JPS60177125A - Manufacture of tough and hard cast iron - Google Patents

Abstract

PURPOSE:To obtain tough and hard cast iron by releasing alloyed graphite cast iron contg. prescribed percentages of C, Si, Mn, Mg, Ni and Mo from a mold at a temp. in the austenite range and by heat treating the cast iron under prescribed conditions. CONSTITUTION:Alloyed graphite cast iron consisting of, by weight, 3-4.5% C, 1.5-3% Si, 0.2-1% Mn, 0.02-0.1% Mg, 0.6-1.4% Ni, 0.2-0.8% Mo and the balance Fe is melted, cast in a mold, and released from the mold at a temp. in the austenite range of 850-950 deg.C. The released cast iron is hardened by controlled cooling from 850-950 deg.C to <=150 deg.C at >=75 deg.C/min average cooling rate, and it is tempered at 400-650 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing strong cast iron, and more specifically, by performing a simple heat treatment using alloy spheroidal graphite cast iron,
The present invention relates to a method for manufacturing strong cast iron that can be made into strong cast iron.

[Prior art]

Traditionally, spheroidal graphite cast iron (JI
S standard FCD70) is used.

When particularly high strength is required, the above JIS
Quenching and tempering standard FCD70, so-called
It is made into strong cast iron by performing constant temperature treatment called austempering treatment.

However, in the above-mentioned heat treatment method, it is necessary to perform the above-mentioned heat treatment by casting and cooling it to room temperature and then reheating it, which not only requires a large amount of heat treatment energy but also requires a large amount of heat treatment. There are problems in that it requires a long processing time, high production cost, and poor productivity.

[Purpose of the invention]

The present invention was made in order to solve the problems of the prior art, and is made by casting using alloy spheroidal graphite cast iron whose hardenability has been improved by adding Ni and Mo, and cooling it after release from the mold. Quenched by controlled cooling in the process, then
The purpose of the present invention is to provide a method for manufacturing strong cast iron that can produce strong cast iron through a simple heat treatment process of tempering.

[Structure of the invention]

Such an objective is achieved according to the invention by weight ratio c; a
, o ~4.5%, Si; 1.5~3.0%, Mn;
0-2~1.0%, Mg; 0.02~0.10%, N
i; 0.6-1.4%, Mo; 0.20-0.80%
After casting in alloyed spheroidal graphite cast iron, the remainder of which is essentially Fe, the mold is released in the austenite region of 850 to 950°C, and then the temperature range from the above temperature range to 150°C or less is cast at 75°C/11in or more. This is achieved by a method for manufacturing strong cast iron, which is characterized by controlling cooling at an average cooling rate, quenching, and then tempering at a temperature range of 400 to 650°C.

[Action of the invention] Hereinafter, the effects of the present invention will be explained.

First, the reason for limiting the range of each alloy additive element in the material of the present invention will be explained.

Note that C, St, Mn, and Mg are in the same range as the general spheroidal graphite cast iron composition, and the range limitation is based on well-known reasons, so the explanation will be omitted.

Ni is effective in improving the hardenability of spheroidal graphite cast iron, but if it is less than 0.6%, the effect is not sufficient;
If it exceeds 6%, the hardenability will improve depending on the amount added, but if it is added in excess of 1.4%, not only will it not be possible to obtain a hardenability improvement effect commensurate with the amount added, but the material cost will be reduced. The price was set at 0.6% to 1.4% because it would cause the price to rise.

In addition, like Ni, Mo is effective because it improves the hardenability of spheroidal graphite cast iron, and in particular, by adding it in combination with Ni, it is possible to ensure stable and excellent hardenability of spheroidal graphite cast iron. However, if it is less than 0.2%, the hardenability improvement effect will not be sufficient. On the other hand, if it is added in excess of 0.8%, it will tend to form carbides and will reduce the ductility. Since it deteriorates material properties, it is set at 0.2 to 0.8%.

Next, alloy spheroidal graphite cast iron to which the alloying elements described above have been added is cast, and after being released from the mold in an austenite region of 850 to 950°C, a region of 150't: or less is cast to 75°C/
Controlled cooling at an average cooling rate of wr i n or higher is as follows:
This is to ensure sufficient quenching hardness by causing martensitic transformation or bainite transformation without causing pearlite transformation or sorbite-troostite transformation in the cooling process.

〔Example〕

Hereinafter, the present invention will be described in detail based on the accompanying drawings.

Molten alloy spheroidal graphite cast iron having the chemical composition shown in Table 1 is poured into a rod-shaped material of φ50m x 200-am. After casting, the mold is released in the austenitic region at 920°C as shown in the heat treatment cycle of Fig. 1. , then 147 by water spray cooling.
It was cooled to 600°C at an average cooling rate of 50°C/min, and then forced air cooled to 100°C at an average cooling rate of 50'C/win for quenching.

Table 1 Shown in Figure 2.

Note that the material structure of the strong cast iron of the present invention material manufactured by the above method was a martensitic structure containing some bainite structure.

For the inventive material, the cast material produced by the method described above was tempered at 600'C for 1 hour, and for the comparative material, a cast material with the same composition and shape as the inventive material was used. , After austempering treatment as shown in the heat treatment cycle in Figure 3, these cast materials J
A tensile test piece of IS standard No. 4 was cut out and a tensile test was conducted.

The test results are shown in Table 2.

Table 2 As is clear from Table 2, the alloy spheroidal graphite cast iron produced by the method of the present invention is a tough cast iron that has strength and toughness comparable to austempered cast iron, which is one of the conventional tough cast irons. It is understood that

〔Effect of the invention〕

As is clear from the above, according to the method for producing strong cast iron according to the present invention, alloy spheroidal graphite cast iron whose hardenability has been improved by adding N1% MO is used for casting, and in the cooling process after demolding, It has the advantage of being able to produce strong cast iron comparable to conventional austempered cast iron through a simple heat treatment process of quenching through controlled cooling and then tempering.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the heat treatment cycle of the method of the present invention, Fig. 2 is a diagram showing the quenching hardness and tempering hardness curves of tough cast iron produced by the method of the present invention, and Fig. 3 is a diagram showing the conventional heat treatment cycle. FIG. 3 is a diagram showing a heat treatment cycle of austempering treatment. 1---------Casting process 2--Mold release process 3--Controlled cooling process 4--Cooling process a---Quenching hardness b・-11111 Tempering hardness curve IIFt1%l (Hr) Smoking t and LIL & (“Co) Fig. 2 Time (Hr) Fig. 3

Claims (1)

[Claims] 1. C by weight ratio: 3.0-4.5%, Si 71.5
~3.0%, +4n; 0.2-1.0%, )IgiO
, 02-0.10%, Ni; 0.6-1.4%, M
o: After casting in alloy spheroidal graphite cast iron consisting of 0.20 to 0.80% and the remainder substantially Fe, it is released from the mold in the austenite region of 850 to 950°C, and then the temperature reaches 150°C or less from the above temperature range. Temperature range: 75℃/mi
After controlled cooling and quenching at an average cooling rate of n or more, 4
A method for producing strong cast iron, characterized by tempering at a temperature range of 00 to 650°C.