Production method of quenching-free surface hardening wire rod for motor shaft

Abstract

The application relates to a production method of a motor shaft free-conditioning surface hardening wire rod, and the chemical composition of the steel is as follows: C=0.38%-0.42%, Si=0.10%-0.35%, Mn=0.60%-0.80%, P<=0.020%, S<=0.008%, Cr=0.9%-1.1%, and the rest is Fe and inevitable impurities. The wire rod is produced by adopting the process flow of converter-LF-RH-continuous casting-rolling. The wire rod is on-line water-penetrated in the hot rolling process, the surface is quenched, and the wire rod is self-tempered through the residual heat. The produced wire rod has high surface hardness and good plasticity in the core, after being drawn by the customer, the wire rod is cold extruded to reach the required part shape, the surface hardness of the part can meet the requirements, the quenching and tempering process is free, the production efficiency can be remarkably improved, and the production cost can be saved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy, and relates to a production method of a new energy motor shaft surface hardening wire rod without quenching and tempering. BACKGROUND

[0002] The motor shaft generally has the characteristics of high rotating speed, frequent starting and easy temperature rise during work. Reasonable selection of materials and processing technology according to the working condition can achieve the effect of good quality and low cost, and double the result with half the effort. With the vigorous development of the new energy related industry of the country, the types and quantities of electric motors are also increasing. The medium carbon steel is generally used to manufacture the motor shaft of small electric motors, and the quenching and tempering process is adopted. The surface hardness of the motor shaft is required to be higher than 23HRC. At present, the motor shaft of small electric motors is produced by adopting the process flow of bar material- blanking- turning- quenching and tempering- inspection. The traditional production process has a long production flow, large metal material loss, and needs quenching and tempering, and has large energy consumption.

[0003] How to use the existing production equipment of the factory to produce the motor shaft wire rod with high surface hardness and good plasticity in the core, so that the customer can draw and then perform cold extrusion deformation to achieve the required part shape, and the surface hardness of the part can meet the requirements. The production process is required to be simple, the metal loss is reduced, and the quenching and tempering process is avoided, so as to improve the production efficiency and save the production cost. SUMMARY

[0004] The purpose of the application is to provide a production method of a motor shaft surface hardening wire rod without quenching and tempering, which can be directly drawn to the target size, formed into a motor shaft by cold extrusion, has qualified surface hardness and good comprehensive performance.

[0005] The technical scheme of the application is as follows:

[0006] A production method of a motor shaft surface hardening wire rod without quenching and tempering, the chemical composition of the steel is as follows: C=0.38%-0.42%, Si=0.10%-0.35%, Mn=0.60%-0.80%, P≤0.020%, S≤0.008%, Cr=0.9%-1.1%, and the rest is Fe and inevitable impurities. The process flow of a converter-LF-RH-continuous casting-rolling is adopted for production, and the process steps are as follows:

[0007] (1) Converter: the end point control is P≤0.010% and C≥0.10%;

[0008] (2) LF: Al particles are used for diffusion deoxidization, so that the LF refining slag is white, and the residual aluminum content is Al≥0.010%;

[0009] (3) RH: vacuum degassing is performed, the vacuum time is ≥8min, Ar gas is blown after the vacuum is broken, and the soft blowing time is ≥10min;

[0010] (4) continuous casting: using a drawing speed of 1-1.1 m / min, a low secondary cooling water ratio of 0.19-0.21 L / kg, controlling the corner straightening temperature of the billet to be greater than or equal to 900 DEG C, and the billet entering the slow cooling pit for greater than or equal to 24 hours;

[0011] (5) rolling: the soaking section temperature is 1150 DEG C + / - 20 DEG C, the post-furnace descaling pressure is not less than 15 MPa, the entry temperature of the finish rolling is 850 DEG C + / - 20 DEG C, post-finish rolling water tank cooling is used, and the coiling temperature is 700 DEG C + / - 20 DEG C.

[0012] Inventive principle:

[0013] Step (1) in the converter, the end point C content is greater than or equal to 0.10%, to ensure that the molten steel is not oxidized, reduce the generation of inclusions in the steel, ensure the purity of the molten steel, and improve the internal quality of the steel.

[0014] Step (2) in the LF, Al particles are used for diffusion deoxidation, the LF refining slag is white, and a certain residual Al content is ensured; Al can refine the grains and improve the plasticity of the steel, to ensure the processing performance of the steel in the subsequent cold extrusion process.

[0015] Step (3) in the RH, vacuum degassing is used, the vacuum time is kept for greater than or equal to 8 min, Ar gas is blown after the vacuum is broken, and the soft blowing time is greater than or equal to 10 min; the vacuum time can reduce the hydrogen content in the steel to below 2 ppm, can improve the purity of the steel, and reduce the risk of hydrogen-induced cracking of the steel during long-term use.

[0016] Step (4) in the continuous casting, a drawing speed of 1 m / min is used, a low secondary cooling water ratio is used, the corner straightening temperature of the billet is controlled to be greater than or equal to 900 DEG C, and the billet enters the slow cooling pit for greater than or equal to 24 hours, which has the effect of using a high drawing speed and a low secondary cooling water ratio to ensure the straightening temperature of the billet, to prevent cracks from occurring on the surface of the billet. The billet is slowly cooled to release the hydrogen content in the steel, to reduce the probability of surface cracks of the steel.

[0017] Step (5) in the rolling, the soaking section temperature is 1150 DEG C + / - 20 DEG C, the post-furnace descaling pressure is not less than 15 MPa, the entry temperature of the finish rolling is 850 DEG C + / - 20 DEG C, post-finish rolling water tank cooling is used, and the coiling temperature is 700 DEG C + / - 20 DEG C. The strong post-rolling water penetration process is used to form a 1 mm or so chilled tempering layer on the surface of the steel, and the hardness of the tempering layer can be up to 22 HRC.

[0018] The advantages of the application are that the surface is quenched during the hot rolling process, and the surface is self-tempered through the residual heat. The surface hardness of the produced rod is high, the core has good plasticity, the customer can draw and then cold extrude to deform to achieve the required part shape, and the surface hardness of the part can meet the requirements. This innovative production process greatly reduces metal loss and eliminates the quenching and tempering process, which can significantly improve the production efficiency and save production costs. DETAILED DESCRIPTION

[0019] The application will be further described in connection with the following examples. Example 1

[0020] A production method of a quenching-free surface hardened wire rod for motor shafts is produced according to a process flow of converter-LF-RH-continuous casting-rolling, and the rolling specification is Φ23 mm. The chemical composition of the steel is as follows: C=0.41%, Si=0.23%, Mn=0.78%, P=0.010%, S=0.003%, Cr=1.08%, and the rest is Fe and inevitable impurities. The production process steps are as follows:

[0021] (1) Converter: the end point P content is 0.009%, and the C content is 0.15%;

[0022] (2) LF: Al particles are used for diffusion deoxidation, white slag is formed in LF, the white slag preservation time is 20 min, and the Al content of the steel grade is 0.020%;

[0023] (3) RH: vacuum degassing, the vacuum holding time is ≥8 min, Ar gas is blown after breaking the vacuum, and the soft blowing time is ≥10 min;

[0024] (4) Continuous casting: the casting speed is 1 m / min, the secondary cooling water ratio is 0.2 L / kg, the corner straightening temperature of the billet is 920 degrees, and the casting billet enters the slow cooling pit for 32 hours;

[0025] (5) Rolling: the soaking temperature is 1150-1160℃, the descaling pressure after the furnace is 15 Mpa, the entry temperature of the finish rolling is 850-860℃, the cooling is carried out in the water tank after the finish rolling, and the coiling temperature is 700-710℃. Example 2

[0026] A production method of a quenching-free surface hardened wire rod for motor shafts is produced according to a process flow of converter-LF-RH-continuous casting-rolling, and the rolling specification is Φ23 mm. The chemical composition of the steel is as follows: C=0.42%, Si=0.25%, Mn=0.77%, P=0.012%, S=0.005%, Cr=1.06%, and the rest is Fe and inevitable impurities. The production process is as follows:

[0027] (1) Converter: the end point P content is 0.009%, and the C content is 0.16%;

[0028] (2) LF: Al particles are used for diffusion deoxidation, white slag is formed in LF, the white slag preservation time is 20 min, and the Al content of the steel grade is 0.024%;

[0029] (3) RH: vacuum degassing, vacuum holding time≥8 min, soft blowing Ar gas after breaking vacuum, soft blowing time≥10 min;

[0030] (4) Continuous casting: using 1 m / min of casting speed, 0.2 L / kg of secondary cooling water ratio, 910 degrees of corner straightening temperature of billet, 35 hours of entering slow cooling pit of casting billet;

[0031] (5) Rolling: 1150-1170℃ of soaking temperature, 15 Mpa of descaling pressure after furnace, 850-860℃ of entering finishing rolling temperature, entering water tank cooling after finishing rolling, 700-710℃ of coiling temperature.

[0032] The surface hardness detection results of the free-adjusted quenching and tempering surface hardened wire rod for motor shaft produced by the examples are shown in Table 1.

[0033] Table 1 Surface hardness of free-adjusted quenching and tempering surface hardened wire rod for motor shaft

[0034] .

[0035] The customer requires that the surface hardness of the part after being drawn reaches 23HRC or above. The surface hardness of the free-adjusted quenching and tempering surface hardened wire rod obtained by the above examples increases by 2-3HRC after being drawn, and can completely meet the requirement that the surface hardness of the finished product reaches 23HRC or above.

Claims

1. A process for producing a quenching-free surface hardened wire rod for motor shafts, characterized by: The steel has a chemical composition in weight percent of C=0.38%~0.42%, Si=0.10%~0.35%, Mn=0.60%~0.80%, P≤0.020%, S≤0.008%, Cr=0.9%~1.1%, and the rest is Fe and inevitable impurities; the process steps include: (1) converter: end point control P≤0.010%, C≥0.10%; (2) LF: using Al particles for diffusion deoxidation, making the LF refining slag white, and keeping the residual aluminum content Al≥0.010%; (3) RH: vacuum degassing, keeping the vacuum time≥8min, after breaking the vacuum, blowing Ar gas, and soft blowing time≥10min; (4) continuous casting: using a casting speed of 1~1.1m / min, a low secondary cooling water ratio of 0.19~0.21L / kg, controlling the corner straightening temperature of the billet≥900℃, and the casting billet entering the slow cooling pit≥24 hours; (5) rolling: the soaking section temperature is 1150±20℃, the post-furnace descaling pressure is not less than 15MPa, the entry temperature of the finishing rolling is 850±20℃, after the finishing rolling, entering the water tank cooling, and the coiling temperature is 700±20℃.