JPH04162984A - 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, Cr, etc., 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, 50 to 80% Ni, 11 to 32% Cr, and the balance Fe. After both materials are welded, the materials are heated and held for >=10 minutes to and at 650 to 1000 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, in the case of welding ferritic stainless steel materials, after welding, heat treatment is carried out at a temperature of 700 to 850°C (for example, "Revised 3rd Edition Welding Handbook" (1983)).
3.1.25) Japan Welding Society of Japan, P, 991).

(Problems to be Solved by the Invention) The above-mentioned side heat treatment after welding requires a large amount of thermal energy because it is performed at high temperature for a long time.Furthermore, ferritic stainless steel materials cannot be heated at 475°C during long-term heating. cause sigma compatibility or sigma compatibility.

That is, 475°C fragility occurs when heated to a temperature of 400 to 550°C for a long time or slowly cooled in this temperature range, whereas sigma fragility occurs when heated to a temperature of 600 to 800°C for a long time. It is caused by heating and significantly reduces ductility and toughness.

The present invention has been made in view of such problems, and is a joining method for welding spheroidal graphite cast iron materials and ferritic stainless steel materials, which can lower the heat treatment temperature and shorten the heat treatment time after welding the rainforest. The present invention provides a method.

(Means for Solving the Problems) The joining method of the present invention combines a spheroidal graphite cast iron material having a ferritic base and a ferritic stainless steel 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,
Ni: 50-80%, Cr: 11-32%, balance Fe
A joining method in which gas-shielded arc welding is performed using a welding wire having an austenitic base, and the method includes heating and holding the rainforest at a temperature of 650 to 1000°C for 10 minutes or more after welding the rainforest, and then cooling it in air. This is a characteristic feature.

(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: a, 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 ferrite base consisting of e and inevitable impurities, or JIS 0 5502 FCD
40 to 45 ferritic spheroidal graphite cast iron or spheroidal graphite cast iron with some barite deposited on the ferritic ground, while the ferritic stainless steel base material is J.
IS G 4304 5US430 (hot rolled ferritic stainless steel sheet) or 5US43O stainless steel sheet, 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: 0°03%
Below, S: 0.03% or less, ~i: 50-80%, Cr
:11 to 32%, the balance is Fe, and has an austenitic base.

Next, the composition of the wire will be explained.

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

Si: 1.00% or less SL 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.

) 4r+: 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: o, o 3% or less P is contained as an impurity and is preferably lower because it promotes welding hot cracking, 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 0.03% or less.

Ni: 50-80% ~j is an austenite-forming element that stabilizes austenite, improving heat resistance, high-temperature strength, creep rupture strength, oxidation resistance, and corrosion resistance, and adding 50-80% Ni prevents toe cracking. is suppressed.

Cr: 11-32% Cr forms a passive film and improves oxidation resistance and corrosion resistance, but if it is less than 11%, the properties cannot be sufficiently maintained.
When Cr exceeds 32%, sigma phase precipitation tends to occur,
Since workability deteriorates in the wire manufacturing process, 11~
It will be 32%.

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. Refers to welding.

(4) Heat Treatment Rain After welding the base metal, heating and holding at 650 to 1000°C for 10 minutes or more increases the rupture strength of the welded part. The holding time is 475℃ brittle or σ
It is preferable that the time is short enough to not cause compatibility. When the heating temperature exceeds 1000° C., a large amount of thermal energy is required regardless of the holding time.

(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) After inserting a ferritic stainless steel pipe (outer diameter: 34 mφ, wall thickness: 1.5 no.) into a ferritic spheroidal graphite cast iron pipe, welding was carried out by M welding using the welding wire shown in Table 1. Both pipes (hereinafter referred to as both base materials) were overlapped and fillet welded to create a welded joint. Table 2 shows the component compositions of both base materials.

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 base metals were put into a furnace and heat treated, but the same effect can be obtained by applying the same heat treatment to the welded parts of the two base metals 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: 50-80%, Cr: 11-32%
, a joining method of gas-shielded arc welding with a welding wire having an austenitic base, the remainder of which is Fe, and after welding the two materials, heating and holding the two materials at a temperature of 650 to 1000 ° C. for 10 minutes or more, Next, a method for joining a spheroidal graphite cast iron material and a stainless steel material, which is characterized by air cooling.