JPH08165542A - Steel for metal mold for plastic molding, excellent in weldability - Google Patents

Abstract

PURPOSE: To produce a steel for a metal mold for plastic molding, excellent in weldability and hardenability, by specifying the chemical composition in a steel and controlling BH value to the prescribed value or below. CONSTITUTION: This steel has a composition which consists of, by weight, 0.10-0.25% C, >0.25-0.35% Si, 1.20-2.20% Mn, <=0.020% P, 0.01-0.05% S, 1.60-3.00% Cr, 0.03-2.00% Mo, 0.01-0.40% V, <=0.002% B, and the balance essentially Fe and in which BH value satisfies the condition represented by the inequality. Further, if necessary, <=1.0% Cu and <=2.0% Ni are incorporated into this composition, and further, one or >=2 kinds among 0.003-0.2% Zr, 0.03-0.20% Pb, 0.01-0.15% Te, 0.0005-0.010% Ca, and 0.01-0.20% Bi are incorporated. By this method, the steel for a metal mold for plastic molding, in which restrictions on raw material blending are relieved by increasing the amount of Si capable of being added and also neither preheating nor postheating is required at the time of welding, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to steel for plastic molding dies, and more particularly to steel for plastic molding dies having excellent weldability.

[0002]

2. Description of the Related Art In a plastic molding die, it is not uncommon for repairs to be made by overlay welding in order to cope with processing errors and design changes during the manufacture of the die. Conventionally, as a material for such a plastic molding die, particularly a relatively large plastic molding die, general structural steel such as S55C or S
Medium-low carbon steel such as CM445 was used.

In the case of a plastic molding die made of these materials, it is necessary to preheat (250 to 350 ° C.) in order to prevent weld cracks during welding, and if necessary post heat. There is also.

However, if such preheating and postheating are applied during welding, a dedicated heating furnace is required, it takes a long time for heating, and welding work is performed on a die in a high temperature state after preheating. It is necessary to do so, and problems such as poor workability have arisen, and its solution has been desired.

Further, as the steel for the plastic molding die,
It has good hardenability and excellent mirror surface workability and grain workability.
Further, it is required to have excellent machinability.

Under these circumstances, the inventors of the present invention have developed and proposed a pre-hardened steel for a plastic molding die which does not require preheating or postheating during welding and is excellent in weld repairability (Japanese Patent Laid-Open No. Hei 3). -177536).

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the steel for plastic molds of the invention of No. 536, the content of Si is regulated to a small amount of 0.25% or less, and at the same time, P and B as impurities are regulated to a certain level, and
The amount of hardenability-improving element is increased and the hardenability BH value on the base metal side of the weld boundary where the maximum stress is applied at the time of welding is suppressed to a predetermined value or less. And the hardness and workability required for plastic mold steel are secured.

However, Si is an element widely used in steel materials, and its content is 0.25%.
In the case of the following restrictions, although the specific characteristics of the steel will be good, there is a large restriction on the raw material blending in the production of the steel for plastic molding dies, and on the other hand, there is the problem of impairing the economic efficiency.

[0009]

The invention of the present application has been made in view of such circumstances. Thus, the invention of the present application is such that the composition of the steel for plastic molding die is C: 0.10 to 0.25% by weight and Si: more than 0.25 to 0.3.
5%, Mn: 1.20 to 2.20%, P: ≤ 0.020
%, S: 0.01 to 0.05%, Cr: 1.60 to 3.
00%, Mo: 0.03 to 2.00%, V: 0.01 to
0.40%, B: ≤ 0.002%, balance consisting essentially of Fe and the following formula BH value = 326 + 847.3 (C%) + 18.3 (Si
%)-8.6 (Mn%)-12.5 (Cr%) ≤460 (Claim 1).

Here, in addition to the above components, one or two of Cu and Ni are used as selective elements, and Cu: ≦ 1.0.
%, Ni: can be contained in the range of ≦ 2.0%,
Zr, Pb, Te, Ca, Bi as other selective elements
Any one or two or more of Zr: 0.003 to 0.
2%, Pb: 0.03 to 0.20%, Te: 0.01 to
0.15%, Ca: 0.0005 to 0.010%, B
i: It can be contained in the range of 0.01 to 0.20%.

[0011]

The present invention alleviates the restrictions on the raw material blending by increasing the amount of Si that can be added, and, like the steel for plastic molding dies described in JP-A-3-177536, preheating during welding, It was made to obtain a steel for plastic molding dies that does not require post-heat and has excellent weldability. The upper limit of the Si content is expanded to 0.35% (the lower limit exceeds 0.25%), and The essence is to optimize the addition amount and the balance of the addition amounts of other alloy components to allow this.

Thus, according to the present invention, since a large amount of Si can be contained, the degree of freedom of raw material mixing, that is, the degree of freedom of usable raw materials is increased in the production of steel for plastic molding dies, which is economical. As a result, it is possible to obtain a steel for a plastic molding die which has excellent properties such as weldability and hardenability.

Next, the functions of the above alloy components and the reasons for limiting the contents will be described in detail. C: 0.10 to 0.25% C is a basic additive element for adjusting the structure and hardness. C is 0.1 in order to secure a required hardness in tempering at about 600 ° C. for removing residual stress of heat treatment (desirably HRC 25 or more, more desirably 28 or more).
0% or more is required. On the other hand, if the content exceeds 0.25%, the weldability is lowered under the Si content below, and the structure becomes a martensite structure, resulting in a decrease in machinability.
Therefore, the upper limit is 0.25%.

Si: over 0.25 to 0.35% Si is an effective component in enhancing deoxidizing action, oxidation resistance, hardenability, and matrix hardness. However, if it is 0.25% or less, the economical efficiency is poor in terms of blending the raw materials, so the amount exceeds 0.25%.
On the other hand, if it exceeds 0.35%, the toughness and weldability deteriorate, so the upper limit is made 0.35%.

Mn: 1.20 to 2.20% Mn is combined with S for machinability for deoxidizing action and for improving hardenability and matrix hardness for obtaining bainite structure. It is an effective component as a component for giving. Further, Mn also has a function of enhancing weldability by adding a certain amount or more. However, for that purpose, it is necessary to contain 1.20% or more. On the other hand, if it exceeds 2.20%, the weldability and machinability deteriorate, so the upper limit is made 2.20%.

P: ≦ 0.020% P is harmful to the weld crack susceptibility, and its upper limit must be 0.020%.

S: 0.01-0.05% S is combined with Mn to impart machinability and is also effective for preventing weld cracks. However, if the amount is too large, the toughness and hot workability deteriorate. In the present invention, it is necessary to contain S in the range of 0.01 to 0.05%.

Cr: 1.60 to 3.00% Cr is oxidation resistance, hardenability for obtaining a bainite structure,
It is an effective component for securing hardness by precipitation of fine carbides during tempering. Further, by setting Cr to 1.60% or more, good weldability can be secured. On the other hand, if it is contained in excess of 3.00%, the structure becomes a martensite structure, the hardness becomes excessive, and the machinability deteriorates.

Mo: 0.03 to 2.00% Mo enhances the hardenability and gives temper softening resistance at 600 ° C. or higher. 0.0 as an essential addition amount for that
3% or more is required. On the other hand, if the content exceeds 2.00%, the machinability decreases and the cost increases, so the upper limit is made 2.00%.

V: 0.01 to 0.40% V is an effective component for securing hardness by precipitation of fine carbide during tempering and for refining crystal grains. Include at least 01%. However, if the content exceeds 0.40%, the machinability and toughness are deteriorated and the weldability is deteriorated.

B: ≤ 0.002% B is harmful to the weld crack susceptibility, and 0.002%
The following needs to be regulated.

Cu: ≦ 1.0% Ni: ≦ 2.0% Cu and Ni are components added to obtain the required hardness, and both are selective addition elements in the present invention. Where C
u is effective for obtaining hardness by precipitation hardening in tempering at 500 ° C. or higher, while if too large, it impairs hot workability. Therefore, in the present invention, the upper limit is set to 1.0%. N
i is an element that contributes to the improvement of hardenability and is contained in a range of 2.0% or less. If this upper limit is exceeded, machinability will deteriorate.

Zr: 0.003 to 0.2% Pb: 0.03 to 0.20% Te: 0.01 to 0.15% Ca: 0.0005 to 0.010% Bi: 0.01 to 0 .20% All of these components are effective components for improving machinability. Of these, Zr also acts to suppress the spread of sulfides and improve toughness, but if it exceeds 0.2%, the machinability is rather reduced. Further, each of the other elements causes ground scratches and black spots when the amount exceeds the above upper limit, so that it is contained within the range of each upper limit or less.

BH value = 326 + 847.3 (C%) + 1
8.3 (Si%)-8.6 (Mn%)-12.5 (Cr
%) ≦ 460 Here, the BH value is a value of hardness (Hv) on the base metal side of the weld boundary portion to which the maximum stress is applied during welding, and is expressed as a function of alloy components in parentheses.

The inventor has found that the hardness B on the base metal side of the weld boundary portion is
It was confirmed that the weld cracking rate sharply changes when the H value is Hv at 460 and the weld cracking rate sharply increases when Hv exceeds 460, and the above-mentioned Japanese Patent Application (JP-A-3-177536).
No.).

The definition of the BH value in the present invention is in line with this. By suppressing the BH value to 460 or less, weld cracking can be suppressed, and even if preheating and post-heating are not performed, the plastic molding die can be treated. It is possible to perform good welding repair.

As shown in the above equation, the BH values are C and S.
It increases as i increases, and conversely decreases as Mn and Cr contents increase. In the present invention, the content of Si is set higher than that of the steel type disclosed in JP-A-3-177536.
At that point, the weldability tends to deteriorate, but on the other hand, the upper limit of C is lowered and the lower limits of the amounts of Mn and Cr added are raised, and the adverse effects on weldability due to the increase of Si are eliminated by them. There is a feature in doing it.

[0028]

EXAMPLES Examples of the present invention will be described in detail below. Table 1
After smelting and forging the steel having the composition shown in (1), a heat treatment was performed under the following conditions to prepare a test piece, and a diagonal Y-type weld cracking test specified in JIS-Z3158 was performed. The results are shown in Table 2 together with the hardness.

<Heat treatment conditions> Quenching 870 to 950 ° C Tempering 620 ° C

[0030]

[Table 1]

[0031]

[Table 2]

From the results shown in the table, it can be seen that the steel types of the present invention have good weldability and high hardness. It should be noted that the above is merely a specific example of the present invention, and the present invention can be implemented in other modes.

[0033]

According to the present invention, it is possible to add a large amount of Si as an alloy component in producing a plastic molding die steel. It is possible to obtain a steel for a plastic molding die which has a high degree of freedom and is excellent in economic efficiency and has excellent characteristics such as weldability and hardenability.

Claims (4)

[Claims] 1. By weight%, C: 0.10 to 0.25% Si: more than 0.25 to 0.35% Mn: 1.20 to 2.20% P: ≤ 0.020% S: 0.0. 01 to 0.05% Cr: 1.60 to 3.00% Mo: 0.03 to 2.00% V: 0.01 to 0.40% B: ≤ 0.002% The balance consists essentially of Fe. And the following formula BH value = 326 + 847.3 (C%) + 18.3 (Si
%) -8.6 (Mn%) -12.5 (Cr%) ≤ 460, which is a steel for a plastic molding die having excellent weldability and having a composition. 2. By weight%, C: 0.10 to 0.25% Si: more than 0.25 to 0.35% Mn: 1.20 to 2.20% P: ≦ 0.020% S: 0.0. 01 to 0.05% Cr: 1.60 to 3.00% Mo: 0.03 to 2.00% V: 0.01 to 0.40% B: ≤ 0.002% In addition to Cu and Ni One or two of them is contained in the range of Cu: ≤ 1.0% Ni: ≤ 2.0%, the balance being substantially Fe and having the following formula: BH value = 326 + 847.3 (C%) + 18. 3 (Si
%) -8.6 (Mn%) -12.5 (Cr%) ≤ 460, which is a steel for a plastic molding die having excellent weldability and having a composition. 3. C: 0.10 to 0.25% Si: more than 0.25 to 0.35% Mn: 1.20 to 2.20% P: ≤ 0.020% S: 0.0. 01 to 0.05% Cr: 1.60 to 3.00% Mo: 0.03 to 2.00% V: 0.01 to 0.40% B: ≤ 0.002% In addition to Zr, Pb, Any one or two or more of Te, Ca and Bi are Zr: 0.003 to 0.2% Pb: 0.03 to 0.20% Te: 0.01 to 0.15% Ca: 0.0005 ˜0.010% Bi: 0.01 to 0.20%, with the balance being essentially Fe and the following formula: BH value = 326 + 847.3 (C%) + 18.3 (Si
%) -8.6 (Mn%) -12.5 (Cr%) ≤ 460, which is a steel for a plastic molding die having excellent weldability and having a composition. 4. C: 0.10 to 0.25% Si: more than 0.25 to 0.35% Mn: 1.20 to 2.20% P: ≤ 0.020% S: 0.04% by weight. 01 to 0.05% Cr: 1.60 to 3.00% Mo: 0.03 to 2.00% V: 0.01 to 0.40% B: ≤ 0.002% In addition to Cu and Ni Any one or two kinds are contained in the range of Cu: ≤1.0%, Ni: ≤2.0%, and Zr, Pb, Te, Ca, B.
Any one or more of i is Zr: 0.003 to 0.2% Pb: 0.03 to 0.20% Te: 0.01 to 0.15% Ca: 0.0005 to 0.010 % Bi: contained in the range of 0.01 to 0.20%, the balance substantially consisting of Fe and the following formula: BH value = 326 + 847.3 (C%) + 18.3 (Si
%) -8.6 (Mn%) -12.5 (Cr%) ≤ 460, which is a steel for a plastic molding die having excellent weldability and having a composition.