JPS6148514A - Quenching method of steel - Google Patents

Abstract

PURPOSE:To quench a steel in a short time to quenched high surface hardness of arbitrary depth, by heating the steel having a specified C content to quenching temp., spray cooling said steel to harden the surface to a desired depth, then holding it at a suitable temp. for a prescribed time. CONSTITUTION:The steel consisting of 0.65-0.85% C preferably further, 0.23- 0.32% Si, 0.4-0.9% Mn, <=2.0% Ni, 0.5-1.5% Cr, 0.10-0.20% Mo and the balance Fe (contg. usual impurities) is heated to about 800-850 deg.C quenchable temp., and spray cooled to an extent in which desired surface hardening depth is obtd. Successively thereto, said steel is held isothermally at 150-<250 deg.C temp. for 10-50min, then quenched by arbitrary cooling. Said spray cooling is performed preferably by water spraying at 4-6kg/cm<2> water pressure and for 0.2-0.8sec. By the quenching, high quenched surface hardness can be obtd. with hardened depth controllable arbitrarily, and arbitrary matrix hardness is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for quenching steel, and more specifically, to a method for quenching steel, which provides high quenched surface hardness at an arbitrary hardening depth, and provides a method for quenching steel at an arbitrary hardening depth. This invention relates to a method for quenching the obtained steel.

Conventional methods for hardening and strengthening steel can be roughly divided into (1) methods of heating and hardening the entire object to be hardened;

(2) The surface of the hardened object was hardened as well as the inside. That is, there is a method of surface hardening and quenching. Among these methods, the method (1) has the disadvantage that the surface is not hardened and the surface hardness is lower than the method (2). On the other hand, common surface hardening methods include carburizing and quenching, induction hardening, and nitriding.However,
Carburizing and quenching has the disadvantage of requiring longer processing times than other methods to obtain hardening depth. the result.

The processing costs are also borne by the city. In addition, although induction hardening can be performed in a shorter time than carburizing, it has the disadvantage that steel with a high carbon content cannot be treated because it causes quench cracking. In addition, the nitriding method has a shallow hardening depth of 7 tons compared to other methods.

The drawback is that it cannot withstand use under high load conditions.

Furthermore, a common drawback of the above three surface hardening methods is that parts other than the surface hardened part of the quenched object (2 points of the surface hardening depth)
~5 times deeper position) hardness.

That is, there is a drawback that the hardness of the base material cannot be adjusted arbitrarily.

Problems to be Solved by the Invention Accordingly, an object of the present invention is to obtain a high hardened surface hardness in a relatively short processing time, and also to be able to arbitrarily adjust the hardening depth within a certain range. □ It is an object of the present invention to provide a method of hardening steel that can obtain a desired base hardness.

Means for Solving the Problems In order to achieve the above object, the steel quenching method according to the present invention heats steel having a carbon content of 0.65 to 0.85% to a temperature at which it can be quenched, and heats the steel to a desired temperature. Spray cooling to S= to obtain a surface hardening depth of
IJf! is maintained at a temperature below the specified time for a predetermined period of time, and then optionally cooled down. j9. In this case, the spray cooling after heating is preferably carried out by water spray cooling.The steel to be applied to the quenching method of the present invention is preferably water spray cooling.

C0165~0.85%, Si 0.23~0.32
%, Mn 0.4-0.9%, N12Q% or less, Cr
y, 5-1.5%, Mo 0.10-0.20%,
Steel with a balance of Pg (containing normal impurities) is preferred.

Effect of the Invention The method of the present invention uses steel having a carbon content that maximizes hardening hardness, heats the object to be hardened to a temperature at which it can be hardened, and cools the object by water spray to obtain the required surface. Cooling is regulated to obtain depth of cure. Subsequently, the entire object to be quenched is held at a temperature near the M5 point of the steel. (Then, at this time, the cooled surface will be heated,
The inside of the object to be hardened is cooled. ) That is, by cooling the object to be hardened to a temperature near 1M, 9 points, the internal hardness of the object to be hardened can be changed.

In other words, by using the method described above, the hardening surface hardness can be maximized, and by appropriately selecting the water spray cooling conditions and the constant temperature maintenance conditions after cooling, an arbitrary hardening depth can be obtained. In this way, a completely new method for quenching steel is provided, which eliminates the drawbacks of the conventional method.

Here, in order to facilitate understanding of the features of the method of the present invention, the differences from the conventional method described above are summarized as shown in Table 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Below, various aspects of the method of the present invention, selection conditions for each step, etc. will be explained while showing one drawing, test results, etc.

α) Materials used Table 2 shows the chemical compositions of the materials used in the various tests and Examples described below. In addition, in the following explanation, the display of the used phthalate is shown with reference to the hawk shown in Table 2.

Table 2 - Chemical composition of steel used) Cooling for surface hardening FIG. 1 shows a schematic diagram of an example of a spray cooling device used for surface hardening in the method of the present invention. In the figure, 1 is the object to be hardened, 2 is a support for supporting the object 1 to be hardened, 03 is a cooling pipe arranged opposite to each other at an interval of one foot, and 4 is a cooling water introduction. The tube, 5, indicates the injection port.

First, the object 1 to be quenched heated to a quenching temperature of 800 to 850° C. is supported by the support 2 and introduced between two cooling pipes 30 disposed opposite to each other.

Then, the water introduced from the cooling water introduction pipe 4 fills the cooling pipe 3 and is injected from the injection port 5, and the water introduced from the cooling water introduction pipe 4 is injected from the injection port 5.
The treated material (hardened material) heated to a hardenable temperature in this manner is spray cooled to the extent that a desired surface hardening depth is obtained. The desired surface hardening depth can be adjusted by cooling time or injection pressure. These relationships will be explained below.

The relationship between cooling time and hardening depth is shown in Figure 2. Figure 2 shows the water pressure when using /I61 and A7 copper in Table 2 as samples. /cJ
The relationship between cooling time and hardening depth is shown when the cooling time is constant. As is clear from FIG. 2, a cooling time of at least 0.8 seconds is required to obtain the maximum hardening depth. However, even if the cooling time is set to 1.0 seconds, the quenching depth hardly increases. Therefore, the maximum value of the cooling time is limited to 0.8 seconds, and it is preferable to keep the cooling time below this. Also, 0.
If the cooling time is less than 2 seconds, a hardening depth of only 0.5- or less can be obtained and has no practical meaning. Therefore, the minimum value of the cooling time is 0.2 seconds, and it is preferable to select a cooling time longer than this. In this way, by keeping the water pressure constant and varying the cooling time, a desired hardening depth can be obtained.

On the other hand, when the hardening depth is investigated using pressure as a variable, a relationship as shown in Figure 3 is obtained. FIG. 3 shows the effect of water pressure on the hardening depth when the cooling time was constant at 0.8 seconds for the rot 7 sample. As is clear from FIG. 3, there is no change in the hardening depth at 4 Ky/ad or more.

A water pressure of 4 to 6 Ky/d is suitable.

In addition, /16g steel can obtain the same hardening depth as No. 7 steel in the tests shown in Figures 2 and 3, but it is not suitable for the treatment of the present invention because it causes quench cracking when cooled. is inappropriate. Therefore, the carbon content of the steel to be treated is 0.85
% or less.

C) Cooling in a constant temperature cooling bath Under a water pressure of 4-6 Ky/ad as described above, after spray cooling for a cooling time to obtain the required hardening depth, the following example is shown in Figure 4. The material to be quenched is placed in a constant temperature cooling tank as shown and held for a predetermined period of time. FIG. 4 shows a schematic configuration of a constant temperature cooling tank used in the examples described later, and 6 is the constant temperature chamber body, which is made of heat-insulating material.
A heater 7 is disposed on the inner wall of. g is a steel container placed inside the thermostatic chamber body 6;

The container s is filled with a coolant 9 such as oil or potassium nitrate salts. The material to be quenched 1 is housed in a container O and immersed in a coolant 9 in the container 8. Reference numeral 11 is a thermocouple, which works in conjunction with the heater 7 to adjust the temperature of the coolant 9.

Next, the operation will be explained. First, when the heater 7 is passed through to generate heat, the container 8 is heated by the heat, and the coolant 9 contained in the container 8 is also heated.

Now, when the temperature is set using the thermocouple 11, the container 8 and the coolant 9 are heated and slowed down to the set temperature. After reaching the set temperature, the material to be hardened 1 housed in the cage 10 is heated with a coolant 9.
After keeping the temperature at the set temperature for a predetermined period of time, it is taken out from the constant temperature cooling tank and cooled down as desired.

Figure 5 shows the relationship between the holding time in a constant temperature cooling bath and the Vickers hardness of the material to be quenched at a constant set temperature (200°C) for various samples.

Further, FIG. 6 shows the relationship between the holding temperature of the constant temperature cooling bath and the substrate hardness (Vickers hardness) for a fixed holding time (held for 10 minutes).

As is clear from Figure 5, the holding temperature is kept constant (200℃).
), the substrate hardness can be changed by changing the holding time. It's Kade.

As shown in Fig. 6, the hardness of the substrate can also be changed by changing the holding temperature while keeping the holding time constant (10 minutes). Therefore, the holding time (Fig. 5) and holding temperature ( In combination with Fig. 6), the hardness of the substrate can be adjusted as desired.

However, since the condition of having a Vickers hardness of 250 or less is meaningless in practical terms, materials of No. 2 are not suitable for the treatment of the present invention. Further, as shown in FIG. 5, a holding time of 50 minutes or more is also not appropriate. Similarly, from Figure 6, a holding temperature of 250°C or higher is inappropriate. It is preferable that the content is 0.65% or more, ■ It is preferable that the holding time is set in a range of 10 minutes or more and less than 50 minutes, ■ The holding temperature is 150
It can be seen that it is preferable to set the temperature in a range of .degree. C. or more and less than 250.degree.

Examples Examples 1 and 2 Steel No. 47 (50 φ x 300 ta) in Table 2 above was heated as a whole at 850°C for 30 minutes, and then spray cooled for 0.8 seconds at a water pressure of 5 Ky/ctd using the apparatus shown in Figure 1. Then, using a constant temperature cooling bath as shown in Fig. 4, the oil was heated to 200°C for 10 minutes (Example 1) and for 40 minutes (Example 2).
It was held and then air cooled. The hardness distribution of the treated steel cross section is shown in FIG.

Furthermore, the results of the 1-bending fatigue test are shown in FIG. The results for conventional back-soaking treated dogs and conventional induction hardening are also shown.

Examples 3 and 4 /I63 steel (50φX 300 tan
) was heated at 850°C for 30 minutes, then cooled by injection at a water pressure of 5 for 27 seconds as in Example I, and then placed in a constant temperature cooling bath at 150°C for 10 minutes (Example 3) and 20 minutes (Example 4). ) and then air cooled. The cross-sectional hardness distribution of the obtained steel is shown in FIG.

Effects of the Invention As described above, the steel quenching method of the present invention has a carbon content that increases the quenching hardness, that is, 0.65 to 0.
Using steel with a carbon content of 85%, the surface is hardened by heating it to a hardenable temperature and rapidly cooling the surface by spray cooling, preferably water spray cooling. High quenched surface hardness can be obtained.

Furthermore, at this time, by appropriately selecting spray cooling conditions, any hardening depth can be obtained. Continued-C,
The material to be hardened is put into a constant temperature cooling hinoki, and the temperature is 150℃ or higher and 250℃.
A high base hardness can be obtained by holding the base at a constant temperature of less than or equal to 100% for a predetermined time and then optionally cooling it, and furthermore, by appropriately selecting the constant temperature maintenance conditions, the base hardness can be adjusted to any desired base hardness.

As described above, according to the method of the present invention, by combining surface cooling by spray cooling and constant temperature cooling, high surface hardness can be obtained at any hardening depth, and the hardness of any substrate up to extremely high hardness can be obtained. A unique effect that cannot be obtained with conventional methods is obtained. Moreover, the processing time is relatively short, and the bending has extremely high fatigue strength compared to conventional methods, and has sufficient resistance to use under high load conditions.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram showing an example of a spray cooling device used in the method of the present invention, Figure 2 is a graph showing the relationship between cooling time and hardening depth by spray cooling, and Figure 3 is a graph showing the relationship between water pressure and hardening depth in spray cooling. Graph showing the relationship with hardening depth,
Figure 4 is a schematic configuration diagram showing an example of a constant temperature cooling tank used in the method of the present invention, Figure 5 is a graph showing the relationship between holding time in the constant temperature cooling tank and substrate hardness, and Figure 6 is a graph showing the relationship between holding temperature and substrate hardness. 7 is a graph showing the hardness distribution of the cross section of steel treated according to Examples I and 2, FIG. 8 is a graph showing the fatigue test results, and FIG. 9 is a graph showing the results of the fatigue test. 3 is a graph showing the cross-sectional hardness distribution of steel treated according to No. 3 and No. 4. FIG. 1... Material to be quenched, 3... Cooling pipe, 5... Injection 0.
6... Constant temperature bucket body, 7... Heater % 9... Coolant % 10... Basket, ++... Thermocouple.

Claims (1)

[Claims] 1. Steel having a carbon content of 0.65 to 0.85% is heated to a temperature at which it can be hardened, spray cooled to the extent that the desired surface hardening depth is obtained, and then kept at a constant temperature. 150℃ or higher25
A method for quenching steel, characterized by holding the temperature at a temperature below 0° C. for a predetermined period of time, and then optionally cooling it. 2, C0.65-0.85%, Si0.23-0.32
%, Mn0.4-0.9%, Ni2.0% or less, Cr0
．． 5-1.5%, Mo0.10-0.20%, balance Fe
2. The method according to claim 1, using steel (containing normal impurities). 3. Spray cooling after heating using water pressure of 4 to 6 kg/cm^
2. The method according to claim 1 or 2, which is carried out by water spray cooling with a spraying time of 0.2 to 0.8 seconds. 4. Maintain constant temperature at a temperature of 150℃ or higher and lower than 250℃ for 10 minutes.
The method according to any one of claims 1 to 3, wherein the method is carried out by holding the method for at least 50 minutes.