JPH03104841A - Spheroidal graphite cast iron - Google Patents

Abstract

PURPOSE:To obtain the inexpensive spheroidal graphite cast iron having induction hardenability suitable for manufacturing a camshaft of an automobile engine or the like by forming it from the compsn. contg. each prescribed amt. of C, Si, Mn, Cu, Mg, P, S, Cr, Mo and Ni. CONSTITUTION:The above spheroidal graphite cast iron is formed from the compsn. contg., by weight, 3.0 to 4.0% C, 1.7 to 2.4% Si, 0.4 to 0.7% Mn, 0.5 to 1.3% Cu, 0.02 to 0.05% Mg, <=0.1% P, <=0.02% S, <=0.15% Cr, <=0.15% Mo, <=0.15% Ni and the balance Fe. In the componential elements of the spheroidal graphite cast iron, particularly the content of Mn and Cu is regulated to the one in the above componential range, by which the amt. of ferrite in the casting stock can be suppressed to 5% areal rate. As the result, by executing induction hardening, the most part of the matrix structure is transformed into a martensitic one, so that the hardened surface having high hardness as well as less dispersion in the hardness and furthermore having uniform and controlled depth can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to spheroidal graphite cast iron, particularly spheroidal graphite cast iron with excellent induction hardening properties.

(Prior Art) In order to reduce the manufacturing cost and quantity of automobile engines, attempts have been made to manufacture crankshafts, camshafts, etc. from spheroidal graphite cast iron. Products obtained by manufacturing casting materials using high-strength spheroidal graphite cast iron (e.g. JIS-FCD70, FCD80, etc.) suitable for the above-mentioned engine crankshafts and camshafts, etc. and then performing the necessary machining are wear-resistant. In order to improve the wear resistance and fatigue strength of spheroidal graphite cast iron crankshafts and camshafts, for example, Attempts have been made to perform induction hardening on necessary parts such as the cam surface of the camshaft. However, the microstructure of ordinary spheroidal graphite cast iron cast iron material is composed of graphite g and zoolite p (
Due to the large amount of ferrite, when induction hardening is performed for a short period of time in the same manner as for carbon steel forgings, the metal structure shown in Figure 2 (FB) is shown in the photograph showing the metal structure. As shown, a considerable amount of ferrite f remained in the precipitated martensite m (base), and as a result, it was confirmed that the surface hardness varied significantly and the old fatigue strength was not sufficiently improved.

(Problems to be Solved by the Invention) When applying induction hardening to a cast rough material of spheroidal graphite cast iron to obtain desired wear resistance and fatigue strength, the heating time may be similar to the induction hardening of the carbon steel forged product.・There is a method of increasing the heating time to more than double the heating time, but due to the long heating time, productivity is low, which naturally increases manufacturing costs.
There is a problem that it becomes difficult to control the quenching depth, which increases the variation in quality. 1. In addition, the cast raw material of spheroidal graphite cast iron is normalized at 860°C for 2 hours to remove as much of the ferrite as possible in the as-cast structure (preferably, the amount of ferrite is 5 or less as an area ratio). ) into zorite, the required parts are machined leaving a polishing allowance, and the machined parts are induction hardened.
Furthermore, if necessary, there is a method of annealing at a low temperature, e.g., 500 to 550°C, for 2 hours, followed by polishing, but this method requires multiple equipment, processing time, handling between processes, etc. This has the disadvantage of inevitably increasing manufacturing costs.

The present invention was devised in view of the above circumstances, and by adding innovation to the constituent elements of spheroidal graphite cast iron, the amount of ferrite that is buttoned in as-cast rough material is suppressed to 5 or less (area ratio), and excessive The object of the present invention is to provide spheroidal graphite cast iron that can obtain excellent induction hardening characteristics without requiring high frequency heating time or troublesome heat treatment.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides carbon 3. 0-4
．． 0 ratio, silicon 1.7~2.4%, manganese 0.4~
0.7, copper 0.5-1.3%, magnesium 0.02
~0.05 section, phosphorus 0. 1% or less, sulfur 0.02% or less, chromium 0. 15% or less, molybdenum 0.15
% or less, and 0.15% or less of nickel (both by weight), and the balance is iron.

(Function) According to the present invention, among the constituent elements of ordinary spheroidal graphite cast iron, manganese is particularly contained in an amount of 0.4 to 0.7% (by weight), and copper is contained in an amount of 0.5 to 1.3%. , the amount of ferrite in the cast raw material can be suppressed to less than 5% (area ratio), and by induction hardening, most of the matrix structure is converted to martensite, resulting in high hardness, less variation in hardness, and evenness. And a hardened surface of controlled depth can be obtained. As the pearlite base of the cast crude material expands when it changes to martensite, compressive stress is generated in the quenched part due to the structure relationship between the unquenched part and the quenched surface layer, which reduces the fatigue strength. will improve.

(Example) The present invention will be specifically described below with reference to Examples.

Camshafts for automobile diesel engines were cast using spheroidal graphite cast irons A to J having various compositions whose chemical components are shown in Table 1 below.

In Table 1 above, test materials D, E, H, I, and J are examples of the present invention, and all of them contain 0.4 to 0.7% manganese and 0.7% copper, which are themselves inexpensive alloy components. The other test materials A, B, C and F. G is a reference material in which the content of manganese or (and) copper deviates from the above range. As mentioned above, it has been recognized that the presence of ferrite in the metal structure impairs the induction hardening properties, so when casting Sicam shafts using the above test materials, the molds should be broken up as soon as possible after casting. Measures were taken to suppress the precipitation of ferrite.

The as-cast camshafts cast with the test materials A to J listed in Table 1 above are characterized by their Purinel hardness, ferrite ratio (area) in the metallographic structure, and whether or not the necessary machining can be performed before induction hardening. The results of the investigation regarding stiffness are shown in Table 2 below.

Table 2 As is clear from Table 2, test material D belonging to the present invention
, E, H, I, and J have a ferrite ratio of 5 or less, a hardness (HB) of 240 to 277, and machinability is good or slightly poor, making them practical in terms of machining. This was recognized. Among the reference test materials, A and F, which contain an excessive amount of copper, have a hardness (HB) of 285 or higher and have poor machinability, and are not suitable for testing induction hardening characteristics, so they are already impractical in terms of machining. This was recognized. Of the reference test materials, B and C, which contain particularly small amounts of copper, have extremely high ferrite percentages and are extremely soft with hardness (HB) of 220 or less. The metallographic structure of the crude material is shown in Figure 2 (At), and as already explained, it consists of graphite g and a large amount of ferrite f and zorite p (base) precipitated around it. There is.

On the other hand, in the test material belonging to the present invention, as is clear from FIG. g
The structure becomes dispersed, and only a small amount of ferrite f is precipitated.

Next, the cam surfaces of the as-cast camshafts cast using the above test materials A to J were machined, and then induction hardened under substantially the same conditions as carbon steel forgings to harden the surface of the cam nose. The results of examining the metallurgy and metal structure are shown in Table 3 below.

Table 3 As shown in Table 3 above, reference test materials B, excluding test materials A and F, which are already impractical in terms of machinability,
C and G have a ferrite ratio of 7 to 2 in the as-cast rough material.
Due to the high 0'l, when ordinary induction hardening is performed, residual ferrite is observed in the metal structure. As an example, the metal structure of material B after induction hardening is shown in Figure 2 (
B). These reference materials B, C, and G have low cam nose surface hardness (HV), therefore, the compressive residual stress is low, and the fatigue strength is naturally low.

On the other hand, in the test materials D, E, H, I, and J belonging to the present invention, since ferrite was not substantially precipitated in the structure of the as-cast rough material, the test materials shown in Fig. 1E (B) as an example As shown in the metallographic structure of the material after induction hardening, pearlite P (base) is substantially all changed to martensite M, and the hardening (HV) of the cam nose surface is also high on average, so there is no compression residue. It has been shown that the greater the stress, the greater the fatigue strength.

As a result of the above, as described in the "Judgment" section of the rightmost column of Table 3, the spheroidal graphite cast irons D, E, H, I, and J according to the present invention are approximately equivalent to carbon steel forged products. It also has high-frequency induction hardening properties, has excellent wear resistance and fatigue strength, and does not require troublesome heat treatment or long induction heating times, and does not contain expensive alloy components, reducing manufacturing costs. It has been confirmed that it is inexpensive and has the advantage of being able to effectively control the quenching depth (usually 3 to 5 m), and is suitable for practical use.

(Effects of the Invention) As described above, the spheroidal graphite cast iron according to the present invention has carbon 3.
0-4.0%, silicon 1.7-2.4%, manganese 0
．． 4-0.7%, copper 0.5-1.3%, magnesium 0
．． 02-0.05%, 0.1% phosphorus or less, 0.02% sulfur
The following contains 0.15% or less of chromium, 0.15φ or less of molybdenum, and 0.15% or less of nickel (all by weight),
It is extremely useful industrially because it is able to provide spheroidal graphite cast iron at a low cost, which is characterized by the remainder being made of iron and has induction hardening characteristics suitable for manufacturing camshafts and crankshafts for automobile engines.

[Brief explanation of drawings]

Figure 1 (A) is a photograph showing the metallographic structure of the as-cast rough material of spheroidal graphite cast iron according to the present invention, and Figure 1 (B) is a photograph showing the as-cast rough material shown in Figure 1 (A). Figure 2 (A) is a photograph showing the metal structure of the material subjected to induction hardening, and Figure 2 (A) is a photograph showing the metal structure of as-cast raw material of spheroidal graphite cast iron, which is not included in the present invention. ) is a photograph showing the metallographic structure of the as-cast rough material shown in Fig. 2 (N) subjected to induction hardening. g... graphite, f... ferrite, p... pearlite, m... ...Martensite O figure 1 (A) O figure (B) ρ] Lusai figure 2 (A) To f Otsu + 2 figure (B) mg'f Procedure amendment (self-proposed) February 7, 1990 Day 1 Display of the case Patent application No. 240396 of 2003 2 Name of the invention Spheroidal graphite cast iron 3 Person making the amendment Relationship to the case Patent applicant address 33-8 Shiba 5-chome, Minato-ku, Tokyo Name (62
8) Mitsubishi Motors Corporation Representative Yutaka Nakamura 4. Agent postal code 227 Attachment 1 Claims Carbon 3.0-4.0%, Silicon 1.7-2.4%, Manganese 0.4-0.8%, Copper 0.5-1.3% , Magnolium 0.02-0.05%, Phosphorus 0.1% or less, Sulfur 0
．． 0.02% or less, chromium 0.15% or less, molybdenum 0.
15% or less, nickel 0.15% or less (all percentages by weight)
spheroidal graphite cast iron characterized in that the remainder consists of iron. Attachment 2 to the scope of claims of the specification of the subject invention of the 6th amendment in the specification of the present application 1. From line 13 on page 3 to line 15 on the same page, it says, ``Additional methods may be available, if necessary.'' There is a way to do this.'' 2. In the 9th line of page 4, the 17th line of the same page, the 3rd line of page 7, and the 6th line of page 12, "0.7%" was replaced with "0.8%".
%” respectively. that's all

Claims (1)

[Claims] Carbon 3.0-4.0%, silicon 1.7-2.4%, manganese 0.4-0.7%, copper 0.5-1.3%, magnesium 0.02-0.05%, Phosphorus 0.1% or less, sulfur 0
．． 0.02% or less, chromium 0.15% or less, molybdenum 0.
15% or less, nickel 0.15% or less (all percentages by weight)
spheroidal graphite cast iron, characterized by containing iron with the remainder being iron.