JPS6320101A - Front end tear preventing rolling method - Google Patents

Abstract

PURPOSE:To surely prevent front end tear by forming a projection having the section smaller than a rolling finish size to the central part at the front end face of a stock and subjecting the stock to hot rolling. CONSTITUTION:The projection having the section smaller than the rolling size is formed to the central part at the front end of the stock at the time of rolling the stock such as a sulfur free-cutting steel or alloy tool steel having the tendency to easily cause the front end tear and having poor hot workability, and then the hot rolling is carried out, cast ingot of a cold working tool steel SKD-11 is pressed and forged to 350mm square and the riser part thereof is scored to 150mm square smaller than the rolling size and is forged and elongated by using chisels 3 simultaneously; finally, the projection having 100mm length is formed and the ingot is hot rolled. The front end part is then not rolled down even if the temp. drop at said part is earlier. The front end tear is thus surely prevented even with the steel, etc. having the tendency to easily cause the front end tear.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hot rolling method that does not cause tip splitting during rolling.

(Prior technology) Conventionally, as a method to prevent tip splitting of steel and alloys that are prone to tip splitting, a separately prepared material with good hot workability is welded to the tip of the material before rolling. Alternatively, the tip may be forged, solvent-treated, or cut/rolled in advance.
A typical method is to sharpen it into a cone or pyramid shape by cutting and then roll it.

(Problems to be Solved) However, among the above methods, the former is not a preferable method because the welded portion often comes off and flies during rolling, and some materials are difficult to weld, and the cost is high. Among the latter, those whose tips are sharpened by solvent or cutting have little effect in preventing cracks, and those made by forging require considerable man-hours and skill for the forging process itself, both of which are unsatisfactory. Met.

(Means for Solving) The present invention has been made in view of the above, and its gist is that the central part of the tip surface of the steel or alloy, which tends to cause tip splitting during hot rolling, is pre-rolled by hot forging. This is a rolling method for preventing tip cracking, which is characterized by forming a protrusion with a cross section of the same size or shape and then hot rolling.

The materials targeted in the present invention are ingots of metal materials with poor hot workability such as sulfur free-cutting steel, alloy tool steel, N1,000 alloy, etc.
Intermediate materials such as slabs, plumes, and billets.

When these materials are normally rolled, as the rolling progresses and fishtails and axial fiber structures are formed, they tend to tear easily, and eventually open wide and become unrollable.

In the present invention, the size of the protrusions is set to be smaller than the final rolling dimensions, but this is because the protrusions may become hard due to temperature drop over time as rolling progresses, and may crack under slight rolling pressure. This is to ensure that the size is such that it does not bite into the roll, as this will damage the roll.

In the present invention, such protrusions are formed by forging because it is advantageous in terms of productivity. It is most advantageous to perform the method of the present invention after forging the main body, but even when only the protrusions are formed, the heat content due to heating for that purpose is followed by rolling heating, so there is no heat loss. It is not.

(Function, Effect) One of the reasons why tip cracking occurs during rolling when no measures are taken to prevent tip splitting is that the tip gets cold easily and quickly reaches a temperature where it is easy to crack.This causes problems in the hot workability of the material itself. This is also an important factor. In the present invention,
Since the tip is kept below the rolling dimension from the beginning, no rolling is applied to the tip until the end, and no matter how much the temperature drops, it will not crack.

The application of the invention is particularly advantageous in the case of ingots or blanks having a feeder section. In this case, the protrusions can be formed at the feeder portion, there is no decrease in yield, and there are advantages in that forging for forming is easy.

(Example) Maximum opposite side dimension of cold work tool steel, 5KD-11 500111
Heating the rectangular pre-cast ingot of
At the same time as forging into an M-square bloom, make a cut with a chisel at the part of the riser near the main body, leaving a 15011ff angle, which is the target rolling dimension, as shown in Figure 1.
As shown in the figure, the feeder part was pressed and forged to the same size as the cut part, and then cut as shown in Figure 3 (leaving a length of 100 m) to form protrusions.

This plume was subsequently heated in a rolling heating furnace, and
Although it was rolled into a ff square billet, no cracking occurred at the tip.

[Brief explanation of the drawing]

FIGS. 1 to 3 are diagrams showing an example of the procedure for forging a reduced tip according to the present invention.

Claims (1)

[Claims] In the hot rolling of steel or alloys that are prone to tip splitting during rolling, a protrusion with a cross section smaller than the finished rolling dimensions is formed in advance at the center of the tip surface of the material by hot forging, and then hot rolling is carried out. A rolling method for preventing tip tearing.