WO2019029533A1

WO2019029533A1 - Cast steel, preparation method for cast steel and use of cast steel

Info

Publication number: WO2019029533A1
Application number: PCT/CN2018/099201
Authority: WO
Inventors: 曹健峰; 徐海波; 赵延阔; 徐贵宝
Original assignee: 中车戚墅堰机车车辆工艺研究所有限公司
Priority date: 2017-08-07
Filing date: 2018-08-07
Publication date: 2019-02-14
Also published as: CN107675104A

Abstract

A cast steel, a preparation method for the cast steel and a part used in the railway field prepared using the cast steel. The cast steel comprises, by mass percentage: 0.12% to 0.22% of carbon, 0.3% to 0.6% of silicon, 0.8% to 1.1% of manganese, less than or equal to 0.020% of phosphorus, less than or equal to 0.020% of sulfur, 0.3% to 0.5% of chromium, 0.35% to 0.5% of nickel, 0.02% to 0.06% of niobium, the balance being iron and unavoidable impurities.

Description

Preparation method and application of cast steel and cast steel

Technical field

The invention relates to the field of alloy materials, in particular to a method for preparing cast steel and cast steel and an application thereof.

Background technique

With the continuous growth of the national economy, China's railway transportation industry and related industries have made great progress. While meeting domestic demand, some products and related parts and components have entered the international market. In recent years, the export volume of railway wagons and related parts and components has continued to increase.

Affected by the geographical environment, high-latitude and high-cold areas put forward higher requirements on the mechanical properties of truck parts, especially low temperature toughness. For example, the enterprise standard of the Russian Locomotive and Rolling Stock Company generally requires that the low-carbon alloy cast steel used in the truck has a shock absorption of not less than 17J at 60 °C. China's railway cast steel materials follow the AAR standard developed B+ grade steel does not require -60 °C impact absorption work, and usually B+ grade steel's -60 °C impact absorption work is less than 10J, so it can not meet the requirements of use in alpine regions.

At present, there are many researches on low-temperature steel at home and abroad, and there are few researches on casting low-temperature steel. The cast low temperature steel commonly used at home and abroad is chrome-nickel austenitic stainless steel. These steel grades have good low temperature toughness, but the comprehensive mechanical properties can not fully meet the requirements of truck parts. Another disadvantage of austenitic stainless steel is that the alloy contains a large amount of valuable elements such as Cr and Ni, and the cost is high.

Regarding the low alloy low temperature cast steel, the Chinese patent publication No. CN 101886223B discloses a preparation method of a high strength, high toughness low alloy manganese type cast steel, and the weight percentage of each component in the cast steel is: C: 0.12 to 0.32 wt. %; Mn: 1.90 to 3.50 wt.%; Si: 0.10 to 0.50 wt.%; P: 0.01 to 0.03 wt.%; S: 0.01 to 0.03 wt.%; Al: 0.01 to 0.05 wt.%; Ti: 0.01 ～0.05wt.%; V: 0-0.05wt.%; B: 0-0.008wt%; Ce: 0.05-0.25wt.%; the balance is Fe. The low alloy cast steel uses Mn as a main alloying element, and adds a small amount of alloying elements such as Al, Ti, V, B and rare earth element Ce, and is cast by a conventional steelmaking process, and then cast by sand casting or precision casting. The tempered martensite structure is obtained by water quenching and medium-high temperature tempering heat treatment. This document discloses that the mechanical properties of cast steel are as follows: tensile strength 800～1100MPa, yield strength 600～900MPa, elongation after fracture 10～18%, reduction of section shrinkage 40～60%, V-notch room temperature impact work 50～120J, V type The gap -40 ° C impact work 30 ~ 90J. The cast steel disclosed in this document is a low alloy manganese cast steel, a plurality of microalloying elements are added to refine the grain size, and a water quenching process is combined to obtain a higher strength. It is mainly suitable for the manufacture of high-strength cast steel structural parts with high requirements on impact toughness, but the water quenching treatment will increase the deformation and cracking tendency of the casting.

The Chinese patent publication No. CN 103194687B discloses a low-alloy low-strength high-strength cast steel and a preparation method thereof. The composition of the cast steel and its mass percentage are: carbon 0.05%, manganese 0.10%, silicon 0.10%, phosphorus 0.005. %, sulfur 0.005%, nickel 0.50%, chromium 0.10%, molybdenum 0.10%, vanadium 0.01%, copper 0.005%, aluminum 0.002%, iron balance. The disclosed cast steel has a tensile strength of 570-590 MPa, a yield strength of 460-475 MPa, an elongation of 25-27%, a section shrinkage of 67-70%, a carbon equivalent of ≤0.45%, and an impact energy of -40 °C. 110J. The cast steel disclosed in this document has good comprehensive mechanical properties, but its phosphorus and sulfur content is too high, and it needs refining furnace refining treatment, which is not convenient for industrial application.

According to the above, it is known that the low temperature toughness of the cast steel in the prior art is difficult to meet the requirements of use in an alpine region.

Summary of the invention

The main object of the present invention is to provide a method for preparing cast steel and cast steel and an application thereof, so as to solve the problem that the low temperature toughness of the cast steel in the prior art is difficult to meet the requirements of use in an alpine region.

In order to achieve the above object, according to one aspect of the present invention, a cast steel is provided which, in terms of mass percentage, comprises: 0.12% to 0.22% of carbon, 0.3% to 0.6% of silicon, and 0.8% to 1.1% of manganese. , phosphorus ≤ 0.020%, sulfur ≤ 0.020%, chromium 0.3% to 0.5%, nickel 0.35% to 0.5%, 铌 0.02% to 0.06%, the balance is iron and inevitable impurities.

Further, in the above cast steel, the mass percentage of nickel is from 0.36% to 0.46%.

Further, in the above cast steel, the sum of the mass percentages of phosphorus and sulfur is ≤0.035%.

Further, in the above cast steel, the mass percentage of carbon is from 0.19% to 0.22%.

Further, in the above cast steel, the mass percentage of silicon is from 0.35% to 0.48%.

Further, in the above cast steel, the mass percentage of chromium is from 0.34% to 0.41%.

Further, in the above cast steel, the mass percentage of niobium is 0.02% to 0.04%.

Further, the tensile strength of the cast steel is 540 MPa or more, preferably, the lower yield strength of the cast steel is 360 MPa or more, preferably the elongation at break of the cast steel is 20% or more; preferably, the Charpy V-type impact of the cast steel at -60 ° C The absorbed energy is greater than or equal to 20J.

Further, the tensile strength of the cast steel is 550 MPa or more, preferably, the lower yield strength of the cast steel is 360 MPa or more, preferably the elongation at break of the cast steel is 20% or more; preferably, the Charpy V type of -60 ° C of the cast steel. The impact absorption energy is greater than or equal to 20J.

According to another aspect of the present invention, there is provided a method for preparing a cast steel, the method comprising: preparing a metal nickel, a Fe-Mn alloy, a Fe-Cr alloy, and an Fe-Nb alloy according to the composition of any of the above cast steels. Fe-Si alloy, carbon powder, iron ore and scrap steel; melting and oxidizing waste steel and metal nickel to obtain iron oxide water; reducing molten iron water by carbon powder to obtain reduced iron water; adding Fe-Mn to reduced iron water The alloy, the Fe-Cr alloy, the Fe-Nb alloy, and the Fe-Si alloy obtain a molten steel; and the molten steel is sequentially cast and heat-treated to obtain a cast steel.

Further, the step of melting and oxidizing the scrap steel and the metal nickel comprises: placing the scrap steel and the metallic nickel in the furnace body of the electric arc furnace, heating the molten pool temperature of the electric arc furnace to 1560 to 1580 ° C; adding iron ore to the furnace body The stone is oxidized by introducing oxygen into the furnace body; and when the carbon content in the material in the furnace is reduced to 0.15% to 0.19% and the temperature of the molten pool is raised to 1590 ° C to 1610 ° C, the oxidation slag is removed to obtain iron oxide water.

Further, the above Fe-Mn alloy, Fe-Cr alloy, Fe-Nb alloy and Fe-Si alloy are baked to 300 ° C to 500 ° C until use after adding reduced molten iron.

Further, the step of sequentially casting and heat-treating the molten steel comprises: pouring steel liquid at 1600 ° C or higher, pouring in a mold at 1550 ° C to 1590 ° C, and cooling to obtain cast cast steel; casting casting The steel is heated to 900 ° C ~ 960 ° C and kept for 3 to 5 hours; the cast cast steel after 3 to 5 hours of heat preservation is cooled to 80 ° C ~ 150 ° C in a normal temperature oil medium for quenching treatment; casting after quenching treatment The cast steel is kept at 600 ° C to 650 ° C for 3 to 5 hours for tempering treatment; and the cast steel after the tempering treatment is air-cooled to room temperature to obtain cast steel.

According to still another aspect of the present invention, there is provided a component of a railway wagon, which is prepared by casting steel, which is any of the above-mentioned cast steels, preferably the railway wagon is in an environment below freezing temperature Railway wagons running.

According to still another aspect of the present invention, a component for use in the railway field is provided, and the component is prepared by using the above cast steel.

According to still another aspect of the present invention, a railway wagon is provided, including a component that is a component described above. By applying the technical solution of the present invention, by reasonably setting the alloy addition content, the type and content of the added alloy are less, and the composition is easy to control, thereby making the production cost of the cast steel low. In addition, the content of phosphorus and sulfur is limited. The embrittlement effect of phosphorus on cast steel is mainly because phosphorus is easily segregated at grain boundaries, thereby reducing the surface energy of grain boundaries. Secondly, phosphorus can also form phosphorus eutectic on grain boundaries. Non-metallic inclusions Fe ₃ P, causing grain boundary embrittlement; and sulfur solubility in steel is very low, easy to form low melting point FeS and other sulfides, such non-metallic inclusions will cause local stress concentration, resulting in steel embrittlement Phosphorus and sulfur will lead to an increase in the ductile-brittle transition temperature. Therefore, the sulfur and phosphorus contents are controlled within the above range, and the low temperature toughness of the cast steel can be increased as much as possible. Nickel is the most effective element to reduce the cold-brittle transition temperature of steel, because nickel is an element that enlarges the austenite region, which can strengthen the matrix and improve toughness. Nickel can increase the activity of carbon and enhance the segregation of carbon atoms around dislocations. The steel is strengthened by precipitation, thereby hindering the movement of dislocations; nickel can improve the plasticity of the steel under various heat treatments, and the above-mentioned content of chromium-nickel has a very high impact toughness.

DRAWINGS

The accompanying drawings, which are incorporated in the claims of the claims In the drawing:

1 shows a metallographic diagram when the metallographic structure of the cast steel of Example 1 of the present invention obtained by using the Observer.A1m type metallographic microscope is magnified 100 times;

Fig. 2 is a view showing a metallographic diagram when the metallographic structure of the cast steel according to Example 1 of the present invention obtained by using the Observer.A1m type metallographic microscope was magnified 500 times.

Detailed ways

It should be noted that the embodiments in the present application and the features in the embodiments may be combined with each other without conflict. The invention will be described in detail below with reference to the drawings in conjunction with the embodiments.

As analyzed by the background art of the present application, the low temperature toughness of the cast steel in the prior art is difficult to meet the requirements of use in an alpine region. To solve this problem, the present application provides a cast steel and a method for preparing the cast steel.

In a typical embodiment of the present application, a cast steel is provided, which comprises, by mass percent, carbon: 0.12% to 0.22%, silicon 0.3% to 0.6%, and manganese 0.8% to 1.1%. , phosphorus ≤ 0.020%, sulfur ≤ 0.020%, chromium 0.3% to 0.5%, nickel 0.35% to 0.5%, 铌 0.02% to 0.06%, the balance is iron and inevitable impurities.

By reasonably setting the alloy addition content, the type and content of the added alloy are small, and the composition is easily controlled, so that the production cost of the cast steel is low. In addition, the content of phosphorus and sulfur is limited. The embrittlement effect of phosphorus on cast steel is mainly because phosphorus is easily segregated at grain boundaries, thereby reducing the surface energy of grain boundaries. Secondly, phosphorus can also form phosphorus eutectic on grain boundaries. Non-metallic inclusions Fe ₃ P, causing grain boundary embrittlement; and sulfur solubility in steel is very low, easy to form low melting point FeS and other sulfides, such non-metallic inclusions will cause local stress concentration, resulting in steel embrittlement Phosphorus and sulfur will lead to an increase in the ductile-brittle transition temperature. Therefore, the sulfur and phosphorus contents are controlled within the above range, and the low temperature toughness of the cast steel can be increased as much as possible. Nickel is the most effective element to reduce the cold-brittle transition temperature of steel, because nickel is an element that enlarges the austenite region, which can strengthen the matrix and improve toughness. Nickel can increase the activity of carbon and enhance the segregation of carbon atoms around dislocations. The steel is strengthened by precipitation, thereby hindering the movement of dislocations; nickel can improve the plasticity of the steel under various heat treatments, and the above-mentioned content of chromium-nickel has a very high impact toughness.

In a preferred embodiment of the present application, in order to further exert the effect of nickel on the low temperature toughness in the low alloy steel on the basis of reducing the cost of the cast steel, it is preferable that the mass percentage of nickel in the cast steel is 0.36%. ~0.46%.

In addition, in order to reduce the negative influence of sulfur phosphorus on the low temperature toughness of the cast steel as much as possible, it is preferable that the sum of the mass percentages of phosphorus and sulfur in the above cast steel is ≤0.035%.

The main role of carbon in cast steel is to form pearlite or dispersed alloy carbides to strengthen the cast steel, but carbon will sharply reduce the low temperature toughness of the steel, and increase the cold brittle transition temperature of the steel, in order to keep the cast steel Good solderability and low ductile-brittle transition temperature, preferably in the above cast steel, the mass percentage of carbon is from 0.19% to 0.22%.

The main role of silicon in cast steel is to improve the strength and hardness of cast steel. The addition of silicon can not only improve the hardenability with manganese, but also effectively inhibit the precipitation and segregation of carbides from martensite during tempering. It can maintain high hardness at higher temperature, and can reduce the critical cooling rate of steel and improve the hardenability of steel, but at the same time reduce the toughness and plasticity of steel to some extent, in order to exert the strengthening effect of silicon. Without damaging the low temperature toughness of the cast steel, it is preferred that the above-mentioned cast steel has a mass percentage of silicon of 0.35% to 0.48%.

The main role of manganese in cast steel is to increase the stability of austenite in cast steel structure, refine pearlite, improve the hardenability of steel, and reduce the phase transition temperature of austenite to ferrite transformation. As the Mn/C ratio in the steel increases, the ductile-brittle transition temperature decreases linearly. In order to fully exert the effective effect of manganese, it is preferable that the mass percentage of silicon in the cast steel is 0.84% to 1.08%.

The main role of chromium in cast steel is to make the cast steel have good hardenability. The chromium with a content below 2% can be completely dissolved in the ferrite, and its strength can be improved without reducing its plasticity. The strength and the toughness after tempering are preferably in the above cast steel, and the mass percentage of chromium is from 0.34% to 0.41%.

The main role of niobium in cast steel is to increase the strength of cast steel by fine grain strengthening. Nb can form carbides or nitrides with C, N or O. These formed carbides or nitrides can hinder grain growth. , to refine the grain, increase the total grain boundary area, increase the micro-crack propagation resistance, and thus increase the fracture strain; secondly, the grain refinement, while the dislocation and dislocation proliferation rates are high, plasticity Uniform deformation, good plasticity; in addition to grain refinement, the energy consumption of cracks passing through the grain increases, the toughness increases; the total grain boundary area increases, the impurities around the grain boundary decrease, the tendency of grain fracture decreases, and finally the most critical It is the grain refinement which can lower the ductile-brittle transition temperature. In order to improve the low-temperature performance of the cast steel, it is preferable that the mass percentage of niobium in the above cast steel is 0.02% to 0.04%.

In a preferred embodiment, the tensile strength of the cast steel is 540 MPa or more, preferably, the lower yield strength of the cast steel is 360 MPa or more, preferably the elongation at break of the cast steel is 20% or more; preferably -60 ° C of the cast steel. The Charpy V-type shock absorption energy is greater than or equal to 20J.

In another preferred embodiment, the tensile strength of the cast steel is 550 MPa or more, preferably, the lower yield strength of the cast steel is 360 MPa or more, and preferably the elongation at break of the cast steel is 20% or more; The Charpy V-type shock absorption energy at 60 ° C is greater than or equal to 20 J.

In another exemplary embodiment of the present application, there is provided a method for preparing a cast steel, the method comprising: preparing a metal nickel, a Fe-Mn alloy, and an Fe-Cr alloy according to the composition of the cast steel of any of the above , Fe-Nb alloy, Fe-Si alloy, carbon powder, iron ore and scrap steel; the scrap steel and metallic nickel are melted and oxidized to obtain iron oxide water; the molten iron water is reduced by carbon powder to obtain reduced iron water; The Fe-Mn alloy, the Fe-Cr alloy, the Fe-Nb alloy, and the Fe-Si alloy are added to the water to obtain a molten steel; and the molten steel is sequentially cast and heat-treated to obtain a cast steel.

The preparation method of the application method has less alloys and contents, and the components are easy to control, so that the production cost of the cast steel is low; the raw materials for forming the cast steel are processed by the above preparation method, and the functions of the components are fully exerted. . And the low temperature toughness of the cast steel is further increased by the heat treatment.

The above preparation method can be carried out not only by the electric arc furnace redox method or the medium frequency induction furnace melting, but also because the smelting process adopted is simple, the ordinary electric arc furnace smelting can also be implemented, and the AOD refining furnace refining process is not required, so that it is more convenient for industrial application, and Scrap steel can be used during smelting, which is conducive to further reduction of cost and efficiency.

In a preferred embodiment of the present application, the step of melting and oxidizing the scrap steel and the metal nickel preferably comprises: placing the scrap steel and the metallic nickel in the furnace body of the electric arc furnace and heating the molten pool temperature of the electric arc furnace to 1560 ° C. At 1580 ° C, iron ore is added to the furnace body, and oxygen is introduced into the furnace to oxidize. During the oxidation process, the molten iron is uniformly boiled and automatically slag is slag. When the boiling is vigorous, the slag is added; when the carbon in the furnace body is carbon When the content is reduced to 0.15% to 0.19% and the temperature of the molten pool is raised to 1590 ° C to 1610 ° C, the oxidized slag is removed to obtain iron oxide water.

In addition, in order to buffer the temperature difference between the alloy to be added and the high-temperature molten steel, to prevent the temperature difference of the high-temperature molten steel from fluctuating too much and the introduction of moisture, the above-mentioned Fe-Mn alloy, Fe-Cr alloy, Fe-Nb alloy and Fe-Si are preferable. The alloy is baked to 300 ° C to 500 ° C until it is added to the reduced molten iron.

In still another preferred embodiment of the present application, the step of sequentially casting and heat-treating the molten steel comprises: pouring the molten steel at 1600 ° C or higher, pouring the molten steel at 1550 ° C to 1590 ° C, and cooling. The cast cast steel is obtained; the cast cast steel is heated to 900 ° C ~ 960 ° C and kept for 3 to 5 hours; the cast cast steel after 3 to 5 hours of heat preservation is cooled to 80 ° C ~ 150 ° C in a normal temperature oil medium for quenching The cast steel after the quenching treatment is kept at 600 ° C to 650 ° C for 3 to 5 hours for tempering treatment; and the cast steel after the tempering treatment is air-cooled to room temperature to obtain cast steel.

In another exemplary embodiment of the present application, a component of a railway wagon is provided, which is prepared by using cast steel, which is any of the above cast steels, preferably the railway wagon is Railway wagons operating in environments below freezing temperatures. In yet another exemplary embodiment of the present application, a railway wagon is provided that includes components that are the components described above. Since the cast steel of the present application has the above-mentioned excellent mechanical properties, the parts produced by the cast steel have excellent mechanical properties and meet the requirements for use of railway wagons in severe cold regions. Advantageous effects of the present application will be further described below in conjunction with the examples and comparative examples.

Since the cast steel of the present application has the above-mentioned excellent mechanical properties, the parts produced by the cast steel have excellent mechanical properties and can meet the requirements for the use of components in the railway field, especially in the railway field in severe cold regions. Claim. In addition to being applicable to railway wagons, the above components can also be applied to other vehicles in the railway sector.

Example 1

The chemical composition (mass percentage) of the low alloy medium strength low temperature cast steel of the present embodiment is: carbon 0.22%, silicon 0.41%, manganese 0.80%, phosphorus 0.015%, sulfur 0.016%, chromium 0.36%, nickel 0.36%,铌 0.03%, the balance is iron and other unavoidable impurities, the unavoidable impurity content is less than 0.1%; the total content of phosphorus + sulfur in the cast steel of the present embodiment is 0.031%.

Using scrap steel as raw material, steelmaking by electric arc furnace oxidation reduction method, the steps are as follows:

1 Loading, after the waste carbon steel is cleaned and rusted, it is added to the furnace of the electric arc furnace at the same time as the metal nickel.

The carbon steel block added therein has a particle size of about 200×200×200 mm, and is densely packed in the furnace body of the electric arc furnace; the molten carbon ensures the decarburization amount in the oxidation period is ≥0.30%, and the carbon powder is added when insufficient. The toner particle size is controlled below 20 mesh.

2 oxidation, using iron ore, oxygen oxidation.

Open the corresponding electrical switches. When the temperature of the molten pool in the electric arc furnace reaches 1560 °C, add iron ore and pass oxygen oxidation. During the oxidation process, the material in the furnace is kept evenly boiled, and the slag is automatically flowed, and the slag is added in time. When the carbon content is reduced to 0.15% to 0.19% and the molten pool temperature reaches 1600 ° C, the oxidation slag is removed and the reduction period is entered.

3 reduction, adding carbon powder (the particle size is controlled below 20 mesh) to the material in the furnace at the end of the oxidation stage in step 2 for reduction, the total amount of carbon powder is 3 to 4 kg / ton of steel, white slag; and the mass percentage of chemical components Controlled addition of Fe-Mn, Fe-Cr, Fe-Nb and Fe-Si alloys.

The above Fe-Mn, Fe-Cr, Fe-Nb and Fe-Si alloys are baked before being added to the molten steel, and baked to 300 ° C to 500 ° C for use.

4 tapping, step 3 to adjust the molten steel chemical composition of molten steel, the tapping temperature is controlled at 1620 ° C ~ 1630 ° C.

5 Final deoxidation, aluminum is used as deoxidizer for final deoxidation when the steel is tapped. The aluminum block is placed at the bottom of the ladle. When the steel is tapped, the molten steel impacts the aluminum block at the bottom of the ladle, and the aluminum block reacts with the oxygen in the molten steel to deoxidize.

6 pouring, pouring the molten steel in the ladle of step 5 into the mold, and the pouring temperature is controlled at 1550 ° C ~ 1590 ° C to obtain steel parts.

The heat treatment of steel parts is as follows:

Firstly, the steel parts are heated to 940 ° C in an electric resistance furnace, and then kept at this temperature for 4 hours, then quenched, and cooled to 120 ° C in a normal temperature oil medium; the quenched cast steel is fed in 6 hours. The electric resistance furnace was tempered at 620 ° C for 4 hours, and after the end of the heat preservation, the furnace was cooled and cooled to room temperature to complete the heat treatment, and the cast steel of Example 1 was obtained.

The metallographic structure of the obtained cast steel was detected by the Observer.A1m metallographic microscope. The test results are shown in Fig. 1 and Fig. 2. Fig. 1 shows the metallographic structure of the low temperature cast steel after the quenching + tempering is magnified 100 times. The metallographic diagram of FIG. 2 is a metallographic diagram of the low-temperature cast steel of the present embodiment after being quenched and tempered by 500 times magnification of the metallographic structure. It can be seen from the figure that the low-temperature cast steel of the present embodiment is quenched and tempered. The treated metallographic structure is a ferrite + sorbite structure.

Examples 2 to 21

The chemical compositions of the low-alloy medium-strength low-temperature cast steels of Examples 2 to 21 are as follows. In Table 1, the inevitable impurity content of the low-alloy medium-strength low-temperature cast steel of each example was less than 0.10%. Further, the smelting method and the heat treatment method of the low alloy cast steel of Examples 2 to 21 were the same as in Example 1.

Table 1

Example 22

The difference from Example 1 is that 2 is oxidized by using ore and oxygen oxidation.

Open the corresponding electrical switches. When the temperature of the molten pool in the electric arc furnace reaches 1580 °C, add iron ore and pass oxygen oxidation. During the oxidation process, the material in the furnace is kept evenly boiled, and the slag is automatically flowed, and the slag is added in time. When the carbon content is reduced to 0.15% to 0.19% and the molten pool temperature reaches 1590 ° C, the oxidation slag is removed and the reduction period is entered.

Example 23

Open the corresponding electrical switches. When the temperature of the molten pool in the electric arc furnace reaches 1560 °C, add iron ore and pass oxygen oxidation. During the oxidation process, the material in the furnace is kept evenly boiled, and the slag is automatically flowed, and the slag is added in time. When the carbon content is reduced to 0.15% to 0.19% and the molten pool temperature reaches 1610 ° C, the oxidation slag is removed and the reduction period is entered.

Example 24

Open the corresponding electrical switches. When the temperature of the molten pool in the electric arc furnace reaches 1555 °C, add iron ore, and pass oxygen oxidation. During the oxidation process, the material in the furnace is kept evenly boiled, and the slag is automatically flowed, and the slag is added in time. When the carbon content is reduced to 0.15% to 0.19% and the molten pool temperature reaches 1615 ° C, the oxidation slag is removed and the reduction period is entered.

Example 25

The difference from Embodiment 1 is that the steel parts are heat treated as follows:

Firstly, the steel parts are heated to 960 ° C in an electric resistance furnace, and kept at this temperature for 3 hours, then quenched and cooled to 80 ° C in a normal temperature oil medium; the quenched cast steel is fed in 6 hours. The electric resistance furnace was tempered at 600 ° C for 3 hours, and after the completion of the heat preservation, the furnace was cooled and cooled to room temperature to complete the heat treatment, and the cast steel of Example 22 was obtained.

Example 26

Firstly, the steel parts are heated to 900 ° C in an electric resistance furnace, and then kept at this temperature for 3 hours, then quenched, and cooled to 150 ° C in a normal temperature oil medium; the quenched cast steel is fed in 6 hours. The electric resistance furnace was tempered at 650 ° C for 3 hours, and after the completion of the heat preservation, the furnace was cooled and cooled to room temperature to complete the heat treatment, and the cast steel of Example 23 was obtained.

Example 27

Firstly, the steel parts are heated to 965 ° C in an electric resistance furnace, and kept at this temperature for 3 hours, then quenched, and cooled to 160 ° C in a normal temperature oil medium; the quenched cast steel is fed in 6 hours. The electric resistance furnace was tempered at 660 ° C for 3 hours, and after the completion of the heat preservation, the furnace was cooled and cooled to room temperature to complete the heat treatment, and the cast steel of Example 24 was obtained.

Example 28

The difference from Embodiment 1 is that

3 reduction, adding carbon powder (the particle size is controlled below 20 mesh) to the material in the furnace at the end of the oxidation stage in step 2 for reduction, the total amount of carbon powder is 3 to 4 kg / ton of steel, white slag; and the mass percentage of chemical components It is controlled to add Fe-Mn, Fe-Cr, Fe-Nb and Fe-Si alloy at normal temperature.

Comparative examples 1 to 14

The chemical compositions of the low-alloy medium-strength low-temperature cast steels of Comparative Examples 1 to 14 are as shown in Table 2 below, and the inevitable impurity content in the low-alloy medium-strength low-temperature cast steel of each example was less than 0.10%. The smelting method and heat treatment method of the low alloy cast steel of Comparative Examples 1 to 14 were the same as in Example 1.

Table 2

The mechanical properties of the cast steels of the above respective examples and comparative examples were measured in accordance with the method specified in the Railway Industry Standards of the People's Republic of China (TB/T2942-2015), and the samples used were Kiel test blocks. The mechanical properties of the cast steel are shown in Table 3, which complies with the relevant provisions of the American Railway Association Standard M-201-05 of the A.A.R standard.

table 3

Comparing the data in Table 3, it can be seen that the carbon content in Examples 4, 8 and 10 is relatively high, and the tensile strength, the lower yield strength and the impact absorption energy of -60 ° C of the cast steel are significantly improved; The content ratio of each element in Example 7 is particularly reasonable, and the impact absorption energy of cast steel at -60 ° C is particularly prominent.

For low-alloy cast steel materials, the toughness decreases with the test temperature, while the toughness decreases remarkably within a certain temperature range. The material changes from microporous aggregated ductile fracture to transgranular cleavage brittle fracture, impact fracture. The morphology changes from dimple-like to crystalline. The phenomenon of transforming a ductile material into a brittle material is called low-temperature brittleness, and the transition temperature is called the ductile-brittle transition temperature. The adjustment of each element component in the present invention is carried out around reducing the ductile-brittle transition temperature of the material. The present invention requires that the Charpy V-type impact absorption energy of -60 ° C is greater than or equal to 20 J, and the material of the present invention is at a temperature of -60 ° C. The better the impact performance, the lower the ductile-brittle transition temperature.

In addition, according to the comparison of Example 12 and Comparative Example 1, it can be found that the carbon content control within the scope of the present application is advantageous for the significant increase of the cast steel strength; according to the comparison of Example 13 and Comparative Example 3, the silicon content control can be found. Within the scope of the present application, it is advantageous to exert the strengthening effect of silicon without damaging the low temperature toughness of the cast steel; according to the comparison of Example 14 and Comparative Example 5, it can be found that the control of the manganese element content is beneficial to increase the cast steel structure within the scope of the present application. The stability of medium austenite, refine pearlite, improve the hardenability of steel; according to the comparison of Example 15 and Comparative Example 7, it can be found that the phosphorus content and the phosphorus-sulfur content are comprehensively controlled within the scope of the application -60 ° C The Charpy V-type impact absorption energy increases, indicating that it is beneficial to reduce the embrittlement effect on the cast steel and reduce the ductile-brittle transition temperature; according to the comparison between Example 16 and Comparative Example 9, it can be found that the chromium element content is controlled within the scope of the present application. It is beneficial to increase the tensile strength of the cast steel and maintain the toughness after tempering; according to the comparison between Example 17 and Comparative Example 11, it can be found that the content of nickel element is controlled within the scope of the present application. It is beneficial to improve the low temperature impact toughness of the cast steel; according to the comparison between Example 18 and Comparative Example 13, it can be found that the control of the niobium element content is beneficial to the grain refinement of the cast steel structure and the increase of -60 ° C Charpy V in the scope of the present application. The type of impact absorbs energy, indicating that it is beneficial to reduce the ductile-brittle transition temperature.

From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects:

The above description is only the preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Claims

A cast steel characterized in that, in terms of mass percentage, the cast steel comprises:

Carbon 0.12% to 0.22%, silicon 0.3% to 0.6%, manganese 0.8% to 1.1%, phosphorus ≤0.020%, sulfur ≤0.020%, chromium 0.3% to 0.5%, nickel 0.35% to 0.5%, 铌0.02% to 0.06 %, the balance is iron and inevitable impurities.
The cast steel according to claim 1, wherein in the cast steel, the nickel has a mass percentage of 0.36% to 0.46%.
The cast steel according to claim 1, wherein in the cast steel, a sum of mass percentages of the phosphorus and the sulfur is ≤ 0.035%.
The cast steel according to claim 1, wherein said cast steel has a mass percentage of carbon of from 0.19% to 0.22%.
The cast steel according to claim 1, wherein in the cast steel, the silicon has a mass percentage of 0.35% to 0.48%.
The cast steel according to claim 1, wherein said cast steel has a mass percentage of chromium of from 0.34% to 0.41%.
The cast steel according to claim 1, wherein in the cast steel, the mass percentage of the niobium is 0.02% to 0.04%.
The cast steel according to claim 1, wherein the cast steel has a tensile strength of 550 MPa or more, preferably, the cast steel has a lower yield strength of 360 MPa or more, and preferably the cast steel has a post-break elongation greater than or equal to It is equal to 20%; preferably, the Charpy V-type impact absorption energy of -60 ° C of the cast steel is 20 J or more.
The cast steel according to claim 1, wherein the cast steel has a tensile strength of 540 MPa or more, preferably, the cast steel has a lower yield strength of 360 MPa or more, and preferably the cast steel has a post-break elongation greater than or equal to It is equal to 20%; preferably, the Charpy V-type impact absorption energy of -60 ° C of the cast steel is 20 J or more.
A method for preparing a cast steel, characterized in that the preparation method comprises:

Metal nickel, Fe-Mn alloy, Fe-Cr alloy, Fe-Nb alloy, Fe-Si alloy, carbon powder, iron ore and scrap steel according to the composition of the cast steel according to any one of claims 1 to 9;

The scrap steel and the metal nickel are melted and oxidized to obtain iron oxide water;

The molten iron water is reduced by using carbon powder to obtain reduced iron water;

Adding the Fe-Mn alloy, the Fe-Cr alloy, the Fe-Nb alloy, and the Fe-Si alloy to the reduced molten iron to obtain a molten steel;

The molten steel is sequentially cast and heat-treated to obtain the cast steel.
The preparation method according to claim 10, wherein the step of melting and oxidizing the scrap steel and the metallic nickel comprises:

After the scrap steel and metallic nickel are placed in the furnace body of the electric arc furnace, the temperature of the molten pool of the electric arc furnace is heated to 1560 to 1580 ° C;

Adding iron ore to the furnace body and introducing oxygen into the furnace for oxidation;

When the carbon content in the material in the furnace is reduced to 0.15% to 0.19% and the temperature of the molten pool is raised to 1590 ° C to 1610 ° C, the oxidation residue is removed to obtain the iron oxide water.
The preparation method according to claim 10, wherein the Fe-Mn alloy, the Fe-Cr alloy, the Fe-Nb alloy, and the Fe-Si alloy are baked before adding the reduced molten iron Bake until 300 ° C ~ 500 ° C for use.
The preparation method according to claim 10, wherein the step of sequentially pouring and heat-treating the molten steel comprises:

After the molten steel is tapped at 1600 ° C or higher, it is poured into a mold at 1550 ° C to 1590 ° C, and cooled to obtain a cast cast steel;

Heating the cast cast steel to 900 ° C ~ 960 ° C and holding for 3 to 5 hours;

The cast cast steel after holding for 3 to 5 hours is cooled to 80 ° C to 150 ° C in a normal temperature oil medium for quenching treatment;

The cast cast steel after quenching treatment is kept at 600 ° C ~ 650 ° C for 3 to 5 hours for tempering treatment;

as well as

The cast-tempered steel after the tempering treatment is air-cooled to room temperature to obtain the cast steel.
A component of a railway wagon prepared by using cast steel, characterized in that the cast steel is the cast steel according to any one of claims 1 to 9, preferably the railway wagon is Railway wagons operating in environments below freezing temperatures.
A railway wagon comprising a component, characterized in that the component is the component of claim 14.
A component for use in the field of railways, the component being prepared from cast steel, characterized in that the cast steel is the cast steel according to any one of claims 1 to 9.