JPH01205063A - Wear-resistant stainless steel parts - Google Patents

Abstract

PURPOSE:To improve wear resistance while maintaining superior corrosion resistance and strength by working a martensitic stainless steel with a specific composition into the desired shape and subjecting the above to ion carburizing treatment under specific conditions and then to heat treatment. CONSTITUTION:A martensitic stainless steel which has a composition consisting of 0.05-0.6% C, <=3.5% Si, <=1.5% Mn, 7.0-20.0% Cr, and the balance Fe and containing, if necessary, <=3.0% Ni and/or one or more kinds among <=5.0% Mo, 0.6-1.4% W, 0.1-0.4% V, 0.1-0.7% Nb, and 0.05-0.15% N is worked into the desired shape. Carburizing is applied to the resulting parts by an ion carburizing method so that surface carbon concentration (C) is regulated to 0.5-4.0% and carbide area ratio (A) in the cross section within 0.1mm from the surface is also regulated to >=15%, followed by heat treatment. At this time, when the concentration C is less than 0.5% and the area ratio A is less than 15%, the required wear resistance cannot be obtained, and, particularly in the latter case, corrosion resistance is remarkably deteriorated. Further, when the concentration C is about 4.0%, the increase in hardness is saturated and, when it exceeds the above, the coarsening of carbide is brought about, on the contrary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to improvements in mechanical parts, particularly tools, made of martensitic stainless steel.

I. PRIOR ART Martensitic stainless steel has high strength as well as corrosion resistance, so its properties are used to make tools and mechanical structural parts, and its uses are expanding.

However, as its uses become more diverse,
Alternatively, there is a growing demand for parts that have wear resistance. For example, localized wear resistance is required on the contact surfaces of tools with other parts and on the bearings of motor shafts.

[Problem to be Solved by the Invention 1] The purpose of the present invention is to meet these demands and provide martensitic stainless steel parts that not only have excellent corrosion resistance and strength but also have wear resistance. be.

[Means to solve the problem] The wear-resistant stainless steel parts of the present invention are C:O.

05-0.6%, Si: 3.5% or less, Mn: 1°5%
A martensitic stainless steel containing ~20.0% of Cr, O, and 20.0% with the remainder being essentially ``e'' is processed into a desired shape and carburized by an ion carburizing method to reduce the surface carbon concentration to 0.0%. 5~4゜0% and 0.1# from the surface
It is heat-treated so that the carbide area ratio becomes 15% or more in the cross section.

As the martensitic stainless steel, in addition to the above-described basic composition, 3.0% or less of Ni may be added. Also, Mo: 5.0% or less, W: 0.6 to 1.4
%, V: 0.1-0.4%, Nb: 0.1-0.7%
It is also possible to use martensitic stainless steels that contain both Ni and elements below MO. It is.

Carburizing using the ion carburizing method is carried out at a vacuum level of 10-2 in the furnace.
The parts are heated by reducing the pressure to about 100 orr, and a hydrocarbon gas is introduced into the furnace as carburizing gas to reduce the pressure in the furnace to about 1000 orr.
This is done by applying a voltage between the component as a cathode and a separately provided anode to generate a glow discharge. Prior to carburizing, it is preferable to continue glow discharge in an Ar and To atmosphere for a while to clean the surface of the part, as shown in the example of redistribution.

The quenching and tempering treatment after carburizing may be performed under the same conditions as conventional heat treatment.

[Function] The function of the alloy components of the martensitic stainless steel used in the present invention and the reason for limiting the composition range will be explained below.

C: 0.05% to 0.6% C is an element added to obtain strength.

If it is added in a small amount less than 0.05%, sufficient strength cannot be obtained, whereas if it is added in a large amount exceeding 0.6%, the toughness of the part 6 decreases and the impact resistance decreases.

Si: 3.5% or less Si is added as a deoxidizing agent during melting.

When the content exceeds 3.5%, hot workability decreases.

Mn: 1.5% 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 a content exceeding 1.5% reduces both forgeability and rigidity.

Cr Ni, O to 20.0% Or, needless to say, is a component that gives corrosion resistance to steel, and if it is added less than 7.0%, sufficient corrosion resistance cannot be obtained. If it is added in an excessive amount exceeding 20.0%, the martensitic region will be exceeded, and network-like carbides will precipitate, resulting in a decrease in mechanical properties.

By adding the following elements to the above basic alloy composition, parts with excellent roughness can be obtained.

Ni: 3.0% or less Ni improves the toughness of steel. Adding more than 3.0% does not increase the effect and increases the cost.

Mo: 5.0% or less W: 0.6 to 1.4% V: 0.1 to 0.4% All of these elements form carbides to ensure the strength of steel in the medium temperature range. Helpful. MO also has the function of improving hardenability and temper softening resistance.

MO, W and V also form carbides during melting of steel,
They are coarse and reduce the fatigue strength of the steel.
To prevent this, we have set the limits as described above.

Nb: 0.1 to 0.7% Nb contributes to grain refinement. Additionally, when the carbon content of stainless steel increases, chromium carbide precipitates at the grain boundaries, which can lead to a lack of Cr near the grain boundaries and cause intergranular corrosion, but this can be suppressed by adding Nb. . This effect is achieved when the Nb content is 0.1% or more. Like MO and the like, Nb also forms coarse carbides during welding, so it should not be added in large amounts, and the upper limit was set at 0.7%.

N: 0.05-0.15% Adding N improves the core strength and corrosion resistance of steel.

This effect is seen from an N content of 0.05%;
Saturation occurs at 15%.

The parts of the present invention are made by processing the above-mentioned steel into a desired shape and having a surface carbon concentration of 0.5 to 4.0%,
It is carburized so that the carbide area ratio in the cross section within O,"Is from the surface is 15% or more.

If the surface carbon concentration is less than 0.5% or the carbide area ratio is less than 15%, the desired wear resistance cannot be obtained. In particular, when the surface carbon concentration is low, the grain boundaries become preferential precipitation sites for C, resulting in significantly poor corrosion resistance. By setting the carbide area ratio to 15% or more, carbides are uniformly precipitated within the grains, intergranular corrosion can be reduced, and corrosion resistance can be maintained.

The wear resistance or hardness obtained is determined by the surface carbon concentration of 4.
It is saturated at about 0%. Carburizing beyond this level is not only ineffective, but also causes coarsening of the carbide, which is undesirable.

Gas carburizing, which is currently the mainstream method for carburizing, tends to cause sooting and uneven carburizing when operated at high carbon potential. Carburizing gas is oxidizing, due to metamorphosis of hydrocarbon gas, etc.
As carburizing occurs, a Cr oxide film is formed on the surface of the component, which inhibits further carburizing. Even if high temperature conditions are adopted, the limit is 950°C. It goes without saying that it takes a long time and costs are high.

Even vacuum carburizing cannot prevent sooting, which not only causes the loss of the brightness characteristic of stainless steel, but also tends to cause uneven carburization, making it impossible to uniformly carburize the material, especially when the shape of the material is complex.

On the other hand, in the ion carburizing process using glow discharge under reduced pressure, 1 mm of non-oxidizing CH4 or C3 is used as carburizing gas, so no oxide film is formed on the surface of the part. Since the process is operated at a pressure approximately 1/100 times lower than that of the vacuum carburizing method, sooting hardly occurs. Since the plasma state generated by the glow discharge covers the entire surface of the part being treated, even parts with complex shapes can be carburized uniformly.

[Example 1 Alloy with composition of Nα1 to 17 shown in Table 1 (balance Fe)
was melted.

A test piece of each material was placed in an ion carburizing furnace and the furnace was heated to 10'T.
After reducing the pressure to Orr and heating to 1050°C, Ar and H
2 was supplied to adjust the furnace pressure to 2 Torr. The test piece was used as a cathode, and a DC voltage of 500 V 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. Next, 03 to 1 was placed in the furnace.
mm, the pressure is 2 Horr, Nα1~8 is 9
3 hours at 80℃, Nα9-17 at 1050℃ for 1 hour,
Carburized.

Thereafter, it was quenched by oil cooling, and tempered by holding it at 250'C for 1 hour and allowing it to cool.

The surface carbon concentration of the parts thus obtained was 0.1 from the surface.
The area ratio of carbides, surface hardness, and specific wear amount in the cross section within s were measured, and a corrosion test was also conducted. The results are shown in Table 2.

The specific wear amount was measured using an Okoshi type wear tester. The measurement conditions are as follows.

Mating disc: 5UJ2 Final load: 3.1Nyf Gap distance: 200 m Full speed: 0.9rL/Sec Corrosion tests involve exposing parts to an atmosphere of 49°C and 100% relative humidity for 96 hours to determine the degree of corrosion. I judged it.
The judgment criteria are as follows.

A...Not corroded B...Slightly corroded C...Slightly corroded D...Significantly corroded For comparison, data for materials that have not been carburized are shown in (). I added it and added it to the table.

Separately, similar measurements were performed on parts that were not carburized according to the present invention, and the results are summarized in Table 3.

As can be seen from the above data, the parts according to the present invention have higher wear resistance than those of the comparative example, and the corrosion resistance of the stainless steel before carburization is well preserved.

[Effects of the Invention] The wear-resistant stainless steel parts of the present invention have improved wear resistance while maintaining the excellent corrosion resistance and strength of stainless steel. If this technology is applied to tools, etc., products with longer lifespans than conventional products can be obtained.

Patent applicant: Daido Steel Co., Ltd. Agent: Patent attorney, Souo Suga

Claims (3)

[Claims] (1) C: 0.05 to 0.6%, Si: 3.5% or less,
Mn: 1.5% or less, and Cr: 7.0 to 20.0%
A martensitic stainless steel containing Fe, with the remainder being substantially Fe, is processed into a desired shape and carburized using an ion carburizing method to achieve a surface carbon concentration of 0.5 to 4.0% and zero carbon from the surface. .A wear-resistant stainless steel part that is heat-treated so that the carbide area ratio in a cross section of 1 mm or less is 15% or more. (2) The component according to claim 1, using stainless steel containing 3.0% or less of Ni in addition to the above composition. (3) In addition to the above composition, Mo: 5.0% or less, W: 0
．． 6-1.4%, V: 0.1-0.4%, Nb: 0.1
The component according to claim 1, using stainless steel containing one or more of N: 0.7% and N: 0.05 to 0.15%.