JPH059767A - Treatment of steel pipe for bearing before pickling - Google Patents

Abstract

PURPOSE:To reduce the descaling time in pickling a steel pipe for the bearing after spheroidizing and to control the generation and depth of the pitting. CONSTITUTION:A steel pipe for the bearing is produced from the seamless steel pipe of high-carbon chromium bearing steel. In this case, a material to be treated spheroidized is extracted from a heat-treating furnace, rapidly cooled from 570-650 deg.C to 400 deg.C at the rate of >=1500 deg.C, then pickled and descaled. More than 60% of the scales are released by the rapid cooling after spheroidizing, hence the pickling time is reduced to 1/3 of that in the conventional process, and the generation and depth of the pitting are drastically reduced.

Description

Detailed Description of the Invention

[0001]

This invention relates to JIS G4805.
Descaling method after spheroidizing heat treatment of a steel tube for high carbon chromium bearings specified in the above.

[0002]

2. Description of the Related Art Bearings, for example, rolling bearings, are subjected to severe rolling loads for a long time during use. On the other hand, ring-shaped members such as an inner ring and an outer ring of a rolling bearing for machines are manufactured by cutting a seamless steel pipe and then quenching it. The inner ring and outer ring of rolling bearings made of high carbon chrome bearing steel specified in JIS G4805 are manufactured with a seamless steel pipe made of high carbon chrome bearing steel to ensure machinability, wear resistance and rolling life. Spheroidizing annealing is performed to give a microstructure in which fine spheroidized carbides are uniformly distributed, and then generally used for cutting.

The manufacturing process of the material used for the cutting process is
Generally, a seamless pipe made of high-carbon chromium bearing steel that is hot-rolled is subjected to spheroidizing annealing, and then cold-worked such as cold rolling or drawing to ensure the desired mechanical properties by annealing. is doing. Spheroidizing annealing of bearing steel pipe requires a long-time treatment in a direct-fire annealing furnace, but since it contains chromium, a tight spinel type scale is formed on the surface of the bearing steel pipe and is then pickled. Descaling was difficult.

Descaling, which is one of the pretreatments for cold working such as cold rolling or drawing of the bearing steel pipe after the spheroidizing annealing, is to prevent seizure of the die and plug during drawing work and to prevent surface defects of the steel pipe. This is a very important work such as surface activation for prevention and lubrication. As the descaling method, steel shot, steel grit, cut wire shot, etc. are applied to the steel pipe at high speed by applying pressure or centrifugal force to the steel pipe to remove or scale the shot blasting method, and at the same time straightening the steel pipe Mechanical methods such as bending roll method for removing mill scale and sulfuric acid pickling, ferrous oxide, ferric oxide and ferric oxide for removing ferrous oxide and ferric oxide as ferrous sulfate There are chemical methods such as acid pickling such as hydrochloric acid pickling, electrolytic pickling and the like for removing iron as ferrous chloride. In the case of a steel pipe for bearings, a pickling method is usually performed in order to facilitate descaling of the inner surface of the pipe and for efficiency.

[0005]

Among the descaling of the seamless pipe made of the high carbon chromium bearing steel which has been subjected to the above spheroidizing annealing, the descaling by shot blasting is inefficient because it is a treatment for each one. In addition, there is a drawback that shot grain pressing defects and cold working (drawing) problems are likely to occur. In addition, the descaling by the bending roll method has a drawback in that the scale may be pressed down by the roll. In the descaling by sulfuric acid pickling, hydrogen cannot penetrate into the tight spinel type scale, descaling is difficult, and dipping for 3 hours or more is required, so that pitching easily occurs. Further, when an acid solution such as hydrochloric acid is used as well as sulfuric acid, the temperature becomes high and the concentration becomes high, so environmental measures are required.

An object of the present invention is to provide a descaling method after spheroidizing heat treatment of a steel pipe for high carbon chromium bearings, which can shorten the descaling time by pickling the steel pipe for bearings and can suppress the pitching depth. ..

[0007]

[Means for Solving the Problems] The inventors of the present invention have conducted earnest research to achieve the above object. As a result, the seamless pipe made of high carbon chromium bearing steel was extracted from the heat-treated furnace after the spheroidizing annealing, and then rapidly cooled at a predetermined cooling rate from a predetermined temperature to a predetermined temperature and then pickled. By doing so, it was clarified that cracks are generated in the scale due to rapid cooling, and the subsequent pickling treatment can be carried out in a short time, and the present invention was reached.

That is, according to the present invention, a seamless steel pipe of high carbon chromium bearing steel is spheroidized and annealed, then pickled, descaled, and cold-worked. The extracted material to be treated is rapidly cooled from a temperature of 570 ° C. to 650 ° C. to 400 ° C. or less at a cooling rate of 1500 ° C./Hr or more, and then descaled by pickling.

[0009]

[Operation] When the material to be treated extracted from the heat treatment furnace after the spheroidizing annealing of the bearing steel pipe is rapidly cooled from the temperature of 570 ° C to 650 ° C to 400 ° C or less at the cooling rate of 1500 ° C / Hr or more, The scale generated on the surface of the material to be processed during pipe manufacturing and spheroidizing annealing has a different shrinkage rate from the base material, so cracks occur in the scale and peeling progresses. Then, by pickling and descaling, the scale peeling due to the generation of cracks promotes the reaction with sulfuric acid or hydrochloric acid, the pickling time can be shortened, and the occurrence of pitching can be suppressed.

In the present invention, the rapid cooling start temperature of the material to be treated extracted from the heat treatment furnace after the spheroidizing annealing is set to 570 ° C. or higher and 650 ° C. or lower because the cooling rate from the soaking temperature to 650 ° C. is 650 ° C. or higher. The pearlite transformation in which spheroidization is performed may not be completed, and 5
This is because if the temperature is 70 ° C. or lower, it is not possible to cool FeO, which has better peelability than Fe ₃ O ₄ . Rapid cooling end temperature 40
The reason why the temperature is 0 ° C. or less is that the supercooling curve of FeO has ended during continuous cooling. Also, the cooling rate is 1500 ℃
/ Hr or more is to prevent the transformation of FeO to Fe ₃ O ₄ .

According to the method of the present invention, about 60% or more of scale is peeled off by visual observation by rapid cooling of the material to be treated extracted from the heat treatment furnace after spheroidizing annealing, and the subsequent pickling treatment time is It can be shortened to 1/3. Further, the occurrence of pitching can be suppressed to the extent that it is scattered in a very shallow depth.

[0012]

[Example] A seamless steel pipe having a diameter of 63.5 mm and a wall thickness of 5.0 mm specified in JIS G4805 SUJ2 is used.
As shown in FIG. 1, after heating to 800 ° C. and holding for 2 hours, it was cooled to 700 ° C. at 40 ° C./Hr and then 770 again.
Heat to ℃, hold for 3 hours to soak, and heat at 6 ℃ at 20 ℃ / Hr.
After cooling to 00 ° C., as shown in Table 1, the cooling rate and the cooling end temperature were changed to perform rapid cooling, and then the scale peeling condition was visually observed. After the observation of the scale peeling condition, the sulfuric acid concentration was 10%, the liquid temperature was 50 ° C., and the material to be treated was immersed in a pickling tank for pickling treatment, and then the site where pitting occurred and the maximum depth were measured. The results are also shown in Table 1. For comparison, the cooling start temperature is 670 ° C,
Rapid cooling and pickling treatment were performed under the same conditions as above except that the temperature was 500 ° C. The results in that case are also shown in Table 1.
In Table 1, ◯ in the scale peeling status column is 60% or more peeling, Δ is 30 to 60% peeling, X is 30% or less peeling, the pitching depth column is in mm, and the spheroidizing structure column is * 1. Is
Surface lamella perlite generation is shown.

[0013]

[Table 1]

As shown in Table 1, the bearing steel pipe obtained by the method of the present invention has a better spheroidized structure and does not generate lamella pearlite, as compared with the bearing steel pipe of the comparative example in which the cooling start temperature is 670 ° C. The time required for pickling and the occurrence of pitting are almost the same. The cooling start temperature is 500 ° C.
Compared with the conventional steel pipe for bearings, the time required for pickling is shortened to about 1/3, and the occurrence of pitting occurs over the entire length.
While the maximum depth is 0.10 to 0.20 mm, the maximum depth is 0.05 mm when scattered.

[0015]

As described above, according to the method of the present invention, 60% or more of the scale of the bearing steel pipe after spheroidizing annealing can be peeled off and subjected to pickling treatment, and the pickling time can be reduced to 1 It has the advantage that it can be shortened to ⅓ and the site where pitching occurs and the depth can be greatly reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view showing spheroidizing annealing conditions of a steel pipe for bearing in an example.

Claims (1)

Claim: What is claimed is: 1. In the production of a bearing steel pipe in which a seamless steel pipe of high carbon chromium bearing steel is spheroidized and then acid-washed, descaled, and cold-worked, after spheroidizing and annealing. A bearing characterized in that a material to be treated extracted from a heat treatment furnace is rapidly cooled from a temperature of 570 ° C to 650 ° C to 400 ° C or less at a cooling rate of 1500 ° C / Hr or more, and then descaled by pickling. Pretreatment method for pickling steel pipes.