JPS58224003A - Hot rolling method of continuous casting ingot - Google Patents

Abstract

PURPOSE:To perform direct rolling which suppresses the generation of hot cracking by controlling adequately the cooling speed of an ingot in the stage of continuous casting as well as the temp. for starting rolling in the stage of direct rolling and the time when said temp. is attained. CONSTITUTION:An ingot for a thick plate or the like produced by continuous casting is subjected, after the casting, to cooling at the average cooling rate Vc ( deg.C/min) from 1,500 deg.C near the surface of the ingot up to 1,300 deg.C satisfying the conditions expressed by a functional equation I with a constant K (where, x: content of C, y: content of O). The ingot is further subjected to hot rolling for the lapse of time tmin since solidification until the rolling is started and at the surface temp. of the ingot in the stage of starting rolling satisfying the conditions of the relation II. Since the rolling free from hot cracking is accomplished with the effective utilization of the heat after the casting by the above-mentioned control for temp. conditions, the cost of energy is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a direct hot rolling method for continuously cast slabs. In general, continuously cast slabs are sent to a rolling process while maintaining the casting temperature'5050 This saves the process for heating the gas, which has the effect of reducing energy costs.

However, when rolling hot slabs as cast, hot cracks generally occur, making continuous rolling from casting difficult.

Therefore, the present inventors investigated various rolling methods that do not cause such hot cracking, and as a result, they controlled the cooling rate during casting, and also controlled the rolling start temperature during direct rolling and the time required to reach that temperature. As a result, they discovered that even when directly rolled, hot cracking can be suppressed.

That is, in the present invention, after casting a continuously cast slab, the average cooling rate from 1500°C to 1300°C in the vicinity of the surface of the slab is determined by the relational expression LogVc>0. 27Log (KX l o')+i
, s 24 = (z+o, o 4 ) (1/-0,0
After cooling under conditions that satisfy 014), rolling is carried out under conditions that satisfy the relationship between the elapsed time tmin from solidification to the start of rolling and the slab surface temperature T°C at the start of rolling. This is a method for hot rolling continuously cast slabs.

The present invention will be explained in detail below.

The composition of the steel targeted by the present invention is ordinary carbon steel or special steel for thin plates, wire rods or thick plates, for example, C: 1%
Hereinafter, Sl: 1% or less, Mn: 2% (2″F・0
"°゛°"°S1゛2"0.03%JgT゛S"0.0
Ordinary steel containing 18% or less, and furthermore, 1% of these
It is a special steel etc. containing at least one type of NbN Tts N15 vs Me 'll in an amount of 1 t or less.

Steel slabs of such composition are manufactured by continuous casting,
The cooling of the slab until the start of rolling was limited as follows:
The average cooling rate vc from °C to 1300U corresponds to the constant K togVc>0.27 #g (Kx l O')+1
．． 824 (range shown in FIG. 1 (shaded area)).

The constant is a value determined by the content of C and 0, K = (z + 0.04) (y - 0,0014) ・
...Displayed in (1). Here, π(wt *
) represents the C content, and y (wt %) represents the C content.

The limit value of vc is 60 (°C/min)<We <s 000 (°C/min)
min, )-...-(2), further K togVc>0.27tog(KXI O')+1.8
24 Control vc so that it falls within the range of (3)0 In this way, after controlling the cooling rate vc, the elapsed time t (min) from solidification to the start of rolling and the casting temperature at the start of rolling are One surface temperature TCQ was selected as follows and the composition was changed to suppress the occurrence of hot cracking.

That is, t〉11 (min) ・・・(4)T〉
1300'30t...(5) 1300 section〉'l'>'800υ...(6)゛These nine relationships are shown in Figure 2, but Figures 1 and 2 When the conditions (2) to (6) are satisfied, the occurrence of hot cracking during direct rolling can be suppressed.
Note that the slab surface temperature T (0 is (5), (6
) formula is controlled f′j・Until the start of rolling・Slab is 8
It is necessary to maintain the temperature above 0°C, and for this reason, the slab is sometimes held in equipment such as a heat retention furnace.

Examples are shown below.

Plate thickness 1 of steel of steel types A-F containing each component shown in Table 1
After continuous casting into a slab of 00~250m, the surface temperature #1 is 1
Charged into a rough rolling mill at 000-1200℃, 40%
0 The results are shown in Table 2.

As is clear from this table, hot cracking did not occur in steel type A rolled under the conditions of the present invention. Hot cracking occurred because the treatment was not within the appropriate range, and in the case of E and F, the solidification cooling rate was within the appropriate range.

As shown in Table 2 and above, according to the method of the present invention, the heat after casting can be effectively used to perform rolling without hot cracking, so it is possible to save energy and cost, and it is extremely suitable for industrial applications. The effect is significant.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between casting cooling rate and constant of the present invention, and FIG. 2 is a diagram showing the relationship between temperature at the start of rolling and time of the present invention.

Claims (1)

[Claims] After casting a continuously cast slab, 15 parts near the surface of the slab are continuously cast.
Average cooling rate Me (c
/mln) as a constant. After cooling under conditions that satisfy the following equation, the relational expression between the elapsed time tmin from solidification to the start of rolling and the slab surface temperature T°C at the start of rolling is added. A method for hot rolling continuously cast slabs, characterized by rolling under conditions that satisfy the formula %.