JPS58207354A - Manufacture of crane parts made of spheroidal graphite cast iron - Google Patents

Abstract

PURPOSE:To improve the strength, toughness, etc. of crane parts made of spheroidal graphite cast iron having a specified composition, by heating and holding the parts under specified conditions and by carrying out quenching, holding for a fixed time and cooling to ordinary temp. to form a bainite matrix structure. CONSTITUTION:Crane parts having >=30mm. diameter or >=15mm. thickness such as sprocket parts for chain winding are made of spheroidal graphite cast iron consisting of, by weight, 3.0-4.0% C, 2.0-3.5% Si, 0.25-1.0% Mn, 0-1.0% Cu, 0.03-0.1% Mg and the balance essentially Fe. The parts are heated and held at 850-950 deg.C for 20min-2hr to austenitize the ferrite matrix. They are quenched in the 1st cooling medium at <=250 deg.C, held for a prescribed time, put in the 2nd cooling medium at 250-400 deg.C, and held for a prescribed time to complete bainitic transformation. They are then allowed to cool in air. Thus, parts with superior wear resistance and other characteristics are obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing spheroidal graphite cast iron lifting-like parts. After heating a spheroidal graphite cast iron product to austenite, it is heated to a predetermined temperature higher than room temperature, maintained at this temperature for a certain period of time, and then cooled to room temperature, which is the so-called austempering treatment, which changes the matrix structure. can be made into a material that is bainitic and has high strength, toughness and ductility, and excellent wear resistance.

The austen-ζ treatment method for converting spheroidal graphite cast iron # into bainite is known. In the case proposed in Japanese Patent Application Laid-Open No. 19-53115, after austenitization, 370
It is said that a bainite phase containing residual ausbunite can be obtained by rapidly cooling in a salt bath at around ℃ and holding it for a specified time, but in this case, the components of normal spheroidal graphite cast iron,
Mo: 0. L U~lJ, 213% is contained, Ni is 2.5% or more F1 is preferred, L< is 0.5~2.5%,
The conditions are that Sn is contained in an amount of 0.03-4J, 2%, and that copper is contained in an amount of 0.3-1.0%.

The present invention provides a method for manufacturing lifting equipment parts having a bainitic microstructure without requiring the inclusion of these expensive alloying elements and using a commonly manufactured ferrite-based spheroidal graphite casting. In terms of weight ratio, C
: ;to~-t, o'3o, si: 20~35%, M
n: 0.2! '+ ~1. U%, CIO,
: 0 to 10%, Mg: 0.03 to 0.1%, and the balance is substantially Fe. Lifting machine parts made of spherical graphite iron, with a diameter of 30 m or more - Tote to plate or parts of 15 rtan or more. After heating and holding at a temperature of 850 to 950°C for 20 minutes to 2 hours, it is rapidly cooled in a first cooling medium of 250°C or less and held for a predetermined time, and then in a second cooling medium of 250 to 400°C. It is characterized by being transferred and held for a predetermined period of time.

Next, an embodiment of the method of the present invention will be described in detail. First, a lifting machine part made of a general ferrite-based spheroidal graphite cast iron is cast, and mechanical processing is performed in an as-cast state with low hardness.

Then 850-950'C(0]41-<Id':)
00 to 92 (1°C) to austenite.

The holding time at that temperature depends on the texture and shape of the parts, if the diameter is less than 30mm or the board is less than 15mm,
20-30 minutes or more directly <f father is meat 11;S
O alter ego weight - within 2 hours.

From this temperature, the continuous cooling transformation curve of spheroidal graphite νJ iron is around 700℃ (as shown in Fig. 1).
(If the pearlite transformation region P exists and the cooling rate of the part 117 is not sufficient t'c, the pearlite transformation will occur)
In the bainitic transformation region B, in the normal composition L which does not contain the bainitic structure (9), which does not contain the alloy component, this pearlite region extends to the gold alloy component 2, and the VC extends to the left of the figure. It will be difficult to avoid the occurrence of pearlite Japanese spelling unless it is sufficiently large.

Therefore, it is necessary to cool the austenite in the first cooling medium at a temperature of 250°C or higher (therefore, the
[UE] Avoid the perverted area. As the first cooling medium, 17
Keep the melon at a constant temperature between 0 and 250°C using a salt bath or water. Part size, meat I
Choose one from Eno PC.

The retention time in the first cooling medium is to rotate the pearlite region and at the same time, it is safe that it does not reach the martensia)Ms transformation region which is around 200~23+)'C, and it depends on the shape and wall thickness of the part. , for 1 to 5 minutes.

Next, 250°C to 400°C (preferably 300 to 360°C)
) into a second cooling medium maintained at a predetermined temperature;
After completing the bainite transformation by maintaining the temperature at a constant temperature for 30 minutes or more and less than 2 hours, it is allowed to cool in the air. As this second cooling medium, a salt bath is used which is maintained at a constant temperature between 2F and 0 to 100C. Through the above operation V, the desired bainite structure can be obtained.

FIG. 2 shows a comparison of cooling curves between this two-stage cooling method and an austempering method in which a 350° C. T4 bath is directly introduced. Curve 8 is the state where the conventional direct θ is applied to the pearlite transformation region, curves b and C are the state where the pearlite transformation region is avoided by the two-stage cooling method according to the present invention, and curve 6 and curve 1 are the state where M's is affected by supercooling. Each shows the state in which the point has been exceeded and the martensite transformation region has been entered.

The wall thickness of the parts is 301IOII or more in diameter, and my father is board 1■
If the temperature is 15 m or more F, the cooling rate is high, so the use of the first cooling medium can be omitted.

The wall thickness of the part is 50y+m or more in diameter J5, or 25 in thickness
If the resistance is exceeded, it is necessary to add not more than 1.0% of Cu to the H material to move the pearlite region back to the right. In this case, it is already known that adding a small amount of Mo or Ni is even more effective.
1 The chain/winding sprocket of small machines is conventionally Vi
The parts were made from forged steel and required many heat treatments and additional treatments to complete the parts. Special 1/('% Chain/Machining of the fitting part required a large amount of work.On the other hand, cast products have the advantage of being able to form shapes without machining.However, As an example of this part is shown in Figures 3 and 4, the area where the chain fitting part receives the most load is the constriction (section 0 in the figure), so a normal cast product would break at the 0 section. Not practical.

A tin rocket for winding/winding made of spheroidal graphite cast iron with a bainitic structure formed by the method of the present invention has a tensile strength of 90 kg/I.
It was found that it had a high strength of II+12 or higher, and also had high elongation, bending strength, and impact resistance, so it could be used satisfactorily.

Depending on the combination of cooling medium temperature and time conditions, the hardness of the part can be freely changed within the range of HRC 28 to 45. Therefore, by setting the hardness to match the hardness of the other chain, it is possible to create a state in which both the sprocket and the chain are not damaged and there is almost no wear, and the period of use can be significantly extended. It became.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a continuous cooling curve of spheroidal graphite cast iron in a time-temperature coordinate system, Fig. 2 is a continuous cooling curve similar to Fig. 1 according to the JJ method of the present invention, and Fig. 3 is a diagram of an example of a chain sprocket. The side view and FIG. 1 are cross-sectional views taken along the line IV-fV. Patent applicant: Sugiyama Casting Co., Ltd. Tadashi Shiokawa Agent: Takashi Nakamura

Claims (2)

[Claims] (1) In terms of weight ratio, C: aO ~ 4.0%, Si: 20
~a5%, Mn: 0.25-1.0%, Cu: υ~
1.0chi, Mg: 0.03~0. t%, the balance being substantially Fe, a spheroidal graphite cast iron lifting-like part with a diameter of 30 m or more or a plate thickness of 15111 m1 or more is heated and held at a temperature of 850 to 950°C for 20 minutes to 2 hours. After that, it is rapidly cooled in a first cooling medium of 250°C or less and held for a predetermined time, and then transferred to a second cooling medium of 250 to 4QO°C and held for a predetermined time. Method of manufacturing lifting-like parts. (2) The method for manufacturing a lifting machine part made of spheroidal graphite cast iron according to claim 1, wherein the lifting machine part made of spheroidal graphite cast iron is a chain winding sprocket part.