JPS60190514A - Heat treatment of steel using carbon muffle in neutral atmosphere as heating element - Google Patents

Abstract

PURPOSE:To obtain a rational treating method which is suitable for treating a large- sized material and permits free selection of heating up time by using a carbon muffle set in a neutral atmosphere as a heating element and heat-treating the steel contained therein. CONSTITUTION:A heat treating furnace 1 is therein with liquid nitrogen or a neutral gaseous atmosphere such as Ar through an inlet valve 2 and is set with a carbon muffle 3 in the neutral atmosphere. Terminals 4, 4 are provided to both ends of the muffle 3 and electricity is conducted thereto to act the muffle 3 as a heating element, then a steel 5 to be treated is contained into the muffle furnace from an inlet door 6 side and is subjected to a heating treatment. The steel is hardened in a cooling chamber 7 and is taken out of an outlet door 8. The heating temp. is so set that the steel is stepwise and slowly heated in an alpha-Fe region to be thoroughly preheated, is then heated up quickly to the hardening temp. in a gamma-Fe region and is thereafter cooled. CO having powerful chemical activity exists slightly in the muffle furnace to improve thermal diffusion without affecting adversely the chamical compsn. on the surface of the jig and tool steel. The homogeneous heat treatment of the steel to distribute richly and uniformly carbide is thus executed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method of heat-treating die steel, cutting tool steel, other tool steels, precision I geometrical parts, etc. in a neutral atmosphere using carbon pine filler as a heating element. This is the result of research on heat treatment methods for steel.

Currently, as industrial heat treatment furnaces in J3, general gold Fl+,
The following treatment methods are often used for heat treatment furnaces for tool steels such as No. 1 steel and cutting tool steel, as well as their heat treatment methods. 1) Salt bath method using neutral salt bath treatment 111, 2) Atmosphere treatment method of heat treatment in various protective gases, 3)
There is a vacuum heat treatment lq1 method using a vacuum furnace, etc., which is widely used in various industrialized countries. All of them have different characteristics and drawbacks. 1) Tsuru 1-bus furnace is the most selectively adopted in each country, but the processing capacity of the furnace is limited, and molds etc. It is inappropriate for processing people (people).

According to the atmosphere treatment method 2), the amount of protective gas used is large;
Attention should be paid to empirical issues and carbon balance.

3) Vacuum heat field 1! I! Furnaces have drawbacks such as being expensive and requiring care to avoid coarsening of crystal grains when high-temperature treatment is required.

An object of the present invention is to provide a method for heat treatment of steel using carbon matsful as a heating element in a neutral atmosphere, which exhibits superior characteristics in place of the various heat treatment methods described above.

Hereinafter, the present invention will be sequentially explained as follows.

■, Overview of the structure and functions of heat treatment furnaces, ■.

Main points of heat treatment methods, ■, Comparison of characteristics of various conventional heat treatment methods and the heat treatment method of the present invention, ■, Differences in heat treatment conditions between various heat treatment methods and the present invention have no effect on the steel to be treated, ■,
Ratio of metallographic structure of 113 after heat treatment of steel under various conditions: 10 (Photo taken by Raiko Koma), ■.

Comparison of wear resistance of steel by various heat treatment methods, Δ:i! ! Sokuo 1 tool steel, B: Mold steel.

1. Outline of the 1F+S construction and function of the heat treatment furnace; In Figure 1, the heat treatment furnace 1 feeds neutral atmosphere gas into the furnace from the atmosphere gas valve 2, and injects carbon pine nuts 3 into the neutral atmosphere.
Set the terminals 4.4 to the appropriate places on both ends of Carbon Matsunoru 3.
Step 1'' is energized and Carbon Matsufuru 3 is used as a heating element.
The steel 5 to be treated is placed in the Matsufuru furnace from the entrance door 6 side,
Heat treated, quenched in cooling chamber 7 and taken out from exit door 8 1
It is configured as follows. The area around the Carbon Matsufuru 3 is separately heat-insulated with carbon powder 9, and the exterior is cooled with a water-cooled dikerat.

■ Main points of the heat treatment method: As mentioned above, a carbon matsful is set in a neutral atmosphere, and electricity is applied to it to make it a heating element. Then, after performing relaxation heating in stages, ]-molecular heat treatment, the temperature is rapidly raised to the hardening temperature of 1200°C in the γ-[θ region, and then cooled. There is a small amount of highly chemically active CO, which is pressurized to 0.02 ko10 IR or more, so it does not harm the chemical composition of the jig steel surface and has good thermal diffusion. , homogeneous heat treatment of steel with abundant and even distribution of carbides is performed.

Thermogeographic striation 1'1. It should be noted that the heating degree in the α-[θ range below the A1 transformation point of the steel (723°C) should be a relaxation curve as much as possible, and sufficient time should be taken to preheat and By uniformly heating the outside, we aim to increase the precipitation of carbides, and by uniformly relaxing heating, we aim to reduce heat treatment distortion. In the γ-'e region, the treated strip 1'1 is heated as quickly as possible to the maximum quenching temperature in April to prevent coarsening of the steel crystal grains.

■ Comparison of characteristics of various heat treatment methods and the heat treatment method according to the present invention: As described above, the heat treatment furnace according to the present invention uses an h-bond Matsufuru installed in a neutral atmosphere as a heating element, and the steel to be treated is contained within the Matsufuru. Atsushi L! I! ! In the method of Measured at the center 3) D, P, and 3110W continuous detection type were not observed, and the CO of the sign (3) was 0.02 to 2.0k (J/
It is recognized that it has the characteristics of reacting to the steel to be treated when pressurized to "all", that it can be maintained at a high temperature of 2800° C. if necessary, and that it is less expensive than a vacuum furnace or the like.

Table 1 shows an example of the heat treatment contents for typical vA type 5KD11 mold steel.CO is about 1l80-400PP, but with some pressure applied, the steel becomes highly activated and reducing CO. It is thought that the effect is overriding. D, P, (
dew point) is maintained at about -57°C to -59°C.

■Differences in thermal striations f1 according to the present invention in various heat treatment methods have no effect on the steel to be treated: Figure 2 shows Hatayama tool steel (SKH51, quenching temperature is 120
This is an example of a heat treatment diagram of a process (approximately 0°C). In the figure, the two-dot chain line shows the neutral salt bath treatment, the solid line shows the vacuum heat treatment, and the dotted line shows the heat treatment conditions of the present invention. This is an example of considering the influence rather than the effectiveness, and it is a fundamental problem.

According to heat treatment theory, the properties of steel that are in the temperature range above the Δ1 transformation point (723℃) are called the γ-Fθ region, and the properties below the A1 point are called the α-Fe region. It is generally known that the properties of steel vary significantly depending on the region.

At temperatures in the α-Fe range, the essential properties of the steel do not change much. In the γ-Fe region, when heated in the atmosphere, mechanical properties deteriorate due to phenomena such as oxidation and decarburization. However, it is well known that the quenching heating temperature for general steel types is that quench hardening is achieved by heating to the γ-[θ range and then rapidly cooling, and that it is impossible to harden the - by heating in the α-Fθ range. It is as follows.

The heat treatment method shown in Figure 2 includes heating in a neutral salt bath, heating in a vacuum, and heating in a J-bondsful (in an N2 atmosphere), and is used in industrial applications such as oxidation and decarburization of J3 steel. Although there is no need to worry about this, if kept at high temperatures in the r-Fe range for a long time, the crystal grains of steel will become coarser, increasing brittleness and significantly reducing wear resistance, cutting properties, etc. do.

In the neutral salt bath heating method indicated by the two-dot chain line in the figure, since the heat capacity of the salt bath is extremely large, the heating time from heating to 80°C to the quenching heating temperature of 1200'C is short. , it takes only a short time to hold at high temperatures.

In addition, the content of heating steel in other general heating furnaces is that the three elements of heat conduction, radiation, and convection are added at the same time, but heating in a vacuum with a vacuum furnace is as follows:
Since the heating is performed by a single factor of radiant heat, the time required to raise the temperature to the quenching temperature is prolonged as shown by the solid line, and the crystal grains of the steel thereby become coarsened significantly.

As mentioned above, when heating the steel to be treated in the OF -1"e region, it is desirable to use relaxation heating and preheat thoroughly over time, but it takes a long time to heat the steel in the OF -1"e region. Ha, lol
4 will become brittle.

The feature of the in-manful heating furnace of the present invention is that
After molecular heat treatment, rapid heating to a high temperature quenching temperature is possible in the γ-Fθ region.

The key point is that the heating time can be freely selected and rational processing is possible.

Comparison of metal structures after heat treatment of various steels (electron micrographs): Table 2
51) and the mold steel (SKDI 1), and Table 3 shows the heat treatment conditions of both ministries.

Figure 5 (photo) does not show an example of the metallographic structure of SKI-151 steel, which was subjected to two types of heat treatment based on Tables 2 and 3, using an electron microscope. (a) Vacuum heat treatment produces coarser grains. (b)
The chemical composition (%) of (C) Table 2 was subjected to the abrasion resistance test.
The results of heat treatment of J3 steel preheated at 1200°C and quenched at 1200°C show that when compared to salt bath treatment, the amount of carbide precipitated is large in the case of the treatment according to the present invention.

The preheating conditions for the α-11-a region (d), shown by the dotted line in Figure 2, are 300℃, 450"C1650"C1ε
The temperature is heated stepwise to 350℃, and the temperature reaches 1 in the γ-Fe region.
Rapid heating to 200°C results in uniform carbide precipitation and a dense structure with no grain boundaries.

■ Comparison of wear resistance of steel by various heat treatment methods: Results for Aha speed tool steel (SK)-151) Figure 3 shows the differences in various heat treatment methods for high speed tool &p'1 (SKH51) and the wear resistance of Aha speed tool steel (SK-151). This is an example showing a comparison of wear properties, and from the results of many preliminary experiments, it is reasonable to set the contact F1 force to 25 ko/am" and the friction speed to 3.4 m/s, and it is reproducible. In this constant wear experiment, the vacuum heat treated steel showed the most μs wear due to the coarsening of crystal grains and other factors, and compared to the neutral salt bath treated steel and the seven-touch steel of the present invention. The wear amount of the treated steel under heat treatment conditions of 850° C. preheating and 1200° C. oil quenching is almost the same, but compared to vacuum treated steel, much better results are obtained.

In addition, the preheating temperature is 300℃-450℃- according to the old Tori method for non-explosion.
650°C-850°C → 1200'C: It was confirmed that the amount of wear of oil-hardened steel was the highest in oil-hardened steel.

Figure 6 (photo) shows an example of the wear surface of 5KH51 steel as a result of a long-distance wear experiment. It shows.

B. Results of mold steel (SKDI 1) 5KD11 steel listed in Table 3 above 1) from ■) in the table
An example is shown in FIG. 7 (photograph) of microstructural photographs taken using an electron microscope of steel treated according to the various heat treatment conditions shown in FIG. 5K
The quenching temperature of D11 steel is generally 1025℃, as shown in the photo (
a) Vacuum treated steel and (b) 30 in the Matsuful of the present invention.
The metal structure of 5KD111il, which has been sufficiently preheated by stepwise heating from 0° C. to 850° C., is almost the same and shows a dense structure, which is better than the result in photo (C).

Photo (d) is a special case of 1040℃ quenching of 5KDII steel. Although there is a slight temperature difference compared to the 1025° C. structure of No.7 true (C), it is recognized that its crystal grains are larger than those in photograph (C).

Figure 4 shows the difference in wear resistance due to various heat treatments of 5KDII steel. According to this, the treated steel showing the structure (b) in Figure 7 (photo) has the least amount of wear and corrosion. However, the metal structure is almost the same as in photos (a) and (b), and As shown in Figure 2, the conditions of the preliminary hu heat treatment in the α-Fe region have almost the same tendency.The reason why only the wear test results are superior or inferior is due to the difference in the atmospheric properties inside the carbon matsufuru. I believe that.

Furthermore, although in a small amount, the CO gas also reacts with n-horns to the treated steel in an activated state as a reducing agent, which does not give good results and is considered to be one of the factors.

To summarize, the present invention has an IC configured as described above.
When the heat treatment method of the present invention is applied, the wear injury of both high-speed tool steel and mold steel is reduced compared to steel treated with other heat treatment methods, and the wear surface in the long-distance wear experiment results is also normal mechanically. A healthy surface that is stable and wears out over time was created.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and Fig. 1 is a cross-sectional side view of a heat treatment furnace. Figure 3 is a comparison diagram of the wear resistance of high-speed tool steel S K l-151 by various heat treatment methods from 1) to iv) in Table 3, and Figure 4 shows the wear resistance of various heat treatment methods from V) to vi) in Table 3. Comparison diagram of wear resistance of mold m5KD11 by heat treatment method. Figure 5 is a metal structure photograph taken by electron microscope after various heat treatments of 1) to ① in Table 3 of Speed Tool Steel S K I-151. in,
(a) Vacuum heat treatment, (b) Neutral salt bath heat treatment, (C) N2 atmosphere heat treatment in a carbon Matsufuru heating furnace, (d) N2 preheating treatment sufficiently performed in a carbon Matsufuru heating furnace.
2-atmosphere heat treatment, Figure 0 is a photograph of the long-distance lubrication sliding wear surface of S K 1151 steel, (a) is neutral salt bath treated steel, (b) is carbon matzuru internally treated steel, Figure 7 is mold steel 5KD11 (a) Vacuum heat treatment, (
b) to (d) N atmosphere heat treatment in a carbon pine full heating furnace; however, d) is a special structure quenched at 1040°C. 3...Carbon Matsufuru, 5...Steel to be treated. No. 3 Figure 1Δ-1) Vacuum heat treatment fH large C63,3)-〇-11)
Neutral salt bath heat treatment (HIIIC64)-e-+++) Cardi/Ma, N2 atmosphere heat treatment in a full heating furnace (TI system C63,3)-Mu-1v) Carbonoma diffluent heat treatment in a N2 atmosphere atmosphere heat treatment in a full heating furnace (0 generation C64 , 5) Friction distance (×
10~) Figure 4 1△-V) Vacuum heat treatment (ThC59,5)-〇-vl)
Neutral salt bath heat treatment (HsC5Q,!i)---Vi) Carb/Ma, N2 atmosphere heat treatment in a full heating furnace (Th
C59,5)-h-■慴) Carbo/Mazafuru heating furnace with N2 atmosphere I! 1 process (TW: 59.5) Friction pressure #(x+o'm) Figure 5 (α) (b) Figure 7 (a) (b. (C) (d) For procedural correction (method) % formula % 2. Name of the invention: Steel hot ground using carbon matsufuru as a heating element in a neutral atmosphere! Law 3. Relationship with the case of the person making the amendment Patent applicant 4. Date of the amendment order 061E, June 1982] (Delivery date: June 26, 1982) 5. Subject of amendment 1) Seal stamp affixed on the application 2) "3. Detailed description of the invention" and "4. Drawings" in the specification Column 6 of "Brief explanation", contents of the amendment as shown in attached sheet 7, catalog of attached documents or attached materials Sheet 1) "Example showing worn surface" in line 18 of page 12 of the specification. 1. Correct. 2) [I
O! Correct worn surface photo 1 to ``Photo of metal structure of worn surface.''

Claims (1)

[Scope of Claims] 1. A neutral atmosphere in which a carbon pine is set in a neutral atmosphere such as liquid nitrogen or argon, and the steel to be treated is placed in the pine and heated using this as a heating element. A method of heat treatment of steel using J3 Riru Carbon Matsufuru as a heating element. 2. In the α-Fe range below the A1 transformation point of steel (723°C), the heating and back-drying rates can be selected rationally and freely in a carbon 7-tuffle heat treatment furnace, where the heating of the steel to be treated is carried out in stages by relaxation heating. , the neutral atmosphere according to claim 1, characterized in that when the steel that has been sufficiently preheated is placed in the γ-Fe region, the steel is rapidly heated and quenched to a predetermined quenching degree. A method of heat treatment of steel using a nokobon matsufuru placed inside as a heating element. 3. In the internal gas atmosphere of Carbon Matsufuru, the oxidizing atmosphere naturally disappears due to the self-cleaning action, producing only Co gas, and the internal pressure is 0.02~5. Oko/'am'' k - Retained I-00 reacts with the treated steel in an activated state as a reducing property, thereby improving wear resistance.The neutrality according to claim 1 A method of heat treatment of steel using carbon matsufuru as a heating element in the atmosphere.