KR19990056684A - Alloy steel for transmission gear and manufacturing method - Google Patents

Abstract

The present invention relates to an alloy steel for a transmission gear and a manufacturing method thereof, and more particularly, in the composition of an alloy steel for a transmission gear containing carbon, silicon, manganese, phosphorus, sulfur, nickel, nitrogen, chromium and molybdenum. To increase the content of molybdenum in order to minimize the content of chromium and silicon forming the secondary alloy and to impart secondary reinforcement characteristics according to the need for maintaining strength at high temperature, and to refine the crystal grains so as to omit the annealing heat treatment process in the production of alloy steel The present invention relates to an alloy steel for a transmission gear having a new composition prepared by newly adding niobium and vanadium, and a manufacturing method thereof.

Description

Alloy steel for transmission gear and manufacturing method

The present invention relates to an alloy steel for a transmission gear and a manufacturing method thereof, and more particularly, in the composition of an alloy steel for a transmission gear containing carbon, silicon, manganese, phosphorus, sulfur, nickel, nitrogen, chromium and molybdenum. To increase the content of molybdenum in order to minimize the content of chromium and silicon forming the secondary alloy and to impart secondary reinforcement characteristics according to the need for maintaining strength at high temperature, and to refine the crystal grains so as to omit the annealing heat treatment process in the production of alloy steel The present invention relates to an alloy steel for a transmission gear having a new composition prepared by newly adding niobium and vanadium, and a manufacturing method thereof.

Alloys for transmission gears generally require excellent wear resistance, fatigue resistance, and impact strength characteristics. Therefore, in order to impart such characteristics to the alloy for transmission gears, conventionally, iron is the main component, and carbon is 0.17 to 0.23 wt%, silicon 0.15 to 0.35 wt%, chromium 0.8 to 1.3 wt%, manganese 0.5 to 1.0 wt%, phosphorus 0.020 Steelmaking, hot-forging, machining, cold-forging using less than or equal to 0.0% by weight, less than or equal to 0.020% by weight of sulfur, 0.15 to 0.4% by weight of molybdenum, and 0.25 to 2.00% by weight of nickel. After annealing, heat treatment (normalizing), machining (machining), high temperature carburizing (Carburizing) process has been prepared.

Here, the annealing heat treatment is preferably not applied as a process for ensuring good homogeneity and workability by forming uniform and fine grains, but if this step is omitted, abnormal coarse particles are formed during the later carburizing process. As a result, thermal deformation is caused and fatigue resistance and toughness are deteriorated, and thus, heat treatment has been required.

In addition, the conventional carburizing treatment is a process for imparting high fatigue strength, abrasion resistance and appropriate toughness. During the carburizing treatment, chromium, silicon dioxide and manganese oxide are combined with chromium, silicon and manganese in the alloying element with oxygen. It occurs intensively at the grain boundary to form a grain boundary oxide layer to not only reduce the fatigue strength, but also to deplete the alloying elements around the oxide to form a non-sintering layer. Therefore, there has been a problem of lowering the overall strength of the alloy steel. In addition, there was a problem that the embrittlement phenomenon of the tampered martensite in the carburized layer occurs.

Accordingly, the present invention is to add a niobium, vanadium to the composition of the conventional alloy steel, to minimize the content of chromium and silicon, to increase the content of molybdenum, to improve the heat treatment properties by improving the content of molybdenum in order to improve the above problems Therefore, it is possible to produce fine particles by cold forging alone, and also to provide a new alloy steel for a transmission gear and a method for manufacturing the same, which are not only endowed with secondary reinforcement at high temperatures but also have increased wear resistance, fatigue resistance and impact resistance. Its purpose is to.

The present invention relates to an alloy steel for a transmission gear having iron as a main component, carbon 0.17 to 0.23 wt%, silicon 0.01 wt% or less, chromium 0.01 wt% or less, manganese 0.3 to 0.5 wt%, phosphorus 0.01 wt% or less, sulfur 0.01 weight It is characterized by the alloy steel for the transmission gear which contains% or less, 0.25 weight% or less of nickel, 0.9 to 1.1 weight% of molybdenum, 0.01 weight% or less of nitrogen, 0.015 to 0.1 weight% of niobium, and 0.1 to 0.5 weight% of vanadium.

In addition, the present invention includes a method for manufacturing an alloy steel for a transmission gear by using the alloy steel of the composition and content described above in the process of steelmaking, hot forging, machining, cold forging, machining and high temperature carburizing.

Referring to the present invention in more detail as follows.

The present invention suppresses the addition of silicon, chromium and manganese in the composition of conventional alloy steel for transmission gears, increases the content of molybdenum, and adds niobium and vanadium, thereby eliminating grain boundary layer and reinforcing strength, The present invention relates to an alloy steel for a transmission gear and a method of manufacturing the same, which can be manufactured in a shorter time by miniaturizing and preventing abnormal grain growth and physical property degradation during carburization and eliminating annealing heat treatment.

In the present invention, the content of carbon is the same as in the prior art, and silicon and chromium, which have been used for the purpose of supplementation of conventional antifertility, are added to the total composition in order to prevent the formation of grain boundary layer, which is a side effect caused by them. The addition is suppressed as much as 0.01 weight% or less.

When manganese is also contained in excess, as with silicon and chromium, there is a problem in that the strength is reduced as it is oxidized to form a grain boundary oxide layer, and the content thereof is preferably limited to 0.3 to 0.5% by weight or less.

In addition, molybdenum is added in an amount ranging from 0.9 to 1.1% by weight in the total composition for the purpose of increasing toughness such as carburization, improving fatigue strength, and secondary reinforcing properties.

In addition, phosphorus is a basic element of the steel material to lower the content to less than 0.01% by weight to prevent the tamburized martensite embrittlement (Embrittlement). If the content of phosphorus exceeds 0.01% by weight, there is a problem of increased brittleness due to grain boundary segregation of Fe ₃ P precipitates.

In addition, sulfur is added to improve processability, and the content thereof is 0.01 wt% or less, and if the sulfur content exceeds 0.01 wt%, a problem of increasing high temperature brittleness occurs.

In addition, nickel and nitrogen each contain 0.25% by weight or less and 0.01% by weight or less as usual.

On the other hand, in the present invention, in order to simplify the process and to increase the strength of the alloy steel to minimize the annealing heat treatment step in the production of alloy steel by miniaturizing the crystal grains, niobium is contained 0.015 ~ 0.1% by weight, vanadium 0.1 ~ 0.5% by weight.

At this time, niobium precipitates fine niobium carbonitrides to perform a pinning action on grain boundaries, and titanium refines crystals by pinning action on grain boundaries by also depositing titanium carbonitrides. Therefore, if the content of niobium is less than 0.015% by weight, there is a problem in that the pinning effect is canceled, and when added in excess of 0.1% by weight there is a problem of desaturation effect due to supersaturation and coarse precipitate.

In addition, vanadium is added for the grain refining effect through the precipitation of carbonitride, but if the content is less than 0.1 wt%, there is a problem that the precipitation effect of carbonitride is insignificant, whereas if it is used more than 0.5 wt%, It is not preferable because there is a problem that brittleness increases.

As described above, in the case of carburizing without annealing heat treatment after cold forging by adding a grain refinement element, an abnormal coarsening phenomenon of grains may be prevented by a peening effect such as Nb-C and V-C. On the other hand, if the annealing heat treatment is omitted after carburizing using a conventional material, abnormal grain coarsening of the grains occurs, resulting in deterioration of physical properties, heat treatment deformation, and the like, and even when carburizing at a high temperature of about 1000 ° C. Carbide action can lead to abnormal grain changes.

The present invention uses the above components and contents in the first steelmaking (melting) and hot forging to the desired size, then machined for cold forging and cold forging. Then, it is machined again without annealing heat treatment and subjected to high temperature carburization at 1000 ° C. in order to give high fatigue strength, wear resistance and toughness. Then, compared with the conventional method, it is possible to obtain an alloy steel for a transmission gear having time saving effect and superior physical properties.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by Examples.

Example 1

Following the manufacturing method presented in the present invention in the content and composition as shown in Table 1, after the steel (melting) in the usual conditions and hot forging to the desired size, the machined for cold forging and cold forging. Then, the machine was machined again without annealing heat treatment and subjected to high-temperature carburization at 1000 ° C. to produce the alloy steel for the transmission gear of the present invention.

Comparative Examples 1 to 3

The following steels SCR 420H, SCM 318H, SNCM 420H having the content and composition as shown in Table 1 were manufactured in accordance with a conventional method through the steelmaking, rolling process for the transmission gear alloy steel.

Experimental Example

The thickness of the grain boundary oxide layer was measured by a microscopic observation method for the alloy steels for the transmission gears prepared in 1 to 3 in the above and comparison. The bending fatigue strength was determined by the diffraction bending fatigue test, and the contact fatigue strength was determined by the roller fitting test. , And the impact strength was measured according to the Charpy impact test method, and the results are shown in Table 1.

division Example Comparative Example 1 (SCR 420H) Comparative Example 2 (SCM 318H) Comparative Example 3 (SNCM 420H) Composition (% by weight) carbon 0.23 0.20 0.21 0.21 silicon 0.044 0.30 0.28 0.28 manganese 0.368 0.70 0.88 0.88 sign 0.0025 0.02 0.016 0.016 sulfur 0.0056 0.002 0.016 0.016 nickel - - 0.10 1.60 chrome 0.01 1.10 1.201 0.54 molybdenum 1.035 - 0.098 0.09 Niobium 0.049 - - - vanadium 0.0108 - - - iron 98.2451 97.678 97.199 96.368 Sum 100 100 100 100 Property test Grain oxide thickness (㎛) 0 25 20 20 Impact Strength (㎏f / ㎠) 2.49 0.80 1.0 1.26 Bending Fatigue Strength (㎏f / ㎠) 100 73 75 86 Contact fatigue strength (㎏f / ㎠) 300 200 230 250

As described above, the alloy steel for the transmission gear according to the present invention can improve the fatigue strength by removing chromium and silicon constituting the grain boundary oxide layer, impart secondary reinforcing characteristics for maintaining strength at high temperature, and crystal grains It can be seen that by miniaturization, the annealing heat treatment step can be omitted, thereby producing an alloy steel for a transmission gear economically in a shorter time.

Claims (2)

In the alloy steel for transmission gear mainly composed of iron, 0.17 to 0.23 wt% of carbon, 0.01 wt% of silicon, 0.01 wt% of chromium, 0.3 to 0.5 wt% of manganese, 0.01 wt% of phosphorus, 0.01 wt% of sulfur, Alloy steel for transmission gear containing 0.25 weight% or less of nickel, molybdenum 0.9-1.1 weight%, nitrogen 0.01 weight% or less, niobium 0.015-0.1 weight%, and vanadium 0.1-0.5 weight%. Method for producing an alloy steel for a transmission gear, characterized in that the steelmaking (MELTING), high temperature forging, machining, cold forging, machining and high temperature carburizing process using the alloy steel of the composition and content of claim 1.