JPS5925924A - Extruding pin for plastic - Google Patents

Abstract

PURPOSE:To obtain an extruding pin for flame retardant plastics with improved corrosion resistance by subjecting a high Cr steel having a specified alloy composition to hardening, subzero treatment and tempering at specified temps. CONSTITUTION:A steel consisting of, by weight, 0.9-1.2% C, <=1.0% Si, <=1.0% Mn, 16.0-19.0% Cr, <=0.75% Mo and the balance Fe with impurities is quenched from 1,000-1,070 deg.C and subjected to subzero treatment at -70--196 deg.C to transform >=about 15% of the residual austenite into martensite by decomposition and to increase the hardness. The hardness of the steel is then regulated by tempering at 300-400 deg.C to obtain an extruding pin for plastics. The pin has high corrosion and wear resistance, so it can be used in the extrusion of flame retardant plastics without requiring Cr plating, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a push-out pin, and particularly to a push-out pin for flame-retardant plastics.

As an extrusion pin for plastics, it must have sufficient toughness so as not to break during use, have high wear resistance on the sliding surface, and have good seizure resistance.

Properties such as not causing any tissue changes or dimensional changes during use are required.

Conventionally, plastic extrusion pins are generally JIS
■R high carbon tool steel such as 8KB2/, SKD/
Hardened and tempered materials to a hardness of around O2θ are widely used. However, as the uses of plastics have expanded, in recent years flame retardant regulations have been put in place for plastic products for electrical and electronic equipment to emphasize safety, and so-called UL standards have come to be applied. .

These flame-retardant plastics are made by adding flame retardants, mainly halogen compounds, to conventional plastics, so they generate corrosive gases such as chlorine gas during injection molding, which can corrode the extrusion pins. Problems started to arise.

As a corrosion countermeasure, extrusion pins such as SK8, 2/, 8KD// are used with chrome plating, but the gas pressure generated during molding causes corrosive gases to pass through the porous parts of the plating layer. This is not a sufficient countermeasure because it corrodes the base, causing bit-like corrosion and peeling of the plating layer.

The present invention was made in view of these problems, and
The object of the present invention is to provide an extruded pin that does not require plating and has better corrosion resistance and wear resistance than conventional extruded pins, and can be used for flame-retardant plastics.

That is, in the present invention, the alloy composition is based on weight, Cθ,
9~/, 2%%Si/, θchi or less, Mn/,
Below θ, Or/O, θ~/2. θchi, Moa, 7j
Using high chromium steel with the remainder iron and impurities,
/θθθ~/θ After quenching from 70℃, sub-zero treatment is performed at a temperature of -7θ~-/9゛C, and then 3θθ~Gθ
HRO by tempering at θ°C) It has the advantage of not requiring chrome plating.

Next, reasons for limiting the composition and heat treatment conditions of the extrusion pin of the present invention will be described. C dissolves in martensite to increase the hardness of the matrix and forms a hard chromium carbide, which has the effect of improving wear resistance, but if Cθ is less than 9%, the wear resistance is insufficient.

/, since the toughness decreases if it exceeds θ, 2 to /1.
Limited to 2 chis. Sl is added as a deoxidizing agent, but if it exceeds θ, the toughness decreases, so it was set to below θ. M
N is also added as a deoxidizing agent, but if it exceeds 7%, residual austenite increases during quenching and the degree of quenching decreases, so it was set to θ or less. Or is effective in improving corrosion resistance and heat resistance, and also combines with C to form carbide, which is useful for improving wear resistance. However, if Or is less than 76L%, corrosion resistance is insufficient, and /9 If it exceeds, the toughness decreases, so /B, θ ~ /9. I set it to θ. Mo improves corrosion resistance and temper softening resistance, but even if it is added in an amount exceeding 6.75%, there is little improvement in the effect, so it was set to 0.7 S% or less.

A vacuum quenching furnace is used to process a steel bar having the alloy composition described above into an extrusion pin shape.

Alternatively, quench hardening is performed in a salt bath furnace, but if the quenching heating temperature is lower than 7000°C, the solid solution of chromium carbide is insufficient and the quenching hardness is low, and if it exceeds 7070°C, retained austenite is formed. The quenching heating temperature was limited to 7,000 to 7,070°C because the amount increases and the quenching hardness decreases, and the crystal grain size becomes coarser and the toughness decreases.

As an extrusion bottle, it is necessary to have high abrasion resistance, and the heat treatment hardness must be +,,cj or higher. In addition, the working temperature during molding of flame-retardant plastic is 7.
? Therefore, in order to avoid structural changes and dimensional changes of the extrusion pin during use, a tempering temperature of 3θθ°C or higher must be adopted. Cθ, 9~/, 2%
, Si /, θchi or less, Mn/, θchi or less, Or
/A-θ~/9. Steel with θ% and Mo0.75% or less has a temperature of 1 when quenched from 7606 to 7070°C.
．． Contains 2S to 3θ retained austenite,
The quenching hardness is around HrO2θ.

When this is tempered at 30θ°C/h, the hardness is HRO54.
- I5, and the hardness is insufficient for an extrusion pin.

Therefore, the inventor has developed an extrusion pin at 7606 to 7070°C.
After quenching, sub-zero treatment is performed at -7θ to -/9℃ to decompose residual austenite by more than /j and transform it into martensite, increasing the hardness. was able to increase HRO Otsu/, J~Otsuyu θ. Even if this was subsequently tempered at 30θ°C/h, the HROj6. It was possible to ensure the hardness of θ for θ~j.

At this time, when the Zabuzero treatment temperature is higher than 17θ°C, the amount of decomposition of retained austenite is 75% or less, and the increase in hardness due to martensite formation is small, and the mata
Since it is practically difficult to lower the temperature to 26°C or lower, the sub-zero temperature is set to -70 to -/6°C. In addition, in the case of -75-C sub-zero treatment, the residual austenite after treatment is /θchi, and in the case of sub-zero treatment, the residual austenite after treatment is g%. The austenite remaining after the sub-zero treatment is very stable and does not decompose at all when heated to qθθ''C, so there is no dimensional change during use of the extrusion pin.

Next, one aspect of the present invention will be explained in detail. Table 1 shows the chemical compositions of the extrusion pin of the present invention and the conventional extrusion bottle. The extrusion pin of the present invention has alO,! ;Chi, Siθ, Guochi.

Mnθ, llo%, or/7. θ%, Moθ, 4/%,
A steel bar with the remainder iron and impurities processed into a bottle shape is heated to 705 mm in a vacuum using a vacuum quenching furnace.
After heating to 0℃, cooling with nitrogen gas, and quenching,
It was subjected to /h subzero treatment at a temperature of -79θ°C, followed by tempering at 3θθ'C, /h, and the hardness was Ha (157). The symbol ^ indicates the extruded pin of the present invention. B is SK S, 2 /, the crossed symbol C is SK
This is an extrusion pin made by D//.

Table 1 Chemical composition of extrusion bottle Table 2 Comparison of corrosion resistance of extrusion pin When injection molding is performed at θθ℃, 2θ
, θθθshot), J5. θθθ shot and Sθ,
A comparison of the corrosion resistance of extrusion pins after θθθ shot is shown. Extrusion bottles made from 8 to 8.2/and SKD// showed pinpoint corrosion after 1.2θ, θθθ shots. In addition, chrome-plated SKS, 2/
and SKD// extrusion bottles are both J5.
No corrosion was shown up to the θθθ shot, but Sθ, θ
Pit-like corrosion was observed after the θθ shot. On the other hand, in the extruded pin of the present invention, no bit-like corrosion was observed even after Sθ and θθθ shots, and it was clearly shown that the corrosion resistance was extremely deteriorated.

As explained above, the extrusion pin of the present invention has a Cθ of 2 to 7.
．． 2%, Si/, less than θ, Mn/, less than θ, Or/
-7θ after quenching from 7006 to 7679°C using high chromium steel with Otsu, θ ~ /, 90 inches, Moa, 73% or less
Sub-zero treatment is performed at a temperature of ~-/2℃, followed by 3
Tempering treatment at θθ~qθθ℃.

[LRC] It is tempered to a hardness of J, θ~jg, θ, has excellent corrosion resistance, and is also a hard chromium carbide.
Due to the presence of these substances, the abrasion resistance is also good, making it suitable as an extrusion bottle for flame-retardant plastics.

Patent applicant: Plus Engineering Co., Ltd. Representative patent attorney: Izawa Izume: 1.111
1

Claims (1)

[Claims] In weight%, 0θ, 2~2cm, Si/, θchi or less, Mn/, θ% or less, Cr/O, θ~/9. θ%, Mo
θ, 73% or less, the balance consists of iron and impurities, and after quenching from 7666 to 7676°C, -7θ to -/9
Sub-zero treatment is performed at a temperature of 4'C, and the 3θθ
An extrusion pin for plastics characterized by being tempered at ~g θθ°C.