JPS6296653A - Nonrefined structural steel - Google Patents

Abstract

PURPOSE:To obtain a nonrefined structural steel having high toughness as hot worked by selecting conditions during the hot working and cooling of a steel alloy having a specified composition so as to give a prescribed crystal grain size number. CONSTITUTION:The composition of a steel alloy is composed of, by weight, 0.3-0.6% C, 0.1-2% Si, 0.2-2.5% Mn, 0.005-0.1% Al, 0.005-0.03% N, <0.5% V and/or <0.5% Nb and the balance Fe. The alloy is hot worked and cooled to ordinary temp. so as to form a ferrite-pearlite structure contg. former austenite grains having average crystal grain size No.5 or above. It is preferable that <0.4% S and <0.1% Te are added to the composition in >=0.04 ratio of Te/S.

Description

[Detailed description of the invention]

1 Kawatatetangu

[Industrial application field]

The present invention relates to a structural steel that has excellent toughness without heat treatment, that is, without undergoing heat treatment such as quenching and tempering while hot working. (Conventional technology) Generally, products made from structural steel are manufactured by hot working, tempering, and then cutting, but if heat refining can be omitted, costs can be reduced. In addition to being able to measure energy efficiency, it can also meet the demand for energy conservation.Therefore, research on this kind of steel is actively being attempted.
In particular, steels to which V, Nb, etc. have been added are developed and strengthened by taking advantage of the fact that these carbides and nitrides precipitate into the ferrite/pearlite structure during the cooling process after hot working, and some of them have been put into practical use. has been done. When rolling is performed as hot working, the steel material is strengthened as it is or is cold or warm plastic worked and then cut into the final product. In addition, when forging is performed, the rolled steel material is die-forged, and the hardened rough material is cut into a product. However, products processed in this way have a disadvantage in that they have lower toughness than those processed through normal heat treatment. [Problems to be Solved by the Invention] An object of the present invention is to overcome this weakness and provide a non-tempered structural steel that is comparable to tempered steel. l” summer seal feeling

[Means for Solving the Problems] The non-tempered structural steel of the present invention, which has excellent toughness even after hot working, has C: 0.30 to 0.60%, s+: o
, 10-2.0%, Mn: 0.20-2°5%, l
:0.005~0.10% and N:0.005~0.
030%, as well as V:O. 5% or less and Nb: 0.5% or less, and the remainder is substantially Fe, and the structure after cooling to room temperature is It is characterized by having prior austenite crystal grains with a grain size number of 5 or more. In addition to the above basic composition, the non-tempered structural steel of the present invention contains S: 0.4% or less and Te: 0.10% or less.
It is recommended that it be contained in a ratio of e/S≧0.04.

[For use]

The role of each component in the alloy composition adopted in the present invention and the reason for its limitation are as follows. C: 0.30-0.60%, the presence of 0.30% or more is essential to ensure the necessary strength. The upper limit was determined from the viewpoint of toughness. 3i: 0.10-2.0%, preferably 0.15-2.0%
1.0% 3i is an element necessary as a deoxidizing agent, and should be contained at 0°10% or more, but non-tempered structural steel is usually made into a product by machining after hot working. Good machinability is desired. Therefore, Si is 2.0% or less,
It should preferably be kept at 1.0%. Mn: 0.20-2.5%, preferably 0.5-1.
8% Needless to say, Mn also acts as a deoxidizing agent, which is important in obtaining high toughness in non-tempered steel. Also in the present invention, a relatively high content is employed, typically around 1.5%. However, from the viewpoint of machinability, it is best to avoid adding too much H. Δρ: 0.005~0.10%, preferably 0.01~
0.05% It also has a deoxidizing effect, but its main role is to refine crystal grains. Since A and ll also have a negative effect on machinability, they are limited to 0.10% or less. N: 0.005-0.30%, preferably 0°23
One of the effects of N up to % is the refinement of crystal grains, and the other is precipitation strengthening due to the formation of nitrides with V or Nb. Too much of this also impairs toughness. V: 0.5% or less, Nb: 0.5% or less (total 0.5% or less if used together) Both form nitrides and contribute to precipitation strengthening and crystal grain refinement. However, N
The influence of b is large, and the higher the content, the wider the upper limit of the appropriate processing temperature. The upper limit was set for the reason of deterioration in hot workability, but since both V and Nb are expensive materials, the amount added should be determined in harmony with the effect of addition and performance. The most distinctive feature of the steel of the present invention is its unique structure in which the aforementioned prior austenite crystal grains have an average grain size number of 5 or more. Needless to say, "prior austenite" grains are those in which ferrite grains with a ferrite-pearlite structure formed by cooling to the hot working recovery temperature cross the austenite grain boundaries that existed at high temperatures. It refers to the presence and size of previous grains. This measurement is based on JIS G 05
It is carried out according to the slow cooling method specified in 51. Considering that the structure of conventional non-tempered steel generally has a grain size number of 2 to 3, the structure selected in the present invention is extremely unique. Regardless of the degree of tempering, it is inevitable that steel materials will have anisotropy in their mechanical properties, albeit to varying degrees.
In the steel of the present invention, when it is particularly desired to lower the directionality of toughness, it is preferable to follow the preferred embodiment in which S and Te are contained as described above. S is, of course, an element that helps improve stiffness, but here the combination of appropriate amounts of S and Te controls the morphology of sulfide inclusions in the steel and reduces the anisotropy of toughness. The effect can be obtained. The upper limits of S and Te were determined mainly based on hot workability. In addition, the following elements may be added within specific ranges to the steel of the present invention, depending on the desired properties and uses, with the expectation of various effects.・When you want to roughly refine the grain size...Ti:
0.5% or less, Ta: 0.5% or less, or Zr: 0
．． 5% or less・When you want to increase weather resistance...Cu: 2.0% or less・
When you want further improvement in machinability...Pb: 0°4%
Below, Bi: 0.4% or less, Se: 0.4% or less, C
a: 0.01% or less・When you want to improve fatigue strength...O: 0.0030
% or less・When increasing the strength...Cr: 5% or less, N
i: 5% or less, MO: 3% or less In order to obtain the above-mentioned structural steel that has high toughness even after hot working, it is necessary to Processing conditions must be selected to achieve a predetermined grain size number. The conditions vary depending on the composition chosen, but the most dominant factors are the N and Nb contents. Now, depending on the magnitude of these contents, the upper limits of the heating temperature and finishing temperature for hot working that give good results are as follows. Heating Temperature Finishing Temperature ■Eaves'' 5 above - 1 ■Works
)0 0.005~0.015 1000
9000 0.015~0.030 1100
1000< 0.1 0.005~(), 01
5 1200 1100< 0.1 0.015~
0.030 1300 12000.1~0.5
0.005-0.030 1300 1300
The actual operating conditions are within the above limits, and the higher the temperature, the lower the resistance to plastic working, but relatively low temperatures are preferred as far as the toughness of the resulting steel is concerned. Again, the choice should be made depending on each case, with a balance between the two. [Example] Steel having the alloy composition shown in Table 1 was melted and cast in a 2 ton arc furnace. (Na Vl * is comparative steel) Low Ω-
1-Mn A, ll N-I O, 490
,240,800,0300,010n O,50
0,261,510,0250,009III O
,510,251,520,0400,0111V
O, 500, 251, 500, 0350, 020V
O,490,241,510,0400,020V
l*0.50 0.25 0.80 0.015 0.
0081 Table V Nb Te S Te/S O, 11---- 0,10---- 〇, 100.05--- 0.100.05--- 0.100.050.0020.0210.10 The ingot was rolled to make a 100m square billet, and the heating temperature and finishing temperature were set to the conditions shown below for forging, resulting in a material with a cross section of 20m x 60m. After the comparative material was forged, it was further quenched and tempered under the conditions of 850 degrees, oil cooling - 600 degrees Celsius, and air cooling. Melon Plate Moto Bean Asahi "U" Mark Die 11 Irisatoi 1300
℃1100℃ air cooling port 1000 1000 ll
C 1000 800 〃2
Table 2 shows the results of various tests performed on the materials obtained as described above. In the table, the numbers marked with * are comparative examples. "-" means not measured. The Charpy impact value was measured at room temperature using a JIS3M test piece. From the data in Table 2, it is clear that the alloy of the present invention, especially one processed under favorable processing conditions, has a prior austenite grain size with a predetermined size, and that steel materials that meet the conditions have good hardness, toughness, and toughness. Regarding the direction of
Furthermore, it is confirmed that when appropriate amounts of S and 1'-e are contained, the directionality of toughness is significantly improved. 2nd No. ill Seed treatment Former austener inclusion
2.72 ■ Ha 6.0
12.03 ■ Mouth
6.3 1B, 44 ■ C 8.1 12.35 1V
A 6.1 12.56
1V 0 8.3
10.07 1V Ha 1
0.0 11.28 v i
6.8 3.39
V mouth B, 0
4.110 V 9.
1 5.011* Vl* 2
10.513.2 5.
3 0.4 2113.4
2412.1 -
-2714.2
2512.2 4.9 0.4
2914.5 4.4 0.3
2716.2 4.9 0.3 24
10.8 B, 6 0.8 301
3.3 10.6 0.8 2616.
0 11.2 0.7 2514.7
5.9 0.4 25 Effects of the Invention According to the present invention, it is possible to obtain structural steel that has high strength and toughness even after hot working, which is widely used in the manufacture of industrial machinery and automobiles. It will be done. Therefore, the heat treatment process can be omitted when manufacturing various mechanical parts, such as crankshafts, connecting rods, axle shafts, spindles, and steering racks, which previously required heat treatment such as quenching and tempering. sex will greatly increase. This benefit is even more pronounced for mass-produced products.

Claims (2)

[Claims] (1) C: 0.30-0.60%, Si: 0.10-2
．． 0%, Mn: 0.20-2.5%, Ar: 0.005
0.10% and N: 0.005 to 0.030%, and one or two of V: 0.5% or less and Nb: 0.5% or less, and the remainder is substantially Fe. For non-heat-refined structure, which is obtained by hot working a steel alloy consisting of the following, and whose structure after cooling to room temperature is ferrite + pearlite, and has prior austenite crystal grains with an average grain size number of 5 or more. steel. (2) C: 0.30-0.60%, Si: 0.10-2
．． 0%, Mn: 0.20-2.5%, Al: 0.005
0.10% and N: 0.005 to 0.030%, and one or two of V: 0.5% or less and Nb: 0.5% or less, and further contains S: 0. 40
% or less and Te: 0.10 or less Te/S: 0.04
It is made by hot working a steel alloy containing Fe in the above ratio, and the structure after cooling to room temperature is ferrite + pearlite, with prior austenite crystals having an average grain size number of 5 or more. A non-tempered structural steel characterized by having grains.