Cold upsetting machines are often damaged to varying degrees in the process of use. The most common quality problem is cold upsetting cracking, which can be roughly divided into internal quality problems of wire rods, surface quality problems of wire rods, and improper deep processing technology of users. The first two types account for the vast majority. In this paper, we mainly analyze the causes of cold heading cracking.

The internal quality problem of wire rods is mainly caused by inclusions. Generally, slag inclusion is caused by slag entrapment during continuous casting. The type and grade of non-metallic inclusions are also another reason that affects the internal quality of wire rods. The experience of producing cold heading machines shows that there are few cold heading cracks caused by non-metallic inclusions.

Relative to the internal quality problems of wire rods, the proportion of wire rod surface quality problems accounts for the vast majority.

There are two characterizations of wire rod surface quality problems: one is the surface crack of wire rod with oxidation characteristics; This is mainly inherited from the slab surface crack. The other is the surface crack of wire rod without oxidation characteristics, including: ① a special surface crack of wire rod without oxidation characteristics. ② The main surface quality problem of wire rod caused by steel rolling is rolling fold defect.

Measures taken:

1、 Steelmaking and continuous casting

Since the liquid level fluctuation is controlled within ± 20mm and the depth of slag inclusion under the skin is less than 2mm, the liquid level fluctuation is controlled within ± 15mm; If the depth of the subcutaneous slag inclusion is less than 2mm, it can be eliminated when heating in the furnace. The liquid level fluctuation increases from ± 5 mm to ± 20 mm, and the longitudinal crack index on the slab surface increases from 0 to 2.0. Considering the actual situation of the steel plant, the liquid level fluctuation should be controlled within ± 15mm. The high temperature molten steel flow in the mold will eat about 2mm of the solidified shell and cause stress concentration when the superheat degree of molten steel is increased by 10 ℃. Therefore, a stable and appropriate superheat degree can reduce the longitudinal cracks on the slab surface. Strictly controlling the cooling uniformity of the secondary cooling zone and controlling the repeated rise of the shell temperature with weak cooling can reduce the edge crack of the slab.

2、 Rolled steel

The measures taken are as follows: ① the rolling cold heading machine shall be inspected frequently and the guide device, guide wheel and sleeve pulling roll shall be replaced; ② According to the rolling of cold heading machine wire rod, adjust the rough rolling pass system reasonably, optimize the setting of finishing mill and reducing sizing mill, improve the process parameters, strictly control the temperature during rolling, delay cooling after rolling, and greatly improve the product quality.