JPS60204873A - Knockout pin having high toughness - Google Patents

Abstract

PURPOSE:To obtain a knockout pin having superior toughness by working a steel bar having a specified composition subjected to soln. heat treatment to a prescribed shape and by carrying out gas nitriding at a specified temp. to increase the surface hardness. CONSTITUTION:A steel bar consisting of, by weight %, <=0.05% C, <=0.3% Si, <=0.3% Mn, 5-13.5% Ni, 2.5-8.0% Cr (Ni+Cr=13.5-19.0%), 1.5-5.0% Mo, 0.1-0.8% Al, 0.1-1.0% Ti, 2.1-4.0% Co and the balance Fe with impurities is subjected to soln. heat treatment including air cooling from about 820 deg.C. It is worked to the shape of a knockout pin, and gas nitriding or gas soft-nitriding is carried out at about 470 deg.C to increase the surface hardness Hv to >=about 900 and the internal hardness HRC to about 49.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates in particular to an extrusion pin for precision plastic molds.

As a small-diameter extruded bottle, it must have sufficient toughness so that it will not break during use, and the sliding surface must have high abrasion resistance.
Properties such as good seizure resistance and no structural or dimensional changes at operating temperatures are required.

Conventionally, as extrusion bottles for plastics, 8 to 8, 2
/, 8KD / /, SKH F, etc., which have been tempered to a hardness of around Hn06θ, and SKD 4 /, which has been tempered and then nitrided, are used.

Table 1 shows the chemical composition of these steel types.

Steel grades 8KB2/, 8KD//, and 8KH have good wear resistance, but have a drawback of low toughness and are prone to breakage, so they cannot be used for small diameter extrusion bottles of φ2θ■ or less.

First expression: Chemical composition and heat treatment hardness of extrusion pin, SKD 4 / is 7050℃ to 60θ℃ after quenching
By tempering at K, the hardness becomes around HR (1,), and the kana toughness is better than high carbon steel, but the wear resistance of the sliding surface is inferior, so it is hardened at 596 to 579℃. Nitriding is performed to increase the surface hardness to Hv9θθ (IIR07).However, 5KDA/ is 8 due to nitriding.
1111I! Therefore, the 6-dimensional accuracy of the diameter of the small diameter bottle is θθθ! ; It is difficult to increase the temperature below tm, and
For use in extrusion bottles of 75 m or less, it still had the drawback of insufficient toughness.

The present invention was made to solve these problems, and has significantly superior toughness than conventional extruded pins, has the same wear resistance, and can be used with small diameters from φθq to φyuθ. The purpose is to provide something that can be used as an extrusion pin.

That is, the present invention provides Cθθj−, below, S
iθ3% or less, Mn93% or less, Ni5'! j~/, R
5%, Or, θ on Z5-, Ni + Or / 3!
;~/9θchi, Mo13~! ;, 0%, A1θ/~θ, Tiθ/~/θchi, Coyu/~kuθchi, the balance is iron and impurities, and the steel is processed from a solution-treated bar.

After shaping it into the desired shape, it was heated to a temperature of around 770℃.

It is characterized by having undergone gas nitriding or gas soft nitriding treatment, and after processing a steel bar that has been subjected to a special 2θ℃ air-cooling solution treatment and finishing it in the shape of an extruded pin,
Gas nitriding or gas nitrocarburizing treatment is performed at around 770°C for several hours to increase the surface hardness to Hv5'θθ or higher, and at the same time age hardening the internal hardness to around HRO getter, resulting in very good toughness. At the same time, it has excellent wear resistance and seizure resistance, and the diameter expansion caused by nitriding is canceled out by the contraction caused by precipitation hardening.
It has the characteristic that there is almost no dimensional change in diameter, and it is easy to improve the dimensional accuracy of the small diameter bottle.

Next, a composition-limited ring of steel for extrusion bottles according to the present invention.

Describe Koma. C stands for the toughness of low carbon martensite.

Since it may cause damage, it is limited to θθj or less. 8i and Mn have a deoxidizing effect, but if the value exceeds θ3, the toughness decreases, so they were each set to θ3 or less.

Ni and Or are necessary to make the structure after solution treatment martensite, but Ni + Or is /, R, 5-
If it is less than 1, the effect will be less, and 15! When θ is exceeded, retained austenite increases and the aging hardness decreases, so NIten Or Co./X! ; ~/9.0%, and Ni is 9
．． If it is less than 3%, there is no effect of forming a martensitic structure.

The fruit is small, and if it exceeds 735%, there will be a lot of retained austenite, so it's a 5! S~/15%.

C" makes the structure martensite, increases the nitrided surface hardness, and also improves corrosion resistance, but if it is less than 1.2.S, the effect is small, and if it exceeds 5%, it is tough.

Since this decreases the performance, θ is set to θ. Mo forms intermetallic compounds with Fe and Ni, minimizing precipitation hardening.
Since θ-chi also decreases toughness, it was set as S-ma0-chi. A2 forms an intermetallic compound with Ni, causes precipitation hardening, and also improves nitriding properties, but if it is less than θ/1, the effect is small, and if it exceeds 05%, the toughness will completely decrease, so θ/~θg% And so. Ti also causes age hardening, but 9
If it is less than 7%, the effect will be small, and if it exceeds /θchi, the toughness will decrease, so it was set as θ/ to /θchi. Also, although Co promotes precipitation hardening, if it is less than 27%, the effect is small, and if it exceeds 0%, the effect is not improved much. , 7 to ri θchi.

When steel with this composition is air cooled from around 2θ°C, its hardness softens to HRo, 2g to 3/3.

Machining is easy, and wire drawing is also easy.

Precipitation hardening occurs by heating around 7θ°C for 3 hours, and hardening occurs around HR0l'.

In the case of the extruded pin of the present invention, the aging treatment temperature and the nitriding treatment temperature are the same, so if the nitriding treatment is performed at guar θ°C for several hours, the surface hardness will harden to Hv9θθ or higher, and at the same time the interior will become HnO'l? As it hardens to a high temperature, it is tough and can be used as an extrusion pin with excellent wear resistance and seizure resistance. In addition, the extrusion bottle of the present invention has the characteristic that almost no dimensional change occurs due to the nitriding treatment, since the expansion of the diameter due to nitriding is canceled out by the contraction due to precipitation hardening.

Next, the present invention will be specifically explained with reference to Examples. Table 2 shows the chemical composition of the extrusion pin. symbol.

A shows an extrusion pin according to the present invention. Symbols B, O,.

D%E is aKs2/, SKD//, 8KH respectively
9 and 8KD Otsu/manufactured extrusion pins are shown.

Table 3: Chemical composition of extrusion pin Table 3 shows the hardness and durability test results of extrusion bottles with φθ6 stages. The extrusion pin according to the present invention of the symbol person is subjected to a tough gas nitriding treatment at 0°C x @ h (hours).
Surface hardness, Hv93'l, internal hardness Table 3 Extrusion bottle durability test results HROg? showed j. Using extrusion pins with symbols A%B, C%D, and E, 1. O. The results of the tests using plastic molds for pan cages are shown in Table 3. /
The presence or absence of breakage of the bottle after θ, θθθ shots and Sθ, θθ0 shots is shown. The extrusion pin according to the present invention with symbol A does not break even after jθ, θθ0 shots, indicating that it has extremely excellent toughness. It shows.

As explained above, the extrusion pin of the present invention has a weight percentage of
Cθθ51 or less, Siθ3 or less, Mnθ3 or less, N
i5! j~/3S-1OrQ! ;-iθchi, Nmu+Or
/Jj~/9θchi, Mo13~! ;, θchi, λLθ/~
θg section, Tiθ/~/θchi, Ooyu/~kuθchi.

A steel consisting of iron and impurities in the balance, which is characterized by being processed into a predetermined shape from a solution-treated bar and then subjected to gas nitriding or gas nitrocarburizing at a temperature of around 770°C. It has excellent toughness and wear resistance, and is ideal as an extrusion pin for plastics with a small diameter of φ2θ■ or less.

Claims (1)

[Claims] In weight %, CθθS or less, 8iθ3% or less, Mnθ3
Below Chi, Ni 5! \j~/3S Chi, Or, 2. j~ to θchi, Ni+Or/, Rj~15! θchi, Mo/:j~
s, oqb, Ajlθ/~θlr'16%TiO,/
~lO%, O. 2/ ~ steel consisting of iron and impurities with the remainder being solution-treated bars that are processed into a predetermined shape and then subjected to gas nitriding or gas nitrocarburizing at a temperature of around 770°C. #1 An extrusion bottle with great toughness.