JP2016089212A - Water hardening device and water hardening method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water hardening device and a water hardening method dissolving the facts that, though hardening treatment mainly copes with gas cooling and oil cooling in a vacuum heat treatment furnace, hardening effect is hard to be obtained to the central part of a material inferior in hardenability and a plate material or a bulk material, further, even in the case water cooling is performed, only by immersing the material to be hardened, high cooling velocity cannot be obtained, and sufficient hardness cannot be obtained to the central part of the material to be hardened.SOLUTION: Provided is a water hardening device where the material to be hardened is heated and held to a high temperature in a vacuum or in an inert gas atmosphere in a heating chamber, the same is dropped within 1 sec to a cooling chamber, thereafter, cooling water is forcedly stirred by high pressure water radiation with a pressurized water jet and a bubble jet (registered trademark) by inert gas jetting, cooling water is forcedly stirred, thus cooling can be performed in a nucleus boiling state, and a water hardening method capable of hardening to the central part of the material to be hardened.SELECTED DRAWING: Figure 2

Description

  The present invention is a water quenching apparatus composed of two chambers, in which a to-be-quenched object heated and held at a high temperature in a vacuum or an inert gas atmosphere is dropped into a cooling chamber, and high-pressure water discharge of a pressurized water jet and an inert gas in the cooling chamber The present invention relates to a water quenching apparatus and a water quenching method that enable rapid cooling by maintaining the surface of an object to be quenched in a nucleate boiling state by vigorously stirring cooling water with a bubble jet (registered trademark) by jetting.

Water quenching is a general heat treatment that improves wear resistance, tensile strength, or fatigue strength by quenching carbon steel or the like heated to a high temperature by water cooling to obtain a high hardness martensite structure. Further, heat treatment such as solution forming of austenitic stainless steel that is rapidly cooled by water cooling from a predetermined high temperature state is also included.

  In the heat treatment in the atmosphere, the problem of surface oxidation is unavoidable because it maintains a high temperature state, but a vacuum or an inert gas atmosphere is the most excellent countermeasure as a non-oxidation heat treatment. For this reason, it is used in many heat treatments to ensure surface cleanliness, radiance, etc. for many parts and products, including molds.

In the heat treatment using a vacuum furnace, at present, quenching treatment is mainly performed by gas cooling or oil cooling for die steels (SKD type) and high-speed steels (SKH type) having good hardenability. In addition, carbon tool steel (SK material), alloy tool steel (SKS material), etc., which are inferior in hardenability, are currently processed mainly using a vacuum oil quenching furnace.

  Patent Document 1 discloses a water quenching apparatus configured by three chambers including a heating chamber, a cooling chamber, and a water cooling device. The to-be-quenched object heated in various atmospheres is transferred to a cooling room adjusted to the same atmosphere as the heating room, and after adjusting the atmosphere in the cooling room to atmospheric pressure, the to-be-quenched object is immersed in a water tank in which cooling water flows at high speed. Perform water quenching.

However, in the three-chamber water quenching apparatus, water quenching can be performed directly connected to an atmospheric heating furnace or a vacuum heating furnace without oxidation. However, heating is performed to adjust to atmospheric pressure after moving to a cooling chamber. Since it takes time from cooling to cooling, a decrease in temperature is inevitable, and there is a disadvantage that the temperature is excessively raised in a heating furnace.

  Patent Document 2 discloses a vacuum heat treatment apparatus in a horizontal vacuum heat treatment furnace including a heating chamber, a communication portion, and a quenching chamber. While opening and closing the open / close door installed in the communication section, the material to be quenched is pushed out by a horizontally moving piston mechanism and discharged into the quenching chamber for water quenching.

However, in the case of the water quenching of the horizontal vacuum heat treatment apparatus, the time spent until the water can be shortened, but depending on the size of the material to be quenched only by immersing the material to be quenched, the effect of the water vapor film generated during the quenching A sufficient cooling rate cannot be secured, and there is a possibility that the quenching effect cannot be obtained over the entire area to be quenched.

JP 2002-97520 A JP 2012-12737 A

Kawahara Zensaku, JFE 21st Century Foundation 2009 Technical Research Report

In the heat treatment in the atmosphere, various water cooling methods are carried out for the water quenching because of easy handling of the object to be quenched, but heating in the atmosphere cannot avoid oxidation and affects the surface roughness and dimensional accuracy.

To harden steel with low alloying elements such as S15C and low C content to the center by quenching, the material to be hardened is heated to a temperature higher than the quenching temperature defined in JIS standards (JISG0561) and quickly kept at this temperature. In addition, it is necessary to rapidly cool the center temperature to near room temperature. In addition, in order to obtain a quenching effect up to the center of an object to be quenched having a large heat capacity such as a thick plate material or a bulk material, it is important how efficiently heat can be taken away and rapidly cooled.

Moreover, the same rapid cooling is required for the solution heat treatment for heating the precipitate to a high temperature of 1000 ° C. or higher, which is a heat treatment method for austenitic stainless steel such as SUS304 steel.

Rapid cooling is generally performed by water cooling with high heat transfer. Especially when materials with poor hardenability, thick plate materials, or bulk materials are water-cooled from a high temperature, the surface of the object to be quenched is simply immersed in water. Water cannot be brought into contact with the object to be quenched due to the water vapor film generated in the film, and cooling cannot be effectively performed (see Non-Patent Document 1). Therefore, in order to obtain the effect of quenching and solution treatment to the center of the object to be quenched, the water vapor film on the surface of the object to be quenched must be destroyed and cooled in a nucleate boiling state.

At present, it is difficult to rapidly cool a material having poor hardenability, a thick plate material, or a bulk material from a state heated to a high temperature in a vacuum or an inert gas atmosphere to the center of the object to be quenched. There is a problem of how to cool the vicinity of the surface of the object to be quenched to a nucleate boiling state.

  The present invention provides a water quenching apparatus and a water quenching method suitable for quenching a to-be-quenched article having poor quenchability in a vacuum or an inert gas atmosphere.

  A first aspect of the invention is a water quenching apparatus having an upper and lower two-chamber structure having a heating function at the upper part and a cooling function at the lower part, and the apparatus for heating the quenching object in a vacuum or an inert gas atmosphere A heating chamber constituted by a device that holds and drops the cooling chamber, a pressurized water jet cooling device that rapidly cools the to-be-quenched object, and a bubble jet (registered trademark) by inert gas injection to strongly agitate the cooling water. A cooling chamber composed of a cooling water tank having a function of maintaining water cooling in the nucleate boiling state near the surface of the object to be quenched, a sliding pressure partition valve between the heating chamber and the cooling chamber, the heating chamber and the cooling chamber Provided is a water quenching device constituted by a plurality of vacuum exhaust devices, a cooling water supply device, and an inert gas supply device connected to each.

A second aspect of the invention is a water quenching method using the water quenching apparatus according to the first aspect of the invention, wherein the object to be quenched is heated to a predetermined temperature in a vacuum or an inert gas atmosphere, and then dropped into a cooling chamber. A water quenching method is provided in which high-pressure water discharge is performed with a pressurized water jet apparatus while holding water, and the cooling water is vigorously stirred with a bubble jet (registered trademark) by inert gas injection to rapidly cool in the cooling chamber.

A third aspect of the invention is a water quenching method according to the second aspect of the invention, wherein the surface of the object to be quenched in the cooling chamber is maintained in a nucleate boiling state by high-pressure water discharge of a pressurized water jet or strong stirring cooling by inert gas injection. Provide a quenching method.

A fourth aspect of the invention is the water quenching method according to the aspect 2 or 3, wherein the inert gas atmosphere and the inert gas injection component are any one of helium gas, argon gas, and nitrogen gas, or A water quenching method comprising two or more mixed gases is provided.

  In the water quenching and water quenching method according to the present invention, the time required for transferring the quenching object from the heating chamber to the cooling chamber can be reduced to 1 second or less, and the quenching object holding the heating temperature is pressurized with a pressurized water jet. The surface of the object to be hardened can be maintained in a nucleate boiling state by vigorously stirring the cooling water with a bubble jet (registered trademark) by water discharge and inert gas injection. Oxidation can also be eliminated.

Further, the water quenching method reduces the difference in cooling rate by cooling the to-be-quenched object from all directions, and uniformly cools the to-be-quenched object, so that the distortion, hardness and internal Variations in texture and grain size can also be reduced.

The schematic block diagram of the water quenching apparatus which concerns on embodiment of this invention. The cooling chamber schematic diagram at the time of the water quenching of the said apparatus. Observation of metal structure and hardness at the center of test material by water quenching test. Metal structure and hardness at the center of the test material due to differences in water quenching test methods. Temperature history of the test material center due to differences in water quenching test methods.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of the water quenching apparatus of the present invention. A heating space 3 constituted by a heat insulating wall 2 is provided in a heating chamber 1 having a water cooling jacket. In this heating space 3, a heater 4 and a guide 5 for preventing toppling of the object to be hardened are provided inside the heater 4 to prevent damage to the heater 4. The chamber lid 6 at the top of the heating chamber 1 is opened and closed, and the object to be quenched 7 and the support base 8 for fixing the object to be quenched 7 are set on the support shutter 9. Cooling water circulates through the support shutter 9, and the support shutter itself is prevented from being overheated by cooling.

After setting, the entire heating chamber 1 is evacuated by the heating chamber oil rotary vacuum pump 10 and the heating chamber oil diffusion vacuum pump 11, and the vacuum state is 6.6 × 10 ⁻³ Pa or less, or helium gas, argon gas, nitrogen The gas is replaced with an inert gas, and heat treatment is performed in a non-oxidized state. Simultaneously with the exhaust of the heating chamber 1, the cooling chamber 13 is exhausted by the cooling chamber oil rotary vacuum pump 14. The exhaust of the cooling chamber 13 is set so that the two chambers have the same pressure by being replaced with a vacuum state or an inert gas as in the heating chamber 1.

After heating the object to be quenched, the heater 4 is turned off, the exhaust valve of the cooling chamber 13 is closed, the slide pressure gate valve 12 is opened, and then the support shutter 9 is opened. After opening, the to-be-quenched object 7 and the support base 8 fall into the cooling chamber 13 within 1 second, and at the same time, the sliding pressure gate valve 12 and the support shutter 9 are closed. By closing, the atmosphere of the heating chamber 1 is not disturbed, and water quenching of the object to be quenched is possible. After the water quenching is completed, a leak valve (not shown) provided with the cooling chamber 13 is opened, and the object 7 and the support base 8 are taken out from the room.

FIG. 2 shows water cooling of the object to be quenched in the cooling chamber 13. Three pressurizing water jet nozzles installed in the cooling chamber 13 when the object 7 to be quenched and the support 8 heated in the heating chamber 1 fall into the mesh-shaped processed material tray 15 and the sliding pressure gate valve 12 is closed. The to-be-quenched object 7 is cooled by the high-pressure water discharge from 16.

The water discharged at high pressure from the pressurized water jet nozzle 16 is stored in advance in a water storage tank 17 provided outside the water quenching apparatus. A pressurizing valve 18 is installed in the water storage tank 17, an inert gas is introduced, and pressurized water is pushed in.

The pressurized water jet nozzle 16 discharges a predetermined flow rate, and stops water discharge after a predetermined amount of water is injected into the cooling chamber 13. The cooling water is strongly stirred by directly injecting the inert gas supplied by the gas supply unit 20 from the gas injection port 19 below the cooling chamber 13 into the cooling water in a state where the cooling water is sufficiently stored by the water discharge. . Cooling water is vigorously stirred with this pressurized water jet and bubble jet (registered trademark) by inert gas injection, and the vicinity of the surface of the object to be quenched 7 can be maintained in a nucleate boiling state. Further, when the pressure in the cooling chamber 13 becomes 0.5 KPa or more due to gas injection, a gas release valve (not shown) installed in the cooling chamber 13 is operated to adjust the indoor pressure.

The heater 4 for heating the water quenching apparatus employs a resistance heating method using a carbon heater in the present invention, but a heater material can be selected according to the purpose. Moreover, if the to-be-quenched thing 7 can be heated and hold | maintained, there will be no problem in high-frequency heating or direct current heating, and the heating method is not particularly limited.

Regarding the pressurized water jet nozzle 16 and the injection port 19 in the cooling chamber 13, the number of installations and the number of installations can be increased as long as the conditions for effective water quenching on the object to be quenched 7 are satisfied in consideration of the size of the water quenching apparatus. There is no need to particularly limit the installation position or discharge flow rate.

When the cooling chamber 13 is not mixed with water or gas in the exhaust before heating the to-be-quenched object, it is not always necessary to close the slide pressure gate valve 12, and the oil rotary vacuum pump for the heating chamber is open. The heating chamber 1 and the cooling chamber 13 can be exhausted and replaced at the same time by the oil diffusion vacuum pump 11 for heating chamber 10 and heating can be started with the opening kept open.

In the cooling chamber 13, the pressurized water jet nozzle 16 can be replaced with a gas nozzle, gas quenching for injecting an inert gas, oil injection nozzle can be replaced with oil quenching by oiling, or cooling can be performed in the cooling chamber 13. It can also cope with quenching speeds slower than quenching.

The heating chamber 1 can be carburized or nitrided by holding the object to be quenched in various gas atmospheres, and can be combined with other heat treatments such as cooling immediately after the treatment.

  In the case of quenching with water, if the material is to be hardened, the cooling water is strongly stirred by a bubble jet (registered trademark) by an inert gas injection from the injection port 19 in the cooling water stored by the pressurized water jet nozzle 16. It is also possible to quench with water without performing the above.

  In water quenching regardless of the surface oxidation of the object to be quenched, heating in a vacuum or inert gas atmosphere can be changed to heating in the atmosphere. If the inside of the cooling chamber 13 does not need a vacuum or an inert gas atmosphere, the cooling water is stored in advance, the heated object to be quenched is directly dropped, and a bubble jet (registered trademark) by inert gas or air injection is used. The cooling water may be vigorously stirred and cooled.

<Example 1>
Normally, carbon steel shifts to a hard structure such as ferrite, bainite, and martensite as the cooling rate increases. Carbon steel requires rapid cooling to produce a martensitic structure as the carbon content decreases. Therefore, S15C, which is a low carbon steel containing 0.15% carbon that is poor in hardenability and easily causes unevenness in quenching, was selected, and a water quenching test was performed in a vacuum. Table 1 shows the component composition range of S15C (JISG4051) used in the water quenching test.

A commercially available S15C material was machined into a water-quenched test material having a diameter of 15 mm and a length of 100 mm. In order to measure the temperature of the test material, a hole with a diameter of 1.0 mm and a depth of 7.5 mm is drilled in the center of the test material, and a 1.0 mm diameter sheath thermocouple (JIS 1605, thermocouple type: SK) is formed in this hole. Sheath material: B) was inserted. After using this S15C test material and putting it in the heating chamber of the vacuum heat treatment furnace of the present invention at room temperature, it was evacuated to 6.6 × 10 ⁻³ Pa or less by an oil rotary vacuum pump and an oil diffusion vacuum pump. At that time, the temperature was measured while the slide pressure gate valve was opened, and the heating chamber and the cooling chamber were set to the same degree of vacuum. The heating was increased to 1200 ° C. in 2 hours, and the temperature at the center of the test material was maintained for 10 minutes after reaching the set temperature, and the heating was stopped. After stopping the heating, the support shutter was opened, the test material was dropped into the cooling chamber, and the sliding pressure gate valve and the support shutter were closed. From the heating to the start of the pressurized water jet is performed within 5 seconds, the pressurized water jet flow rate is 55 L / min, and the high pressure water discharge is performed. ) The cooling water was vigorously stirred. When the pressurized water jet was stored up to 40 L in the cooling chamber, the water discharge was stopped, and the argon gas injection from the lower portion of the cooling chamber into the cooling water was stopped after the center temperature of the test material was cooled to 50 ° C. or lower.

In addition, although there was a risk of water being discharged into the vacuum vessel, there was a risk of sudden pressure increase due to the instantaneous evaporation of water or the generation of a large amount of heat of vaporization. However, smooth rapid cooling was possible even under conditions of 6.6 × 10 ⁻³ Pa or less.

The metal structure observation and hardness measurement results at the center of the test material before and after the quenching test are shown in FIG. The test material before quenching had a structure composed of ferrite and pearlite, and the hardness was in the range of Vickers hardness (hereinafter referred to as Hv) 135 and Hv 117 to 156, which is the normalization hardness of a general S15C material. By cooling this test material with the water quenching method of the present invention, a martensitic structure was obtained up to the center of the test material, and the hardness was sufficiently high as Hv394, and the entire test material had a quenching effect.

<Comparative Example 1>
Heating was performed under the same conditions as in Example 1, and cooling after dropping the test material used only a pressurized water jet, and a comparative test was performed without performing argon gas injection. The water injection conditions were the same as those in Example 1, and after the heating, the pressurized water jet was started within 5 seconds. The water jet flow amount was high pressure water discharge at 55 L / min, and the water discharge was stopped after storing up to 40 L in the cooling chamber.

FIG. 4 shows the results of metal structure observation and hardness measurement at the center of the test material performed in Comparative Example 1. In Comparative Example 1 in which strong stirring by bubble jet (registered trademark) with argon gas injection was not performed, the quenching effect as in Example 1 was not sufficiently obtained. As a result, most of the central portion became ferrite, and the hardness became Hv167 without shifting to the martensite structure.

Table 2 shows the cooling time of the center temperature of the test materials of Example 1 and Comparative Example 1, and there was a difference of 100 seconds or more in cooling from 1200 ° C to 100 ° C. In Example 1, not only cooling while destroying a vapor film by high-pressure water discharge of a pressurized water jet, but also strong stirring of cooling water by bubble jet (registered trademark) by argon gas injection greatly affects the acceleration of the cooling rate. I understand that. In particular, from 800 ° C. (around 40 seconds), even when the test material is completely immersed in the cooling water by discharging the pressurized water jet, the test material is brought into the cooling water tank by vigorous stirring of the bubble jet (registered trademark) by argon gas injection. The nucleate boiling state in which the entire surface of the test material is cooled while in direct contact with water while moving around vigorously is maintained. Compared with Example 1, in Comparative Example 1 in which strong stirring by argon gas injection is not performed, when the test material is completely immersed in the cooling water, the cooling rate at the center of the test material is greatly reduced as shown in FIG. The reason is that the high temperature test material is cooled only by convection heat transfer and radiant heat transfer through the water vapor film by shifting to a film boiling state where it evaporates before coming into contact with water.

DESCRIPTION OF SYMBOLS 1 Heating chamber 2 Heat insulation wall 3 Heat treatment space 4 Heater 5 Fall prevention guide 6 Chamber lid 7 Hardened object 8 Support stand 9 Support shutter 10 Oil rotary vacuum pump 11 for oil heating chamber Oil diffusion vacuum pump 12 Sliding pressure gate valve 13 Cooling chamber 14 Oil rotary vacuum pump for cooling chamber 15 Processed object tray 16 Pressurized water jet nozzle 17 Reservoir tank 18 Pressurization valve 19 Injection port 20 Gas supply unit

  The water quenching device and the quenching method using this device enable quenching to the center of a poorly hardened material, thick plate material, or bulk material. Diversion to structural members for construction is expected.

Claims (4)

A water quenching apparatus having an upper and lower two-chamber structure having a heating function at the upper part and a cooling function at the lower part, comprising a device for heating the material to be quenched and a device for holding the material to be quenched and dropping it into the cooling chamber In addition, the water-cooling in the vicinity of the surface of the object to be quenched can be performed by vigorously stirring the cooling water with a pressurized water jet cooling device that rapidly cools the object to be quenched and a bubble jet (registered trademark) by inert gas injection. A cooling chamber composed of a cooling water tank having a function of maintaining a nucleate boiling state, a sliding pressure gate valve between the heating chamber and the cooling chamber, a plurality of vacuum exhausts connected to each of the heating chamber and the cooling chamber A water quenching apparatus comprising an apparatus, a cooling water supply apparatus, and an inert gas supply apparatus. A water quenching method using the water quenching apparatus according to claim 1, wherein the object to be quenched is heated and held to a predetermined temperature in a vacuum or an inert gas atmosphere, then dropped into a cooling chamber, and pressurized water is maintained while maintaining a high temperature. A water quenching method characterized in that high-pressure water is discharged by a jet device, and cooling water in the cooling chamber is vigorously stirred and rapidly cooled by bubble jet (registered trademark) by inert gas injection. 3. The water quenching method according to claim 2, wherein the cooling of the surface of the object to be quenched in the cooling chamber by water is maintained in a nucleate boiling state. The water quenching method according to claim 2 or 3, wherein the inert gas atmosphere and the inert gas injection component are any one of helium gas, argon gas, nitrogen gas, or a mixture of two or more. A water quenching method comprising a gas.