JPH0669573B2 - High alloy hot rolling slope manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is based on Alloy825 (trade name, the same applies hereinafter) (22Cr-42N
The present invention relates to a method for producing a high alloy hot-rolled sheet having excellent surface properties by using a difficult-to-work austenitic high alloy represented by i).

(Prior Art) It is well known that the hard workable austenitic high alloy represented by Alloy 825 described above has a small hot deformability and is prone to work cracking during hot rolling.

Therefore, JP-A-59-190320 discloses a method of performing hot rolling while avoiding the temperature range of 1050 ° C. to 900 ° C. in the rolling process in order to prevent the occurrence of work cracks.

(Problems to be Solved by the Invention) However, in ordinary production, it is difficult to avoid the temperature range on the high temperature side and to carry out the production due to a temperature drop during rolling. Also, avoiding it on the low temperature side is often difficult in practice because the deformation resistance increases.

Further, according to the experiments of the present inventor, hot work cracking that occurs in austenitic high alloy hot-rolled sheet of difficult workability is generally said to have good hot workability at a high temperature range of about 1050 ° C. or higher. Has already occurred in the 1st pass to the 2nd pass of the rough rolling, and it has been found that the hot working cracks are enlarged by the rough rolling and finish rolling in the latter stage.

The present invention solves the above-mentioned problems and provides a method for producing an austenitic high alloy hot-rolled sheet which has excellent surface properties with less hot-working cracks and is difficult to work.

(Means for Solving Problems) In the method for producing a high alloy hot-rolled sheet according to the present invention, the Ni content is
When manufacturing the hard-working austenitic high alloy hot-rolled sheet of 15 to 50% by weight, the first pass or 1 at the time of rough rolling
5 to 20 per pass between 1250 and 1000 ℃ for the 2nd and 2nd passes
The gist is to perform rolling with a rolling reduction of%.

In the present invention, the rolling of the first pass or the first pass and the second pass during rough rolling with a reduction amount of 5 to 20% per pass between 1250 and 1000 ° C. was carried out by many experiments by the present inventors. It is based on the obtained results.

That is, as is clear from the attached drawings showing an example thereof,
The amount of reduction in the 1st pass of rough rolling has an extremely large effect on the surface cracking condition of the hot-rolled sheet (thickness: 6 mm) that has been finish-rolled at 900 ° C, which is a temperature range where hot workability is poor. Was found. In other words, by performing the reduction amount per pass at 5% or more and 20% or less, the hot workability of the high alloy is significantly improved, and the finish is performed in the temperature range that is generally inferior to the hot workability. The surface cracks were reduced even after rolling.

The reason why the hot workability is improved and the surface cracks are reduced by the method of the present invention is supposed to be as follows.

The surface cracking during hot is austenite grain boundary cracking, and it is speculated that the precipitation condition near the austenite grain boundary changes due to the required reduction, and cracking is less likely to occur during rolling in the next process. However, if the reduction amount is small, this effect is small, and if the reduction amount is large, partial recrystallization occurs in the vicinity of grain boundaries, and cracks are likely to occur during rolling in the next step. Needless to say, if a large reduction is applied, cracking will occur from the first pass.

That is, the Ni content of the high alloy to be used in the present invention is 15 to 50% by weight, Ni is an element excellent in corrosion resistance, but if the Ni content is less than 15%, ferrite In addition to the fear of the inclusion of Al, the corrosion resistance, especially stress corrosion cracking in Cl ^- atmosphere is likely to occur, while when it is added in excess of 50% by weight, the austenite grain boundary becomes brittle and surface cracking easily occurs. Is.

The reason why the first pass during rough rolling is to be rolled between 1250 and 1000 ° C is that when a hot rolled sheet is manufactured from a difficult-to-work austenitic high alloy with a Ni content of 15 to 50% by weight. ,
This is because at a temperature higher than 1250 ° C, the solubility product is large, so there is little possibility of precipitation even during rolling, and there is little effect as a countermeasure against austenite grain boundary cracks that occur during rolling in the next step. Further, if the first pass of rough rolling is carried out at a temperature lower than 1000 ° C, the rolling end temperature will be remarkably lowered and the hot deformation resistance will be high, making rolling practically impossible.

Further, the reason why the amount of reduction per pass is set to be 5% or more and 20% or less is that if it is less than 5%, precipitation due to the reduction does not occur, which is insufficient as a countermeasure against intergranular cracking.
This is because if the content exceeds%, austenite partially recrystallizes in the vicinity of the grain boundaries, and grain boundary cracks are likely to occur during rolling in the next step. On the other hand, rolling with a rolling reduction of 5 to 20% per pass produces uniform precipitates in the grain boundaries and within the grain due to the reduction (reversely segregates and reduces precipitation at the grain boundaries). The hot workability of the process is improved. It should be noted that this effect is more effective when the reduction is performed twice than when the reduction is performed once.

In the present invention, the reduction is performed in the first to second passes of the rough rolling because in the case of a normally high alloy, the deformation resistance is small at the initial stage of the rough rolling in the high temperature region, and therefore 20% per pass. Although larger rolling is performed, if crack buds or cracks occur in the high alloy hot-rolled sheet at this time, the hot-work cracking state after rough rolling to finish rolling will be performed even if the required reduction is performed in the next process. It is not useful for improving.

Further, regarding the chemical composition of the hard-to-work austenitic high alloy to which the method of the present invention is applied, the Ni content (15 to 50
(% By weight), but not limited thereto, C ≦ 0.1
% By weight, Si≤0.5% by weight, Mn≤2.0% by weight, P≤0.030% by weight, S≤0.005% by weight, 15.0% by weight≤Cr≤30.0% by weight, and the remaining substantially Fe.

Furthermore, it is preferable to add one or more of the following elements, if necessary.

0.01 wt% ≤ Al ≤ 0.20 wt%, 1.0 wt% ≤ Cu ≤ 3.0 wt%, 1.0 wt% ≤ Mo ≤ 6.0 wt%, 0.05 wt% ≤ Ti ≤ 2.0
% By weight, 0.005% by weight ≦ N ≦ 0.200% by weight.

(Operation) In the present invention, when a hot-rolled sheet is produced from a difficult-to-work austenitic high alloy having a Ni content of 15 to 50% by weight, the first pass or the first pass and the second pass at the time of rough rolling are used. 1250-10
Since rolling is carried out at a temperature of 00 ° C with a rolling reduction of 5 to 20% per pass, austenite grain boundary cracking does not occur.

(Examples) Examples (NO. 6 to No. 28) according to the method of the present invention are shown in Table 2 below. At the same time, the case of not using the method of the present invention is compared with the comparative example (N
o.1 to No.5).

The chemical composition of the difficult-to-work high alloy used in this example is
Shown in the table.

As shown in Table 2 below, it can be seen that the hot-rolled sheet produced by the method of the present invention has significantly superior surface properties as compared with the comparative example.

(Effects of the Invention) As described above, the present invention, when producing a hot-rolled sheet from a difficult-to-work austenitic high alloy having a Ni content of 15 to 50% by weight, the first pass during rough rolling or Since the first pass and the second pass are rolled between 1250 and 1000 ° C with a reduction amount of 5 to 20% per pass, the hot deformability is small and work cracks tend to occur during hot rolling. Austenite grain boundary cracks do not occur even when hot rolling high alloys,
Therefore, the occurrence of surface cracks can be effectively prevented, and the yield can be improved.

[Brief description of drawings]

The drawing is a drawing showing the influence of the reduction amount in the first pass of rough rolling on the surface cracks of a 6 mm thick 900 ° C finish rolled plate Alloy 825.

Claims (1)

[Claims] 1. A method for producing a hot-rolled sheet from a hard-to-work austenitic high alloy having a Ni content of 15 to 50% by weight, wherein the first pass or the first and second passes during rough rolling is performed.
A method for producing a high alloy hot-rolled sheet, which comprises rolling between 1250 and 1000 ° C with a rolling reduction of 5 to 20% per pass.