CN101279363B - Method for inhibiting segregation in large-sized steel ingot - Google Patents

Abstract

The invention is a method for suppressing segregation of large steel ingots, which involves the casting process of large steel ingots of all levels of metal molds below 600t, and is applied to the casting process of carbon steel and alloy steel ingots under vacuum and non-vacuum conditions. The segregation of various components has inhibitory effect. The specific steps of the present invention are: 1) the material of the steel ingot mold 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 2:1; 4 ) The steel ingot is made of carbon steel or alloy steel; 5) Pre-cast the ventilation pipe in the chassis of the ingot mold, and place breathable bricks around the bottom of the ingot mold; 6) After the steel ingot is poured, the compressed air starts to pass 1 to 8 hours, and the ingot body is completely solidified Ventilation was then stopped. The invention designs a cooling system with compressed air passing through the side wall of a large steel ingot, which greatly improves the cooling speed of the large steel ingot, accelerates the solidification speed of the steel ingot, shortens the demoulding time, effectively improves the production efficiency of the large steel ingot, and has a certain effect on the segregation of the large steel ingot Very good inhibitory effect.

Description

A method of suppressing segregation of large steel ingot

technical field

The invention is a method for suppressing segregation of large steel ingots, which involves the casting process of large steel ingots of all levels of metal molds below 600t, and is applied to the casting process of carbon steel and alloy steel ingots under vacuum and non-vacuum conditions. The segregation of various components has inhibitory effect.

Background technique

In recent years, with the rapid development of my country's electric power industry, nuclear industry and petrochemical industry, the demand for large castings and forgings is increasing, and the quality requirements for large castings and forgings are also getting higher and higher. Large steel ingots are the early products of large castings and forgings, and their quality is particularly important for improving the quality of large castings and forgings. The solidification process of large steel ingots is very long, ranging from tens of hours to hundreds of hours depending on the tonnage of the steel ingots. , such as the influence of hot solute convection, etc., make the chemical composition of different regions of the steel ingot uneven, resulting in macro-segregation and micro-segregation. The factory has limited pits and vacuum chambers for vacuum pouring of large steel ingots, and the problem of low productivity has become increasingly prominent. Speeding up the cooling of steel ingots and suppressing segregation of steel ingots are the only ways to increase production efficiency and improve the quality of steel ingots.

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, such as the determination of segregation type and segregation location, the progress in segregation control measures is slow, and there is almost no effective measure to suppress macro-segregation. For decades, in the production of large steel ingots, the factory has adopted the method of allowing it to cool naturally, and only when the ingot body is completely solidified and the riser is not completely solidified, the method of removing the insulation riser is used to increase productivity. This method can only be used A few hours in advance, compared with tens or even hundreds of hours of solidification time of large steel ingots, the effect is limited.

Contents of the invention

The object of the present invention is to provide a method for suppressing the segregation of large steel ingots, so as to solve the problems of segregation of large steel ingots and low production efficiency in factories.

Technical scheme of the present invention is:

The present invention has developed a method for suppressing the segregation of large steel ingots, comprising 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 2:1;

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

5) Pre-cast ventilation pipes in the chassis of the ingot mold, and place ventilation bricks around the bottom of the ingot mold;

6) Start to pass compressed air 1 to 8 hours after the steel ingot is poured, and stop the ventilation when the ingot body is completely solidified.

In the present invention, the steel ingot mold material is gray cast iron: HT150, HT200 or HT250.

In the chemical composition of the material used in the present invention, by weight percentage, C: 0.01-0.75%, P≤0.02%, S≤0.02%.

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 1:1-2:1.

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.

The invention arranges pipelines in the chassis. The diameter of the pipelines is determined according to the tonnage of the steel ingots. The inner diameter ranges from 30 to 200 mm. Permeable bricks are evenly distributed around the bottom of the steel ingot mold so that the molten steel cannot penetrate when pouring, and the solidified layer on the side wall of the steel ingot reaches 150 mm. ~250mm, when the air gap reaches a width of 5~30mm, start to pass compressed air to speed up the cooling of the steel ingot.

According to the thickness of the solidified layer of the steel ingot and the change of the air gap between the steel ingot and the ingot mould, etc., the present invention determines the time to start ventilation, the flow rate of the gas and the time to stop the ventilation. Start to pass compressed air in order to prevent the steel ingot from cracking or even breaking due to the high stress caused by the solidification speed of the steel ingot.

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 5-10 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 the large steel ingot, the method of passing compressed air on the side wall of the large steel ingot is adopted, which greatly improves the cooling speed of the large steel ingot, can significantly shorten the solidification time of the steel ingot, and shorten 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 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. With the present invention, the solidification time of the steel ingot is greatly shortened, and it has obvious inhibitory effect on various types of macro-segregation of large steel ingots, especially the "A" type segregation that seriously affects the quality of subsequent forgings.

4. The present invention is applicable to the manufacture of large steel ingots of various materials. Utilizing the present invention to produce large steel ingots has the characteristics of low segregation, compact structure, low cost and short cycle time, and is easily recognized by numerous research institutes and factories. Once widely adopted, the production efficiency of large steel ingots can be greatly accelerated, and the quality of steel ingots can be improved. There will be tens to tens of billions of benefits.

Description of drawings

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

1 steel ingot mould; 2 steel ingot; 3 thermal insulation riser; 4 thermal insulation board; 5 riser cover; 6 heating agent; 7 thermal insulation covering agent;

Fig. 2 Simulation results of temperature field of large steel ingot;

Fig. 3 Simulation results of solid phase fraction after pouring of large steel ingot;

Figure 4 Schematic diagram of the sampling position of feature points;

Figure 5. Radial displacement results of stress simulation for large steel ingots;

Fig. 6 The temperature field when the 600t steel ingot is completely solidified;

Fig. 7 Segregation prediction results of 600t steel ingot "A" under natural cooling conditions;

Fig. 8 Segregation prediction results of 600t steel ingot "A" under the condition of ingot side wall ventilation;

Fig.9 Simulation results of temperature field during solidification of 500t steel ingot;

Fig. 10 Segregation prediction results of 500t steel ingot "A" under natural cooling conditions;

Fig. 11 Segregation prediction results of 500t steel ingot "A" under the condition of side wall ventilation.

Detailed ways

The method that the present invention suppresses large steel ingot segregation is as follows:

1. The present invention uses 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 maintaining the temperature at the top of the ingot, so that the riser metal liquid can feed the steel ingot body and avoid shrinkage cavity porosity. The height of the insulation riser is calculated by computer simulation software.

Fig. 1 is a schematic diagram of the assembly of a large steel ingot mold. The steel ingot mold 1 is arranged on the chassis 10, 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, The cavity in the steel ingot mold 1 forms a steel ingot 2, and the top of the heat preservation riser 3 is provided with a heating agent 6 and a heat preservation covering agent 7, and a ventilating pipe 9 is precast in the chassis 10, and ventilating bricks 8 are placed around the bottom of the steel ingot mold 1. Ventilation bricks 8 are placed around the top of the mold 1, and the ventilation duct 9 communicates with the ventilation bricks 8 at the bottom of the ingot mold 1.

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.

2. Due to the long pouring time of large steel ingots, the heat capacity is very large. Usually, computer simulations assume that they are filled instantaneously. Because one of the key parameters involved in the present invention is exactly the time of passing compressed air, and the variation of the thickness of the solidified layer on the outer layer of the steel ingot determines the best ventilation time. As shown in Figure 3, the simulation results of the solid phase fraction after pouring of the large steel ingot, it can be seen that after the pouring of the large steel ingot, the thickness of the solidified layer at the bottom of the steel ingot has reached 100 mm. Assuming that the temperature field is filled instantaneously, the result of the calculation of the temperature field is that the solidification time is relatively long, and the timing of compressed air determined thereby has a high safety factor.

3. Next, use the assumption that the cavity is filled instantaneously to simulate the temperature field to determine the best ventilation time. As shown in Figure 4, the schematic diagram of the sampling position of the feature points, several feature points were taken on the longitudinal section of the steel ingot to determine the time when the solidified layer of the steel ingot reached a certain thickness, and the results are shown in Table 1. During aeration, since the cooling rate will increase significantly, the stress will be significantly increased, so it is necessary for the steel ingot to produce a sufficient thickness of the solidified layer before the aeration can be started.

Table 1 The solidification time corresponding to the thickness of the solidified layer (hours)

Height from chassis (mm) 520 1000 1550 4551 The solidification time when the thickness of the solidified layer is 150mm 1.8 2.2 2.3 2.5 The solidification time when the thickness of the solidified layer is 250mm 2.5 3.5 3.5 4

It can be seen from the simulation calculation that after 3 hours, the thickness of the solidified layer can reach 150mm on the entire height of the steel ingot. Considering the assumption of instantaneous filling during solidification simulation, since the pouring time is as long as more than 1 hour, the simulated steel ingot is simulated by calculation. The thickness of the solidified layer at the bottom has reached 100mm, while the solidified layer on the upper part of the ingot is thinner, so ventilation can be started 3 to 4 hours after the filling is completed.

4. The present invention is based on the physical phenomenon that the steel ingot solidifies and shrinks when it solidifies, and an air gap is generated between the steel ingot and the steel ingot mould. The time when the air gap is generated can be finally obtained by using simulation software for stress simulation, such as Figure 5 shows. After 3 hours of solidification, the width of the upper air gap of the steel ingot has reached 22 mm, and the width of the bottom air gap has also reached 8 mm, so it is feasible to pass compressed air 3 to 4 hours after the completion of pouring.

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 thermal insulation riser, the taper of the riser is 11.5%, and the height-to-diameter ratio of the steel ingot is 1.15:1; pouring molten metal The weight is 600 tons, the pouring time is 80min, vacuum casting, the pouring temperature is 1590°C, by weight percentage, the chemical composition of 508-3 low alloy steel: C: 0.18%, Si: 0.20%, Mn: 1.45%, Mo: 0.5% , Ni: 0.75%, Cr: 0.15, P≤0.005%, S≤0.002%, Fe balance. After pouring, fill the top of the riser with heating agent and thermal insulation covering agent; 3 hours after the pouring of the steel ingot, start to pass the compressed air, and record the solidification time of the steel ingot.

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) Compressed air starts to flow 3 hours after the steel ingot is poured. The ventilation volume should be small at the beginning, and then gradually increase the flow rate, which can reduce the temperature of the steel ingot mold while taking away the surface heat of the steel ingot, and significantly increase the solidification speed of the steel ingot.

In this embodiment, the flow rate of the compressed air varies within the range of 6-10 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 6, the temperature field when the steel ingot riser is completely solidified. The complete solidification of the ingot riser is reduced from 85 hours to 46 hours, and the productivity is increased by 45.9%. 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 7, the prediction results of 600t steel ingot "A" type segregation under the condition of natural cooling, compared with the prediction results of 600t steel ingot "A" type segregation under the condition of side wall ventilation in Figure 8, the cooling of the side wall is obvious under the same criterion value The tendency towards "A" type segregation is mitigated.

Example 2

The difference from Example 1 is that 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 a thermal insulation riser, the taper of the riser is 10%, and the ratio of height to diameter of the steel ingot is 1:1; The weight of pouring molten metal is 500 tons, and the pouring time is 60 minutes.

In this embodiment, the flow rate of the compressed air varies within the range of 5-8 kg/s, and the pressure of the compressed air is 6 atmospheres.

The present invention adopts computer simulation software to simulate the temperature field and casting defects, as shown in Fig. 9, the temperature field simulation result diagram in the solidification process. The complete solidification of the ingot riser is reduced from 80 hours to 42 hours, and the productivity is increased by 47.5%. 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 10, the prediction results of 500t steel ingot "A" type segregation under the condition of natural cooling, compared with the prediction results of "A" type segregation of 500t steel ingot under the condition of side wall ventilation in Figure 11, the side wall cooling is significantly reduced under the same criterion value The trend of "A" type segregation is shown.

Working process and result of the present invention:

Since the present invention adopts the method of passing compressed air from the side wall of the steel ingot after a certain period of time after the pouring is completed, it can not only take away the heat from the outer surface of the steel ingot in time, but also reduce the temperature inside the steel ingot mold and increase the radiation from the steel ingot to the steel ingot mold Heat transfer greatly accelerates the cooling rate of steel ingots, which can significantly improve the production efficiency of large steel ingots and significantly improve the 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 side wall ventilation cooling method can significantly improve the solidification speed of large steel ingots, shorten the demoulding time, significantly improve the production efficiency of steel ingots, and Inhibit the segregation of large steel ingots, especially the "A" type segregation that seriously affects the quality of subsequent forgings. It is suitable for the manufacture of large steel ingots of various materials such as carbon steel or alloy steel.

Claims (5)

1. a method that suppresses macrotype ingot aliquation is characterized in that comprising the steps:

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: 1～2: 1, and described ratio of height to diameter is the ratio of steel ingot height and average diameter;

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

5) precasting breather line in the ingot mould chassis is laid air brick around the ingot mould bottom;

6) ingot steel casting finishes the back and began logical compressed air in 3～4 hours, stops ventilation after the ingot body solidifies fully.

2. according to the method for the described inhibition macrotype ingot aliquation of claim 1, it is characterized in that: the ingot mould material is grey cast-iron: HT150, HT200 or HT250.

3. according to the method for the described inhibition macrotype ingot aliquation of claim 1, it is characterized in that: insulated feeder is up-small and down-big, and material adopts high-alumina brick, corundum, mullite, magnesia brick, magnalium goods or alumina silicate, and there is one deck asbestos insulation board the material outside.

4. according to the method for the described inhibition macrotype ingot aliquation of 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%, P≤0.02%, S≤0.02%.

5. according to the method for the described inhibition macrotype ingot aliquation of claim 1, it is characterized in that: in the chassis, arrange pipeline, pipe diameter is determined according to the steel ingot tonnage is different, inside diameter ranges 30～200mm, at the ingot mould bottom periphery air brick that evenly distributes, the steel ingot side wall solidified layer thickness reaches 150～250mm, when air gap reaches 5～30mm width, begin logical compressed air, to accelerate the steel ingot cooling.

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