CN110241363B

CN110241363B - Cast steel material and casting method thereof

Info

Publication number: CN110241363B
Application number: CN201910673002.XA
Authority: CN
Inventors: 陈杰华; 冯顺宇; 邵新波; 樊周强; 王兴宇; 王新宇
Original assignee: Zhengzhou Coal Machinery Intelligent Working Face Technology Co ltd
Current assignee: Zhengzhou Coal Machinery Intelligent Working Face Technology Co.,Ltd.; Zhengzhou Coal Mining Machinery Group Co Ltd
Priority date: 2019-07-24
Filing date: 2019-07-24
Publication date: 2020-10-09
Anticipated expiration: 2039-07-24
Also published as: CN110241363A

Abstract

The invention discloses a novel cast steel material and a casting method thereof, wherein the cast steel material comprises the following formula components in percentage by weight: 0.29 to 0.37 percent of C, 0.6 to 1.0 percent of Mn0.3 to 0.6 percent of Si0.3, less than or equal to 0.03 percent of P, less than or equal to 0.03 percent of S, 0.45 to 0.65 percent of Cr0.22 to 0.27 percent of Mo0.7 to 0.9 percent of Ni0.7 to 0.9 percent of Al, less than or equal to 0.04 percent of Cu, less than or equal to 0.3 percent of N, V, and the balance of Fe; the carbon equivalent is CE, and CE is C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is less than or equal to 0.72 percent. On the premise of not increasing the cost, the contents of elements such as S, P, Cu, Cr, Ni and the like are reduced as much as possible, meanwhile, the contents of elements such as Mo, Mn and the like are properly increased, and the mechanical property and the welding property of the material are ensured to the maximum extent.

Description

Cast steel material and casting method thereof

Technical Field

The invention relates to the technical field of alloy materials, in particular to a cast steel material and a casting method thereof.

Background

Because mining machinery has harsh use environment, poor working road condition, low environmental temperature and long working time and is subjected to larger impact load during working, the key parts of the mining machinery, such as the rocker arm shell, the planet carrier, the bearing seat and other castings, have higher mechanical properties. At present, the material strength and the weldability of the key parts cannot better meet the use and maintenance requirements, especially the welding performance and the shock resistance, and cannot be stably guaranteed. In addition, some parts need local induction quenching, so that the hidden danger of quenching cracking exists, and the heat treatment performance is poor.

Disclosure of Invention

The invention provides a cast steel material and a casting method thereof.

In order to achieve the purpose, the invention provides the following technical scheme:

a novel cast steel material comprises the following formula components in percentage by weight:

0.29 to 0.37 percent of C, 0.6 to 1.0 percent of Mn0.3 to 0.6 percent of Si0.3, less than or equal to 0.03 percent of P, less than or equal to 0.03 percent of S, 0.45 to 0.65 percent of Cr0.22 to 0.27 percent of Mo0.7 to 0.9 percent of Ni0.7 to 0.9 percent of Al, less than or equal to 0.04 percent of Cu, less than or equal to 0.3 percent of V, and the balance of Fe;

the allowable deviation of chemical composition refers to the specification in GB/T222;

the carbon equivalent is CE, and CE is C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is less than or equal to 0.72 percent.

The carbon content increases, the yield point and tensile strength of the steel increase, but the plasticity and impact properties decrease, and when the carbon content exceeds 0.23%, the weldability of the steel deteriorates, and therefore, low alloy structural steels for welding generally have a carbon content of not more than 0.20%. Meanwhile, the high carbon content can reduce the atmospheric corrosion resistance, and the high-carbon steel in an open-air stock yard is easy to rust. In addition, carbon can increase the cold brittleness and age sensitivity of the steel.

Silicon is used as a reducing agent and a deoxidizing agent in the steel making process, so the killed steel contains 0.15 to 0.30 percent of silicon. If the silicon content in the steel exceeds 0.50 to 0.60%, the alloying elements are not included. Silicon can significantly improve the elastic limit, yield point and tensile strength of steel, and is widely used as spring steel. 1.0-1.2% of silicon is added into the quenched and tempered structural steel, so that the strength can be improved by 15-20%. Silicon is combined with molybdenum, tungsten, chromium and the like, so that the corrosion resistance and the oxidation resistance are improved, and the heat-resistant steel can be manufactured. Low carbon steel containing 1-4% of silicon has very high magnetic permeability and is used as silicon steel sheet in electrical industry. At the same time, the amount of silicon increases, which may degrade the weldability of the steel.

The manganese is used as a good deoxidizer and desulfurizer in the steel-making process, and the manganese content in the steel is 0.30-0.50%. When more than 0.70 percent of manganese steel is added into carbon steel, compared with the steel with the common steel amount, the manganese steel has enough toughness, higher strength and hardness, the hardenability of the steel is improved, and the hot workability of the steel is improved, for example, the yield point of the 16Mn steel is 40 percent higher than that of A3. The steel containing 11-14% of manganese has extremely high wear resistance and is used for buckets of excavators, lining plates of ball mills and the like. Meanwhile, the manganese content is increased, the corrosion resistance of the steel is weakened, and the welding performance is reduced.

In general, phosphorus is a harmful element in steel, increases cold brittleness of steel, deteriorates welding properties, reduces plasticity, and deteriorates cold bending properties. Therefore, it is generally required that the phosphorus content in the steel is less than 0.045%, and the demand for high-quality steel is lower.

Sulfur is also a harmful element in general, and causes hot brittleness of steel, reduces ductility and toughness of steel, and causes cracks in forging and rolling. Sulfur is also detrimental to welding performance and reduces corrosion resistance. Therefore, it is generally required that the sulfur content is less than 0.055% and the high-quality steel is less than 0.040%. Machinability is improved by adding 0.08-0.20% sulphur to the steel, commonly known as free-cutting steel.

Chromium can significantly improve strength, hardness and wear resistance, but at the same time reduces plasticity and toughness in structural and tool steels. Chromium can improve the oxidation resistance and corrosion resistance of steel, so that chromium is an important alloy element of stainless steel and heat-resistant steel. However, chromium significantly increases the brittle transition temperature of steel and promotes temper brittleness of steel.

The nickel can improve the strength of steel, maintain good plasticity and toughness, improve the processability and weldability of steel, greatly improve the hardenability of steel, and the chromium-nickel-molybdenum steel matched with chromium and molybdenum can obtain comprehensive mechanical properties with good matching of strength and toughness after heat treatment. The nickel has higher corrosion resistance to acid and alkali and has antirust and heat-resisting capabilities at high temperature. However, since nickel is a scarce resource, other alloy elements should be used as far as possible to replace nickel-chromium steel.

Molybdenum can refine the crystal grains of the steel, improve hardenability and heat strength, and maintain sufficient strength and creep resistance at high temperature. The addition of molybdenum to the structural steel improves the mechanical properties and also suppresses brittleness of the alloy steel due to tempering. The red color can be improved in the tool steel. The main adverse effect of molybdenum is its tendency to graphitize low alloy molybdenum steels.

Copper can improve the strength and toughness, especially atmospheric corrosion performance, and has the disadvantages that hot brittleness is easy to generate during hot processing, the plasticity is obviously reduced when the copper content exceeds 0.5 percent, and welding is not influenced when the copper content is less than 0.50 percent.

Aluminum is a commonly used deoxidizer in steel. A small amount of aluminum is added into the steel, so that the crystal grains can be refined, and the impact toughness can be improved, for example, 08Al steel used as deep drawing sheet. The aluminum also has oxidation resistance and corrosion resistance, and the combination of the aluminum, the chromium and the silicon can obviously improve the high-temperature non-peeling performance and the high-temperature corrosion resistance of the steel. Aluminum has the disadvantage of affecting the hot workability, weldability and machinability of the steel.

The vanadium has strong affinity with carbon, ammonia and oxygen, and is easy to form corresponding stable compounds. Vanadium is mainly present in steel in the form of carbides, and its main function is to refine the structure and grains of the steel, reducing the strength and toughness of the steel.

The cast steel material adopted by the existing mining machinery is ZG40CrNiMo, the chemical composition of the cast steel material is shown in Table 1, and the mechanical property of the cast steel material is shown in Table 2.

Table 1: chemical composition of ZG40CrNiMo

The carbon equivalent CE of the steel, CE + C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15, is 0.85%.

Table 2: mechanical properties of ZG40CrNiMo

The inventor analyzes to obtain: the content of S, P, Cu and other impurity elements in ZG40CrNiMo does not reach the standard of high-quality steel (GB/T3077), the phenomenon of hot brittleness, cold brittleness and the like of the material is easily caused when the impurity elements exceed the standard, the processing, welding and heat treatment of parts are influenced, the carbon equivalent is 0.85%, and the welding performance is very poor. Based on the above influence factors, the inventor adjusts appropriate equivalent of alloy elements, so as to reduce carbon equivalent and greatly improve welding performance while ensuring better comprehensive strength. On the premise of not increasing the cost, the content of elements such as S, P, Cu, Cr, Ni and the like is reduced as much as possible, the nickel content is greatly reduced, the risk of heat treatment cracks is greatly reduced, the heat treatment performance of the material is improved, and the heat treatment performance is easy to realize. Meanwhile, the contents of Mo, Mn and other elements are properly increased, and the mechanical property and the welding property of the material are ensured to the maximum extent.

Preferably, the formula comprises the following components in percentage by weight:

0.32% of C, 0.8% of Mn0.38% of Si, 0.021% of P, 0.016% of S, 0.55% of Cr0.55%, 0.24% of Mo0.76% of Ni0.03%, 0.06% of Cu0.028% and the balance of Fe.

The invention also provides a casting method of the novel cast steel material, which comprises the following steps:

s1, melting: adding the scrap steel into an electric arc furnace to be melted into molten steel, detecting the contents of nickel and molybdenum in a molten steel sample, and adding nickel and molybdenum alloys calculated according to the weight percentage;

s2, oxidation: blowing oxygen for decarburization, continuously discharging slag and making new slag in the decarburization process, sampling and detecting C, P content, and stopping blowing oxygen when the content of oxidized P is less than 0.03% and the content of C is 0.3-0.4%;

s3, decarburization: the method comprises the following steps of (1) transferring molten steel from an electric arc furnace to an AOD furnace for smelting by using a cradle, blowing oxygen for decarburization by using inert gas, adding aluminum alloy according to weight percentage, uniformly stirring, sampling and detecting the content of C, and stopping decarburization when the content of C is 0.25-0.32%;

s4, reduction: according to the weight percentage, manganese alloy, silicon alloy, chromium alloy and vanadium alloy are sequentially added, the mixture is uniformly stirred to obtain molten steel, and the molten steel is discharged from a furnace and stands in a bottom pouring steel ladle to be poured into a casting;

s5, heat treatment: and (3) sequentially carrying out high-temperature normalizing, primary tempering, quenching and secondary tempering on the casting to obtain the steel.

Preferably, in step S1, the chromium content in the scrap steel is not more than 0.30%, the copper content is not more than 0.20%, and the carbon content is more than 0.50%.

Preferably, in step S2, a pre-reduction treatment is performed after the oxidation in the electric arc furnace, when the temperature of the molten steel reaches more than 1580 ℃, the oxidized slag in the electric arc furnace is removed, 0.20-0.30% ferrosilicon is added to reduce and produce thin slag, and when the temperature reaches more than 1650 ℃, the slag is removed completely.

Preferably, in step S3, when the cradle is used to transfer the molten steel from the electric arc furnace to the AOD furnace for smelting, the cradle is baked for at least 1 hour, and the AOD furnace uses argon as the inert gas during decarburization.

Preferably, in step S4, before the AOD furnace is reduced, slag flowing treatment is performed, and before the molten steel is tapped, chemical components of the molten steel are adjusted according to the weight percentage of the formula components according to the molten steel detection result, and the tapping temperature of the molten steel is 1600-.

Preferably, in step S5, the high-temperature normalizing temperature is 880-.

Preferably, the heating and heat-preserving time of the high-temperature normalizing and quenching is calculated according to the effective thickness of the casting by 0.5h/inch, the heat-preserving time of the first tempering and the second tempering is 1.5-2 times of the heating and heat-preserving time of the high-temperature normalizing and quenching when the effective thickness of the casting is less than 1 h.

The invention has the beneficial effects that:

by adjusting the alloy elements with proper equivalent, the comprehensive strength is ensured to be better ensured, the carbon equivalent is reduced, and the welding performance is greatly improved. On the premise of not increasing the cost, the contents of elements such as S, P, Cu, Cr, Ni and the like are reduced as much as possible, meanwhile, the contents of elements such as Mo, Mn and the like are properly increased, and the mechanical property and the welding property of the material are ensured to the maximum extent.

Drawings

FIG. 1 is a diagram of a metallographic structure of a casting, namely tempered sorbite, according to a first embodiment of the invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The first embodiment is as follows:

a casting method of a novel cast steel material comprises the following steps:

firstly, 1880Kg of dry, oil-free and rust-less Q235 steel plate (Cr0.28 percent and Cu0.06 percent) leftover materials are selected to be smelted in an electric arc furnace matched with the weight of parts (2 tons), when the scrap steel is smelted and the temperature is 1537 ℃, a sample No. 1 is taken, and 0.45 percent of C, 0.22 percent of Ni0.06 percent of Mo0.06 percent of P and 5Kg of electrolytic nickel and FeMo60-A ferromolybdenum alloy are added.

And secondly, blowing oxygen for decarburization, continuously discharging slag and making new slag in the decarburization process, observing flame and furnace atmosphere, taking a No. 2 sample, and measuring C0.29%, Ni0.79%, Mo0.25% and P0.009%. When the temperature is measured to 1593 ℃, FeSi75A10.5-A ferrosilicon 5Kg alloy is added for pre-reduction, the temperature is continuously raised, and when the temperature reaches 1673 ℃, the slag is removed completely.

And thirdly, transferring the mixture into a shaking ladle which is required to have no residual steel and residue, and baking for 1.5 hours. Transferring the molten steel into a 2-ton AOD furnace, measuring the temperature at 1523 ℃, adding 11Kg of aluminum ingot, heating, and adding O: ar is 3: 1, blowing oxygen for decarburization, taking a No. 3 sample after blowing, and measuring 0.28 percent of C, 0.01 percent of Si, 0.15 percent of Mn, 0.015 percent of P, 0.013 percent of S, 0.17 percent of Cr0.17 percent of Ni, 0.78 percent of Mo, 0.25 percent of Cu, 0.06 percent of V and 0.007 percent of V, wherein the content of C is at the lower limit, and slag flows downwards in a furnace body.

Adding 29Kg of FeMn78CO.2 ferromanganese, 10Kg of FeSi75A10.5-A ferrosilicon, 6Kg of FeCr55CO.25 ferrochrome and 43Kg of lime, shaking up the furnace body and stirring for 5 minutes, pouring the furnace to measure the temperature to 1633 ℃, taking a No. 4 sample, measuring C0.3%, Si 0.38%, Mn 1.15%, Cr 0.55%, Ni 0.76%, Mo 0.27%, P0.021%, S0.016% and Cu 0.04%, adding 1Kg of FeV50-A ferrovanadium, shaking up the furnace body and stirring for 1 minute, taking a No. 5 sample, measuring C0.32%, Si 0.38%, Mn 0.8%, Cr 0.55%, Ni 0.76%, Mo24%, P0.021%, S0.016%, V0.02%, Cu 0.04% and Al 0.03%, and balancing Fe, pouring the rest until the bottom pouring, measuring the temperature, aligning with a pouring area, pouring the casting, and standing for 5 minutes.

And finally, performing heat treatment on the casting by adopting a trolley type resistance furnace model RT3-1020-6, and specifically, sequentially performing high-temperature normalizing, primary tempering, cleaning, ultrasonic flaw detection, rough machining, quenching and tempering treatment (quenching and secondary tempering treatment), ultrasonic flaw detection, magnetic particle flaw detection, cleaning, rust prevention, packaging and warehousing on the casting. Wherein the high-temperature normalizing temperature is 880-: the special medium/oil is adopted, the secondary tempering temperature is 620 +/-10 ℃, the heat preservation time is 9 hours, the casting hardness requirement is 269-321HB, the heating and heat preservation time of the high-temperature normalizing and quenching is calculated according to the effective thickness of the casting by 0.5h/inch, the heat preservation time of the primary tempering and the secondary tempering is 1.5-2 times of the heating and heat preservation time of the high-temperature normalizing and quenching when the heating and heat preservation time is less than 1 h.

The casting material prepared in this example was named XYZ-M1, and its mechanical properties are shown in Table 3. The XYZ-M1 material is subjected to heat treatment to obtain a metallographic structure of a casting, namely tempered sorbite, as shown in figure 1.

Table 3: XYZ-M1 mechanical property

Compared with table 2, the cast steel material prepared in this example has better strength, wear resistance and toughness. That is, the present invention can ensure good toughness and improve heat treatability while ensuring strength and hardness.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims

1. The cast steel material is characterized by comprising the following formula components in percentage by weight:

the carbon equivalent is CE, and CE is C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15 is less than or equal to 0.72 percent;

the novel cast steel material is obtained by the following casting method:

s5, heat treatment: sequentially carrying out high-temperature normalizing, primary tempering, quenching and secondary tempering on the casting;

the high-temperature normalizing temperature is 880-.

2. The cast steel material according to claim 1, comprising the following formulation components in weight percent:

3. The cast steel material as claimed in claim 1 or 2, wherein in step S1, the chromium content in the scrap is not more than 0.30%, the copper content is not more than 0.20%, and the carbon content is more than 0.50%.

4. The cast steel material as claimed in claim 3, wherein in step S2, after the electric arc furnace is oxidized, the electric arc furnace is pre-reduced, when the temperature of the molten steel reaches more than 1580 ℃, the oxidized slag in the electric arc furnace is removed, 0.20-0.30% ferrosilicon is added to reduce and produce rarefied slag, and when the temperature reaches more than 1650 ℃, the slag is removed completely.

5. The cast steel material as claimed in claim 4, wherein in step S3, the cradle is baked for at least 1h while the cradle is used to transfer the molten steel from the electric arc furnace to the AOD furnace for smelting, and the AOD furnace uses argon as the inert gas for decarburization.

6. The cast steel material as claimed in claim 5, wherein in step S4, the chemical composition of the molten steel is adjusted according to the weight percentage of the formulation components based on the result of the molten steel detection before tapping the molten steel, and the tapping temperature of the molten steel is 1600-.

7. The cast steel material as claimed in claim 6, wherein the holding time for the high-temperature normalizing and quenching is 0.5h/inch in terms of the effective thickness of the cast, and the holding time for the first tempering and the second tempering is 1.5 to 2 times the holding time for the high-temperature normalizing and quenching.