JPS5848026B2 - Low temperature nitriding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low temperature nitriding method for forming a nitrided layer on the surface of a steel workpiece in a heated and molten salt bath.

The conventional nitriding method involves inserting a heated steel workpiece into a high-temperature ammonia gas furnace and applying nitrogen from a generator to cause the nitrogen to penetrate into the surface of the steel and nitriding it. Ta.

Since this method heats the workpiece to a high temperature, there was a risk of deformation or internal alteration of the workpiece, but recently a low-temperature nitriding method using a salt bath has been developed, and this drawback has been overcome. Ta.

According to this low-temperature nitriding method, the ammonia gas nitriding method is
~100 hours of processing time compared to 530~5
Nitriding can be carried out at a temperature of 50° C. for 1 to 3 hours.

That is, between 0.01 and 0. A nitride layer of 15 mm and 0.
0 6 ~ 0. A nitrogen diffusion layer of 10y+oa is obtained, and although the hardness of the layer is lower than that of the ammonia gas nitriding method, its fatigue strength and wear resistance are inferior.

An example of this conventional salt bath method is to add sodium cyanide (NaCN) and potassium cyanide (KCN) to 60%
A solution of neutral salt or carbonate at a ratio of :40 is placed in a tank made of heat-resistant titanium steel, and the workpiece is immersed in the tank heated to 550°C.

However, with this method, the generated gas contains cyanide and is poisonous, and the bathtub made of heat-resistant titanium steel is extremely expensive.
Moreover, there is a drawback that if this is not used, the wall of the tank will break prematurely.

The present invention is a low-temperature nitriding method that uses a neutral salt agent that does not contain cyanide, which is completely different from conventional salt bath agents, and uses ordinary carbon steel as the bath, and is less toxic than conventional low-temperature nitriding methods. Moreover, it was invented with the aim of obtaining a method that can carry out nitriding using inexpensive equipment.

The details of the present invention will be explained below.

Some of the salt bath agents used in this method are potassium chloride (K(J'), 15% sodium chloride (Na(J!), and 5% barium chloride (B).
aCe2) At 80%, this was placed in a salt bath point and heated to 690°C to melt it, and into this melt was added sodium titanate (NaTiCO 3) and an active substance corresponding to 3% of the weight of the workpiece. Nitrogen source red blood salt (KFe (CN)
) 6) is added to increase the activity of nitrogen in the melt, and the workpiece is immersed in this melt for 1 to 3 hours to form a nitrided layer on the surface of the workpiece.

The salt bath pot used in the above process is made of ordinary SS41 steel that does not contain titanium, but it does not cause breakage or other malfunctions.

The reason for this is that self-nitridation of the salt bath pot occurs during the nitriding process, that is, heating increases the nitrogen diffusion layer on the inner wall of the pot and adds heat resistance due to titanium (Ti). It's for a reason.

Furthermore, titanium (Ti) has a catalytic effect and has the effect of promoting the activation of nitrogen.

Therefore, it is sufficient that the amount of titanate inotope added is such that it can exert a catalytic effect, that is, it is added in a catalytic amount.

Furthermore, as mentioned above, since the red blood salt is a nitrogen source, it is used in an amount of 3% of the weight of the workpiece, but there is no harm in using too much.

Next, an example of the equipment used in this method will be explained in the order of the nitriding process.

(a) Preheating furnace Heat the workpiece to approximately 300°C.

(bJ nitriding layer It is a point type heated by gas or electricity, and its size is cylindrical with a diameter of 300 mm and a length of about 600 mm. The material of the tank is ordinary steel 8841, and an automatic temperature controller is installed.

This tank generates exhaust gases such as carbon dioxide (CO2), nitrogen (N2), and salts that corrode metals, so an exhaust gas purification device is installed.

(c) The volume of the quenching tank is 1 m or more, and a waste water treatment device is required because weak saline water is discharged.

(dJ cleaning equipment is a liquid honing equipment, and a wastewater treatment equipment is installed.

Next, the results of nitriding according to the present invention will be described.

The following table shows the results of three types of tests, Arashi 1 to Arashi 3, using steel plates of 2 mm x 30 mm x 40 mm as test pieces and nitriding times of 1 hour, 2 hours, and 3 hours.

The hardness distribution state from the surface of the test piece to a depth of 1 m7IL in this first test is as shown in the attached drawing.

As described above, according to the method of the present invention, (a) effects superior to conventional methods can be obtained in only 1 to 3 hours.

This is thought to be because sodium titanate (NaTiCO3) and red blood salt (KFe(CN)6) are used as additives, so the activation of nitrogen is promoted by the catalytic action of titanium (Ti). .

(bJ Self-nitriding of the salt bath takes place as a secondary effect, and it is a great advantage in terms of equipment that ordinary steel, not high carbon steel such as SS41, can be used in place of the conventional expensive titanium steel salt bath.

(c) In the present invention, since a neutral salt bath agent containing no cyanide is mainly used, the toxicity is minimal, and the drawback of the conventional low-temperature nitriding method of emitting toxic gases can be eliminated.

(dJ Because nitriding occurs at a temperature below the metal's transformation point, the deformation and dimensional change of the workpiece are minimal, so the cam,
Suitable for nitriding complex shapes such as gears that cannot be processed later.

feJ The nitrided surface obtained by the method of the present invention has excellent abrasion resistance and is so-called sticky, making it suitable for processing cutlery, etc., and also exhibits heat resistance.

[Brief explanation of the drawing]

The drawing is a diagram showing changes in hardness with respect to depth from the surface for three examples of nitriding according to the present invention.

Claims (1)

[Claims] 1. A salt bath consisting of 15% potassium chloride, 5% sodium chloride, and 80% barium chloride was heated to 690°C, and red blood salt was added as an active nitrogen source to a melt of 3% of the weight of the workpiece. , a catalytic amount of sodium titanate is added to promote the activation of nitrogen, and an iron-based metal is immersed in the salt bath agent to form a nitride layer on the surface of the metal. low temperature nitriding method.