JPH01168856A - Method for case-hardening steel - Google Patents

Abstract

PURPOSE:To form a TiN film having excellent adhesive property and wear resistance by specifying the accelerating voltage for nitrogen ion, current density, Ti vapor-deposition rate, total nitrogen ion input, and Ti vapor-deposition amt. at the time of forming the hard TiN layer on the steel product such as a rolling roll, a bearing, and a metallic mold by ion implantation and vacuum deposition. CONSTITUTION:When the rolling roll, bearing, metallic mold, etc., requiring wear resistance is case-hardened, a hard TiN layer is formed on the surface of the steel member to be treated by an ion mixing process wherein ion implantation and vacuum deposition are simultaneously or alternately carried out. The accelarating voltage for nitrogen ion in this case is controlled to 10-40kV, the current density of nitrogen ion to 0.5-2.0mA/cm<2>, the Ti vapor deposition rate to >5Angstrom /sec, the total nitrogen input to >10<18>ion/cm<2>, and the Ti vapor- deposition amt. to >5X10<18>ion/cm<2>. A TiN film having excellent adhesive strength and water resistance is formed on the surface of the steel member to be treated.

Description

Detailed Description of the Invention (Industrial Field of Application) Surface hardening of steel materials such as rolls, other rollers, bearings, molds, etc. used in various rolling and processing processes that require wear resistance. Regarding the method, the following describes the results of development research that aimed to utilize ion mixing processing, in which ion implantation and vacuum deposition are performed simultaneously or alternately, in order to form a TiN film with good adhesion and high wear resistance. .

For example, in the recent field of cold rolling technology, high-speed reduction rolling and continuous rolling are being used to improve rolling efficiency, increase the number of difficult-to-roll materials, and improve product quality. Furthermore, as the diameter of work rolls continues to become smaller, the environment in which work rolls are used is becoming more severe year by year, and wear of the rolls in particular is severe, becoming a bottleneck in rolling operations.

During rolling, work rolls are subject to severe wear, particularly at the passing edges, resulting in a large difference in roughness between the passing edges and non-passing areas that do not contact the rolling plate.

Therefore, when rolling is transferred from a narrow plate to a wide plate, there is a problem in that the local roughness differences of the work roll are directly transferred to the rolled plate. Scheduled rolling, similar to rolling plates, is performed.

Furthermore, when rolling is transferred from a narrow width plate to a wide width plate, the current situation is that rolling is performed using re-ground rolls.

In the current situation where such schedule rolling is performed, no matter how much we try to improve rolling efficiency, there is a limit to it.

Therefore, the ideal rolling operation is to abolish schedule rolling, that is, to perform schedule-free rolling, and research and development is actively being conducted on work rolls with excellent wear resistance that can be used with this rolling method. . .

Here, trends in rolling rolls, especially cold rolling work rolls, are cited as a representative example, but the requirements for wear resistance are the same not only for general rolls and rollers, but also for bearings, molds, etc.

(Prior art) Many proposals have been made regarding the roll material, such as in JP-A-61-21300 and JP-A-57-47849. , forged steel rolls with hard carbides dispersed in their structure, and cast iron rolls with a Cr content of about 20% have been proposed, but none of them can be said to have sufficient wear resistance.

Furthermore, as a surface treatment roll, it is also possible to form an ultra-hard coating such as TiN or TiC using a hard Cr plating roll or an ion-blating method, as described in Japanese Patent Laid-Open No. 61-2011.
No. 800 and Japanese Unexamined Patent Publication No. 61-273206 have proposed these proposals, but although they both satisfy the wear resistance, there is a problem in that the adhesion between the base material and the surface treatment film is insufficient. There is.

Furthermore, in JP-A No. 62-180062, a roll surface treatment device using the ion mixing method was proposed, and as a specific example, Ti was deposited on the surface of the roll by 1 to 3 μm, and nitrogen ions were implanted simultaneously or alternately. to 1
It has been shown that 0" to 10"1ons/cm" is implanted. However, even in the ion mixing process,
It has been found that it is difficult to obtain a film with excellent adhesion only by changing the amount of Ti vapor deposited or the amount of nitrogen ions added.

(Problems to be Solved by the Invention) In order to solve the above-mentioned problems, in addition to the acceleration voltage and current density of nitrogen ions, the amount of Ti evaporation and the input amount of nitrogen ions, the rate of Ti evaporation Our objective is to provide a surface hardening method for steel materials that performs ion mixing under optimized conditions and enables the formation of a TiN film with superior adhesion and wear resistance compared to conventional methods. This is the object of the invention.

(Means for Solving the Problems) According to the present invention, when forming a TiN film on a steel material by ion mixing treatment, the nitrogen ion acceleration voltage is set at 10 to 40 kV, and the nitrogen ion current density is set at 0.5 to 2.0 kV. 0m^/cm”sTi deposition rate 5
This is a surface hardening method for steel materials, characterized in that the total amount of nitrogen ions introduced is 10"1 ounces/cm" or more, and the total amount of Ti vapor deposited is 5XIO"1 ons/cm" or more.

Figure 1 shows that the total input amount of nitrogen ions is 10I [1ions/
cm" to 10"1 ons/c+++", and the total amount of Ti deposited is 5 XIO"tons/cm"
The relationship between nitrogen ion current density and Ti deposition rate on adhesion at a nitrogen ion accelerating voltage of 30 kV when ion mixing treatment is performed under conditions such that Shown in a graph.

This adhesion test was carried out using a two-circle W type abrasion tester under the following conditions: Hertzian stress of 100 kgf/in'', slip rate of 20%, hardness of the mating material Hv of 200.3%, mineral oil emulsion lubrication, and after 10,000 rotations. The presence or absence of peeling is categorized by ・ and ○ marks.

Adhesion is poor when the nitrogen ion current density is less than 0.5 m^/cm'' and the Ti evaporation rate is less than 5 Å/s.
/cm'' or more and the Ti evaporation rate is 5 Å/s or more, excellent adhesion is shown.

Figure 2 shows nitrogen ion current density of 0.5 to 2.0 mA.
7 cm", and a Ti vapor deposition rate of 5 to 30 Å/s. FIG.

The total nitrogen ion input amount is less than 1018 ions/cm",
Further, if the total amount of Ti added is less than 5 XIO" 1 oz/cm", peeling occurs as indicated by the mark ., and the adhesion is poor. The total nitrogen ion input amount is 10" 1 ounces/cm" or more, and the total Ti vapor deposition amount is 5 XIO" 1 ons.
/cm2 or more, excellent dense layer properties are exhibited as indicated by O in the figure.

In this way, an appropriate nitrogen ion current density (0.5 to 2.
0mA/ctA) and Ti evaporation rate (5λ/s ~ 30 people/
s) Furthermore, the total amount of nitrogen ions finally implanted (
The balance between the total amount of Ti deposited (10XIO"tons/clll) and the total amount of Ti deposited greatly influences the adhesion.

In addition, during the ion mixing process, the energy density input onto the steel material by accelerated nitrogen ions is 10 J/c.
If the input energy density is less than 80 J/cm, it will be difficult to obtain a TiN film with excellent adhesion, whereas if the input energy density exceeds 80 J/cm, the steel surface will become hot (more than 700 C) and deteriorate. , the input energy density is 10~
A range of 80 J/c+++'' is preferred.

(Function) The reason for limiting the conditions for obtaining a TiN film with excellent adhesion and wear resistance will be described.

Nitrogen ion current density: 0.5 to 2.0 mA/c If the nitrogen ion current density is less than 0.5 mA/c, the adhesion is poor, and if it exceeds 2.0 mA/cm2, the steel surface may become hot. This causes the surface to deteriorate. Therefore, the nitrogen ion current density was set in the range of 0.5 to 2.0 +mA/c+a''.

Nitrogen ion acceleration voltage 2 10 to 40 kV The nitrogen ion acceleration voltage must be in the range of 10 to 40 kV, taking into account constraints on nitrogen ion current density and input energy density.

Ti evaporation rate: 2 If the Ti evaporation rate is less than 5 Å/s, the adhesion is poor and the processing time is long, so the Ti evaporation rate is 5 people/s.
Requires ec or higher.

Note that if the Ti deposition rate exceeds 30 Å/s, it becomes necessary to increase the nitrogen ion current density, which deteriorates the surface of the steel material, so it is desirable to lower the Ti deposition rate to 36 or 8.

Total amount of nitrogen ion input: 10"tons/cm" or more, total amount of Ti vapor deposited: 5 XIO" 1ons/c+++
``The total nitrogen ion input amount is 10 tons/cm''
Above, the total amount of Ti deposited is 5XIO"1ons/am"
If either or both of the above are not satisfied, the adhesion will be poor and peeling will occur. Therefore, the total amount of nitrogen ions introduced must be 10''1 ounces/cm'' or more, and the total amount of Ti deposited must be 5×1016 ions/cm2 or more.

In addition, the total nitrogen ion input amount is 10I9ions/cm"
The upper limit is preferably 10' drops/1 ounce/cm" or less, since processing time will be longer if the drop exceeds 1 oz/cm".

Regarding the upper limit of the total amount of Ti vapor deposited, from the economic point of view, 5.
Even if it exceeds XIO" 1ons/cm2, it is not possible to expect a commensurate economic effect, so 5xto" 1on
s/cm" or less is preferable.

Next, regarding the material of steel, it is suitable for use in fields such as rolls or rollers used in various rolling processes that require wear resistance, as well as bearings and molds. In addition to wear resistance, steel with excellent strength, toughness, and fatigue properties is required.

Therefore, for example, when targeting rolling rolls, C
: 0.85 ~ 1.2%, St: 0.1 ~
1.6%, Mn:o. 1-1.5%, Ni: 0
．． 1 to 1.0%, Cr:2.0 to 12, 0%, Mo
: 0.3 to 2.0%, V: 0.1 to 2.
0%.

P: 0.025% or less, S: 0.010% or less, the remainder is Fe and unavoidable impurities, and the surface hardness is Hv500 to Vickers hardness.
A range of 900 is preferred.

(Example) An ion mixing treatment was performed on the outer circumferential surface of a steel material having a shape of 30 mm in outer diameter, 16 mm in inner diameter, 3 III in 11 in width, and a wear test assuming actual cold rolling was conducted. For the wear test, a two-cylindrical wear tester was used. Table 1 shows the chemical composition of steel materials.
Shown below.

Table 2 shows the ion mixing treatment conditions and the adhesion and wear test results.

Table 1. The chemical composition of the rope material (contains tl) The ion mixing treatment
A press spatter treatment was carried out under a reduced pressure of r, and the purpose of cleaning the surface of the steel material was before the ion mixing treatment.

Adhesion and abrasion tests were performed using a Hertzian stress of 100 kgf/
m”, slip rate 20%, hardness of mating material HV200.3%
The tests were carried out under conditions of mineral oil emulsion lubrication. Adhesion was evaluated by the presence or absence of peeling after 10,000 rotations, and abrasion resistance was evaluated by the amount of wear after 3 million rotations.

A TiN film obtained by ion mixing treatment outside the range of conditions specified in this invention peels off after 10,000 rotations and has poor adhesion. On the other hand, the TiN coating obtained by the ion mixing process obtained by the method of the present invention does not peel off after 10,000 rotations and has excellent adhesion.

Figure 3 shows the wear test results.

The TiN coating produced by the ion mixing treatment according to the present invention has an abrasion loss of 0.5n+g or less after 3 million rotations, which is approximately 1/10 of that of the untreated case, and has excellent abrasion resistance. I understand that.

It should be noted that the TiN coating obtained by the ion mixing treatment under different conditions from the present invention exhibited weight loss of more than 1 inch due to peeling after 10,000 rotations.

(Effects of the Invention) The present invention has a mixed layer containing Fe, Ti, and N between the steel base material and the coating by an ion mixing process in which ion implantation and vacuum deposition are performed simultaneously or alternately, and In a film forming method for forming a TiN film on a mixed layer,
Nitrogen acceleration voltage is 10 to 40 kV, nitrogen ion current density is 0.5 to 2.0 m17 cm, Ti deposition rate is 5 people/sec or more, and total nitrogen ion input is 10 to 1 ounce/cm. ”The total amount of Ti deposited is 5X.
It is a coating formation method characterized by an IO of 1 ounce/cm or more, and can be applied to parts and tools that require wear resistance, such as rolling rolls and rollers, as well as bearings and molds, to achieve excellent performance. The effect is great.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between nitrogen ion current density and Ti evaporation rate and adhesion. Figure 2 is a graph showing the relationship between total nitrogen ion input amount and total Ti deposition amount and adhesion. Figure 3 is a graph showing the relationship between adhesion and nitrogen ion current density and Ti evaporation rate. , is a graph showing the results of a wear test.

Claims (1)

[Claims] 1. When forming a TiN film on a steel material by ion mixing treatment, the nitrogen ion acceleration voltage is 10 to 40 kV, the nitrogen ion current density is 0.5 to 2.0 mA/cm^2,
The Ti deposition rate is 5 Å/s or more, and the total nitrogen ion input is 10^1^6 ions/cm^2.
As described above, a method for surface hardening a steel material, characterized in that the total amount of Ti deposited is 5×10^1^8 ions/cm^2 or more.