JPH01201459A - Parts combining high toughness with wear resistance - Google Patents

Abstract

PURPOSE:To obtain parts combining high toughness with wear resistance by subjecting a steel with a specific composition to the prescribed carburizing treatment by an ion carburizing method and then to quench-and-temper treatment. CONSTITUTION:A steel having a composition consisting of 0.3-0.7% C, <=1.5% Si, <=2.0% Mn, 3-15% Cr, <=5.0% Mo, further <=2.0% V and/or <=3.0% W, and the balance Fe with inevitable impurities is refined. This steel is carburized by an ion carburizing method so that the area ratio of carbide in the cross section within 0.1mm from the surface is regulated to >=10% and is then subjected to quench-and-temper treatment under the ordinary conditions, by which the parts combining high toughness with wear resistance can be prepared. Further, it is desirable that the above parts are tools for cold working.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to parts having high toughness and wear-resistant surfaces, particularly tools for cold working. [Prior Art] When manufacturing structural parts that make up various machines, there is a growing tendency to only perform warm or cold processing without hot processing. Along with this, the processing conditions for cold working are becoming increasingly strict. For this reason, tools used for cold working, such as forging dies, are required to have high toughness in addition to surface wear resistance in order to withstand use under harsh conditions. has been done. [Problems to be Solved by the Invention] An object of the present invention is to meet these demands and provide a component, particularly a cold working tool, that has both wear resistance and high toughness.

[Means to solve the problem]

The high toughness wear-resistant parts of the present invention have C: 0.7% exceeding 0.3%.
% or less, Si: 1.5% or less, Mn: 2.0% or less, C
In addition to r: 3 to 15% and Mo: 5.0% or less, V
A steel containing one or two selected from: 2.0% or less and 3.0% or less W, with the remainder being Fe and unavoidable impurities is carburized by an ion carburizing method to remove O, O,
The carbide area ratio in a cross section within 1 m is 10% or more, and is quenched and tempered. Carburizing treatment using the ion carburizing method uses a carburizing furnace with a vacuum level of 1O.
The pressure is reduced to about -2 TOrr, the parts are heated, and hydrocarbon gas, which is carburizing gas, is introduced into the furnace, and the pressure inside the furnace is reduced to several Torr.
rr and apply a voltage between the component as a cathode and a separately provided anode to generate glow discharge. Prior to carburizing, it is preferable to carry out glow discharge under an Ar and river mist atmosphere for a while to clean the surface of the part, as shown in the examples below. The quenching and tempering treatment of the carburized layer may be performed under the same conditions as conventional heat treatment. Typically, 1000
Quenching by oil cooling or gas cooling from ~1100℃→5
After holding at 00 to 700''C for 30 minutes to 2 hours, tempering is performed by air cooling.

[Function] Conventionally, tools used for cold working are made of steel with a high carbon content and have high hardness from the surface layer to the joint, but their toughness is not very high.
Therefore, the inventors focused on the fact that tool steel for hot working has relatively high toughness, and by carburizing the parts manufactured using this tool to harden the surface, they imparted wear resistance to the surface layer. By taking advantage of the toughness of this material, we succeeded in creating tool parts for cold working that can withstand harsh working conditions. The functions of the alloy components of the steel used in the present invention and the reasons for limiting the composition range will be explained below. C: more than 0.3% and less than 0.7% C is an element added to increase the strength of parts. 0.3
If the content does not exceed %, sufficient joint strength cannot be obtained,
On the other hand, if the content exceeds 0.7%, the joint becomes too hard and the toughness decreases. Si: 1.5% or less If a large amount of 3i is contained, forgeability is reduced, carburizability is inhibited, and decarburization is promoted, so 1.5% is set as the upper limit. 1.47 Mn: 2.0% or less Mn is added to improve hardenability. It may be added in an appropriate amount taking into consideration the balance with other elements, but if the content exceeds 2.0%, machinability will deteriorate. Cr: 3-15% Cr is added as a carbide-forming element to ensure a predetermined amount of carbide. The C concentration during carburization increases as the Or content increases. Further, when Cr is included, spheroidization of carbide is promoted. If the content is less than 3%, these effects will not be sufficient, while if it exceeds 15%, the amount of carbon in the carburized layer will be too large, and network-like carbides will precipitate, reducing mechanical properties. 1 selected from Mo: 5.0% or less, V: 2.0% or less, and W: 3.0% or less
Species or two These are both carbide-forming elements, and as their content increases, the amount of carburization increases. However, these elements also form carbides during material production, and especially coarse temporary carbides deteriorate toughness and fatigue strength. To prevent this, we have set the limits as described above. The parts of the present invention are obtained by carburizing the above-mentioned steel so that the area ratio of carbides in the cross section within 0.1 inch from the surface is 10% or more. If the area ratio of carbides is less than 10%, sufficient wear resistance cannot be obtained. Gas carburizing, which is currently the mainstream method for carburizing, tends to cause sooting and uneven carburizing when operated at high carbon potential. Further, since the carburizing gas used by modifying hydrocarbon gas or the like is oxidizing, it is inevitable that a grain boundary oxidation layer will be formed on the surface of the part as a result of carburizing. As a result, the hardenability near the surface deteriorates, resulting in an incompletely hardened structure. Therefore, strong cooling is required to reduce the required hardness by 1q, and there is a problem that quench cracking is likely to occur. The vacuum carburizing method tends to cause uneven carburizing, and cannot uniformly carburize parts with complex shapes. On the other hand, in the ion carburizing process using glow discharge under reduced pressure, Cl-13 or 03H8 is used as the carburizing gas, so no grain boundary oxidation layer is formed. In addition, since the process is operated at a pressure approximately 1/100 times lower than that of vacuum carburizing, sooting hardly occurs. In general, since the plasma state caused by the glow discharge covers the entire surface of the part being treated, it is possible to uniformly carburize even parts with complex shapes.

【Example】

An alloy having the composition shown in the table was melted. Nα1 is a comparative example and NQ2-8 are materials according to the invention. A test piece of each material was placed in an ion carburizing furnace, and the inside of the furnace was heated to 1O-2.
The pressure was reduced to Torr, heated to 1050°C, and Ar and H2 were supplied to adjust the furnace internal pressure to 2 Torr. The test piece was used as a cathode, and a DC voltage of 50 O was applied between it and the anode to cause glow discharge. As a pretreatment, the surface was cleaned with Ar and H ions for 20 minutes, and then the Ar and gas were evacuated. Subsequently, C3H8 was fed into the furnace and carburized at a pressure of 2 Torr for 1 hour. At that time, the test piece, which had been heated to 1050°C, was quenched by gas cooling by blowing N2. However, the Nα8 test piece was quenched by heating to 1150°C and cooling with oil. For tempering, the Nα1 test piece was held at 500°C, and the other test pieces were held at 600°C for 1 hour, and then allowed to cool. The surface hardness, carbide area ratio within 0.18 from the surface, impact value (IOR notch value Charpy test piece), and specific wear amount of the obtained test piece were measured. The specific wear amount was measured using an Odate type wear tester. The measurement conditions are as follows. Mating disc SK6 HRB90 Final load 6.51 Friction distance 200am Friction speed 2.0TrL/sec The above results are shown in the table. As can be seen from this data, parts according to the invention are tougher than those of the comparative example and have approximately the same wear resistance.

【Effect of the invention】

As the name suggests, the high-toughness wear-resistant parts of the present invention have high toughness at the joints and wear resistance at the surface layer. If this is applied to tools for cold working, for example, it becomes possible to perform cold working under severe conditions that would not be possible with conventional tools. Patent applicant Daido Steel Co., Ltd. Agent Patent attorney Souo Suga

Claims (2)

[Claims] (1)C: over 0.3% but not more than 0.7%, Si: 1.5%
Below, Mn: 2.0% or less, Cr: 3-15% and M
In addition to o: 5.0% or less, V: 2.0% or less and W
: A steel containing one or two selected from 3.0% or less, with the balance consisting of Fe and unavoidable impurities, is carburized by the ion carburizing method to reduce the carbide area ratio to 10% in a cross section within 0.1 mm from the surface. A high toughness wear-resistant part made by quenching and tempering the above. (2) The part according to claim 1, which is a cold working tool.