JPH0251972B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention particularly relates to a high manganese steel with excellent rolling fatigue properties and a method for producing the same. [Conventional technology] Conventionally, mechanical parts that suffer from rolling fatigue,
For example, rotating parts such as gears, kiln rollers, etc. may be subjected to a surface hardening treatment such as induction hardening, carburizing, nitriding or thermal spraying, or if such surface hardening is not possible, e.g. due to cost considerations. In cases where the design or shape or size of the parts is significantly inappropriate for surface hardening, these parts have become consumables that must be replaced when peeling occurs due to rolling fatigue. [Problems to be Solved by the Invention] However, replacing parts every time peeling occurs is costly, and may cause an accident if the machine is operated without noticing peeling. In addition, surface hardening treatment is costly and, for example, when carburizing steel with a low carbon content and almost no manganese, grain boundary oxidation occurs.
In the case of thermal spraying, the process generally lacks stability, such as poor consistency between the welded metal and the base metal, resulting in peeling, and many accidents occur due to this. Furthermore, in the case of surface hardening treatment, if the surface hardening layer is removed due to wear or similar causes, the effect will be completely lost. The high manganese steel of the present invention solves the above-mentioned problems of the conventional surface hardening treatment, and has high rolling fatigue properties equivalent to or higher than carburized steel subjected to surface hardening treatment. That is, high manganese steel normally has a hardness of around Hv200, but when a load such as an impact force is applied, the surface layer of that part becomes hard. For this reason, not only can a stable surface hardening layer be easily obtained during use without surface hardening treatment, but even if the surface hardening layer is removed due to wear or similar causes, the surface hardening layer beneath it can be It has the advantage that the layer is hardened.
Furthermore, high manganese steel is much cheaper than surface-hardened steel, and there are no restrictions on shape or size. However, in case of carburizing, for example, the surface hardening layer
Compared to Hv700-800, in the case of use conditions where rolling fatigue occurs, that is, in the case of use conditions where stress is applied during rotation but no impact force is applied, Table 1 below. As shown in the figure, the surface layer of high manganese steel like the one of the present invention is
Hv is only about 430 to 450, and it cannot be assumed from the hardness of this surface layer that high manganese steel has high rolling fatigue properties equivalent to or higher than surface hardened steel. , it was not used in parts where high rolling fatigue would be a problem. [Means and effects for solving the problems] In the present invention, in order to solve these problems, a high manganese steel having high rolling fatigue properties was obtained. In the present invention, high manganese steel is
So, C: 0.7~1.5%, Si: 0.8% or less, Mn: 10~
15%, the balance consisting of Fe and unavoidable impurities,
A high manganese steel with high rolling fatigue characteristics with a rolling fatigue durability limit of 120 kgf/mm ² or more was used. In the present invention, the high rolling fatigue property is limited to a rolling fatigue durability limit of 120 Kgf/mm ² or more so that the rolling fatigue durability limit is dramatically higher than that of conventional steel. In the present invention, high manganese steel with these components is used, and the high manganese steel is heated to 500 to 700 °C, tempered here and subjected to pearlitization heat treatment, and then reheated to a temperature of 950 to 1100 °C. A re-solution heat treatment was performed at ℃, followed by rapid cooling at the end to obtain a high manganese steel with high rolling fatigue properties. Alternatively, high manganese steel with these components, 500
The material is heated to ~600°C, tempered here, and pearlitized, then reheated at 4~100°C/min, re-solution heat treated at 800~950°C, and finally rapidly cooled. In this way, a high manganese steel with high rolling fatigue properties was obtained. Next, the reason why the composition of the high manganese steel of the present invention is limited as described above will be explained. In addition, all component compositions are expressed in weight %. (a) C, Mn C, Mn components influence the stability of austenite in the matrix structure and work hardening properties, and are 0.7 to 1.5
%C, 10-15% Mn has the most stable austenite and high work hardening properties. Therefore, C was set at 0.7 to 1.5%, and Mn was set at 10 to 15%. (b) Si Si is an essential component to improve the flow of the metal, but its effect is saturated even if it is contained in excess of 0.8%, so the upper limit was set at 0.8%. [Example] The steel of the present invention is subjected to three types of heat treatment as shown in Figs. 1 to 3, as necessary. The details of this heat treatment will be described below. After heating at 1000-1100°C for 2 hours, cool with water. Heat treatment shown below→→ or→
Apply in this order. After heating to 1000-1200℃, air or water cooling is performed. After heating at 500-700℃ for more than 10 hours, air cool. After heating to 950-1100℃, cool with water. Heat treatment shown below→→ or→
Apply in this order. After heating to 1000-1200℃, air or water cooling is performed. After heating at 500-600℃ for 10 hours or more, air cooling. After heating to 800-950℃, cool with water. The heating time in each step of the heat treatment was 1 to 5 hours, although it varied depending on the thickness and size of the object to be heat treated. Under the above heat treatment conditions, the heating temperature of the steel is
The temperature range of 1000 to 1100℃ is above 1000℃, and high manganese steel becomes austenite single phase.
This is because by water-cooling this, an austenite structure that is stable at room temperature can be obtained. Furthermore, the reason why the upper limit was set at 1100°C is that no further heating is necessary to obtain an austenite single-phase structure. The heat treatment is a heat treatment that refines crystal grains. That is, after obtaining an austenite single-phase structure in the process, pearlite is precipitated in the temperature range of 500 to 700℃ where pearlite is most likely to precipitate, and in the process of forming a solid solution of pearlite in the process, crystal grains are formed. Obtain a fine austenite single phase structure. However, normally, the heat treatment of →→ is performed, but if the as-cast condition is such that no acicular carbides are precipitated and only pearlite is precipitated, this step may be omitted. As shown above, →→ or →
Since steel subjected to heat treatment has fine grains, it is used particularly when toughness or particularly high rolling fatigue properties are required. In other words, as will be explained in the examples below, the results of rolling fatigue tests on high manganese steel not only showed superior rolling fatigue properties compared to conventional forged products (crystal grains are on the order of several mm), but also showed superior rolling fatigue properties during the heat treatment process. This is because the cast products subjected to the heat treatment process to refine the crystal grains exhibited rolling fatigue properties that were approximately the same as the forged products subjected to the heat treatment process. The heat treatment for is almost the same as the heat treatment for , but the main difference is that the temperature in the process is slightly different. In this example, a structure in which spherical carbides are dispersed in an austenite base is obtained in the step. At that time, the heat treatment temperature is 800 to 950℃.
to obtain the amount of spherical carbide dispersed as required.

【table】

[Table] For the purpose of investigating the rolling fatigue durability limit of this steel, approximately 100 kg of steel whose composition is shown in Table 1 was melted in a high-frequency melting furnace. This ingot is steel number 1,
Steel No. 2 was subjected to the heat treatment of the steps (in the order of →→), and the sample of steel No. 3 was forged at a forging ratio of 10 and then subjected to the heat treatment of the steps. A Nishihara type metal wear tester was used as the tester, and the fatigue durability limit of the test piece 1 shown in FIGS. 4 and 5 was examined at a slip of 9% and a rotational speed of the roller 2 of 800 rpm. As the test piece 1, a ring-shaped one was used. The results are shown in FIG. 6 and the right column of Table 1.
The steels of the present invention (steel numbers 1, 2, and 3) exhibited significantly superior fatigue durability limits compared to the conventional steels (steel numbers 4, 5, and 6). Furthermore, the characteristics of the steel of the present invention are cast products (steel number 2)
However, through heat treatment, it is possible to obtain a rolling fatigue durability limit comparable to that of forged products (Steel No. 3). In other words, a forged product of Steel No. 3 exhibits a fatigue durability limit that is approximately 1.5 times that of a cast product of Steel No. 1, but
By applying process heat treatment to the cast product, steel number 2
We were able to obtain a fatigue durability limit comparable to that of forged products. [Effects of the Invention] The steel of the present invention, particularly the high manganese steel obtained by the manufacturing method of the present invention, has extremely excellent high rolling fatigue properties. Therefore, even when these are used in rotating members to which high pressure is applied, surface peeling does not occur and the service life can be extended. Note that, according to the manufacturing method of the present invention, even materials that cannot be carburized can be easily carburized, so it is extremely practical.

[Brief explanation of the drawing]

Figures 1 to 3 are views showing different examples of heat treatment applied to the steel of the present invention, Figures 4 and 5 are front and side views showing the shape of the test piece subjected to the rolling fatigue test, Figure 6 is a contact stress diagram showing the results of a rolling fatigue test. 1...Test piece.

Claims (1)

[Claims] 1% by weight, C: 0.7 to 1.5%, Si: 0.8% or less,
Mn: 10-15%, the balance consists of Fe and unavoidable impurities, rolling fatigue durability limit is 120Kgf/mm ²
High manganese steel with high rolling fatigue properties. 2 In weight%, C: 0.7 to 1.5%, Si: 0.8% or less,
High manganese steel consisting of Mn: 10~15%, the balance being Fe and unavoidable impurities is heated to 500~700℃,
Here, tempering and pearlitization heat treatment are performed, followed by reheating, re-solution heat treatment at 950 to 1100℃, and finally rapid cooling to obtain high manganese steel with high rolling fatigue properties. A method for producing high manganese steel having high rolling fatigue properties. 3 In weight%, C: 0.7 to 1.5%, Si: 0.8% or less,
High manganese steel consisting of Mn: 10~15%, the balance Fe and unavoidable impurities is heated to 500~600℃,
Here, it is tempered and pearlitized heat treated, then reheated at 4 to 100℃/min, and then heated to 800 to
A method for producing a high manganese steel having high rolling fatigue properties, in which a high manganese steel having high rolling fatigue properties is obtained by performing re-solution heat treatment at 950°C and finally quenching.