JPS60162723A - Surface hardening method of large-diameter cast iron member - Google Patents

Abstract

PURPOSE:To form a relatively thick and effective hardened layer in the prescribed part of a large-diameter cast iron member in the stage of preheating the entire part of said member and subjecting the surface layer of the prescribed part to regular heating by induction heating then to quick cooling by performing preheating, regular heating and quick cooling under specific conditions. CONSTITUTION:Preheating over the entire part of a large-diameter member consisting of a cast iron is accomplished in such a way that the temp. difference between the surface temp. of the member right after quick cooling and the temp. of the heat stagnating in the inside thereof is kept within the heating limit temp. range where the thermal stress generated by the quick cooling does not exceed the substantial strength of the member. The regular heating is accomplished at the moving speed at which the local part of the member facing a heating coil moving successively and relatively from one end to the other end of the prescribed part of the member can be heated instantaneously to the prescribed hardening temp. down to the prescribed depth of said part. The local part which is subjected successively to the regular heating is immediately subjected to quick cooling. The effective hardened layer of about >=2mm. is thus formed to the large-diameter casting iron member.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to forming an effective hardened layer as thick as possible on a predetermined portion of the surface layer of a large member made of cast iron, particularly a solid large diameter member or a thick large diameter cylindrical member, by induction heating. The present invention relates to a method of forming by heat treatment using the present invention.

In recent years, machinery has become more precise and larger.
Along with this, the size of the elements used has also increased. Since increasing the size of element members requires the use of a large number of materials, the production cost is extremely influenced by the cost of raw materials, so those skilled in the art use the cheapest materials possible. Adding mechanical properties required by design only to necessary parts...For example, heat treatment, etc.
We strive to create parts that have mechanical properties equivalent to or better than those obtained when using expensive raw materials.

By the way, an inexpensive material for a large element member is an FC material such as gray cast iron.

However, with FC materials, for example, the material surface can be heated rapidly in a very short period of time using an induction heating coil to which a high-frequency current is passed, raising the temperature of the material surface to a predetermined quenching temperature, and then rapidly cooling it immediately. It is sufficient to form a hardened layer, except in cases where an extremely thin effective hardened layer is obtained, such as when hardening the sliding surface of a bed of a machine tool. Since quenching cracks occur in most cases, deep quenching has traditionally been considered impossible and avoided.

For this reason, solid large-diameter members with lengths of several meters and diameters from 700 m+ to over 1,000 m, and wall thicknesses of 200 m+
For large parts that require a large amount of material, such as large-diameter cylindrical parts with a diameter of 1111 or more, the mechanical properties can be sufficiently satisfied if a relatively thick effective hardened layer is not formed on the surface layer of a predetermined part of the part. However, even if there is, it is necessary to use parts made of forged or cast steel materials, which are more than twice as expensive as cast iron, but do not have the risk of quench cracking. was.

Therefore, in the conventional heat treatment method using induction heating to form a hardening hole of a desired depth in a predetermined portion of a large member made of forged material or cast steel material with no risk of quench cracking, the entire member is heated in advance in an electric furnace. etc., and then preheat the predetermined part to be treated multiple times with an induction heating coil that moves relatively to raise the temperature to near the predetermined quenching temperature, and immediately quench it to the predetermined quenching temperature with the final relative movement heating, or It is customary to use one of several (9) methods of relative movement heating and rapid cooling for a predetermined portion to be treated, which eliminates preheating of the entire member. The reason for preheating the entire part and preheating and main heating the predetermined part to be treated multiple times using an induction heating coil is as follows.
With large parts, the area to be treated is inevitably large (as a result, heating is performed by relative movement between the part and the induction heating coil, but even the highest output class power source for current #j heating equipment, such as 600 F), can be applied. This is due to lack of energy.

The present invention is directed to materials made of forged or cast steel for large-diameter solid members and thick-walled cylindrical members that are used by forming a hardened layer of a desired depth in a predetermined portion using the method described above. This product provides a new surface hardening method for cast iron, which was previously considered impossible to comply with laws and regulations. It is possible to impart other required mechanical properties to FC materials, thereby significantly reducing the cost of the product.

Among the many experiments conducted in the process of completing the present invention, we will first show an example of an experiment performed on a large member made of cast iron using the conventional method applied to large members made of forged material or cast steel.

Experimental example 1゜ (1) Specimen material: FC30 equivalent material Dimensions: Outer diameter 1,160m Inner diameter 560■ Thickness: 300 yam Length: 898m In addition, the specimen is a stress line produced by an electric furnace. It has been pretreated by annealing at 550°C for 9 hours.

(2) Target surface hardness of surface hardening layer: Hardening depth of Hs68 or more; Hardening depth of 2.0W or more (H Hatake 60) (3) Heat treatment 1 preheating; Whole heating with electric furnace 180'Cx 7) Ir peeling molecular heat; Main heating and rapid cooling: The preheated specimen was repeatedly heated six times (preheating five times and heating once with After the surface was brought to the quenching temperature by heating, it was rapidly cooled and quenched. The heating conditions and cooling conditions were as follows, and the surface temperature increase state during each heating process of the specimen was as shown in Table 1.

Heating conditions; power output 54011 (Same conditions for all 6 times) Frequency: 3KHz Feed rate 2.0-Δ- Cooling conditions: Transfer during the final heating process. Follows the induction heating coil during operation injection from the cooling jacket The quenching temperature is raised with a cooling liquid. The flooded surface of the specimen was rapidly cooled.

The coolant used is 0.81% PVA solution. The surface of the specimen after quenching The temperature was approximately 80°C.

Table 1 (4) Experimental results: The heat-treated specimens exhibited scalar cracking over the entire length in the axial direction after about 5 minutes.

In addition, the hardness measurement results of the surface layer of the specimen are as shown in Figure 1, and although the interface hardness has finally reached the target value Hs68, the hardening depth is 1.75 vm (I (@ 60
) L, I got it, and I didn't get it.

Experimental example 1 above. Although this was a violation of conventional avoidance and resulted in a deserved result, the inventor here
We hypothesized that the cause of quench cracking during deep heat treatment is that the thermal stress generated during rapid quenching exceeds the material strength.

In order to prove this hypothesis and to obtain more data to help formulate heat treatment conditions, the following experiment was conducted.

Experimental example 2゜(1) Specimen Both material and dimensions are the same as those in Experimental example 1. is the same as
It has also been pretreated.

(2) Target hardened surface layer Same as Experimental Example 1 (3) Heat treatment 1 preheating; 'Overall heating in an electric furnace at 330°C x 9HrH partial molecular heating, main heating and rapid cooling; Experimental Example 1
Using the same induction heating coil and the same heating conditions, the surface was brought to the quenching temperature by repeated movement heating three times (two preheatings and one main heating), and then rapidly cooled and heated. Hardened.

During this time, as shown in Figure 2 (,) φ3■ in the specified position of the specimen T Drill the holes to a specified depth. Measure temperature with thermocouple Ta. During each heating process of the specimen Table 2 shows the surface temperature rise condition. That's right.

Table 2 (3) Experimental results: During the rapid cooling after main heating, the specimen developed a curved quench crack that started from the thermoelectric element insertion hole and spanned the entire length in the axial direction.

In addition, the temperature characteristic curves calculated from the temperature measurements of the specimen immediately after main heating (before quenching) and immediately after quenching are shown in Figure 2 (b), respectively.
and B. In addition, the cross-sectional hardness measurement results of the specimen are as shown in Figure 2 (C), and it is shown that a hardened layer of 1g60 line or more, shown by the broken line, was formed to a depth of 3.4 m from the surface. Ta.

Experimental example 2 above. From the temperature characteristic curve diagram in Figure 2(b), it can be seen that the temperature characteristic curve A immediately after main heating (before quenching > m degrees) and the temperature characteristic curve B immediately after quenching intersect at around 350°C, and the surface temperature The temperature difference with the internal temperature is extremely large,
It is estimated that the tensile stress generated in the surface layer due to quenching has a large influence on the interior, which maintains a high temperature, and exceeds the actual strength of the specimen.
Based on the distribution, we analyzed the thermal stress generated in the member at that point. The thermal stress analysis results are shown in Figure 2 (d), and the tensile stress on the surface of the specimen is 53 Kff/iJ, which far exceeds the tensile strength of Fe12 material, which is 30W4f/sJ. This proved the inventor's hypothesis.

On the other hand, an attempt was made to compare Experimental Examples 1 and 2 from the viewpoint of heat treatment conditions.

First, from the point of view of forming a hardened layer, Experimental Example 1. So 1
Even if the surface of the specimen reaches a considerably high temperature during relative movement preheating for 6 times, by the time the next preheating starts, a large drop in surface temperature is observed due to the high thermal conductivity, which is a characteristic of FC material. Experimental example 2: After repeated heating, the predetermined hardening temperature was finally obtained and rapid cooling was performed, but the result was insufficient hardening.Based on this result, the preheating temperature for preheating the entire specimen was increased. In this case, a hardened layer sufficiently satisfying the desired PFR depth was formed by repeated heating and rapid cooling three times. On the other hand, considering the occurrence of quench cracking, Experimental Example 1. In Experimental Example 2, it occurs after the heat treatment is completed. In this example, the cooling jacket following the heating coil during the third repeated heating occurs while the heated specimen is being rapidly cooled. Therefore, it was pointed out that there was an extremely contradictory correlation between the whole preheating of the specimen and the partial preheating.

The present invention was completed based on numerous experiments including the above-mentioned experimental examples.

The purpose of the first invention of the present application, which expresses the basic technical idea of the present invention, is as follows: (1) A method for forming an effective hardened layer as thick as possible in a predetermined portion of a large diameter member made of cast iron is (2) a method described above. The entire member is preheated, and then a predetermined portion of the surface layer is heated by induction heating and then rapidly cooled. (4) The main heating is carried out from one end of a predetermined part of the member to the other end. (5) The rapid cooling is applied immediately to the local parts that are sequentially subjected to the main heating. A method for surface hardening a large diameter cast iron member.

In other words, although it is necessary to preheat the entire member due to the mass of the member, the surface m of the member immediately after the rapid cooling must be
Preheating is performed such that the temperature difference between the preheating temperature and the preheating temperature heated inside is kept within a predetermined temperature increase limit temperature range, and heating is performed to raise the temperature of the coating layer in a predetermined portion to a predetermined quenching temperature. Movement heating is performed preferably once from one end to the other end of a predetermined portion by relative movement between the member and the heating coil, and the moving speed of the movement heating is adjusted at least twice to the surface of the local part of the member facing the heating coil. The speed at which the above specified depth reaches the above temperature at once is repeated several times as is the usual method for hardening large diameter parts, avoiding heat accumulation inside 5, and immediately quenching and hardening the local parts that have been heated to the above temperature one after another. It is intended to form a layer.

In addition, the gist of the second invention of the present application for realizing the basic technical idea 4 of the first invention of the present application is as follows: (1) A large diameter member made of cast iron is preheated in advance, and a predetermined portion of the member is placed opposite to the large diameter member. In a moving table that sequentially heats locally with a relatively moving heating coil and rapidly cools it to form an effective hardening nozzle as thick as possible in the predetermined part, (2) the preheating is 1. the actual strength of the member; A process of estimating or experimenting to estimate or experiment the member surface temperature and member internal temperature distribution immediately after the above-mentioned rapid cooling -8 Thermal stress generated in the member from the above-determined member surface temperature and member internal temperature distribution. The process of calculating (3) A method for surface hardening a large-diameter cast iron member, characterized in that the internal temperature of the member immediately before quenching is maintained below the temperature increase limit temperature.

The second invention of the present application will be described in detail below according to examples.

Example (1) Component Material: FC30 material, but pre-treatment 8! Dimensions: As shown in Figure 3 (,), the outer diameter of a cylindrical body with an irregularly closed end surface is 1,160■ Inner diameter: 560■ Thickness: 4-...300sa+ Length: Curvature: 3,010m 2) Target hardened surface layer; Surface hardness to form the following hardened layer on the surface over a predetermined length range shown as h in Figure 3 (&)・・・・・Ha6g or more Hardening depth・・・2.0− or more (Hs60) 3
) Setting of preheating conditions for the entire member 1. Substantive strength of the member: 31 Kff, however, the value measured by an Amsler tensile tester using a test piece.

- Surface temperature and internal temperature distribution of a member immediately after quenching after preheating and main heating: Experimental example 2.
Since it is made of the same material and has the same wall thickness as the specimen in Experiment Example 2. Use the measured value determined by

Calculation of steel and thermal stress: Calculations were made using the following formula and varying the amount of temperature change. The calculation results are shown in Table 3.

S==, * j,, (&f:T, , M+/rTr
-dr-Tarsu・4kuυ However, σθ; Thermal stress α in the circumferential direction; Thermal expansion coefficient...12"X10°6E;Young's modulus...12,5001 adV; Poisson's ratio...0.26r; Distance a from the center of the member; Inner radius...580m, which is the innermost temperature measurement position b; Outer radius... 1,160■ Tr: Temperature change at the position r from the center (used as a quadratic function) T: Temperature at the position r from the center The above calculation formula (1) is calculated based on the numerical values shown in each term. Ta.

■ From thermal stress and actual strength, set the temperature increase limit inside the member so that the thermal stress does not exceed the actual strength; Using the calculation results of internal thermal stress of the member shown in Table 3, the actual strength of the member is Although it is a 31 wheel drive race, considering the safety factor, it is 20 Kff.
7'i-, and when determining the temperature limit temperature of the member, it was determined that the temperature of the inner diameter portion of the member should be 150° C. or less immediately after quenching as a condition for preheating. @Cough heat stress analysis results are shown in Figure 3 (b).

(4) Preheating of the entire member: Considering the time from preheating to main heating, the entire member was preheated using an electric furnace under the following conditions.

180°C While heating, the local parts of the member facing the heating coil were sequentially main-heated and rapidly cooled.

Heating conditions: Power output...600KIE frequency
・・・・・・・・・・・・3 KHz relative movement speed...
...1.0 Clearance between main parts and coils...5m Coolant; 1.0
Part surface temperature before starting PVA solution heating: 120 to 130°C Under the above heating conditions using a relatively moving heating coil, the member is successively locally heated until the surface temperature reaches approximately 860°C, and then sprayed from the following cooling jacket. It was rapidly cooled by the cooling liquid.

(6) Heat treatment results: No quench cracking occurred. The hardened layer formed on the member had a surface hardness Ha of 74 to 77 and a hardening depth of 3.4.

Incidentally, FIG. 3(c) shows a temperature characteristic curve diagram obtained from the thermometer values of the member immediately before and immediately after rapid cooling using a thermocouple attached to a predetermined position. In the figure, [Curve A represents the internal temperature distribution of the member immediately before quenching, and curve B represents the internal temperature distribution of the member immediately after quenching.

In the above example, the present invention is applied to a large-diameter member made of Fe12 material. A thick effective hardening layer is formed.

In the example, a predetermined part of the member after the entire preheating is heated once by relative movement at an extremely slow movement speed of 1ml/11e to locally heat it to 860°C and rapidly cool it. However, for example, if the power supply output is insufficient, In such a case, the relative movement may be repeated a plurality of times before quenching, as long as the internal temperature of the member immediately before quenching can be maintained below the temperature increase limit temperature. However, in this case, although there is no risk of quench cracking, it may not be satisfactory if a sufficient hardening depth is expected.

As mentioned above, the present invention makes it possible to form an effective hardened layer of 2 m or more by heat treatment on large diameter cast iron members, which were previously considered impossible to comply with, so conventional forged materials or pongee-like materials had to be used. Cast iron can be used as the material for the large-diameter member, and the manufacturing cost can be greatly reduced, resulting in extremely large effects.

[Brief explanation of drawings]

Figure 1 is a diagram showing the surface layer hardness of the specimen in Example 1, Figure 2 (,) is a partial front and II side view showing the temperature measurement position of the specimen in Experimental Example 2, and Figure 2 (b) is a diagram showing the surface hardness of the specimen in Example 1. Figure 2 (C) is a diagram showing the internal temperature distribution of the specimen immediately before and immediately after rapid cooling obtained in Experimental Example 2 as A and B, respectively. Figure 2(d) shows the results of thermal stress analysis in Experimental Example 2. Figure 3(a) is a front view of a portion of a large-diameter cast iron member according to an embodiment of the present invention.
Figure 3 (b) shows the thermal stress analysis results in the example of the present invention. Figure 3 (c) shows the internal temperature distribution of the member immediately before and after rapid cooling in the example of the present invention as curved edges A and B, respectively. It is a line diagram. Agent Patent Attorney Fu Kobayashi Figure 1 s 0123456mm Figure 2 (b) Figure 2 (C) s 0 1 23, 456mm Figure 2 (d) mm 8 surface

Claims (1)

[Claims] 1) A method for forming an effective hardened layer as thick as possible in a predetermined portion of a large-diameter member made of cast iron is to preheat the entire member and then main-heat the predetermined portion of the surface layer by rust induction heating. In addition, the preheating of the entire member increases the temperature difference between the surface temperature of the member immediately after the quenching and the temperature of internal retained heat, and the thermal stress caused by the quenching reduces the actual strength of the member. The heating coil is applied so as to stay within the vortex rising limit temperature range that cannot be exceeded, and the main heating is performed by sequentially moving relatively from one end of a predetermined part of the member to the other end of the member, to a predetermined depth, at once to a predetermined quenching temperature. A method for surface hardening a large-diameter cast iron member, characterized in that the surface hardening is performed by moving heating performed at a moving speed that allows the temperature to rise, and the quenching is immediately applied to local areas that are successively subjected to main heating. 2) The surface hardening method for a large diameter cast iron member according to claim 1, wherein the thickness of the effective hardened layer to be formed is at least 2- or more. 3)! # A large-diameter member made of iron is preheated in advance, and a predetermined portion of the member is successively locally heated and rapidly cooled using a heating coil that moves relative to the predetermined portion of the member to form an effective hardened layer as thick as possible in the predetermined portion. In the case of forming, the preheating is 1, the actual strength of the member; the process of determining the tensile strength, the step of estimating or experimenting the member surface temperature and internal temperature distribution of the member immediately after the quenching, and the above calculation. The process calculates the thermal stress occurring in the member from the obtained member surface temperature and internal temperature distribution, and calculates the internal temperature of the member such that the thermal stress does not exceed the actual strength from the above calculated thermal stress and the above determined substantial strength. A method for surface hardening a large-diameter cast member, characterized in that the surface hardening is performed within the temperature range obtained by the step of determining the temperature increase limit temperature, and the internal temperature of the member immediately before quenching is maintained below the temperature increase limit temperature. .