of axial looseness of 130t steel ingot under chassis and side wall ventilation conditions;

Fig. 9 is the solid phase fraction simulation result diagram after solidification for 5 hours under natural cooling conditions;

Figure 10 The temperature field when the riser of a 380t steel ingot is completely solidified under the condition of chassis and side wall ventilation;

Figure 11 segregation prediction results of 380t steel ingot "A" under natural cooling conditions;

Fig. 12 Segregation prediction results of 380t steel ingot "A" under the condition of chassis and side wall ventilation.

Detailed ways

A kind of manufacturing method of the present invention obtains low segregation large steel ingot by accelerating bottom, side wall cooling as follows:

1. The present invention adopts a high-quality thermal insulation riser to keep the molten steel at the top of the ingot at a high temperature, which is beneficial to maintain the temperature at the top of the steel ingot, so that the riser metal liquid can feed the steel ingot body and avoid shrinkage cavity loosening. The height of the thermal insulation riser is controlled by computer simulation software obtained after calculation.

Figure 1 is a schematic diagram of the assembly of a large steel ingot mold. The components include steel ingot mold 1, steel ingot 2, thermal insulation riser 3, thermal insulation board 4, riser cover 5, heating agent 6, thermal insulation covering agent 7, chassis 8, ventilation pipe 9, etc. The steel ingot mold 1 is set on the chassis 8, the top of the steel ingot mold 1 is provided with a thermal insulation riser 3, the outer side of the thermal insulation riser 3 is provided with a thermal insulation board 4, and the outer side of the thermal insulation board 4 is provided with a riser cover 5, and the cavity in the steel ingot mold 1 forms a steel ingot 2. A heating agent 6 and a heat preservation covering agent 7 are placed on the top of the heat preservation riser 3, and a ventilation pipe 9 is arranged in the middle and lower part of the side wall of the ingot mold 1 and the chassis 8. The inner diameter of the ventilation pipe 9 ranges from 30 to 200mm.

Figure 2 is the simulation result of the temperature field of a large steel ingot. It can be seen from the figure that the isotherm is U-shaped, which can form a sequential solidification from the bottom of the steel ingot to the riser, which is conducive to the reduction of shrinkage porosity.

3. Due to the long solidification time of large steel ingots, after the thickness of the solidified layer reaches a certain thickness at the bottom of the steel ingot, the thermal resistance is at the solidified part of the steel ingot. If the side wall ventilation is strengthened and the cooling time is too early, it may cause the side wall of the steel ingot to cool too quickly and increase The tendency to loosen the center of the ingot. As shown in Figure 3, the simulation results of the solid phase fraction when the chassis is ventilated for 1.5 hours after the pouring of the large steel ingot, it can be seen that the tail of the steel ingot has been completely solidified at this time, and the thickness of the solidified layer at the bottom has reached more than 150mm. compressed air.

4. The present invention starts from the mechanism of macro segregation of large steel ingots. Based on the fact that the solidification time and solidification sequence of steel ingots have an important impact on the generation of macro segregation, the solidification of large steel ingots is shortened by strengthening the heat exchange conditions between large steel ingots and the external environment. Time, strengthen the solidification sequence, so as to achieve the purpose of inhibiting the segregation of large steel ingots.

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

Example 1

As shown in Figure 1, the material of the steel ingot mold is gray cast iron HT150, the preheating temperature of the steel ingot mold is 100°C, the riser adopts a thermal insulation riser, the taper of the riser is 15.6%, and the ratio of height to diameter of the steel ingot is 1:1; pouring molten metal The weight is 130 tons, the pouring time is 25min, vacuum casting, the pouring temperature is 1580°C, the steel type used in the present invention is H13, and its chemical composition is C: 0.32-0.45%, Si: 0.80-1.20%, Mn : 0.20-0.50%, Cr: 4.75-5.50%, Mo: 1.10-1.75%, V: 0.80-1.20%, S, P: <0.030%, the balance of Fe. After pouring, fill the top of the riser with heating agent and thermal insulation covering agent; after the ingot pouring, the chassis can start to pass compressed air, and after 2 to 3 hours, the side wall of the ingot mold can start to pass compressed air.

In this embodiment, the air volume of compressed air should be small at the beginning, and then gradually increase the flow rate, the flow rate of compressed air changes in the range of 3-8 kg/s, and the pressure of compressed air is 6 atmospheres.

The following process is adopted: (1) Top pouring is adopted, and vacuum is drawn before pouring to reduce secondary oxidation. (2) Simultaneously use thermal insulation riser, heating agent and thermal insulation covering agent to minimize the shrinkage cavity and loose defects of steel ingots. (3) After the steel ingot is cast, the chassis can start to pass the compressed air, and after 2 to 3 hours, the side wall of the steel ingot mold can start to pass the compressed air.

The present invention uses computer simulation software to simulate the temperature field and casting defects, as shown in Figure 4, the temperature field when the 130t steel ingot riser is completely solidified under the condition of ventilation on the chassis and side walls, compared with Figure 2, it can be seen that the cooling effect of external compressed air Obviously, the temperature in the lower part of the steel ingot drops rapidly. The criterion of "A" type segregation of large steel ingots is used to evaluate the trend of steel ingot segregation. The smaller the criterion value is, the easier it is to produce "A" type segregation. As shown in Figure 5, the "A" type segregation prediction result diagram of 130t steel ingot under the condition of natural cooling, compared with the prediction result diagram of "A" type segregation of 130t steel ingot under the condition of chassis and side wall ventilation in Fig. Wall cooling significantly mitigates the tendency for "A" type generation. As shown in Figure 7, the prediction results of axial porosity of 130t steel ingot under the condition of natural cooling; Figure 8, the prediction results of axial porosity of 130t steel ingot under the condition of chassis and side wall ventilation. For compactness, it also has a significant effect on inhibiting "V" type segregation.

The solidification time of steel ingots has been reduced from 34 hours to 30 hours, and the productivity has been increased by 12%. However, it can be seen from the simulation that after the chassis and the side wall of the ingot mold are ventilated, the solidification speed of the ingot at the beginning stage is significantly accelerated, so that the solidification front quickly passes through the area where "A" type segregation is likely to occur, and the "A" type segregation is alleviated. trend. As shown in Figure 9, the solid phase fraction simulation results after solidification for 5 hours under natural cooling conditions, the distance between the solidification front and the bottom of the bottom of the steel ingot is 920mm, but it only takes 3 hours for the solidified layer to reach the same thickness after aeration. Therefore, the effect of ventilation is actually to reduce the height-to-diameter ratio of the ingot during solidification. After the ingot is ventilated and solidified for 3 hours, the height-to-diameter ratio of the unsolidified part is only 0.67. At the same time, the solidification time of the ingot is significantly shortened, and the ingot is effectively suppressed. macro segregation.

Example 2

The difference from Example 1 is:

The material of the steel ingot mold is gray cast iron HT250, the preheating temperature of the steel ingot mold is 150°C, the riser adopts thermal insulation riser, the taper of the riser is 13.2%, the ratio of height to diameter of the steel ingot is 1.4:1; the weight of pouring molten metal is 380 tons, and the pouring time 60 minutes; After the ingot pouring, the chassis can start to pass the compressed air, and after 4 to 5 hours, the side wall of the steel ingot mold can start to pass the compressed air.

In this embodiment, the air volume of compressed air should be small at the beginning, and then gradually increase the flow rate, the flow rate of the compressed air changes in the range of 5-9 kg/s, and the pressure of the compressed air is 8 atmospheres.

The present invention uses computer simulation software to simulate the temperature field and casting defects, as shown in Figure 10 is the temperature field simulation result diagram during the solidification process. The complete solidification of steel ingot riser is reduced from 58 hours of natural cooling to 50 hours now, and the productivity is increased by 13.8%. The criterion of "A" type segregation of large steel ingots is used to evaluate the trend of steel ingot segregation. The smaller the criterion value is, the easier it is to produce "A" type segregation. As shown in Figure 11, the prediction results of 380t steel ingot "A" type segregation under the condition of natural cooling, compared with the prediction results of "A" type segregation of 380t steel ingot under the condition of side wall ventilation in Figure 12, under the same criterion value, the chassis and side wall cooling Significantly reduce the tendency of "A" type segregation.

Working process and result of the present invention:

Because the present invention adopts the method that the chassis starts to pass the compressed air after the pouring is completed, and after 1 to 6 hours, the side wall of the steel ingot mold starts to pass the compressed air. It can not only take away the heat from the outer surface of the ingot mold in time, reduce the temperature of the ingot mold and the chassis, shorten the solidification time of the steel ingot, but also significantly speed up the cooling speed in the initial stage of the ingot, so that the solidification front quickly passes through the area prone to segregation, Significantly improved the macro segregation problem of large steel ingots.

The result of the embodiment shows that the present invention is based on the computer simulation results of large steel ingots, and the designed large steel ingot chassis and side wall ventilation cooling method can significantly improve the solidification speed of large steel ingots, shorten the demoulding time, and improve the solidification state of large steel ingots. It has a good inhibitory effect on various segregation of large steel ingots, especially the "A" type segregation that seriously affects the quality of steel ingots. It is suitable for the manufacture of large steel ingots of various materials such as carbon steel or alloy steel.

Claims (6)

1. one kind by accelerating the manufacture method that bottom, sidewall cooling obtain low-segregation large-sized steel ingot, it is characterized in that:

1) the ingot mould material is a grey cast-iron;

2) rising head adopts insulated feeder, and the rising head tapering is 8～16%;

3) ratio of height to diameter of steel ingot is 1: 1～3: 1;

4) the steel ingot material is carbon steel or steel alloy;

5) precasting breather line in ingot mould middle and lower part and ingot mould chassis;

6) ingot steel casting finishes rear chassis and can begin logical compressed air, and the ingot mould sidewall begins logical compressed air after 1～6 hour, and the ingot body stops ventilation when solidifying fully.

2. described by accelerating the manufacture method of bottom, sidewall cooling acquisition low-segregation large-sized steel ingot according to claim 1, it is characterized in that: the ingot mould material is a grey cast-iron: comprise HT150, HT200 or HT250.

3. described by accelerating the manufacture method of bottom, sidewall cooling acquisition low-segregation large-sized steel ingot according to claim 1, it is characterized in that: insulated feeder is up-small and down-big, material is a high-quality refractory material, can adopt high-alumina brick, corundum, mullite, magnesia brick, magnalium goods or aluminum silicate insulation material, there is one deck asbestos insulation board the outside.

4. described by accelerating the manufacture method of bottom, sidewall cooling acquisition low-segregation large-sized steel ingot according to claim 1, it is characterized in that: in the chemical composition of carbon steel or alloy steel ingot, by weight percentage, C 0.01～0.75%, S, P :≤0.030%.

5. described by accelerating the manufacture method of bottom, sidewall cooling acquisition low-segregation large-sized steel ingot according to claim 1, it is characterized in that: in ingot mould sidewall middle and lower part and chassis, arrange pipeline, inside diameter ranges 30～200mm.

6. described by accelerating the manufacture method of bottom, sidewall cooling acquisition low-segregation large-sized steel ingot according to claim 1, it is characterized in that: when steel ingot bottom solidification thickness reached the above thickness of 150mm, sidewall began logical compressed air.

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