WO2018001355A1 - Low alloy cast steel, heat treatment method therefor and use thereof in railway industry - Google Patents

Abstract

Provided is a low alloy cast steel, and the components of the low alloy cast steel and the weight percentages thereof relative to the total weight of the low alloy cast steel are as follows: 0.20-0.30% of carbon, 0.20-0.40% of silicon, 0.95-1.05% of manganese, less than or equal to 0.020% of phosphorus, less than or equal to 0.020% of sulphur, 0.45-0.55% of chromium, 0.50-0.60% of nickel, 0.35-0.45% of molybdenum, 0.02-0.06% of aluminium, 0.01-0.05% of niobium and less than or equal to 0.20% of copper, wherein 0.03% ≤ aluminium + niobium ≤ 0.09% must be satisfied; and the balance of iron and other unavoidable elements. The properties of the low alloy cast steel having undergone a normalizing treatment and a tempering treatment are: a tensile strength of ≥ 931 MPa, a yield strength of ≥ 793 MPa, an elongation of ≥ 14%, a reduction of area of ≥ 30%, a Charpy V impact work at -40ºC of ≥ 35 J and a hardness range of 288-325 HBW. The low alloy cast steel has a superior weldability, can be generally used in the manufacture of railway locomotive vehicle parts, such as a car coupler body, a coupler knuckle and a coupler yoke, and can also be used for other parts with equivalent mechanical property requirements.

Description

Low alloy cast steel and heat treatment method thereof and application in railway industry Technical field

The invention belongs to the technical field of alloy steel, relates to a low alloy cast steel and a heat treatment method thereof, and particularly relates to a novel low alloy cast steel suitable for preparing railway locomotive vehicle parts and a heat treatment method thereof.

Background technique

The American Railway Association (AAR) revised and released the M-201-05 standard in 2005 to meet the material requirements of cast parts in the railway industry, including A-grade, B-grade, B+-grade, C-grade, and E-grade steel. Chemical composition range and mechanical properties. Manufacturers usually choose low-alloy cast steel with a strength class of E to make parts such as coupler hooks and knuckles. However, in the actual application process, due to the harsh conditions of the railway working conditions in China and the higher requirements for heavy loads, the early damage of the hook knuckles is caused by the large tensile stress and impact stress, and the strength and Resilience can not fully meet the working conditions. Therefore, it is believed that only by further improving the strength grade of the material and improving the comprehensive mechanical properties of the material can it be more beneficial to improve the early fatigue failure of such castings.

Based on this understanding, people have been looking for suitable cast steel components to meet the chemical composition range and carbon equivalent specifications specified in A.A.R, in order to obtain better mechanical properties than E-grade steel. For example, CN101880838A patent proposes a technical scheme for a new type of cast steel composition. The performance index that the program can achieve is: tensile strength ≥ 910 MPa, yield strength ≥ 760 MPa, elongation ≥ 14%, and area shrinkage ≥ 30%. -40 ° C Charpy V-type impact work ≥ 33J. It uses a high-manganese component system to increase strength through carbon and manganese. Its technical solution is in application There are two obvious problems in the process: First, the actual carbon equivalent of the technical scheme ranges from 0.80 to 0.83. However, the maximum carbon equivalent of the E-grade steel widely used in China is ≤0.81, and the average value is controlled at about 0.70. This will inevitably lead to poor soldering repair due to the increase of carbon equivalent; secondly, the technical scheme uses high content of manganese to improve the strength and hardenability, but when the manganese in the casting exceeds 1.2%, the composition segregation of the casting is likely to be intensified. Affect the consistency of casting performance.

Therefore, in view of the performance requirements and weldability requirements of railway rolling stock parts, there is a need in the art for an alloy cast steel that satisfies the existing E-grade steel carbon equivalent requirements in order to have superior weldability, and at the same time, After heat treatment, the mechanical performance requirements of E-grade cast steel superior to American Railway Association Standard M-201-05 should be obtained.

Summary of the invention

The object of the present invention is to provide a novel low-alloy cast steel which, after heat treatment, obtains mechanical performance requirements of E-grade cast steel superior to American Railway Association Standard M-201-05, and has strong weldability.

The object of the present invention is achieved by the following technical solutions:

According to a first aspect of the invention, a low alloy cast steel, the components thereof and their weight percentages relative to the total weight of the low alloy cast steel are as follows: carbon 0.20% to 0.30%, silicon 0.20% to 0.40%, Manganese 0.95% to 1.05%, phosphorus ≤0.020%, sulfur ≤0.020%, chromium 0.45% to 0.55%, nickel 0.50% to 0.60%, molybdenum 0.35% to 0.45%, aluminum 0.02% to 0.06%, 铌0.01% to 0.05 %, copper ≤ 0.20%, and must meet 0.03% ≤ aluminum + 铌 ≤ 0.09%; the balance is iron and other unavoidable elements.

According to a second aspect of the present invention, a heat treatment method for the above low alloy cast steel includes first performing a normalizing treatment and then performing a quenching and tempering treatment.

According to a third aspect of the invention, the above low alloy cast steel is used for preparing a railway locomotive The use of cast parts.

According to a fourth aspect of the invention, a railway rolling stock casting component is produced using the above low alloy cast steel.

In the low alloy cast steel of the present invention, the carbon equivalent can be controlled from 0.62% to 0.79%, and further optimized to 0.65% to 0.71%.

The low-alloy cast steel of the invention adopts the idea of adding a small amount of a small amount, and the main added reinforcing elements are carbon, silicon, manganese, chromium, nickel, molybdenum, and selecting a suitable ratio thereof, can improve the hardness and toughness of the low alloy cast steel. And the microstructure of the obtained steel casting after heat treatment is substantially tempered sorbite. The addition of the alloying elements aluminum and lanthanum and the selection of the appropriate ratio can effectively inhibit the austenite grain growth during the casting process, refine the grains, strengthen the matrix and improve the hardenability of the steel casting. The grain size of the low alloy cast steel of the present invention is about 8 grades. The additional action of the alloying element aluminum can be used for deoxidation.

After the heat treatment process of the low alloy cast steel of the invention, the mechanical properties are as follows: tensile strength ≥ 931 MPa, yield strength ≥ 793 MPa, elongation ≥ 14%, reduction of area ≥ 30%, Charpy V of -40 ° C Type impact energy ≥ 35J, hardness range is 288HBW ~ 325HBW. Further optimization, the elongation can be increased to ≥15%.

Compared with the prior art, the present invention maintains the carbon equivalent without increasing the strength of the E-grade steel, and also improves the impact toughness.

The low alloy cast steel of the invention can be generally used for the preparation of railway rolling stock parts, such as the hook body, the knuckle, the hook frame, etc., and can also be used for other parts with the same mechanical performance requirements.

DRAWINGS

1 is a picture showing a 100-fold magnification of a metallographic structure of a low-alloy cast steel of the present invention after normalizing treatment and quenching and tempering treatment.

2 is a metallographic group of the low alloy cast steel of the present invention after normalizing treatment and quenching and tempering treatment Weave a picture that is magnified 500 times.

detailed description

The application provides the following technical solutions:

Technical Solution 1. A low alloy cast steel, characterized in that each component and its weight percentage relative to the total weight of the low alloy cast steel are as follows: carbon 0.20% to 0.30%, silicon 0.20% to 0.40%, manganese 0.95% to 1.05%, phosphorus ≤0.020%, sulfur ≤0.020%, chromium 0.45% to 0.55%, nickel 0.50% to 0.60%, molybdenum 0.35% to 0.45%, aluminum 0.02% to 0.06%, 铌0.01% to 0.05% , copper ≤ 0.20%, and must meet 0.03% ≤ aluminum + 铌 ≤ 0.09%; the balance is iron and other inevitable elements.

The low-alloy cast steel according to claim 1, characterized in that the weight percentage of carbon is 0.23% to 0.29%, 0.24% to 0.28%, or 0.25 with respect to the total weight of the low alloy cast steel. % to 0.27%, or 0.24% to 0.26%.

The low-alloy cast steel according to claim 1 or 2, wherein the weight percentage of silicon is 0.21% to 0.39%, or 0.22% to 0.38%, relative to the total weight of the low alloy cast steel. , either 0.24% to 0.35%, or 0.25% to 0.32%, or 0.26% to 0.31%, or 0.23%, or 0.27%, or 0.28%, or 0.29%, or 0.30%, or 0.36%, or 0.37%.

The low-alloy cast steel according to any one of claims 1 to 3, wherein the weight percentage of manganese is 0.96% to 1.04%, or 0.96, based on the total weight of the low alloy cast steel. %~1.02%, or 0.98%~1.01%, or 0.97%, or 0.99%, or 1.00%.

The low-alloy cast steel according to any one of claims 1 to 4, wherein the weight percentage of phosphorus is ≤0.018% or ≤0.016%, relative to the total weight of the low-alloy cast steel. Or ≤0.014%, or ≤0.012%, or ≤0.010%.

The low alloy cast steel according to any one of claims 1 to 5, wherein It is characterized in that the weight percentage of sulfur is ≤0.017%, or ≤0.014%, or ≤0.012%, or ≤0.010%, relative to the total weight of the low alloy cast steel.

The low-alloy cast steel according to any one of claims 1 to 6, wherein the weight percentage of chromium is 0.46% to 0.54%, or 0.47, based on the total weight of the low alloy cast steel. %~0.51%, or 0.48%~0.50%.

The low-alloy cast steel according to any one of claims 1 to 7, characterized in that the weight percentage of nickel is 0.52% to 0.59%, or 0.53, relative to the total weight of the low alloy cast steel. % to 0.57%, or 0.54% to 0.58%, or 0.55% to 0.56%.

The low-alloy cast steel according to any one of claims 1 to 8, characterized in that the weight percentage of molybdenum is 0.36% to 0.44%, or 0.37, relative to the total weight of the low alloy cast steel. % to 0.43%, or 0.37% to 0.42%, or 0.39% to 0.41%.

The low-alloy cast steel according to any one of claims 1 to 9, characterized in that the weight percentage of aluminum is 0.03% to 0.05%, or 0.03, relative to the total weight of the low alloy cast steel. %~0.04%.

The low-alloy cast steel according to any one of claims 1 to 10, characterized in that the weight percentage of niobium is 0.02% to 0.04%, or 0.02, relative to the total weight of the low alloy cast steel. %~0.03%.

The low-alloy cast steel according to any one of claims 1 to 11, characterized in that the weight percentage of copper is ≤0.18% or ≤0.15%, relative to the total weight of the low alloy cast steel. Or ≤0.12%, or ≤0.10%, or ≤0.08%.

The low-alloy cast steel according to any one of claims 1 to 11, characterized in that the carbon equivalent CE is between 0.62% and 0.79%, or between 0.65% and 0.71%, or Between 0.66% and 0.71%, or between 0.67% and 0.68%, The carbon equivalent is calculated according to the following formula: CE = C + (Mn + Si) / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15.

The low-alloy cast steel according to any one of claims 1 to 13, characterized in that it is not subjected to normalizing treatment and quenching and tempering treatment.

The low-alloy cast steel according to any one of claims 1 to 13, characterized in that it has been subjected to normalizing treatment and quenching and tempering treatment.

The method of heat treatment of a low-alloy cast steel according to any one of claims 1 to 14, characterized in that it comprises a normalizing treatment and then a quenching and tempering treatment.

The heat treatment method according to claim 16, wherein the normalizing treatment comprises heating the low alloy cast steel to 920 ° C to 940 ° C, preferably 925 to 935 ° C, for 2 to 5 hours of heat preservation. Preferably, it is 3 to 4 hours, and then air-cooled to room temperature.

The heat treatment method according to claim 16, wherein the quenching treatment in the quenching and tempering treatment comprises heating the low alloy cast steel to 900 ° C to 920 ° C, preferably 910 ° C, and holding the heat 2 5 hours, preferably 3 to 4 hours, and then cooled in water, the temperature of the water is 20 ° C ~ 40 ° C.

The heat treatment method according to claim 16, wherein the tempering in the quenching and tempering treatment comprises heating the quenched low alloy cast steel to 590 ° C to 610 ° C, preferably 600 ° C, and holding the heat for 3 ～. 5 hours, preferably 3.5 to 4 hours, and then air-cooled to room temperature.

Technical Solution 20. The use of the low alloy cast steel according to any one of claims 1 to 15 for preparing a cast component of a railway rolling stock.

The invention according to claim 20, wherein the component is a coupler hook body, a knuckle, a hook frame or other components having the same mechanical performance requirements.

Technical Solution 22. A cast component of a railway rolling stock, characterized in that it is produced using the low alloy cast steel according to any one of claims 1-15.

The invention relates to a cast part of a railway rolling stock according to claim 22, which is characterized in that it is a hook body, a knuckle, a hook frame or other parts having the same mechanical performance requirements.

The inevitable impurities described in this application refer to impurities that cannot be completely smelted and removed in scrap steel or ore during smelting, such as As, Sn, Pb, Sb, Bi and other trace elements. The content of these elements usually needs to be controlled. As ≤ 0.01%, Sn ≤ 0.01%, Pb ≤ 0.01%, Sb ≤ 0.01%, Bi ≤ 0.01%, if these elements are too high, it will have a certain adverse effect on the toughness properties in the product.

The smelting process can be carried out using conventional heating equipment such as a power frequency, an intermediate frequency furnace or an electric arc furnace which are commonly used in the art, and the main purpose is to obtain the required components and ratios, and to minimize other harmful elements in the steel. Reduce impurities. Suitable hot working forming (for example, casting, etc., may be carried out according to a conventional method) depending on the final product. The heat treatment after hot working forming includes normalizing treatment and quenching and tempering treatment. The low-alloy cast steel of the invention comprises not only low-alloy cast steel which has not been subjected to normalizing treatment and quenching and tempering treatment, but also low-alloy cast steel which has been subjected to normalizing treatment and quenching and tempering treatment, and after casting, after heat treatment use. The mechanical properties of the low alloy cast steel which have been subjected to normalizing treatment and quenching and tempering treatment according to the present invention are as follows: tensile strength ≥ 931 MPa, yield strength ≥ 793 MPa, elongation ≥ 14%, reduction of area ≥ 30%, -40 ° C Charpy V-type impact energy ≥ 35J, hardness range is 288HBW ~ 325HBW.

The invention will now be described in detail with reference to the following specific embodiments. However, it will be readily understood by those skilled in the art that the embodiments herein are for illustrative purposes only, and the scope of the invention is not limited thereto.

In the present invention, the mechanical properties are determined based on the A.A.R standard American Railroad Association standard. For the relevant provisions of quasi-M-201-05, the sample used is the Kiel test block, in which the calculation of carbon equivalent: CE=C+(Mn+Si)/6+(Cr+Mo+V)/5+(Ni+Cu ) /15. The hardenability test was performed in accordance with the requirements of ASTM Standard A255, wherein the hardness of J13 represents the hardness at 13 mm from the water quenched end face.

In the following examples, the component contents are all based on their weight percentages.

Example 1

Smelting by a conventional intermediate frequency furnace or electric arc furnace, a low alloy cast steel is obtained, the weight percentage of each component and its total weight relative to the low alloy cast steel is as follows: carbon 0.25%, silicon 0.31%, manganese 0.98 %, phosphorus 0.015%, sulfur 0.012%, chromium 0.47%, nickel 0.55%, molybdenum 0.40%, copper 0.07%, aluminum 0.03%, 铌0.03%, aluminum + 铌 0.06%, balance and other unavoidable elements . The carbon equivalent is 0.68.

After the low alloy cast steel is cast by conventional methods (preferably describing the casting process used and the parameters used), heat treatment is performed. The heat treatment includes first normalizing treatment and then quenching and tempering. The normalizing process is to heat the low alloy cast steel to 940 ° C for 4 hours, and then air-cooled. The quenching and tempering process is to heat the low alloy cast steel to 910 ° C for 3 hours, and then perform water quenching at a water temperature of 25 ° C; then the quenched steel castings are heated to 600 ° C for 3.5 hours, and then cooled to room temperature in air. .

After the above-mentioned normalizing and quenching and tempering treatment of the low alloy cast steel, the obtained metallographic structure is basically tempered sorbite, and the metallographic structure photograph thereof is shown in FIG. 1 and FIG. A typical tempered sorbite metallographic morphology can be seen from Figures 1 and 2.

The mechanical properties of the low alloy cast steel were tested and found to be: tensile strength 996 MPa, yield strength 879 MPa, elongation 17.5%, section shrinkage 51%, and -40 °C Charpy V-type impact work (average ) 56J, hardness 298 HBW. The hardness at J13 is 38 HRC.

Examples 2-15

The low alloy cast steel was prepared in substantially the same manner as the preparation and treatment process described in Example 1. The specific components and contents and carbon equivalents are shown in Table 1, wherein the content is the weight percentage relative to the total weight of the low alloy cast steel (%) weight). The corresponding mechanical properties and hardness at J13 are shown in Table 2 below:

Table 1 Composition and content and carbon equivalent of low alloy cast steel of Examples 2-15

Table 2 Mechanical properties of low alloy cast steels of Examples 2-15 and hardness data at J13

It can be seen from the above data that the mechanical properties of the low-alloy cast steel of the present invention after the heat treatment according to the present invention are as follows: tensile strength ≥ 931 MPa, yield strength ≥ 793 MPa, elongation ≥ 14%, The section shrinkage rate is ≥30%, the Charpy V-type impact energy of -40°C is ≥35J, and the hardness range is 288HBW～325HBW. Its performance is better than The American Railroad Association standard M-201-05 has the mechanical properties of E-grade cast steel and has strong weldability.

While some aspects of the present invention have been shown and described, it will be understood by those skilled in the <RTIgt; The content is limited.

Claims (18)

A low alloy cast steel characterized in that the weight percentage of each component and its total weight relative to the low alloy cast steel is as follows: carbon 0.20% to 0.30%, silicon 0.20% to 0.40%, manganese 0.95% to 1.05 %, phosphorus ≤0.020%, sulfur ≤0.020%, chromium 0.45% to 0.55%, nickel 0.50% to 0.60%, molybdenum 0.35% to 0.45%, aluminum 0.02% to 0.06%, 铌0.01% to 0.05%, copper ≤0.20 %, and must meet 0.03% ≤ aluminum + 铌 ≤ 0.09%; the balance is iron and other unavoidable elements. The low alloy cast steel according to claim 1, wherein the weight percentage of carbon is from 0.24% to 0.28% with respect to the total weight of the low alloy cast steel. The low alloy cast steel according to claim 1, wherein the weight percentage of silicon is from 0.24% to 0.35% with respect to the total weight of the low alloy cast steel. The low alloy cast steel according to claim 1, wherein the weight percentage of manganese is 0.96% to 1.02% with respect to the total weight of the low alloy cast steel. The low-alloy cast steel according to claim 1, wherein the weight percentage of chromium is 0.47% to 0.51% with respect to the total weight of the low-alloy cast steel. The low alloy cast steel according to claim 1, wherein the weight percentage of nickel is from 0.53% to 0.57% with respect to the total weight of the low alloy cast steel. The low alloy cast steel according to claim 1, wherein the weight percentage of molybdenum is from 0.37% to 0.42% with respect to the total weight of the low alloy cast steel. The low alloy cast steel according to claim 1, wherein the weight percentage of copper is ≤ 0.12% with respect to the total weight of the low alloy cast steel. The low alloy cast steel according to claim 1, wherein the carbon equivalent CE is between 0.62% and 0.79%, and the carbon equivalent is calculated according to the following formula: CE = C + (Mn + Si) / 6 + (Cr +Mo+V)/5+(Ni+Cu)/15. A low alloy cast steel according to claim 9 wherein the carbon equivalent CE is between 0.65% and 0.71%. A low-alloy cast steel according to any one of claims 1 to 10, which is not subjected to normalizing treatment and quenching and tempering treatment. A low-alloy cast steel according to any one of claims 1 to 10, characterized in that it has been subjected to normalizing treatment and quenching and tempering treatment. The method of heat-treating a low-alloy cast steel according to any one of claims 1 to 11, characterized in that it comprises first performing a normalizing treatment and then performing a quenching and tempering treatment. The heat treatment method according to claim 13, wherein the normalizing treatment comprises heating the low alloy cast steel to 920 ° C to 940 ° C for 2 to 5 hours, and then air-cooling to room temperature. The heat treatment method according to claim 13, wherein the quenching treatment in the quenching and tempering treatment comprises heating the low alloy cast steel to 900 ° C to 920 ° C for 2 to 5 hours, and then cooling the water in a furnace. The temperature of the water is from 20 ° C to 40 ° C. The heat treatment method according to claim 13, wherein the tempering treatment in the quenching and tempering treatment comprises heating the quenched low alloy cast steel to 590 ° C to 610 ° C for 3 to 5 hours, and then cooling the air to room temperature. . A casting component for a railway rolling stock, characterized in that it is produced using a low alloy cast steel according to any one of claims 1-12. The railway rolling stock casting component according to claim 17, wherein the hook body, the knuckle, the hook frame or other components having the same mechanical performance requirements.

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