JPS63157834A - Carbon steel for electron beam welding - Google Patents

Abstract

PURPOSE:To improve the toughness of a weld zone and to prevent a crack or porosity, by specifying the amount of B and Ti in a carbon steel and limiting the total amount of P and S and the amount of O to specific values. CONSTITUTION:The carbon steel contains, by weight, 0.001-0.004% B and 0.01-0.06% Ti and limitation is regulated to (P+S)<=0.04%, O<=(200-t)ppm and N<=(250-t)ppm; in which (t) denotes the plate thickness (mm) of the carbon steel. In this way, deterioration of the toughness is prevented by incorporating B and Ti into the carbon steel. The welding crack is then prevented by limiting the amount of (P+S) and the porosity is furthermore prevented by limiting the amount of O+N.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to carbon steel applicable to electron beam welding, and in particular to improving the toughness of welded parts when electron beam welding thick plates of products such as pressure vessels and penstocks. Regarding carbon steel that prevents the occurrence of porosity and cracks.

[Conventional technology]

Since electron beam welding can weld thick plates in one pass, when applied to large structures made of thick plates, it is possible to reduce costs and improve quality. However, when ordinary carbon steel is electron beam welded, its toughness at low temperatures is poor both as welded and after heat treatment after welding, making it unsuitable for use in important structures. Further, there is a problem that when the P and 8 contained in the steel material increase, weld cracking occurs, and when the gas component increases, porosity occurs.

[Problem that the invention seeks to solve]

In view of the problems of the conventional carbon steel for electron beam welding, the present invention aims to develop a carbon steel for electron beam welding that has good toughness in the welded part and does not generate cracks or porosity even when electron beam welded. That is.

[Failure to solve the problem]

The present invention applies α001≦B≦[L
00.04%, α01≦Ti≦(L
4% or less, the amount of 0 is limited to not more than (2oo-t) ppm, and the amount of N is limited to not more than (250-t) ppm (however, t is the value expressed by the plate thickness of carbon steel with -). This is carbon steel for electron beam welding.

That is, the present invention contains B and Ti in carbon steel to prevent the toughness from deteriorating, and also to prevent weld cracking by adding CP+
8) It is a carbon steel in which the amount of 0 and N is regulated to prevent porosity.

[Effect]

Ti forms titanium nitride to make the microstructure uniform, and B forms poron nitride to fix nitrogen. Furthermore, the (P+El) regulation reduces elements that cause weld cracking, and the 0 and N regulations eliminate porosity sources.

The steel type targeted by the present invention is EXXO material.

EIM material, 8s material, SMA material, SB material, 8P'V material.

Examples include all general carbon steels such as EA material and BGV material. In these carbon steels, C is added to increase the strength, but if the content exceeds α55% by weight, weldability deteriorates, so the C content should be 0.55% or less. is desirable. Furthermore, Si and Mn are added as deoxidizing agents, but if their amounts increase, weldability deteriorates. Therefore, Si and Mn are added in weight% (115 to 75% by weight, and Mn is 0.6011 to 1.60% by weight). (Hereinafter, % means weight %) In the present invention, B and Ti are added because titanium nitride homogenizes the microstructure and boron nitride fixes nitrogen. This is because the effect of improving the toughness is particularly large. However, if the B content is too large, the nitrogen fixing effect is lost and the toughness is reduced due to the negative effects of B. Also, if the Ti content is too large, the nitrogen fixing effect is lost. However, titanium precipitates in titanium nitride, reducing toughness. Therefore, B is α01≦T≦004%.
In addition, Ti is set to satisfy α01≦Ti≦0.06%.

The reason why the total amount of P and S is set to 1.o4% or less is as follows. That is, if r and S are included, lPe5 (
Melting point 1.190℃), IFe, P (melting point 1.166℃)
In the Fee-FeO eutectic, 988°C, 'IPe,
The P-FeO eutectic has a melting point of 1.050°C. This is because the presence of a liquid phase with a low melting point is a cause of hot cracking, and it is better to reduce P and day as much as possible. Therefore, the lower limit values of P and S are zero.

The amount of O is (200-t) ppm or less, and the amount of N is (250-t) ppm or less.
-t) ppm or less (however, t is a value expressed by the plate thickness of carbon steel) for the following reason. That is, in electron beam welding, even thick plates are welded in one pass, so when the plate is thick, porosity tends to remain inside the thickness of the plate. Therefore, it is necessary to adjust the amounts of O and N according to the thickness of the plate, and as a result of the examples described later, they were regulated as described above.

〔Example〕

The effect of improving the toughness in the welded joints of B and 'f'i was investigated by performing electron beam welding on a carbon steel sheet with a thickness of 1006 @ having the composition shown in Table 1, and examining the Charpy absorbed energy.

The results are shown in FIG. Figure 1: Sha B is 0.001≦
B≦Q, range of 00.04%, Ti is 101≦Ti≦0
．． It can be seen that the range of 064 is good.

Table 1 Chemical Composition of Test Materials (H) Next, for the carbon steels shown in Table 2, the effect of the amount of (I'+8) on weld cracking was investigated using a Fisco-type restrained cracking test. The results are also shown in Table 2 and Figure 2. From Table 2 and FIG. 2, it can be seen that weld cracking can be prevented by limiting the amount of (P+8) to 0.04% or less.

Table 2 shows the occurrence of porosity using carbon steel with the composition shown in Table 3, with a plate thickness of 50 wm and 100 mm.

150g was investigated. The results are shown in FIGS. As is clear from FIGS. 3 to 5, the limit of porosity generation differs depending on the plate thickness. Figure 6 summarizes these boundary conditions. From the boundary condition in Figure 6, O
The amount of N is (200-t) ppm or less, and the amount of N is (250-t) ppm or less.
-t ) ppm or less (where t is a numerical value customarily expressed as the plate thickness of carbon steel), it is understood that the occurrence of porosity accompanying electron beam welding of carbon steel can be prevented.

In FIGS. 1 to 6, ◯ indicates no porosity, △ indicates partial porosity, and . indicates porosity.

Table 5 Chemical composition of carbon steel sample (%) [Effects of the invention] If the carbon steel has the composition of the present invention, a good weld metal with good toughness and no weld cracks or porosity can be obtained even when electron beam welding is performed. It will be done.

[Brief explanation of the drawing]

Figures 1 to 6 are diagrams showing the effects of the present invention. Figure 1 shows the relationship between B and Ti contents and Charpy absorbed energy, and Figure 2 shows the relationship between the (P+EI) amount and weld cracking. 5 to 5 are charts showing the relationship between the 0 amount and the N amount and the porosity distribution at a plate thickness of 50.100.150+w+, and FIG. 6 is a chart showing the porosity limit conditions. Sub-Agents 1) Meifuku Agent Ryo Hagiwara - Sub-Agent Atsuo Anzai (MDD) Q

Claims (1)

[Claims] In carbon steel, 0.001≦B≦0.004 in weight%
%, B and Ti so that 0.01≦Ti≦0.06%.
furthermore, the total amount of P and S is 0.04% or less,
The amount of O is (200-t) ppm or less, the amount of N is (250-t)
) ppm or less (where t is a value expressed by the plate thickness of the carbon steel in mm), carbon steel for electron beam welding.