JPS6041131B2 - Rigid rotary sub-zero processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sub-zero treatment method, and particularly to a method suitable for sub-zero treatment large steel products such as rolling mill rolls.

When manufacturing steel products that require wear resistance, a heat treatment called quenching is generally applied.

Rolling mill rolls are often made by phosphorizing multistage steel.
The purpose of quenching is to transform the copper into martensitic structure, which is the hardest structure among all steels. However, it is not so easy to make the entire hardened layer have a single martensitic structure.

For example, in large articles such as rolling mill rolls, residual austenite is present inside the hardened layer because the cooling rate cannot be increased. Therefore, in such cases, after quenching is completed, an operation called SapZero treatment is performed to cool the quenched material to room temperature or below.

Sub-zero treatment must be performed immediately after quenching, otherwise austenite will be stabilized and martensitic formation will be less likely to occur. In order to convert residual austenite into martensite through sub-zero treatment, the cooling process is important. If the entire surface of the object to be treated is not cooled uniformly, some areas will remain that are not converted into martensite, resulting in uneven hardness. . Conventionally, sub-zero processing equipment has widely adopted a horizontal system in which the material to be processed is fixed horizontally and a cooling medium is swirled around it, and this has been considered common sense.

A mixture of alcohol and dry ice or carbon dioxide gas is usually used as the cooling medium. However, the best method for all of these methods is to cool the workpiece to -75°C, and for this reason, for objects with a diameter of 40 mm or more, the cooling rate becomes slow and the quenched layer is removed. It has the disadvantage that it cannot be sufficiently converted into martensitic material and a deep quenched hardened layer cannot be obtained. In addition, since the material to be treated is fixed, there is a drawback that the entire surface cannot be cooled to a uniform temperature. In order to uniformly cool the entire surface of the object, it is sufficient to rotate the object, but in order to do this, a driving pupil must be built into the container that houses the object. As the container becomes larger, a large amount of cooling medium is required.

In addition, as the size of the container increases, the cooling time becomes longer, so that stabilization of austenite is more likely to occur, and there is a fear that it will become martensite. However, it is extremely difficult to provide a drive device for the object to be processed outside the container in terms of manufacturing a sub-zero processing device.

For the reasons mentioned above, it was not suitable for converting the large steel products of the conventional square-shaped Sapzero processing equipment into martensitic material.

Furthermore, when a large steel product such as a rolling mill roll is intentionally cooled using conventional equipment, there is a problem in that some parts are not converted to martensite, and destruction progresses from there. An object of the present invention is to provide a sub-zero treatment method that can obtain a deep hardened layer without causing uneven hardness.

In the present invention, an object to be treated is placed in a rigid shape and rotated, and a cooling medium is directly sprayed onto the object from the surroundings, and during the spraying, the atmosphere around the object is blown. be. As an example, a sub-zero processing apparatus that implements the present invention includes a device that suspends and rotates a workpiece, a nozzle that injects a cooling medium toward the workpiece that is arranged around the workpiece, and a nozzle that injects a cooling medium toward the workpiece. a muffle disposed outside the nozzle so as to surround the object to be treated, and a blower disposed inside the muffle below the object to be treated.

The reason why we chose a vertical rotation system in which the material to be processed is hung from above and rotated is because roll quenching is usually done with the rolls standing upright, so the vertical type allows for faster transition to Sapze-O treatment than the horizontal type. 4. The storage container for the workpiece can be opened, the support and rotation mechanism for the workpiece is simpler than when the workpiece is rotated horizontally, and the cooling medium can be sprayed uniformly around the workpiece. This is because of this. Furthermore, the muffle and the blower are provided because the atmosphere within the muffle is rotated and circulated by blowing air, thereby making the temperature distribution within the muffle uniform. It is preferable to use liquid nitrogen as the cooling medium. If liquid nitrogen is used, the hardened layer can be sufficiently turned into martensitic material. An embodiment of a vertical sub-zero processing apparatus embodying the present invention will be described with reference to the schematic diagram shown in FIG. 1, and then specific effects of processing using this apparatus will be described. In this Sapzero processing apparatus, a heat insulating material 4 is filled between an outer layer 1 and an inner layer 2 to form a wall of a cooling container.

The lid 8 of the cooling container also has a heat insulating structure as described above.
This cooling container has a circular cross section to improve thermal efficiency. Steel pipes 5 for injecting a cooling medium are arranged at four locations on the circumference and at four locations in the length direction, and each pipe is provided with a cooling medium injection nozzle.
The steel pipe 5 is connected to a cooling medium supply pipe 12,
The supply pipe 12 is led out of the cooling vessel and is connected there to a not-shown cooling medium reservoir. Furthermore, a muffle 3 is installed between the injection nozzle and the inner layer 2 of the cooling container. A steel pipe 5 is provided with a light inside the muffle. A blower is provided at the bottom of the cooling container to control the atmosphere inside the muffle 3. Number 6 in Figure 1
indicates a blower fan. By blowing air through the muffle 3, the atmosphere is circulated around the object to be treated and in the direction of the arrow. For this reason muffle 3
There is almost no difference in temperature between the upper and lower parts of the chamber, and the temperature distribution is made more uniform. If the atmosphere inside the muffle 3 is circulated in the direction of the arrow while swirling along the wall of the muffle, the temperature distribution can be made even more uniform. The object 7 to be processed is placed on a rotary table 9 supported by rotating rollers 11 in order to be rotated while suspended by a hanger 10.

The rotating rollers 11 are provided at three locations, one of which is driven by a motor. After the objects to be processed, such as rolls, are placed in the container, they are suspended in a cooling container by a hanger 10 and rotated. Immediately, liquid nitrogen is sprayed onto the surface of the roll. When the inside of the cooling container and the object to be processed are not yet sufficiently cooled and are at room temperature, the injected liquid nitrogen immediately vaporizes. However, as the temperature of the object to be treated decreases, liquid nitrogen becomes difficult to vaporize and is sprayed in the form of a spray.
The blown liquid nitrogen forms a vapor film on the roll surface. The cooling process of the processed material consists of the generation of a vapor film, the spheroidization of the vapor pus, and the collapse of the vapor film, and the faster this process progresses, the greater the cooling effect becomes and the easier it becomes to become martensite.
In the method of the present invention, even if a vapor film is formed, it is covered by the liquid nitrogen that is sprayed later, so the process proceeds quickly. By directly spraying liquid nitrogen onto the roll surface, the oxide film formed on the roll surface during the phosphorization stage is destroyed, and the depth of the hardened layer increases. When the blower fan rotates, the atmosphere inside the muffle 3 is circulated in the direction of the arrow. For this reason, the inside of the Matsufuru 3 is adjusted to a substantially uniform temperature, and the entire object to be processed is cooled at a uniform rate. 0.91 wt% carbon {C'-3.05
wt% chromium (Cr) - 0.21 wt% molybdenum (M
o) After quenching the steel roll (arm diameter unevenness 50 x body length 1465 sails x total length 3375 ribs), using the apparatus shown in Fig. 1 -
Figure 2 shows the migratory temperature results when sub-zero processing was carried out until 150:00.

Liquid nitrogen was used as the cooling medium. When liquid nitrogen is injected, the ambient temperature rapidly decreases, and the temperature of the roll body also decreases, reaching -15% in just 5 hours after cooling begins.
Reach 0qo. Moreover, the temperature variations at the top, middle, and bottom of the roll body at that time were all within a range of 5° C., and the roll body was cooled uniformly. FIG. 3 shows the hardness distribution of the hardened layer on the roll surface.

The hardness of the sub-zero-treated rolls near the roll surface is increased by the thickness of the roll compared to the rolls that are not subjected to the sub-zero treatment. As described above, the rotary type rotary type is suitable for sub-zero treatment immediately after quenching of the treated material.

In the present invention, since the cooling medium is directly sprayed onto the workpiece and the atmosphere around the workpiece is controlled, uneven hardening does not occur.
The depth of the quenched hardened layer can also be increased compared to the blind type fixed type or cooling medium rotating type.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view showing an embodiment of the present invention, Fig. 2 is a cooling curve showing the relationship between ambient temperature and roll body temperature and processing time in sub-zero processing, and Fig. 3 is a distance from the roll surface. FIG. 3 is a characteristic diagram showing the relationship between hardness and hardness. 1. ...Outer layer, 2...Inner layer, 3...
...Matsuful, 5...Steel pipe, 6...
Blower fan, 9... Rotating table, 10... Hanging odor. Purple Figure 2/Figure 3

Claims (1)

[Claims] 1. The object to be treated is arranged in a rigid shape and rotated, and a cooling medium is directly sprayed from the surroundings onto the object to be treated, during the spraying,
A rigid rotary sub-zero processing method characterized by stirring the atmosphere around the object to be processed.