JPH04162987A - Method for joining spheroidal graphite cast iron material and stainless steel material - Google Patents

Abstract

PURPOSE:To improve productivity and to reduce costs by welding the above cast iron material and stainless steel material by a welding wire which contains specific weight % of C, Si, Mn, Ni, P, and S, and consists of the balance Fe, then heating and holding the materials for a specific period of time to and at a specific temp., and air cooling the materials. CONSTITUTION:The spheroidal graphite cast iron material having a ferrite base and the ferritic stainless steel material are welded. These materials are then subjected to gas shielded arc welding by the welding wire of the austenite base consisting, by weight %, of <=0.15% C, <=1.00% Si, <=3.5% Mn, <=0.03% P and S, >=80% Ni, and the balance Fe. After both materials are welded, the materials are heated and held for >=(-0.8XT+57O) minutes to and at 600 to 700 deg.C and are then air cooled. The heat treating time is reduced in this way and the breaking strength of the weld zone is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for joining a spheroidal graphite cast iron material having a ferritic base and a ferritic stainless steel material.

(Prior Art) When welding spheroidal graphite cast iron materials or ferritic stainless steel materials, heat treatment is performed after welding. That is,
When welding spheroidal graphite cast iron materials, annealing is performed. Immediately after welding, the welded material is transferred to a furnace heated to 200 to 400°C, and then heated to 900°C. After holding at that temperature for 2 hours, it was gradually cooled to 700°C, held at that temperature for 5 hours, cooled to 250°C in the furnace, taken out from the furnace, and placed in still air at room temperature. (For example, "Revised 3rd Edition Welding Handbook" (1986)
3.1.25) Japan Welding Society, P.

868). On the other hand, when welding ferritic stainless steel materials, heat treatment is carried out at 700 to 850℃ after welding, at an appropriately selected temperature (e.g., "Revised 3rd Edition Welding Handbook" (1986)).
3.1.25) Japan Welding Society of Japan, P, 991).

(Problems to be Solved by the Invention) The above-mentioned surface heat treatment after welding requires a large amount of heat energy because it is carried out at high temperatures for a long time.Furthermore, ferritic stainless steel materials have a temperature of 475°C during long-term heating. cause compatibility or σ compatibility.

That is, 475°C susceptibility occurs when heated to a temperature of 400 to 550°C for a long period of time or is gradually cooled in this temperature range, while σ compatibility occurs when heated to a temperature of 600 to 800°C for a long period of time. This occurs due to the deterioration of ductility and toughness.

The present invention has been made in view of these problems, and is a joining method for welding a spheroidal graphite cast iron material and a ferritic stainless steel material, in which the heat treatment temperature and heat treatment time after welding of the art materials can be lowered and the heat treatment time can be reduced. The present invention provides a method.

(Means for Solving the Problems) The joining method of the present invention is to combine a spheroidal graphite cast iron material having a ferritic base and a ferritic stainless steel mesh material by weight% of C.
: 0.15% or less, Si: 1.00% or less, Mn: 3.
5% or less, P: 0.03% or less, S: 0.03% or less,
A joining method in which Ni: 80% or more, the balance being Fe, and gas-shielded arc welding is performed using a welding wire having an austenitic base, and after welding the art material, the art material is
It is characterized by being heated and maintained at a temperature T''C of 700''C for (-0,8XT+570) minutes or more, and then air-cooled.

(1) The base material is spheroidal graphite cast iron and ferritic stainless steel having a ferritic base, and the spheroidal graphite cast iron base material is
In weight%, C: 3°5-4.2%, si: 3.5-4
．． 3%, Mn: 0.8% or less, P: 0.1% or less, S:
0.03% or less, Mg: 0.03-0.1%, remainder F
Spheroidal graphite cast iron with ferritic ground consisting of e and inevitable impurities, or JIS G 5502 FC
It is formed from D40 to D45 ferritic spheroidal graphite cast iron or spheroidal graphite cast iron with some pearlite precipitated on the ferritic ground, while the ferritic stainless steel base material is
JIS G 4304 5US430 (hot rolled ferritic stainless steel plate) or 5US430 series stainless steel plate, or JIS G 4305 5US
430 (cold rolled ferritic stainless steel plate) to 5US430 series stainless steel plate.

(2) Welding wire Welding wire, in weight%, C: 0.15% or less, Si:
1.00% or less, Mn: 3.5% or less, p:o.

0.03% or less, S: 0.03% or less, Ni: 80% or more,
The remainder consists of Fe and has an austenite base.

Next, the composition of the wire will be explained.

C: O, 15% or less C increases the strength, but if it exceeds 0.15%, workability deteriorates in the wire manufacturing process, so the content should be 0°15% or less.

Si: 1.00% or less Si improves oxidation resistance and improves hot water washing of weld metal. If it exceeds 1%, in the wire manufacturing process,
Since workability deteriorates, it should be 1% or less.

Mn: 3.5% or less Mn is added as a deoxidizing/desulfurizing agent, but if it is too large, corrosion resistance and oxidation resistance will deteriorate as well as workability in the wire manufacturing process, so it should be kept at 2.5% or less.

P: 0.03% or less P is contained as an impurity and promotes welding hot cracking, so a lower content is desirable, but since it is difficult to dephosphorize during steel manufacturing, the allowable upper limit is 0.03%.

S: 0.03% or less S is particularly harmful to weld hot cracking, so the allowable upper limit is 0.003% or less.

Ni 80% or more Ni is an austenite-forming element that stabilizes austenite, improving heat resistance, high temperature strength, creep rupture strength, oxidation resistance, and corrosion resistance, and suppressing toe cracking when added at 80% or more. .

remainder The remainder is Fe and unavoidable impurities.

(3) Gas-shielded arc welding Gas-shielded arc welding is arc welding performed in an atmosphere containing an inert gas such as Ar or He, or a small amount of active gas added to these gases, and includes MIG welding, TIG welding, and plasma welding. Point.

(4) After welding the heat-treated materials on both sides, the temperature T”C (-
When the weld is heated and held for more than 0.8XT+570) minutes, the breaking strength of the weld increases. The holding time is set to such an extent that the ferritic stainless steel does not cause 475° C. embrittlement or σ compatibility, and a shorter holding time is preferable.

(Function) Since the present invention has the above-described configuration, the heat treatment temperature after welding the spheroidal graphite cast iron material having a ferritic base and the ferritic stainless steel material is lowered, and the heat treatment time is significantly shortened. The breaking strength of the part increases.

(Example) A ferritic stainless steel pipe (outer diameter 834 mmφ, wall thickness: 1.5 mm) was inserted into a ferritic spheroidal graphite cast iron pipe, and then both were welded by M welding using the welding wire shown in Table 1. A welded joint was created by overlapping and fillet welding the pipes (hereinafter referred to as both-bank materials). Table 2 shows the composition of the materials on both banks.

Next, the joint was put into an electric furnace and heat treated under the heating conditions shown in Table 3, and then air cooled outside the furnace (cooling rate: 1.9°C).
/second). Thereafter, the joint was subjected to a tensile test to examine the breaking strength and the breaking position.

The joint obtained by the joining method of the present invention has an increased breaking strength and the stainless steel pipe breaks, but the joint obtained by the joining method of the comparative example has a small breaking strength and the heat affected zone of the joint is small. It can be seen that it will break.

In this example, the entire welded material on both sides was put into a furnace and heat treated, but the same effect can be achieved even if the welded part of the material on both sides is heat treated in the same manner as in the above example. play.

Table 3 (Effects of the Invention) According to the present invention, the heat treatment time is significantly shortened, the breaking strength of the welded part is increased, and a welded product of spheroidal graphite cast iron material and ferritic stainless steel material can be easily obtained. Therefore, it is possible to significantly improve productivity and reduce costs.

Claims (1)

[Claims] A spheroidal graphite cast iron material having a ferritic base and a ferritic stainless steel material, in weight percent, C: 0.15% or less, Si: 1.00% or less, Mn: 3.5% or less, P: 0.03% or less, S: 0.
03% or less, Ni: 80% or more, the balance consists of Fe,
A joining method in which gas-shielded arc welding is performed using a welding wire having an austenitic base, and after welding the two materials, the two materials are brought to a temperature of 600 to 700°C (-0.8×T+5
70) A method for joining a spheroidal graphite cast iron material and a stainless steel material, the method comprising heating and holding the material for at least 70 minutes, and then air cooling.