JPH057454B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a railway wheel that has good wear resistance and excellent breakage resistance. Railway wheels are for locomotives, passenger cars, and freight cars.
Wheels of various sizes, shapes, and materials are used depending on their purpose, but the service life of these wheels is usually determined by the wear of their treads and flange surfaces, so the basic Therefore, materials with good wear resistance were required for wheel steel. As a result of much experience and research in the past, we have found that a high-hardness material in which most of the structure is pearlite, that is, high carbon pearlite structure steel, best satisfies the above requirements among carbon steels and low alloy steels. It was discovered that this high carbon pearlitic steel was forged to make railway wheels, which has traditionally been the most common practice. However, in recent years, as railway wheels have become faster, monolithic wheels have come to be used due to safety issues, especially at high speeds.
As speeds have increased, the heat generated by brakes has increased, leading to an increase in thermal distortion, and in addition to wear resistance, crack resistance has come to play a large role in railway wheels. It was. By the way, wheel breakage occurs when the thermal stress caused by severe braking or friction with the rail increases, causing fine thermal cracks in the diametrical direction of the wheel's tread or flange surface, causing damage to the material. If fracture toughness is insufficient, one or more of the cracks will grow, and the moment the thermal crack reaches a certain critical length, it will undergo a rapid brittle fracture and crack. This is an extremely dangerous form of damage that must be avoided for safety reasons. Therefore, there is a strong demand for modern railway wheels to have both high resistance to cracking and good wear resistance. These characteristics are based on mutually contradictory properties for steel, and there was a view that the realization of a material that satisfies both at the same time was a long way off. For this reason, wheel manufacturing currently requires
Under usage conditions where wear resistance is important, we ignore the slight lack of toughness and use medium carbon steel (C:; 0.65 ~
0.75% by weight), and under usage conditions where crack resistance is important, yield strength and wear resistance are ignored to some extent, and medium carbon steel with high toughness and excellent crack resistance and low carbon content ( C: 0.45 to 0.55% by weight) was selected and used as a common measure in countries around the world. In addition, the C content is 0.45 to 0.55% (hereinafter referred to as %
In order to obtain wear resistance, we performed induction hardening on a medium carbon steel that increased the ferrite mass and secured toughness by lowering the ferrite mass (% by weight), and changed only the surface to martensite or bainitic structure close to martensite. Attempts have also been made to improve the hardness of the surface, but the result was that the wear resistance was still insufficient. From the above-mentioned viewpoint, the inventors of the present invention aimed to provide a railway wheel that has the mutually contradictory characteristics of wear resistance and cracking resistance. However, based on the above test results showing that the wear resistance was inferior to pearlite structure steel, we conducted repeated research with the aim of improving the toughness without reducing the wear resistance of pearlite structure steel. As a result, (a) Adding a specific alloying element to pearlitic steel to strengthen its ferritic base improves the yield strength of the steel, but as a steel for wheels, in terms of yield strength, it is comparable to pearlitic steel on the high C side. is sufficient, so adding the above alloying element makes it possible to lower the amount of C. Therefore, if the amount of C is reduced, the amount of co-rected C is also reduced, the cementite layer in pearlite becomes thinner, and the fracture toughness of the cementite portion is improved. This also means that the thinner the cementite layer is, the higher the toughness value, and the thicker the ferrite layer strengthened by the alloying elements. Due to the mutual effect of the expansion of the cementite layer and the thinning of the cementite layer,
Unexpectedly, the fracture toughness value of the steel is significantly improved without deteriorating its wear resistance. (b) In particular, if the ferrite part of pearlite is strengthened with Ni, the toughness improvement effect of the ferrite part is further (c) When V is added to the above steel, the structure of the steel becomes finer and the toughness increases. We have come to the knowledge shown in (a) to (c) above that this will further improve the results. This invention was made based on the above findings, and includes: C: more than 0.40% to 0.80%, Si: 0.40% or less, Mn: 0.60% to 0.90%, Ni: 1.5 to 2.5%, Al: 0.060% or less. , P: 0.030% or less, S: 0.030% or less, and further contains V: 0.05 to 0.15%, if necessary, Fe and other unavoidable impurities: the remainder, Moreover, by being constructed of high-strength, high-toughness steel having a structure mainly composed of pearlite, the railway wheel is characterized by having both wear resistance and cracking resistance. Next, the reason why the composition of the steel constituting the railway wheel of the present invention is limited as described above will be explained. (i) CC The C component is included in order to generate a pearlite structure and obtain good wear resistance. The value of 0.40% corresponds to almost the lower limit for commonly used steels, and if the C content is less than this, the wear of the wheels becomes significant, causing a practical problem. On the other hand, the upper limit of the C content of ordinary steel is set at approximately 0.75%, which is the eutectoid C content, taking into account the decrease in cracking resistance due to cementite precipitation. Ni
Good cracking resistance can be obtained by adding C or V, and cracking does not occur up to a C content of 0.80%. Therefore, the C content should be more than 0.40%
It was set at 0.80%. (ii) Si Si component is necessary as a deoxidizing agent, but if its content exceeds 0.40%, Ni and Mn
Due to the additive effect with other alloying elements such as, it becomes easier to generate batonite and martensitic structures other than pearlite during hardening of wheels, so its content was set at 0.40% or less. (iii) Mn The Mn component has the effect of preventing grain boundary embrittlement due to FeS, but if the content is less than 0.60%, the desired effect cannot be obtained, while if the content exceeds 0.90%, the desired effect cannot be obtained. Even if Mn is added, no further improvement effect can be obtained, so the Mn content is
It was set at 0.60-0.90%. (iv) Ni The Ni component has the effect of improving the toughness of the pearlite structure, but if the content is less than 1.5%, the desired significant effect cannot be obtained in this effect, while if the content exceeds 2.5%, the desired effect cannot be obtained. If you let Si
Due to the interaction effect with other alloying elements such as and Mn,
Since bainite and martensite structures other than pearlite structures are likely to be generated during quenching and cooling of wheels, the Ni content was set at 1.5 to 2.5%. (v) Al The Al component is useful as a deoxidizing agent,
In addition, the crystal grains of steel are refined to improve cracking resistance (toughness).
It has the effect of improving the
When it exceeds 0.040%, the crack resistance begins to decrease,
If the content exceeds 0.060%, the properties will be comparable to those of the Al-free material. Therefore, Al
The content was set at 0.060% or less. (vi) P and S These elements are contained as unavoidable impurities, and P causes micro-segregation.
S generates sulfide-based inclusions, both of which reduce cracking resistance (toughness), so it is desirable to have as little S as possible. However, if the content of any of them is 0.030% or less, the effect is small, so the contents of P and S were each determined to be 0.030% or less. (vii) V The V component has the effect of refining the crystal grains of steel and significantly improving cracking resistance (toughness).
If the V content is less than 0.05%, the desired effect cannot be obtained in the above action, and on the other hand, if the content exceeds 0.15%, no further improvement effect can be obtained. Therefore, the V content is set to 0.05 to 0.15%. Established. Next, the railway wheel of the present invention will be explained through examples and in comparison with comparative examples. Example 1 This example also has the purpose of accurately evaluating the effect of adding alloying elements (Si, Mn, Ni, and Cr) to pearlitic steel.
Wheel materials A to I made of steel having the compositions shown in Table 1 were produced by a conventional method. In addition,
Wheel material A is a conventional wheel material used for conventional railway wheels, and wheel materials B to I each have their C content reduced by the amount that the eutectoid C amount decreases depending on the amount of alloying elements added. Wheel materials B to F and wheel materials H to I are comparative wheel materials, and wheel material G is an inventive wheel material used for the railway wheel of the invention. . Next, these samples were subjected to isothermal transformation heat treatment to create samples with a constant pearlite-lamellar spacing in the steel, and the lamellar spacing was varied between the samples to determine the effect and analyze it separately from the influence of the components. .

[Table] The results are shown in Figures 1 and 2. Figure 1 is a plot diagram showing the influence of alloying elements and pearlite-lamellar spacing on proof stress, which represents strength, and Figure 2 is a diagram showing the influence of alloying elements and pearlite-lamellar spacing on impact fracture transition temperature (FATT), which is representative of toughness. As is clear from the results shown in FIGS. 1 and 2, the wheel material G of the present invention used for the railway wheel of the present invention is superior to the conventional wheel material A, comparative wheel materials B to F, and H to I. It can be seen that the strength is the same or higher, and the toughness is excellent in both cases. In particular, Si and Ni are used for strength, while Ni and Mn are used for toughness.
It is clear that the 2% Ni added steel constituting the wheel material G of the present invention is the most effective in terms of both strength and toughness. Example 2 This example also has the purpose of confirming the effects of C and V on 2% Ni pearlite structure steel. Wheel materials J to N composed of the following were melt-manufactured. These wheel materials are designed to improve wear resistance.

[Table] As a target, the amount of C was increased by 0.10% compared to the eutectoid C amount (wheel materials M and N, in which granular cementite was precipitated in the pearlite structure), and the eutectoid C
Quantity (100% pearlite structure: wheel materials J to L)
Wheel materials J are conventional wheel materials used in conventional railway wheels. Fracture toughness (K・Q) of each of these wheel materials
The results of the measurements are shown in Figure 3. From the results shown in Fig. 3, wheel materials K and M, which are wheel materials of the present invention, have better toughness (fracture toughness) than wheel materials J, which are conventional wheel materials, and furthermore, by adding V, fine It can be seen that the textured wheel materials L and N, which are the wheel materials of the present invention, have further improved toughness (fracture toughness) than the conventional wheel material J. As mentioned above, the railway wheel of the present invention has good wear resistance equivalent to that of conventional wheels made of high carbon steel, has excellent cracking resistance, and does not require special equipment. can be manufactured,
This will bring about industrially useful effects, such as the ability to further improve the safety of current railway wheels, which are moving at higher speeds.

[Brief explanation of drawings]

Figure 1 is a plot diagram showing the influence of alloying elements and pearlite-lamellar spacing on the yield strength of wheel materials A to I. Figure 2 is a plot diagram showing the effects of alloying elements and pearlite on the impact fracture transition temperature of wheel materials A to I.・A diagram showing the influence of lamellar spacing. FIG. 3 is a graph showing the influence of C, Ni, and V on fracture toughness for wheel materials J to N.

Claims (1)

[Claims] 1 C: more than 0.40% to 0.80%, Si: 0.40% or less, Mn: 0.60 to 0.90%, Ni: 1.5 to 2.5%, Al: 0.060% or less, P: 0.030% or less, S: Constructed of high-strength, high-toughness steel that contains 0.030% or less, the remainder contains Fe and other unavoidable impurities, and has a composition (or more by weight) consisting of: and a structure mainly composed of pearlite. Railway wheels with excellent wear resistance and breakage resistance. 2 Contains C: more than 0.40% to 0.80%, Si: 0.40% or less, Mn: 0.60 to 0.90%, Ni: 1.5 to 2.5%, Al: 0.060% or less, P: 0.030% or less, S: 0.030% or less. In addition, it also contains V: 0.05 to 0.15%, Fe and other unavoidable impurities: the remainder, and has a component composition (the above weight %) consisting of, and has a structure mainly composed of pearlite. Railway wheels with excellent wear resistance and cracking resistance, characterized by being constructed from high-strength, high-toughness steel.