Steel casting heat treatment process

Abstract

The invention discloses a steel casting heat treatment process which comprises the following steps: step 1, heating a steel casting to a complete austenitizing temperature (30-50 DEG C above Ac3), and preserving heat; secondly, the austenitized steel casting is discharged out of the furnace, an aqueous solution quenching mode is adopted, the steel casting is rapidly cooled, and the steel casting is rapidly cooled through an aqueous solution, taken out and left to stand till the steel casting is cooled to the room temperature; and thirdly, the cooled steel casting is subjected to high-temperature tempering at the temperature of 500-650 DEG C, and heat preservation is conducted. The steel casting is subjected to heat treatment by adopting annealing, quenching and tempering processes, and barium hydroxide is added in the aqueous solution in the quenching process step, so that the cooling capacity of the aqueous solution can be improved, and the problem of corrosion of the steel casting does not need to be worried about.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cast steel heat treatment, in particular to a cast steel heat treatment process. BACKGROUND

[0002] The heat treatment of steel is a process method of heating, holding and cooling steel in solid state in a proper way to change its internal organization so as to obtain the required performance. Through heat treatment, the defects in the part blanks (such as castings, forgings, etc.) can be eliminated, the processing performance of the steel can be improved, and more importantly, the mechanical properties of the steel can be significantly improved, the potential of the steel can be fully utilized, the production cost can be saved, the use performance of the part can be improved, and the service life of the product can be prolonged. Therefore, heat treatment occupies a very important position in mechanical manufacturing.

[0003] The quenching process in the existing heat treatment step often uses water or oil immersion as the quenching medium. In order to improve the cooling effect of water, salt or alkali is added to the water to improve the cooling effect. However, the liquid with added salt or alkali is easy to rust the steel parts, and rust marks are easy to occur in some areas once not cleaned properly. SUMMARY

[0004] According to the above-mentioned technical problems to be solved, a cast steel heat treatment process is provided.

[0005] To achieve the above-mentioned purpose, in a preferred embodiment, the present application is configured to include the following steps: step one, heating the cast steel to a complete austenitizing temperature (Ac3 above 30-50℃), and then holding;

[0006] Step two, taking the austenitized cast steel out of the furnace, and using water solution quenching method to rapidly cool the cast steel, and then standing after taking out by water solution rapid cooling until cooling to room temperature;

[0007] Step three, high temperature tempering the cooled cast steel at 500-650℃, and holding.

[0008] In a preferred embodiment, the present application can be further configured that the holding time in the holding is the maximum wall thickness of the cast steel multiplied by the holding coefficient, wherein the holding coefficient is 0.5min / mm-1.5min / mm.

[0009] In a preferred embodiment, the present application can be further configured that in step one, the cast steel is heated to an austenitizing temperature of 850℃, and then held, and the holding coefficient is 0.8min / mm.

[0010] In a preferred embodiment, the present application can be further configured that in step two, the cooling speed of the water solution is 80℃ / min-120℃ / min, and then room temperature natural cooling is performed below 300℃.

[0011] In a preferred embodiment of the present application, the cooling speed of the water solution in step two is 115℃ / min.

[0012] In a preferred embodiment of the present application, the cooled cast steel piece is tempered at a high temperature of 630℃ in step three, and is kept for a certain time, and the holding time is the maximum wall thickness of the cast steel piece multiplied by a holding coefficient, wherein the holding coefficient is 0.8 min / mm.

[0013] In a preferred embodiment of the present application, the water solution in step two is barium hydroxide and water, and sulfuric acid is added after the cooling of the cast steel piece in the water solution is completed, and the sulfuric acid preferentially reacts with the barium hydroxide, and the reaction equation is H2SO4+Ba(OH)2=BaSO4↓+2H2O, and finally the cast steel piece is taken out.

[0014] In a preferred embodiment of the present application, the concentration of the barium hydroxide is the same as the concentration of the sulfuric acid, and the volume of the barium hydroxide is the same as the volume of the sulfuric acid.

[0015] Beneficial effects, the cast steel piece heat treatment process of the present application adopts annealing, quenching and tempering process to heat treat the cast steel piece, and hydrogen

[0016] oxide barium is added in the water solution in the quenching process step, which can increase the cooling capacity of the water solution, and there is no need to worry about the corrosion problem of the cast steel piece. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0018] A cast steel piece heat treatment process comprises the following steps: step one, heating the cast steel piece to a complete austenitizing temperature (Ac3 above 30-50℃) and keeping for a certain time; step two, taking out the austenitized cast steel piece and rapidly cooling the cast steel piece by using a water solution quenching method, and then standing until the cooling to room temperature; step three, tempering the cooled cast steel piece at a high temperature of 500-650℃ and keeping for a certain time.

[0019] The holding time in the keeping is the maximum wall thickness of the cast steel piece multiplied by a holding coefficient, wherein the holding coefficient is 0.5 min / mm-1.5 min / mm, and the thickest part is taken as the reference, which can ensure that the temperature penetration of the whole steel piece reaches the maximum and reduces the low-temperature non-penetrating area.

[0020] In step one, the cast steel piece is heated to an austenitizing temperature of 850 DEG C and then is kept at this temperature, the holding coefficient is 0.8 min / mm, the temperature is the temperature range of full annealing, so as to obtain the heat treatment process effect of the nearly balanced structure.

[0021] In step two, the cooling speed of the water solution is 80 DEG C / min-120 DEG C / min, until 300 DEG C or below, then the natural cooling at room temperature is carried out, the cooling speed of the water solution in step two is 115 DEG C / min, the purpose of quenching is to obtain the martensite structure, and the undercooling austenite has different incubation periods at different temperatures, so the cooling speed and the temperature are required.

[0022] In step three, the cooled cast steel piece is tempered at a high temperature of 630 DEG C and is kept at this temperature, the holding coefficient is 0.8 min / mm, after quenching, the hardness and the plasticity can be improved, and the internal stress can be eliminated.

[0023] In step two, the water solution is barium hydroxide and water, when the cooling of the cast steel piece in the water solution is finished, sulfuric acid is added, the sulfuric acid preferentially reacts with the barium hydroxide, the reaction equation is H2SO4+Ba(OH)2=BaSO4↓+2H2O, finally the cast steel piece is taken out, the concentration of the barium hydroxide is the same as the concentration of the sulfuric acid, and the volume of the two is also the same, in order to increase the cooling effect of the water medium, the barium hydroxide is increased, but if the steel piece is not cleaned in the later period, rust is easily produced, therefore, after the steel piece enters the mixed solution of water and barium hydroxide, a certain amount of sulfuric acid is added, because the priority of the acid-base neutralization reaction is higher than that of the displacement reaction of the metal and the acid, the sulfuric acid preferentially reacts with the barium hydroxide, so it is not necessary to worry about the rust on the surface of the steel piece caused by the residual material, only the water on the surface of the steel piece needs to be dried.

[0024] It should be noted that, in the present document, relational terms such as first and second and the like can be used solely to distinguish one entity from another entity without necessarily requiring or implying any actual such relationship or order between or among these entities.

[0025] The above examples are only illustrative of the present application, and do not constitute a limitation on the protection scope of the present application, any design same as or similar to the present application belongs to the protection scope of the present application.

Claims

1. A heat treatment process for cast steel parts, characterized in that... Includes the following steps: Step 1: Heat the cast steel part to the temperature of full austenitization (30-50℃ above Ac3) and then hold it at that temperature; Step 2: Remove the austenitized cast steel parts from the furnace and use an aqueous solution quenching method to rapidly cool the cast steel parts. After being rapidly cooled by the aqueous solution, let them stand until they cool to room temperature. Step 3: Temper the cooled cast steel parts at a high temperature of 500-650℃ and keep them at that temperature.

2. The heat treatment process for cast steel parts according to claim 1, characterized in that, The heat preservation time is the maximum wall thickness of the cast steel part multiplied by the heat preservation coefficient, where the heat preservation coefficient is 0.5 min / mm-1.5 min / mm.

3. The heat treatment process for cast steel parts according to claim 2, characterized in that, In step one, the cast steel part is heated to the austenitizing temperature of 850℃ and then held at that temperature with a holding coefficient of 0.8 min / mm.

4. The heat treatment process for cast steel parts according to claim 3, characterized in that, In step two, the cooling rate of the aqueous solution is 80℃ / min-120℃ / min until it drops below 300℃, at which point it is allowed to cool naturally to room temperature.

5. The heat treatment process for cast steel parts according to claim 4, characterized in that, In step two, the cooling rate of the aqueous solution is 115℃ / min.

6. The heat treatment process for cast steel parts according to claim 5, characterized in that, In step three, the cooled cast steel parts are tempered at a high temperature of 630℃ and held at that temperature with a holding coefficient of 0.8 min / mm.

7. The heat treatment process for cast steel parts according to claim 1, characterized in that, In step two, the aqueous solution is barium hydroxide and water. After the cast steel part is placed in the aqueous solution and cooled, sulfuric acid is added. The sulfuric acid preferentially reacts with the barium hydroxide to neutralize it. The reaction equation is H2SO4 + Ba(OH)2 = BaSO4↓ + 2H2O. Finally, the cast steel part is taken out.

8. The heat treatment process for cast steel parts according to claim 7, characterized in that, The concentration of barium hydroxide is the same as that of sulfuric acid, and their volumes are also the same.