A high performance heat treatment process for pick body

Abstract

The invention discloses a high-strength steel for high-performance pick and a heat treatment process thereof. Through a heat treatment process different from conventional quenching and tempering, the impact toughness of the alloy steel is significantly improved without reducing the strength, and the impact toughness is improved from Aku55J-65J in the quenching and tempering process to Aku85J-95J, and the performance is stable. The heat treatment process of the pick body after die forging is as follows: normalizing by heating at 800°C, then heating to 920°C and keeping the temperature for 20 minutes, then keeping the temperature in a salt bath furnace at 260°C for 5 minutes, then air cooling to room temperature, then sending it into a roller furnace for tempering at 260°C for 2 hours, and air cooling after tempering. Compared with the existing national standard (the impact energy of the pick body is greater than Aku40J, and the hardness is greater than HRC38), the high-strength steel and heat treatment process provided by the present invention can greatly improve the performance of the pick body (the impact energy of the pick body is greater than Aku85J, and the hardness is greater than HRC51). The provided high-strength steel pick body fundamentally solves the problems of low impact toughness value and low hardness of existing picks, easy fracture and poor wear resistance when cutting hard rock.

Description

Technical field:

[0001] The invention relates to the technical field of manufacturing picks for coal mining, and in particular to high-strength steel for high-performance picks and a heat treatment process thereof. Background technology:

[0002] The pick is a key component for directly cutting coal and rock on the fully mechanized mining unit in the coal industry. The pick is composed of a carbide tooth tip embedded in the concave hole of the alloy steel pick body head and fixed by brazing. The failure of the pick is manifested as the carbide tooth tip falling off, the tooth tip breaking, the tooth body bending or breaking after the head of the pick body is worn. Among them, the failure of the tooth tip falling off caused by the wear of the head of the pick body accounts for about 85% of all failure forms. The reason for the falling off is that during the mining process, the entire pick extends into the coal mine layer, and the front end of the tooth body is subjected to strong friction from the ore and rock layer. The pick body is not wear-resistant enough, and the carbide tooth tip falls off prematurely, causing the entire pick to be damaged and fail prematurely.

[0003] In order to increase the service life of the pick, the surface of the pick must first be sufficiently resistant to wear, corrosion and impact. And with the increase in the power of coal mining machines, the pick is required to have higher strength and impact resistance. Therefore, a high-performance high-strength steel for the pick is developed, and a special heat treatment technology is used to significantly increase the impact energy of the high-strength steel to more than twice the national standard without reducing the strength, thereby extending the service life of the pick.

[0004] Chinese invention patent CN95112052.2 discloses a composite process for medium frequency welding and quenching of coal mining machine picks in one step. The pick tooth body is placed in the copper coil of the medium frequency induction heating equipment for medium frequency heating and welding of the carbide cutter head. The welded tooth body with the carbide cutter head is then directly placed in a nitrate bath at 260-290°C for quenching and cooling, thereby completing the welding and quenching composite process in one step.

[0005] For example, Chinese invention patent CN201210425945.9 discloses a method for producing coal mining machine picks, which comprises welding the picks and the tooth heads together by induction heating, (1) matching the tooth body hole with the tooth head; (2) successively entering the heating zone of the inductor; (3) when the picks enter the welding zone of the inductor, first sprinkle borax on the alloy tooth head, and after the copper melts, gently shake the alloy so that the copper liquid fills the area around the weld; (4) isothermal heat treatment, the temperature of the isothermal bath is controlled at 230°C to 270°C, the welded picks are immersed in the salt solution of the isothermal bath, and water is supplied to cool down when the temperature reaches 265°C, and it is ensured that the temperature of the isothermal bath is not less than 230°C after adding water; (5) the picks are kept in the isothermal bath at a constant temperature state with a change of no more than 20°C for not less than 30 minutes; (6) after the isothermal time is reached, the picks are lifted out of the liquid surface, and the product is quickly cleaned and cooled after being sprinkled with salt to obtain the product.

[0006] The main content of the above invention patent is that the material used for the pick body is 35CrMo or 42CrMo, and the heat treatment technology of the pick adopts the isothermal quenching process to obtain a bainite structure. The performance of the pick body is Aku40J and the hardness reaches HRC38. Although the impact energy can be improved by isothermal quenching technology, it is often accompanied by a decrease in hardness, and the purpose of simultaneously improving hardness and toughness is not achieved. Summary of the invention:

[0007] The object of the present invention is to provide a high-strength steel for high-performance pick and a heat treatment process thereof.

[0008] The present invention is implemented by the following technical solutions:

[0009] A high-strength steel for high-performance picks, wherein the chemical composition of the high-strength steel blank is as follows: carbon: 0.30%, silicon: 2.2%, manganese: 1.0%, chromium: 1.0%, molybdenum: 0.10%, nickel: 1.0%, sulfur: 0%-0.01%, phosphorus: 0%-0.01%, and the rest is Fe and unavoidable impurities.

[0010] A high performance pick heat treatment process, the process steps comprising:

[0011] Step 1: using the above-mentioned high-strength steel billet, the pick body is formed by warm extrusion, and the pick body is subjected to normalizing pretreatment, the heating temperature is 800°C, and the temperature is kept for 1 hour and then air-cooled;

[0012] Step 2: Heat the pick to 920°C, keep it warm for 20 minutes, immerse the pick in a salt bath at 260°C, keep it warm for 20 seconds, and then take it out of the furnace and air cool it;

[0013] Step 3: Perform secondary tempering on the pick after air cooling. The tempering temperature is 260℃ and the tempering time is 2h. After tempering, air cool to room temperature;

[0014] Step 4: Repeat the above tempering steps to complete the secondary tempering

[0015] By adopting the above process steps, the performance of the pick body reaches a tensile strength of 1750MPa, an impact energy greater than Aku85J, and a hardness greater than HRC51.

[0016] Advantages of the present invention:

[0017] 1. Unique alloy composition design: Silicon: 2.2%, Manganese: 1.0%, Nickel: 1.0%. Such a high silicon content increases the solid solution strengthening effect, inhibits the formation of carbides, and improves fatigue performance and impact energy; such a high manganese content increases the density of movable dislocations, improves plasticity and toughness; by adding nickel, the toughness is further improved, and the proportion of nickel and manganese is matched in a 1:1 ratio to obtain high impact energy.

[0018] 2. Unique heat treatment process: The pick body formed by warm extrusion has a large number of slender ferrite. The normalizing process of heating to 800℃ and keeping warm for 1h is adopted to eliminate the slender orientation defects of ferrite grains caused by warm extrusion and realize equiaxed grains. It lays the foundation for the pretreatment organization to stabilize and improve the impact energy.

[0019] 3. The process of keeping at 260℃ for 20s below Ms point and then cooling in air is adopted, so that part of austenite is first transformed into low-temperature bainite when keeping at 260℃, and the residual austenite structure is refined. The subsequent air cooling transforms the residual austenite into finer martensite or bainite.

[0020] 4. The pick body is made of new high-strength steel, which significantly improves the strength, toughness and hardness of the pick body. The tensile strength reaches 1750MPa, the impact energy reaches Aku85J or more, and the hardness reaches HRC51 or more.

[0021] 5. The hardness, strength and impact performance of the pick body can be greatly improved, especially the impact performance, which can be increased by 2 times, significantly avoiding the occurrence of pick body breakage. Specific implementation method:

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The present invention provides the following technical solution: a high-strength steel for high-performance picks, wherein the chemical composition mass percentage of the high-strength steel blank is: carbon: 0.30%, silicon: 2.2%, manganese: 1.0%, chromium: 1.0%, molybdenum: 0.10%, nickel: 1.0%, sulfur: 0% to 0.01%, phosphorus: 0% to 0.01%, and the rest is Fe and unavoidable impurities, and the composition range is controlled within the national standard deviation.

[0024] A high performance pick heat treatment process, the process steps comprising:

[0025] Step 1: The above-mentioned high-strength steel billet is used to form a pick body after warm extrusion. The pick body is subjected to normalizing pretreatment, the heating temperature is 800°C, and the pick body is air-cooled after being kept warm for 1 hour. This key heat treatment process can significantly eliminate the grain orientation defects caused by warm extrusion, realize grain equiaxing, significantly improve the impact energy, and stabilize the impact energy of the pick in a higher range;

[0026] Step 2: Heat the pick to 920°C, keep it warm for 20 minutes, immerse the pick in a salt bath at 260°C, keep it warm for 20 seconds, and then take it out of the furnace and air cool it;

[0027] Step 3: Perform secondary tempering on the pick after air cooling. The tempering temperature is 260℃ and the tempering time is 2h. After tempering, air cool to room temperature;

[0028] Step 4: Repeat the above tempering steps to complete the secondary tempering

[0029] By adopting the above process steps, the performance of the pick body reaches a tensile strength of 1750MPa, an impact energy greater than Aku85J, and a hardness greater than HRC51.

[0030] The working principle and use process of the present invention:

[0031] In Example 1, manganese: 1.0% and nickel: 1.0% are added, and a quenching and tempering process is adopted without a normalizing pretreatment process. The impact energy is Aku55J-65J, and HRC51-53.

[0032] Example 2 Based on the composition of the invention steel, a normalizing pretreatment process is adopted before quenching and tempering, and the impact energy of the pick body is increased from Aku55J-65J to between Aku75J-85, HRC52-55.

[0033] Example 3 adopts the process of pre-forming low-temperature bainite structure to refine the residual austenite transformation structure, that is, adopting the process of keeping at 260°C below Ms point for 20s and then air cooling, and the impact energy is increased from Aku75J-85J to Aku85J-95, HRC52-55.

[0034] The above processes are all followed by a secondary tempering step.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high performance pick body heat treatment process, characterized in that: The process steps include: step 1: using a high-strength steel billet, the chemical composition mass percentage of the high-strength steel billet is: carbon: 0.30%, silicon: 2.2%, manganese: 1.0%, chromium: 1.0%, molybdenum: 0.10%, nickel: 1.0%, sulfur: 0%-0.01%, phosphorus: 0%-0.01%, and the rest is Fe and unavoidable impurities, and the pick body is subjected to normalizing pretreatment after warm extrusion molding, the heating temperature is 800°C, and the pick body is air-cooled after being kept warm for 1 hour; step 2: using a high-strength steel billet, the chemical composition mass percentage of the high-strength steel billet is: carbon: 0.30%, silicon: 2.2%, manganese: 1.0%, chromium: 1.0%, molybdenum: 0.10%, nickel: 1.0%, sulfur: 0%-0.01%, phosphorus: 0%-0.01%, and the rest is Fe and unavoidable impurities, and the pick body is subjected to normalizing pretreatment after being heated to 800°C, and the pick body is air-cooled after being kept warm for 1 hour; step 3: Step 2: Heat the pick body to 920°C again, keep it warm for 20 minutes, immerse the pick body in a salt bath at 260°C, keep it warm for 20 seconds, and air-cool it after taking it out of the furnace; Step 3: Temper the air-cooled pick body; tempering temperature 260°C, tempering time 2h; air-cool to room temperature after tempering; Step 4: Repeat the above tempering steps to complete the secondary tempering; Using the above process steps, the performance of the pick body reaches a tensile strength of 1750MPa, an impact energy greater than Aku85J, and a hardness greater than HRC51.