JP2000192192A - White spot preventive steel, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel capable of preventing the occurrence of white spots while obviating the necessity of particular treatment requiring large amounts of energy and much time, and its manufacturing method. SOLUTION: This white spot preventive steel has a composition consisting of, by weight, 0.01-0.70% C, 0.1-1.0% Si, 0.1-1.0% Mn, 0.1-8.0% of one or >=2 elements among Cr, Ni, Mo, V, and W, 0.01-0.10% Al, 0.01-0.10% of Ti or Zr, and the balance Fe with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a steel for preventing white spots and a method for producing the same.

[0002]

2. Description of the Related Art White spots (hydrogen cracks) occur in machine structural steel and low carbon steel even when the hydrogen content in the molten metal is about 2 ppm after being processed into an intermediate product or a final product by hot forging or rolling. Cheap. In addition, even if the generation of white spots in the intermediate product can be prevented, it may occur again by re-forging or the like.

[0003] As a preventive measure, hydrogen diffusion removal treatment for as long as 1000 hours has been carried out (edited by the Iron and Steel Institute of Japan,
Heat treatment of steel, 5th edition, P662) Even today, when degassing technology has advanced, as described in JP-B-57-25605, a refining additive such as calcium carbide used for refining is pre-heated and added. To control the cooling rate after hot working, as disclosed in JP-B-64-10564 and JP-B-59-37724, which reduce the amount of water brought in from the furnace and prevent an increase in molten hydrogen during refining. In this way, the formation of white spots is prevented by increasing the strength or obtaining a structure with low hydrogen cracking susceptibility.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a special treatment requiring a large amount of energy and time when the hydrogen content is about 5 ppm, that is, an extension of the degassing time, an extension of the ingot heating time, and a product. It is an object of the present invention to provide a steel capable of preventing generation of white spots without requiring special treatment such as quenching and tempering of steel, and a method for manufacturing the same.

[0005]

In order to achieve the above object, the gist of the present invention is that C: 0.01 to 0.70 wt.
%, Si: 0.1-1.0 wt%, Mn: 0.1-1.
0 wt%, 0.1 to 8.0 wt% of one or more of Cr, Ni, Mo, V, W, Al: 0.01 to 0.10
wt%, Ti or Zr: 0.01 to 0.10 wt%, the balance being Fe and unavoidable impurities, white spot generation preventing steel and C: 0.01 to 0.70 wt%,
Si: 0.1 to 1.0 wt%, Mn: 0.1 to 1.0 w
1% or more of at least one of Cr, Ni, Mo, V, and W, and 0.1 to 8.0 wt%, with the balance being Fe and unavoidable impurities. Hydrogen was reduced to a level of 5 ppm with a gas device, and Al (0.0%).
(1 to 0.10 wt%) to remove N and O, and then add Ti or Zr (0.01 to 0.10 wt%) to deviate to the cooling process after hot working and gasify. Hydrogen before trapping as a hydrogen compound of Ti or Zr.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the first invention relating to the white spot prevention steel according to the present invention, C: 0.01 to 0.70 wt%, S
i: 0.1 to 1.0 wt%, Mn: 0.1 to 1.0 wt%
%, One or more of Cr, Ni, Mo, V, W, 0.1 to 8.0 wt%, Al: 0.01 to 0.10 wt%
%, Ti or Zr: 0.01 to 0.10 wt%, with the balance being Fe and unavoidable impurities. The reasons for limiting the component composition as described above are as follows.

C, Si, Mn, Cr, Ni, Mo, V,
For W, SC, SCM, S specified in JIS standard
In order to obtain various properties required when used as carbon steel or alloy steel for machine structural use such as NCM, these are components that are absolutely necessary. In the present invention, these compositions are represented by C:
0.01-0.70 wt%, Si: 0.1-1.0 wt
%, Mn: 0.1 to 1.0 wt%, Cr, Ni, Mo,
One or two or more of V and W are set to 0.1 to 8.0 wt%.

[0008] Ti or Zr is 0.01 to 0.10 wt%
And Ti or Zr combines with hydrogen to form a compound such as a hydride, thereby capturing the hydrogen and preventing the generation of white spots. If the content is less than 0.01%, no effect can be obtained, and if it is too large, harmful inclusions are formed and the toughness is reduced. Therefore, the upper limit was made 0.10%.

[0009] Al is in the range of 0.01 to 0.10 wt%. Al functions as a deoxidizing and denitrifying agent, and Ti and Zr
Has the effect of preventing oxides and nitrides from forming and being consumed, but if the amount is too small, the effect cannot be obtained. Conversely, if the amount is too large, hot workability is impaired.
% And the upper limit was 0.10 wt%.

In the second invention, N: 150 ppm or less, O: 50 ppm or less. The N and O may be contained as impurities in some cases, and even in such a case, the object of the present invention can be achieved. That is, N and O combine with Ti and Zr to form nitrides and oxides, and consume Ti and Zr which form hydrides and the like, so that less is desirable. Therefore, in the second invention, nitrogen is set to 150 ppm or less and oxygen is set to 50 ppm or less in relation to the contents of Ti and Zr.

Furthermore, in the third invention, the content of H is 5 p
pm or less. The reason is that up to a hydrogen content of about 5 ppm, dehydrogenation can be easily performed by a normal out-of-furnace smelting apparatus or degassing apparatus, and within this range, the object of the present invention can be achieved. Therefore, in the third invention, the hydrogen content is set to 5 ppm or less.

[0012]

EXAMPLES Materials having the chemical components shown in Table 1 (carbon steel S
C, SCM, SNCM materials for machine structural use) 40t
on, melted in an electric furnace, vacuum degassed in a degassing tank, then cast into an ingot case, 10 ton to 15 ton
Was produced. After solidification, heat is sent to the forging heating furnace and
After soaking at 200 to 1230 ° C for 8 to 12 hours, a forged steel product of φ300 to 500 mm is manufactured by hot forging, and then left to cool after forging. Investigated by sonography.

[0013]

[Table 1]

When Ti or Zr is not added, the defect occurrence rate due to white spot defects is high irrespective of the component system and the oxygen and nitrogen levels, particularly when the hydrogen content is 3 ppm or more. . On the other hand, when Ti or Zr was added, the incidence of white spot defects was suppressed to 0 irrespective of the hydrogen level, confirming the effect of adding Ti or Zr.

[0015]

As described above, according to the present invention, up to a hydrogen content of about 5 ppm, special treatments such as prolongation of degassing time and ingot heating time, quenching and tempering of products, and the like can be performed. There are various effects such that the generation of white spots can be prevented without much, and a large amount of energy can be consumed and the processing time can be reduced.

Claims (4)

[Claims] 1. C: 0.01 to 0.70 wt%, Si:
0.1-1.0 wt%, Mn: 0.1-1.0 wt%,
0.1 for one or more of Cr, Ni, Mo, V, W
To 8.0 wt%, Al: 0.01 to 0.10 wt%, T
i or Zr: 0.01 to 0.10 wt%, with the balance being Fe and unavoidable impurities, white spot prevention steel. 2. C: 0.01 to 0.70 wt%, Si:
0.1-1.0 wt%, Mn: 0.1-1.0 wt%,
0.1 for one or more of Cr, Ni, Mo, V, W
To 8.0 wt%, Al: 0.01 to 0.10 wt%, T
i or Zr: 0.01 to 0.10 wt%, N: 150 p
pm or less, O: 50 ppm or less, the balance being Fe and unavoidable impurities, a white spot preventing steel. 3. C: 0.01 to 0.70 wt%, Si:
0.1-1.0 wt%, Mn: 0.1-1.0 wt%,
0.1 for one or more of Cr, Ni, Mo, V, W
To 8.0 wt%, Al: 0.01 to 0.10 wt%, T
i or Zr: 0.01 to 0.10 wt%, N: 150 p
pm, O: 50 ppm or less, H: 5 ppm or less, the balance being Fe and unavoidable impurities. 4. C: 0.01 to 0.70 wt%, Si:
0.1-1.0 wt%, Mn: 0.1-1.0 wt%,
0.1 for one or more of Cr, Ni, Mo, V, W
~ 8.0 wt%, the remainder is made of a material consisting of Fe and unavoidable impurities, and 5 p
pm level of hydrogen, Al (0.01 ~
0.10 wt%) to remove N and remove O.
Adding Ti or Zr (0.01-0.10 wt%),
A method for producing a white spot prevention steel, wherein hydrogen deviating from a cooling process after hot working and before gasification is captured as a hydrogen compound of Ti or Zr.